U.S. patent application number 10/208764 was filed with the patent office on 2003-08-28 for method of forming metal lines having improved uniformity on a substrate.
Invention is credited to Marxsen, Gerd, Nopper, Markus, Preusse, Axel.
Application Number | 20030162385 10/208764 |
Document ID | / |
Family ID | 27740416 |
Filed Date | 2003-08-28 |
United States Patent
Application |
20030162385 |
Kind Code |
A1 |
Preusse, Axel ; et
al. |
August 28, 2003 |
METHOD OF FORMING METAL LINES HAVING IMPROVED UNIFORMITY ON A
SUBSTRATE
Abstract
In a method of forming damascene metallization lines on a
substrate by electroplating and chemical mechanical polishing, the
metal layer thickness profile is shaped in correspondence to the
removal rate during the chemical mechanical polishing. Thus, any
non-uniformity of the chemical mechanical polishing process may be
compensated for by appropriately depositing the metal layer so that
erosion and dishing of the finally obtained metal lines are within
tightly selected manufacturing tolerances.
Inventors: |
Preusse, Axel; (Radebeul,
DE) ; Nopper, Markus; (Dresden, DE) ; Marxsen,
Gerd; (Radebeul, DE) |
Correspondence
Address: |
WILLIAMS, MORGAN & AMERSON, P.C.
10333 RICHMOND, SUITE 1100
HOUSTON
TX
77042
US
|
Family ID: |
27740416 |
Appl. No.: |
10/208764 |
Filed: |
July 30, 2002 |
Current U.S.
Class: |
438/633 ;
257/E21.175; 257/E21.304; 257/E21.583; 257/E21.585 |
Current CPC
Class: |
H01L 21/7684 20130101;
H01L 21/3212 20130101; B24B 37/042 20130101; H01L 21/76877
20130101; H01L 21/2885 20130101; B24B 37/013 20130101 |
Class at
Publication: |
438/633 |
International
Class: |
H01L 021/28 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2002 |
DE |
102 08 166.2 |
Claims
What is claimed:
1. A method of forming metal lines, comprising: providing a
substrate having formed therein a recessed portion in a first
region and a second region; obtaining an estimated expected removal
rate of the metal in the first region and the second region of the
substrate during a chemical mechanical polishing to be subsequently
performed; depositing the metal on the substrate by electroplating,
wherein a deposition thickness of the metal in the first and second
regions is adjusted in correspondence to the estimated expected
removal rate in the first and second regions; and removing excess
metal by chemical mechanical polishing to produce the metal
line.
2. The method of claim 1, wherein obtaining an estimated expected
removal rate includes performing an endpoint detection at the first
and second regions of one or more previously processed
substrates.
3. The method of claim 1, wherein obtaining an estimated expected
removal rate includes determining at least one of dishing and
erosion of the metal line in the first and second regions of a
previously processed substrate.
4. The method of claim 1, wherein obtaining an estimated expected
removal rate includes determining removal rate values from a model
of the chemical mechanical polishing process.
5. The method of claim 4, wherein said model is represented by
removal rate values for the first and second regions obtained by at
least one of calculation on the basis of a parameter of the
chemical mechanical polishing process and experiment.
6. The method of claim 1, wherein depositing the metal includes
controlling at least one of the electrical field and electrolyte
flow in the first and second regions during electroplating.
7. The method of claim 6, wherein an electrical field is controlled
to be different in the first and second regions by providing a
plurality of correspondingly located anode elements in the
electroplating bath.
8. The method of claim 6, wherein an electrical field is controlled
to be different in the first and second regions by providing a
conductive shield between an anode and the substrate during
electroplating.
9. The method of claim 6, wherein an electrical field is controlled
to be different in the first and second regions by providing a
non-conductive shield between an anode and the substrate during
electroplating.
10. The method of claim 6, wherein a diffuser element having a
diffusing pattern formed therein is provided between an anode and
the substrate during electroplating.
11. The method of claim 6, wherein electrolyte flow to the second
region is restricted during electroplating.
12. The method of claim 1, wherein the first region is a central
region and the second region is a peripheral region.
13. The method of claim 1, wherein the metal is copper.
14. The method of claim 1, wherein the substrate comprises a third
region, the third region exhibiting a removal rate during the
chemical mechanical polishing that differs from that of the first
and second regions and wherein a deposition thickness in the third
region corresponds to the removal rate of the third region.
15. The method of claim 1, further comprising depositing a seed
layer prior to depositing the metal layer, wherein an average
thickness of the seed layer in the first region differs from that
of the second region so that during electroplating a deposition
rate in the first region differs from that of the second
region.
16. The method of claim 15, wherein the seed layer is deposited by
one of chemical vapor deposition and physical vapor deposition,
whereby at least one of a shape of a plasma, a shape of a target
material, a fluid flow to the substrate and a temperature
distribution on the substrate is controlled to obtain a different
seed layer thickness in the first and second regions.
17. A method of forming metal lines comprising: providing a
substrate with a central region and a peripheral region, the
central region and the peripheral region each having a recessed
portion defining a height dimension; depositing a metal layer over
the substrate, wherein an averaged layer thickness of the
peripheral region is different from an averaged layer thickness of
the central region; and removing excess metal from the substrate by
chemical mechanical polishing, wherein the difference of the
averaged layer thickness of the peripheral and the central regions
is adjusted during the deposition of the metal such that the height
of the metal in the recessed portions is within a predefined
tolerance after the removal of the excess metal.
18. The method of claim 17 wherein adjusting the difference of the
averaged layer thickness is carried out by obtaining, prior to
depositing the metal layer, the height of the metal in the recessed
portion in the central region and the peripheral region of a
previously processed substrate.
19. The method of claim 17, wherein adjusting the difference of the
averaged layer thickness is carried out on the basis of endpoint
detection results of one or more previously processed
substrates.
20. The method of claim 17, wherein adjusting the difference of the
averaged layer thickness is carried out on the basis of measurement
results of an immediately previously processed substrate to
continuously update the controlling of the layer thickness in the
first and second regions.
21. The method of claim 17, wherein the metal layer is deposited by
electroplating and adjusting the difference of the averaged layer
thickness includes controlling at least one of an electrical field
and an electrolyte flow during the electroplating.
22. The method of claim 21, wherein the electrical field is
controlled so as to be different in the central and peripheral
regions by providing a plurality of correspondingly located anode
elements in the electroplating bath.
23. The method of claim 21, wherein the electrical field is
controlled so as to be different in the central and peripheral
regions by providing a conductive shield between an anode and the
substrate during electroplating.
24. The method of claim 21, wherein the electrical field is
controlled so as to be different in the central and peripheral
regions by providing a non-conductive shield between the anode and
the substrate during electroplating.
25. The method of claim 21, wherein a diffuser element having a
diffusing pattern formed therein is provided between an anode and
the substrate during electroplating.
26. The method of claim 21, wherein the electrolyte flow to the
peripheral region is restricted during electroplating.
27. The method of claim 17, further comprising depositing a seed
layer prior to depositing the metal layer, wherein an averaged
thickness of the seed layer in the central region differs from that
of the peripheral region so that during electroplating a deposition
rate of the central region differs from that of the peripheral
region.
28. The method of claim 27, wherein the seed layer is deposited by
one of chemical vapor deposition and physical vapor deposition,
whereby at least one of shape of plasma, shape of target material,
fluid flow to the substrate and temperature distribution on the
substrate is controlled to obtain a different seed layer thickness
in the central and peripheral regions.
29. The method of claim 17, wherein a maximum layer thickness in
the central region exceeds a layer thickness at the perimeter of
the substrate by approximately 50-120 nm.
30. The method of claim 17, wherein the substrate comprises a third
region, the third region exhibiting an averaged removal rate during
a chemical mechanical polishing that differs from that of the
central and peripheral regions, and a deposition thickness in the
third region that corresponds to the removal rate of the third
region.
31. A method of forming metal lines in a first and a second region
of a substrate, the method comprising: depositing a seed layer on
the substrate; depositing a metal layer by electroplating while
controlling at least one of an electrical field and electrolyte
flow to the substrate so as to be different in the first and second
regions to obtain a greater metal thickness in one of the first and
second regions that is expected to have a higher removal rate in a
subsequent chemical mechanical polishing step; and removing excess
metal in the first and second regions by chemical mechanical
polishing of the substrate.
32. The method of claim 31, further comprising obtaining at least
one of an estimated removal rate and a parameter value indicative
thereof for the first and second regions.
33. The method of claim 32, wherein obtaining at least one of an
expected removal rate and a parameter value indicative thereof
includes performing an endpoint detection at the first and second
regions of one or more previously processed substrates.
34. The method of claim 32, wherein obtaining at least one of an
expected removal rate and a parameter value indicative thereof
includes determining at least one of dishing and erosion at the
first and second regions of one or more previously processed
substrates.
35. The method of claim 32, wherein obtaining at least one of an
expected removal rate and a parameter value indicative thereof
includes determining removal rate values and parameter values from
a model of the chemical mechanical polishing process.
36. The method of claim 35, wherein said model is represented by
removal rate values obtained by at least one of calculation,
evaluation of process parameters of the chemical mechanical
polishing process and experiment.
37. The method of claim 31, wherein controlling at least one of
electrical fields and electrolyte flow includes controlling the
electrical field so as to be different in the first and second
regions by providing a plurality of correspondingly located anode
elements in the electroplating bath.
38. The method of claim 31, wherein the electrical field is
controlled so as to be different in the first and second regions by
providing a conductive shield between an anode and the substrate
during electroplating.
39. The method of claim 31, wherein the electrical field is
controlled so as to be different in the first and second regions by
providing a non-conductive shield between an anode and the
substrate during electroplating.
40. The method of claim 31, wherein controlling at least one of
electrical field and electrolyte flow is carried out by providing a
diffuser element between an anode and a substrate during
electroplating, wherein the diffuser element comprises a suitable
diffusing pattern.
41. The method of claim 31, wherein the electrolyte flow to the
second region is restricted during electroplating.
42. A method of forming a metal line in a first and a second region
of the substrate, comprising: depositing a seed layer on the
substrate while controlling an averaged seed layer thickness in the
first region to be different from an averaged seed layer thickness
in the second region; depositing a metal by electroplating to fill
the metal lines, wherein a deposition rate during electroplating is
different in the first and second regions in correspondence to the
different averaged seed layer thicknesses; and removing excess
metal from the substrate.
43. The method of claim 42, wherein depositing the seed layer is
performed by sputter deposition.
44. The method of claim 43, wherein a collimator is provided
between a target material and the substrate, the collimator
supplying target atoms to the substrate differently in the first
and second regions.
45. The method of claim 43, wherein at least one of a shape of a
plasma, a radio frequency power, a feed gas supply and a substrate
temperature is controlled to obtain a different averaged layer
thickness in the first and second regions.
46. The method of claim 42, wherein the seed layer is deposited by
chemical vapor deposition.
47. The method of claim 46, wherein a mask element is provided in
the vicinity of the substrate to control the deposition rate of the
seed layer in the first and second regions.
48. The method of claim 46, wherein at least one of feed gas
supply, pressure and temperature of the substrate is controlled to
obtain a different deposition rate in the first and second
regions.
49. The method of claim 42, further comprising obtaining one of a
removal rate and a parameter value indicative thereof for the first
and second regions in a subsequent chemical mechanical polishing
step prior to removing the excess metal.
50. The method of claim 49, wherein obtaining at least one of a
removal rate and a parameter value indicative thereof includes
performing an endpoint detection in the first and second regions of
one or more previously processed substrates.
51. The method of claim 49, wherein obtaining at least one of a
removal rate and a parameter value indicative thereof includes
determining one of dishing and erosion in the first and second
regions of one or more previously processed substrates.
52. The method of claim 49, wherein obtaining at least one of a
removal rate and a parameter value indicative thereof includes
determining corresponding values from a model of the chemical
mechanical polishing process.
53. The method of claim 42, wherein the substrate comprises at
least one third region, the third region exhibiting an average
removal rate during chemical mechanical polishing that differs from
that of the first and second regions, and an averaged seed layer
thickness in the third region that corresponds to the removal rate
of the third region.
54. A method of forming metal lines on a plurality of substrates,
the method comprising: obtaining parameter values indicative of a
quality of a chemical mechanical polishing process to be performed
for each of the substrates; relating the parameter values for each
substrate to a corresponding metal layer thickness profile;
depositing a metal layer on each substrate while controlling
deposition parameters to substantially generate said metal
thickness profile for each substrate; and removing excess metal
from each of the substrates by chemical mechanical polishing.
55. The method of claim 54, wherein said parameter values are
obtained from a model of the chemical mechanical polishing process
of an individual substrate having a specified metal layer thickness
profile.
56. The method of claim 55, wherein said specified metal layer
thickness profile is varied until said model predicts the quality
of the chemical mechanical polishing process to be within a
predefined tolerance.
57. The method of claim 55, wherein said parameter values are
obtained from a model of the chemical mechanical polishing process
and a model of the deposition process.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to the field of
fabrication of integrated circuits, and, more particularly, to
producing interconnect lines required in the various metallization
layers of integrated circuits, such as CPUs, memory chips, and the
like.
[0003] 2. Description of the Related Art
[0004] In the fabrication of integrated circuits, such as CPUs,
memory chips, application specific circuits and the like, it is
generally necessary to provide one or more metal layers, so-called
metallization layers, on the circuit substrate that serve to
electrically connect the individual devices, such as transistor
elements, capacitors, and the like, to one another. Depending on
the complexity of the involved circuitry, the type of material used
for the metallization and the dimensions of the metallization
lines, which in turn are partly determined by the type of material
and the available space on the substrate, a plurality of
metallization layers may be necessary to provide the required
functionality. The reproducible manufacturing of the individual
metallization layers is of great importance for the performance and
reliability of the integrated circuit, whereby the characteristics
of each metallization line in every metallization layer must
predictably lie within specified tolerances, as failure of a single
line alone may jeopardize the complete circuit.
[0005] Since semiconductor manufacturers not only have to cope with
requirements in terms of performance and reliability of the
integrated circuits, but also in view of minimal production costs,
the substrates on which the integrated circuits are fabricated are
steadily increasing in diameter, since the majority of the process
steps during manufacturing of the integrated circuit are carried
out on a substrate basis rather than on a die basis so that a large
number of chips may be processed in a single process step.
Increasing substrate diameters, however, requires precise
controlling of the process parameters to produce device features
across the entire substrate that have characteristics as uniform as
possible regardless of their location on the substrate.
[0006] Traditionally, aluminum has been used for metallization
layers; however, semiconductor manufacturers have recently begun to
employ copper as the metallization layer due to the superior
characteristics of copper with respect to conductivity and
electromigration, which are extremely important aspects for the
production of integrated circuits with reduced feature sizes. One
commonly used process for producing metallization layers is the
so-called damascene process, where holes (also referred to as
vias), trenches and/or other recessed portions are formed in an
insulating layer, for example, a silicon dioxide layer, and are
subsequently filled with the metal, such as copper. A preferred
technique for supplying the copper to the vias and trenches is
electroplating, since electroplating allows moderate deposition
rates with a reasonable uniformity across large substrate areas
compared to other deposition methods, thereby providing high
cost-effectiveness. Electroplating requires, prior to deposition of
the bulk material, the provision of a metallic seed layer, which is
used to conduct electrical current during the bulk deposition. In
some cases, the seed layer may also serve as a diffusion barrier
layer and/or an adhesion layer for the bulk material, for example,
copper, filled in the vias and trenches. In general, the seed layer
is a very thin layer of metal having a thickness of about 100 nm
and may be deposited by any known method, such as physical vapor
deposition (PVD) or chemical vapor deposition (CVD). After
deposition of the seed layer, the substrate is brought into contact
with a electrolyte bath containing ionic compounds including metal
ions of the required type and a voltage is established between an
anode within the electrolyte bath and the substrate which acts as a
cathode, whereby the seed layer serves to distribute the current
across the entire substrate area. The metal layer is plated to an
extent to form an overlying layer, thereby providing a metal layer
that fills the trenches and vias and extends slightly above these
device features. Typically, the thickness of the metal layer is on
the order of 1 .mu.m.
[0007] After deposition of the metal layer, excess metal has to be
removed to complete the patterning of metal lines. In the damascene
process, chemical mechanical polishing (CMP) has proven to be the
preferred technique for removing excess metal. During the chemical
mechanical polishing, the combined action of a chemical removal
agent and an abrasive is used to commonly react and grind and
polish the exposed metal surface, thereby planarizing the residual
substrate surface. Although CMP is very successfully employed in
fabricating metallization layers, establishing a CMP technique that
provides minimum non-uniformity across the entire substrate area
has been found to be a challenging task for process engineers,
especially for large-diameter substrates. In providing a uniform
planarized surface after removal of excess metal, it is not only
important during a CMP process to keep the removal of the metal and
the surrounding dielectric material, which are also referred to as
dishing and erosion, within specified tolerances regarding the
various feature patterns on a single chip, but to maintain these
specified tolerances in view of dishing and erosion also at
locations that are spaced more distantly, for example at the center
and the periphery of the substrate.
[0008] With reference to FIGS. 1a and 1b, a typical metallization
pattern is schematically depicted to demonstrate the effects of
dishing and erosion during CMP. In FIG. 1a, a metallization
structure 100 comprises an insulating layer 101 having formed
therein a single metal line 102 and a plurality of closely spaced
metallization lines 103. The insulating layer 101 may, for example,
be made of silicon dioxide and the metal lines 102 and 103 may
primarily comprise copper. The metallization structure 100 may be
positioned, for example, at a central location of the substrate.
While the metallization structure 100 is subjected to the CMP
process, insulating material is removed from the initial insulating
layer 101 as represented by the arrows E. This removal of material
compared to the initial material layer is referred to as erosion
and may depend on the type of feature pattern formed in the
insulating layer 101. For example, the erosion in the vicinity of
the single metal line 102 may be significantly smaller than in the
vicinity of the plurality of metal lines 103. Additionally, copper
within the metal lines 102 and 103 is removed more intensely than
material of the surrounding insulating layer 101. This excess
material removal process within the metal lines 102 and 103 is
referred to as "dishing" and is indicated by D in FIG. 1a.
[0009] FIG. 1b schematically depicts a metallization structure 150
comprising an insulating layer 151 and metal lines 152 and 153
formed in the insulating layer 151. In principle, the metallization
structure 150 corresponds to the structure 100, but is, however,
located at the periphery of the substrate. Since in the CMP process
under consideration the removal rate at the periphery of the
substrate is reduced compared to a central location, erosion and
dishing in the metallization structure 150 is reduced compared to
the structure 100. Accordingly, the metallization lines 152, 153
exhibit an increased cross-section and, therefore, an enhanced
conductivity compared to the metal lines 102, 103. In order to
secure reliability and performance of integrated circuits
fabricated all over the substrate area, design rules must take into
account the above-mentioned non-uniformities of the metal lines in
different substrate areas. This contributes to process complexity
and, thus, production costs.
[0010] In view of the above problems, there is a need for an
improved process sequence for forming metallization layers
exhibiting a higher degree of uniformity at different locations of
the substrate.
SUMMARY OF THE INVENTION
[0011] The present invention is generally directed to a method that
allows effective compensation for process variations during the
formation of metallization layers by controlling the deposition of
a metal layer in correspondence to process variations of the CMP
process. Thus, a differing removal rate at a plurality of different
areas on a substrate may be compensated for by controlling the
deposition rate at each of the plurality of areas so as to
correspondingly increase the layer thickness in an area having a
high removal rate or to correspondingly decrease the layer
thickness in an area having a reduced removal rate. In this way,
even complex polishing variations, i.e., variations having a
complex profile such as M-shaped or W-shaped profiles along the
substrate diameter, may be corrected.
[0012] According to one embodiment, a method of forming metal lines
comprises providing a substrate having formed therein a recessed
portion in a first and a second region. The method further
comprises obtaining an estimated expected removal rate of the metal
at the first region and the second region of the substrate during a
chemical mechanical polishing process to be performed.
Additionally, the method includes depositing the metal on the
substrate by electroplating, wherein a deposition thickness of the
metal in the first and second regions is adjusted in correspondence
to the estimated expected removal rate in the first and second
regions. Moreover, excess metal is removed by chemical mechanical
polishing to produce the metal lines.
[0013] In a further embodiment, a method of forming metal lines
comprises providing a substrate with a central region and a
peripheral region, wherein the central region and the peripheral
region each have a recessed portion defining a height dimension.
Moreover, a metal layer is deposited over the substrate, wherein an
averaged layer thickness of the peripheral region is different from
an averaged layer thickness of the central region. Additionally,
the method includes removing excess material from the substrate by
chemical mechanical polishing, wherein the difference of the
averaged layer thickness of the peripheral and the central region
is adjusted during the deposition of the metal such that the height
of metal in the recessed portions is within a predefined tolerance
after removal of the excess metal.
[0014] According to a another embodiment, a method of forming metal
lines in a first and a second region of a substrate comprises the
deposition of a seed layer on the substrate. Furthermore, the metal
is deposited by electroplating while controlling at least one of an
electrical field and electrolyte flow so as to be different at the
first and second regions to obtain a greater metal thickness in one
of the first and second regions that is expected to have a greater
removal rate in a chemical mechanical polishing process to be
performed. Moreover, the method includes the removal of excess
metal in the first and second regions.
[0015] According to a further embodiment, a method of forming a
metal line in a first and a second region of a substrate comprises
depositing a seed layer on the substrate while controlling an
averaged seed layer thickness in the first region to be different
from an averaged seed layer thickness in the second region.
Moreover, the method includes depositing the metal by
electroplating to fill the metal lines and removing excess
metal.
[0016] In another embodiment, a method of forming metal lines on a
plurality of substrates comprises obtaining parameter values
indicative of a quality of a chemical mechanical polishing process
to be performed for each of the substrates. Moreover, the method
includes relating the parameter values for each substrate to a
corresponding metal layer thickness profile and depositing a metal
layer on each substrate while controlling deposition parameters to
substantially generate said metal thickness profile for each
substrate. The method additionally comprises removing excess metal
from each of the substrates by chemical mechanical polishing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0018] FIGS. 1a and 1b schematically show a cross-sectional view of
a typical metallization structure at different positions on a
substrate;
[0019] FIG. 2 is a diagram depicting a typical process flow of one
embodiment of the present invention;
[0020] FIG. 3a schematically depicts an exemplary reactor for
electroplating to form a metal layer having a desired profile in
accordance with one embodiment;
[0021] FIG. 3b schematically depicts an embodiment using a
diffusing element to obtain a desired metal profile;
[0022] FIG. 3c shows a plan view of the diffusing element of FIG.
3b;
[0023] FIG. 4 schematically depicts a process chamber of a sputter
tool to produce a seed layer having a desired thickness profile in
accordance with a further embodiment; and
[0024] FIGS. 5a-5e are diagrams depicting measurement results of
various metal layer profiles with respect to the obtained erosion
in a subsequent CMP process.
[0025] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0027] The present invention will now be described with reference
to the attached figures. Although the various regions and
structures of a semiconductor device are depicted in the drawings
as having very precise, sharp configurations and profiles, those
skilled in the art recognize that, in reality, these regions and
structures are not as precise as indicated in the drawings.
Additionally, the relative sizes of the various features and doped
regions depicted in the drawings may be exaggerated or reduced as
compared to the size of those features or regions on fabricated
devices. Nevertheless, the attached drawings are included to
describe and explain illustrative examples of the present
invention. The words and phrases used herein should be understood
and interpreted to have a meaning consistent with the understanding
of those words and phrases by those skilled in the relevant art. No
special definition of a term or phrase, i.e., a definition that is
different from the ordinary and customary meaning as understood by
those skilled in the art, is intended to be implied by consistent
usage of the term or phrase herein. To the extent that a term or
phrase is intended to have a special meaning, i.e., a meaning other
than that understood by skilled artisans, such a special definition
will be expressly set forth in the specification in a definitional
manner that directly and unequivocally provides the special
definition for the term or phrase.
[0028] As has been pointed out in the introductory part of the
application, CMP and electroplating are the preferred techniques
for forming metallization layers, in particular for forming a
copper metallization, wherein presently a great deal of effort is
made to optimize the individual processes in view of uniformity
across the entire substrate surface. The inventors of the present
application recognized that the insufficiency inherent to the
individual processes may advantageously be employed in combination
so as to obtain an enhanced metallization structure as described
herein.
[0029] FIG. 2 depicts generally the process flow according to one
illustrative embodiment of the present invention. In a first step
201 removal rates and/or parameters indicative of removal rates
during a CMP process at at least two different regions on a
substrate are determined. The determination of the removal rates
and/or of the parameter values indicative of the removal rates may
be attained by preparing corresponding test wafers that are subject
to a CMP process as performed during the processing of product
wafers.
[0030] According to one particular embodiment, the test wafers may
bear trenches, vias and recessed portions that correspond to the
device features of the product wafers. As is indicated in step 204,
measurement of characteristics of metal lines, for example the
erosion and dishing of selected lines, may be performed and the
obtained results may be used for the determination of the removal
rates and/or the parameter values indicating the removal rates. For
instance, the erosion may represent a parameter that quantitatively
describes the quality and thus removal rate uniformity of the CMP.
According to this embodiment, also the product wafers or at least
some of the product wafers may serve as the test wafers, thereby
significantly reducing the number of test wafers or even rendering
the employment of test wafers completely obsolete. Moreover, by
determining the removal rates and/or the parameter values
indicative thereof, such as erosion and/or dishing and/or the final
layer thickness, on the basis of the measurement results of product
wafers, the quality of the CMP process may continuously be
monitored so that subtle changes in the CMP parameters due to, for
example, degradation of the polishing pad, can be detected and
taken into consideration for the determination of the corresponding
removal rates and/or parameter values. For instance, any time
dependence of the removal rates and/or of the parameter values can
be taken into account after having established an initial removal
rate and/or parameter value for the CMP station under
consideration.
[0031] Furthermore, the determination of the removal rates and/or
the parameter values indicative thereof can be carried out on the
basis of a theoretical model of the CMP process. That is,
calculations for erosion rates and dishing rates may be performed
online or in advance, and the results thereof may be used for
further processing. In one example, a series of test measurements
is carried out and removal rates and/or corresponding parameter
values may be obtained without further measurements once
corresponding model data has been established from the empirical
data.
[0032] According to step 202, a product substrate, such as a
silicon wafer, bearing metallization structures at a first and a
second region, such as the metallization structures 100 and 150 of
FIGS. 1a and 1b (of course without metal), is subjected to
electroplating, wherein process parameters of the electroplating
process are controlled so as to obtain a metal thickness in the
first and the second region that is correlated with the removal
rates and/or the parameter values determined in step 201. For
instance, as previously explained, the removal rate of copper in a
typical copper metallization process may be higher in the central
region of the substrate than in the periphery. Accordingly, the
process parameters of the electroplating process are controlled so
as to obtain an increased metal thickness in the central region
such that the actual removal rates in the central region and the
peripheral region are within specified tolerances when the removal
rates and/or the parameter values determined in step 201 are used
as a basis. In particular, erosion and dishing values may be used
for evaluating the removal rates, or may directly be used as the
control parameters.
[0033] The controlling of the deposition thickness in the first and
second regions, i.e., the controlling of the process parameters of
the electroplating process, will now be described with reference to
FIGS. 3 and 4. FIG. 3a schematically depicts an electroplating
reactor 300 for depositing a metal layer on a substrate 301. The
substrate 301 comprises a working surface 302 on which the metal,
for example copper, is to be deposited. The substrate 301 is
supported by a substrate holder 303 that is also configured to
provide an electrical connection to a voltage source not shown in
FIG. 3. The reactor 300 further comprises a reactor cavity 304
containing an electrolyte with metal ions that are to be deposited
on the working surface 302. The electrolyte may be introduced into
the reactor cavity 304 by a fluid line 305 that is also connected
to a vertical riser pipe 306 arranged to supply electrolyte to the
central portion of the substrate surface 302. A fluid distribution
means 307 is located within the reactor cavity 304 and comprises
two or more blades or vanes 308, which in turn may comprise a fluid
passage 309 and a shield 310. The fluid distribution means 307 is
rotatable around the central riser pipe 306 by appropriate driving
means not shown in the figure. A large area anode 311 is arranged
at the bottom of the reactor cavity 304 and is in contact with the
electrolyte.
[0034] In operation, the fluid distribution means 307 rotates and
electrolyte is supplied to the working surface 302, which now
serves as a cathode, so that metal deposits on the working surface
302. The fluid distribution means 307 may be rotated by any
appropriate drive system, such as an electrical motor, by coupling
to a rotating magnetic field, and the like. Since the electric
field prevailing at the surface 302 significantly depends on the
shape of the shields 310 due to the ion transportation path
determined by the shield 310, the deposition rate at specific
regions on the substrate surface 302 is influenced by the shape of
the shields 310. Accordingly, by appropriately selecting the shape
of the shields 310, the thickness profile of the finally obtained
metal layer can be adjusted. For instance, the shape of the shields
310 may be selected to obtain a "dome-like" thickness profile
wherein the working surface 302 takes on an increased averaged
metal thickness in the central region. Alternatively, and depending
on the subsequent CMP process, a thickness profile may be attained
in which the central region has a decreased metal thickness.
Alternatively or additionally, in one embodiment, the flow of
electrolyte to the working surface 302 may be controlled so as to
obtain the desired thickness profile. In this respect, the shields
310 or additional shields may be arranged so as to restrict the
fluid flow of electrolyte in substrate regions where a decreased
metal thickness is desired. For example, additional shields may be
provided at the periphery of the substrate 301 to restrict fluid
flow in these regions. The shields 310 and the additional shields
may be made of a non-conductive, preferably inert, material, such
as Teflon.RTM., so as to not react with the electrolyte. Moreover,
by influencing the fluid flow, the electrical field is also
affected in these regions.
[0035] FIG. 3b schematically depicts a further embodiment similar
to the embodiment illustrated in FIG. 3a, wherein like parts have
like numerals. Between the fluid distribution means 307 and the
substrate 301 a diffusing element 312 is provided, having formed
therein a pattern of openings 313 that shapes the electric field
and/or controls the fluid flow to respective regions on the
substrate 301 to thereby control the deposition rate and thus the
finally obtained thickness profile. In FIG. 3b, the pattern 313 is
constituted by substantially equally-sized openings that are
provided in the central region more densely than at the periphery.
However, the illustrated pattern 313 is only of exemplary nature
and any appropriate shape and number of openings may be arranged to
obtain the required flow distribution. For example, the openings
can be arranged more densely in the periphery when a higher
deposition rate is required in this region. Moreover, the material
of the diffusing element 312 may be conductive so that the
electrical field influencing the paths of the ions within the fluid
flow may also be controlled.
[0036] FIG. 3c depicts the diffusing element 312 in more detail. As
can be seen, the openings 313 form a pattern that allows an
increased fluid flow to the central region of the substrate
301.
[0037] In a further embodiment, the anode 311 may be made of a
plurality of distinct anode elements, which are arranged to provide
a required electric field distribution for obtaining the desired
thickness profile. In one embodiment, anode elements of
substantially equal size are provided below the substrate, wherein
in a region corresponding to the central region of the substrate
significantly more anode elements are arranged than in a region
corresponding to the periphery of the substrate. Therefore, a
higher current density and thus deposition rate may be attained in
the central region of the substrate.
[0038] It should be noted that the above-explained methods of
attaining the desired thickness profile may also be used in
combination. Moreover, in the art of electroplating, great efforts
are made to obtain a uniform metal layer, whereby a variety of
parameters influencing the finally obtained profile of the metal
layer have been investigated. The corresponding results may thus be
employed to adjust the corresponding parameters to "deform" the
metal layer for obtaining a thickness profile required to
compensate for the varying removal rates during a CMP process.
[0039] With reference to FIG. 4, a further embodiment is described
in which process parameters for depositing a metal layer on a
substrate are controlled so as to obtain a required thickness
profile. In FIG. 4, a sputter tool 400 comprises a reaction chamber
401 including a plurality of magnets 402, a plasma shield 403 and a
sputter target 404. On a substrate stage 405, a substrate 406 is
provided including a first substrate region 407 and a second
substrate region 408. A collimator 409 is located between the
sputter target 404 and the substrate stage 405. The collimator 409
comprises openings 410, the diameters of which vary along the
radius of the collimator 409, such that the openings 410
corresponding to the first region 407 have a larger diameter than
the openings 410 corresponding to the second region 408. For the
sake of convenience, in FIG. 4, any other means required for the
operation of the sputter tool 400, such as feeding lines, plasma
excitation means, radio frequency generator, bias voltage supply
source and the like, are omitted.
[0040] As previously explained, in depositing a metal layer by
electroplating, a thin seed layer is required that serves as a
current distribution layer. As is well known, the deposition rate
during electroplating depends, among other things, on the current
density at the respective location of the substrate. Thus, if the
initial capability for current transportation of the seed layer is
designed to have a required profile, the initial deposition rate
during electroplating, and thus the deposition rate during
approximately the whole deposition process, may be increased or
decreased as required. In particular, the initially decreased
deposition rate in the center region of the substrate that is
caused by the increased electrical resistance can be positively
compensated for by the sputter tool shown in FIG. 4.
[0041] In operation, target atoms are liberated from the sputter
target 404 by incoming charged particles of the plasma (not shown)
and move towards the collimator 409. Due to the profile of the
openings 410, a larger amount of target atoms hits the substrate
406 in the first region 407 than it does in the second region 408.
The finally obtained thickness profile of the seed layer
essentially conforms to the profile of the openings 410. In the
present embodiment, the thickness profile of the seed layer will
entail the dome-like thickness profile of the final metal layer
obtained by the subsequent electroplating. According to this
embodiment, conventional electroplating reactors may be used since
no further control of process parameters, except for conventional
process control for forming a uniform metal layer, during
electroplating is necessary. In further embodiments, however,
additional process parameters of the electroplating may be
controlled in the manner as pointed out above with reference to
FIG. 3.
[0042] In a further embodiment, the thickness profile of the seed
layer may be controlled by varying the plasma shape, for example,
by introducing correspondingly shaped plasma shields and/or by
influencing the deposition rate by controlling the temperature of
the substrate 406. It should be noted that the process parameters
of other deposition methods for forming the seed layer may be
controlled so as to obtain the required thickness profile. For
instance, in one embodiment, chemical vapor deposition may be
employed, wherein an appropriately formed deposition mask is
provided that effectively varies the deposition rate on the
substrate. Moreover, the temperature of the substrate may be
controlled to modify the deposition rate.
[0043] Again referring to FIG. 2, after depositing the metal layer,
the substrate is subjected to the CMP process, in which an endpoint
detection is carried out to determine clearance of the wafer
surface. In a particular embodiment, endpoint detection is
performed in the first and the second regions and the measurement
results are used for the determination of the removal rates and/or
the parameter values indicative for the removal rates. For
instance, the time difference between the occurrence of the
clearance in the first and second regions may be used as a measure
of the difference in removal rates of these regions and a
corresponding correction value for the deposition of the metal
layer in a subsequent substrate may be obtained. This procedure is
advantageous when electroplating and CMP take place substantially
at the same time so that any corrections required in shaping the
profile of the metal layer may immediately be transmitted to the
electroplating station to correspondingly change the deposition
rate. In most cases, however, electroplating takes place for a lot
of substrates prior to the lot being subjected to the CMP process,
and any deviations in the removal rates and/or the parameter values
indicative thereof may be gathered on, for example, lot basis and
employed for the deposition process of subsequently plated
substrate lots. A systematic parameter drift during the CMP process
can therefore be detected and taken into account on a lot
basis.
[0044] In one embodiment, a "forward" correction of "actual" CMP
variations may be carried out, even if the metal deposition is
completed. To this end, a model of the CMP may produce simulation
results for an initially profiled substrate and "predict" results
during the "progress" of the (simulated) CMP. The modeled CMP may
be represented by erosion values, dishing values, layer thickness
and the like.
[0045] The calculations may be performed on a (model) wafer basis
and the simulation results may immediately be entered into the
process control of the actual electroplating process. For instance,
if in general a "dome-like" profile is required, the maximum dome
height can be finely tuned individually on the basis of simulation
results obtained from the CMP model for this substrate. To further
enhance accuracy of this process, actual measurement results
obtained on a lot basis of the actual CMP may be fed back to the
CMP model to compensate for slight discrepancies between the model
and the actual process.
[0046] After the CMP is completed, according to step 204,
measurement of characteristics of the metal lines may be performed
so as to determine, for example, erosion and dishing in the first
and second regions. The corresponding measurement results may also
be used to determine the removal rates and/or any parameter values.
In one particular embodiment, these measurement results are
employed for establishing a model, for example in the form of
tables containing erosion and/or dishing values to process
parameter values related to controlling the electroplating process.
Thus, the determination of removal rates and/or any parameters
indicative thereof may be accomplished for a plurality of
substrates once initial removal rates at the beginning of a new
process cycle have been established. For instance, an initial lot
of substrates is processed in accordance with the sequence of FIG.
2, wherein initially removal rates have been determined in advance
to control the deposition and thus the thickness profiles during
electroplating. In step 204, erosion and dishing values are
obtained and immediately fed back to the electroplating station to
take into consideration any corrections necessary for obtaining the
required tolerances. In this way, a sort of closed feedback loop is
established in which possible changes in the electroplating and the
CMP process may be compensated.
[0047] With reference to FIGS. 5a-5e, a further illustrative
embodiment will now be described. A plurality of substrates in
wafer form having a diameter of about 300 mm have been prepared
such that each of the wafers comprises a plurality of vias and
trenches formed in an insulating layer, for example in the manner
as shown in FIG. 1. In each wafer, a central region located at the
center of the wafer and extending over at least several millimeters
and a peripheral region located at the perimeter of the wafer and
extending inwardly at least about several millimeters comprise at
least one metal line that may be used for measurements to determine
removal rates and/or other parameters indicative of the removal
rates, such as erosion and/or dishing. A first wafer receives a
copper metal layer of about 1 .mu.m thickness in accordance with
standard process parameters, i.e., the electroplating parameters
are adjusted to obtain a copper surface as uniform as possible. A
second wafer is prepared with a profiled copper layer, wherein the
wafer comprises a dome-like profile with a maximum thickness at the
middle of the central region that exceeds the metal thickness at
the perimeter by about 50 nm. A third wafer has been prepared with
a thickness in the middle of the central region exceeding the
perimeter by about 80 nm, and a fourth and a fifth wafer are
prepared in the same manner having an excess thickness of 100 nm
and 150 nm, respectively. The first to fifth wafers are then
subjected to a CMP process under similar conditions, wherein the
end of the CMP step is determined by endpoint detection in the
peripheral and central regions. In subsequent measurements, the
erosion of the at least one metal line in each of the central and
peripheral regions of the first to fifth wafers have been
determined at seven positions separated radially. In FIGS. 5a-5e,
the erosion in the central regions is indicated by circles and the
erosion in the peripheral regions is indicated by squares.
[0048] In FIG. 5a, the erosion in the central region is
significantly larger than the peripheral region, indicating that
the removal rate in the central region exceeds the removal rate in
the peripheral region. The CMP process was performed for 99 seconds
and required an overpolish time of 18 seconds until the peripheral
region was entirely cleared.
[0049] In FIG. 5b, representing the dome profile with 50 nm excess
height, it is indicated that the removal rates in the central and
peripheral regions are quite similar, since the erosion measured in
the central region is only slightly larger than that measured in
the peripheral region. The endpoint was detected in the central
region at 109 seconds and an overpolish time of 18 seconds was
added.
[0050] FIG. 5c shows the result for the dome-like structure with an
excess height of 80 nm and indicates that the removal rates in the
central and peripheral regions are substantially equal. Moreover,
according to the endpoint detection, clearance in the peripheral
and the central regions set in substantially simultaneously after
86 seconds and an overpolish time of 18 seconds was used.
[0051] FIG. 5d shows the results for the dome-like structure with
an excess height of 100 nm. The increased erosion of the peripheral
region indicates that now the removal rate in the peripheral region
is higher than in the central region. Moreover, a polish time of
111 seconds was necessary with an overpolish time of 18
seconds.
[0052] FIG. 5e clearly indicates that the removal rate in the
peripheral region is now significantly larger than in the central
region, since erosion at the peripheral region is dramatically
increased.
[0053] From the above results, the dome-like profile with an excess
height of 80 nm is selected and offers a minimum deviation of the
erosion of the metal lines compared to the conventionally employed
process (FIG. 5a) and additionally provides a reduced process
time.
[0054] It should be noted that in the illustrative embodiments
described so far, the substrates are divided into a first and a
second region, however a more complex profile may be employed
pursuant to process requirements. For instance, for current feature
sizes and line densities, the above-established 80 nm dome height
may be successfully implemented in the process, but other values
for different lay-outs, feature sizes, metal/via layers and
technologies may be required. Depending on future technologies a
complete reverse shape (bowl shape) may be necessary. Furthermore,
more complex or sophisticated polishing processes may require more
complex profiles such as W-shapes or M-shapes and the like.
[0055] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. For example, the process steps
set forth above may be performed in a different order. Furthermore,
no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below.
It is therefore evident that the particular embodiments disclosed
above may be altered or modified and all such variations are
considered within the scope and spirit of the invention.
Accordingly, the protection sought herein is as set forth in the
claims below.
* * * * *