U.S. patent application number 12/659334 was filed with the patent office on 2010-07-01 for plating apparatus and plating method.
Invention is credited to Keisuke Hayabusa, Takashi Kawakami, Keiichi Kurashina, Tsutomu Nakada, Satoru Yamamoto.
Application Number | 20100163408 12/659334 |
Document ID | / |
Family ID | 38575851 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100163408 |
Kind Code |
A1 |
Kurashina; Keiichi ; et
al. |
July 1, 2010 |
Plating apparatus and plating method
Abstract
A plating apparatus can form a plated film having a more uniform
thickness over an entire surface of a substrate and can securely
fill interconnect recesses with the metal without forming voids in
the embedded metal even when the substrate has a high sheet
resistance in the surface. The plating apparatus includes a
substrate holder for holding a substrate, a cathode portion
including a cathode for contact with the substrate held by the
substrate holder to feed electricity to the substrate, and an
anode, partly or wholly having a high resistance, disposed opposite
a surface of the substrate held by the substrate holder, wherein
plating of the surface of the substrate is carried out while
filling between the anode and the substrate held by the substrate
holder with a plating solution.
Inventors: |
Kurashina; Keiichi; (Tokyo,
JP) ; Nakada; Tsutomu; (Tokyo, JP) ; Kawakami;
Takashi; (Tokyo, JP) ; Yamamoto; Satoru;
(Tokyo, JP) ; Hayabusa; Keisuke; (Fujisawa-shi,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
38575851 |
Appl. No.: |
12/659334 |
Filed: |
March 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11396572 |
Apr 4, 2006 |
|
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12659334 |
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Current U.S.
Class: |
204/242 |
Current CPC
Class: |
H01L 21/7684 20130101;
C25D 17/001 20130101; C25D 7/123 20130101; H01L 21/2885 20130101;
H01L 21/76877 20130101 |
Class at
Publication: |
204/242 |
International
Class: |
C25B 9/00 20060101
C25B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 5, 2005 |
JP |
2005-108408 |
Jun 28, 2005 |
JP |
2005-188311 |
Aug 10, 2005 |
JP |
2005-232118 |
Jan 13, 2006 |
JP |
2006- 6077 |
Claims
1-13. (canceled)
14. A plating apparatus comprising: a substrate holder for holding
a substrate; a cathode portion including a cathode for contact with
the substrate held by the substrate holder to feed electricity to
the substrate; an anode disposed opposite a surface of the
substrate; and a contact member disposed between the substrate held
by the substrate holder and the anode movably in a direction closer
to or away from the substrate, said contact member having
through-holes extending linearly through the contact member in said
movement direction.
15. The plating apparatus according to claim 14 further comprising
a press mechanism for pressing a contact surface, which faces the
surface of the substrate held by the substrate holder, of the
contact member against the surface of the substrate.
16. The plating apparatus according to claim 14, wherein a press
member for pressing the contact surface of the contact member
against the surface of the substrate is disposed between the
contact member and the anode.
17. The plating apparatus according to claim 14, wherein a flexible
cushioning material for uniformly pressing the contact surface of
the contact member against the surface of the substrate is disposed
between the contact member and the anode.
18. The plating apparatus according to claim 14, wherein the
through-holes provided in the contact member have a circular
cross-sectional shape with a diameter of not more than 12 .mu.m,
and are distributed at a density of 1.0.times.10.sup.5 to
1.0.times.10.sup.9/cm.sup.2.
19. The plating apparatus according to claim 14, wherein the
contact surface of the contact member has an Ra value, indicative
of surface roughness, of not more than 1 .mu.m.
20. The plating apparatus according to claim 14, wherein the
contact member is composed of an insulating material.
21. The plating apparatus according to claim 20, wherein the
insulating material is polycarbonate, a ceramic, carbon, polyester,
glass, silicon, a resist material or a fluorocarbon resin.
22. The plating apparatus according to claim 14 further comprising
an etching mechanism for etching a plated film formed on the
surface of the substrate.
23. The plating apparatus according to claim 14, wherein the
through-holes provided in the contact member are tapered such that
the cross-sectional area gradually decreases with distance from the
contact surface.
24-58. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating apparatus and a
plating method, and more particularly to a plating apparatus and a
plating method used for filling fine interconnect recesses (circuit
pattern) formed in a substrate, such as a semiconductor substrate,
with metal (interconnect material) such as copper so as to form
interconnects.
[0003] The present invention also relates to an electrolytic
processing apparatus and an electrolytic processing method used for
electrolytic processing such as electroplating.
[0004] 2. Description of the Related Art
[0005] In recent years, instead of using aluminum or aluminum
alloys as a material for forming interconnect circuits on a
semiconductor substrate, there is an eminent movement towards using
copper that has a low electric resistivity and high
electromigration resistance. Such copper interconnects are
generally formed by filling copper into fine interconnect recesses
formed in a surface of a substrate. Various techniques for forming
such copper interconnects are known, including CVD, sputtering, and
plating. According to any such techniques, a copper film is formed
in the substantially entire surface of a substrate, followed by
removal of unnecessary copper by performing chemical mechanical
polishing (CMP).
[0006] FIGS. 1A through 1C illustrate, in sequence of process
steps, an example of forming such a substrate W having copper
interconnects. First, as shown in FIG. 1A, an insulating film 2,
such as an oxide film of SiO.sub.2 or a film of low-k material, is
deposited on a conductive layer 1a in which semiconductor devices
are formed, which is formed on a semiconductor base 1. Contact
holes 3 and interconnect trenches 4 as interconnect recesses are
formed in the insulating film 2 by the lithography/etching
technique. Thereafter, a barrier layer 5 of TaN or the like is
formed on the surface, and a seed layer 7 as an electric supply
layer for electroplating is formed on the barrier layer 5 by
sputtering, or CVD, or the like.
[0007] Then, as shown in FIG. 1B, copper plating is performed onto
a surface of the seed layer 7 of the substrate W to fill the
contact holes 3 and the trenches 4 with copper and, at the same
time, deposit a copper film 6 on the insulating film 2. Thereafter,
the copper film 6, the seed layer 7 and the barrier layer 5 on the
insulating film 2 are removed by chemical mechanical polishing
(CMP) so as to make the surface of the copper film 6 filled in the
contact holes 3 and the trenches 4, and the surface of the
insulating film 2 lie substantially on the same plane.
Interconnects composed of the copper film 6 are thus formed in the
insulating film 2, as shown in FIG. 1C.
[0008] In recent years, more and more fine interconnects are formed
in copper interconnects forming process for semiconductor devices,
and design rules for such fine interconnects are considered to be
changing from the 0.18 .mu.m generation to the 0.13 .mu.m
generation and further to the 0.10 .mu.m generation Depending on
circumstances, the advent of the seed-layer-less generation of
semiconductor devices may not be impossible. With those more and
more fine interconnects, unless a thickness of the seed layer is
further reduced, the seed layer overhangs at the inlets of
interconnect recesses, tending to produce voids in the plating
process. In the 0.18 .mu.m generation of design rules, the
thickness of the seed layer is generally in the range from about
150 to 200 nm on the flat surface of the substrate. In the 0.13
.mu.m generation of design rules, the thickness of the seed layer
is about 50 nm in order to prevent voids from being produced in the
plating process. In the 0.10 .mu.m generation of design rules, the
thickness of the seed layer will possibly be reduced to a range
from about 5 to 25 nm.
[0009] When carrying out copper electroplating on a surface of a
seed layer formed in a substrate, an anode of a low (almost zero)
resistance is employed, and a plating current is passed between the
anode and the seed layer while keeping the peripheral region of the
seed layer in contact with an electrode (electrical contact) to
feed electricity to the seed layer. Therefore, the thinner the seed
layer is, the higher is the sheet resistance of the seed layer
immediately after initiation of plating, and the plating current is
more likely to concentrate in the peripheral region of the seed
layer.
[0010] In particular, when a current circuit is considered in which
an electric current fed from a power source to the anode flows
through a plating solution to the surface (surface to be plated),
i.e., the seed layer, of the substrate, only the resistance of the
plating solution exits in a current pathway to the peripheral
region of the seed layer where there are feeding points. In a
current pathway to the center of the seed layer, on the other hand,
the electric resistance of the seed layer itself from its center to
the peripheral region in which the feeding points are present,
i.e., the sheet resistance of the seed layer, also exits in
addition to the resistance of the plating solution. As a thickness
of a seed layer, formed in a pre-plating step, becomes thinner with
finer circuit patters formed on a substrate, the electric
resistance (sheet resistance) of seed layer becomes larger. This
produces a larger difference in resistance between a current
pathway running through the center of a substrate and a current
pathway running through the peripheral region of the substrate,
thus decreasing an electric current passing the center of the
substrate. Thus, the amount of plating becomes increasingly larger
in the peripheral region of a substrate, whereas the amount of
plating is increasingly smaller around the substrate center distant
from feeding points. The effect of the electric resistance, which
increases with distance from a feeding point, is called "terminal
effect".
[0011] Conventionally, in order to improve the unevenness of a
thickness of a plated film due to the terminal effect, it has been
practiced to interpose a doughnut-shaped shielding plate between an
anode and a surface of a substrate so that an electric current more
easily flows to the center of the substrate. It is also practiced
to provide a dummy to-be-plated electrode, called thief electrode,
outside a substrate to disperse electricity passing in the
peripheral region of the substrate, thereby decreasing the amount
of plating in the peripheral region of the substrate. A method has
also been practiced which involves inserting a porous structure
between an anode and a substrate to increase the resistance of the
plating solution so as to make the effect of the sheet resistance
of the surface (surface to be plated) of the substrate relatively
small, thus reducing the terminal effect.
[0012] The applicant has proposed a plating apparatus wherein a
plating power source is connected individually to a plurality of
split anodes to increase a current density at those split anodes
positioned in a central area of the substrate to a level higher
than at those split anodes positioned in a peripheral area of the
substrate only during a certain period of time in which an initial
plated film is formed on the substrate, thereby preventing the
plating current from concentrating on the outer circumferential
portion of the substrate, but allowing the plating current to flow
to the central area of the substrate to make it possible to form a
uniform plated film even if the sheet resistance is high (for
example, see Japanese laid-open patent publication No.
2002-129383).
[0013] By using a low-k material, which has a high dielectric
constant, for an insulating film in which interconnects are to be
formed, the reliability of fine interconnects can be enhanced.
Low-k materials, however, generally have low mechanical strength.
Accordingly, when filling trenches, formed in an insulating film of
a low-k material, with copper by plating, and then removing
unnecessary copper on the insulating film by CMP processing,
dishing is likely to occur in the surface of the insulating film.
Suppression of dishing in CMP makes complete removal of unnecessary
copper difficult. There is, therefore, a demand for the formation
of such a plated film that can reduce the burden on a CMP
processing as much as possible by plating.
[0014] When carrying out plating of a surface of a substrate, as
shown in FIG. 2, a cathode 200 is connected to an peripheral region
of an conductive layer, such as a seed layer 7, formed on a surface
of a substrate W, and a plating solution 204 is filled into between
the substrate W and an anode 202 disposed opposite the substrate W.
A plated film is deposited on the conductive layer of the substrate
W by passing a plating current between the anode 200 and the
cathode 202 from a power source 206.
[0015] Semiconductor wafers and liquid crystal substrates for LSI's
tend to increase in area year by year. In line with this tendency,
the substrates are posing problems. In detail, as the area of the
substrate W increases, the electric resistance (sheet resistance)
of the conductive layer, such as a seed layer 7, ranging from the
cathode 200 on the periphery of the substrate W to the center of
the substrate W also increases. As a result, a potential difference
produces in the surface of the substrate W, causing a difference in
the plating rate. FIG. 2 is an electrical equivalent circuit
diagram of general electroplating, and the following resistance
components exist in this circuit:
[0016] R1: Power source wire resistance between power source 206
and anode 202, and various contact resistances
[0017] R2: Polarization resistance at anode 202
[0018] R3: Resistance of plating solution 204
[0019] R4: Polarization resistance at cathode 200
[0020] R5: Resistance of conductive layer (sheet resistance)
[0021] R6: Power source wire resistance between cathode 200 and
power source 206, and various contact resistances
[0022] As shown in FIG. 2, when the resistance R5 of the conductive
layer becomes higher than the other electric resistances R1 to R4
and R6, the potential difference arising between both ends of this
resistance R5 of the conductive layer increases, and accordingly, a
difference occurs in the plating current. Thus, the plated film
growth rate lowers at a position distant from the cathode 200. If
the film thickness of the conductive layer is small, the resistance
R5 further increases, and this phenomenon appears conspicuously.
This fact means that the current density differs in-plane of the
substrate W, and the characteristics of a plated film itself
(resistivity, purity, burial characteristics, etc. of the plated
film) are not uniform in-plane.
[0023] Even in electrolytic etching in which the substrate is an
anode, the same problems occur, merely with the direction of
electric current being reversed. In a manufacturing process for a
large-diameter wafer, for example, the etching rate at the center
of the wafer slows compared with the peripheral edge portion.
[0024] As a method for avoiding these problems, it is conceivable
to increase the thickness of the conductive layer or decrease the
electric conductivity of the conductive layer. However, the
substrate is subject to various restrictions even in manufacturing
steps other than plating. For example, when a thick conductive
layer is formed on a fine pattern by sputtering, voids easily occur
inside the pattern. Thus, it is impossible to easily increase the
thickness of the conductive layer or change the film type of the
conductive layer.
[0025] In order to solve above problem, the applicant has proposed
a plating apparatus wherein a high-resistance structure 208, which
has lower electric resistivity than the electric resistivity of the
plating solution, is disposed between an anode 202 and a substrate
W, as shown in FIG. 3. With this structure, an electric equivalent
circuit diagram is shown in FIG. 3., and a resistance Rp of the
high-resistance structure 208 is added as compared to the electric
equivalent circuit diagram shown in FIG. 2. Therefore, if a value
of the resistance Rp of the high-resistance structure 208 becomes
high, a value ((R2+R3+Rp+R4)/(R2+R3+Rp+R4+R5)) comes near one, the
influence of the resistance R5, i.e., a resistant factor (sheet
resistance) of the conductive layer becomes low.
SUMMARY OF THE INVENTION
[0026] As a seed layer becomes thinner and the sheet resistance of
a surface (surface to be plated) of a substrate becomes higher with
the progress toward seed layer-less substrates, it becomes more and
more difficult to form a plated film having a uniform thickness
over an entire surface of a substrate having fine interconnect
recesses formed in the surface while securely filling the
interconnect recesses with the metal (interconnect material)
without forming voids in the embedded metal.
[0027] For example, the use of a porous structure having an
apparent porosity of 20% (in accordance with JIS R 2205) as the
high-resistance structure 208 shown in FIG. 3 may provide a plated
film having a sufficient in-plane uniformity of plated film
thickness in the current 65 nm-node generation, as shown in FIG. 4.
It is considered, however, that variation in the thickness of a
plated film formed on a surface or a substrate becomes increasingly
larger in the next 45 nm-node generation and the following 32
nm-node generation and the formation of a plated film having a
sufficient in-plating uniformity of plated film thickness becomes
increasingly difficult.
[0028] Further, it is generally difficult to produce such a plated
film as not to impose a burden on a CMP processing while preventing
deterioration of the quality of the plated film and scratches in a
surface of the plated film. In this sense, the existing
semiconductor manufacturing process is not perfect.
[0029] The present invention has been made in view of the above
situation. It is therefore a first object of the present invention
to provide a plating apparatus and a plating method which can form
a plated film having a more uniform thickness over an entire
surface of a substrate and can securely fill interconnect recesses
with the metal without forming voids in the embedded metal even
when the substrate has a high sheet resistance in the surface.
[0030] It is a second object of the present invention to provide a
plating apparatus and a plating method which can form a plated film
that facilitates a CMP processing, thus reducing the burden on the
next-step CMP processing.
[0031] It is a third object of the present invention to provide an
electrolytic processing apparatus and an electrolytic processing
method which, when applied to e.g. an electroplating apparatus, can
form a plated film having an enhanced in-plane uniformity of film
thickness on a surface of a substrate even when the substrate is a
large-area substrate with a thin conductive layer having a high
electric resistance formed in the surface.
[0032] In order to achieve the above objects, the present invention
provides a plating apparatus comprising: a substrate holder for
holding a substrate; a cathode portion including a cathode for
contact with the substrate held by the substrate holder to feed
electricity to the substrate; and an anode, partly or wholly having
a high resistance, disposed opposite a surface of the substrate
held by the substrate holder; wherein plating of the surface of the
substrate is carried out while filling between the anode and the
substrate held by the substrate holder with a plating solution.
[0033] By carrying out plating using the anode partly or wholly
having a high resistance, it becomes possible to allow the anode to
have its own terminal effect. Further, by providing a feeding point
to the anode at a certain one point in the center of the anode, it
becomes possible to cause the anode to produce a terminal effect,
in the reverse direction to the terminal effect of the surface of
the substrate, which increases voltage drop with distance from the
center of the anode. Further, by making the resistances (sheet
resistances) of the anode and the surface of the substrate, facing
each other, at the same level, the sum of the voltage drop in the
surface of the substrate and the voltage drop in the anode can be
made equal for a current pathway running through the center of the
substrate surface, for a current pathway running through the
peripheral region of the substrate, and for any intermediate
current pathway between them. Thus, the electric resistance can be
made equal for any current pathway, whereby electric current can be
distributed evenly over the substrate surface and the thickness of
a plated film formed on the substrate surface can be made
uniform.
[0034] As a plated film grows on a surface of a substrate, the
electric resistance (sheet resistance) of the surface of the
substrate decreases and the terminal effect in the surface of the
substrate becomes smaller gradually. When plating is continued,
because of the terminal effect of the anode, the resulting plated
film will be thick in the center of the substrate and thin in the
peripheral region of the substrate. If a feeding point to the
anode, partly or wholly having a high resistance, is provided not
in the center but in the peripheral region of the anode, the
direction of the terminal effect of the anode will be the same as
the terminal effect of the surface of the substrate. Accordingly,
when plating is continued using such an anode, the resulting plated
film will be thin in the center of the substrate and thick in the
peripheral region of the substrate.
[0035] Thus, in the case of carrying out plating with the use of an
anode, partly or wholly having a high resistance, a change in the
position of a feeding point to the anode produces a significant
difference in the thick distribution of plated film. By providing
feeding points to the anode both in the center and in the
peripheral region of the anode so that plated films having reverse
thickness distributions are combined, a plated film having a
uniform thickness distribution over the entire substrate surface
can be formed. Further, by providing each of the feeding points, to
the center and to the peripheral portion of the anode, with a
switch capable of on/off switching of a power source or an electric
current and controlling the current ratio or the on/off time ratio,
a plated film having a more uniform thickness distribution can be
obtained. Furthermore, when an additional feeding point to the
anode is provided between the central and the peripheral feeding
points, a more precise control of the thickness distribution of
plated film becomes possible.
[0036] In a preferred embodiment of the present invention, the high
resistance of the anode is set at the same level as the resistance
of the anode-facing surface of the substrate held by the substrate
holder.
[0037] By making the high resistance (sheet resistance) of part or
the whole of the anode at the same level as the resistance (sheet
resistance) of the substrate surface (surface to be plated), the
terminal effect produced in the anode can be made at the same level
as the terminal effect produced in the substrate surface, thereby
counterbalancing the influence of both terminal effects.
[0038] Preferably, the high resistance of part or the whole of the
anode is higher than the electric resistance of the plating
solution.
[0039] In a preferred aspect of the present invention, the high
resistance of part or the whole of the anode is provided radially
from the center of the anode.
[0040] This makes it possible to produce a terminal effect in the
anode in the reverse direction to the terminal effect of the
surface of the substrate by feeding electricity to the anode from
its center. In this regard, a high resistance is necessary only in
the radial direction from the center of an anode in order to
increase voltage drop with distance from the center. Thus, the
anode may have a low resistance in the height direction or in the
circumferential direction. By utilizing this, it is possible to
attach a ring-shaped contact to the anode so as to improve
uniformity of the anode potential in the circumferential direction.
The anode may be made to have a high resistance radially with
distance from its center by decreasing the cross-sectional area
radially from the center, i.e., by gradually decreasing the
thickness of the anode with distance from the center.
[0041] The part or the whole of the anode having the high
resistance is preferably composed of a material having a high
resistivity.
[0042] The anode can be made to partly or wholly have a high
resistance by using a material having a high resistivity. Examples
of the material having a high resistivity include a conductive
plastic, such as a conductive PEEK (polyether ether ketone) having
a slight conductivity, a conductive ceramic and a conductive glass.
It is possible to use a material having a high resistivity in
combination with a material having a low resistivity.
[0043] Preferably, a thin metal film and/or a thin metal oxide film
is provided on a substrate-facing surface of the anode which faces
the surface of the substrate held by the substrate holder.
[0044] The provision of a thin metal film on a substrate-facing
surface of the anode enables a plating current to flow evenly
between the anode (thin metal film) and the surface of a substrate.
Further, by covering the thin metal film with a thin metal oxide
film, the thin metal film can be prevented from being oxidized or
peeled off from the anode. The thin metal film can be exemplified
by titanium, and the thin metal oxide film can be exemplified by
iridium oxide.
[0045] In a preferred aspect of the present invention, a central
contact, in contact with a feeding wire, for feeding electricity to
the anode is provided in the center of the anode.
[0046] By feeding electricity to the anode, partly or wholly having
a high resistance, from the center of the anode so as to allow an
electric current to flow in the anode from the center toward the
periphery, a terminal effect in the reverse direction to the
terminal effect of the surface of the substrate can be produced in
the anode.
[0047] In a preferred aspect of the present invention, a peripheral
contact, in contact with a feeding wire, for feeding electricity to
the anode is provided in the peripheral region of the anode
continuously over the entire circumference.
[0048] By feeding electricity to the anode, partly or wholly having
a high resistance, from the peripheral region of the anode so as to
allow an electric current to flow in the anode from the peripheral
region toward the center, a terminal effect in the same direction
as the terminal effect of the surface of the substrate can be
produced in the anode. Further, by providing a ring-shaped
peripheral contact over the entire circumference of the anode,
uniformity of the anode potential in the circumferential direction
can be improved.
[0049] Preferably, at least one intermediate contact, in contact
with a feeding wire, for feeding electricity to the anode is
provided between the central contact and the peripheral contact of
the anode continuously over the entire circumference.
[0050] By thus increasing the number of points for feeding
electricity to the anode, an electric current flowing in the anode
can be finely adjusted to form a plated film having a more uniform
thickness on the surface of the substrate.
[0051] Preferably, the plating apparatus has plating power sources
respectively for each of the feeding wires for feeding electricity
to the anode.
[0052] This makes it possible to independently control an electric
current flowing in the anode from the center toward the peripheral
region of the anode, an electric current flowing in the anode from
the peripheral region toward the center of the anode, etc., thereby
forming a plated film having a more uniform thickness on the
surface of the substrate.
[0053] Preferably, the plating apparatus has switches for on/off
switching of electric current respectively for each of the feeding
wires for feeding electricity to the anode.
[0054] This makes it possible to independently change the time for
an electric current to flow in the anode from the center toward the
peripheral region of the anode, the time for an electric current to
flow in the anode from the peripheral region toward the center of
the anode, etc., thereby forming a plated film having a more
uniform thickness on the surface of the substrate. Further, the
cost and the size of the apparatus can be reduced as compared to
the case of providing an independent power source for each feeding
wire.
[0055] The plated film to be formed on the surface of the substrate
is, for example, copper.
[0056] The present invention provides a plating method comprising:
preparing a substrate having interconnect recesses covered with a
barrier layer or a seed layer in a surface; disposing an anode,
partly or wholly having a high resistance, opposite the surface of
the substrate; filling between the substrate and the anode with a
plating solution; and carrying out plating by feeding electricity
to the barrier layer or the seed layer from its peripheral region
and feeding electricity to the anode from its center in the early
stage of plating, and carrying out plating by feeding electricity
to the barrier layer or the seed layer from its peripheral region
and feeding electricity to the anode from its peripheral region in
the later stage of plating.
[0057] The present invention provides another plating apparatus
comprising: a substrate holder for holding a substrate; a cathode
portion including a cathode for contact with the substrate held by
the substrate holder to feed electricity to the substrate; an anode
disposed opposite a surface of the substrate; and a contact member
disposed between the substrate held by the substrate holder and the
anode movably in a direction closer to or away from the substrate,
said contact member having through-holes extending linearly through
the contact member in said movement direction.
[0058] When carrying out plating of a substrate by providing a
contact member, having through-holes linearly extending vertically
to an anode and the substrate, between the anode and the substrate
and bringing the contact member into contact with the surface of
the substrate, a surface of the substrate in non-interconnect
regions, except portions facing the through-holes provided in the
contact member, directly contacts the contact member and the
plating solution is excluded from the contact area. Accordingly,
columnar plated films (columnar portions), which have grown along
the through-holes, are formed. On the other hand, the interior
surfaces of interconnect recesses, such as trenches, in
interconnect regions are not in contact with the contact member,
and the recesses are filled with the plating solution. Accordingly,
in the interconnect regions a plated film first grows such that it
fills in the recesses such as trenches and, after the plated film
has grown to come into contact with the surface of the contact
member, the plated film further grows in the form of columns along
the through-holes of the contact member. Foots of the columnar
plated films (columnar portions) formed in the non-interconnect
regions and the interconnect regions lie on the same level.
[0059] When polishing the surface, having such columnar plated
films, by CMP, the numerous columnar plated films on the surface
can be easily removed with a relatively small force. After the
removal of the numerous columnar plated films, the substrate
surface takes on a flat surface with few irregularities, which is
easier to polish with CMP as compared with a conventional plated
film having surface irregularities.
[0060] Preferably, the plating apparatus further comprises a press
mechanism for pressing a contact surface, which faces the surface
of the substrate held by the substrate holder, of the contact
member against the surface of the substrate.
[0061] Thus, the substrate-facing contact surface of the contact
member can be kept pressed against the surface of the substrate,
held by the substrate holder, by the press mechanism while the
contact member is in contact with the substrate.
[0062] A press member for pressing the contact surface of the
contact member against the surface of the substrate may be disposed
between the contact member and the anode.
[0063] Thus, the contact surface of the contact member may be kept
pressed against the surface of the substrate by the press member
while the contact member is in contact with the substrate. The
contact member may be composed of a material, such as a porous
material, which can pass electricity therethrough, i.e., can pass a
plating solution therethrough.
[0064] A flexible cushioning material for uniformly pressing the
contact surface of the contact member against the surface of the
substrate may be disposed between the contact member and the
anode.
[0065] Thus, the entire contact surface of the contact member can
be pressed against the surface of the substrate at a more uniform
pressure by the cushioning member, thereby preventing the contact
surface of the contact member from separating from the surface of
the substrate locally.
[0066] The through-holes provided in the contact member may have a
circular cross-sectional shape with a diameter of, for example, not
more than 12 .mu.m, and may be distributed at a density of
1.0.times.10.sup.5 to 1.0.times.10.sup.9/cm.sup.2.
[0067] In this case, the columnar plated films formed on the
surface of the substrate have a cylindrical shape having a diameter
of not more than 12 .mu.m and are distributed at a density of
1.0.times.10.sup.5 to 1.0.times.10.sup.9/cm.sup.2. Such cylindrical
plated films can be easily removed by later CMP. Further, this can
prevent a case in which a through-hole is too large compared to an
interconnect recess, such as a trench, to form a columnar
(cylindrical) plated film in the interconnect region.
[0068] The contact surface of the contact member preferably has an
Ra value, indicative of surface roughness, of not more than 1
.mu.m.
[0069] By making the Ra value (center-line average roughness) of
the contact surface of the contact member not more than 1 .mu.m,
the contact surface can be made to make tight contact with the
surface of the substrate, thus preventing the formation of a gap
between the contact surface and the substrate surface upon their
contact. This can prevent an extra plated film being formed in a
non-interconnect region and imposing a burden on a later CMP
processing.
[0070] The contact member is preferably composed of an insulating
material.
[0071] For example, the contact member is composed of
polycarbonate, a ceramic, carbon, polyester, glass, silicon, a
resist material or a fluorocarbon resin.
[0072] Resist materials for photolithography or X-ray lithography
can be used as the resist material. For example, the use of PMMA
(polymethyl methacrylate) or SU-8 (trade name, manufactured by
Kayaku Microchem Corp.) enables fine patterning at a high aspect
ratio and can provide a thick film (contact member) having fine
through-holes.
[0073] A contact member composed of a fluorocarbon resin may be
exemplified by a contact member of PFA having fine through-holes
which have been formed by a lithography technique.
[0074] Preferably, the plating apparatus further comprises an
etching mechanism for etching a plated film formed on the surface
of the substrate.
[0075] The burden on a later CMP processing can be further reduced
by etching away columnar plated films, which have been formed on
the surface of the substrate, by the etching mechanism. Examples of
the etching mechanism include etching by a power source capable of
reversing polarity or an equivalent circuit, and etching with a
chemical (chemical etching).
[0076] Preferably, each of the through-holes provided in the
contact member is tapered such that the cross-sectional area
gradually decreases with distance from the contact surface.
[0077] Pointed tapered columnar, plated films will therefore be
formed on the surface of the substrate. When providing such tapered
through-holes, e.g., having a large diameter, in the contact member
and forming tapered plated films in the through-holes, the plated
films can be easily drawn out of the through-holes after
plating.
[0078] The present invention provides another plating method
comprising: preparing a substrate having interconnect recesses
formed in a surface; disposing an anode opposite the surface of the
substrate; disposing a contact member, having linearly-extending
through-holes, between the substrate and the anode such that a
contact surface, which faces the surface of the substrate, of the
contact member is in pressure contact with the surface of the
substrate; and carrying out plating of the surface of the substrate
by passing a plating current between the anode and the surface of
the substrate while filling between the anode and the substrate
with a plating solution.
[0079] Preferably, the plating of the surface of the substrate is
carried out while keeping the contact member stationary with
respect to the substrate.
[0080] Preferably, after carrying out the plating of the surface of
the substrate, the position of the contact surface of the contact
member relative to the surface of the substrate is changed, and
additional plating of the surface of the substrate is carried
out.
[0081] When interconnect recesses, such as trenches, are deep and a
lot of time is therefore necessary for plating, this manner of
plating can prevent columnar plated films from growing so much that
the films cannot be easily drawn out of the through-holes provided
in the contact member.
[0082] The position of the contact surface of the contact member
relative to the surface of the substrate may be changed after
separating the contact member from the surface of the
substrate.
[0083] When again pressing the contact member against the surface
of a substrate after separating the contact member from the
substrate surface, the contact member will push down columnar
plated films which have been formed till then. New columnar plated
films can then be grown on the fallen plated films by the next
plating. By repeating this, a level difference in the surface
irregularities of a plated film can be gradually decreased without
damage to the contact member and columnar plated films, which have
been formed on the substrate surface when embedding of the plated
metal in interconnect recesses is completed, can be made relatively
low. Such columnar plated films can be drawn out of the porous
contact member without damage to the contact member. The relative
position between the contact member and the substrate can, of
course, be changed by actively moving the contact member or the
substrate. In addition, the relative position can also be changed
by a dimensional design error or allowance.
[0084] Preferably, before carrying out the additional plating of
the surface of the substrate, a plated film formed on the surface
of the substrate is subjected to etching.
[0085] In a preferred aspect of the present invention, the etching
is carried out by reversing the polarities in plating of the anode
and the surface of the substrate while filling between the anode
and the substrate with the plating solution.
[0086] The etching is preferably carried out while keeping the
contact member at a distance from the surface of the substrate.
[0087] When carrying out etching in this manner, the flow of
electric current is concentrated in protruding columnar plated
films, whereby the columnar plated films are etched preferentially
than the plated film embedded in interconnect recesses. After the
columnar plated films are removed by etching, the next plating is
carried out. By repeating this procedure, a level difference in the
surface irregularities of a plated film can be gradually decreased
without damage to the contact member and columnar plated films,
which have been formed on the substrate surface when embedding of
the plating metal in the interconnect recesses is completed, can be
made relative low. Such columnar plated films can be drawn out of
the contact member without damage to the contact member. Further,
by carrying out the etching under isotropic-etching conditions by
applying the reverse electric field to that of plating between the
anode and the surface of the substrate so as to etch away those
parts of columnar plated films which correspond to half of the
thickness, the columnar plated films can be removed by etching
irrespective of their heights.
[0088] The present invention provides a substrate processing method
comprising: carrying out plating of a substrate by the plating
method according to claim 23; and then polishing a surface of the
substrate by a CMP apparatus, thereby removing an extra plated film
present outside interconnect portions.
[0089] The present invention provides another substrate processing
method comprising: carrying out plating of a substrate by the
plating method according to claim 23; subsequently removing
columnar portions on a surface of the substrate by an etching
apparatus to flatten the surface; and then polishing the substrate
surface by a CMP apparatus, thereby removing an extra plated film
present outside interconnect portions.
[0090] The present invention provides a plated film comprising
numerous columnar portions, obtained by a plating process
comprising plating a surface of a substrate while keeping a contact
member, having linearly-extending through-holes, in contact with a
surface of the substrate to grow the columnar portions linearly
along the through-holes.
[0091] Preferably, the columnar portions are circular portions
having a diameter of not more than 12 .mu.m.
[0092] The present invention provides an electrolytic processing
apparatus comprising: a substrate holder for holding a substrate; a
first electrode for contact with a substrate to feed electricity to
a surface of the substrate; a second electrode disposed opposite
the surface of the substrate held by the substrate holder; a porous
structure having a pressure loss of not less than 500 kPa, disposed
between the substrate held by the substrate holder and the second
electrode; an electrolytic solution injection section for injecting
an electrolytic solution into between the substrate held by the
substrate holder and the second electrode; and a power source for
applying a voltage between the first electrode and the second
electrode.
[0093] The electric resistance between a substrate (first
electrode) and the second electrode can be made still larger by
disposing a porous structure having a pressure loss of not less
than 500 kPa between the substrate (first electrode) and the second
electrode. This can further reduce the effect of the electric
resistance of a conductive layer formed on a surface of the
substrate and make the electric field more uniform over the entire
surface of the substrate. Thus, when the electrolytic processing
apparatus is employed as an electroplating apparatus, a practical
plated film having a high in-plane uniformity of film thickness
with a thickness variation of no more than about 2% can be formed
on the surface of the substrate.
[0094] In a preferred aspect of the present invention, the porous
structure has a pressure loss of not less than 1000 kPa. This
enables the formation on a surface of a substrate of a plated film
having a higher in-plane uniformity of film thickness with a film
thickness variation of no more than about 1.2%. The pressure loss
of the porous structure is more preferably not less than 1500
kPa.
[0095] The present invention provides another electrolytic
processing apparatus comprising: a substrate holder for holding a
substrate; a first electrode for contact with a substrate to feed
electricity to a surface of the substrate; a second electrode
disposed opposite the surface of the substrate held by the
substrate holder; a porous structure having an apparent porosity of
not more than 19%, disposed between the substrate held by the
substrate holder and the second electrode; an electrolytic solution
injection section for injecting an electrolytic solution into
between the substrate held by the substrate holder and the second
electrode; and a power source for applying a voltage between the
first electrode and the second electrode.
[0096] The electric resistance between a substrate (first
electrode) and the second electrode can be made larger by disposing
a porous structure having an apparent porosity of not more than 19%
between the substrate (first electrode) and the second electrode.
This can reduce the effect of the electric resistance of a
conductive layer formed in a surface of the substrate and make the
electric field more uniform over the entire surface of the
substrate. Thus, when the electrolytic processing apparatus is
employed as an electroplating apparatus, a plated film having a
higher in-plane uniformity of film thickness can be formed on the
surface of the substrate. In order to reduce variation in the
thickness of plated film, the apparent porosity of the porous
structure is preferably not more than 15%, more preferably not more
than 10%.
[0097] The present invention provides yet another electrolytic
processing apparatus comprising: a substrate holder for holding a
substrate; a first electrode for contact with a substrate to feed
electricity to a surface of the substrate; a second electrode
disposed opposite the surface of the substrate held by the
substrate holder; a porous structure, disposed between the
substrate held by the substrate holder and the second electrode,
having an overall electric resistance which is not less than 0.02
time the sheet resistance of a surface conductive layer of the
substrate, said overall electric resistance being the electric
resistance between the upper and lower surfaces of the porous
structure with its interior filled with an electrolytic solution;
an electrolytic solution injection section for injecting the
electrolytic solution into between the substrate held by the
substrate holder and the second electrode; and a power source for
applying a voltage between the first electrode and the second
electrode.
[0098] By thus making the overall electric resistance between upper
and lower surfaces of a porous structure with its interior filled
with an electrolytic solution sufficiently high with respect to the
sheet resistance (electric resistance) of a conductive layer formed
in a substrate surface, the electric field can be made more uniform
over the entire surface of the substrate. Thus, when the
electrolytic processing apparatus is employed as an electroplating
apparatus, a plated film having a higher in-plane uniformity of
film thickness can be formed on the surface of the substrate.
[0099] In a preferred aspect of the present invention, the porous
structure has a resistivity of not less than 1.0.times.10.sup.5
.OMEGA.cm.
[0100] When the electrolytic processing apparatus is employed as an
electroplating apparatus, the use of the porous structure whose own
resistivity is high makes it possible to carry out plating with
voltage highly-reproducible and stable to plating current. The
resistivity of the porous structure is preferably not less than
1.0.times.10.sup.6 .OMEGA.cm.
[0101] The porous structure is composed of, for example, silicon
carbide, silicon carbide with oxidation-treated surface, alumina or
a plastic, or a combination thereof.
[0102] The electric processing may be electroplating of Cr, Mn, Fe,
Co, Ni, Cu, Zn, Ga, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os, Ir, Pt, Au,
Hg, Tl, Pb or Bi, or an alloy thereof, or electrolytic etching.
[0103] The present invention provides an electrolytic processing
method comprising: filling between a surface of a substrate, in
contact with a first electrode, and a second electrode disposed
opposite the surface of the substrate with an electrolytic
solution; disposing in the electrolytic solution a porous structure
of which the apparent porosity is adjusted to not more than 19%, or
the pressure loss is adjusted to not less than 500 kPa, or at least
one of the specific gravity and the water absorption is adjusted;
and applying a voltage between the first electrode and the second
electrode.
[0104] According to this method, electrolytic processing of a
surface of a substrate can be carried out with the electric field
at the surface of the substrate adjusted to the desired state so
that the substrate after electrolytic processing can have a
processed surface in the intended state. The electric field can be
made more uniform over an entire surface of a substrate by
adjusting the apparent porosity of the porous structure to not more
than 19%, preferably not more than 15%, more preferably not more
than 10%, or adjusting the pressure loss to not less than 500 kPa,
preferably not less than 1000 kPa, more preferably not less than
1500 kPa. Thus, in the case where the electrolytic processing is
plating, the in-plane uniformity of a thickness of a plated film
formed on a surface of a substrate can be enhanced.
[0105] The present invention provides another electrolytic
processing method comprising: filling between a surface of a
substrate, in contact with a first electrode, and a second
electrode disposed opposite the surface of the substrate with an
electrolytic solution; disposing in the electrolytic solution a
porous structure of which the apparent porosity is adjusted to not
more than 19%, or the overall electric resistance is adjusted to
not less than 0.02 time the sheet resistance of a surface
conductive layer of the substrate, said overall electric resistance
being the electric resistance between the upper and lower surfaces
of the porous structure with its interior filled with the
electrolytic solution, or at least one of the specific gravity and
the water absorption is adjusted; and applying a voltage between
the first electrode and the second electrode.
[0106] The electric field can be made more uniform over an entire
surface of a substrate also by adjusting the overall electric
resistance between upper and lower surfaces of a porous structure
with its interior filled with an electrolytic solution to not less
than 0.02 time the sheet resistance of a surface conductive layer
of the substrate. Thus, in the case where the electrolytic
processing is plating, the in-plane uniformity of a thickness of a
plated film formed on the surface of the substrate can be
enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0107] FIGS. 1A through 1C are diagrams illustrating, in a sequence
of process steps, a process for forming copper interconnects by
plating;
[0108] FIG. 2 is a diagram showing a conventional electroplating
apparatus;
[0109] FIG. 3 is a diagram showing an electroplating apparatus
having a high-resistance structure;
[0110] FIG. 4 is a graphical diagram showing thickness
distributions of plated films which are expected to be obtained
when plating is carried out on substrates of the current
generation, the next generation and its next generation by using a
porous structure having an apparent porosity of 20% as the
high-resistance structure of the electroplating apparatus shown in
FIG. 3;
[0111] FIG. 5 is an overall plan view of a substrate processing
apparatus incorporating a plating apparatus according to an
embodiment of the present invention;
[0112] FIG. 6 is a plan view of the plating apparatus shown in FIG.
5;
[0113] FIG. 7 is an enlarged cross-sectional view of a substrate
holder and a cathode portion of the plating apparatus shown in FIG.
5;
[0114] FIG. 8 is a front view of a pre-coating/recovery arm of the
plating apparatus shown in FIG. 5;
[0115] FIG. 9 is a plan view of the substrate holder of the plating
apparatus shown in FIG. 5;
[0116] FIG. 10 is a cross-sectional view taken along line B-B of
FIG. 9;
[0117] FIG. 11 is a cross-sectional view taken along line C-C of
FIG. 9;
[0118] FIG. 12 is a plan view of the cathode portion of the plating
apparatus shown in FIG. 5;
[0119] FIG. 13 is a cross-sectional view taken along line D-D of
FIG. 12;
[0120] FIG. 14 is a plan view of an electrode arm section of the
plating apparatus shown in FIG. 5;
[0121] FIG. 15 is a schematic cross-sectional diagram of the
plating apparatus shown in FIG. 5, showing an electrode head and a
substrate held by the substrate holder during plating;
[0122] FIG. 16 is a diagram illustrating an anode having a high
resistance in the radial direction;
[0123] FIG. 17 is a diagram illustrating provision of a switch for
each feeding contact to an anode;
[0124] FIG. 18 is a diagram illustrating provision of a central
contact, a peripheral contact and an intermediate contact in a
surface of an anode;
[0125] FIG. 19 is a perspective view showing another anode;
[0126] FIG. 20 is a schematic cross-sectional diagram of a plating
apparatus according to another embodiment of the present invention,
showing an electrode head and a substrate held by a substrate
holder immediately before plating;
[0127] FIG. 21 is a schematic cross-sectional diagram of the
plating apparatus of FIG. 20, showing the electrode head and the
substrate held by the substrate holder during plating;
[0128] FIG. 22 is an enlarged view of the main portion of FIG.
21;
[0129] FIGS. 23A through 23D are diagrams illustrating a process of
the formation of plated film in a non-interconnect region by a
plating method according to an embodiment of the present
invention;
[0130] FIGS. 24A through 24D are diagrams illustrating a process of
the formation of plated film in an interconnect region by the
plating method according to the embodiment of the present
invention;
[0131] FIGS. 25A and 25B are diagrams illustrating a process of
removing, by CMP processing, columnar plated films formed by the
plating method according to the embodiment of the present
invention;
[0132] FIGS. 26A through 26E are diagrams illustrating a process of
the formation of plated film on a surface of a substrate by a
plating method according to another embodiment of the present
invention;
[0133] FIGS. 27A and 27B are diagrams illustrating a process of
removing columnar plated films by etching in the course of
plating;
[0134] FIGS. 28A and 28B are diagrams illustrating a process of
removing columnar plated films by isotropic etching in the course
of plating;
[0135] FIGS. 29A and 29B are cross-sectional diagrams showing the
main portion of a plating apparatus according to yet another
embodiment of the present invention;
[0136] FIG. 30 is a cross-sectional diagram showing the main
portion of a plating apparatus according to yet another embodiment
of the present invention;
[0137] FIG. 31 is a schematic diagram of a plated film, as viewed
obliquely from above, obtained by carrying out plating of a surface
of a substrate while keeping a contact member, having
linearly-extending through-holes, in contact with the substrate
surface;
[0138] FIG. 32 is a schematic front view of a plated film obtained
by carrying out plating of a surface of a substrate while keeping a
contact member, having linearly-extending through-holes, in contact
with the substrate surface;
[0139] FIG. 33 is a schematic cross-sectional diagram of a plating
apparatus (electrolytic processing apparatus) according to yet
another embodiment of the present invention, showing an electrode
head and a substrate held by a substrate holder during
electroplating;
[0140] FIG. 34 is a diagram showing the positional relationship
between the substrate, a sealing member and a plating solution
injection section during plating in the plating apparatus shown in
FIG. 33;
[0141] FIG. 35 is a graphical diagram showing the relationship
between the pressure loss and the electric resistivity of a porous
structure of silicon carbide, as obtained by using porous
structures having various pressure losses in the range of 100-2800
kPa; and measuring the voltage between a cathode (first electrode)
and an anode (second electrode) when a predetermined current is
passed between them, and calculating the electric resistivity of
the porous structure from the relationship between the measured
voltage and the current;
[0142] FIG. 36 is a graphical diagram showing the relationship
between the electric resistivity of a porous structure and
variation (relative standard deviation) of plated film thickness in
a substrate surface (in the radial direction), as obtained by a
simulation calculation;
[0143] FIG. 37 is a graphical diagram showing the relationship
between the pressure loss of a porous structure and variation of
plated film thickness, obtained from the data of FIGS. 35 and
36;
[0144] FIG. 38 is a graphical diagram showing the relationship
between the apparent porosity and the electric resistivity of a
porous structure of alumina, as obtained by using porous structures
having various apparent porosities in the range of 1-30%; and
measuring the voltage between a cathode (first electrode) and an
anode (second electrode) when a predetermined current is passed
between them, and calculating the electric resistivity of the
porous structure from the relationship between the measured voltage
and the current;
[0145] FIG. 39 is a graphical diagram showing the relationship
between the apparent porosity of a porous structure and variation
of plated film thickness, obtained from the data of FIGS. 36 and
38;
[0146] FIG. 40 is a graphical diagram showing the relationship
between current and voltage, as observed when carrying out copper
plating of a substrate by using porous structures of silicon
carbide having an apparent porosity of 15% and a resistivity of
1.0.times.10.sup.3 to 1.0.times.10.sup.6 .OMEGA.cm, and passing
electric current between a cathode (first electrode) and an anode
(second electrode);
[0147] FIG. 41 is a graphical diagram showing the results of
analysis of a plated film thickness in a substrate surface (in the
radial direction), as analyzed by changing the ratio R: the overall
electric resistance between upper and lower surfaces of a porous
structure with its interior filled with a plating solution/the
sheet resistance of a seed layer (conductive layer) of ruthenium
formed on a silicon substrate, in the range of 0.002-1
(R.sub.0<R.sub.1<R.sub.2<R.sub.3);
[0148] FIG. 42 is a graphical diagram showing the relationship
between the electric resistance ratio R and variation of plated
film thickness, calculated from the analytical results shown in
FIG. 41;
[0149] FIGS. 43A and 43B are diagrams showing variations of the
electrode head;
[0150] FIG. 44 is a diagram showing the main portion of a plating
apparatus (electrolytic processing apparatus) according to yet
another embodiment of the present invention together with a plating
solution (electrolytic solution) circulation system; and
[0151] FIG. 45 is a diagram showing the positional relationship
between a substrate, a sealing member and a plating solution
injection section during plating in the plating apparatus shown in
FIG. 44.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0152] Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. The following
embodiments relate to the application of the present invention
useful for forming interconnects of copper by embedding copper in
fine interconnect recesses formed in a surface of the
substrate.
[0153] FIG. 5 is an overall layout showing a substrate processing
apparatus incorporating a plating apparatus according to an
embodiment of the present invention. As shown in FIG. 5, this
substrate processing apparatus has a facility which houses therein
two loading/unloading units 10 for housing a plurality of
substrates W therein, two plating apparatuses 12 for performing
plating process, a transfer robot 14 for transferring substrates W
between the loading/unloading units 10 and the plating apparatuses
12, and plating solution supply equipment 18 having a plating
solution tank 16.
[0154] The plating apparatus 12, as shown in FIG. 6, is provided
with a substrate processing section 20 for performing plating
process and processing incidental thereto, and a plating solution
tray 22 for storing a plating solution is disposed adjacent to the
substrate processing section 20. There is also provided an
electrode arm portion 30 having an electrode head 28 which is held
at the front end of a pivot arm 26 pivotable about a rotating shaft
24 and which is swung between the substrate processing section 20
and the plating solution tray 22. Furthermore, a
pre-coating/recovering arm 32, and fixed nozzles 34 for ejecting
pure water or a chemical liquid such as ion water, and further a
gas or the like toward a substrate are disposed laterally of the
substrate processing section 20. In this embodiment, three of the
fixed nozzles 34 are disposed, and one of them is used for
supplying pure water.
[0155] The substrate processing section 20, as shown in FIG. 7, has
a substrate holder 36 for holding a substrate W with its surface
(surface to be plated) facing upward, and a cathode portion 38
located above the substrate holder 36 so as to surround a
peripheral portion of the substrate holder 36. Further, a
substantially cylindrical bottomed cup 40 surrounding the periphery
of the substrate holder 36 for preventing scatter of various
chemical liquids used during processing is provided so as to be
vertically movable by an air cylinder (not shown).
[0156] The substrate holder 36 is adapted to be raised and lowered
by the air cylinder 44 between a lower substrate transfer position
A, an upper plating position B, and a pretreatment/cleaning
position C intermediate between these positions. The substrate
holder 36 is also adapted to rotate at an arbitrary acceleration
and an arbitrary velocity integrally with the cathode portion 38 by
a rotating motor and a belt (not shown). Substrate carry-in and
carry-out openings (not shown) are provided in confrontation with
the substrate transfer position A in a side panel of the plating
apparatus 12 facing the transfer robot 14. When the substrate
holder 36 is raised to the plating position B, a sealing member 90
and cathodes 88 (to be described below) of the cathode portion 38
are brought into contact with the peripheral edge portion of the
substrate W held by the substrate holder 36. On the other hand, the
cup 40 has an upper end located below the substrate carry-in and
carry-out openings, and when the cup 40 ascends, the upper end of
the cup 40 reaches a position above the cathode portion 38 closing
the substrate carry-in and carry-out openings, as shown by
imaginary lines in FIG. 7.
[0157] The plating solution tray 22 serves to wet a porous
structure 110 and an anode 98 (to be described later on) of the
electrode arm portion 30 with a plating solution, when plating has
not been performed. The plating solution tray 22 is set at a size
in which the porous structure 110 can be accommodated, and the
plating solution tray 22 has a plating solution supply port and a
plating solution drainage port (not shown). A photo-sensor is
attached to the plating solution tray 22, and can detect brimming
with the plating solution in the plating solution tray 22, i.e.,
overflow, and drainage.
[0158] The electrode arm portion 30 is vertically movable by a
vertical movement motor, which is a servomotor, and a ball screw
(not shown), and swingable between the plating solution tray 22 and
the substrate processing section 20 by a swing motor (not shown).
An air actuator may be used instead of a motor.
[0159] As shown in FIG. 8, the pre-coating/recovering arm 32 is
coupled to an upper end of a vertical support shaft 58. The
pre-coating/recovering arm 32 is swingable by a rotary actuator 60
and is also vertically moveable by an air cylinder (not shown). The
pre-coating/recovering arm 32 supports a pre-coating nozzle 64 for
discharging a pre-coating liquid, on its free end side, and a
plating solution recovering nozzle 66 for recovering the plating
solution, on a portion closer to its proximal end. The plating
solution recovering nozzle 66 is connected to a cylinder pump or an
aspirator, for example, to draw the plating solution on the
substrate from the plating solution recovering nozzle 66.
[0160] As shown in FIGS. 9 through 11, the substrate holder 36 has
a disk-shaped substrate stage 68, and six vertical support arms 70
are disposed at spaced intervals on the circumferential edge of the
substrate stage 68 for holding a substrate W in a horizontal plane
on respective upper surfaces of the support arms 70. A positioning
plate 72 is mounted on an upper end one of the support arms 70 for
positioning the substrate by contacting the end face of the
substrate. A pressing finger 74 is rotatably mounted on an upper
end of the support arm 70, which is positioned opposite to the
support arm 70 having the positioning plate 72, for abutting
against an end face of the substrate W and pressing the substrate W
to the positioning plate 72 when rotated. Chucking fingers 76 are
rotatably mounted on upper ends of the remaining four support arms
70 for pressing the substrate W downwardly when rotated.
[0161] The pressing finger 74 and the chucking fingers 76 have
respective lower ends coupled to upper ends of pressing pins 80
that are normally urged to move downwardly by coil springs 78. When
the pressing pins 80 are moved downwardly, the pressing finger 74
and the chucking fingers 76 are rotated radially inwardly into a
closed position. A support plate 82 is disposed below the substrate
stage 68 for engaging lower ends of the opening pins 80 and pushing
them upwardly.
[0162] When the substrate holder 36 is located in the substrate
transfer position A shown in FIG. 7, the pressing pins 80 are
engaged and pushed upwardly by the support plate 82, so that the
pressing finger 74 and the chucking fingers 76 rotate outwardly and
open. When the substrate stage 68 is elevated, the opening pins 80
are lowered under the resiliency of the coil springs 78, so that
the pressing finger 74 and the chucking fingers 76 rotate inwardly
and close.
[0163] As shown in FIGS. 12 and 13, the cathode portion 38
comprises an annular frame 86 fixed to upper ends of vertical
support columns 84 mounted on the peripheral edge of the support
plate 82 (see FIG. 11), a plurality of, six in this embodiment,
cathodes 88 attached to a lower surface of the annular frame 86 and
projecting inwardly, and an annular sealing member 90 mounted on an
upper surface of the annular frame 86 in covering relation to upper
surfaces of the cathodes 88. The sealing member 90 is adapted to
have an inner peripheral edge portion inclined inwardly downwardly
and progressively thin-walled, and to have an inner peripheral end
suspending downwardly.
[0164] When the substrate holder 36 has ascended to the plating
position B, as shown FIG. 7, the cathodes 88 are pressed against
the peripheral edge portion of the substrate W held by the
substrate holder 36 for thereby allowing electric current to pass
through the substrate W. At the same time, an inner peripheral end
portion of the sealing member 90 is brought into contact with an
upper surface of the peripheral edge of the substrate W under
pressure to seal its contact portion in a watertight manner. As a
result, the plating solution supplied onto the upper surface
(surface to be plated) of the substrate W is prevented from seeping
from the end portion of the substrate W, and the plating solution
is prevented from contaminating the cathodes 88.
[0165] In this embodiment, the cathode portion 38 is vertically
immovable, but rotatable in a body with the substrate holder 36.
However, the cathode portion 38 may be arranged such that it is
vertically movable and the sealing member 90 is pressed against the
surface, to be plated, of the substrate W when the cathode portion
38 is lowered.
[0166] As shown in FIGS. 14 and 15, the electrode head 28 of the
electrode arm section 30 includes a anode holder 94 which is
coupled via a ball bearing 92 to the free end of the pivot arm 26,
and a porous structure 110 which is disposed such that it closes
the bottom opening of the anode holder 94. In particular, the anode
holder 94 has the shape of a downwardly-open bottomed cup and has a
recessed portion 94a at a lower position in the inner peripheral
surface. The porous structure 110 has at its top a flange portion
110a that fits in the recessed portion 94a. The porous structure
110 is held in the anode holder 94 by fitting the flange portion
110a into the recessed portion 94a. A hollow plating solution
chamber 100 is thus formed in the anode holder 94.
[0167] In this embodiment, the porous structure 110 is composed of
porous ceramics such as alumina, SiC, mullite, zirconia, titania or
cordierite, or a hard porous material such as a sintered compact of
polypropylene or polyethylene, or a composite material comprising
these materials, or a woven or non-woven fabric. For example, the
porous structure 110 may be used having a pore diameter of 30 to
200 .mu.m in the case of an alumina ceramic, or not more than 30
.mu.m in the case of SiC, a porosity of 20 to 95%, and a thickness
of 1 to 20 mm, preferably 5 to 20 mm, more preferably 8 to 15 mm.
The porous structure 110, in this embodiment, is constituted of
porous ceramics of alumina having a porosity of 30%, and an average
pore diameter of 100 .mu.m. The porous ceramic plate per se is an
insulator, but it is constituted to have lower electric
conductivity than the electric conductivity of the plating solution
by causing the plating solution to enter its interior complicatedly
and follow a considerably long path in the thickness direction.
[0168] The porous structure 110, which has the high resistance, is
disposed in the plating solution chamber 100. Hence, the influence
of the resistance of the seed layer 7 (see FIG. 1A) becomes a
negligible degree. Consequently, the difference in current density
over the surface of the substrate due to electrical resistance on
the surface of the substrate W becomes small, and the uniformity of
the plated film over the surface of the substrate improves. In this
embodiment, the porous structure 110 is provided so that the
plating solution itself has high resistance, but the porous
structure 110 may be omitted.
[0169] A disk-shaped mesh-like anode 98, which allows a plating
solution to pass therethrough, is disposed in the plating solution
chamber 100 above the porous structure 110. An anode, which has a
number of vertical through holes defined therein, may be used as
the anode 98. The anode holder 94 has a plating solution discharge
port 103 for discharging, under suction, the plating solution from
the plating solution chamber 100. The plating solution discharge
port 103 is connected to a plating solution discharge pipe 106
extending from the plating solution supply equipment 18 (see FIG.
5). A plating solution injection section 104 is provided in a
peripheral wall of the anode holder 94 at a position laterally of
the anode 98 and the porous structure 110. In this embodiment, the
plating solution injection section 104 comprises a tube having a
lower end shaped as a nozzle, and is connected to a plating
solution supply pipe 102 extending from the plating solution supply
equipment 18 (see FIG. 5). The plating solution injection section
104 and the plating solution discharge comprises a plating solution
exchanging section.
[0170] When the substrate holder 36 is in plating position B (see
FIG. 7), the electrode head 28 is lowered until the gap between the
substrate W held by the substrate holder 36 and the porous
structure 110 becomes about 0.5 to 3 mm, for example, and then the
plating solution injection section 104 pours the plating solution
into a region between the substrate W and the porous structure 110
from laterally of the anode 98 and the porous structure 110. The
nozzle at the lower end of the plating solution injection section
104 is open toward a region between the sealing member 90 and the
porous structure 110. A shield ring 112 of rubber is mounted on the
outer circumferential surface of the porous structure 110 for
electrically shielding the porous structure 110.
[0171] When the plating solution is introduced, the plating
solution introduced from the plating solution injection section 104
flows in one direction along the surface of the substrate W. The
flow of the plating solution pushes and discharges the air out of
the region between the substrate W and the porous structure 110,
filling the region with the fresh plating solution whose
composition has been adjusted that is introduced from the plating
solution injection section 104. The plating solution is now
retained in the region defined between the substrate W and the
sealing member 90.
[0172] When copper plating is performed, copper
(phosphorus-containing copper) containing 0.03 to 0.05% of
phosphorus is generally used as an anode for suppressing the
generation of slime. An insoluble electrode composed of an
insoluble metal such as platinum or titanium, or an insoluble
electrode comprising metal, on which platinum or the like is
plated, is widely used as an anode. Such an anode is a resistance
element having a resistance of almost zero, therefore a current
flow is not impeded by the anode.
[0173] In this embodiment, the anode 98 has the shape of a mesh,
such as a triangular lattice, which allows the plating solution to
pass smoothly therethrough, and is composed of a material having a
high resistivity, for example, a material comprising as the base
material a ceramic having a slight electric conductivity, so that
its resistance is at least higher than the resistance of the
plating solution. The resistance (sheet resistance) of the
substrate W-facing surface of the anode 98 is preferably at the
same level as the resistance (sheet resistance) of the anode
98-facing surface of the substrate W held by the substrate holder
36. For example, when the sheet resistance of e.g., a surface seed
layer of the substrate W is 40.OMEGA./.quadrature., the sheet
resistance of the substrate W-facing surface of the anode 98 is
preferably not less than 20.OMEGA./.quadrature.. The anode 98 may
be composed of a conductive plastic, such as a conductive PEEK
having a slight conductivity, a conductive glass, or the like.
[0174] By making the sheet resistance of the substrate W-facing
surface of the high-resistance anode 98 at the same level as the
sheet resistance of the surface (surface to be plated) of the
substrate W, the terminal effect produced in the anode can be made
at the same level as the terminal effect produced in the substrate
surface, thereby counterbalancing the both terminal effects.
[0175] Further, by providing the anode 98 with a high resistance in
the radial direction from the center of the anode 98 so as to
produce a potential gradient in the anode 98 itself, it becomes
possible to produce a terminal effect in the anode 98 in the
reverse direction to the terminal effect of the surface of the
substrate W when feeding electricity to the anode 98 from its
center. In this regard, a high resistance is necessary only in the
radial direction from the center of the anode 98, as shown in FIG.
16, in order to increase voltage drop with distance from the center
of the anode 98. Thus, the anode 98 may have a low to high
resistance in the height direction or in the circumferential
direction. By utilizing this, it is possible to attach a
ring-shaped contact to the anode so as to improve uniformity of the
anode potential in the circumferential direction.
[0176] Though not depicted, the anode may be made to have a high
resistance in the radial direction from its center by decreasing
the cross-sectional area radially from the center, i.e., by
gradually decreasing the thickness of the anode with distance from
the center.
[0177] A central contact 120 is provided in the center of the
substrate W-counterfacing surface (upper surface) of the anode 98,
and a ring-shaped peripheral contact 122 continuously extending
over the entire circumference is provided in the peripheral region
of the upper surface of the anode 98. In this embodiment, two power
sources are provided: a power source 124 for feeding electricity to
the central contact 120 and to the cathode 88; and a power source
126 for feeding electricity to the peripheral contact 122 and to
the cathode 88. A feeding wire 128a on the cathode side of the
power source 124 is connected to the cathode 88, and a feeding wire
128b on the anode side is connected to the central contact 120; and
a feeding wire 130a on the cathode side of the power source 126 is
connected to the cathode 88, and a feeding wire 130b on the anode
side is connected to the peripheral contact 122.
[0178] By feeding electricity from the power source 124 to the
anode 98 from the center of the anode 98 so that an electric
current flows in the anode 98 from the center toward the periphery
of the anode 98, it becomes possible to cause the anode 98 to
produce a terminal effect in the reverse direction to the terminal
effect of the surface of the substrate W, i.e., a terminal effect
which increases voltage drop radially with distance from the center
of the anode 98. Further, by feeding electricity from the power
source 126 to the anode 98 from the peripheral region of the anode
98 so that an electric current flows in the anode 98 from the
peripheral region toward the center of anode 98, it becomes
possible to cause the anode 98 to produce a terminal effect in the
same direction of the terminal effect of the surface of the
substrate W, i.e., a terminal effect which increases voltage drop
radially with distance from the peripheral region of the anode
98.
[0179] The provision of the two power sources 124, 126 makes it
possible to independently control an electric current flowing in
the anode 98 from the center toward the peripheral region of the
anode 98, and an electric current flowing in the anode 98 from the
peripheral region toward the center of the anode 98, thereby
forming a plated film having a more uniform thickness on the
surface of the substrate W.
[0180] The substrate W-facing surface (lower surface) of the anode
98 is coated with a thin metal film 132 of e.g. titanium, and the
surface of the thin metal film 132 is coated with a thin metal
oxide film 134 of e.g. iridium oxide. The provision of the thin
metal film 132 in the substrate W-facing surface of the anode 98
enables a plating current to flow evenly between the anode (thin
metal film) 98 and the surface of the substrate W. Further, by
covering the thin metal film 132 with the thin metal oxide film
134, the thin metal film 132 can be prevented from being oxidized
or peeled off from the anode 98.
[0181] Next, the operation of the substrate processing apparatus
incorporating the plating apparatus 12 of this embodiment will now
be described.
[0182] First, a substrate W to be plated is taken out from one of
the loading/unloading units 10 by the transfer robot 14, and
transferred, with the surface (surface to be plated) facing
upwardly, through the substrate carry-in and carry-out opening
defined in the side panel, into one of the plating apparatuses 12.
At this time, the substrate holder 36 is in lower substrate
transfer position A. After the hand of the transfer robot 14 has
reached a position directly above the substrate stage 68, the hand
of the transfer robot 14 is lowered to place the substrate W on the
support arms 70. The hand of the transfer robot 14 is then
retracted through the substrate carry-in and carry-out opening.
[0183] After the hand of the transfer robot 14 is retracted, the
cup 40 is elevated. Then, the substrate holder 36 is lifted from
substrate transfer position A to pretreatment/cleaning position C.
As the substrate holder 36 ascends, the substrate W placed on the
support arms 70 is positioned by the positioning plate 72 and the
pressing finger 74 and then reliably gripped by the fixing fingers
76.
[0184] On the other hand, the electrode head 28 of the electrode
arm portion 30 is in a normal position over the plating solution
tray 22 now, and the porous structure 110 or the anode 98 is
positioned in the plating solution tray 22. At the same time that
the cup 40 ascends, the plating solution starts being supplied to
the plating solution tray 22 and the electrode head 28. Until the
step of plating the substrate W is initiated, the new plating
solution is supplied, and the plating solution discharge pipe 106
is evacuated to replace the plating solution in the porous
structure 110 and remove air bubbles from the plating solution in
the porous structure 110. When the ascending movement of the cup 40
is completed, the substrate carry-in and carry-out openings in the
side panel is closed by the cup 40, isolating the atmosphere in the
side panel and the atmosphere outside of the side panel from each
other.
[0185] When the cup 40 is elevated, the pre-coating step is
initiated. Specifically, the substrate holder 36 that has received
the substrate W is rotated, and the pre-coating/recovering arm 32
is moved from the retracted position to a position confronting the
substrate W. When the rotational speed of the substrate holder 36
reaches a preset value, the pre-coating nozzle 64 mounted on the
tip end of the pre-coating/recovering arm 32 intermittently
discharges a pre-coating liquid which comprises a surface active
agent, for example, toward the surface (surface to be plated) of
the substrate W. At this time, since the substrate holder 36 is
rotating, the pre-coating liquid spreads all over the surface of
the substrate W. Then, the pre-coating/recovering arm 32 is
returned to the retracted position, and the rotational speed of the
substrate holder 36 is increased to spin the pre-coating liquid off
and dry the surface to be plated of the substrate W.
[0186] After the completion of the pre-coating step, the plating
step is initiated. First, the substrate holder 36 is stopped
against rotation, or the rotational speed thereof is reduced to a
preset rotational speed for plating. In this state, the substrate
holder 36 is lifted to plating position B. Then, the peripheral
edge of the substrate W is brought into contact with the cathodes
88, when it is possible to pass an electric current, and at the
same time, the sealing member 90 is pressed against the upper
surface of the peripheral edge of the substrate W, thus sealing the
peripheral edge of the substrate W in a watertight manner.
[0187] Based on a signal indicating that the pre-coating step for
the loaded substrate W is completed, on the other hand, the
electrode arm portion 30 is swung in a horizontal direction to
displace the electrode head 28 from a position over the plating
solution tray 22 to a position over the plating position. After the
electrode head 28 reaches this position, the electrode head 28 is
lowered toward the cathode portion 38. The electrode head 28 is
stopped when the porous structure 110 has reached a position close
to and not being into contact with the surface of the substrate W,
the position being at a distance of about 0.5 mm to 3 mm from the
surface of the substrate W. When the descent of the electrode head
28 is completed, a plating solution is poured into the region
between the substrate W and the porous structure 110 from the
plating solution injection section 104 to fill the region with the
plating liquid.
[0188] In the early stage of plating, electricity is fed from the
power source 124 to the anode 98 from the center of the anode 98
while electricity is fed through the cathode 88 to the surface, for
example the seed layer 7 (see FIG. 1A), of the substrate W from the
peripheral region of the substrate W, thereby forming a plated film
on the surface of the substrate W. During plating, an electric
current flows in the anode 98 from its center toward the periphery,
producing a terminal effect in the anode 98 in the reverse
direction to the terminal effect of the surface of the substrate W,
i.e., a terminal effect which increases voltage drop radially with
distance from the center of the anode 98. Accordingly, by making
the resistances (sheet resistances) of the anode 98 and the surface
of the substrate W, facing each other, at the same level, the sum
of the voltage drop in the surface of the substrate W and the
voltage drop in the anode 98 can be made equal for a current
pathway running through the center of the surface of the substrate
W, for a current pathway running through the peripheral region of
the substrate W, and for any intermediate current pathway between
them. Thus, the electric resistance can be made equal for any
current pathway, whereby electric current can be distributed evenly
over the surface of the substrate W and a plated film having a
uniform thickness can be formed on the surface of the substrate W.
During plating, the substrate holder 36 is rotated at a low speed,
according to necessity.
[0189] As a plated film grows on the surface of the substrate W,
the electric resistance (sheet resistance) of the surface of the
substrate W decreases and the terminal effect in the surface of the
substrate becomes smaller gradually. If plating is continued,
because of the terminal effect of the anode 98, the resulting film
will be thick in the center of the substrate W and thin in the
peripheral region of the substrate W.
[0190] Therefore, when a thickness of the plated film has reached a
predetermined thickness, the power source 124 is disconnected, and
electricity is fed from the power source 126 to the anode 98 from
the peripheral region of the anode 98 while electricity is fed
through the cathode 88 to the surface of the substrate W from the
peripheral region of the substrate W, thereby further forming a
plated film on the above-described plated film which has been
formed on the surface of the substrate W. During plating, an
electric current flows in the anode 98 from the peripheral region
to the center of the anode 98, producing a terminal effect in the
anode 98 in the same direction as the terminal effect of the
surface of the substrate W, i.e., a terminal effect which increases
voltage drop radially with distance from the peripheral region of
the anode 98. Accordingly, the plated film formed by this plating
is thin in the center of the substrate W and thick in the
peripheral region of the substrate W.
[0191] By thus combining plated films having reverse thickness
distributions, the resulting film can have a uniform thickness
distribution. This makes it possible to form a plated film having a
more uniform thickness over an entire surface of a substrate and
can securely fill fine interconnect recesses, such as contact holes
3 and trenches 4 (see FIG. 1A), with the metal without forming
voids in the embedded metal.
[0192] When the plating process is completed, the electrode arm
portion 30 is raised and then swung to return to the position above
the plating solution tray 22 and to lower to the ordinary position.
Then, the pre-coating/recovering arm 32 is moved from the retreat
position to the position confronting to the substrate W, and
lowered to recover the remainder of the plating solution on the
substrate W by the plating solution recovering nozzle 66. After
recovering of the remainder of the plating solution is completed,
the pre-coating/recovering arm 32 is returned to the retreat
position, and pure water is supplied from the fixed nozzle 34 for
supplying pure water toward the central portion of the substrate W
for rinsing the plated surface of the substrate. At the same time,
the substrate holder 36 is rotated at an increased speed to replace
the plating solution on the surface of the substrate W with pure
water. Rinsing the substrate W in this manner prevents the
splashing plating solution from contaminating the cathodes 88 of
the cathode portion 38 during descent of the substrate holder 36
from the plating position B.
[0193] After completion of the rinsing, the washing with water step
is initiated. That is, the substrate holder 36 is lowered from the
plating position B to the pretreatment/cleaning position C. Then,
while pure water is supplied from the fixed nozzle 34 for supplying
pure water, the substrate holder 36 and the cathode portion 38 are
rotated to perform washing with water. At this time, the sealing
member 90 and the cathodes 88 can also be cleaned, simultaneously
with the substrate, by pure water directly supplied to the cathode
portion 38, or pure water scattered from the surface of the
substrate W.
[0194] After washing with water is completed, the drying step is
initiated. That is, supply of pure water from the fixed nozzle 34
is stopped, and the rotational speed of the substrate holder 36 and
the cathode portion 38 is further increased to remove pure water on
the substrate surface by centrifugal force and to dry the substrate
surface. The sealing member 90 and the cathodes 88 are also dried
at the same time. Upon completion of the drying, the rotation of
the substrate holder 36 and the cathode portion 38 is stopped, and
the substrate holder 36 is lowered to the substrate transfer
position A. Thus, the gripping of the substrate W by the chucking
fingers 76 is released, and the substrate W is just placed on the
upper surfaces of the support arms 70. At the same time, the cup 40
is also lowered.
[0195] All the steps including the plating step, the pretreatment
step accompanying to the plating step, the cleaning step, and the
drying step are now finished. The transfer robot 14 inserts its
hand through the substrate carry-in and carry-out opening into the
position beneath the substrate W, and raises the hand to receive
the plated substrate W from the substrate holder 36. Then, the
transfer robot 14 returns the plated substrate W received from the
substrate holder 36 to one of the loading/unloading units 10.
[0196] Though the two power sources 124, 126 are provided in this
embodiment, as shown in FIG. 14, it is also possible to provide one
power source 140, branch a feeding wire 142 extending from the
anode of the power source 140 into two feeding wires 142a, 142b,
connect one feeding wire 142a to the central contact 120 and
connect the other feeding wire 142b to the peripheral contact 122,
and interpose an on/off switch 144 in each of the feeding wires
142a, 142b. As with the above-described case, a feeding wire 146
extending from the cathode of the power source 140 is connected to
the cathodes 88.
[0197] This makes it possible to independently change the time for
an electric current to flow in the anode 98 from the center toward
the peripheral region of the anode 98 and the time for an electric
current to flow in the anode 98 from the peripheral region toward
the center of the anode 98, or the ratio between these times by the
switches 144, thereby forming a plated film having a more uniform
thickness on the surface of the substrate W. Further, the cost and
the size of the apparatus can be reduced as compared to the case of
providing an independent power source for each feeding wire.
[0198] As shown in FIG. 18, it is also possible to provide a
ring-shaped intermediate contact 150, extending continuously over
the entire circumference, between the central contact 120 and the
peripheral contact 122 on the upper surface of the anode 98, and
connect a feeding wire 152 extending from the anode of a power
source (not shown) to the intermediate contact 150. As with the
case shown in FIG. 17, it is possible also in this case to provide
a single common power source and to connect a branched feeding
wire, extending from the anode of the power source, with an on/off
switch interposed therein to the intermediate contact 150.
[0199] By thus increasing the number of points for feeding
electricity to the anode 98 to thereby more finely adjust an
electric current flowing in the anode 98, a plated film having a
more uniform thickness can be formed on the surface of a substrate.
A plurality of intermediate contacts 150 may be provided so as to
more finely control an electric current flowing in the anode
98.
[0200] FIG. 19 shows another anode. The anode 160 is comprised of
an anode body 162 in the shape of a mesh, such as a triangular
lattice, and composed of a material having a high resistivity, for
example, a material comprising as the base material a ceramic
having a slight electric conductivity, and low-resistance members
164 mounted on and scattered over a surface of the anode body 162.
As in this case, a high-resistance material and a low-resistance
material may be combined arbitrarily. The use of copper for the
low-resistance members 164 can make a soluble high-resistance
anode.
[0201] According to this embodiment, by disposing the porous
structure 110 between the anode 98 and a substrate W held by the
substrate holder 36 and impregnating the porous structure 110 with
a plating solution, the plating solution between the anode 98 and
the substrate W is allowed to have such a high resistance as to
make the effect of the sheet resistance of the substrate surface
negligible, so that a plated film having a more uniform thickness
can be securely formed even when the substrate has a high sheet
resistance. It is, however, of course possible not to use such a
porous structure.
[0202] Though copper is used as an interconnect material, a copper
alloy, silver or a silver alloy may be used instead of copper.
[0203] According to this embodiment, even when the sheet resistance
of a surface of a substrate becomes higher as a seed layer becomes
thinner or with the progress toward seed-less substrates which
necessitate direct plating on a surface of a barrier layer, a
plated film having an enhanced in-plane uniformity can be formed on
a surface of a substrate irrespective of the degree of a terminal
effect in the substrate surface.
[0204] FIGS. 20 and 21 show an electrode head 228 of a plating
apparatus according to another embodiment of the present invention.
The electrode head 228 includes a housing 294 coupled to the free
end of a pivot arm 26 via a ball bearing 292, and a flat plate-like
press member 310 comprised of a porous structure, disposed such
that it closes the lower-end opening of the housing 294. In
particular, the housing 294 has in its lower portion an
inwardly-protruding portion 294a, and the press member 310 has at
its top a flange portion 310a. The press member 310 is held in the
housing 294 with the flange portion 310a engaging the
inwardly-protruding portion 294a and a spacer 296 interposed. A
hollow plating solution chamber 300 is thus formed in the housing
294.
[0205] As with the preceding embodiment, when a substrate holder
236 is raised to the plating position B (see FIG. 7), cathodes 288
are pressed against the peripheral region of a substrate W held by
the substrate holder 236 to feed electricity to the peripheral
region while the inner end of a sealing member 290 is brought into
pressure contact with the peripheral region of the upper surface of
the substrate W, thereby water-tightly sealing the contact portion
and preventing a plating solution, which has been supplied onto the
upper surface (surface to be plated) of the substrate W, from
leaking out of the end of the substrate W.
[0206] A flat plate-like cushioning material 311 comprised of an
elastic porous material is attached, e.g., with an adhesive, to a
lower surface of the press member 310, and a flat plate-like
contact member 312 comprised of a porous material, having a large
number of through-holes 312a extending vertically and linearly
through the contact member 312, is attached, e.g., with an
adhesive, to a lower surface of the cushioning material 311. Thus,
a contact surface (lower surface) 312b, which faces the surface of
the substrate W held by the substrate holder 236, of the contact
member 312 can be brought into pressure contact with the surface
(upper surface) of the substrate W by the press member 310.
[0207] The press member 310 may be composed of a porous ceramic,
such as alumina, SiC, mullite, zirconia, titania or cordierite, or
a hard porous body, such as a sintered body of polypropylene or
polyethylene, or a composite thereof, or a woven or non-woven
fabric. For example, a porous ceramic plate may be used having a
pore diameter of 30 to 200 .mu.m in the case of an alumina ceramic,
or not more than 30 .mu.m in the case of SiC, a porosity of 20 to
95%, and a thickness of 1 to 20 mm, preferably 5 to 20 mm, more
preferably 8 to 15 mm. According to this embodiment, the press
member 310 is composed of a porous alumina ceramic plate, for
example, having a porosity of 30% and an average pore diameter of
100 .mu.m. The porous ceramic plate per se is an insulator, but it
is constituted to have lower electric conductivity than the
electric conductivity of the plating solution by causing the
plating solution to enter its interior complicatedly and follow a
considerably long path in the thickness direction.
[0208] The provision of the press member 310, which can thus have a
high electric resistance, in the plating solution chamber 300 can
make the effect of the resistance of the seed layer 7 (see FIG. 1A)
as small as negligible. Thus, a difference in current density in
the surface of the substrate W due to the electric resistance of
the substrate surface can be made small, thereby improving the
in-plane uniformity of a plated film.
[0209] The cushioning material 311 is, for example, polyurethane,
polyethylene or polyvinyl alcohol. Specifically, for example,
SOFLAS manufactured by AION Co., Ltd, or SUBA manufactured by NITTA
Corp. can be used as the cushioning material 311. By interposing
the flexible cushioning material 311 between the press member 310
and the contact member 312, the entire contact surface 312b of the
contact member 312 can be pressed against the surface of the
substrate W at a more uniform pressure, thereby preventing the
contact surface 312b of the contact member 312 from separating from
the surface of the substrate W locally.
[0210] The contact member 312 is composed of, for example, an
insulting material, such as polycarbonate, a ceramic, carbon,
polyester, glass, silicon, a resist material or a fluorocarbon
resin; and Whatman filter paper, Nuclepore filter manufactured by
Osmonics, Inc., etc. can be used as the contact member 312. The
large number of vertically-extending through-holes 312a provided in
the contact member 312 may have a circular cross-sectional shape
with a diameter of, for example, not more than 12 .mu.m and may be
distributed at a density of 1.0.times.10.sup.5 to
1.0.times.10.sup.9/cm.sup.2. In this case, columnar plated films
having a diameter of not more than 12 .mu.m will be formed on a
surface of a substrate. Such cylindrical plated films can be easily
removed by later CMP. Further, by setting the density of the
through-holes at 1.0.times.10.sup.5 to 1.0.times.10.sup.9/cm.sup.2
and selecting an appropriate combination of hole diameter and
density, plating can be effected for all interconnect recesses.
[0211] A resist material, such as PMMA, which has undergone fine
submicron-processing (formation of through-holes) by performing the
lithography technique, can also be used as the contact member 312.
In this case, a contact member having a thickness of not more than
several hundred .mu.m can be produced.
[0212] The Ra value (center-line average roughness), indicative of
surface roughness, of the contact surface 312b of the contact
member 312 is set at not more than 1 .mu.m. This allows good
contact of the contact surface 312b of the contact member 312 with
a surface of a substrate W, thus preventing the formation of a gap
between the contact surface 312b and the surface of the substrate W
upon their contact. This can prevent an extra plated film being
formed in a non-interconnect region and imposing a burden on a
later CMP processing.
[0213] Though not depicted, the through-holes provided in the
contact member may be tapered such that the cross-sectional area
gradually decreases with distance from the contact surface, i.e.,
upwardly. Pointed tapered columnar plated films will therefore be
formed on the surface of a substrate. When providing such tapered
through-holes, e.g., having a large diameter, in the contact member
and forming tapered plated films in the through-holes, the plated
films can be easily drawn out of the through-holes after
plating.
[0214] Located above the press member 310, an anode 298 is disposed
in the plating solution chamber 300. The anode 298 is mounted to a
lower surface of a plating solution introduction pipe 304 disposed
above the anode 298. The plating solution introduction pipe 304 has
a plating solution introduction inlet 304a to which is connected a
plating solution supply pipe extending from the plating solution
supply facility 18 (see FIG. 5). Further, a plating solution
discharge pipe 306, communicating with the plating solution chamber
300, is connected to a plating solution discharge outlet 294b
provided in the upper surface of the housing 294.
[0215] The plating solution introduction pipe 304 has a manifold
structure so that a plating solution can be supplied uniformly to
the surface (surface to be plated) of the substrate W. Thus, a
number of narrow tubes 316, which are communicated with the plating
solution introduction pipe 304, are coupled to the plating solution
introduction pipe 304 at predetermined positions along the long
direction of the pipe 304. The anode 298 has narrow holes at
positions corresponding to the narrow tubes 316, and the narrow
tubes 316 extend downwardly in the narrow holes.
[0216] The plating solution, introduced from the plating solution
supply pipe 302 into the plating solution introduction pipe 304,
passes through the narrow tubes 316 and reaches the upper surface
of the press member 310 and fills the plating solution chamber 300,
immersing the anode 298 in the plating solution, while the plating
solution passes through the press member 310, the cushioning
material 311 and the contact member 312 and reaches the lower
surface of the contact member 312, and discharged by suction
through the plating solution discharge pipe 306.
[0217] In order to inhibit the formation of a slime, the anode 298
is composed of copper (phosphorus-containing copper) containing
0.03 to 0.05% of phosphorus. It is, however, possible to use an
insoluble metal, such as platinum or titanium, or insoluble
electrode comprising metal on which platinum or the like is plated.
The use of an insoluble metal or an insoluble electrode is
preferred from the viewpoint of no need for replacement. Because of
easy passage of plating solution, a net-shaped electrode, e.g.,
insoluble one, may also be used.
[0218] When carrying out plating, the cathode 288 is electrically
connected to the cathode of a plating power source 314, and the
anode 298 is electrically connected to the anode of the plating
power source 314. In this embodiment, the plating power source 314
is designed to be capable of changing the direction of electric
current optionally so that the plating apparatus can have an
etching function of etching a plated film. Thus, etching of a
plated film can be carried out in the presence of a plating
solution by reversing the cathode 288 to an anode and reversing the
anode 298 to a cathode by the power source 414.
[0219] A press mechanism 322 for pressing the contact surface 312b
of the contact member 312 against the surface of the substrate W is
provided between the ball bearing 292 and the pivot arm 26. In
particular, the press mechanism 322 includes a compression coil
spring 328 bridging a pair of plates 324, 326 disposed at a
distance from each other, and a stopper 330 which is fixed at its
one end to the one plate 324 and which has at the other end a head
portion 330a which is made in contact with the other plate 326 so
as to limit the distance between the pair of plates 324, 326. The
pivot arm 26, on the other hand, is designed to be vertically
movable by a lifting motor 332 comprised of a servomotor, and a
ball screw 334. Instead of the lifting mechanism, it is also
possible to use an air-pressure activator.
[0220] When the contact member 312 is not in contact with the
surface of the substrate W, the electrode head 228 moves vertically
(and pivots) together with the pivot arm 26 through the elastic
force of the compression coil spring 328. When the pivot arm 26 is
lowered after the contact member 312 has come into contact with the
surface of the substrate W, the compression coil spring 328
contracts as the pivot arm 26 lowers. The elastic force of the
compression coil spring 328 acts on the contact member 312 via the
cushioning material 311, so that the contact surface 312b of the
contact member 312 presses on the surface of the substrate W. The
pressing force of the contact surface 312b can be controlled by
controlling the contraction (displacement) of the compression coil
spring 328.
[0221] The operation of the plating apparatus having the electrode
head 228 of this embodiment will now be described.
[0222] In non-plating time, the electrode head 228 is in the normal
position above the plating solution tray 22 (see FIG. 6), and the
contact member 312 is positioned in the plating solution tray 22.
Before proceeding to plating, a plating solution is supplied to the
plating solution tray 22 and the electrode head 228 while
discharging the plating solution by suction through the plating
solution discharge pipe 306, thereby carrying out replacement and
defoaming of the plating solution present in the press member 310,
the cushioning material 311, and the contact member 312.
[0223] As with the above-described embodiment, based on a signal
indicating the completion of pre-coating of a substrate W which has
been carried into the plating apparatus and held by the substrate
holder 236, the electrode head 228 is moved from above the plating
solution tray 22 to above the plating position. Thereafter, the
electrode head 228 is lowered toward the substrate W held by the
substrate holder 236, and stopped when the contact surface 312b of
the contact member 312 has come to a position closed to but not
being into contact with the surface of the substrate W, for
example, at a distance of about 0.1 mm to 3 mm from the substrate
W. The plating solution is then supplied from the plating solution
supply pipe 302 into the electrode head 228, thereby impregnating
the press member 310, the cushioning material 311 and the contact
member 312 with the plating solution and filling the space between
the upper surface (surface to be plated) of the substrate W and the
ceiling of the plating solution chamber 300 with the plating
solution, as shown in FIG. 20.
[0224] The electrode head 228 is further lowered to bring the
contact surface 312b of the contact member 312 into tight contact
with the surface of the substrate W, as shown in FIG. 21. As shown
particularly in FIG. 22, the contact surface 312b of the contact
member 312 makes tight contact with the surface of a seed layer 7
covering an insulating film 2 deposited on the substrate W. The
flexible cushioning member 311, interposed between the press member
310 and the contact member 312, enables tight contact of the
contact surface 312b of the contact member 312 with the surface of
the substrate W without a gap therebetween while preventing the
contact surface 312b from separating from the surface (seed layer
7) of the substrate W locally. Thereafter, the cathodes 288 are
connected to the cathode of the power source 314 and the anode 298
is connected to the anode of the power source 314 to carry out
plating of the surface (surface of the seed layer 7) of the
substrate W.
[0225] When carrying out plating of the substrate W while keeping
the contact surface 312b of the contact member 312, having the
large number of vertically-extending through-holes 312a, in contact
with the surface of the seed layer 7 of the substrate W, the
surface of the seed layer 7 in non-interconnect regions, except
portions facing the through-holes 312a provided in the contact
member 312, directly contacts the contact surface 312b of the
contact member 312 and the plating solution is excluded from the
contact area, as shown in FIG. 23A. Accordingly, as shown in FIGS.
23B and 23C, columnar plated films (columnar portions) 6a grow
along the through-holes 312a. After plating, the columnar plated
films 6a are drawn out of the though-holes 312a of the contact
member 312, leaving the columnar plated films 6a on the surface of
the seed layer 7, as shown in FIG. 23D.
[0226] On the other hand, as shown in FIG. 24A, the interior
surfaces of interconnect recesses such as trenches 4, formed in the
insulating film 2, in interconnect regions are not in contact with
the contact surface 312b of the contact member 312 and the recesses
such as trenches 4 are filled with the plating solution.
Accordingly, as shown in FIG. 24B, a plated film (copper film) 6b
first grows such that it fills in the interconnect recesses such as
trenches 4. After the plated film 6b has grown to come into contact
with the contact surface 312b of the contact member 312, the plated
film further grows along the through-holes 312a of the contact
member 312 to form columnar plated films (columnar portions) 6c on
the surface of the plated film 6b, as shown in FIG. 24D. After
plating, the columnar plated films 6c are drawn out of the
through-holes 312a of the contact member 312, leaving the columnar
plated films 6c on the surface of the plated film 6b embedded in
the interconnect recesses such as trenches 4.
[0227] Foots of the columnar plated films (columnar portions) 6a,
6c formed in the non-interconnect regions and the interconnect
regions of the substrate lie on the same level. Further, by
providing through-holes 312a each having a circular cross-sectional
shape with a diameter of not more than 12 .mu.m in the contact
member 312, each of the columnar plated films 6a, 6c formed on the
surface of the substrate have a cylindrical shape having a diameter
of not more than 12 .mu.m. Such cylindrical plated films 6a, 6b can
be easily removed by later CMP. Further, this can prevent a case in
which a cylindrical plated film 6c is too large compared to an
interconnect recess, such as a trench 4, to form a cylindrical
plated film 6c in the interconnect region.
[0228] FIGS. 31 and 32 are schematic diagrams of a plated film as
formed by carrying out plating of a surface of a substrate while
keeping a contact member, having linearly-extending through-holes,
in contact with the surface of the substrate in the above-described
manner. FIGS. 31 and 32 show the formation of cylindrical plated
films (columnar portions) standing together in large numbers.
[0229] After the completion of plating, the electrode head 228 is
raised and pivoted to return it to above the plating solution tray
22, and the electrode head 228 is lowered to the normal position.
The substrate after plating is then subject to the same processings
as in the preceding embodiment, and is returned to the
loading/unloading section 10 (see FIG. 5).
[0230] Thereafter, the substrate W is transported to a CMP
apparatus. The surface of the substrate W is polished by the CMP
apparatus to first remove the numerous columnar plated films
(columnar portions) 6a, 6c shown in FIG. 25A, thereby flattening
the surface of the substrate W, as shown in FIG. 25B. Since the
foots of the numerous columnar plated films 6a, 6b lie on the same
level, the plated films 6a, 6b can be easily removed with a
relatively small force, i.e., by a low-pressure high-speed CMP
processing. After the removal of the numerous columnar plated films
6a, 6c, the surface of the plated film takes on a flat surface with
few irregularities, which is easier to polish with CMP as compared
to a conventional plated film with surface irregularities.
[0231] The above-described plating process relates to the case
where interconnect recesses, such as trenches 4, are relatively
shallow. In the case where interconnect recesses, such as trenches
4, are relatively deep, on the other hand, columnar plated films
can grow to a considerable height during the period of time for the
interconnects to be filled with e.g. copper and, because of
increased adhesion between the contact member and the surface of
the substrate due to increased anchor effect, the contact member
can be damaged upon drawing the columnar plated films out of the
contact member.
[0232] FIGS. 26A through 26E illustrate, in a sequence of process
steps, a plated film-forming method which makes it possible to fill
interconnect recesses, such as trenches 4, e.g. with copper and
easily draw columnar plated films out of a contact member without
damage to the contact member.
[0233] First, as with the above-described embodiment, plating of a
substrate W is carried out while keeping the contact surface 312b
of the contact member 312, having the large number of through-holes
312a, in tight contact with the surface seed layer 7 of the
substrate W, thereby forming columnar plated films (columnar
portions) 6a in the non-interconnect regions and forming a plated
film 6b in interconnect recesses, such as trenches 4, to fill the
recesses with the plated film, as shown in FIG. 26A. The cathode
288 and the anode 298 are disconnected from the power source 314,
according to necessity, and then the electrode head 228 is raised,
thereby drawing the columnar plated films 6a out of the contact
member 312, as shown in FIG. 26B. Thereafter, at least one of the
electrode head 228 and the substrate holder 236 is rotated so as to
change the relative position between the contact surface 312b of
the contact member 312 and the surface of the substrate W.
[0234] Next, as shown in FIG. 26C, the electrode head 228 is
lowered again to again bring the contact surface 312b of the
contact member 312 into tight contact with the surface seed layer 7
of the substrate W. Upon the contact, the contact member 312 pushes
down the columnar plated films 6a. Thereafter, the cathodes 288 and
the anode 298 are connected to the plating power source 314 to
carry out plating of the substrate W, thereby forming second
columnar plated films (columnar portions) 6d (see FIG. 26D) on the
fallen columnar plated films 6a while growing the plated film 6b
embedded in the interconnect recesses such as trenches 4. Though in
this embodiment, the operation of pushing down the columnar plated
films 6a with the contact member 312 and then carrying out
additional plating is carried out once, the operation may be
repeated a plurality of times, according to necessity. This makes
it possible to gradually decrease a level difference in the surface
irregularities of a plated film without damage to the contact
member 312.
[0235] The plated film 6b in the interconnect recesses, such as
trenches 4, grows to come into contact with the contact surface
312b of the contact member 312. Plating is terminated when columnar
plated films 6c, which have grown along the through-holes 312a of
the contact member 312, are formed on the surface of the plated
film 6b, as shown in FIG. 26D. After plating, the columnar plated
films 6c, 6d are drawn out of the through-holes 312a of the contact
member 312, as shown in FIG. 26E.
[0236] According to this method, the columnar plated films 6c, 6d,
which have been formed on the surface of plated film when embedding
of the plated film, e.g., copper film, in the interconnect recesses
such as trenches 4 is completed, can be made relatively low. Such
columnar plated films 6c, 6d can be easily drawn out of the contact
member 312 without damage to the contact member 312. In the case of
this method, while the plated film 6b formed in the interconnect
recesses, such as trenches 4, is dense, the plated films 6a, 6d
formed in the non-interconnect regions can contain voids because
some gaps can be formed between the fallen columnar plated films
6a. This, however, poses no problem because the plated films formed
in the non-interconnect regions will be removed by the next-step
CMP processing.
[0237] When a plating apparatus is used which, like the plating
apparatus of this embodiment, uses such a power source as the power
source 314 that is capable of changing the direction of electric
current optionally, and thus has an etching function of etching a
plated film, it is possible to carry out plating in multiple stages
and carry out etching of a plated film after each plating step.
[0238] Thus, for example, after drawing the columnar plated films
6a out of the contact member 312 by raising the electrode head 228,
as shown in FIG. 26B, etching of the plated films 6a, 6b is carried
out in the presence of the plating solution by reversing the
cathodes 288 to anodes and reversing the anode 298 to a cathode by
the plating power source 314, as shown in FIG. 27A. When carrying
out etching in this manner, the flow of electric current is
concentrated in the protruding columnar plated films 6a, whereby
the columnar plated films 6a are etched preferentially than the
plated film 6b embedded in the interconnect recesses such as
trenches 4. Accordingly, most of the plated film 6b embedded in the
interconnect recesses, such as trenches 4, remains after the
columnar plated films 6a are completely removed, as shown in FIG.
27B.
[0239] After the removal of the columnar plated films 6a, the next
plating is carried out. By repeating this series of processings a
plurality of times according to necessity, a level difference in
the surface irregularities of a plated film can be gradually
decreased without damage to the contact member 312 and columnar
plated films, which have been formed on the surface of a plated
film when embedding of the plated film, e.g. copper film, in the
interconnect recesses, such as trenches 4, is completed, can be
made relatively low. Such columnar plated films can be drawn out of
the contact member without damage to the contact member.
[0240] In the case where the columnar plated films 6a are circular
films having a diameter d, as shown in FIG. 28A, etching may be
carried out under isotropic-etching conditions by applying the
reverse electric field (reverse electrolysis) to that of plating
between the anode and the surface of the substrate so as to etch
away those parts of the columnar plated films 6a which correspond
to half of the thickness, i.e., d/2. This makes it possible to etch
away the columnar plated films 6a irrespective of their heights, as
shown in FIG. 28B.
[0241] FIG. 29 shows the main portion of a plating apparatus
according to yet another embodiment of the present invention. As
shown in FIG. 29A, the plating apparatus of this embodiment uses
the contact member 312, having a large number of through-holes 312a
therein, singly between the anode 298 and a surface of a substrate
W, and brings the contact surface (lower surface) 312b of the
contact member 312 into tight contact with the surface of the
substrate W, i.e., the surface of the seed layer 7 covering the
insulating film 2 in carrying out plating.
[0242] FIG. 30 shows the main portion of a plating apparatus
according to yet another embodiment of the present invention. In
the plating apparatus of this embodiment, the contact member 312,
having a large number of through-holes 312a therein, is mounted
directly to the lower surface of the press member 310 without
interposing a cushioning material between them.
[0243] Though copper is used as an interconnect material in the
plating method of this embodiment, a copper alloy, silver or a
silver alloy may also be used instead of copper.
[0244] According to this embodiment, columnar plated films whose
foots lie on the same level can be formed while filling
interconnect recesses, such as trenches, with a plated film. Such
columnar plated films can be easily removed in the next CMP step,
and a surface of a plated film after the removal of the columnar
plated films is relative flat. The burden on the CMP processing can
thus be reduced.
[0245] FIG. 33 shows an electrode head 328 of a plating apparatus
according to yet another embodiment of the present invention. As
with the above-described embodiments, this plating apparatus can be
employed also as an electrolytic processing apparatus such as an
electrolytic etching apparatus. The following description mainly
illustrates the use of this apparatus as a plating apparatus, also
referring to the case of using it as an electrolytic etching
apparatus according to necessity.
[0246] As shown in FIG. 33, the plating apparatus (electrolytic
processing apparatus) includes an electrode holder 394 coupled via
a ball bearing 392 to the free end of a pivot arm 26, and a porous
structure 410 disposed such that it closes the lower-end opening of
the electrode holder 394. In particular, the electrode holder 394
has the shape of a downwardly-open bottomed cup and has a recessed
portion 394a at a lower position in the inner peripheral surface.
The porous structure 410 has at its top a flange portion 410a that
fits in the recessed portion 394a. The porous structure 410 is held
in the electrode holder 394 by fitting the flange portion 410a into
the recessed portion 394a. A hollow plating solution chamber 400 is
thus formed in the electrode holder 394.
[0247] As with the preceding embodiment, when a substrate holder
(not shown) is raised to the plating position B (see FIG. 7),
cathodes 388 (first electrode) are pressed against a peripheral
region of a substrate W held by the substrate holder to feed
electricity to the peripheral region while the inner end of a
sealing member 390 is brought into pressure contact with the
peripheral region of the upper surface of the substrate W, thereby
water-tightly sealing the contact portion and preventing a plating
solution, which has been supplied onto the upper surface (surface
to be plated) of the substrate W, from leaking out of the end of
the substrate W.
[0248] The porous structure 410 has a pressure loss (as measured at
room temperature by passing nitrogen gas at a linear velocity of
0.01 m/s through 14 mm-thick porous structure) of not less than 500
kPa, preferably not less than 1000 kPa, more preferably not less
than 1500 kPa, or an apparent porosity (in accordance with JIS R
2205) of not more than 19%, preferably not more than 15%, more
preferably not more than 10%, and has a resistivity of not less
than 1.0.times.10.sup.5 .OMEGA.cm. The porous structure 410 is
composed of silicon carbide, silicon carbide with oxidation-treated
surface, alumina, or a plastic, such as a sintered body of
polypropylene or polyethylene, or a combination thereof. A
thickness of the porous structure 410 is generally about 1 to 20
mm, preferably about 5 to 20 mm, more preferably about 8 to 15 mm.
The porous structure 410 used in this embodiment is composed of
silicon carbide (SiC), having a pressure loss of 1500 kPa or an
apparent porosity of 10% and having a resistivity of
1.0.times.10.sup.6 .OMEGA.cm. Though the porous structure 410 per
se is an insulating material, but it is constituted to have lower
electric conductivity than the electric conductivity of the plating
solution by causing the plating solution to enter its interior
complicatedly and follow a considerably long path in the thickness
direction.
[0249] By providing the porous structure 410 of, e.g., silicon
carbide, having a pressure loss of not less than 500 kPa,
preferably not less than 1000 kPa, more preferably, not less than
1500 kPa or an apparent porosity of not more than 19%, preferably
not more than 15%, more preferably not more than 10% and having a
resistivity of not less than 1.0.times.10.sup.5 .OMEGA.cm, in the
plating solution chamber 400, and allowing the porous structure 410
to have a high electric resistance, it becomes possible to make the
effect of the electric resistance of a seed layer 7 (see FIG. 1A)
of a substrate W as small as negligible even when the substrate W
has a large area and the seed layer 7 is thin and has a large
electric resistance. Thus, a difference in current density in the
surface of the substrate W due to the electric resistance of the
substrate surface can be made small, thereby improving the in-plane
uniformity of a plated film.
[0250] In the plating solution chamber 400 and located above the
porous structure 410 is disposed an anode (second electrode) 398
having a large number of vertically-extending through-holes 398a.
The anode (second electrode) 398 will serve as a cathode during
electrolytic etching. The electrode holder 394 has a plating
solution discharge outlet 403 for discharging by suction a plating
solution in the plating solution chamber 400. The plating solution
discharge outlet 403 is connected to a plating solution discharge
pipe extending from the plating solution supply facility 18 (see
FIG. 5). Further, a plating solution injection section 404,
positioned beside the anode 398 and the porous structure 410 and
vertically penetrating the peripheral wall of the electrode holder
394, is provided within the peripheral wall of the electrode holder
394. According to this embodiment, the plating solution injection
section 404 is comprised of a tube with a nozzle-shaped lower end,
and connected to a plating solution supply pipe extending from the
plating solution supply facility 18 (see FIG. 5).
[0251] The plating solution injection section 404 is to inject a
plating solution from the side of the anode 398 and the porous
structure 410 into the space between the substrate W and the porous
structure 410 when the substrate holder is in the plating position
B (see FIG. 7) and the electrode head 328 is in such a lowered
position that the distance between the substrate W held by the
substrate holder and the porous structure 410 is, for example,
about 0.5 to 3 mm. The lower-end nozzle portion opens to the space
between a sealing member 390 and the porous structure 410. A rubber
shielding ring 412 is attached to a circumferential surface of the
porous structure 410 for electrical shielding the circumferential
surface of the porous structure 410.
[0252] The plating solution, injected from the plating solution
injection section 404 at the time of injection of the plating
solution, flows in one direction along the surface of the substrate
W, as shown in FIG. 34, and by the flow of plating solution, air in
the space between the substrate W and the porous structure 410 is
forced out of the space. The space is thus filled with the fresh,
composition-adjusted plating solution injected from the plating
solution injection section 404, and the plating solution is stored
in the space defined by the substrate W and the sealing member
390.
[0253] By thus injecting the plating solution from the side of the
anode 398 and the porous structure 410 into the space between the
substrate W and the porous structure 410, filling of plating
solution can be carried out without provision of, for example, an
electrolytic solution supply tube composed of an insulating
material, which may disturb the electric field distribution, within
the porous structure 410. This can make the electric field
distribution uniform over an entire surface of a substrate even
when the substrate has a large area. Furthermore, the plating
solution held in the porous structure 410 can be prevented from
leaking out of the porous structure 410 upon the injection of a
fresh plating solution. Accordingly, the fresh composition-adjusted
plating solution can be supplied into the space between the
substrate W held by the substrate holder and the porous structure
410.
[0254] In the case of this electroplating apparatus, a reaction can
occur upon filling of a plating solution, and the reaction can make
embedding of a plated film impossible, or can partly change the
properties of a plated film. In order to prevent this, it is
desirable to inject a plating solution at a linear velocity of 0.1
to 10 m/s and finish filling of the plating solution within 5
seconds e.g. for a 300-mm wafer. The plating solution injection
section 404 is preferably configured to meet this requirement.
[0255] In this embodiment, the anode 398 is composed of copper
(phosphorus-containing copper) containing 0.03 to 0.05% of
phosphorus in order to inhibit the formation of a slime. It is,
however, possible to use an insoluble anode.
[0256] In this embodiment, the cathodes (first electrode) 388 are
electrically connected to the cathode of the plating power source
414 and the anode (second electrode) 398 is electrically connected
to the anode of the plating power source 414. When the apparatus is
used as an etching apparatus, the first electrode 388 is connected
to the anode of the power source and the second electrode 398 is
connected to the cathode of the power source.
[0257] As described above, the first electrode 388 is made serve as
a cathode and the second electrode 398 is made serve as an anode by
the power source 414. When the substrate holder is in the plating
position B (see FIG. 7), the electrode head 328 is lowered until
the distance between the substrate W held by the substrate holder
and the porous structure 410 becomes, for example, about 0.5 to 3
mm. Thereafter, a plating solution is injected from the plating
solution injection section 404 into the space between the substrate
W and the porous structure 410, so that the plating solution fills
the space and is stored in the space defined by the substrate W and
the sealing member 390 for plating.
[0258] Electrolytic etching can be carried out instead of the
plating by using an electrolytic etching solution instead of the
plating solution and making the first electrode 388 serve as an
anode and the second electrode 398 serves as a cathode by the power
source 414.
[0259] According to this embodiment, the electric resistance
between the anode (second electrode) 398 and a substrate W in
contact with the cathodes (first electrode) 388 can be made still
larger by using, as the porous structure 410 disposed between the
cathode (first electrode) 388 and the anode (second electrode) 398,
one having a pressure loss of not less than 500 kPa, preferably not
less than 1000 kPa, more preferably not less than 1500 kPa or an
apparent porosity of not more than 19%, preferably not more than
15%, more preferably not more than 10%. This can further reduce the
effect of the electric resistance of a surface seed layer 7 of a
substrate W and make the electric field more uniform over the
entire surface of the substrate W even when the substrate W has a
large area and the seed layer 7 is thin and has a large electric
resistance. Accordingly, a plated film having a high in-plane
uniformity of film thickness can be formed on the surface of the
substrate W.
[0260] This is for the following reasons. FIG. 35 shows the
relationship between the pressure loss (kPa) and the electric
resistivity (.OMEGA.cm) of porous structure 410 of silicon carbide,
as obtained by using porous structures 410 having various pressure
losses in the range of 100-2800 kPa; and measuring the voltage
between the cathodes (first electrode) 388 and the anode (second
electrode) 398 when a predetermined current is passed between them,
and calculating the electric resistivity of the porous structure
410 from the relationship between the measured voltage and the
current. The electric resistivity of a porous structure refers to
the electric resistivity of the porous structure with its interior
filled with a plating solution, and can be determined by the
following equation 1:
Electric resistivity=(A.sub.1-A.sub.0).times.S/L (.OMEGA.cm)
(1)
[0261] wherein A.sub.0: Slope of current-voltage relationship as
obtained when only a plating solution is present between the
electrodes (.OMEGA.) [0262] A.sub.1: Slope of current-voltage
relationship as obtained when a porous structure is provided
between the electrodes (.OMEGA.) [0263] S: Area of the opening of
shielding ring (cm.sup.2) [0264] L: Thickness of porous structure
(cm)
[0265] FIG. 36 shows the relationship between the electric
resistivity (.OMEGA.cm) of porous structure 410 and variation (%)
(relative standard deviation) of plated film thickness in a
substrate (wafer) surface (in the radial direction), as obtained by
a simulation calculation. FIG. 37 shows the relationship between
the pressure loss of porous structure 410 and variation of plated
film thickness, obtained from the data of FIGS. 35 and 36.
[0266] The simulation is made based on assumed copper plating of a
surface (upper surface) of a 300 mm-diameter silicon substrate held
face up. The assumed substrate has a thin ruthenium (Ru) film as a
conductive layer (seed layer) formed over the upper surface
(surface to be plated), and the assumed plating solution contains
copper ions, sulfuric acid, chloride ions and additives (an
inhibitor, a promoter and a flattening agent) and has an electric
conductivity of 23 S/m. This holds also for the below-described
simulation.
[0267] A plated film is required to have such an in-plane
uniformity of film thickness that its variation (relative standard
deviation) is not more than 2%. As apparent from FIG. 37, the use
of a porous structure 410 having a pressure loss of not less than
500 kPa can control variation (relative standard deviation) of
plated film thickness within 2.0%, meeting the in-plane uniformity
requirement for plated film thickness. The use of a porous
structure 410 having a pressure loss of not less than 1000 kPa can
control variation (relative standard deviation) of plated film
thickness within 1.2%, thus further enhancing the in-plane
uniformity of plated film thickness. The use of a porous structure
410 having a pressure loss of not less than 1500 kPa is preferred
for further reducing variation of plated film thickness.
[0268] FIG. 38 shows the relationship between the apparent porosity
(%) and the electric resistivity (.OMEGA.cm) of porous structure
410 of alumina, as obtained by using porous structures 410 having
various apparent porosities in the range of 1-30%; and measuring
the voltage between cathodes (first electrode) and an anode (second
electrode) when a predetermined current is passed between them, and
calculating the electric resistivity of the porous structure from
the relationship between the measured voltage and the current as
with the above-described manner. FIG. 39 shows the relationship
between the apparent porosity of porous structure 410 and variation
of plated film thickness, obtained from the data of FIGS. 36 and
38.
[0269] A plated film is required to have such an in-plane
uniformity of film thickness that its variation (relative standard
deviation) is not more than 2%. As is apparent from FIG. 39, the
use of a porous structure 410 having an apparent porosity of not
more than 19% can control variation (relative standard deviation)
of plated film thickness within 2.0%, thus meeting the in-plane
uniformity requirement for plated film thickness. It is preferred
to use a porous structure 410 having an apparent porosity of not
more than 15%, more preferably not more than 10% for further
reducing variation of plated film thickness.
[0270] The porous structure 410 has a resistivity of not less than
1.0.times.10.sup.5 .OMEGA.cm for the following reasons. FIG. 40
shows the relationship between current and voltage, as observed
when carrying out copper plating of a substrate by using porous
structures 410 of silicon carbide having an apparent porosity of
15% and a resistivity of 1.0.times.10.sup.3 to 1.0.times.10.sup.6
.OMEGA.cm, and passing electric current between the cathodes (first
electrode) 388 and the anode (second electrode) 398. As is apparent
from FIG. 40, there is a proportional relationship between current
and voltage when the resistivity of the porous structure 410
(itself) is not less than 1.0.times.10.sup.5 .OMEGA.cm. It has been
confirmed that the proportional relationship is reproducible. It
has also been confirmed that when the resistivity of the porous
structure 410 is not more than 1.0.times.10.sup.4, voltage rapidly
rises as current exceeds a certain level and, in addition, there is
no reproducible relationship between current and voltage.
[0271] Thus, the use of a porous structure 410 having a resistivity
of not less than 1.0.times.10.sup.5 makes it possible to carry out
plating with voltage highly-reproducible and stable to plating
current. Taking account of high-current plating, it is preferred to
use a porous structure 410 having a resistivity of not less than
1.0.times.10.sup.6.
[0272] It is also possible to use a porous structure 410 whose
overall resistance A (.OMEGA.), which is the electric resistance
between the upper and lower surfaces of the porous structure 410
with its interior filled with a plating solution (electrolytic
solution), is adjusted to not less than 0.02 time the sheet
resistance (electric resistance) B (.OMEGA./.quadrature.) of a
surface seed layer (conductive layer) 7 of a substrate W
(A/B.gtoreq.0.02).
[0273] This can also make the overall electric resistance A
(.OMEGA.) between the upper and lower surfaces of the porous
structure 410 with its interior filled with the plating solution
(electrolytic solution) sufficiently large with respect to the
sheet resistance B (.OMEGA./.quadrature.) of the surface seed layer
7 of the substrate W such that the sheet resistance Bis negligible,
thereby making the electric field more uniform over the entire
surface of the substrate and forming a plated film having higher
in-plane uniformity of film thickness on the surface of the
substrate. This is for the following reasons.
[0274] FIG. 41 shows the results of simulation analysis of plated
film thickness in a substrate surface (in the radial direction), as
analyzed by changing the ratio R (=A/B): the overall electric
resistance A (.OMEGA.) between the upper and lower surfaces of a
porous structure with its interior filled with a plating
solution/the sheet resistance B (.OMEGA./.quadrature.) of a seed
layer (conductive layer) of ruthenium formed on a 300 mm-diameter
silicon substrate, in the range of 0.002-1
(R.sub.0<R.sub.1<R.sub.2<R.sub.3). FIG. 42 shows the
relationship between the electric resistance ratio R and variation
of plated film thickness, calculated from the analytical results
shown in FIG. 41.
[0275] A plated film is required to have such an in-plane
uniformity of film thickness that its variation (relative standard
deviation) is not more than 2%. As is apparent from FIG. 42,
variation (relative standard deviation) of plated film thickness
can be controlled within 2% to meet the in-plane uniformity
requirement for plated film thickness by adjusting the overall
electric resistance A between the upper and lower surfaces of the
porous structure with its interior filled with a plating solution
to not less than 0.02 time the sheet resistance (electric
resistance) B of seed layer (A/B.gtoreq.0.02). It is preferred to
adjust the overall electric resistance A between the upper and
lower surfaces of the porous structure with its interior filled
with a plating solution to not less than 0.04 time the sheet
resistance (electric resistance) B of seed layer for further
reducing variation of plated film thickness.
[0276] In operation of the plating apparatus of this embodiment
having the electrode head 328, similarly to the above-described
plating apparatus having the electrode head 28 shown in detail in
FIG. 15, the electrode head 328 is lowered until the porous
structure 410 comes to a position as close as about 0.5 mm to 3 mm
to the surface of a substrate W, a given voltage is applied from
the plating power source 414 to between the cathodes 388 and the
anode 398, and a plating solution is injected from the plating
solution injection section 404 into the space between the substrate
W and the porous structure 410 to fill the space with the plating
solution, thereby to carry out plating of the surface (surface to
be plated) of the substrate W. The other processings are the same
as those of the above-described plating apparatus having the
electrode head 28, and hence a description thereof is omitted.
[0277] Though the electrolytic processing apparatus is employed for
electroplating in this embodiment, the apparatus, as it is, can be
employed for carrying out electrolytic etching by reversing the
direction of electric current, i.e., reversing the polarities of
the power source. Uniform etching can be effected by such
electrolytic etching. It is known in a plating process for copper
interconnects in an LSI to carry out electrolytic etching in the
course of the plating process by reverse electrolysis processing.
For example, the following processing can be carried out using the
present apparatus: Plating is carried out at a current density of
20 mA/cm.sup.2 for 7.5 seconds to form a copper plated film with a
thickness of 50 nm; the polarities of the power source is reversed
to carry out etching at a current density of 5 mA/cm.sup.2 for 20
seconds, thereby etching off the copper plated film by 33 nm, and
then final plating is carried out. It has been confirmed that this
processing can effect uniform etching and improve embedding of the
copper plated film.
[0278] Though the porous structure 410 used in this embodiment has
a pressure loss of 1500 kPa or an apparent porosity of 10% and has
a resistivity of 1.0.times.10.sup.6 .OMEGA.cm, and is composed of
silicon carbide, it is also possible to use a porous structure
composed of e.g. silicon carbide, having an adjusted pressure loss
of not less than 500 kPa, preferably not less than 1000 kP, more
preferably not less than 1500 kPa, or an adjusted apparent porosity
of not more than 19%, preferably not more than 15%, more preferably
not more than 10%, and preferably having an adjusted resistivity of
not less than 1.0.times.10.sup.5 .OMEGA.cm, or a porous structure
of which at least one of the bulk specific gravity and the water
absorption is adjusted, in carrying out plating of a substrate by
applying a voltage between the cathodes (first electrode) 388 and
the anode (second electrode) 398. This makes it possible to carry
out electrolytic processing, such as electroplating, of a substrate
with the electric field at the surface of the substrate adjusted to
the desired state so that the substrate after electrolytic
processing can have a processed surface in the intended state.
[0279] It is also possible to use a porous structure 410 whose
overall electric resistance A (.OMEGA.), i.e., the resistance
between the upper and lower surfaces of the porous structure 410
with its interior filled with a plating solution (electrolytic
solution), is adjusted to not less than 0.02 time the sheet
resistance (electric resistance) B (.OMEGA./.quadrature.) of a
surface seed layer (conductive layer) 7 of a substrate W
(A/B.gtoreq.0.02).
[0280] FIGS. 43A and 43B show variations of the electrode head. The
electrode head of FIG. 43A uses, as the plating solution injection
section 404 which is connected to the above-described plating
solution supply pipe and which supplies a plating solution into the
space between the substrate W in the plating position and the
porous structure 410, a tube which, at a lower point, is bent
orthogonally inwardly so as to jet the plating solution inwardly in
the radial direction of the substrate W and force the plating
solution to collide against the circumferential surface of the
porous structure 410. In the electrode head of FIG. 43B, the
tubular plating solution injection section 404 disposed beside the
porous structure 410 is tilted such that the lower-end nozzle is
oriented inwardly and obliquely downwardly so as to create with the
plating solution jetted from the nozzle a flow of the plating
solution that flows in one direction over the substrate
surface.
[0281] FIG. 44 shows an electrolytic processing apparatus, employed
as an electroplating apparatus, according to yet another embodiment
of the present invention. The electroplating apparatus adds the
following construction to the electroplating apparatus of the
above-described embodiment mainly shown in FIG. 33.
[0282] The electrode holder 394, on the opposite side of the
substrate W from the plating solution injection section 404, is
provided with a plating solution suction section 430, disposed
beside the anode 398 and the porous structure 410, for sucking in
the plating solution injected into the space between the substrate
W and the porous structure 410. A plating solution supply line 436,
having a delivery pump 432 and a filter 434 in it, is connected at
one end to the plating tank 16 (see FIG. 5) and connected at the
other end to the plating solution injection section 404. Further, a
plating solution discharge line 440, having a suction pump 438 in
it, is connected at one end to the plating solution tank 16 and
connected at the other end to the plating solution suction section
430. A plating solution circulation system 442 is thus constructed
in which by the actuation of the pumps 432, 438, the plating
solution in the plating solution tank 16 is supplied into the space
between the substrate W and the porous structure 410 and stored in
the space defined by the substrate W and the sealing member 390
while the thus-stored plating solution is returned to the plating
solution tank 16.
[0283] According to this embodiment, similarly to the
above-described embodiments, when the substrate holder is in the
plating position B (see FIG. 7), the electrode head 328 is lowered
until the distance between the substrate W held by the substrate
holder and the porous structure 410 becomes, for example, about 0.5
to 3 mm, and the plating solution is injected from the plating
solution injection section 404 into the space between the substrate
W and the porous structure 410. The injected plating solution fills
the space and is stored in the space defined by the substrate W and
the sealing member 390 while the plating solution is sucked in by
the plating solution suction section 430. Plating of the surface
(lower surface) of the substrate W is carried out while keeping the
space between the substrate W and the porous structure 410 filled
with the plating solution flowing in one direction, as shown in
FIG. 45.
[0284] This embodiment can thus eliminate the need for provision
of, for example, an electrolytic solution supply tube composed of
an insulating material, which may disturb the electric field
distribution, within the porous structure 410. This can make the
electric field distribution uniform over the entire surface of a
substrate W. Furthermore, the plating solution held in the porous
structure 410 can be prevented from leaking out of the porous
structure 410 upon the injection of plating solution. Further
according to this embodiment, the plating solution is injected from
the side of the porous structure 410 into the space between the
substrate W held by the substrate holder and the porous structure
410, and the plating solution is allowed to circulate so that the
plating solution constantly flows between the substrate W and the
porous structure 410. This can prevent the formation of plating
defects, i.e., non-plated portions, caused by a stop of the flow of
plating solution during electroplating. Further, by rotating the
substrate W according to necessity, the plating solution is allowed
to flow at a more even speed over the central and peripheral
regions of the substrate W.
[0285] The electroplating apparatus of this embodiment is further
provided with a deaerator for removing dissolved gas from the
plating solution circulated and used in the above-described manner.
In particular, the plating solution tank 16 is provided with an
auxiliary circulation line 444 for circulating the plating solution
in the plating solution tank 16 by the actuation of a circulation
pump 441, and a deaerator 446 is provided in the auxiliary
circulation line 444. By thus circulating the plating solution
while deaerating it with the deaerator 446 and using the deaerated
plating solution in plating, dissolved gas in the plating solution
can be prevented from becoming gas bubbles upon the injection of
the plating solution and remaining in the plating solution.
[0286] This holds also for the plating solution injected into the
space between a substrate and a porous structure and used in
plating in the above-described embodiments.
[0287] Though in this embodiment the present apparatus is employed
as a copper electroplating apparatus for carrying out copper
plating, the present apparatus can also be used for electroplating
of Cr, Mn, Fe, Co, Ni, Zn, Ga, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Os,
Ir, Pt, Au, Hg, Tl, Pb or Bi, or an alloy thereof.
[0288] According to this embodiment, the effect of the electric
resistance (sheet resistance) of a surface conductive layer of a
substrate can be reduced, thereby making the electric field more
uniform over the entire surface of the substrate. Thus, in the case
of an electroplating apparatus, a plated film having a high
in-plane uniformity of thickness can be formed on a surface of a
substrate (conductive layer) even when the substrate has a large
area and a conductive layer, which is thin and has a large electric
resistance, is formed on the surface.
* * * * *