U.S. patent application number 10/023175 was filed with the patent office on 2002-09-12 for process for the chemical-mechanical polishing of isolation layers produced using the sti technology, at elevated temperatures.
Invention is credited to Chen, Li-Mei, Min, Chun-Kuo, Puppe, Lothar, Vogt, Kristina.
Application Number | 20020127954 10/023175 |
Document ID | / |
Family ID | 7667929 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020127954 |
Kind Code |
A1 |
Vogt, Kristina ; et
al. |
September 12, 2002 |
Process for the chemical-mechanical polishing of isolation layers
produced using the STI technology, at elevated temperatures
Abstract
A process for the chemical-mechanical polishing of isolation
layers based on the shallow trench isolation (STI) technology,
using a basic polishing slurry which contains from about 5 to about
12.5% by weight of a colloidal silica abrasive, characterized in
that the polishing slurry is applied to the wafer surface at a
temperature of about 35.degree. C. to about 80.degree. C.,
increases the polishing selectivity with regard to the rate at
which silica is removed compared to the rate at which silicon
nitride is removed.
Inventors: |
Vogt, Kristina; (Koln,
DE) ; Puppe, Lothar; (Burscheid, DE) ; Min,
Chun-Kuo; (Taipei, TW) ; Chen, Li-Mei;
(Hsinchu, TW) |
Correspondence
Address: |
BAYER CORPORATION
PATENT DEPARTMENT
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
7667929 |
Appl. No.: |
10/023175 |
Filed: |
December 17, 2001 |
Current U.S.
Class: |
451/41 ;
257/E21.244 |
Current CPC
Class: |
C09G 1/02 20130101; H01L
21/31053 20130101 |
Class at
Publication: |
451/41 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2000 |
DE |
10063492.3 |
Claims
What is claimed is:
1. A chemical-mechanical polishing process comprising applying a
basic polishing slurry containing from about 5 to about 12.5% by
weight of a colloidal silica abrasive to a wafer surface at a
temperature ranging from about 35.degree. C. to about 80.degree. C.
and polishing the wafer surface.
2. The process according to claim 1, wherein the polishing slurry
is applied at a temperature ranging from about 65.degree. C. to
about 75.degree. C.
3. The process according to claim 1, wherein the polishing slurry
contains from about 6 to about 10% by weight of a colloidal silica
abrasive.
4. The process according to claim 1, wherein the polishing slurry
contains from about 8 to about 15% by weight of a metal
fluoride.
5. The process according to claim 4, wherein the metal fluoride is
selected from the group consisting of lithium fluoride, sodium
fluoride and potassium fluoride.
6. The process according to claim 5, wherein the metal fluoride is
potassium fluoride.
7. The process according to claim 1, wherein the process polishes a
composite material which contains silica and silicon nitride.
8. The process according to claim 1, wherein the pH at 22.degree.
C. of the polishing slurry is higher than about 10.5.
9. The process according to claim 1, wherein the colloidal silica
has a mean particle size ranging from about 10 nm to about 1
.mu.m.
10. A process comprising applying, at a temperature ranging from
about 35.degree. C. to about 80.degree. C., a basic polishing
slurry containing from about 5 to about 12.5% by weight of a
colloidal silica abrasive to a surface of a wafer comprising a
trench filled with SiO.sub.2 and surface covered with a film of
silica and polishing the wafer surface.
11. The process according to claim 10, wherein the polishing slurry
is applied at a temperature ranging from about 65.degree. C. to
about 75.degree. C.
12. The process according to claim 10, wherein the polishing slurry
contains from about 6 to about 10% by weight of a colloidal silica
abrasive.
13. The process according to claim 10, wherein the polishing slurry
contains from about 8 to about 15% by weight of a metal
fluoride.
14. The process according to claim 4, wherein the metal fluoride is
selected from the group consisting of lithium fluoride, sodium
fluoride and potassium fluoride.
15. The process according to claim 5, wherein the metal fluoride is
potassium fluoride.
16. The process according to claim 10, wherein the process polishes
a composite material which contains silica and silicon nitride.
17. The process according to claim 10, wherein the pH at 22.degree.
C. of the polishing slurry is higher than about 10.5.
18. The process according to claim 10, wherein the colloidal silica
has a mean particle size ranging from about 10 nm to about 1
.mu.m.
19. In a shallow trench isolation process in which a trench is
filled with SiO.sub.2, a wafer surface is covered with a film of
silica and in which planarization is carried out with a
chemical-mechanical polishing, the improvement comprising applying
to the wafer surface at a temperature ranging from about 35.degree.
C. to about 80.degree. C. a basic polishing slurry containing from
5 to 12.5% by weight of a colloidal silica abrasive and polishing
the wafer surface.
Description
BACKGROUND
[0001] The present invention relates to a process for the
chemical-mechanical polishing of SiO.sub.2 isolation layers
produced using the STI (shallow trench isolation) technology, and
in particular to a polishing process which is carried out at
elevated temperatures.
[0002] Nowadays, chemical-mechanical polishing (CMP) is a preferred
method in the fabrication of integrated circuits (ICs) in order to
achieve global planarization on wafers. A wafer is a polished disc
of silicon on which integrated circuits are constructed. First of
all, a polishing slurry is applied to an elastomeric polishing pad
or directly to the wafer surface which is to be polished. The
polishing pad is then pressed against the surface which is to be
polished and, in the process, is moved relative to the wafer plane,
so that the particles of the polishing slurry are pressed onto the
wafer surface. The movement of the polishing pad causes the
polishing slurry to be distributed and therefore causes the
particles on the wafer surface to be distributed, leading to
chemical and mechanical removal of the substrate surface.
[0003] Polishing slurries can be divided into two categories. One
category comprises a suspension of pyrogenic silica as abrasive,
and the other category contains colloidal silica as abrasive. The
methods for preparing the polishing slurries from pyrogenic silica
and from colloidal silica, also known as silica sol, are different.
The suspension of pyrogenic silica is obtained by dispersing
pyrogenic silica in an aqueous medium. For polishing slurries which
contain colloidal silica, the colloidal silica is produced
directly, by means of the sol-gel technique, from an aqueous
solution, e.g. from a sodium silicate solution. At no time during
production is the colloidal silica in a dry state which may lead to
agglomeration or aggregation, as is the case with the pyrogenic
silica. The suspension of pyrogenic silica has a wider particle
size distribution than the polishing slurry from the colloidal
silica category. This leads to the particles of the polishing
slurry comprising pyrogenic silica agglomerating or forming a
sediment during storage and/or polishing, which additionally leads
to a non-uniform particle size distribution. Therefore, when using
the polishing slurry comprising pyrogenic silica, defects such as
surface roughness and microscratches are produced on the polished
semiconductor surface. The seriousness of this phenomenon increases
if the line width of the IC component falls to 0.25 .mu.m or 0.18
.mu.m or below. Therefore, the polishing slurry belonging to the
colloidal silica category is becoming increasingly widespread.
[0004] In integrated semiconductor technology, it is usually
necessary for a plurality of active and passive elements within the
integrated circuit structure to be isolated from one another. This
is often achieved using the STI technique, which is able to resolve
the problems of field oxide diffusion which occurs in the LOCOS
process and of mechanical stresses and has the advantage of
resulting in a good isolating action and of increasing the
integration density and planarization of the IC component.
Therefore, STI has become the principal isolation technique used
for the 0.18 .mu.m CMOS technology.
[0005] The STI technique comprises the generation of a narrow
trench in the silicon, filling the narrow trench with silica
(SiO.sub.2), with the entire wafer surface at the same time being
covered with a film of silica, followed by planarization using the
CMP technique. It is customary for a harder silicon nitride
(Si.sub.3N.sub.4) film previously to have been formed beneath the
silica film which is to be polished, so that the silicon nitride
film acts as a stop layer during the polishing. An ideal polishing
slurry which is eminently suitable for use is, on the one hand,
able to effectively polish the silica film above the narrow trench
without, on the other hand, polishing off the silicon nitride film.
This means that it is desirable to use a polishing slurry in which
the rate of polishing of the silica film is as high as possible and
the rate of polishing of the silicon nitride film is virtually
zero.
[0006] An index which is customarily used to assess the rate of
polishing of silica on silicon nitride is the polishing
selectivity, which is defined by dividing the polishing rate of
silica by the polishing rate of silicon nitride. If a polishing
slurry with a low SiO.sub.2/Si.sub.3N.sub- .4 selectivity is used
to polish the SiO.sub.2 which is situated above the trench, what is
known as dishing of the SiO.sub.2 and erosion of the
Si.sub.3N.sub.4 occur.
[0007] In current IC fabrication, the selectivity of the CMP
polishing slurries used is not sufficiently high. Therefore, one
shortens the duration of polishing and, to avoid the problem known
as dishing of the SiO.sub.2, uses the reactive ion etching (RIE)
technique. However, this combined RIE+CMP process lengthens the
overall production time by approximately 40% and therefore
increases production costs.
[0008] Various polishing slurries have been developed for
increasing the polishing selectivity with regard to the rate at
which silica is removed compared to the rate at which silicon
nitride is removed. U.S. Pat. No. 4,526,631 describes a polishing
slurry comprising 6% by weight of colloidal silica, which is set to
a pH at 22.degree. C. of approximately 12 using KOH, with a
polishing ratio of approximately 10 SiO.sub.2 to 1 Si.sub.3N.sub.4.
In U.S. Pat. No. 5,738,800, the polishing composition for polishing
a combination of silica and silicon nitride contains an aromatic
compound which forms complexes with silica and silicon nitride. In
U.S. Pat. No. 5,759,917, the composition comprises ammonium cerium
nitrate, acetic acid and pyrogenic silica. In U.S. Pat. No.
5,733,819, the polishing composition contains fine silicon nitride
powder, water and an acid. In EP-A-853 335, the composition
comprises pyrogenic silica as abrasive, a tetramethyl-ammonium salt
and hydrogen peroxide. EP-A 853 110 provides an alkalized polishing
slurry for improving the polishing selectivity, this slurry
containing a fluoride salt.
[0009] Therefore, the object of the present invention is to solve
the above problems and to provide a process for chemical-mechanical
polishing which has a high polishing selectivity in terms of the
rate at which the silica is removed compared to the rate at which
silicon nitride is removed.
[0010] The above-mentioned object is achieved by a process for the
chemical-mechanical polishing of isolation layers based on the STI
technology, using a basic polishing slurry which contains from 5 to
12.5% by weight of a colloidal silica abrasive, characterized in
that the polishing slurry is applied to the wafer surface at a
temperature of 35.degree. C. to 80.degree. C.
[0011] After the STI technique has been carried out, i.e. after the
narrow trenches have been produced and the silica has subsequently
been deposited, the polishing in accordance with the present
invention is carried out by applying a polishing slurry to the
wafer surface at a temperature of from 35.degree. C. to 80.degree.
C., in order to planarize the semiconductor surface. In particular,
the process according to the invention is used to polish a
composite material which contains silica and silicon nitride. In
particular, the process is used to polish a dielectric film, such
as for example a silica film, which is formed on a silicon nitride
film. The silicon nitride film is used as a stop layer.
SUMMARY
[0012] The invention relates to a chemical-mechanical polishing
process comprising applying a basic polishing slurry containing
from about 5 to about 12.5% by weight of a colloidal silica
abrasive to a wafer surface at a temperature ranging from about
35.degree. C. to about 80.degree. C. and polishing the wafer
surface.
[0013] In one embodiment, the invention relates to a process
comprising applying, at a temperature ranging from about 35.degree.
C. to about 80.degree. C., a basic polishing slurry containing from
about 5 to about 12.5% by weight of a colloidal silica abrasive to
a wafer surface comprising a trench filled with SiO.sub.2 and
surface covered with a film of silica with and polishing the wafer
surface. These and other features, aspects, and advantages of the
present invention will become better understood with reference to
the following description and appended claims.
DESCRIPTION
[0014] The novel feature of the present invention consists in the
fact that the polishing is carried out at elevated temperature. The
polishing temperature is preferably 65.degree. C. to 75.degree. C.
The hydrolysis reactions of both silica and silicon nitride are
exothermic. Therefore, when the polishing temperature is increased,
the polishing rates of both silica and silicon nitride decrease.
However, the polishing rate of silicon nitride decreases to a
greater extent than that of silica. Therefore, the polishing
selectivity with regard to the rate at which silica is removed
compared to the rate at which silicon nitride is removed can be
improved by increasing the polishing temperature.
[0015] With the polishing slurry used in the present invention, the
colloidal silica abrasive is preferably present in a quantity of
from 6 to 10% by weight. The colloidal silica may have a mean
particle size of 10 nm to 1 .mu.m, preferably 20 nm to 100 nm.
[0016] The mean particle size is determined in an
ultracentrifuge.
[0017] The polishing slurry may furthermore contain 8 to 15% by
weight, preferably 8 to 12% by weight, of a metal fluoride.
Examples of particularly suitable metal fluorides are lithium
fluoride, sodium fluoride and potassium fluoride.
[0018] The polishing slurry used in the present invention is basic.
The pH at 22.degree. C. of the polishing slurry is preferably
higher than 10.5.
[0019] The following examples are intended to explain the process
and the advantages of the present invention more completely,
without restricting the scope thereof, since numerous modifications
and variations will be evident to the person skilled in the art.
All parts and percentages are by weight unless otherwise
indicated.
EXAMPLES
[0020] The polishing slurries of the examples and comparative
examples were produced in accordance with the instructions given
below. The polishing slurries were used to polish films on silicon
wafers by means of a Westech-372 polishing machine, the films
comprising either low-pressure CVD silica (SiO.sub.2) or
low-pressure CVD silicon nitride (Si.sub.3N.sub.4). The results are
given in Table 1. The polishing rate is calculated by dividing the
difference in thickness before and after the polishing by the
polishing duration, the film thickness being measured by Nanospec.
The polishing selectivity is calculated by dividing the polishing
rate of silica by the polishing rate of silicon nitride.
Example 1
[0021] Levasil.RTM. 50 CK, a colloidal polishing slurry of the
silica category procured from Bayer AG, Leverkusen, was diluted
with deionized water, resulting in a polishing slurry containing
7.5% by weight of colloidal silica. The mean particle size of the
colloidal silica is 60 to 90 nm, and the specific surface area is
50 to 180 m.sup.2/g. The pH at 22.degree. C. of the polishing
slurry was 11.8. The polishing was carried out at 65.degree. C. The
results are given in Table 1.
Example 2
[0022] Levasil.RTM. 50 CK was diluted with deionized water, so that
a polishing slurry containing 6% by weight of colloidal silica was
obtained. 8% by weight of potassium fluoride was added to the
dilute suspension and thorough mixing was carried out. The pH at
22.degree. C. of the polishing slurry was 11.2. The polishing was
carried out at 35.degree. C. The results are given in Table 1.
Comparative Example 1
[0023] The same processes as in Example 1 were used, except that
the polishing was carried out at 25.degree. C. The results are
given in Table 1.
Comparative Example 2
[0024] The same processes as in Example 2 were used, except that no
potassium fluoride was added and the polishing was carried out at
25.degree. C. The results are given in Table 1.
Comparative Example 3
[0025] SS 25, a polishing slurry procured from Cabot
Microelectronics, Aurora, Ill., USA containing pyrogenic silica was
diluted with deionized water, so that a polishing slurry containing
7.5% by weight of silica was obtained. The pH of the polishing
slurry was 11.2. The polishing was carried out at 25.degree. C. The
results are given in Table 1.
Comparative Example 4
[0026] The same processes as in Comparative Example 3 were used,
except that the polishing slurry employed contains 6% by weight of
silica. The results are given in Table 1.
1TABLE 1 Silica Potassium fluoride Polishing concentration
concentration temperature Polishing rate Polishing Examples Silica
source (% by weight) (% by weight) (.degree. C.) pH (.ANG./min)
selectivity Example 1 Colloidal Silica 7.5% 0 65 11.8 1179 11
Example 2 Colloidal Silica 6% 8% 35 11.2 930 7.8 Comp. Ex. 1
Colloidal Silica 7.5% 0 25 11.8 755 3 Comp. Ex. 2 Colloidal Silica
6% 0 25 11.2 472 1.5 Comp. Ex. 3 Pyrogenic Silica 7.5% 0 25 11.2
780 2.5 Comp. Ex. 4 Pyrogenic Silica 6% 0 25 11.2 450 1.2
[0027] It can be seen from the above examples that, on account of
the increase in the polishing temperature, the polishing
selectivity of a polishing slurry belonging to the colloidal silica
category can be increased in terms of the rate at which silica is
removed compared to the rate at which silicon nitride is removed.
Furthermore, the selectivity can also be improved through the
addition of the metal fluoride.
[0028] The above description of the preferred embodiments of this
invention has been given for reasons of explanation and
description. Evident modifications or variations are possible in
view of the above teaching. The embodiments have been selected and
described in order to offer the best illustration of the principles
of this invention and its practical application and, in this way,
to enable the person skilled in the art to employ the invention in
various embodiments and using various modifications which are
appropriate to the specific use intended. All modifications and
variations lie within the scope of the present invention.
* * * * *