U.S. patent application number 10/132572 was filed with the patent office on 2003-10-30 for chemical-mechanical polishing slurry with improved defectivity.
Invention is credited to Leng, Yaojian.
Application Number | 20030203705 10/132572 |
Document ID | / |
Family ID | 29248802 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030203705 |
Kind Code |
A1 |
Leng, Yaojian |
October 30, 2003 |
Chemical-mechanical polishing slurry with improved defectivity
Abstract
The copper CMP in a damascene structure composes of copper
removal step, which removes majority or all of the redundant
copper, and subsequent barrier removal step. The embodiment of the
present invention includes the removal of the barrier layer with a
slurry blended from abrasive silica particles, chemical materials,
and de-ionized water. The blended slurry is aged for at least 4
days before use to achieve an improved defect performance.
Inventors: |
Leng, Yaojian; (Plano,
TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
29248802 |
Appl. No.: |
10/132572 |
Filed: |
April 26, 2002 |
Current U.S.
Class: |
451/36 ;
257/E21.244; 257/E21.304; 257/E21.583 |
Current CPC
Class: |
C09G 1/02 20130101; H01L
21/3212 20130101; H01L 21/7684 20130101; H01L 21/31053
20130101 |
Class at
Publication: |
451/36 |
International
Class: |
B24B 001/00 |
Claims
What I claim is:
1. A method of providing a slurry used for CMP process comprising
the steps of: mixing abrasive part and chemical part of said slurry
and aging said mixture at least five days or the equivalent before
polishing a wafer using the aged slurry.
2. The method of claim 1, wherein said CMP process is copper CMP
barrier removal.
3. The method of claim 1, wherein said abrasive part is silica
(SiO2).
4. The method of claim 1, wherein said abrasive part is a colloid
silica.
5. The method of claim 1, wherein said chemical part contains a
corrosion inhibitor.
6. The method of claim 1, wherein said chemical part contains a
corrosion inhibitor know as BTA (Benzotriazole).
7. The method of claim 1, wherein said slurry is Rodel
electrapolish, blended from Rodel CUS1201A, Rodel CUS1201B, and DI
water.
8. The method of claim 1, wherein said aged slurry composition
includes Electrapolish. aged for at least six days.
9. The method of claim 1, wherein said equivalent aging process is
by one or more accelerated steps of elevated temperature,
mechanical stirring or re-circulation in a slurry supply loop.
10. A method of CMP processing a wafer using a slurry comprising
the steps of: mixing abrasive part and chemical part of said
slurry; aging said mixture at least five days or the equivalent
thereof by an accelerating step; and polishing the wafer using the
aged slurry.
11. The method of claim 10, wherein said CMP process is copper CMP
barrier removal.
12. The method of claim 10, wherein said abrasive part is silica
(SiO2).
13. The method of claim 10, wherein said abrasive part is a colloid
silica.
14. The method of claim 10, wherein said chemical part contains a
corrosion inhibitor.
15. The method of claim 10, wherein said chemical part contains a
corrosion inhibitor know as BTA (Benzotriazole).
16. The method of claim 10, wherein said slurry is Rodel
electrapolish, blended from Rodel CUS1201A, Rodel CUS1201B, and DI
water.
17. The method of claim 10, wherein said aged slurry composition
includes Electrapolish. aged for at least six days.
18. The method of claim 10, wherein said equivalent aging process
is by one or more accelerated steps of elevated temperature,
mechanical stirring or re-circulation.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to the field of
chemical mechanical polishing (CMP) process used to fabricate
semiconductor devices. Specifically, the invention relates to the
treatment of slurry used in CMP processes where copper is used as
interconnecting material in the semiconductor devices.
[0003] 2. Description of Related Art
[0004] Over last decade, copper has gradually become the
interconnecting material of choice for the integrated circuits in
semiconductor industry due to its lower resistivity and better
resistance to electro-migration. Due to the difficulty of etching
copper using plasma, the method of damascene is typically used to
create the copper interconnect on chip. When the trench and via are
formed simultaneously on the wafer, the process is called dual
damascene, and when the trench or via are formed separately on the
wafer, the process is called single damascene. In a typical
damascene structure, trench and/or via is etched into dielectric
layer, barrier (typically Ta, TaN) and seed copper are deposited
into the trench and/or via, and bulk copper is deposited by
electroplating. Typically, the electro-chemically plated copper not
only filled the desired area on the wafer (trench and/or via), it
also over burden on the other area, leaving an un-planarized wafer
surface. Chemical mechanical polishing (CMP) is used to remove the
redundant copper and to planarize the wafer surface. Copper CMP is
a multi-step process. During the 1.sup.st step, a slurry of high
selectivity of copper to barrier is used in the removal of a
majority or all redundant copper from the wafer surface. The high
selectivity of copper removal rate to barrier removal rate is
designed so the polish can stop on the barrier layer. Hence, the
non-uniformity form electro-chemical deposition will not be
transferred into the final copper thickness variation. However,
after the high selectivity slurry removes the copper layers, the
copper layer disposed inside the trenches also may become polished
with the high selectivity copper-polishing slurry. This
over-polishing of the copper layer disposed inside the trenches
causes a depression of the copper layer, such that the copper layer
becomes uneven, an effect which is known as dishing. In the
2.sup.nd step, a barrier slurry is used to polish off the barrier.
In a low selectivity slurry (LSS) integration scheme, the barrier
polish removes barrier material, dielectric material, and copper at
similar rates to improve process margin and to reduce dishing.
Sometime, a 3.sup.rd step, called buff step, is also used to
improve defectivity on the wafer.
[0005] The defectivity in copper CMP is one of the most difficult
challenges due to the softness of the copper film. The defectivity
from copper CMP is mainly scratch, sometime residue coming from the
degraded polishing pads, mostly when a soft pad is used to buff out
scratches. The defectivity in copper CMP is a major concern because
it causes yield lost, and some reliability concern. Effort has been
focused to reduce the copper CMP defectivity. Slurry filtration,
including filtration in a re-circulation loop and point of use, is
routinely used. However, the benefit of slurry filtration is
limited. If a very aggressive filter is chosen, the filter removes
not only the unwanted large particles/agglomerates, it might also
remove the primary abrasive particles suspended in the slurry,
hence change the polish characterization. Also, over aggressive
filtering of slurry causes the sheering of the slurry, introducing
more defects. It also clogs the filter easier to make it much less
manufacturable. Soft pads are also used to buff out the
micro-scratches at the top surface. However, the soft pad has lower
planarization efficiency, relative shorter life, and generates
residue during its degradation.
[0006] Therefore, a need has arisen for processes that overcome
these and other shortcomings of the related art.
SUMMARY OF THE INVENTION
[0007] In accordance with an embodiment of the present invention
the barrier is polished with improved defectivity during the CMP
process with an aged barrier slurry.
[0008] In an embodiment of the present invention, the treatment of
slurry used to polish copper barrier includes the steps of mixing
the components of the slurry, aging the mixture for at least five
days, and polishing the wafer with the aged slurry.
[0009] In another embodiment of the present invention, the mixed
slurry is re-circulated in a slurry supply loop for a period of at
least five days before used for polishing.
[0010] Other features and advantages will be apparent to persons of
ordinary skill in the art in view of the following detailed
description of the invention and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present invention,
needs satisfied thereby, and the features and advantages thereof,
reference now is made to the following descriptions taken in
connection with the accompanying drawings.
[0012] FIGS. 1a-1d are cross-sectional schematics depicting general
concept of the utilization of copper CMP.
[0013] FIG. 2 illustrates an improved method according to one
embodiment of the present invention.
[0014] FIGS. 3a-3b are the data obtained from aging study wherein
FIG. 3a is a plot of Sum of Defect (SOD) vs. age in days and FIG.
3b is a chart of age, sample size, average defect count, and
standard deviation.
[0015] FIG. 4 illustrates copper defect improvement due to slurry
aging, demonstrated in a manufacturing environment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0016] Referring to FIGS. 1a-1d, a schematic diagram demonstrating
the concept of copper CMP is provided. For the sake of simplicity,
only single damascene with trench is illustrated, although the same
concept applies to the dual damascene structures. A wafer substrate
with prior layer of interconnect (102) is provided. The dielectric
layer (106) is also provided. The wafer is patterned and etched,
trench (103), (104) is formed. Barrier layer (110) and copper seed
layer (112) is deposited. The wafer is then subjected to
electro-chemical plating, and copper (120) is deposited and fill
the trench. The copper profile in FIG. 1c represents two typically
filling characteristics, conformal filling with wide trench (103)
and bottom-up filling with narrow trench (104). CMP is then used to
planarize the surface. In the 1.sup.st step of CMP, a slurry of
high selectivity of copper to barrier is used in the removal of a
majority or all redundant copper from the wafer surface. The high
selectivity of copper removal rate to barrier removal rate is
designed so the polish can stop on the barrier layer. Hence, the
non-uniformity form electro-chemical deposition will not be
transferred into the final copper thickness variation. However,
after the high selectivity slurry removes the copper layers, the
copper layer disposed inside the trenches also may become polished
with the high selectivity copper-polishing slurry. This
over-polishing of the copper layer disposed inside the trenches
causes a depression of the copper layer, such that the copper layer
becomes uneven, an effect which is known as dishing. The resulting
wafer is illustrated in FIG. 1d. In the 2.sup.nd step, a barrier
slurry is used to polish off the barrier. In a low selectivity
slurry (LSS) integration scheme, the barrier polish removal
barrier, dielectric material, and copper at similar rates to
improve process margin and reduce dishing. Sometime, a 3.sup.rd
step, called buff step is also used to improved defectivity on the
wafer.
[0017] In the prior art, it is suggested that a slurry composition
that includes Electrapolish (Rodel electrapolish, blended from
Rodel CUS1201A, Rodel CUS1201B, and DI water) is stable for about 1
week after mixing, but it is preferable to mix fresh every day. It
is also generally believed that as a slurry ages, the contaminants
(unwanted particle existing in the slurry) tend to grow and/or
coalesce, causing substantial defectivity on the polished wafer.
Contrary to that, applicants' have discovered that it is better for
use after aging the slurry for at least about 5 to 6 days. It is
also found that polishing performance is not sensitive to the
degradation of oxidizer due to aging. The impact of oxidizer
degradation can be further minimized by adding a stabilizing agent,
which reduces the degradation rate of the oxidizer.
[0018] In accordance with one embodiment of the present invention a
method of providing an improved slurry used for copper barrier CMP
processing as illustrated in FIG. 2 comprises the Step 1 of mixing
abrasive part and chemical part of said slurry and Step 2 of aging
said abrasive part and chemical part that has been mixed for at
least five days or the equivalent thereof before being used for
copper barrier CMP processing. In one embodiment the abrasive part
is colloid silica (SiO2) and the chemical part contains a corrosion
inhibitor such as BTA ((Benzotriazole). In Step 3 of FIG. 2, the
aged slurry is used for copper barrier polishing.
[0019] In accordance with a preferred embodiment of the present
invention the slurry is Rodel electrapolish, blended from Rodel
CUS1201A, Rodel CUS1201B, and DI (de-ionized ) water. In particular
the slurry composition includes Electrapolish that is aged for at
least six days. During this time the slurry may be mechanically
stirred and re-circulated in a slurry supply loop. It is further
recognized that the aging may be enhanced by an elevated
temperature above normal room temperature, mechanical stirring and
re-circulation.
[0020] FIGS. 3a and 3b demonstrate the improvement of defectivity
by barrier slurry aging. The electro-chemically plated blank copper
wafers were used in the experiment to monitor the defectivity
improvement. The experiment conditions are listed below:
1 Equipment: Applied Materials Mirra Polisher Polish pad: Rodel
IC1010 on all three platens Monitor Wafers: 12,000 A copper Pilots,
annealed at 400 C. Defect Metrology: KLA-Tencor SP1 Slurry: Rodel
CUS1201 or electrapolish, blended by volume partA:partB:DIW =
33%:50%:17%. The blended slurry is aged by days as indicated before
polishing. Slurry Delivery: Drawn by peristaltic pump from buckets
behind tool, without point of use filter.
[0021] FIG. 4 is a demonstration of defectivity improvement by
barrier slurry aging. Each data point in the graph represents a run
to qualify the defectivity performance of the polisher. The
Vertical axis represents the sum of defects (SOD) on polished blank
copper pilots measured by SP1 with 0.24 um sensitivity. The
horizontal axis is the date, when the qualification run was
performed in the format of YYMMDD. The qualification run is
typically performed daily. The polishing condition used to collect
data on FIG. 4 is similar to that outlined for FIGS. 3a and 3b
except the slurry being delivered from loop, with a loop filter
(Mykrolis, Planargard, CMP701E06) and POU filter (Mykrolis,
Solaris, SLR0313E1). The day tank is re-filled with slurry when it
is dropped below a designated level. The refilling slurry is
blended before refill. The arrow in the graph indicate the onset of
the using of the aged slurry. A clear improvement of defectivity
can be observed.
[0022] While the invention has been described in connecting with
preferred embodiments, it will be understood by those of ordinary
skill in the art that other variations and modifications of the
preferred embodiments described above may be made without departing
from the scope of the invention. Other embodiments will be apparent
to those of ordinary skill in the art from a consideration of the
specification or practice of the invention disclosed herein.
* * * * *