U.S. patent application number 11/225999 was filed with the patent office on 2006-02-23 for semiconductor device with silicon dioxide layers formed using atomic layer deposition.
Invention is credited to Kang-soo Chu, Joo-won Lee, Jae-eun Park, Jong-ho Yang.
Application Number | 20060040510 11/225999 |
Document ID | / |
Family ID | 30772286 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060040510 |
Kind Code |
A1 |
Lee; Joo-won ; et
al. |
February 23, 2006 |
Semiconductor device with silicon dioxide layers formed using
atomic layer deposition
Abstract
Improved methods are disclosed for catalyst-assisted atomic
layer deposition (ALD) to form a silicon dioxide layer having
superior properties on a semiconductor substrate by using a first
reactant component consisting of a silicon compound having at least
two silicon atoms, or using a tertiary aliphatic amine as the
catalyst component, or both in combination, together with related
purging methods and sequencing.
Inventors: |
Lee; Joo-won; (Suwon-si,
KR) ; Park; Jae-eun; (Yongin-si, KR) ; Yang;
Jong-ho; (Seoul-si, KR) ; Chu; Kang-soo;
(Suwon-si, KR) |
Correspondence
Address: |
MILLS & ONELLO LLP
ELEVEN BEACON STREET
SUITE 605
BOSTON
MA
02108
US
|
Family ID: |
30772286 |
Appl. No.: |
11/225999 |
Filed: |
September 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10459943 |
Jun 12, 2003 |
|
|
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11225999 |
Sep 14, 2005 |
|
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Current U.S.
Class: |
438/787 ;
257/E21.279; 438/789 |
Current CPC
Class: |
H01L 21/31612 20130101;
H01L 21/3141 20130101; H01L 21/02277 20130101; H01L 21/02208
20130101; C23C 16/56 20130101; H01L 21/0228 20130101; H01L 21/02337
20130101; C23C 16/45534 20130101; H01L 21/0234 20130101; H01L
21/3122 20130101; H01L 21/02164 20130101; C23C 16/402 20130101 |
Class at
Publication: |
438/787 ;
438/789 |
International
Class: |
H01L 21/31 20060101
H01L021/31 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2002 |
KR |
02-39428 |
Jan 30, 2003 |
KR |
03-6370 |
Claims
1-36. (canceled)
37. A semiconductor device comprising a substrate having a highly
uniform, substantially impurity-free silicon dioxide thin film
having enhanced silicon richness along at least a surface thereof,
wherein said silicon dioxide thin film was formed by the steps of:
(a) loading the substrate into a chamber; (b) supplying a first
reactant, a catalyst, and optionally an inert gas to the chamber,
wherein said first reactant is a silicon halide compound having at
least two silicon atoms and said catalyst is selected from the
group consisting of ammonia and amine; (c) purging reaction
byproducts and unreacted first reactant and catalyst from the
chamber; (d) supplying a second reactant, a catalyst, and
optionally an inert gas to the chamber, wherein said second
reactant is a compound having 0 components and said catalyst is
selected from the group consisting of ammonia and amine; (e)
purging reaction byproducts and unreacted second reactant and
catalyst from the chamber; and, (f) repeating steps (a)-(e) until
the silicon dioxide thin film reaches the desired thickness.
38. A semiconductor device according to claim 37 wherein the method
of forming the silicon dioxide thin film further included the step
of using a tertiary aliphatic amine as the catalyst.
39. A semiconductor device according to claim 37 wherein the first
reactant was Si.sub.2Cl.sub.6.
40. A method according to claim 37 wherein said first reactant is
one selected from the group consisting of Si.sub.2X.sub.6,
Si.sub.3X.sub.8, Si.sub.4X.sub.10, and Si.sub.3X.sub.6 (Triangle),
wherein X is a halogen.
41. A semiconductor device according to claim 37 wherein said
catalyst is trimethyl amine.
42. A semiconductor device according to claim 37 comprising
carrying out steps (b) through (e) according to the following
sequence: feeding said first reactant and catalyst to said chamber
during a process time period t.sub.1; purging the chamber with an
inert gas during a time period t.sub.2 immediately following period
t.sub.1; pumping the chamber to at least partially evacuate inert
gas and other gaseous materials from the chamber during a time
period t.sub.3 immediately following period t.sub.2; feeding said
second reactant and catalyst to the chamber during a time period
t.sub.4 immediately following period t.sub.3; purging the chamber
with an inert gas during a time period t.sub.5 immediately
following period t.sub.4; and, pumping the chamber to at least
partially evacuate inert gas and other gaseous materials from the
chamber during a time period t.sub.6 immediately following period
t.sub.5.
43. A semiconductor device according to claim 37 comprising
carrying out steps (b) through (e) according to the following
sequence: feeding said first reactant and catalyst to said chamber
during a process time period t.sub.1; pumping the chamber to at
least partially evacuate gaseous materials from the chamber during
a time period t.sub.2 immediately following period t.sub.1; purging
the chamber with an inert gas during a time period t.sub.3
immediately following period t.sub.2; feeding said second reactant
and catalyst to the chamber during a time period t.sub.4
immediately following period t.sub.3; pumping the chamber to at
least partially evacuate gaseous materials from the chamber during
a time period t.sub.5 immediately following period t.sub.4; and,
purging the chamber with an inert gas during a time period t.sub.6
immediately following period t.sub.5.
44. A semiconductor device comprising at least a substrate having a
silicon dioxide layer deposited on a surface of said substrate
using a catalyst-assisted atomic layer deposition process
comprising the sequential steps of exposing a functionalized
surface of the substrate to a first mixture consisting essentially
of first reactant and first catalyst and thereafter exposing that
surface to a second mixture consisting essentially of second
reactant and second catalyst to form a silicon dioxide monolayer on
the substrate surface, and further comprising one or more of the
following: (a) using a first reactant consisting essentially of at
least one member selected from the group consisting of silicon
compounds having at least two silicon atoms; (b) using a first
catalyst consisting essentially of at least one member selected
from the group consisting of tertiary aliphatic amine compounds;
and, (c) using a first reactant consisting essentially of at least
one member selected from the group consisting of silicon compounds
having at least two silicon atoms in combination with using a first
catalyst consisting essentially of at least one member selected
from the group consisting of tertiary aliphatic amine
compounds.
45. A semiconductor device according to claim 44 wherein said first
reactant used in forming said silicon dioxide layer consists
essentially of a silicon-halide compound.
46. A semiconductor device according to claim 44 wherein said first
catalyst used in forming said silicon dioxide layer consists
essentially of a tertiary aliphatic amine compound having the
general formula NR.sub.3, where each R represents the same or a
different aliphatic group having from 1 to 5 carbon atoms.
47. A semiconductor device according to claim 44 wherein said first
reactant used in forming said silicon dioxide layer consists
essentially of Si.sub.2Cl.sub.6 and said first catalyst used in
forming said silicon dioxide layer consists essentially of
trimethyl amine.
48. A semiconductor device formed according to claim 44 wherein the
silicon dioxide layer deposition is carried out at a temperature
ranging from about 90.degree.-110.degree. C.
49. A semiconductor device formed according to claim 44 wherein the
silicon dioxide layer deposition is carried out at a pressure
ranging from about 500 mmtorr-5 torr.
50. A semiconductor device formed according to claim 44 wherein the
silicon dioxide layer deposition further includes removing
unreacted reactant, catalyst and reaction byproducts from the
region of the substrate surface following each reaction step.
51. A semiconductor device formed according to claim 44 wherein the
silicon dioxide layer deposition further includes: (a) a first
reaction period during which first reactant and catalyst are fed
through respective first reactant and catalyst feed lines to the
substrate surface along with inert gas fed through a second
reactant feed line; (b) a first purge period during which the feeds
of first reactant and catalyst are stopped and, instead, inert gas
is fed through the first and second reactant and catalyst feed
lines; (c) a second reaction period during which second reactant
and catalyst are fed through their respective feed lines to the
substrate surface along with inert gas fed through the first
reactant feed line; and, (d) a second purge period during which the
feeds of second reactant and catalyst are stopped and, instead,
inert gas is fed through the first and second reactant and catalyst
feed lines.
52. A semiconductor device formed according to claim 44, further
comprising repeating the silicon dioxide layer deposition multiple
times on the same substrate to obtain a silicon dioxide thin film
of a desired thickness greater than one monolayer.
53. A semiconductor device formed according to claim 44, further
comprising hardening the deposited silicon dioxide layer.
54. A semiconductor device formed according to claim 53 wherein
said hardening step is selected from one of the following: (a) a
thermal treatment comprising annealing the silicon dioxide layer at
about 300.degree. C.-900.degree. C. in the presence of an inert gas
selected from the group consisting of N.sub.2, O.sub.2, H.sub.2 and
Ar; (b) a plasma treatment comprising annealing the silicon dioxide
layer at about 200.degree. C.-700.degree. C. in the presence of
O.sub.2 or H.sub.2; or, (c) an ozone treatment comprising exposing
the silicon dioxide layer to O.sub.3 at a temperature of about
25.degree. C.-700.degree. C.
55. A substrate having a silicon dioxide thin film deposited on a
surface of said substrate by the steps of: (a) loading the
substrate into a chamber; (b) supplying a first reactant, a
catalyst, and optionally an inert gas to the chamber, wherein said
first reactant is a silicon-halide compound having at least two
silicon atoms and said catalyst is selected from the group
consisting of ammonia and amine; (c) purging reaction byproducts
and unreacted first reactant and catalyst from the chamber; (d)
supplying a second reactant, a catalyst, and optionally an inert
gas to the chamber, wherein said second reactant is a compound
having O components and said catalyst is selected from the group
consisting of ammonia and amine; (e) purging reaction byproducts
and unreacted second reactant and catalyst from the chamber; and,
(f) repeating steps (a)-(e) until the silicon dioxide thin film
reaches a desired thickness greater than one monolayer.
56. A substrate formed according to claim 55 wherein said first
reactant is Si.sub.2Cl.sub.6.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/459,943, filed on Jun. 12, 2003, which relies for priority
upon Korean Patent Application No. 02-39428, filed on Jul. 8, 2002
and Korean Patent Application No. 03-6370, filed Jan. 30, 2003, the
contents of which are herein incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to improved methods
for growing silicon dioxide layers on substrates, such as in
semiconductor manufacture, using atomic layer deposition processes.
The methods of this invention facilitate exercising extremely
precise control over the properties of a silicon dioxide layer
applied, for example, to a gate oxide or a dielectric layer. The
methods of this invention have particular utility in fabricating
gate spacers, gate oxides, silicide blocking layers, bit line
spacers, inter-level dielectric layers, etch stoppers, and related
final or intermediate products in semiconductor fabrication.
[0004] 2. Description of the Related Art
[0005] In manufacturing a semiconductor device, a silicon dioxide
layer is typically formed on a substrate surface by such
conventional techniques as chemical vapor deposition (CVD),
low-pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD). These
techniques are recognized as providing a good step coverage at a
comparatively low temperature. As the density of a semiconductor
device increases, however, so too do the heights of the respective
elements which comprise the device. As a result, a problem arises
due to increased pattern density variation and a corresponding
decrease in uniformity.
[0006] As taught in U.S. Pat. No. 6,090,442 (Klaus '442), which
patent is incorporated herein by reference, one approach to these
recognized problems was to use an atomic layer deposition (ALD)
technique. Klaus '442 teaches, however, that the big drawback to
ALD techniques was that they typically required temperatures
greater than 600.degree. K. and reactant exposures of greater than
10.sup.9 L (where 1 L=10.sup.-6 Torr sec) for the surface reactions
to reach completion. Such high temperature and high exposure
procedures are not desirable for ultra-thin film deposition
applications for various reasons including the difficulty of
carrying out such procedures.
[0007] An improved approach to such problems was taught by the
Klaus '442 patent. Klaus '442 provides a method for growing atomic
layer thin films on functionalized substrates at room temperatures
utilizing catalyzed binary reaction sequence chemistry. More
particularly, according to the Klaus '442 patent, a two-step atomic
layer deposition (ALD) process, using two catalyst-assisted
"half-reactions" carried out at room temperature, can be used to
grow a silicon dioxide film on an OH terminated substrate.
[0008] In a specific embodiment, Klaus '442 utilizes SiCl.sub.4 as
a "first molecular precursor" and pyridine as a catalyst. First,
the substrate is functionalized with OH.sup.- as a "first
functional group," for example using H.sub.2O. Next, the
functionalized substrate is exposed to a catalyst that is a Lewis
base or Lewis acid (e.g., pyridine) and a first molecular precursor
which includes the primary element of the film to be grown as well
as a second functional group (e.g., SiCl.sub.4). As described by
Klaus '442, in the first "half-reaction," the catalyst interacts
with the first functional group of the functionalized substrate;
then, the first molecular precursor reacts with the first
functional group (which has been activated by the catalyst)
resulting in a displacement of the catalyst and a bond between the
first functional group of the substrate and the primary element of
the first molecular precursor. Taken together, these two reactions
comprise the first "half-reaction" and represent the beginning of
film formation with the second functional group now located across
the surface of the film.
[0009] At this point in the Klaus '442 process, excess first
molecular precursor and any byproducts are purged from the reaction
chamber, and the partially-reacted substrate is exposed to
additional catalyst and a second molecular precursor. The catalyst
activates the exposed second functional group along the surface of
the film by reacting with it and with a second molecular precursor,
resulting in a displacement of the second functional group and also
resulting in a bond to the primary element of the first molecular
precursor. Now, the second molecular precursor reacts with the bond
between the primary element of the first molecular precursor and
the catalyst resulting in a displacement of the catalyst and the
deposition of the first functional group on the newly-grown surface
layer, thereby completing a full growth/deposition cycle and
restoring the substrate surface to a functionalized state in
preparation for the next cycle.
[0010] Although the catalyst-assisted deposition processes of the
Klaus '442 patent represent substantial advances in ALD technology,
and do make possible room-temperature ALD, it has been found that
the surface density, uniformity and quality of thin films grown
using the Klaus '442 technique will not meet increasingly demanding
standards in the semiconductor industry. With the seemingly
never-ending evolution toward ever-smaller microelectronic
components, ever-more precise control is required over the
properties of semiconductor devices. Such precision control
requires increasingly highly uniform surface properties and pattern
density. It has now been found that novel improvements in ALD
techniques in accordance with this invention produce thin films for
semiconductor devices having superior surface density and
significantly more uniform surface properties than could be
achieved with prior art methods resulting in surprisingly more
precise control over the properties of a thin film layer and in
higher quality semiconductor devices suitable for modern
miniaturization applications.
[0011] The Klaus '442 patent represents that: "Strong amine bases
like triethylamine ((C.sub.2H.sub.5).sub.3N) have been shown to
form salt compounds like triethylammonium chloride
(NH+(C.sub.2H.sub.5)3Cl--) in the presence of chlorosilanes. These
salts could poison the surface and degrade the reaction efficiency
as they build up." (column 9, line 24.about.28). Thus, Klaus '442
appears to teach away from the presence of triethylamine, i.e.
tertiary aliphatic amine, in ALD applications. But, in this
invention, control of process conditions coupled with a variety of
purge methods have been found to solve the above problems.
OBJECTS OF THE INVENTION
[0012] Accordingly, a general object of this invention is to
provide improved methods for using atomic layer deposition (ALD) to
grow highly uniform thin films having superior surface density,
extremely high purity, and with highly precise control of surface
properties.
[0013] A further object of this invention is to provide ALD methods
for forming silicon dioxide layers on a semiconductor substrate
using silicon compounds having at least two silicon atoms as one of
the reactant materials.
[0014] Still another object of this invention is to provide ALD
methods for forming silicon dioxide layers on a semiconductor
substrate using tertiary aliphatic amine compounds as a catalyst
material.
[0015] Yet another object of this invention is to provide optimum
temperature and pressure ranges for carrying out the methods of
this invention.
[0016] Another object of this invention is to provide
reaction/purging process sequences, and timing and techniques for
carrying out such deposition cycles, to enhance the benefits of the
methods of this invention.
[0017] Still another object of this invention is to provide methods
for hardening a silicon dioxide thin film formed on a substrate by
the methods of this invention.
[0018] Yet another object of this invention is to provide improved
semiconductor devices having a substrate with a silicon dioxide
layer which has superior surface density and is of extremely high
purity and uniformity deposited along a surface of the substrate
for use in such applications as gate spacers, gate oxides, silicide
blocking layers, bit line spacers, interlevel dielectric layers,
etch stoppers, and the like.
[0019] A specific object of this invention is to provide
catalyst-assisted ALD methods for forming silicon dioxide layers on
a semiconductor substrate using Si.sub.2Cl.sub.6 as the first
reactant, or using a tertiary aliphatic amine as the catalyst, or
both.
[0020] These and other objects, advantages and improvements of the
present invention will be better understood by the following
description which is to be read in conjunction with the several
Figures and Drawings as discussed hereinafter.
SUMMARY OF THE INVENTION
[0021] The invention consists of improved methods for using
catalyst-assisted atomic layer deposition (ALD) to form silicon
dioxide thin films having enhanced properties and purity on
semiconductor substrates. In one invention embodiment, a silicon
compound having at least two silicon atoms, e.g., Si.sub.2Cl.sub.6,
is used as the first reactant in an ALD process. In a second
invention embodiment, a tertiary aliphatic amine compound, e.g.,
trimethyl amine, is used as the catalyst in an ALD process. In a
third invention embodiment, a silicon compound having at least two
silicon atoms is used as the first reactant and a tertiary
aliphatic amine is used as the catalyst in an ALD process. In other
invention embodiments, methods for hardening the deposited silicon
dioxide thin films are provided, optimum temperature and pressure
conditions for carrying out the methods of this invention are
established, and alternative reaction/purging process sequences for
the methods of this invention are described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a flow chart that schematically illustrates the
steps of the ALD methods of this invention for forming a silicon
dioxide thin film on a substrate.
[0023] FIG. 2 is a schematic illustration of the several chemical
reaction steps, showing what is theorized to be the underlying
chemistry, on which the improved ALD methods of this invention are
based.
[0024] FIG. 3 compares the silicon dioxide deposition rate on a
substrate for an ALD method according to this invention with that
for a prior art ALD process.
[0025] FIG. 4 compares the silicon "richness" of a thin film
SiO.sub.2 layer formed on a substrate using an ALD method according
to this invention with that for a prior art ALD process.
[0026] FIG. 5A compares the silicon bonding status of silicon in a
SiO.sub.2 monolayer formed using an ALD method according to this
invention with that for a prior art ALD process. FIG. 5B
schematically illustrates what is theorized to be the different
silicon chemical bonding arrangements which account for the
differences in bonding status established by FIG. 5A.
[0027] FIG. 6 compares the wet etch rate of a SiO.sub.2 thin film
formed using an ALD method according to this invention with that
for a prior art ALD process.
[0028] FIG. 7 is a chromatograph confirming the formation of
unwanted particulate byproducts having Si--N bonds when an ALD
process is carried out according to prior art teachings using a
catalyst containing one or more N--H bonds.
[0029] FIG. 8 illustrates a gas pulsing method of supplying
reactant and catalyst feeds to the reactant chamber in accordance
with one embodiment of this invention.
[0030] FIG. 9-12 illustrate alternative possible representative
"recipes" or sequencing cycles for gas pulsing/pumping and/or
purging to be used in carrying out ALD methods in accordance with
this invention.
[0031] FIG. 13 illustrates how the SiO.sub.2 deposition rate on a
substrate using an ALD method in accordance with this invention
varies in relation to process temperature.
[0032] FIG. 14 illustrates how the impurity content (as measured by
carbon present) of a SiO.sub.2 thin film formed using an ALD method
in accordance with this invention varies in relation to process
temperature.
[0033] FIG. 15 illustrates how the SiO.sub.2 deposition rate on a
substrate using an ALD method in accordance with this invention
varies in relation to process pressure.
[0034] FIG. 16 illustrates how the non-uniformity of a SiO.sub.2
thin film formed using an ALD method in accordance with this
invention varies in relation to process pressure.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] Table 1 below is a summary comparing the theoretical
chemical reactions underlying the prior art high-temperature ALD
technique and the catalyst-assisted ALD technique of the Klaus '442
patent with three illustrative embodiments of the present
invention, as described hereinafter. TABLE-US-00001 TABLE 1
High-Temperature ALD Si--OH* + SiCl.sub.4 .fwdarw.
Si--O--Si--Cl.sub.3* + HCl Si--Cl* + H.sub.2O.fwdarw. Si--OH* + HCl
Klaus '442 patent Si--OH* + C.sub.5H.sub.5N + SiCl.sub.4 .fwdarw.
Si--O--Si--Cl.sub.3* + HCL + C.sub.5H.sub.5N Si--O--Si--Cl.sub.3* +
C.sub.5H.sub.5N + H.sub.2O .fwdarw. Si--O--OH* + HCl +
C.sub.5H.sub.5N Present Invention: Si--OH* + Si.sub.2Cl.sub.6 +
C.sub.5H.sub.5N 1st ex. embodiment .fwdarw.
Si--O--Si(Cl.sub.2)--Si--Cl.sub.3* + HCl + C.sub.5H.sub.5N
Si--O--Si(Cl.sub.2)--Si--Cl.sub.3* + C.sub.5H.sub.5N + H.sub.2O
.fwdarw. Si--O--Si--O--Si--OH* + HCl + C.sub.5H.sub.5N Present
Invention: Si--OH* + SiCl.sub.4 + R.sub.3N 2nd ex. embodiment
.fwdarw. Si--O--Si--Cl.sub.3* + HCl + C.sub.5H.sub.5N
Si--O--Si--Cl.sub.3* + R.sub.3N + H.sub.2O .fwdarw. Si--O--Si--OH*
+ HCl + C.sub.5H.sub.5N Present Invention: Si--OH* +
Si.sub.2Cl.sub.6+ R.sub.3N 3rd ex. embodiment .fwdarw.
Si--O--Si(Cl.sub.2)--Si--Cl.sub.3* + HCL + R.sub.3N
Si--O--Si(Cl.sub.2)--Si--Cl.sub.3* + R.sub.3N + H.sub.2O .fwdarw.
Si--O--Si--O--Si--OH* + HCl + R.sub.3N (Wherein the asterisk*
designates the surface species)
[0036] Table 2 below is a summary of illustrative combinations of
catalyst, first reactant and second reactant corresponding to
different illustrative embodiments of the present invention as
described hereinafter. TABLE-US-00002 TABLE 2 2.sup.nd Catalyst
1.sup.st reactant reactant 1st ex. Ammonia, amine Si.sub.2Cl.sub.6
H.sub.2O, embodiment H.sub.2O.sub.2, ozone 2nd ex. Tertiary
aliphatic amine SiCl.sub.4 H.sub.2O, embodiment (R.sub.3N)
H.sub.2O.sub.2, ozone 3rd ex. Tertiary aliphatic amine
Si.sub.2Cl.sub.6 H.sub.2O, embodiment (R.sub.3N) H.sub.2O.sub.2,
ozone
[0037] FIG. 1 is a flow chart that schematically illustrates the
several steps, procedures and sequential chemical reactions which
apply generically to the methods of this invention for forming
silicon dioxide thin films on a substrate by means of a catalyzed
atomic layer deposition (ALD) procedure. The steps illustrated in
the flow chart of FIG. 1 are discussed below.
Step 110
[0038] A suitable functionalized substrate is loaded into a
reaction chamber.
Step 120
[0039] The substrate is preheated until the temperature of the
substrate reaches a suitable temperature for starting the silicon
dioxide ALD process, typically about 25.degree.-150.degree. C. The
reaction chamber is exhausted either at the same time as or
immediately following the preheating. Evacuating the chamber might
typically take under 60 seconds.
Step 130
[0040] A new silicon dioxide layer is formed on the substrate
surface by ALD. The cycle is repeated until a desired thickness of
a silicon dioxide thin film is grown on the substrate. Step 130 is
comprised of substeps 132-138, which are discussed individually
below.
Steps 132-138
Step 132
[0041] A mixture of the first reactant and catalyst is supplied to
the reaction chamber. The catalyst acts by lowering reaction
activation energy of the first reactant on the substrate. As a
result, the process temperature is lowered to about room
temperature or slightly above room temperature.
[0042] When the first reactant is supplied, the process temperature
in the chamber is typically about 25.degree.-150.degree. C.,
preferably about 90.degree.-110.degree. C. The process pressure in
the chamber is typically about 0.1.about.100 torr, preferably about
0.5.about.5 torr. An inert gas, for example, argon (Ar), may be
supplied to the chamber along with first reactant and catalyst.
[0043] The H of the --OH reaction sites reacts with a halogen atom
of the first reactant in the presence of the first base catalyst to
form halogen acid. The halogen acid is neutralized with the first
base catalyst, and a salt is produced. At the same time, Si atoms
of the first reactant react with the 0 on a reaction site on the
substrate to form a chemisorbed layer of the first reactant.
Step 134
[0044] By-products of the first reaction process (step 132), for
example, salt, unreacted first reactant, etc. are removed.
Step 136
[0045] A mixture of the second reactant (which contains O and H)
and a second base catalyst is now supplied to the chamber causing
the chemisorbed layer of the first reactant to chemically react
with the second reactant.
[0046] An example of the second reactant is H.sub.2O,
H.sub.2O.sub.2, or ozone. In one preferred embodiment, the second
base catalyst is the same as the first base catalyst.
[0047] When the second reactant is supplied to the reaction
chamber, the ranges of temperature and pressure in the chamber are
typically substantially the same as the ranges of temperature and
pressure used in step 132.
[0048] In this step, the O element of the second reactant reacts
with Si which is chemisorbed on the substrate surface. In the
presence of the second base catalyst, the H element of the second
reactant reacts with the halogen atom, so halogen acid is produced.
Salt is then produced by neutralization between such halogen acid
and the base catalyst.
Step 138
[0049] The by-products of the second reaction process (step 136)
are removed.
Step 140
[0050] The reaction chamber is exhausted to remove any remaining
deposition by-products in the chamber, a step desirably completed
in about 90 seconds. During step 140, no gas is supplied to the
chamber.
Step 150
[0051] The substrate with an SiO.sub.2 thin film along its surface
is unloaded from the chamber.
Step 160
[0052] This step involves hardening the newly deposited SiO.sub.2
thin film. There are three alternative methods which may be used
for hardening the silicon dioxide layer deposited in accordance
with this invention. [0053] 1. Thermal treatment: Annealing the
substrate at about 300.degree. C.-900.degree. C. in the presence of
a substantially inert gas (i.e., inert relative to the substrate
surface), e.g., N.sub.2, O.sub.2, H.sub.2, Ar, etc. [0054] 2.
Plasma treatment: Annealing the substrate at about 200.degree.
C.-700.degree. C. in the presence of O.sub.2 or H.sub.2. [0055] 3.
O.sub.3 treatment, typically at about 25.degree. C.-700.degree.
C.
[0056] Any of the three foregoing hardening methods may be used in
situ with SiO.sub.2 thin films grown using a catalyzed ALD process
in accordance with this invention. Hardening methods 2 and 3 above
have been found to work especially well.
First Exemplary Embodiment
[0057] According to a first exemplary embodiment of the present
invention, silicon dioxide thin films are grown on the
functionalized surface of a substrate having hydroxyl groups using
Si.sub.2Cl.sub.6 or a comparable compound, e.g., a silicon halide
having two or more silicon atoms, as the first reactant; a compound
containing 0 and H elements, e.g., H.sub.2O and/or H.sub.2O.sub.2,
as the second reactant; and a base compound, e.g., ammonia or an
amine, as the catalyst. For this embodiment of the invention, the
first reactant is a silicon compound having at least two silicon
atoms, for example a silicon-halide compound selected from the
group consisting of: Si.sub.2X.sub.6, Si.sub.3X.sub.8,
Si.sub.4X.sub.10, and Si.sub.3X.sub.6 (Triangle), which has the
following chemical structure: ##STR1## wherein X is a halogen such
as F, Cl, Br, I. In a preferred embodiment, the first reactant is
selected from the group consisting of Si.sub.2Cl.sub.6,
Si.sub.3Cl.sub.8, Si.sub.4Cl.sub.10 and Si.sub.3Cl.sub.6(Triangle).
For this embodiment of the invention, the second reactant is a
compound containing oxygen (O) and hydrogen (H) components selected
from the group consisting of H.sub.2O; H.sub.2O.sub.2; and
ozone.
[0058] As schematically illustrated in FIG. 2, by exposing the
hydroxyl group functionalized surface of the substrate to a mixture
of the first reactant and the catalyst in a first step, a
chemisorbed layer of the first reactant is formed along the
substrate surface. Unreacted first reactant and byproducts are then
removed from the region of the substrate. In the next process step,
also illustrated in FIG. 2, the chemisorbed layer of the first
reactant is reacted with the second reactant in the presence of a
base compound as the catalyst, which may be the same catalyst used
in reacting the first reactant or a different base compound
catalyst. Unreacted second reactant and byproducts of this second
reaction step are removed from the substrate region. The surface of
the substrate, now containing a new SiO.sub.2 monolayer, is
restored to the hydroxyl group functionalized state ready to begin
a new ALD cycle.
[0059] Although the foregoing process is generally similar to the
catalyst-assisted ALD technique described in the Klaus '442 patent,
the selection of different reactants and catalyst(s) has been found
to have dramatic and surprising impacts on the nature and quality
of the thin film surface layer of the substrate. One important
difference is that whereas the Klaus '442 patent teaches the use of
SiCl.sub.4, a silicon halide having only a single silicon atom, the
above-described embodiment of the present invention utilizes a
silicon halide, e.g., Si.sub.2Cl.sub.6, that has at least two
silicon atoms. It has been found in accordance with this invention
that this difference results in a significant improvement in the
growth rate. In particular, it has been found that a SiCl.sub.4
monolayer has large spaces between the molecules. In the case of
SiCl.sub.4, when a Si atom reacts with the O--H site on the
substrate and forms a single bond with O, SiCl.sub.4 is rotated.
Due to the steric hindrance of Cl (which does not participate in
the reaction), the next O--H site cannot react with another
SiCl.sub.4. By contrast, a Si.sub.2Cl.sub.6 monolayer can react
with two Si atoms at the same time and thus speeds up the ALD
process. Furthermore, the quality of the resulting silicon dioxide
layer is better because the molecular packing along the surface is
denser.
[0060] FIGS. 3-6, as discussed further below, compare the
properties and performance of SiO.sub.2 monolayers grown on a
substrate using the hexachlorodisilicon (HCD) method of this
invention with SiO.sub.2 monolayers grown using the
tetrachlorosilicon (TCS) method of Klaus '442.
[0061] For example, the graph in FIG. 3 compares the deposition
rates of SiO.sub.2 monolayers on a substrate utilizing the prior
art SiCl.sub.4 approach with those obtained utilizing the
Si.sub.2Cl.sub.6 technique of this invention at varying process
temperatures. FIG. 3 shows that, at every process temperature, the
deposition rate utilizing Si.sub.2Cl.sub.6 (circular points) is
approximately double the deposition rate using SiCl.sub.4 (square
points).
[0062] FIG. 4 compares the "silicon richness" of a thin film layer
grown on a substrate using the prior art TCS (SiCl.sub.4) approach
with that of a thin film grown using the HCD (Si.sub.2Cl.sub.6)
approach of this invention. Using Auger electron spectroscopy to
measure atomic concentrations of Si and 0 on the substrate surface
at varying sputter times, FIG. 4 shows that the ratio of Si to O
using the TCS technique is 1:1.95 while the Si to O ratio using the
HCD technique is 1:1.84. In other words, the thin film SiO.sub.2
layer which is formed using the HCD approach is desirably "richer"
in silicon.
[0063] FIG. 5A uses XPS data to compare the silicon bonding status
of silicon in a SiO.sub.2 monolayer grown using the HCD approach of
this invention with the bonding status of silicon in a monolayer
grown using the prior art TCS method. The difference in bonding
status seen in the graph of FIG. 5A, as well as the difference in
silicon "richness" shown by FIG. 4, is believed to be explained by
the different type of silicon bonds formed when the SiO.sub.2
monolayer is grown by the HCD method instead of the TCS method. As
schematically illustrated in FIG. 5B, the TCS method is believed to
result in adjacent silicon atoms in a SiO.sub.2 monolayer being
bonded to each other only through an intermediate oxygen atom,
whereas the HCD method of this invention is believed to result in
at least some direct Si--Si bonding in the SiO.sub.2 monolayer.
[0064] FIG. 6 compares the wet etch rate of SiO.sub.2 thin films
formed using the HCD method of this invention with the wet etch
rate for SiO.sub.2 thin films formed using the prior art TCS
method. (The vertical scale of the bar graph of FIG. 6 has been
made discontinuous to accommodate the data.) FIG. 6 shows that the
wet etch rate of SiO.sub.2 thin films formed using the HCD method
of this invention is about six times better than for SiO.sub.2 thin
films formed using the TCS method.
Second Exemplary Embodiment
[0065] According to a second exemplary embodiment of this present
invention, silicon dioxide thin films are grown on a functionalized
surface of a substrate using a silicon halide as the first
reactant; a second reactant containing O and H atoms, e.g.,
H.sub.2O and/or H.sub.2O.sub.2; and a tertiary aliphatic amine
catalyst. In this embodiment of the invention, by exposing the
functionalized surface of the substrate to a mixture of the first
reactant and the catalyst in a first process step, a chemisorbed
layer of the first reactant is formed along the substrate surface.
Unreacted first reactant and byproducts are then removed from the
region of the substrate. In the next process step, the chemisorbed
layer of the first reactant is reacted with the second reactant in
the presence of the tertiary aliphatic amine catalyst. Byproducts
of this second reaction step are removed from the substrate
region.
[0066] In accordance with this invention embodiment, it has been
found that the use of a tertiary aliphatic amine as the reaction
catalyst produces novel and entirely unexpected benefits in terms
of process efficiency, the elimination or minimization of unwanted
byproducts, and in the purity and quality of resultant SiO.sub.2
thin films deposited on the substrate. More particularly, it has
been found that if an amine which has even one nitrogen-hydrogen
(N--H) bond, for example ammonia (NH.sub.3) or a unitary or binary
aliphatic amine (NR, H.sub.2 or NR.sub.2H), is used as the
catalyst, there will be a tendency to form unwanted byproducts
having silicon-nitrogen (Si--N) bonds, as illustrated in equations
(1) and (2) below:
SiCl.sub.4+NR.sub.2H.fwdarw.Cl.sub.3Si--NR.sub.2+HCl
SiCl.sub.4+NH.sub.3.fwdarw.Cl.sub.3Si--NH.sub.4.sup.+Cl.sup.-(salt)
(2) wherein R is an aliphatic group (C.sub.xH.sub.y) having between
about 1 and 5 carbon atoms, and further wherein the aliphatic
groups R may be the same or different.
[0067] It has been found, however, that byproducts having Si--N
bonds (for example, as illustrated on the right sides of equations
(1) and (2) above) are main causes of particulate formation which
leads to surface layer impurities and degrades the quality of the
deposited SiO.sub.2 thin films. By contrast, if a tertiary
aliphatic amine catalyst having the general formula NR.sub.3, where
R is an aliphatic group (C.sub.xH.sub.y) having between about 1 and
5 carbon atoms, is used as the reaction catalyst, it has been found
that substantially no particulate byproducts having Si--N bonds are
formed. As a result, much purer SiO.sub.2 thin films having higher
quality and superior uniformity are deposited by the methods of
this invention.
[0068] FIG. 7 and Table 3 as discussed below demonstrate the
validity and the enormous importance of this finding. FIG. 7 is a
result of RGA analysis that confirms the formation of solid
particulate byproducts when an ALD process is carried out using an
amine catalyst that is not a tertiary aliphatic amine. FIG. 7 is
based on a catalyzed ALD process as taught by Klaus '442 using
SiCl.sub.4 as the first reactant with dimethylamine
((H.sub.3C).sub.2NH), an amine with a single N--H bond, as the
catalyst. A residual mass spectrum apparatus was connected to the
ALD reaction chamber to analyze byproducts coming from the
reaction. The mass spectrum of FIG. 7 confirmed the formation of
Cl.sub.3Si--N(CH.sub.3).sub.2 as an unwanted byproduct of the
reaction. Such byproduct formation means that some of the Si from
the SiCl.sub.4 first reactant is being wasted in forming the
byproduct instead of being deposited on the substrate surface as
SiO.sub.2.
[0069] Further evidence of the advantage of this invention
embodiment relative to the prior art is shown in Table 3 below.
TABLE-US-00003 TABLE 3 Triethylamine Catalyst Trimethylamine
Dimethylamine NH3 Particle Several tens Several thousands Tens of
thousands (size .16 .mu.m) @Tencor
[0070] Table 3 compares the number of undesired particles (having a
size of at least 0.16 .mu.m) which were deposited on substrate
surfaces of the same area when catalyzed ALD was carried out using
SiCl.sub.4 as a first reactant with different amines as the
catalyst. Table 3 shows that using ammonia (NH.sub.3) as the ALD
catalyst, a molecule with three vulnerable N--H bonds, the ALD
process resulted in tens of thousands of byproduct particles on the
surface of the SiO.sub.2 thin film. This very high level of
particulate contamination on an SiO.sub.2 thin film adversely
affects performance of the semiconductor device and is completely
unacceptable for many of the most demanding modern semiconductor
applications.
[0071] Table 3 also shows that the use of dimethylamine as the ALD
catalyst, a molecule with only one vulnerable N--H bond, is
effective in somewhat reducing the production of particulate
byproduct by about one order of magnitude. Even particulate
production in the thousands range on an SiO.sub.2 thin film, as
obtained with dimethylamine catalyst, is still far in excess of
acceptable limits for very high performance semiconductor devices.
Table 3 further shows, however, that the use of trimethylamine as
the ALD catalyst, thereby eliminating all vulnerable N--H bonds,
has the dramatic and unexpected result of reducing the production
of particles of byproduct to only several tens, a three order of
magnitude reduction relative to ammonia, and a two order of
magnitude reduction even relative to dimethylamine.
[0072] Another advantage of this embodiment of the invention
relative to the prior art is that this invention embodiment uses a
tertiary aliphatic amine catalyst instead of the pyridine which is
the preferred catalyst for example in the Klaus '442 patent.
Pyridine is a heterocyclic compound containing a ring of five
carbon atoms and one nitrogen atom having the formula
C.sub.5H.sub.5N. It exists at room temperature as a toxic liquid
having a pungent, characteristic odor, which must be carefully
handled. When used as a catalyst in an ALD process, pyridine must
be vaporized to the gaseous state (the boiling point of pyridine is
115.5.degree. C.). Thus, the equipment for treating pyridine is
complicated, and a pyridine supply line is easily contaminated.
[0073] By contrast, a low molecular weight tertiary aliphatic
amine, for example trimethylamine, is a gas at ambient conditions,
which makes it easier to use than a catalyst prone to undergo a
phase change at normal reaction conditions. Furthermore, the
toxicity of trimethylamine is much lower than that of pyridine and
the boiling point of trimethylamine is only 3.about.4.degree.
C.)
Third Exemplary Embodiment
[0074] According to a third particularly preferred embodiment of
the present invention, many if not all of the advantages and
benefits of both of the earlier-described embodiments of this
invention can be realized. In this embodiment, silicon dioxide thin
films are grown on a functionalized surface of a substrate using a
silicon compound having at least two or more silicon atoms, e.g., a
silicon halide such as Si.sub.2Cl.sub.6, as the first reactant; a
compound containing O and H atoms, e.g., H.sub.2O and/or
H.sub.2O.sub.2, as the second reactant; and, a tertiary aliphatic
amine catalyst.
[0075] Thus, in accordance with this invention embodiment, the
functionalized surface of the substrate is exposed to a mixture of
the first reactant and the tertiary aliphatic amine catalyst in a
first process step to form a chemisorbed layer of the first
reactant along the substrate surface. Unreacted first reactant and
any byproducts are then removed from the region of the substrate.
In the next process step, the chemisorbed layer of the first
reactant is reacted with the second reactant in the presence of the
tertiary aliphatic amine catalyst. Byproducts of this second
reaction step are removed from the substrate region.
[0076] In still another embodiment of the present invention, it has
been found that the use of a gas pulsing/purging method for one or
more of the several process steps 132-138 of FIG. 1 can improve the
efficiency of the methods of this invention, reduce process
contamination, as well as improve the quality of resulting
SiO.sub.2 thin films grown on substrates. FIG. 8 illustrates a gas
pulsing method for carrying out steps 132-138 of FIG. 1, as
described below.
Step 132
[0077] A first reactant and a suitable catalyst are flowed into the
reaction chamber through separate respective supply lines. At this
time, inert gas, for example, argon gas, can be flowed into the
chamber through a second reactant supply line to prevent the
contamination from the mixture gas of first reactant and a
catalyst.
Step 134
[0078] Inert gas for purging flows into the chamber through each of
the first reactant supply line, the second reactant supply line,
and the catalyst supply line.
Step 136
[0079] A second reactant which contains O and H, and a suitable
catalyst are flowed into the chamber through separate respective
supply lines. At this time, inert gas, for example, argon gas, can
be flowed into the chamber through the first reactant supply line
to purge the first reactant supply line.
Step 138
[0080] Inert gas for purging flows into the chamber through each of
the first reactant supply line, the second reactant supply line,
and the catalyst supply line.
[0081] Some representative "recipes" or sequences for gas
pulsing/pumping or purging the various feed lines and the reactant
chamber in accordance with steps 132-138 of FIG. 1 over 10 second
process time intervals are illustrated in FIGS. 9-12. FIG. 9
illustrates a process purge sequence comprising the following steps
per cycle being conducted at and over selected process time periods
using an inert gas to purge and remove byproducts: 0-2 seconds
process time--HCD feeding; 2-4 seconds process time--purging; 4-7.5
seconds process time-H.sub.2O feeding; and 7.5-10 seconds--purging.
FIG. 10 illustrates a process pumping sequence, wherein the pumping
pressure is lower than the first and second reactant supply
pressures, comprising the sequenced steps per cycle of: 0-2 seconds
process time--HCD feeding; 2-4 seconds process time--pumping; 4-7.5
seconds process time--H.sub.2O feeding; and 7.5-10 seconds process
time--pumping. FIG. 11 illustrates a process purge-pumping
sequence, wherein pumping is used after purging, comprising the
sequences steps per cycle of: 0-2 seconds process time--HCD
feeding; 2-3 seconds process time--purging; 3-4 seconds process
time--pumping; 4-7.5 seconds process time--H.sub.2O feeding;
7.5-8.5 seconds process time--purging; and 8.5-10 seconds process
time--pumping. FIG. 12 illustrates a process pumping--purge
sequence, wherein purging is used after pumping, comprising the
sequenced steps per cycle of: 0-2 seconds process time--HCD
feeding; 2-3 seconds process time--pumping; 3-4 seconds process
time--purging; 4-7.5 seconds process time--pumping; 7.5-8.5 seconds
process time pumping; and 8.5-10 seconds process time--purging.
[0082] In yet another embodiment of the present invention,
temperature conditions for carrying out catalyst-assisted ALD for
growing SiO.sub.2 thin films on substrates according to this
invention are optimized by balancing two competing process
parameters. On the one hand, as illustrated in FIG. 13, the
deposition rate for forming SiO.sub.2 thin films using
catalyst-assisted ALD and a multiple-silicon atom compound (e.g.,
Si.sub.2Cl.sub.6) as the first reactant is inversely proportional
to temperature. FIG. 13 shows that, in general, the higher the
process temperature, the slower the deposition rate. This appears
to be due to desorption rate, and it is a distinctive feature of an
ALD process because ALD is a surface reaction. The higher the
process temperature, the higher the surface desorption activation
energy of atoms participating in the reaction. As a result, the
"staying time" at the surface becomes shorter than the necessary
minimum time for the reaction to take place, in accordance with the
following equation: k.sub.d=Ae.sup.-E.sup.d.sup./RT [0083] kd:
Desorption Rate [0084] A: Arrhenius Constant [0085] Ed: Desorption
Activation Energy [0086] R: Gas Constant [0087] T: Temperature
[0088] The higher the process temperature, the more easily the O--H
chain at the substrate surface is dehydroxylated. Thus, the number
of reaction sites along the surface is reduced, and the deposition
rate is reduced.
[0089] On the other hand, as illustrated in FIG. 14, a SIMS
(secondary ion mass spectrometer) graph of carbon content over time
at three different process temperatures, the carbon content of an
ALD-deposited SiO.sub.2 thin film also varies according to process
temperature. In general, at lower process temperatures,
carbon-containing byproducts of the ALD reaction processes are not
fully removed from the substrate surface during processing and
become trapped in the SiO.sub.2 thin films being deposited. The
resulting increase in the impurity level of the thin films results
in a lower quality semiconductor device.
[0090] Accordingly, these two process parameters must be balanced
against one another to optimize the process temperature conditions.
Based on the foregoing considerations, it has been determined in
accordance with this embodiment of the invention that the optimum
process temperature range is about 90.degree.-110.degree. C.
[0091] In still another embodiment of the present invention,
pressure conditions for carrying out catalyst-assisted ALD for
growing SiO.sub.2 thin films on substrates according to this
invention are optimized by balancing two competing process
parameters. On the one hand, as illustrated in FIG. 15, the
deposition rate for forming SiO.sub.2 thin films using
catalyst-assisted ALD is directly proportional to process condition
pressure, i.e., the higher the pressure, the thicker the layer of
SiO.sub.2 deposited over a given time period/number of ALD
cycles.
[0092] On the other hand, FIG. 16 illustrates that a non-linear
relationship exists between process pressure and non-uniformity of
the SiO.sub.2 thin film. Thus, FIG. 16 shows that, up to a point,
higher process pressure reduces non-uniformity of the layers
deposited; but, beyond that point, higher pressure is correlated
with higher non-uniformity.
[0093] Accordingly, these process parameters must be balanced
against each other to optimize the process pressure conditions.
Based on the foregoing considerations, it has been determined in
accordance with this embodiment of the invention that the optimum
process pressure range is about 500 mmtorr-5 torr.
[0094] It will be apparent to those skilled in the art that other
changes and modifications may be made in the above-described
improved catalyst-assisted ALD formation of SiO.sub.2 thin layers
on substrate surfaces for use in high performance semiconductor
devices without departing from the scope of the invention described
herein, and it is intended that all matter contained in the above
description shall be interpreted in an illustrative and not a
limiting sense.
* * * * *