U.S. patent application number 10/868969 was filed with the patent office on 2005-12-22 for chemical mechanical polishing slurry for polishing copper layer on a wafer.
Invention is credited to Fann, Yang-Jiann, Pan, Wen-Chueh, Shih, Zong-Whie, Tsay, Ming-Tseh.
Application Number | 20050279964 10/868969 |
Document ID | / |
Family ID | 35479675 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050279964 |
Kind Code |
A1 |
Tsay, Ming-Tseh ; et
al. |
December 22, 2005 |
Chemical mechanical polishing slurry for polishing copper layer on
a wafer
Abstract
A chemical mechanical polishing slurry is provided for the
copper layer on a wafer. The slurry contains colloidal silica and a
chemical etching agent composed of hydrogen peroxide, acetic acid,
and phthalic acid. The hydrogen peroxide oxides the surface of the
copper layer. The acetic acid then reacts with the copper oxide to
form copper acetate. This selective and functional chemical
reaction mechanism can speed up the polishing removal rate and
reduce scratches. The phthalic acid functions as both a pH
buffering agent and a complexing agent to make the reaction
concentration at each point of the wafer surface more homogeneous.
Therefore, the copper layer during the chemical mechanical
polishing process has a high removal rate and uniformity.
Inventors: |
Tsay, Ming-Tseh; (Longtan
Township, TW) ; Shih, Zong-Whie; (Longtan Township,
TW) ; Pan, Wen-Chueh; (Longtan Township, TW) ;
Fann, Yang-Jiann; (Longtan Township, TW) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
35479675 |
Appl. No.: |
10/868969 |
Filed: |
June 17, 2004 |
Current U.S.
Class: |
252/62 ;
257/E21.304 |
Current CPC
Class: |
H01L 21/3212 20130101;
C23F 3/06 20130101; C09G 1/02 20130101; C09K 3/1409 20130101; C09K
3/1463 20130101 |
Class at
Publication: |
252/062 |
International
Class: |
E04B 001/74 |
Claims
1. A chemical mechanical polishing (CMP) slurry for polishing the
copper layer on a wafer, comprising polishing particles, hydrogen
peroxide, acetic acid, and phthalic acid; wherein the polishing
particles are of a particle diameter of 10.about.100 nm and include
a concentration of 0.5.about.10 wt % colloidal silica; wherein the
concentration of the hydrogen peroxide is 0.6.about.2.5 V %, and
wherein the pH value is 2.5-5.5.
2-4. (canceled)
5. The CMP slurry of claim 1, wherein the concentration of the
acetic acid is 0.1.about.1.0 V %.
6. The CMP slurry of claim 1, wherein the concentration of the
phthalic acid is 0.1.about.0.8 wt %.
7. (canceled)
8. The CMP slurry of claim 1, wherein the concentration ratio of
hydrogen peroxide to acetic acid is 0.6.about.25.
9. The CMP slurry of claim 1, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
10. The CMP slurry of claim 5, wherein the concentration of the
phthalic acid is 0.1.about.0.8 wt %.
11. The CMP slurry of claim 5, wherein the concentration ratio of
hydrogen peroxide to acetic acid is 0.6.about.25.
12. The CMP slurry of claim 6, wherein the concentration ratio of
hydrogen peroxide to acetic acid is 0.6.about.25.
13. The CMP slurry of claim 10, wherein the concentration ratio of
hydrogen peroxide to acetic acid is 0.6.about.25.
14. The CMP slurry of claim 5, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
15. The CMP slurry of claim 6, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
16. The CMP slurry of claim 10, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
17. The CMP slurry of claim 11, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
18. The CMP slurry of claim 12, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
19. The CMP slurry of claim 13, wherein the concentration ratio of
acetic acid to phthalic acid is 0.125.about.10.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The invention relates to a chemical mechanical polishing
(CMP) slurry and, in particular, to a slurry with a special
chemical etching agent and colloidal silica for the CMP process of
the copper layer on a wafer.
[0003] 2. Related Art
[0004] As IC devices become smaller in size, the metal wires on
chips are also miniaturized. However, smaller wire widths result in
larger resistance and narrower separations result in larger
capacitance. As the sizes of devices continue to shrink, there will
be more signal delays. Therefore, copper wires with better
conductivity have replaced conventional aluminum wires in order to
increase the signal transmission speed.
[0005] For a high-density multiple-layer copper wire production
process, one can employ chemical mechanical polishing (CMP) to
satisfy the requirement of a uniform wafer. The basic principle is
to use a chemical etching agent in the slurry to react with the
wafer surface. Along with the abrasive mechanical actions of
polishing particles, the dielectric layers, barriers, or metal
layers on the wafer are removed in order to achieve global
planarity of the wafer. In the abrasive mechanism, the chemical and
mechanical forces have to form an optimized dynamical interaction
in order to reach high-quality polishing results. Simply using
chemical reactions cannot achieve the global planarity. Likewise,
considering only the mechanical actions will reduce the removal
rate and are likely to scratch the wafer surface. To have
appropriate material removal energy, it is desirable to have a
slurry that can reduce the structural strength on the surface of
the material through chemical reactions. This can reduce the stress
(including normal forces and shear stress) required to take away
polishing particles in the material polishing and removal process.
It can further achieve the goals of no scratch, high removal rate,
and global planarity.
[0006] The CMP slurry used in wafers is comprised of a slurry
(chemical etching agent) and polishing particles. The slurry is
responsible for chemical etching, while the polishing particles are
responsible for mechanical polishing. Tests of the polishing slurry
include the polishing removal rate, uniformity, surface scratches,
and stability. Moreover, the slurry has to be cheap and safe for
industrial uses.
[0007] As a polishing slurry for the copper layer, most of the
polishing particles in the prior art are fumed alumina which have a
high rigidity and irregular shapes (as in the U.S. Pat. Nos.
6,217,416 and 6,432,828) or fumed silica (as in the U.S. Pat. No.
6,309,560). This type of polishing particles synthesized by burning
is expensive. Since they are hard to become dispersed, one usually
has to add a separating agent. Although they have a higher removal
rate in polishing, scratches are often left on the wafer
surface.
[0008] The polishing removal rate of colloidal silica is not as
good as fumed alumina or fumed silica; nonetheless, the particles
have a uniform size, a better separating property, and a cheaper
price. They have a spherical shape and a lower rigidity. Therefore,
scratches can be avoided. The only problem in the prior art is that
no appropriate chemical etching agent has been found for the
colloidal silica.
SUMMARY OF THE INVENTION
[0009] In view of the foregoing, an objective of the invention is
to provide a low-cost and highly efficient polishing slurry for the
chemical mechanical polishing (CMP) of the copper layer on a
wafer.
[0010] To achieve the above objective, the disclosed CMP slurry
comprises colloidal silica and a chemical etching agent composed of
hydrogen peroxide, acetic acid, and phthalic acid. The chemical
mechanical removal mechanism is to have the hydrogen peroxide and
the copper layer surface react to form copper oxide. The acetic
acid then reacts with the copper oxide to form copper acetate to be
readily removed (the acetic acid does not react with copper).
Afterwards, the colloidal silica polishing particles remove the
copper acetate from the wafer surface. The phthalic acid functions
as both a pH buffering agent and a complexing agent of the
polishing slurry, making the reaction concentration at each point
of the wafer surface more homogeneous. Moreover, the required
concentration of the chemical etching agent according to the
invention is very low. The cost can thus be greatly reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention will become more fully understood from the
detailed description given hereinbelow illustration only, and thus
are not limitative of the present invention, and wherein:
[0012] Table 1 shows the solid content and pH value of the
colloidal silica in various particle diameters;
[0013] Table 2 shows the effects of polishing particles of various
abrasive diameters on the removal rate and the non-uniformity;
[0014] Table 3 shows the effects of different solid contents of the
colloidal silica on the removal rate and the non-uniformity;
[0015] Table 4 shows the effects of slurries with the same
composition but different pH values on the removal rate and the
non-uniformity; and
[0016] Table 5 shows the effects of the composition and
concentration of the chemical etching agent in the slurry on the
removal rate and the non-uniformity.
DETAILED DESCRIPTION OF THE INVENTION
[0017] According to a preferred embodiment of the invention, the
chemical mechanical polishing (CMP) slurry contains:
[0018] (1) nano-scale colloidal silica with a concentration of
0.5.about.10 wt %, the average particle diameter being 10.about.100
nm;
[0019] (2) hydrogen peroxide with a concentration of 0.6.about.2.5
V %;
[0020] (3) acetic acid with a concentration of 0.1.about.1 V %;
and
[0021] (4) phthalic acid with a concentration of 0.1.about.0.8 wt
%.
[0022] Moreover, the concentrations of hydrogen peroxide, acetic
acid, and phthalic acid satisfy (hydrogen peroxide)/(acetic
acid)=0.6.about.25 and (acetic acid)/(phthalic
acid)=0.125.about.10. The pH value of the polishing slurry is
2.5.about.5.5. The above configuration can achieve better polishing
efficiency.
[0023] The polishing machine used in subsequent analyses is the
CMP-300P machine made by Chung-Sun Institute of Science &
Technology. We also use an 8-inch floating polishing head. Other
details are as follows. The down force is 3 psi. The platen speed
is 47 rpm. The head speed is 49 rpm. The slurry supply rate is 150
ml/min. The polishing pad is Rodel IC-1400. The polishing moisture
time is 30 sec. The removal rate and uniformity are measured using
NAPSON RT-80/RG-120 surface resistance meter.
[0024] Test 1
[0025] The current test evaluates the effects of colloidal silica
particle sizes on polishing results. The solid content of colloidal
silica in various sizes and their pH values are indicated in Table
1. The concentrations of the hydrogen peroxide, acetic acid, and
phthalic acid are fixed to 1.2 V %, 0.375 V %, and 0.2 wt %,
respectively. The concentration of the polishing particles is 3.0
wt %. The pH values and polishing results of the slurries are given
in Table 2. The experiments show that the disclosed slurry has a
high removal rate and achieves a high uniformity. The removal rate
is maximized when the particle diameter is 35.7 nm; however, its
uniformity is not as good as those with an abrasive diameter of
19.7 nm and 90.5 nm.
1TABLE 1 Abrasive diameter (nm) Solid content (wt %) pH 19.7 14.78
11.59 35.7 22.87 3.71 69.8 30.4 11.16 90.5 28.22 11.09
[0026]
2TABLE 2 Cu removal rate Abrasive diameter (nm) pH (.ANG./min)
Non-uniformity (%) 19.7 4.80 4196 4.05 35.7 2.90 6383 7.81 69.8
3.25 5457 7.95 90.5 3.35 4991 5.93
[0027] Test 2
[0028] This test evaluates the effects of the solid content of the
colloidal silica on the polishing removal rate and the uniformity.
The abrasive particle diameter of all slurries is fixed to 90.5 nm.
The concentrations of the hydrogen peroxide, acetic acid, and
phthalic acid are fixed to 1.2 V %, 0.375 V %, and 0.2 wt %,
respectively. The pH value and polishing results are shown in Table
3. It can be seen that the removal rate does not increase
significantly when the abrasive slid content is 1.about.3 wt %.
Both the removal rate and the non-uniformity increase
simultaneously when the solid content is greater than 3 wt %.
3TABLE 3 Abrasive solid Cu removal rate content (wt %) PH
(.ANG./min) Non-uniformity (%) 1 3.04 4900 2.78 3 3.35 4991 5.93 6
3.35 6334 6.57
[0029] Test 3
[0030] In this test, we want to see the effects by changing the pH
value of the slurry in the same composition. The polishing
particles in all slurries have a concentration of 3 wt % and an
abrasive diameter of 90.5 nm. The concentrations of the hydrogen
peroxide, acetic acid, and phthalic acid are fixed to 1.2 V %,
0.375 V %, and 0.2 wt %, respectively. The slurries are then added
with diluted ammonia to adjust their pH values, as listed in Table
4. The results show that the removal rate decreases as the pH value
increases. The non-uniformity, on the other hand, increases with
the pH value.
4TABLE 4 pH Cu removal rate (.ANG./min) Non-uniformity (%) 3.35
4991 5.93 4.00 4693 7.91 5.00 3974 7.83
[0031] Test 4
[0032] This test checks the effects of changing the composition and
concentration of the chemical etching agent. The polishing
particles in all slurries have a concentration of 3 wt % and an
abrasive diameter of 90.5 nm. The pH values and polishing results
of all prepared slurries are shown in Table 5. It shows that the
uniformity is not good when only acetic acid is added. The removal
rate is greatly enhanced while the non-uniformity is reduced for
slurries that have both acetic acid and phthalic acid. When the
concentration ratios (hydrogen peroxide)/(acetic acid) and (acetic
acid)/(phthalic acid) are fixed, simultaneously increasing the
concentrations of the hydrogen peroxide, acetic acid, phthalic acid
can increase the removal rate and the uniformity. With both the
concentration ratio (hydrogen peroxide)/(acetic acid) and the
phthalic acid concentration being fixed, increasing the
concentration ratio (acetic acid)/(phthalic acid) can increase the
removal rate without affecting the uniformity to a good
approximation. With the same concentrations of hydrogen peroxide
and acetic acid, decreasing the concentration ratio (acetic
acid)/(phthalic acid) (or increasing the phthalic acid
concentration at the same time) can increase the removal rate and
the uniformity.
5TABLE 5 (hydrogen (acetic hydrogen acetic peroxide)/ phthalic
acid)/ Cu removal Non- peroxide acid (acetic acid (phthalic rate
uniformity (V %) (V %) acid) (wt %) acid) pH (.ANG./min) (%) 0.8
0.25 3.2 0 -- 4.01 2475 11.44 1.2 0.375 3.2 0 -- 3.82 3476 11.66
1.6 0.5 3.2 0 -- 3.69 4207 8.73 0.8 0.35 2.28 0 -- 3.87 3444 10.83
0.8 0.45 1.78 0 -- 3.76 4261 8.42 0.8 0.25 3.2 0.2 1.25 3.20 3825
4.12 1.2 0.375 3.2 0.2 1.875 3.35 4991 5.93 1.6 0.5 3.2 0.2 2.5
3.24 6011 5.29 1.2 0.375 3.2 0.3 1.25 2.98 5661 3.92 1.6 0.5 3.2
0.4 1.25 3.07 6522 3.70
[0033] From the above tests, one can readily see that the disclosed
slurry composition can achieve the goals of high removal rates and
uniformity.
[0034] It should be emphasized that the CMP slurry for the copper
layer on a wafer first have the hydrogen peroxide interact with the
copper surface to form copper oxide. The acetic acid then reacts
with the copper oxide to form copper acetate, which is then removed
by colloidal silica polishing particles. This can achieve a high
removal rate. The invention further proposes to use the phthalic
acid as the pH buffering agent and complexing agent in the slurry
to increase the polishing uniformity at the same time.
[0035] Although the disclosed embodiment uses colloidal silica as
the polishing particles in the slurry, other appropriate polishing
particles can be employed in the chemical etching agent to enhance
the removal rate and the uniformity.
[0036] Certain variations would be apparent to those skilled in the
art, which variations are considered within the spirit and scope of
the claimed invention.
* * * * *