The present invention provides a method of removing silicon nitride at about the same removal rate as silicon dioxide by CMP. The method utilizes a polishing slurry that includes colloidal silica abrasive particles dispersed in water and additives that modulate the silicon dioxide and silicon nitride removal rates such that they are about the same. In one embodiment of the invention, the additive is lysine or lysine mono hydrochloride in combination with picolinic acid, which is effective at a pH of about 8. In another embodiment of the invention, the additive is arginine in combination with picolinic acid, which is effective at a pH of about 10

Babu, Suryadevara V.

Natarajan, Anita

NASA Technical Reports Server

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(12) United States Patent 	 (io) Patent No.:	 US 7,629,258 B2
Babu et al.	 (45) Date of Patent:	 *Dec. 8, 2009
(54) METHOD FOR ONE-TO-ONE POLISHING OF
SILICON NITRIDE AND SILICON OXIDE
(75) Inventors: Suryadevara V. Babu, Potsdam, NY
(US); Anita Natarajan, Potsdam, NY
(US)
(73) Assignees: Clarkson University, Potsdam, NY
(US); Infotonics Technology Center
Inc., Canandaigua, NY (US)
(*) Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 9 days.
This patent is subject to a terminal dis-
claimer.
(21) Appl. No.: 11/562,453
(22) Filed:	 Nov. 22, 2006
(65)	 Prior Publication Data
US 2008/0116172 Al	 May 22, 2008
(51) Int. Cl.
HOIL 211302	 (2006.01)
HOIL 211461	 (2006.01)
(52) U.S. Cl . ........................ 438/691; 438/692; 438/693
(58) Field of Classification Search ....................... None
See application file for complete search history.
(56)	 References Cited
U.S. PATENT DOCUMENTS
6,436,834 B1 8/2002 Lee et al.
6,491,843 B1 12/2002 Srin et al.
6,533,832 B2 3/2003 Steckenrider et al.
6,544,892 B2 4/2003 Srinivasan et al.
6,702,954 B1 3/2004 Her et al.
7,005,382 B2 2/2006 Nishimoto et al.
2003/0110710 Al* 6/2003 Oshima et al .	 ................	 51/307
2003/0176151 Al 9/2003 Tam et al.
2004/0132305 Al 7/2004 Nishimoto et al.
2004/0152309 Al 8/2004 Carter et al.
2004/0186206 Al 9/2004 Yoneda et al.
2005/0028450 Al 2/2005 Xu et al.
2005/0042877 Al* 2/2005 Salfelder et al .	 ............ 438/691
2005/0079709 Al * 4/2005 Delehanty et al............ 438/689
2005/0136673 Al 	 6/2005 Xu et al.
2006/0216935 Al * 	 9/2006 Oswald et al . .............. 438/691
2007/0093182 Al * 	 4/2007 Kollodge ..................... 451/41
OTHER PUBLICATIONS
Natarajan, Anita; Hedge, Sharath; and Babu, S.V.; Selective chemi-
cal-mechanical planarization of polysilicon during fabrication of
MEMS devices; poster; Mar. 28,2005; exhibited during the Materials
Research Society Spring Meeting in San Francisco, California.
Carter, Philip W.; and Johns, Timothy P.; Interfacial Reactivity
Between Ceria and Silicon Dioxide and Silicon Nitride Surfaces,
Organic Additive Effects; Electrochemical and Solid-State Letters, 8
G218-G221 (2005); The Electrochemical Society, Inc.
Anjur, Sriram; Dysard, Jeffrey; Feeney; Paul; Johns, Timothy;
Kason, Mark; Perez, Maria; and Romine, Richard; Selective Silicon
Nitride Polishing; presentation paper; Oct. 10, 2006; 2006 Interna-
tional Conference on Planarization/CMP Technology; Foster City,
California.
Kim, Sang-Kyun; Sohn, Hyung-Min; Paik, Ungyu; Katoh, Takeo;
and Park, Jea-Gun; A Reverse Selectivity Ceria Slurry for the Dama-
scene Gate Chemical Mechanical Planarization Process; Japanese
Journal ofApplied Physics, vol. 43, Not. I IA, 2004, pp. 7434-7438;
The Japan Society of Applied Physics.
Commonly Owned Application Serial No. 11562443, filed Nov. 22,
2006.
Commonly Owned Application Serial No. 11562447, filed Nov. 22,
2006.
* cited by examiner
Primary Examiner Duy-Vu N Deo
(74) Attorney, Agent, or Firm Rankin, Hill & Clark LLP
(57)	 ABSTRACT
The present invention provides a method of removing silicon
nitride at about the same removal rate as silicon dioxide by
CMP. The method utilizes a polishing slurry that includes
colloidal silica abrasive particles dispersed in water and addi-
tives that modulate the silicon dioxide and silicon nitride
removal rates such that they are about the same. In one
embodiment of the invention, the additive is lysine or lysine
mono hydrochloride in combination with picolinic acid,
which is effective at a pH of about 8. In another embodiment
of the invention, the additive is arginine in combination with
picolinic acid, which is effective at a pH of about 10.
5 Claims, No Drawings
https://ntrs.nasa.gov/search.jsp?R=20100006893 2019-08-30T08:52:48+00:00Z
US 7,629,258 B2
1
METHOD FOR ONE-TO-ONE POLISHING OF
SILICON NITRIDE AND SILICON OXIDE
The U.S. Government has a paid-up license in this inven-
tion and the right in limited circumstances to require the
patent owner to license others on reasonable terms as pro-
vided for by the terms of Grant No. NAG3-2744 awarded by
NASA. The Government has certain rights in the invention.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to compositions and methods
for removing silicon nitride and silicon dioxide at about the
same removal rate by chemical-mechanical polishing.
2. Description of Related Art
Silicon nitride is widely used as a barrier layer and/or as an
etch stop layer to protect underlying devices from being
removed during chemical-mechanical polishing (CMP) in
integrated circuit (IC) fabrication. Accordingly, most CMP
polishing slurries and processes have attempted to minimize
the silicon nitride removal rate while attaining relatively high
removal rates for other layers. CMP polishing slurries and
processes that are highly selective for silicon dioxide in pref-
erence to silicon nitride have been developed and utilized in
the shallow trench isolation (STI) manufacturing process.
There are emerging technologies in the semiconductor
industry where it would be advantageous to have CMP slur-
ries and processes whereby the removal rate of silicon nitride
is about the same as the removal rate of silicon dioxide.
Suppressing the silicon dioxide removal rate while at the
same time achieving a substantially equal silicon nitride
removal rate is immensely challenging because the removal
of silicon nitride via CMP typically follows a mechanism in
which the surface of the silicon nitride is hydrolyzed to silicon
dioxide (Si3N4+6H20-3Si02+4NH3), which is then
removed during CMP. Accordingly, additives conventionally
used in CMP slurries to suppress the silicon dioxide removal
rate tend to suppress the silicon nitride removal rate because
the silicon nitride is converted to silicon dioxide and removed
as such.
SUMMARY OF INVENTION
The present invention provides a method of removing sili-
con nitride at about the same removal rate as silicon dioxide
by CMP. The method utilizes a polishing slurry that includes
colloidal silica abrasive particles dispersed in water and addi-
tives that modulate the silicon dioxide and silicon nitride
removal rates such that they are about the same. In one
embodiment of the invention, the additive is lysine or lysine
mono hydrochloride in combination with picolinic acid,
which is effective at a pH of about 8. In another embodiment
of the invention, the additive is arginine in combination with
picolinic acid, which is effective at a pH of about 10. Appli-
cants hypothesize that the positively charged amino acid con-
stituent of the additive (lysine mono hydrochloride, lysine
and arginine) becomes adsorbed on the negatively charged
silica abrasive particles and the silicon dioxide film. This
would typically cause suppression of the silicon dioxide
removal rate due to electrostatic repulsion. However, the pres-
ence of picolinic acid in the slurry increases the silicon diox-
ide removal rate. The combination of arginine and lysine with
picolinic acid is used in order to modulate the silicon dioxide
removal rate such that it is equal to the silicon nitride removal
rate.
2
On the other hand, lysine at pH 8 may not adsorb on the
silicon nitride film as pH 8 is far from the IEP of silicon nitride
(9.7), and arginine adsorbs on the siliconnitride film at pH 10.
In both cases, picolinic acid adsorbs to the silicon nitride film,
5 and silica abrasives when used with picolinic acid enhance
the silicon nitride removal rate. The lysine coated silica abra-
sive also contributes to the increase in the silicon nitride
removal rate. The compositions of the positively charged
amino acids and picolinic acid are chosen such that the silicon
io dioxide and silicon nitride removal rates are about the same.
The foregoing and other features of the invention are here-
inafter more fully described and particularly pointed out in
the claims, the following description setting forth in detail
certain illustrative embodiments of the invention, these being
15 indicative, however, of but a few of the various ways in which
the principles of the present invention may be employed.
DETAILED DESCRIPTION OF THE PREFERRED
EMBODIMENTS
20
The method of the present invention comprises disposing a
polishing slurry between a polishing pad and a surface com-
prising silicon nitride (sometimes abbreviated as "Si3N4")
and silicon dioxide (sometimes abbreviated as "S'0 2") and
25 pressing the polishing pad against the surface while the pol-
ishing pad and surface are moving relative to each other with
the polishing slurry disposed therebetween to remove silicon
nitride and silicon dioxide from the surface at about the same
removal rate.
30 The removal rates are about the same when the ratio of the
removal rate of silicon dioxide to silicon nitride is suitably in
the range of about 0.3 to about 3, desirably in the range of
about 0.5 to about 2, preferably in the range of about 0.7 to
about 1.3, and most preferably about 1.
35 The silicon nitride and/or the silicon dioxide can be in the
form of a surface film, which may overly or lay next to a film
of the other material. The surface may also comprise one or
more additional materials, such as polysilicon, for example.
The poli shing slurry used in accordance with the method of
4o the invention preferably comprises colloidal silica abrasive
particles dispersed in water and additives that modulate the
silicon dioxide and silicon nitride removal rates such that they
are about the same.
45 Desirable additive compounds include organic compounds
containing an alpha-amino carboxylic acid functional group
and an additional functional group, wherein the additional
functional group comprises an amino group or a guanidine
group.
50 Organic compounds that have an amino group and an acid
group attached to the same carbon are referred to as alpha-
amino carboxylic acids. Many alpha-amino carboxylic acid
compounds are known and there are twenty "natural' amino
acids, that is, amino acids that are used as basic components
55 of proteins in living organisms.
In addition to an amino acid functional group, desirable
additive compounds have an additional functional group,
which can be protonated and consequently can acquire a
positive charge. Useful functional groups include amino
60 groups and guanidine groups. In particular, primary amino
groups having a pKa of about 9.0 or greater are desirable.
An example of a compound having both an alpha-amino
carboxylic acid functional group and an additional amino
functional group is lysine. Arginine is an example of a com-
65 pound having both an alpha-amino carboxylic acid functional
group and an additional guanidine substituent. In one
embodiment the additive compound is selected from the
US 7,629,258 B2
3
group consisting of arginine, lysine and lysine mono hydro-
chloride. Illustrative useful compounds are listed below.
H2N
/CH—CH2—CHz—CHz—CHz—NH2
H02C
lysine
HZN\
H—CH2—CH2—CH2—NH2
H02C
	
H2 N	 C H3/CH—CH2—CH—CH2—CH2—NH2
H02C
H2 \
CH—CH2—CH—CH—CH2—NH2
	
H02C	 CH2CONHCH3
	
Hz \	 /NH2
C
H— CH2— CH2 — CH2 — NH — C^
H02C	 NH
arginine
H2N	 NH2
CH_ CH2 — cx2—cx2— cx2— NH — C^
H02C	 NH
	
H2N	 CH2O00H3
H — CH2 — CH — CH2 — CH2 —
 NH2
H02C
In one embodiment of the invention, the additive includes
an alpha -amino carboxylic acid compound containing an
additional amino group, and the pH of the slurry is in the
range of about 7.5 to about 8.5, that is, about 8±0.5. In another
embodiment of the invention, the additive includes an alpha-
amino carboxylic acid compound containing an additional
guanidine group, and the pH of the slurry is in the range of
about 9.5 to about 10.5, that is, about 10±0.5.
In addition to the additive compound, a second compound
is also present, wherein the second compound is picolinic
acid or a derivative thereof. Useful derivatives of picolinic
acid include compounds of formula 1, wherein r r -r4 indepen-
dently represent hydrogen or a substituent such as, for
example, a substituted or unsubstituted alkyl group, such as a
methyl or ethyl group, a halogen, such as a chloro group, or a
substituted or unsubstituted aromatic group such as a phenyl
group. In one desirable embodiment, r r -r4 represent hydrogen
and formula 1 represents picolinic acid.
r3
r2 /	 r4
r 1	 N	 CO2H
In one embodiment of the invention, the additive is lysine
or lysine mono hydrochloride, which is effective at a pH of
4
about 8. In another embodiment of the invention, the additive
is arginine in combination with picolinic acid, which is effec-
tive at a pH of about 10.
The colloidal silica particles present in the polishing slurry
5 preferably have a mean average diameter of from about 25 nm
to about 75 nm, and more preferably of about 50 nm.
The amino acid component of the additive (the first com-
pound) is preferably present in an amount from about 1.0% to
about 4.0% by weight, and more preferably, from about 2.0%
io to about 3.0% by weight. The second compound, picolinic
acid or a derivative thereof, is typically added in an amount
from about 1.0% to about 3.0% by weight. The composition
of the polishing pad is not per se critical, and conventional
polishing equipment can be used.
15 Applicants hypothesize that lysine or lysine mono hydro-
chloride and arginine are positively charged at pH 8 and 10
respectively. In both instances, the silicon dioxide surface
(i.e., the surface of the colloidal silica abrasive particles and
any silicon dioxide surface films) are negatively charged.
20 Therefore, due to electrostatic interactions, the positively
charged amino acid component will adsorb onto the colloidal
silica abrasive as well as on any silicon dioxide surface films.
This would typically cause suppression of the silicon dioxide
removal rate due to electrostatic repulsion. However, thepres-
25 ence of picolinic acid in the slurry increases the silicon diox-
ide removal rate. The combination of arginine and lysine with
picolinic acid is used in order to modulate the silicon dioxide
removal rate such that it is equal to the silicon nitride removal
rate.
30 On the other hand, lysine at pH 8 may not adsorb on the
silicon nitride film as pH 8 is far from the IEP of silicon nitride
(9.7), and arginine adsorbs on the siliconnitride film at pH 10.
In both cases, picolinic acid, which has a pKa of about 6,
adsorbs to the silicon nitride film, and silica abrasives when
35 used with picolinic acid enhance the silicon nitride removal
rate. The lysine coated silica abrasive also contributes to the
increase in the silicon nitride removal rate. The compositions
of the positively charged amino acids and picolinic acid are
chosen such that the silicon dioxide and silicon nitride
4o removal rates are about the same.
Another aspect of the invention includes a device including
silcon, for example, a device including silicon dioxide or
silicon nitride, fabricated by the methods of the present inven-
tion. Examples of useful devices include integrated circuits,
45 micro-electro -mechanical devices, and micro -opto-electro-
mechanical (MEMS) devices.
The following examples are intended to illustrate the
invention without limiting it in any way. All raw materials
referenced in the examples are standard pigment grade pow-
5o ders unless otherwise indicated.
EXAMPLE
Five CMP slurries were separately prepared by dispersing
55 10% by weight of colloidal silica particles having a mean size
of about 50 nm in water. The additives listed in Table 1 below
in weight percent were added to the respective CMP slurries
(where "Lys" means lysine; `Arg" means arginine; "LysHCP'
means lysine mono hydrochloride; and "Pico' means
60 picolinic acid). The pH of the CMP slurries was adjusted as
shown in Table 1 below by adding a sufficient amount of
potassium hydroxide.
The CMP slurries were then separately used to polish blan-
ket silicon dioxide and silicon nitride films for one minute
65 using a Westech-372 polisher using a down force as shown in
Table 1, a carrier/platen speed of 75/75 rpm, a slurry flow rate
of 200 ml/min and an IC-1400, k-groove polishing pad. The
US 7,629,258 B2
5
polishing pad was conditioned for one minute before every
polishing experiment. The removal rates of reported in Table
1 are an average of the removal rates of two wafers each of
silicon dioxide and silicon nitride.
TABLE 1
S 13N4
RR
Operating S'02 RR	 (nm/	 Selectivity
Sample Additive	 pH Pressure mrn/min)	 min)	 Si02:Si3N4
IA None	 9	 4 psi	 32 ± 8	 12 ± 3	 —2.7
113 Lys-	 8	 4psi	 62±14 59±10	 —1
lwt%
Pico -
0.5 wt %
1C LysHCI -	 8	 4 psi	 57 ± 4	 64 ± 10	 —0.9
2wt%
Pico -
lwt%
1D LysHCI -	 8	 4 psi	 73 ± 17 55 ± 10	 —1.3
1 Wt %
Pico -
lwt%
lE Arg-	 10	 4psi	 5±3	 6±2	 —0.8
Wt %
Pico -
0.5 wt %
The data in Table 1 shows that it is possible to use colloidal
silica-based slurries to remove silicon nitride and silicon
dioxide at about the same removal rate by CMP.
Additional advantages and modifications will readily
occur to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and illus-
trative examples shown and described herein. Accordingly,
various modifications may be made without departing from
6
the spirit or scope of the general inventive concept as defined
by the appended claims and their equivalents.
What is claimed is:
1. A method for removing silicon nitride and silicon diox-
5 ide from a surface, the method comprising:
a) providing a polishing slurry having a pH of about 8±0.5
that comprises colloidal silica abrasive particles dis-
persed in water and an additive comprising:
i) about 1.0% to about 4.0% by weight of lysine mono
10	 hydrochloride; and
ii) picolinic acid or a derivative thereof,
b) disposing the polishing slurry between a polishing pad
and the surface; and
c) pressing the polishing pad against the surface while the
15 polishing pad and surface are moving relative to each
other with the polishing slurry disposed therebetween to
remove silicon nitride from the surface at about the same
rate as silicon dioxide is removed from the surface.
2. The method according to claim 1 wherein the polishing
20 slurry comprises from about 5% to about 15% by weight of
silica particles having a mean average diameter of from about
25 nm to about 75 nm.
3. The method according to claim 1 wherein the polishing
slurry comprises from about 1.0% to about 3.0% by weight of
25 picolinic acid.
4. The method according to claim 1 wherein the polishing
slurry comprises about 10% by weight of silica particles
having a mean average diameter of about 50 nm and from
about 1% to about 3% by weight of lysine mono hydrochlo-
3o ride.
5. The method according to claim 4 wherein the polishing
slurry comprises from about 1.0% to about 3.0% by weight of
picolinic acid.


Method for one-to-one polishing of silicon nitride and silicon oxide

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