U.S. patent application number 09/912112 was filed with the patent office on 2002-01-03 for the dome: shape and temperature controlled surfaces.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Hanawa, Hiroji, Ishikawa, Tetsuya, Staryuk, Pavel.
Application Number | 20020000198 09/912112 |
Document ID | / |
Family ID | 25345085 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000198 |
Kind Code |
A1 |
Ishikawa, Tetsuya ; et
al. |
January 3, 2002 |
The dome: shape and temperature controlled surfaces
Abstract
The present invention provides an HDP-CVD tool using
simultaneous deposition and sputtering of doped and undoped silicon
dioxide capable of excellent gap fill and blanket film deposition
on wafers. The tool of the present invention includes: a dual RF
zone inductively coupled plasma source; a dual zone gas
distribution system; temperature controlled surfaces within the
tool; a symmetrically shaped turbomolecular pumped chamber body; a
dual cooling zone electrostatic chuck; an all ceramic/aluminum
alloy chamber; and a remote plasma chamber cleaning system.
Inventors: |
Ishikawa, Tetsuya; (Santa
Clara, CA) ; Staryuk, Pavel; (San Jose, CA) ;
Hanawa, Hiroji; (Sunnyvale, CA) |
Correspondence
Address: |
Patent Counsel
APPLIED MATERIALS, INC.
P.O. Box 450-A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
25345085 |
Appl. No.: |
09/912112 |
Filed: |
July 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09912112 |
Jul 23, 2001 |
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08865267 |
May 29, 1997 |
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6286451 |
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Current U.S.
Class: |
118/715 ;
118/724 |
Current CPC
Class: |
H01J 37/3244 20130101;
H01J 37/321 20130101; C23C 16/4411 20130101; C23C 16/4405 20130101;
C23C 16/52 20130101; H01J 37/32522 20130101; C23C 16/507
20130101 |
Class at
Publication: |
118/715 ;
118/724 |
International
Class: |
C23C 016/00 |
Claims
What is claimed is:
1. An apparatus for processing substrates, comprising: (a) a
chamber having: (i) a sidewall; (ii) a lid disposed at one end of
the sidewall; and (iii) a bottom disposed at the opposite end of
the sidewall; (b) a substrate support member cantilever mounted on
the sidewall; (c) one or more gas inlets disposed through one or
more of the sidewall and the lid to admit gas into the chamber; (d)
one or more gas inlets disposed through one or more of the sidewall
and the lid to admit one or more cleaning gases into the chamber;
and (e) an exhaust port disposed in the bottom of the chamber.
2. The apparatus of claim 1 wherein the lid comprises a dome
comprised of a dielectric material.
3. The apparatus of claim 2 wherein the dome comprises a material
selected from the group consisting of Al.sub.2O.sub.3, AlN,
SiO.sub.2 or combinations thereof.
4. The apparatus of claim 3 wherein the dome further comprises a
generally annular sidewall and a generally planar top.
5. The apparatus of claim 2 further comprising a heat transfer
assembly disposed adjacent to the lid.
6. The apparatus of claim 5 wherein the heat transfer assembly
comprises one or more heat transfer plates.
7. The apparatus of claim 6 wherein the one or more heat transfer
plates comprise a heating plate and a cooling plate.
8. The apparatus of claim 7 wherein the heating and cooling plates
are comprised of a thermally conductive material.
9. The apparatus of claim 8 wherein the thermally conductive
material is selected from the group consisting of AlN, SiN, Al or
combinations thereof.
10. The apparatus of claim 9 wherein the heating plate includes a
resistive heating element disposed therein.
11. The apparatus of claim 10 wherein the cooling plate includes
one or more fluid passages disposed therein.
12. The apparatus of claim 11 wherein a heat conducting member is
disposed between the heating plate and the cooling plate.
13. The apparatus of claim 12 wherein the heat conducting member
comprises a heat transfer material such as grafoil, chromerics, or
combinations thereof.
14. The apparatus of claim 13 wherein the heat conducting member
comprises one or more pucks disposed between the heating and
cooling plates.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an apparatus and method for
processing semiconductor substrates, and more particularly, to a
high density plasma (HDP) chemical vapor deposition (CVD) tool for
deposition of films, preferably .alpha.C, .alpha.FC, SiN, SiON,
doped and undoped SiO.sub.2 and BiN, onto substrates.
BACKGROUND OF THE INVENTION
[0002] Plasma tools used for semiconductor processes such as
chemical vapor deposition (CVD), etching, reactive ion etching and
so forth typically employ either inductive coupling or capacitive
coupling to strike and maintain a plasma. One advantage of
inductively coupled plasmas over capacitively coupled plasmas is
that the inductively coupled plasma is generated with a much
smaller bias voltage on the substrate, reducing the likelihood of
damage thereto. In addition, inductively coupled plasmas have a
higher ion density thereby providing higher deposition rates and
mean free paths, while operating at a much lower pressure than
capacitively coupled plasmas. These advantages allow in situ
sputtering and/or ion directionality during processing.
[0003] More recently, high density plasma (HDP) CVD processes have
been used to provide a combination of chemical reactions and
physical sputtering. HDP-CVD processes promote the disassociation
of the reactant gases by the application of radio frequency (RF)
energy to the reaction zone proximate the substrate surface thereby
creating a plasma of highly reactive ionic species. The relatively
non-reactive ionic constituents, i.e., Ar, are given high momentum
(e field) used to dislodge deposited film material selectively from
specific areas along the profile of the film based on a sputter
yield curve. The high reactivity of the released ionic species
reduces the energy required for a chemical reaction to take place,
thus lowering the required temperature for these processes.
[0004] The goal in most HDP-CVD processes is to deposit a film of
uniform thickness across the surface of a substrate, while also
providing good gap fill between lines and other features formed on
the substrate. Deposition uniformity and gap via fill are very
sensitive to source configuration, gas flow changes, source radio
frequency generator power, bias radio frequency generator power,
gas nozzle design, including symmetry in distribution of nozzles,
the number of nozzles, the height the nozzles are disposed above
the substrate support and the lateral position of the nozzles
relative to the substrate support. These variables change as
processes performed within the tool change and as process gases
change.
[0005] One problem encountered in semiconductor fabrication is
generation and maintenance of plasma density uniformity above the
substrate. Plasma uniformity is dependent upon magnetic and
electric fields generated in the tool as well as gas flow into and
out of the tool. As substrate sizes increase, i.e., to 300 mm,
uniformity over a larger area becomes even more difficult
achieve.
[0006] Another problem which affects deposition uniformity is
uneven gas distribution over the substrate surface. Typically, a
gas plenum is provided around the perimeter of a processing region
and a plurality of nozzles extend radially inwardly to provide
gases to the substrate surface. In some applications, the gases
tend to be unevenly distributed across the substrate surface, with
more gas provided towards the edge of the substrate and less gas
provided towards the center of the substrate. In addition, reactant
gases are typically mixed in the gas injection system prior to
their introduction into the chamber. In these instances, material
tends to deposit within the gas injection system itself, thereby
clogging some gas injectors further heightening non-uniform gas
distribution.
[0007] Still another problem encountered is maintaining a uniform
temperature across the substrate surface. As a substrate is
processed, there exists a significant heat load due to plasma
radiation and ion bombardment exposed to the substrate surface. If
a temperature gradient exists across the substrate surface, the
deposition of the film can proceed in a non-uniform manner.
Therefore, it is important to precisely control the temperature of
the substrate.
[0008] Another problem is deposition of material on the tool
itself. During processing, deposition material deposits throughout
the tool, on the substrate support member, and on the gas
distribution components. Over time, such material build up can
flake off into the chamber resulting in particle contamination on
the substrate which can compromise the integrity of the devices
being fabricated. Thus, the tool must be periodically cleaned. A
favored method of cleaning is to introduce cleaning gases into the
chamber to react with the deposited material to form a product
which can be exhausted from the chamber. Typically, a cleaning gas,
such as a fluorinated gas, is introduced into the chamber and a
plasma is struck in the chamber. The resultant excited products
react with the deposition material to form gas phase byproducts
which are then exhausted from the chamber. One problem with this
process is that cleaning is typically localized in regions adjacent
to the plasma. In order to enhance cleaning of all exposed chamber
surfaces, the time period in which the cleaning process is
performed is increased, thereby decreasing throughput, and/or the
cleaning process is performed using high temperatures, thereby
effectively over cleaning some of the chamber surfaces and
increasing the cost of consumables and/or maintenance
intervals.
[0009] Therefore, there is a need for a process tool which provides
more uniform conditions for forming thin CVD films on a substrate,
including enhanced cleaning features and high throughput, in a more
manufacturing worthy way.
SUMMARY OF THE INVENTION
[0010] An embodiment of the present invention provides an HDP-CVD
tool using deposition and sputtering of doped and undoped silicon
dioxide capable of excellent gap fill and blanket film deposition
on wafers having sub 0.5 micron feature sizes having aspect ratios
higher than 1.2:1. The tool of the present invention includes: a
dual RF zone inductively coupled plasma source; a dual zone gas
distribution system; temperature controlled chamber components; a
symmetrically shaped, turbomolecular pumped chamber body; a dual,
cooling zone electrostatic chuck; an all ceramic/aluminum alloy
chamber construction; and a remote plasma chamber cleaning
system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features,
advantages and objects of the present invention are attained can be
understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to the
embodiments thereof which are illustrated in the appended
drawings.
[0012] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are,
therefore, not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0013] FIG. 1 is a cross sectional view of a process chamber of the
present invention;
[0014] FIGS. 2A-2C are electrical schematic views showing three
various RF matching configurations which can be used to advance in
the present invention;
[0015] FIG. 3 is a schematic cross sectional view showing the dual
zone RF plasma source of the present invention;
[0016] FIG. 4 is an exploded view of the top temperature control
assembly and top antenna;
[0017] FIG. 5 is a cross sectional view of a substrate support
member of the present invention;
[0018] FIG. 6 is a top cross sectional view of a substrate support
member of the present invention;
[0019] FIG. 7 is a top cross sectional view of a chamber having a
substrate support member disposed therein;
[0020] FIG. 8 is a top view of one embodiment of an electrostatic
chuck;
[0021] FIG. 8a is an alternative embodiment of the electrostatic
chuck;
[0022] FIG. 9 is a cross sectional view of one embodiment of the
electrostatic chuck of FIG. 8;
[0023] FIG. 10 is a flow diagram of the temperature control aspects
of the electrostatic chuck of FIG. 8 and 9;
[0024] FIG. 11 is a cross-sectional view of an electrostatic chuck
and a cover ring;
[0025] FIG. 12 is a cross-sectional view of a cover ring disposed
in proximity to a source coil;
[0026] FIG. 13 is a side view partially in section showing the gas
control system of the present invention;
[0027] FIG. 14 is a side view partially in section showing the gas
distribution ring and first gas channel;
[0028] FIG. 15 is a side view partially in section showing the gas
distribution ring and the second gas channel;
[0029] FIG. 16 is a side view partially in section showing the
center gas feed assembly;
[0030] FIG. 17 is an exploded view of the gas distribution ring and
the lose plate of the lid assembly;
[0031] FIG. 18 is a schematic side view partially in section
showing the microwave remote plasma clean and its location on the
chamber;
[0032] FIG. 19 is a top view of a gas diffuser;
[0033] FIG. 20 is a side view of a gas diffuser; and
[0034] FIG. 21 is a perspective view of a gas baffler.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0035] The tool will be described in detail below with reference to
each of the following subassemblies: a chamber body, a chamber lid
assembly, a cathode and lift assembly, a process kit, a gas
distribution assembly and a remote plasma source.
[0036] Chamber Body
[0037] FIG. 1 is a cross sectional view of a processing tool 10 of
the present invention. The processing tool 10 generally includes a
chamber body 12, a lid assembly 14 and a cantilevered, removable
substrate support member 16. These members in combination form a
physically and electrically symmetric, evacuable enclosure and
exhaust passage 22 in which substrate processing is carried
out.
[0038] The chamber body 12 is preferably a unitary, machined
structure having a sidewall 18 which defines an inner annular
processing region 20 and tapers towards its lower end to define a
concentric exhaust passage 22. The chamber body 12 defines a
plurality of ports including at least a substrate entry port 24
sealed by a slit valve 44 and a side port 26 through which the
cantilever mounted substrate support member 16 is disposed. The
substrate entry port 24 and the support member port 26 are
preferably disposed through opposite sides of the chamber body 12.
Two additional side ports are disposed on opposite sides of the
chamber wall 18 at about the level of the upper surface of the
substrate support member 16 and are connected to a gas channel 28
formed in the chamber wall 18. Cleaning gases, such as
disassociated fluorine containing gases, are introduced into the
channel 28 from a remote plasma source 30 and into the chamber
through the gas inlet ports provided therefor and shown in FIG. 18.
The location of the openings of the ports into the chamber are
provided to direct gases towards areas of the reactor where heavy
build-up occurs. The remote plasma source and cleaning gas delivery
will be described in more detail below.
[0039] The upper surface of the chamber wall 18 defines a generally
flat landing area on which a base plate 33 of the lid assembly 34
is supported. One or more o-ring grooves 36 are formed in the upper
surface of the wall 18 to receive one or more o-rings 38 to form an
airtight seal between the chamber body 12 and the base plate 33.
The lid assembly will be described in more detail below.
[0040] The substrate support member 16 partially extends through
the side access port 26 formed in the chamber wall 18 and is
mounted to the chamber wall 18 on a flange 46 to provide a
generally annular substrate receiving surface 200 in the center of
the chamber. When the support member 16 is positioned in the
chamber, an outer wall 50 of the annular support member 16 and an
inner wall 52 of the chamber define an annular fluid passage 22
that is substantially uniform about the entire circumference of the
support member 16. It is preferred that the substantially uniform
passage 22 and the exhaust port 54 be substantially concentric with
the substrate receiving surface of the support member. The exhaust
port 54 is centered below the substrate receiving portion of the
support member 16 to draw the gases evenly through the uniform
passage 22 and out of the chamber. This enables more uniform gas
flow over the substrate surface about the entire circumference
thereof and radially downwardly and outwardly from the chamber
through exhaust port 54 centered in the base of the chamber. The
uniform fluid passage 22 promotes uniform deposition of film layers
by maintaining pressure and residence time uniformity, lacking in
existing processing chambers, such as substrate locations with
differing proximity in relation to the pumping port.
[0041] A pumping stack comprising a twin blade throttle assembly
56, a gate valve 58 and a turbomolecular pump 60 is mounted on the
tapered lower portion of the chamber body to provide pressure
control within the chamber. The twin blade throttle assembly 56 and
the gate valve 58 are mounted between the chamber body 12 and the
turbomolecular pump 60 to allow isolation via gate valve 58 and/or
pressure control at pressures of from about 0 to about 100
milliTorr as determined by settings of the twin blade throttle
assembly 56. A 1600 L/sec turbo pump is a preferred pump, however,
any pump which can achieve the desired pressure in the chamber can
be used. A foreline 57 is connected to the exhaust port 54 at
positions upstream and downstream from the turbo pump. This
provides backing pump capability. The foreline is connected to the
remote mainframe pump, typically a roughing pump. A port 59 is
formed in the pumping stack to mount a flange 61 of the foreline.
During chamber cleaning, cleaning gases are flown into the chamber
at a high rate, thereby increasing the pressure in the chamber. In
one aspect of the invention, therefore, the turbo pump is isolated
from the chamber by the gate valve 58 and the mainframe pump is
used to maintain the pressure in the chamber during the cleaning
process.
[0042] During processing of a substrate in the chamber, the vacuum
pump evacuates the chamber to a pressure in the range of about 4 to
about 6 milliTorr, and a metered flow of a process gas or gases is
supplied through the gas distribution assembly and into the
chamber. The chamber pressure is controlled by directly measuring
the chamber pressure and feeding this information to a controller
that opens and closes the valves to adjust pumping speed. Gas
flows/concentrations are controlled directly by mass flow
controllers through a software set point provided in a process
recipe. By measuring the flow rate of gases being pumped out of the
chamber through the exhaust port 54, a mass flow controller (not
shown) on the inlet gas supply can also be used to maintain the
desired pressure and gas concentration in the chamber.
[0043] Chamber Lid Assembly
[0044] The chamber lid assembly 34 is generally comprised of an
energy transmitting dome 32, an energy delivery assembly 62 and a
temperature control assembly 64 supported on a hinge mounted base
plate 33. The base plate 33 defines an inner annular channel in
which a gas distribution ring is disposed. O-ring grooves are
formed in the top of the gas distribution ring to receive an o-ring
to seal the dome 32 and the top of the gas distribution ring. In
combination, the lid assembly provides both the physical enclosure
of the plasma processing region as well as the energy delivery
system to drive processing. A cover is preferably provided over the
entire lid assembly to house the various components.
[0045] The dome 32 is generally comprised of a cylindrical sidewall
66 which is closed on one end by a flat top 68. The cylindrical
sidewall is generally perpendicular to the upper surface of the
substrate support member 16 and the planar top 68 is generally
parallel to the upper surface of the support member 16. The
junction 70 between the sidewall and the top is rounded to provide
a curved inner wall of the dome 32. The dome 32 is made of a
dielectric material which is transmissive to RF energy, preferably
a ceramic such as aluminum oxide (Al.sub.2O.sub.3), aluminum
nitride (AIN) or quartz (SiO.sub.2).
[0046] Two separately powered RF coils, a top coil 72 and a side
coil 74, are wound external to a dielectric dome 32. The side coil
74 is preferably covered by a ground shield to reduce electrical
crosstalk between the coils 72 and 74. The RF coils 72 and 74 are
powered by two variable frequency RF sources 76 and 78.
[0047] Each power source includes a control circuit which measures
reflected power and which adjusts a digitally controlled
synthesizer in the RF generator to sweep frequencies, typically
starting at 1.8 MHZ, to minimize the reflected power. When the
plasma ignites, the circuit conditions change because the plasma
acts as a resistor in parallel with the coil. At this stage, the RF
generator continues to sweep the frequency until a minimal
reflected power point is again reached. The power source circuitry
is designed so that each set of windings resonates at or near the
frequency at which the minimum reflected power point is reached, so
that the voltage of the windings is high enough to drive sufficient
current to sustain the plasma. Thus, frequency tuning guarantees
that the system remains close to resonance even if the resonance
point of the circuit changes during processing. In this way,
frequency tuning eliminates the need for circuit tuning and
impedance matching by varying the values of impedance matching
components (e.g., capacitors or inductors).
[0048] Each power source ensures that the desired power is
delivered to the load despite any impedance mismatches, even
continuously varying impedance mismatches which can arise due to
changes in the plasma impedance. To ensure that the correct power
is delivered to the load, each RF generator dissipates the
reflected power itself and increases the output power so that the
delivered power remains at the desired level.
[0049] FIGS. 2(a),(b) and (c) show three separate local RF match
configurations schematically. FIG. 2(a) shows a matching
configuration for use with a coil L having one end grounded. The
two capacitors C1 and C2 form an RF voltage divider. In FIG. 2(b),
a balanced coil L having two shunt capacitors C2 and C3, where
C2.apprxeq.C3, across it to ground is used to match the load
(plasma) frequency. Finally, in FIG. 2(c), a pi (.pi.) network
match is used having two variable capacitors to ground across the
coil L. Since the output impedance of most conventional RF
generators is designed to be 50 ohms, matching networks 2(a), (b)
or (c) can be used to transfer maximum power to plasmas ranging in
impedance from as low as 5 ohms to as high as 900 ohms (in the
balanced load case). This dual coil system allows control of the
radial ion density profiles in the reaction chamber.
[0050] FIG. 3 is a schematic side view of the chamber showing
principally the coil geometry and RF feeds for top coil 72 and side
coil 74. The pi network matching system described in FIG. 2(c) is
shown in FIG. 3. A Langmuir probe was introduced into the chamber
13 to measure the plasma ion density at different positions across
the chamber 13 using the top coil only, and the side coil only, to
generate the plasma. The dual coil arrangement, when properly tuned
to a substrate being processed, can generate uniform ion density
across its surface.
[0051] Uniform ion across the substrate surface contributes to the
uniform deposition and gap-fill performance onto the wafer and
helps alleviate plasma charging of device gate oxides due to
nonuniform plasma densities. When the action of the coils is
superimposed, uniform plasma density results and deposition
characteristics may be vastly improved.
[0052] The dome 32 also includes a temperature control assembly 64
to regulate the temperature of the dome during the various process
cycles, i.e., deposition and clean. FIG. 4 is an exploded view of
the temperature control assembly 64 and the top coil 72. The
temperature control assembly generally comprises a heating plate 80
and a cooling plate 82 disposed adjacent each other and preferably
having a thin layer 84 of a thermally conductive material, such as
grafoil, disposed therebetween. Preferably, about a 4 mil to about
8 mil layer of grafoil is disposed therebetween. A thermally
conductive plate 86, such as an AlN plate, is provided with grooves
formed in its lower surface to house the coil 72. A second layer 88
of grafoil, preferably about 1 to about 4 mils thick, is disposed
between the thermally conductive plate 86 and the heating plate 80.
A third thermally conductive layer 90 is disposed between the coil
72 and the dome 32. The third layer is preferably a layer of
chromerics having a thickness of about 4 mils to about 8 mils. The
thermally conductive layers facilitate heat transfer to and from
the dome 32. During cleaning it is preferred to heat the dome,
while during processing it is preferred to cool the dome. As a
result, a thermally conductive path is provided to achieve these
advantages.
[0053] The cooling plate 82 includes one or more fluid passages
formed therein through which a cooling fluid such as water is
flown. The water channel in the cooling plate is in series with
cooling channels 88 formed in the chamber body. A pushlock type
rubber hose with quick disconnect fittings supplies water to the
chamber body and the cooling channel in the lid. The return line
has a visual flowmeter with an interlocked flow switch. The
flowmeter is factory calibrated for a 0.8 gpm flow rate at a
pressure of about 60 psi. A temperature sensor is mounted on the
dome to measure the temperature thereof. The heating plate 80
preferably has one or more resistive heating elements disposed
therein to provide heat to the dome during the cleaning phase.
Preferably the heating plate is made of cast aluminum, however
other materials known in the field may be used. A controller is
connected to the temperature control assembly to regulate the
temperature of the dome.
[0054] Each of the components 80, 82, 84, 86, and 88 define two
channels through which the ends of the top coil 72 extend. Two
insulative sleeves 94, 96 are disposed in each channel formed in
the heating plate 80, the cooling plate 82 and the grafoil layers
to insulate the coil leads extending therethrough. The insulative
sleeves may include silicon suction cups disposed on their lower
ends to provide a seal at the insulative plate 86.
[0055] By direct conduction, the heating plate 80 and the cooling
plate 82 are used to control the dome temperature. Control of the
dome temperature to within .apprxeq.10.degree. K improves wafer to
wafer repeatability, deposition adhesion and has been found to
reduce flake or particle counts in the chamber. The dome
temperature is generally kept within the range of from about
100.degree. C. to about 200.degree. C. depending on processing
requirements. It has been shown that higher chamber clean rates
(etch rates) and better film adhesion to the substrate can also be
obtained at higher dome temperatures.
[0056] Cathode and Lift Assembly
[0057] The cathode and lift assembly will now be described with
reference to FIGS. 5-10. The support member includes elements which
are positionable within the chamber and elements positionable
outside of the chamber. The elements of the support member 16
positionable within the chamber extend through access port 26
provided in the sidewall 18 of the chamber and are supported to the
sidewall by elements positionable outside of the chamber. FIG. 5 is
a cross-sectional view of the substrate support member 16. The
support member 16 generally includes a base 94 having a flange 46
for attachment to the chamber wall, a cantilevered arm portion 96
extending radially inward therefrom, and a substrate receiving
portion 98 located at the end of the cantilevered arm 96. The
flange 46 mounts the base 94 of the support member to the chamber
wall 18 about the substrate support member access port 26. The base
94 extends inwardly from the flange 46 to define an inner
curvilinear wall portion 51. The curvilinear wall 51 is preferably
an arc or segment of a circle having a radius (r) substantially
equal to the overall inner radius (R) of the chamber. The surface
of the curvilinear wall 51 in the circumferential direction is
received adjacent the inner wall 52 of the chamber. The curvilinear
wall 51 along with the inner wall 52 of the chamber form a
symmetrical and continuous inner chamber wall when the support
member 16 is located in the chamber for processing as shown in FIG.
7.
[0058] The cantilevered arm 96 extends inwardly from the lower
portion of the base 94 to support the ESC receiving portion 98
having a substrate receiving surface 99 thereon. The ESC receiving
portion 98 includes an upwardly extending annular pilot 100. The
annular pilot 100 includes a larger inner diameter portion and a
smaller inner diameter portion which form an inner annular step to
support an insulative member 102 thereon. An ESC 104 is preferably
supported on insulative plate 102 to provide a substrate receiving
surface 99. The outer wall 50 of the ESC receiving portion 98
defines a continuous annular face.
[0059] The ESC receiving portion 98 also defines a recess 108 in
which a substrate positioning assembly 110 is disposed. A bottom
plate 112 is secured to the lower portion of the receiving portion
by a threaded screw arrangement to protect the inner components of
the support member 16 from the processing environment.
[0060] FIG. 7 is a top sectional view showing a support member 16
disposed in a chamber. The cantilevered arm 96 extends across the
symmetric fluid passage 22 to support the ESC receiving portion 98
within the chamber. It is preferred that the cantilevered arm
minimize interruption, restriction or disturbance of the fluid flow
through the fluid passage 22 by including a fluid passage or
plurality of passages 114, such as a radial passage, therethrough.
It is also preferred that the support arm 116, include a passage or
plurality of passages 118 therethrough to minimize interruption,
restriction or disturbance of fluid flow through the uniform fluid
passage.
[0061] It is also preferred that the cantilevered arm 96 attach to
the ESC receiving portion 98 at a point remote from the substrate
receiving surface, such as along the bottom of the ESC receiving
portion 98, in order to further minimize the effect on the gases
near the surface of the substrate caused by any interruption,
restriction or disturbance of fluid as it passes through and around
the cantilevered arm. More generally, it is preferred that any
nonuniformity in the fluid passage 22 be minimized and positioned a
sufficient distance from the ESC receiving surface 98 to avoid
affecting the flow of fluid over a substrate placed thereon.
[0062] The substrate lift assembly 120 includes a plurality of
radially extending substrate support pins 122 which are aligned
with and spaced about the periphery of the ESC receiving member 98
and are received on a winged mounting plate 123. The mounting plate
123 is disposed within a generally rectangular recess 124 formed in
the support member 16, and is actuated by a vertically moveable
elevator assembly 126. As shown in FIG. 5, the elevator mechanism
126 includes a vertically moveable shaft 128 that mounts a plate
130 at the upper end thereof. The shaft 128 is moved vertically up
and down by an actuator, preferably a pneumatic cylinder located
outside of the chamber.
[0063] The support pins 122 are received in sleeves 132 located in
bores 134 disposed vertically through the ESC receiving member 98
and move independently of support member 16 within the enclosure.
Support pins 122 extend from the support member 16 to allow the
robot blade to remove a substrate from the enclosure, but must sink
into the support member 16 to locate a substrate on the upper
surface of the ESC 104. Each pin includes a cylindrical shaft
terminating in a lower spherical portion and an upper spherical
portion.
[0064] In operation, an external blade 138 (with a substrate to be
processed supported thereon) is inserted through the slit valve 24
into the chamber to position a substrate over the support member
16. One example of a suitable blade 138 and an associated robot
substrate handling system is described in co-pending, commonly
assigned U.S. patent application Ser. No. 944,803, entitled
"Multichamber Integrated Process System", filed in the name of Dan
Maydan, Sasson Somekh, David N. K. Wang, David Cheng, Masato
Toshima, Isak Harari, and Peter Hoppe, which is hereby incorporated
herein by reference. The elevator mechanism 126 raises the
substrate support pins 122 above the blade to pick up the
substrate. The blade is then withdrawn from the chamber and a
pneumatic cylinder closes a door over the blade access slot to seal
chamber. The elevator mechanism 126 is actuated to lower support
pins 122 until the substrate is received on the upper surface 98 of
the support member 16 in position for processing.
[0065] After processing, the elevator mechanism raises the support
pins 122 to lift the substrate off the substrate support member 16.
The door is then opened and the blade is again inserted into the
chamber. Next, elevator mechanism 126 lowers the substrate support
pins 122 to deposit the substrate on the blade. After downwardly
moving pins 122 clear the blade, the blade is retracted.
[0066] During processing, the plasma of the CVD process environment
gives off large quantities of heat, the total heat generated by the
plasma being at least partially dependent on the power density of
the plasma. A portion of this heat is transferred into the
substrate, and must be removed from the substrate to maintain the
temperature of the substrate, below a pre-defined critical
temperature. To remove this heat, a heat transfer system is
provided in the substrate support member 16 to control the
temperature of the support member and the substrate being
processed. FIG. 6 is a top sectional view showing the heat transfer
system of the support member 16. Water inlet 140 and outlet 142 are
connected by passages 144 and 146. A water manifold 148 is located
within the support member 16 to facilitate heat transfer from the
support member to the coolant fluids. The temperature of the
support member 16 is selected to eliminate premature deposition
within the gas manifold upstream from the processing region of the
chamber. Coolant channels 144, 146 received through the mass of the
substrate support member 16 are provided for the passage of coolant
fluids therethrough. In addition, grooves in the surface of the ESC
104 (which will be described below), wherein gases are flown,
transfer heat from the substrate into the support member 16 and
subsequently into the coolant fluids.
[0067] FIG. 8 is a top view of one embodiment of an electrostatic
chuck 104 according to the present invention. FIG. 8a is an
alternative embodiment which is symmetric and eliminates a wafer
flat area. Instead of having a smooth top surface, a number of
grooves are provided in the surface to form a large number of
protrusions 166. A central zone 168 of these protrusions is
separated from a peripheral zone 170 by a seal 172. Seal 172 is
simply an area which has not had grooves formed in it to provide
protrusions, thus forming a solid surface to minimize flow between
separate zones. An outer seal 174 provides a barrier to minimize
leakage of helium gas into the chamber.
[0068] Helium gas is inserted into periphery zone 170 through a
ring 176 which is a groove having a series of holes in it which
receive higher-pressure helium into this zone from helium line 47
of FIG. 1. An inner ring 178 allows a lower pressure gas to the
central zone 168 from pressure helium line 147. In operation, after
establishing an initial low helium pressure in central zone 168,
helium ring 178 typically will be removing helium gas leaking
through seal area 172 to maintain the desired low pressure helium.
In an optional embodiment, vacuum holes 180, which may be lift pin
holes, can be used to pump out the gas in the central zone using
vacuum line 135 of FIG. 1 to further lower the pressure in the
central zone. Optionally, additional vacuum holes could be
added.
[0069] Helium groove 178 is preferably positioned near seal area
172. By positioning it as close as possible, the desired heat
transfer step function can be approached. The high pressure gas is
thus contained in a narrow region by the periphery. If the high
pressure gas extends too far toward the center of the wafer, the
cooler center will become even cooler, partially offsetting the
reduction in heat differential provided by the higher pressure
gas.
[0070] In operation, for heating the wafer, lower pressure helium
(1-15 torr) is provided into the central zone 168, and higher
pressure helium (1-20 torr) is provided to peripheral zone 170. The
higher pressure helium in the peripheral zone provides better heat
transfer at the periphery of the wafer.
[0071] In one embodiment, the seals are made of the same ceramic
coating as the remainder of the top of electrostatic chuck 164.
Such a ceramic coating has small interstices, and thus the seal
areas do not provide a perfect seal. In addition, the substrate or
wafer will have some backside roughness, and may have more
roughness than the substrate support. Accordingly, the seal area
should have sufficient width to prevent significant leakage of
helium from one area to the other.
[0072] It has been determined by testing that for a ceramic covered
electrostatic chuck with the pressure ranges set forth above, that
a seal width of {fraction (1/10)} inch, or 100 mils, is effective.
Preferably, the seal width is in the range of 50 to 300 mils. For
the outer seal 174, it is desirable to minimize the width because
the area of the wafer above this seal will not have the benefit of
the heat conduction from the high-pressure helium. At the same
time, the seal must be wide enough to prevent significant leakage
of helium into the chamber which could undermine its intended heat
transfer capability by reaching the sustained helium pressure due
to higher flow levels or affect the reaction in the chamber. The
same 100 mil width has been found effective, with an optimum seal
width being in the range of 50 to 300 mils. Alternate widths may be
appropriate for different materials and smoothness of the substrate
support and substrate. For example, if a polymer film, such as
Kapton.TM., available from many well-known suppliers, is used, a
small width can be achieved because of its compliancy.
[0073] A preferred heat transfer gas is helium because it is inert
and relatively inexpensive. Alternately, argon, oxygen, CF.sub.4,
or other gases could be used, or a mixture of gases may be used. A
mixture could be used, for instance, to give additional pressure
control capabilities. The particular gas could be chosen to be
compatible with the chemical process in the chamber so that any
leaking gas will have minimal effect on the chemical reactions. For
example, in an etching reaction using fluorine as an etching
species, it may be desirable to use CF.sub.4 as the backside heat
transfer gas.
[0074] Because heat conduction occurs primarily through the helium
gas, it is desirable to minimize the size and number of the
protrusions and seal areas for this purpose. Thus, there should be
less contact area than non-contact area over the area of the
substrate. On the other hand, the seals are required to prevent gas
leakage and the protrusions must be of sufficient size and spacing
to mechanically support the wafer. In addition there are other
factors to be optimized. The height of the protrusions, which
determine the gap between the substrate and the substrate support
between the protrusions, must be sufficient to allow the gas to
quickly become distributed throughout the zones without affecting a
process start up time. Typically, this must be on the order of a
few seconds, and preferably the gas is distributed in 10 seconds or
less.
[0075] For optimum heat transfer, the gap should be small enough so
that heat transfer primarily occurs by molecules traveling directly
from the substrate to the substrate support without colliding with
another gas molecule, giving free molecular heat transfer. Thus,
the gap should be less than the mean free path of the gas (or the
average free path if a mixture of gases is used).
[0076] The mean free path is a function of the pressure of the gas
and the molecular collisional cross-section. Where a variety of
pressures will be used, the mean free path will vary. In a
preferred embodiment, the mean free path of the maximum pressure,
to be applied is used to determine the gap dimension.
[0077] In addition, the ratio of the gap to the overall dielectric
thickness must be kept small to avoid local anomalies on the
substrate. If this ratio is significant, the equivalent capacitance
will vary significantly between the spaces and the protrusions,
applying a significantly different electric field to the substrate.
This different field can affect the chemical process, causing
non-uniformities in the film that is being deposited, etched,
doped, or undergoing other property transformations. Some
difference will necessarily be present, but it is desirable to
minimize this.
[0078] The significance of the ratio also varies depending on the
dielectric material, in particular the difference between the
dielectric constant of the material and the heat transfer gas
(essentially one). The closer the two dielectric constants, the
less the concern with a larger gap.
[0079] Another concern in setting the gap size is to avoid having a
plasma generated with the heat transfer gas between the substrate
support and the backside of the wafer. It is believed that this
would begin to be a concern if the gap size were several times the
mean free path of the heat transfer gas.
[0080] For one embodiment of an electrostatic chuck, the thickness
of the ceramic coating is on the order of 7-10 mils. If Kapton.TM.
is used, a thickness of 1-2 mils may be used. Ideally, for chucking
purposes, the dielectric is as thin as possible within the limits
of maintaining manufacturing consistency and avoiding dielectric
breakdown. The mean free path of helium at the pressures for the
two zones described above is about 1-5 mils (at very high
pressures, the mean free path may be less than one). Accordingly,
protrusion heights of 0.7-1.2 mils have been chosen, tested, and
found effective. This gives a gap less than the mean free path of
helium at the desired pressures. Preferably, the gap is less than
twice the mean free path of the heat transfer gas at the pertinent
pressures, and more preferably less than the mean free path.
[0081] The spacing between the protrusions is as large as possible
while still supporting the substrate without bowing. In one
embodiment, the substrate is kept planar, while in other
embodiments it may be desirable to vary the protrusion height, or
alternately the top surface of the substrate support (with the
protrusions of equal height), to properly support a curved
substrate. Another factor is avoiding sharp points that could cause
local anomalies in the electric field. Too large a spacing can also
affect the movement of charge during dechucking, causing
damage.
[0082] It has been determined that an optimum center-to-center
spacing of the protrusions is in the range of 100-300 mils, more
preferably approximately 300 mils. The size of the protrusions
themselves is preferably between 10 and 150 mils, more preferably
approximately 130 mils in diameter. Square protrusions are shown
simply because of their ease in manufacture, and other shapes could
be used as well. Annular shapes could be used, for example.
[0083] In the embodiment shown, no openings for removing gas are
shown in the outer peripheral region, although this can be provided
in an alternative embodiment. The control of helium pressure can be
done either by providing high or low pressure helium, or by more
pumping through a vacuum pump. Similarly, for the central region,
the pressure can be controlled in either of these ways or through a
combination of both. The placement of the helium source as a ring
near the edges in combination with a vacuum near the middle of the
support provides an additional pressure gradient within the central
region, decreasing towards the center.
[0084] An alternate embodiment of the present invention thus
provides a coarse adjustment of the heat transfer through the two
pressure zones, with a fine tuning occurring through the placement
of the helium inlet and vacuum outlets in the central portion. In
alternate embodiments, more than one zone could be used for finer
adjustments, with the trade off of requiring more hardware.
[0085] FIG. 9 is a side view of one embodiment of an ESC 104
showing a varying dielectric thickness of a dielectric 186. A wafer
182 is shown mounted on the chuck. The chuck includes an electrode
portion 184 covered by dielectric 186. The dielectric extends
across the top and along the sides 190 of the electrostatic chuck.
As can be seen, the dielectric is thicker at a central portion 192,
and thinner at peripheral portions 194. The side view shows the
multiple protrusions 170 and also shows the inner seal 172 and the
outer seal 174.
[0086] The thinner dielectric at peripheral portions 194 provides a
stronger electrostatic force at these portions. This is beneficial
for a number of reasons. First, it holds the wafer more tightly,
ensuring better heat transfer by providing better contact with the
top of the electrostatic chuck. Second, a tighter force helps hold
in the higher pressure helium between seals 172 and 174 near the
periphery. In addition, if the peripheral portion of the wafer has
a temperature different from the central portion, this may cause it
to bend relative to the central portion, and it may bow up or down,
further exacerbating the heat differential problem. This can be
overcome by an appropriately higher electrostatic force at the
peripheral portion.
[0087] In an alternate embodiment, the varying dielectric thickness
can be used without the two pressure zones, or without the
protrusions. The varying in the dielectric coating can be
continuous, or stepwise. A stepwise difference makes the
manufacturing simpler and less expensive.
[0088] Another advantage of the seal area 174 and the stronger
electrostatic force at the edge of the wafer is to prevent arcing
of the plasma to exposed metal near the top surface of the
electrostatic chuck. Such exposed metal would typically be at the
helium inlet ports, which would come up through the aluminum
electrode, thus exposing through those holes a path to the
electrode. Arcing is prevented by providing a tighter seal,
locating the helium inlet holes sufficiently away from the edges of
the electrostatic chuck, or putting a groove there to prevent such
arcing.
[0089] As shown in FIG. 9, a temperature sensor 196 can be placed
in the space between the top surface of the electrostatic chuck and
the wafer. The temperature of the wafer can thus be inferred from
the sensor.
[0090] FIG. 10 is a feedback control system signal flow diagram
illustrating the temperature control. The FIG. 10 diagram is for a
closed loop temperature control system for controlling the helium
pressure. Alternately, an open loop system could be used without
the temperature sensor. Prior experimentation could dictate the
appropriate helium pressure for the desired process parameters, and
thus the temperature sensor could be eliminated in an alternate
embodiment. FIG. 9 contains both functions performed in a
processor, and physical effects.
[0091] A temperature set point is provided as a user-programmed
input to a controller from a control program in a memory 245. The
temperature set point value is multiplied by a constant 198 by the
controller, which adds the result to a feedback signal 213 as
indicated by an add function 202. The result of the add function is
used by the controller to control the helium pressure by
controlling flow restrictors or valves in the helium supply. This
varies the extent of the heat transfer of the helium gas. In a
preferred embodiment, the helium pressure is controlled according
to a mathematical model; however, empirical results could also be
used as the basis of the pressure control. The mathematical model
is described below. The helium pressure controls the heat transfer
to the ESC as indicated by block 202 (alternately, any type of
substrate support may be used). The ESC is either cooled by heat
exchanger 233, or heated by heater 243, with the amount of heat
transfer to the wafer controlled by the helium pressure. This heat
transfer can be offset by the heat generated by energy transferred
from the plasma (as illustrated by block 204), which combines (as
illustrated by block 206) with the heat transfer to the ESC. The
total heat transfer, applied to the wafer thermal mass (as
illustrated by block 208), produces the temperature 210 of the
wafer. Note that alternate substrates may be used rather than a
semiconductor wafer. The final temperature 210 of the wafer also
impacts the amount of heat transfer to the electrostatic chuck, as
indicated by feedback line 211. The heat transfer function between
the ESC and the wafer indicated in block 202 is a function of the
temperature of the wafer, as well as the temperature of the ESC. As
shown, the heat transfer to the ESC removes heat from the wafer
while the heat from the plasma adds heat to the wafer. However,
these can be reversed when the electrostatic chuck is used to heat
the wafer, and thus provides heat input while heat is removed due
to the plasma at a lower temperature, or simply by the chamber in
the absence of a plasma.
[0092] A block 212 illustrates the transformation of the
temperature into an electrical signal by the temperature sensor.
Block 214 illustrates the transfer function applied in the
processor before combining the temperature signal with the
temperature set point as a feedback. Such a transfer function could
in its simplest form be a multiplication by a constant, which could
be unity, or simply a transformation from an analog signal to a
digital signal.
[0093] The functions performed by the controller are done under the
control of a program in memory 245. That program will include
instructions for performing the various steps, such as instructions
for reading the temperature indication from the temperature sensor,
an instruction for comparing that temperature to the desired input
set temperature, and an instruction for controlling the pressure
valve (or flow restrictor) to vary the pressure of the gas in a
particular pressure zone. Other instructions are provided to shut
off the gas in the event of a fault, etc.
[0094] The helium pressure can be controlled by increasing or
decreasing the pressure where a simple one pressure electrostatic
chuck is used. Alternately, where two pressure zones are used as in
the preferred embodiment of the invention, the outer and inner
helium pressures can be controlled separately. The temperature of
each region can be inferred from a single temperature sensor which
may be placed, for instance, near the intersection of the two
zones. Alternately, two different temperature sensors could be
used. In other alternate embodiments, the temperature sensor could
be attached to the top surface of the electrostatic chuck, or
alternately be put in direct contact with the wafer itself. The
temperature sensor may be used to infer the pressure, such as where
there is leakage between zones causing a pressure variance. A
pressure regulator may detect only the pressure at its output,
which would typically be some distance from the wafer, which could
thus have a different pressure under it. A temperature sensor could
be used to infer the actual pressure under the wafer. Depending on
the wafer surface roughness, the leakage could vary, and the
pressure provided may need to be varied.
[0095] The control system typically will have certain constraints
on it. For instance, the helium pressure is limited so that the
wafer is not lifted off the electrostatic chuck, or so much of a
pressure differential is provided to cause a thermal gradient that
damages the wafer due to thermal stress. In the event that such
constraints are exceeded, or some other defined fault occurs, the
gas flow is stopped. Process Kit The process kit is comprised of a
collar and a cover. Additionally, a skirt may also be used. The
ceramic collar is wafer size and type specific and is disposed
between the electrostatic chuck and the quartz cover. The primary
purpose of the collar is to protect the electrostatic chuck flange
from the effects of the plasma. The cover extends from the collar
to the outer periphery of the cathode assembly and its primary
purpose is to protect the cathode assembly from the effects of the
plasma. A skirt may be disposed on the lower chamber to protect the
spacer and o-ring which seal the upper and lower chamber from the
effects of the plasma.
[0096] In one aspect, the present invention provides an improved
process kit or shield for an electrostatic chuck in a semiconductor
processing chamber that inhibits or resists the deposition of
gaseous products thereon. In addition, the shield provides faster
removal of oxide deposition which results in enhancing the
throughput of the wafer manufacturing process.
[0097] In one embodiment, the collar or cover may include a
conducting material disposed on one or more surfaces or therein to
enhance cleaning of its surface. Generally, the inductive coils
disposed about the dielectric dome 32 are used to heat the
conducting material in or on the collar or cover which then results
in heating the collar or cover surfaces. It has been shown that in
situ cleaning processes performed using fluorinated chemistry or
other reactive gases is enhanced at elevated temperatures. Using
the inductive coil and a conductor disposed in or on the process
kit components elevates the temperature of the surfaces of these
components to increase cleaning rates.
[0098] As one example, a metal can be deposited on one surface of a
process kit component, such as a collar or cover, to provide a
conductor in which a current can be induced. The operation of the
heating process is similar to that which is seen in a transformer
with the coil being the external winding and the metal layer being
the internal winding.
[0099] FIG. 11 is a cross-sectional view of a electrostatic chuck
and a processing kit. A substrate support assembly 230 comprises a
support body 232 preferably fabricated as an integral block from an
electrically conducting material having a high thermal mass and
good thermal conductivity to facilitate absorption of heat from a
wafer cooled over its upper surface. Aluminum or anodized aluminum
is the preferred material for support body 232 because it has a
high thermal conductivity of approximately 2.37 watts/cm-.degree.
C. and it is generally process compatible with the semiconductor
wafer. Support body 232 may comprise other metals, such as
stainless steel or nickel, and support body 232 may comprise an
additional non-conducting material or the entire support body 232
may comprise a non-conducting or semi-conducting material. In an
alternative embodiment, support body 232 comprises a monolithic
plate of ceramic. In this configuration, the ceramic plate
incorporates a conducting element imbedded therein. The conducting
element may comprise a metallic element, green printed
metalization, a mesh screen or the like. Support body 232 defines
an annular mounting flange 234 extending outwardly from the outer
surface of support body 232. A voltage, preferably about 700 Volts,
is applied to the substrate support assembly 230 by a DC voltage
source (not shown) to generate the electrostatic attraction force
which holds a wafer W in close proximity to the upper surface of
support body 232.
[0100] Referring to FIG. 11, substrate support assembly 230
comprises a smooth layer of dielectric material 236 covering an
upper surface 238 of support body 232 for supporting the lower
surface of wafer W. Dielectric layer 236 covers the entire upper
surface 238 of support body 232 except for the region overlying
four lift pin holes 240. Dielectric layer 236 preferably comprises
a thin ceramic dielectric layer (preferably on the order of about
0.10 to 0.30 inches) of alumina, aluminum oxide or an
alumina/titania composite that is plasma sprayed over upper surface
238 of support body 232.
[0101] In one embodiment, shield 242 comprises a thin annulus of
conducting material 244 deposited underneath the collar 246. The
collar 246 is supported by an annular flange 234 and held by a
cover 248. Cover 248 is preferably a ceramic outer jacket for
covering and protecting the lateral surfaces of support body 232 to
decrease the time required to clean the chamber. The collar 246 is
preferably separated from annular flange 234 by a small
interstitial gap 250. Gap 250 is created by the natural surface
roughness of the upper surface of the annular flange 234 and the
lower surface of the conducting material 244 or the collar 246. Gap
250 is preferably about 0.5 to about 5 mills thick. In the
relatively low-pressure environment of the processing chamber
(typically on the order of about 5 milliTorr), gap 250 establishes
a thermal barrier that inhibits thermal conduction between the
collar 246 and the support body 232.
[0102] As shown in FIGS. 11, the collar 246 preferably has an inner
diameter larger than the diameter of support body 232 to define a
second gap 252 therebetween. Gap 252 provides room for expansion of
support body 232 when it is heated in the process chamber and also
ensures that the shield 242 can be installed and removed without
damaging the substrate support 230 or the collar 246. Collar 246 is
comprised of an insulating or dielectric material, preferably
ceramic or ceramic, that serves to prevent or inhibit the plasma in
the processing chamber above the wafer from contacting, and thereby
eroding, part of the electrostatic chuck. However, collar 246 is
not necessarily limited to an insulating material and, in fact,
applicant has found that a collar 246 made of a semiconducting
material may effectively protect the electrostatic chuck from the
plasma within the processing chamber.
[0103] The collar 246 is a thin ring 254 having a curved upper
surface 256 that is exposed to deposition from gases in the process
chamber. The ratio of the surface area of exposed upper surface 256
to the thermal mass of collar 246 is preferably high, usually about
0.1 to 5 cm.sup.2K/J and preferably about 1 to 1.6 cm.sup.2K/J. The
high ratio of exposed surface area to thermal mass of collar 246
causes it to be heated to a substantially high temperature from the
RF energy in the chamber. Since the oxide deposition rate is
generally inversely proportional to the temperature of a surface in
the process chamber, the heat received by the collar 246 inhibits
oxide deposition on the exposed upper surface. Thus, the geometry
of collar 246 (i.e., the high ratio of exposed surface to thermal
mass) minimizes the rate of deposition on upper surface 256.
[0104] During a deposition process, oxide from process gases is
deposited onto wafer W and onto a substantial portion of the
exposed surfaces of the chamber, such as the inner walls of the
enclosure and upper surface 256 of collar 246. Since the thermal
mass of collar 246 is relatively small compared to the surface area
of surface 256, collar 246 will receive a relatively large amount
of heat from the RF power supply. Collar 246 is also heated by the
thin annulus of conducting material 244 which generates heat
through the RF power. This further decreases the rate of oxide
deposition onto upper surface 72.
[0105] As shown in FIG. 11, collar 246 is preferably sized so that
upper surface of collar 246 is positioned below the upper surface
of the wafer when the wafer rests on or is adjacent to the upper
surface of dielectric layer 236. Positioning collar 246 below the
upper surface of the wafer further lowers the oxide deposition rate
on upper surface 256 and provides an improved line of sight to the
wafer edges. Therefore, the edges of the wafer may receive a higher
deposition rate than if the shield 242 were to extend above the
wafer. In some processes, this may be advantageous to compensate
for the higher deposition rate in the center of the wafer that
typically occurs during processing.
[0106] Referring to FIG. 12, a cross-sectional view of the process
kit in a processing chamber, the source RF coil 260 in an inductive
HDP source can be used to heat the ceramic process The thin annulus
of conducting material 244, which can be disposed on one or more
surfaces or within the ceramic process kit, acts as the secondary
coil of a transformer and conducts the current induced by RF
currents in the source RF coil 260 which generates heat for the
process kit. The resistance of the secondary coil is of primary
importance because either too low or too high of a resistance
results in inefficient power transfer and thus inefficient heating
of the process kit.
[0107] For the circular geometry indicated in FIG. 12, the
resistance R is approximately 2.pi.rp/w.multidot.d, where r is a
measure of the radial dimension of the outer radius of the thin
annulus of conducting material, w is the width of the conducting
material, d is the thickness of the conducting material, and .rho.
is the resistivity of the conducting material. The resistance R is
preferably controlled by varying w.multidot.d, the cross-sectional
area of the conducting material 244. To achieve optimal contact
with collar 246, it is preferred that w be as large as possible but
smaller than the width of the collar 246. One preferred method of
obtaining the optimal value of d is empirically monitoring the
heating rates of various samples with different thickness d of
conducting material. In one preferred embodiment, a process kit
having graphite as the conducting material with the annulus having
an inner radius of 10 cm and outer radius of 12 cm and thickness of
0.13 mm was heated inductively to a temperature of about
288.degree. C.
[0108] In another aspect of the invention, the clean rate or
deposition removal rate of the process kit is typically a function
of its temperature (i.e., the hotter the shield becomes during
processing, the faster it can be cleaned). During cleaning, the
conducting material 244 acts as the secondary coil of a transformer
which conducts the current induced by RF currents in the source RF
coil 260 which generates heat for the process kit. Thus, with
increased temperature, the clean rate of collar 246 will be
increased, which reduces the downtime of apparatus 2, thereby
enhancing the throughput of the process.
[0109] Gas Distribution Assembly
[0110] The gas distribution assembly 300 will be described below
with reference to FIGS. 1320 16. FIG. 13 is a cross sectional view
through a chamber of the present invention showing the gas
distribution assembly 300. Generally, the gas distribution system
comprises an annular gas ring 310 disposed between the lower
portion of the dome and the upper surface of the chamber body and a
centrally located center gas feed 312 positioned through the top of
the dome. Gases are introduced into the chamber through both
circumferentially mounted gas nozzles 302, 304 located near the
bottom of the dome 32, and a centrally located gas nozzle 306
located in the top plate of the dome. One advantage of this
configuration is that a plurality of different gases can be
introduced into the chamber at select locations within the chamber
via the nozzles 302, 304, 306. In addition, another gas, such as
oxygen or a combination of gases, can be introduced along side
nozzle 306 through a gas passage 308 disposed around nozzle 306 and
mixed with the other gases introduced into the chamber.
[0111] The gas distribution ring and the centrally located gas
manifold will be described separately below.
[0112] Generally, the gas distribution ring 310 comprises an
annular ring made of aluminum or other suitable material 314 having
a plurality of ports formed therein for receiving nozzles therein
and which are in communication with one or more gas channels 316,
318. Preferably, there are at least two separate channels formed in
the gas ring to supply at least two separate gases into the
chamber. Each of the ports for receiving the nozzles is connected
to at least one of the gas distribution channels 316, 318 formed in
the ring. In one embodiment of the invention, alternating ports are
connected to one of the channels, while the other ports are
connected to the other channel. This arrangement allows for the
introduction of separate gases, such as SiH.sub.4 and O.sub.2,
separately into the chamber, as one example.
[0113] FIG. 14 is a cross sectional view showing a first gas
channel 316 connected to one port 314 having a nozzle 302 disposed
therein. As shown, the gas channel 316 is formed in the upper
surface of the chamber body wall and is preferably annular around
the entire circumference the chamber wall. The annular gas ring has
a first set of channels 320 longitudinally disposed within the ring
which are connected to each of the ports 314 provided for
distribution of the gas in that channel. When the gas ring is
positioned over the gas channel, the passages are in communication
with the channel. The gas distribution ring is sealed in the top
surface of the chamber wall via two separately placed o-rings 322,
324 disposed outwardly from the channel to prevent gas leaks to the
interior of the chamber. A Teflon seal 326, or the like, is
disposed inwardly of the channel in a recess 328 to prevent gas
leakage into the chamber.
[0114] The nozzles 302, 304 disposed in the ports 314 are
preferably threaded and mate with threads in the port to provide a
seal therebetween and to provide quick and easy replacement. A
restricting orifice 330 is located in the end of each nozzle and
can be selected to provide the desired distribution of the gas
within the chamber.
[0115] FIG. 15 is a cross sectional view showing the second gas
channel 318. The second gas channel 318 is formed in the upper
portion of the annular gas distribution ring and is similarly
disposed in an annular configuration around the circumference of
the gas distribution ring. A horizontally disposed passage 332
connects the second gas channel to one or more ports formed in the
gas ring and in which additional gas nozzles are disposed. The
upper containing surface of the second gas channel is formed by the
portion of the lid which supports the dome 32 and is sealed at the
top by the base plate 33. The gas ring 310 is bolted to the base
plate 33 which is hingedly mounted to the chamber body.
[0116] One advantage of the present invention is that the gas
distribution ring can be easily removed and replaced with a ring
having ports formed for receiving and positioning the tips of the
nozzles at various angles so that the distribution pattern of gases
can be adjusted. In other words, in certain applications it may be
beneficial to angle some of the gas nozzles upwardly in the
chamber, or conversely to angle some of them downwardly in the
chamber. The ports formed in the gas distribution ring can be
milled so that a desired angle can be selected to provide the
desired process results. In addition, having at least two gas
channels which can deliver at least two gases separately into the
chamber allows greater control of the reaction which occurs between
the various gases. Still further, reaction of the gases within the
gas distribution assembly can be prevented by delivering the gases
separately into the chamber.
[0117] FIG. 16 is a cross sectional view showing the center gas
feed 312 disposed through the dome 32. The top gas feed 312 is
preferably a tapered structure having a base 334 which is disposed
on the top of the dome and a tapered body 336 disposed in a recess
formed in the dome. Two separate o-rings 336, 338, one the lower
surface of the taper body 336 and one on the side surface of the
taper body 338 towards the lower end, provided sealable contact
between the gas feed 312 and the dome of the chamber. A port 340 is
formed in the lower portion of the body of the top gas feed to
receive a nozzle 306 for delivering gases into the chamber. At
least one gas passage 342 is disposed through the gas feed 310
connected to the port to deliver gases to the back of the nozzle.
In addition, the nozzle 306 is tapered and the port 340 define a
second gas 308 passage which delivers a gas along side of the
nozzle 306 and into the chamber. A second gas channel 304 is
disposed through the gas feed 312 to deliver gas into the passage
308. A gas, such as oxygen, can be delivered along side a gas such
as SiH.sub.4.
[0118] FIG. 17 is an exploded view showing the base plate 33 of the
lid assembly and the gas distribution ring 310. A channel 350 is
formed in the lower portion of the base plate 33 to receive the gas
distribution ring 310. The gas ring 310 is bolted, or otherwise
mounted, to the base plate 33. The base plate is hingedly mounted
to the chamber body.
[0119] A first gas source 352 and a first gas controller 354
control entry of a first gas via line 356 into a first gas channel
316 formed in the chamber wall. Similarly, a second gas source 358
and a second gas controller 360 supply a second desired gas via
line 362 into the second gas channel 318 formed in the gas
distribution ring.
[0120] A third gas source 364 and a third gas controller 366 supply
a third gas via line 368 to a gas channel disposed on the top of
the chamber. A fourth gas source 370 and a fourth gas controller
372 supply a fourth gas via line 374 to gas passage 308. The gas
introduced through the third gas nozzle and fourth gas nozzle 64
and O.sub.2 are mixed in the-upper portion of chamber as both gases
enter the chamber.
[0121] Remote Plasma Cleaning System
[0122] The remote plasma source generally includes a remote chamber
having a gas inlet and a gas outlet, a power source coupled to the
chamber by a waveguide, and an applicator tube disposed through the
chamber between the gas inlet and gas outlet. FIG. 18 shows a
schematic view of a remote plasma source 500 connected to a
chamber. A chamber 502 is a cylindrical chamber, preferably made of
aluminum, having a gas inlet 504 and a gas outlet 506 disposed on
opposite ends thereof. The chamber is preferably cooled using
either a fan disposed through a wall of the chamber or by using a
fluid cooling system such as a series of coils having a heat
transfer fluid such as water flown therethrough. An applicator tube
508, such as a sapphire tube, or other energy transmissive tube, is
disposed between the gas inlet and gas outlet within the chamber
502. A water cooled delivery conduit 510 connects the gas outlet to
a gas channel 28 formed in the lower portion of the processing
chamber 10. A power source is coupled to the chamber by a waveguide
512. One remote plasma source which can be used to advantage in the
present invention is described in U.S. patent application Ser. No.
08/278,605, filed on Jul. 21, 1994, which is incorporated herein by
reference.
[0123] Preferably, power in the range of from about 2000 W to about
5000 W is delivered into the chamber 502. The optimum power needed
to dissociate the gas should be used. Any additional power is
wasted and is typically used in generating additional heat. Lower
power than optimum results in an incomplete dissociation of the
cleaning gas and a decrease in the clean rate and efficiency. In
one embodiment, a single power source is used to drive both the
source antenna and the remote plasma chamber.
[0124] In the chamber, it is believed that the cleaning reactions
which proceed most rapidly are of the type:
4F*.sub.(Gas)+SiO.sub.3.fwdarw.SiF.sub.4(Gas)+O.sub.2(Gas)
and
2F*.sub.(Gas)+SiO.sub.2
(Gas).fwdarw.SiF.sub.2(Gas)+O.sub.2(Gas)
[0125] producing gaseous products which are removed from chamber 13
by vacuum pumping the gas phase. The reactant gases which are most
effective at producing high concentrations of long lived excited
neutral Fluorine species F* are NF.sub.3, F.sub.2, SF.sub.6,
ClF.sub.3, CF.sub.4, and C.sub.2F.sub.6. However, other cleaning
gases which are excitable by Microwaves and react with deposition
material within the chamber may be used. For the remote microwave
cleaning system of FIG. 9 in the present invention, it is preferred
to use NF.sub.3 and F.sub.2 diluted to concentrations of from about
10% to about 50% in inert argon gas. The desired cleaning reactions
produced by the use of the remote plasma source proceed without any
ion bombardment of the chamber or substrate support structures,
therefor, the need for cover wafers on the ESC 104, or periodic
replacement of critical chamber assemblies is avoided. Thus, a much
more efficient use and throughput of the system is provided.
[0126] FIG. 18 also shows the cleaning gas delivery channels formed
in the chamber walls. Gas is delivered from the remote source 500
to a first gas channel 28 disposed horizontally in the back wall
520 of the chamber. The first gas channel 28 extends the length of
the back wall to deliver gases to opposed sides of the chamber. A
central gas 522 connection is formed in the lower portion of the
chamber and connects to the first gas channel 28 to the delivery
conduit 510.
[0127] A second gas channel 524 is formed in each of the side walls
of the chamber and terminate in a slit opening 526 within the
chamber. A corner cover is made with a channel formed therein to
connect the ends of the first gas channel 28 with each of the side
gas channels 524 formed in the sidewalls. The corner cover is
preferably welded in position on the chamber body and facilitates
gas delivery through the chamber body to the slit openings 526 in
the chamber.
[0128] A first gas diffusing member 528 is preferably disposed in
the slit openings 526 of the second gas channels 524 to guide the
cleaning gases into the chamber. FIG. 19 is a top view of the gas
diffusing member 528 showing the curved side faces 530, 532 which
deliver the cleaning gases to opposite sides of the chamber. The
curved surfaces 530, 532 are disposed across the second gas
channels 524 to guide the gases outwardly into the chamber.
[0129] FIG. 20 is a side view of the gas diffusing member 528 . The
back portion 534 of the gas diffuser is tapered to allow gases to
pass beyond the gas diffuser disposed in the channel 524 so that
gas is guided into both sides of the chamber. A recess 536 is
formed in one end of the gas diffuser to provide wedged engagement
of the diffuser in position within the gas channel. A wedge 538 is
provided to mate with the recess and a screw forces the wedge into
position within the recess and connects the wedge to the diffuser
and connects the diffuser to the chamber body.
[0130] In an alternative embodiment, a gas baffler can be disposed
in the chamber adjacent to each slit opening 526 in the chamber to
direct the cleaning gases upwardly and over the process kit and ESC
104. FIG. 21 shows a perspective view of a baffler 540 which is
mounted to the gas diffuser 528 by a flange 542. The body 544 of
the baffler provides a curved face 546 which is angled slightly
upwardly when positioned in the chamber to urge the cleaning gases
upwardly in the chamber and over the ESC 104 and the process
kit.
[0131] It has been found that the clean process is most efficient
when the cleaning gases enter the chamber from above the ESC and
process kit. In addition, it is preferred that the gases flow
upwardly in the chamber and away from the ESC and process kit to
prevent the cleaning gases from pushing particles or residue
loosened during the cleaning process onto the ESC. If particles
remain on the ESC, the likelihood that helium leaks will occur
during chucking increases. The baffle diverts the gas flow upwards
to enhance cleaning and prevents deposition of particles on the
ESC.
[0132] While the foregoing is directed to the preferred embodiment
of the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof, and the scope thereof is determined by the claims which
follow.
* * * * *