U.S. patent application number 10/938789 was filed with the patent office on 2005-02-24 for method of etching and etching apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Adachi, Kenji, Kobayashi, Noriyuki.
Application Number | 20050042876 10/938789 |
Document ID | / |
Family ID | 27800249 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050042876 |
Kind Code |
A1 |
Kobayashi, Noriyuki ; et
al. |
February 24, 2005 |
Method of etching and etching apparatus
Abstract
Silicon oxide film having, as a sublayer, a silicon nitride film
layer serving as a protective film layer for gate formed on silicon
substrate is etched by introducing a processing gas including a
gaseous mixture containing at least C.sub.4F.sub.6, Ar, O.sub.2 and
N.sub.2 into an airtight processing chamber and carrying out a
plasma treatment in a self-alignment contact process, thereby
forming contact hole. For the processing gas, e.g., the ratio of
N.sub.2 gas flow rate to C.sub.4F.sub.6 gas flow rate ranges from
25/8 to 85/8, the ratio of O.sub.2 and N.sub.2 gas flow rate to
C.sub.4F.sub.6 gas flow rate ranges from 15/4 to 45/4 and the ratio
of N.sub.2 gas flow rate to O.sub.2 gas flow rate ranges from 5 to
17. Accordingly, stable contact holes of high aspect ratio
exhibiting desirable control characteristics is formed while
minimizing etching the silicon nitride film, a protective film
layer for gate.
Inventors: |
Kobayashi, Noriyuki;
(Yamanashi, JP) ; Adachi, Kenji; (Hsin-chu City,
TW) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
27800249 |
Appl. No.: |
10/938789 |
Filed: |
September 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10938789 |
Sep 13, 2004 |
|
|
|
PCT/JP03/02870 |
Mar 11, 2003 |
|
|
|
Current U.S.
Class: |
438/690 ;
257/E21.252; 257/E21.507; 438/691 |
Current CPC
Class: |
H01L 21/31116 20130101;
H01L 21/76897 20130101 |
Class at
Publication: |
438/690 ;
438/691 |
International
Class: |
H01L 021/00; H01L
021/302; H01L 021/461 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2002 |
JP |
2002-66343 |
Claims
What is claimed is:
1. An etching method, in which a processing gas is fed into an
airtight processing chamber to generate a plasma therein and a
silicon-containing oxide film formed on an object to be processed
disposed in the processing chamber is selectively etched against a
silicon nitride film, wherein the processing gas is a gaseous
mixture including at least a fluorocarbon-based gas, a first
deposit removing gas and a second deposit removing gas having a
weaker deposit removing capability than the first deposit removing
gas.
2. The etching method of claim 1, wherein an etching selectivity of
the silicon-containing oxide film to the silicon nitride film is
set to a predetermined value by a ratio of a total flow rate of the
first and the second deposit removing gas to a flow rate of the
fluorocarbon-based gas, and a ratio of a flow rate of the second
deposit removing gas to the flow rate of the fluorocarbon-based
gas.
3. The etching method of claim 1, wherein the silicon-containing
oxide film is a silicon oxide film.
4. The etching method of claim 1, wherein the fluorocarbon-based
gas is a C.sub.4F.sub.6 gas, the first deposit removing gas is an
oxygen gas and the second deposit removing gas is a nitrogen
gas.
5. The etching method of claim 4, wherein, in the processing gas, a
ratio of a flow rate of the N.sub.2 gas to a flow rate of the
C.sub.4F.sub.6 gas is greater than or equal to about 25/8 and less
than or equal to about 85/8, and a ratio of a total flow rate of
O.sub.2 and N.sub.2 to the flow rate of the C.sub.4F.sub.6 gas is
greater than or equal to about 15/4 and less than or equal to about
45/4.
6. The etching method of claim 4, wherein, in the processing gas, a
ratio of a flow rate of the N.sub.2 gas to a flow rate of the
C.sub.4F.sub.6 gas is greater than or equal to about 25/8 and less
than or equal to about 85/8, and a ratio of the flow rate of the
N.sub.2 gas to a flow rate of the O.sub.2 gas is greater than or
equal to about 5 and less than or equal to about 17.
7. The etching method of claim 1, wherein the processing gas
includes an inert gas.
8. The etching method of claim 1, wherein an upper and a lower
electrode are installed opposite to face each other in the
processing chamber, a first high frequency power is applied to the
upper electrode and a second high frequency power is applied to the
lower electrode, a frequency of the second high frequency power is
lower than that of the first high frequency power.
9. The etching method of claim 8, wherein the frequency of the
first high frequency power is about 60 MHz and that of the second
high frequency power is about 2 MHz.
10. The etching method of claim 3, wherein the silicon nitride film
exists under the silicon oxide film.
11. The etching method of claim 10, wherein the silicon oxide film
is etched in a self-alignment contact process.
12. An etching apparatus, in which a processing gas is fed into an
airtight processing chamber to generate a plasma therein and a
silicon-containing oxide film formed on an object to be processed
disposed in the processing chamber is selectively etched against a
silicon nitride film, wherein the processing gas is a gaseous
mixture including at least a fluorocarbon-based gas, a first
deposit removing gas and a second deposit removing gas having a
weaker deposit removing capability than the first deposit removing
gas.
13. The etching apparatus of claim 12, wherein an etching
selectivity of the silicon-containing oxide film against the
silicon nitride film is set by a ratio of a total flow rate of the
first and the second deposit removing gas to a flow rate of the
fluorocarbon-based gas and a ratio of a flow rate of the second
deposit removing gas to the flow rate of the fluorocarbon-based
gas.
14. The etching apparatus of claim 12, wherein the
silicon-containing oxide film is a silicon oxide film.
15. The etching apparatus of claim 12, wherein the
fluorocarbon-based gas is a C.sub.4F.sub.6 gas, the first deposit
removing gas is an oxygen gas, and the second deposit removing gas
is a nitrogen gas.
16. The etching apparatus of claim 15, wherein, in the processing
gas, a ratio of a flow rate of the N.sub.2 gas to a flow rate of
the C.sub.4F.sub.6 gas is greater than or equal to about 25/8 and
is less than or equal to about 85/8, and a ratio of a total flow
rate of O.sub.2 and N.sub.2 to the flow rate of the C.sub.4F.sub.6
gas is greater than or equal to about 15/4 and is less than or
equal to about 45/4.
17. The etching apparatus of claim 15, wherein, in the processing
gas, a ratio of a flow rate of the N.sub.2 gas to a flow rate of
the C.sub.4F.sub.6 gas is greater than or equal to about 25/8 and
less than or equal to about 85/8, and a ratio of the flow rate of
the N.sub.2 gas to a flow rate of the O.sub.2 gas is greater than
or equal to about 5 and less than or equal to about 17.
18. The etching apparatus of claim 12, wherein the processing gas
includes an inert gas.
19. The etching apparatus of claim 12, wherein an upper and a lower
electrodes are installed opposite to face each other in the
processing chamber, a first high frequency power is applied to the
upper electrode, and a second high frequency power is applied to
the lower electrode, a frequency of the second high frequency being
lower than that of the first high frequency power.
20. The etching apparatus of claim 19, wherein the frequency of the
first high frequency power is about 60 MHz, and that of the second
high frequency power is about 2 MHz.
21. The etching apparatus of claim 14, wherein the silicon nitride
film exists under the silicon oxide film.
22. The etching apparatus of claim 21, wherein the silicon oxide
film is etched in a self-alignment contact process.
Description
[0001] This application is a Continuation Application of PCT
International Application No. PCT/JP03/02870 filed on Mar. 11,
2003, which designated United States.
FIELD OF THE INVENTION
[0002] The present invention relates to an etching method and an
etching apparatus, employed to a manufacturing process of a
semiconductor device.
BACKGROUND OF THE INVENTION
[0003] As shown in FIG. 4, in case of forming a contact hole 20 by
a plasma etching through an insulating film layer 16, which covers
a gate 12 formed on a semiconductor substrate 10 such as a silicon
substrate, and is made of a silicon oxide film such as SiO.sub.2, a
self-alignment contact technology may be applied. In the
self-alignment contact technology, the contact hole 20 is formed in
a self-aligning manner in a small and compact area between gates 12
while a protective film layer 14 such as a silicon nitride (SiN)
film is formed on each gate 12, thereby preventing the gate 12 from
being etched in the course of forming the contact hole 20.
[0004] When the contact hole 20 is formed by employing the
self-alignment contact technology, there is used a CF-based gas,
such as C.sub.4F.sub.8, as a processing gas in case of processing
the plasma etching, and a gaseous mixture including O.sub.2 is used
as an etching gas for removing deposits.
[0005] With a recent improvement in the integration of the
semiconductor devices and increased demands for a miniaturization
of various elements formed on a semiconductor substrate, the design
rule has become even finer. Consequently, it has become necessary
to reduce a gap between gates (electrodes) formed on the
semiconductor substrate and thus a high aspect ratio of a contact
hole formed between the gates (electrodes) is required.
[0006] However, the plasma etching employing the conventional
processing gases as described above is disadvantageous in that as
the aspect ratio of the contact hole becomes higher, because of the
narrow gaps between the gates, the etching time becomes longer to
prevent degradation of the capability to pierce an etching target
and occurrence of an etching stop. However, as shown in FIG. 4, a
large portion of a shoulder (edge) 14a of the silicon nitride film,
acting as a protective film layer formed on a surface of the gate
12, is extended into an inner space of the contact hole 20 to be
formed through the silicon oxide film acting as the insulating film
layer 16. Therefore, the shoulder 14a may be very readily etched.
Furthermore, the shoulder (edge) 14a of the protective film layer
14 may be severely etched depending on etching selectivity of the
insulating film layer 16 over the protective film layer 14 of the
gate 12, thereby rendering the gate 12 undesirably exposed
thereto.
SUMMARY OF THE INVENTION
[0007] Therefore, the present invention has been made to ameliorate
the above-described disadvantages in the prior arts and an object
of the present invention is to provide a novel and improved etching
method and etching apparatus thereof assuring an excellent
controllability, in which etching selectivity of a silicon oxide
film layer against a silicon nitride film layer of a gate can be
increased. Thereby, the silicon nitride film layer, acting as a
protective film layer of the gate, can be strongly prevented from
being etched while it becomes possible to form a contact hole with
a high aspect ratio possible.
[0008] In accordance with one aspect of the invention, there is
provided an etching method, in which a processing gas is fed into
an airtight processing chamber to generate a plasma therein and a
silicon-containing oxide film formed on an object to be processed
disposed in the processing chamber is selectively etched against a
silicon nitride film, wherein the processing gas is a gaseous
mixture including at least a fluorocarbon-based gas, a first
deposit removing gas and a second deposit removing gas having a
weaker deposit removing capability than the first deposit removing
gas.
[0009] In accordance with another aspect of the invention, there is
provided an etching apparatus, in which a processing gas is fed
into an airtight processing chamber to generate a plasma therein
and a silicon-containing oxide film formed on an object to be
processed disposed in the processing chamber is selectively etched
against a silicon nitride film, wherein the processing gas is a
gaseous mixture including at least a fluorocarbon-based gas, a
first deposit removing gas and a second deposit removing gas having
a weaker deposit removing capability than the first deposit
removing gas.
[0010] Further, in the etching method and the apparatus thereof, an
etching selectivity of the silicon-containing oxide film over the
silicon nitride film is preferably set to a predetermined value by
a ratio of a total flow rate of the first and the second deposit
removing gases to a flow rate of the fluorocarbon-based gas, and a
ratio of a flow rate of the second deposit removing gas to the flow
rate of the fluorocarbon-based gas.
[0011] Furthermore, in the etching method and the apparatus
thereof, the silicon-containing oxide film is preferably a silicon
oxide film, the fluorocarbon-based gas is C.sub.4F.sub.6 gas, the
first deposit removing gas is oxygen gas and the second deposit
removing gas is nitrogen gas preferably. Additionally, the
processing gas preferably includes an inert gas.
[0012] Moreover, in the etching method and the apparatus thereof,
as for the processing gas, a ratio of a flow rate of the N.sub.2
gas to a flow rate of the C.sub.4F.sub.6 gas is preferably greater
than or equal to about 25/8 and less than or equal to about 85/8,
and a ratio of a total flow rate of the O.sub.2 gas and the N.sub.2
gas to the flow rate of the C.sub.4F.sub.6 gas is preferably
greater than or equal to about 15/4 and less than or equal to about
45/4.
[0013] Further, in the etching method and the apparatus thereof, as
for the processing gas, the ratio of the flow rate of the N.sub.2
gas to the flow rate of the C.sub.4F.sub.6 gas is preferably
greater than or equal to about 25/8 and less than or equal to about
85/8, and a ratio of the flow rate of the N.sub.2 gas to the flow
rate of the O.sub.2 gas is preferably greater than or equal to
about 5 and less than or equal to about 17.
[0014] Furthermore, in the etching method and the apparatus
thereof, an upper and a lower electrodes are installed opposite to
face each other in the processing chamber, a first high frequency
power is applied to the upper electrode, a frequency of a second
high frequency power is applied to the lower electrode, a frequency
of the second high frequency power being lower than that of the
first high frequency power. The frequency of the first high
frequency power is about 60 MHz and that of the second high
frequency power is about 2 MHz, preferably.
[0015] Moreover, in the etching method and the apparatus thereof,
the silicon nitride film exists under the silicon oxide film, and
the silicon oxide film is etched in a self-alignment contact
process.
[0016] In accordance with the present invention as described above,
it is possible to increase the etching rate of the silicon oxide
film acting as an insulating film layer, while preventing an
etching stop from occurring. Further, it is possible to improve
etching selectivity of the silicon oxide film over the silicon
nitride film, acting as a protective film layer of a gate.
Therefore, the silicon nitride film, acting as the protective film
layer of the gate, is prevented from being etched and a contact
hole with a high aspect ratio may be stably formed while assuring
an excellent controllability. Thereby, the present invention
satisfies recent demands for improved integration of a
semiconductor device and miniaturization of various elements formed
on a semiconductor substrate.
[0017] Meanwhile, throughout the specification, 1 mTorr is
equivalent to (10.sup.-3.times.101325/760) Pa and 1 sccm is
equivalent to (10.sup.-6/60) m.sup.3/sec.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects and features of the present
invention will become apparent from the following description of
preferred embodiments given in conjunction with the accompanying
drawings, in which:
[0019] FIG. 1 schematically illustrates an etching apparatus, to
which an etching method in accordance with the present invention
may be applied;
[0020] FIGS. 2a and 2b are sectional views of an objective
substrate illustrating the etching of the objective substrate in
accordance with the present invention;
[0021] FIG. 3 is a graph showing the results of the etching of a
silicon oxide film layer in accordance with the present invention;
and
[0022] FIG. 4 is a sectional view of an objective substrate
illustrating the etching of the objective substrate in accordance
with a conventional etching method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Hereinafter, preferred embodiments of an etching method and
an etching apparatus in accordance with the present invention will
now be described in detail with reference to the accompanying
drawings. FIG. 1 schematically illustrates a parallel plate type
plasma etching apparatus, which is an embodiment of the etching
apparatus in accordance with the present invention.
[0024] The plasma etching apparatus 100 includes a processing
chamber 104 defined by a securely grounded processing vessel 102,
and a vertically movable lower electrode 106 included in a
suscepter is installed in the processing chamber 104. An
electrostatic chuck 110 connected to a high voltage DC power supply
108 is provided at an upper part of the lower electrode 106 and an
object to be processed, for example a semiconductor wafer
(hereinafter, referred to as "wafer") W, is loaded on the
electrostatic chuck 106. Further, an insulating focus ring 112 is
installed around the wafer W loaded on the lower electrode 106.
Furthermore, the lower electrode 106 is connected to a second high
frequency power supply 120 via a matching unit 118.
[0025] In addition, an upper electrode 122 having a plurality of
gas discharge openings 122a is provided at a top of the processing
chamber 104, the top thereof facing against the lower electrode
106. An insulator 123 is interposed between the upper electrode 122
and the processing vessel 102 to electrically isolate the upper
electrode 122 from the processing vessel 102. As well, the upper
electrode 122 is connected via a matching unit 119 to a first high
frequency power supply 121 generating high frequency power to
produce a plasma.
[0026] In this regard, a first high frequency power having a
frequency ranging from about 13.56 to about 150 MHz, and preferably
about 60 MHz, is applied from the first high frequency power supply
121 to the upper electrode 122. Furthermore, a second high
frequency power is applied from the second high frequency power
supply 120 to the lower electrode 106, a frequency of the second
high frequency power being lower than that of the first high
frequency power generated from the first high frequency power
supply 121. For example, the frequency of the second high frequency
power ranges from about 2 to about 13.56 MHz, and is preferably
about 2 MHz.
[0027] A gas supply line 124 communicates with the gas discharge
openings 122a, wherein the gas supply line 124 is connected to a
processing gas supplying system 126a for supplying, for example,
C.sub.4F.sub.6, a processing gas supplying system 126b for
supplying, for example, Ar, a processing gas supplying system 126c
for supplying, for example, N.sub.2, and a processing gas supplying
system 126d for supplying, for example, O.sub.2.
[0028] Each of the processing gas supplying systems 126a, 126b,
126c and 126d includes each of opening/closing valves 132a, 132b,
132c and 132d, respectively; includes each of flow rate controlling
valves 134a, 134b, 134c and 134d, respectively; and are connected
to a C.sub.4F.sub.6 gas supply source 136a, an Ar gas supply source
136b, a N.sub.2 gas supply source 136c and an O.sub.2 gas supply
source 136d, respectively.
[0029] Additionally, a gas exhaust line 150 communicating with a
vacuum exhaust unit (not shown) is formed at a lower part of the
processing vessel 102 and an inner space of the processing chamber
104 is maintained under reduced pressure by the vacuum exhaust
unit.
[0030] Hereinafter, there will be described the etching method
employing the above-described etching apparatus in accordance with
the present invention, with reference to FIGS. 2A and 2B. Referring
to FIG. 2A, there is illustrated an example of layered structure of
films, which will be etched in accordance with the present
invention.
[0031] The layered structure of films is formed in accordance with
the following procedure. After a gate 202 is formed on a silicon
(Si) substrate 200 as a semiconductor substrate, a silicon nitride
film layer 204 as a protective film layer is formed thereon in such
a way that the gate 202 is coated over therewith. Subsequently, a
silicon oxide film layer 206, which includes SiO.sub.2 and the like
and acts as an insulating film layer, is formed on an entire
surface of the resulting substrate by, for example, a chemical
vapor deposition (CVD) process. Successively, a photoresist film is
applied on the silicon oxide film layer 206 and then patterned to
form a contact hole 210 therethrough, thereby forming the
photoresist layer 208.
[0032] Next, the silicon oxide film layer 206 of the resulting
layered structure of films is selectively etched against the
silicon nitride film layer 204 by the etching method in accordance
with the present invention to form the contact hole between the
gates 202. In detail, a processing gas, which includes a
C.sub.4F.sub.6 gas as a fluorocarbon-based gas, an O.sub.2 (oxygen)
gas as a first deposit removing gas, a N.sub.2 (nitrogen) gas as a
second deposit removing gas and a gaseous mixture containing Ar, is
introduced into the processing chamber 104 to conduct a plasma
process, thereby performing the etching. At this time, the
C.sub.4F.sub.6 gas is used as an etching gas, and the Ar-containing
gas is used as a dilution gas. Additionally, the O.sub.2 and the
N.sub.2 gas are used to remove deposits generated by the
etching.
[0033] With respect to this, the reason why N.sub.2 gas is included
as the gas for removing the deposits in addition to O.sub.2 gas is
because it is much easier to achieve a fine tuning in control over
removing the deposits by controlling the flow rate of N.sub.2 than
controlling that of O.sub.2, since N.sub.2 is much less powerful in
removing the deposits than O.sub.2. To be more specific, an amount
of the deposits removed is increased as a flow rate of the deposit
removing gas such as N.sub.2 or O.sub.2, increases. In such a case,
O.sub.2 and N.sub.2 have different deposit removing rates from each
other. For the case of N.sub.2, an increase rate of the removed
amount of deposit to an increase of its flow rate (a deposit
removing capability) is a level of about {fraction
(1/10)}-{fraction (1/20)} of that of O.sub.2. For the case of
O.sub.2, a small increase in the flow rate of O.sub.2 causes a big
increase in the amount of the deposits removed, resulting in an
excessive removal of the deposits.
[0034] In the case of the layered structure of films in accordance
with the present embodiment, if the deposit is excessively removed,
an etching selectivity of the silicon oxide film layer 206, acting
as the insulating film layer, over the silicon nitride film layer
204, acting as the protective film layer of the gates, cannot be
maintained high. Therefore, N.sub.2, which removes a relatively
small amount of the deposit for an increase in its flow rate, is
contained in the processing gas to readily control the amount of
the removed deposit.
[0035] However, if the processing gas does not contain O.sub.2 but
N.sub.2, and then since the N.sub.2 gas has relatively poor deposit
removing capability, the deposit is insufficiently removed, thereby
rendering an etching stop occurring. Therefore, in the present
invention, O.sub.2 as well as N.sub.2 is included in the processing
gas.
[0036] Furthermore, since N.sub.2 has some deposit removing
capability even though it is relatively poor, the etching
selectivity of the silicon oxide film layer 206 over the silicon
nitride film layer 204 cannot be made high, when its flow rate is
excessively high. Therefore, it is necessary to properly control
respective flow rates of gases, including N.sub.2.
[0037] In this respect, there will be described a result of an
experiment in which an etching of the silicon oxide film layer 206
was performed, in the layered structure of films as shown in FIG.
2a, which was conducted in order to find respective preferable flow
rates of the gases. The etching experiment was conducted under
basic conditions that pressure in the processing chamber 104 was 30
mTorr, a high frequency power applied to the upper electrode 122
was 1530 W at 60 MHz, a high frequency power (bias power) applied
to a lower electrode 106 was 1350 W at 2 MHz and a gap between the
upper and the lower electrodes 122 and 106 was 25 mm. Further, a
flow rate ratio of C.sub.4F.sub.6/Ar/O.sub.2 (a flow rate of
C.sub.4F.sub.6/a flow rate of Ar/a flow rate of O.sub.2) was 16
sccm/800 sccm/10 sccm, temperatures of the lower and the upper
electrodes in the processing chamber 104 were 40.degree. C. and
60.degree. C., respectively and a temperature of a sidewall of the
processing chamber 104 was 50.degree. C. Pressures of a cooling gas
as a back pressure gas (He gas) applied to the center and edges of
a backside of the wafer were 5 Torr and 10 Torr, respectively.
[0038] In this regard, when forming a contact hole with a height H
of 1.4 .mu.m and a diameter of 0.4 .mu.m and having a silicon
nitride film layer 204 having a height of 0.35 .mu.m from a surface
of the silicon substrate 200, as shown in FIG. 2b, the etching
could be conducted under a 100% over-etching condition by only
controlling the flow rate of N.sub.2. At this time, the 100%
over-etching condition means that the etching was performed for a
time required to remove a layer that was twice as thick as the
silicon oxide film layer 206.
[0039] When the flow rate of N.sub.2 was 200 sccm, in other words,
when a flow rate ratio of C.sub.4F.sub.6/Ar/N.sub.2/O.sub.2 (the
flow rate of C.sub.4F.sub.6 /the flow rate of Ar/the flow rate of
N.sub.2/the flow rate of O.sub.2) was 16 sccm/800 sccm/200 sccm/10
sccm, etching rates of the silicon oxide film layer at the center
portion, at an intermediate portion between an end portion and the
center portion and at the end portion of the wafer W were 491.3
nm/min, 478.0 nm/min and 449.3 nm/min, respectively. Additionally,
removal amounts t's of the shoulder (edge) 204a of the silicon
nitride film layers 204 were 112 nm, 118 nm and 134 nm,
respectively, while selectivities of the silicon oxide film layer
206 over the shoulder (edge) 204a of the silicon nitride film
layers 204 [an etching rate of the silicon oxide film layer/an
etching rate of the shoulder part (edge part) of the silicon
nitride film layer] were 17.4, 15.9 and 12.6, respectively. At this
time, selectivities of the silicon oxide film layer 206 over the
shoulder parts (edge part) of the photoresist layer 208 [an etching
rate of the silicon oxide film layer/an etching rate of the
shoulder part (edge part) of the photoresist layer] were 4.6, 5.2
and 5.0, respectively.
[0040] In this respect, the removed amount of the shoulder (edge)
204a of the silicon nitride film layer 204 was represented by a
distance t between two straight lines which were inclined by an
angle of 45 degrees with respect to the silicon substrate 200 and
were drawn at the shoulder 204a before and after, respectively, the
silicon nitride film layer 204 was etched as shown in FIG. 2B. As
well, a removed amount of a shoulder part (edge part) of the
photoresist layer 208 was represented by a distance u between an
upper surface of the photoresist layer 208 before the photoresist
layer 208 was etched and a point, at which an etched portion of the
photoresist layer 208 met a wall of the contact hole after the
photoresist layer 208 was etched as shown in FIG. 2B.
[0041] Furthermore, when the flow rate of N.sub.2 was 150 sccm, in
other words, when the flow rate ratio of
C.sub.4F.sub.6/Ar/N.sub.2/O.sub.2 (the flow rate of
C.sub.4F.sub.6/the flow rate of Ar/the flow rate of N.sub.2 / the
flow rate of O.sub.2) was 16 sccm/800 sccm/150 sccm/10 sccm,
etching rates of the silicon oxide film layer at the center
portion, at the intermediate portion between the end portion and
the center portion and at the end portion of the wafer W were 508.7
nm/min, 502.0 nm/min and 474.0 nm/min, respectively. Additionally,
the removal amounts t's of the shoulder (edge) 204a of the silicon
nitride film layers 204 were 84 nm, 73 nm and 84 nm, respectively,
while the selectivities of the silicon oxide film layer 206 over
the shoulder (edge) 204a of the silicon nitride film layers 204 [an
etching rate of the silicon oxide film layer/an etching rate of the
shoulder part (edge part) of the silicon nitride film layer] were
23.1, 26.0 and 20.5, respectively. At this time, the selectivities
of the silicon oxide film layer 206 over the shoulder parts (edge
part) of the photoresist layer 208 [the etching rate of the silicon
oxide film layer/the etching rate of the shoulder part (edge part)
of the photoresist layer] were 5.2, 7.8 and 7.8, respectively.
[0042] Additionally, when the flow rate of N.sub.2 was 100 sccm, in
other words, when the flow rate ratio of
C.sub.4F.sub.6/Ar/N.sub.2/O.sub.2 (the flow rate of
C.sub.4F.sub.6/the flow rate of Ar/the flow rate of N.sub.2/the
flow rate of O.sub.2) was 16 sccm/800 sccm/100 sccm/10 sccm, the
etching rates of the silicon oxide film layer at the center
portion, at the intermediate portion between the end portion and
the center portion and at the end portion of the wafer W were 539.3
nm/min, 524.0 nm/min, and 500.0 nm/min, respectively. Further, the
removed amounts t's of the shoulder (edge) 204a of the silicon
nitride film layers 204 were 47 nm, 51 nm and 65 nm, respectively,
while the selectivities of the silicon oxide film layer 206 over
the shoulder (edge) 204a of the silicon nitride film layers 204 [an
etching rate of the silicon oxide film layer/an etching rate of the
shoulder part (edge part) of the silicon nitride film layer] were
41.3, 36.4 and 26.6, respectively. At this time, the selectivities
of the silicon oxide film layer 206 over the shoulder parts (edge
part) of the photoresist layer 208 [the etching rate of the silicon
oxide film layer/the etching rate of the shoulder part (edge part)
of the photoresist layer] were 6.6, 6.8 and 10.0, respectively.
[0043] The above results are shown in FIG. 3. A horizontal axis
represents the flow rate of the N.sub.2 gas and vertical axes
correspond to the etching rate and selectivity of the silicon oxide
film layer, respectively. Further, averages of the values at the
center portion, at the intermediate portion between the end portion
and the center portion, and at the end portion of the wafer W are
taken and plotted in FIG. 3.
[0044] In this regard, a line y1 is a graph showing an
interrelation between the flow rate of N.sub.2 and the etching rate
of the silicon oxide film layer, a line y2 is a graph showing an
interrelation between the flow rate of N.sub.2 and the selectivity
of the silicon oxide film layer over the shoulder part of the
photoresist layer and a line y3 is a graph showing an interrelation
between the flow rate of N.sub.2 and the selectivity of the silicon
oxide film layer over the shoulder part of the silicon nitride film
layer. Additionally, for the above basic etching conditions, when
the flow rate of N.sub.2 was less than or equal to about 50 sccm,
the etching stop occurred.
[0045] From the graph y1, it can be seen that, as the flow rate of
N.sub.2 becomes lower, the etching rate of the silicon oxide film
layer becomes higher. As well, in the case of the graphs y2 and y3,
the lower the flow rate of N.sub.2 is, the higher the selectivities
of the silicon oxide film layer over the shoulder of the
photoresist layer and over the shoulder of the silicon nitride film
layer are.
[0046] In this regard, while an increasing rate of the selectivity
of the silicon oxide film layer over the shoulder of the silicon
nitride film layer is significantly large as the flow rate of
N.sub.2 becomes reduced. In addition, the selectivity of the
silicon oxide film layer over the shoulder part of the photoresist
layer is slightly increased, however, remains almost unchanged with
the reduction of the flow rate of N.sub.2. To sum up, the reduction
in the flow rate of N.sub.2 results in increased etching rate of
the silicon oxide film layer and the improved selectivity of the
silicon oxide film layer over the silicon nitride film layer while
the selectivity of the silicon oxide film layer over the
photoresist layer remains almost unchanged.
[0047] Accordingly, the desirable flow rate of N.sub.2 is
preferably within a range at which the selectivity of the silicon
oxide film layer over the silicon nitride film layer is greater
than or equal to about 20.0, and more preferably, within a range at
which the selectivity of the silicon oxide film layer over the
silicon nitride film layer is greater than or equal to about 30.0,
practically. Specifically, under the above basic etching
conditions, the flow rate of N.sub.2 is preferably less than or
equal to about 170 sccm, and more preferably, less than or equal to
about 120 sccm as shown in the graph y3. At this time, when the
flow rate of N.sub.2 becomes excessively low, the etching stop
occurs. Therefore it is necessary that the flow rate of N.sub.2 is
at least more than or equal to about 50 sccm. Resultantly, the flow
rate of N.sub.2 is preferably greater than or equal to about 50
sccm and less than or equal to about 170 sccm, and more preferably
greater than or equal to about 80 sccm and less than or equal to
about 120 sccm.
[0048] In the case of converting the above-mentioned flow rate into
a flow rate ratio, a ratio of the flow rate of N.sub.2 to the flow
rate of C.sub.4F.sub.6 is preferably greater than or equal to about
50/16 and less than or equal to about 170/16 (i.e. greater than or
equal to about 25/8 and less than or equal to about 85/8), and more
preferably greater than or equal to about 80/16 and less than or
equal to about 120/16 (i.e. greater than or equal to about 10/2 and
less than or equal to about 15/2). Additionally, a ratio of the
flow rate of gaseous mixture, which contains N.sub.2 and O.sub.2,
acting as the deposit removing gas to the flow rate of
C.sub.4F.sub.6, acting as the etching gas, is preferably greater
than or equal to about 60/16 and less than or equal to about 180/16
(greater than or equal to about 15/4 and less than or equal to
about 45/4), and more preferably greater than or equal to about
90/16 and less than or equal to about 130/16 (greater than or equal
to about 45/8 and less than or equal to about 65/8).
[0049] Furthermore, as the deposit removing gas, a ratio of the
flow rate of N.sub.2 to the flow rate of O.sub.2 is preferably
greater than or equal to about 50/10 and less than or equal to
about 170/10 (greater than or equal to about 5 and less than or
equal to about 17), and more preferably greater than or equal to
about 80/10 and less than or equal to about 120/10 (greater than or
equal to about 8 and less than or equal to about 12).
[0050] Based on the above description, when the layered structure
of films shown in FIG. 2A is etched by a plasma under the
preferable etching conditions, the contact hole 210 may be formed
in a self-aligning manner between the gates 202 while the silicon
nitride film layer 204, acting as the protective film layer of the
gates 202, is prevented from being etched as shown in FIG. 2B.
[0051] With respect to this, test results for the conventional
etching method are presented for a comparison with the test results
by the etching method in accordance with the present invention. In
this regard, the conventional etching was conducted under
conditions where the high frequency power applied to the upper
electrode 122 was 1500 W at 60 MHz, the high frequency power (bias
power) applied to the lower electrode 106 was about 1300 W at about
2 MHz, a flow rate ratio of C.sub.5F.sub.8/Ar/O.sub.2 (a flow rate
of C.sub.5F.sub.8/a flow rate of Ar/a flow rate of O.sub.2) was
about 16 sccm/800 sccm/18 sccm, temperatures of the lower and the
upper electrodes in the processing chamber 104 were about
40.degree. C. and 60.degree. C., respectively and a temperature of
a sidewall of the processing chamber 104 was about 50.degree. C.
Pressures of the cooling gas (He gas) as a back pressure gas
applied to the center and edges of the backside of the wafer were
about 5 Torr and 10 Torr, respectively.
[0052] When the layered structure of films as shown in FIG. 2A was
etched by a plasma under the conventional etching conditions
described above, the following results were obtained. At this time,
the following results are average values of respective values
measured at the center portion, at the intermediate portion between
the end portion and the center portion, and at the end portion of
the wafer W.
[0053] The etching rate of the silicon oxide film layer was about
500 nm/min, a removed amount t of the etched shoulder (edge) 204a
of the silicon nitride film layer 204 was about 8 nm. Additionally,
the selectivity of the silicon oxide film layer 206 over the
shoulder (edge) 204a of the silicon nitride film layer 204 [the
etching rate of the silicon oxide film layer/the etching rate of
the shoulder (edge) of the silicon nitride film layer] was about
20.0. The selectivity of the silicon oxide film layer 206 against
the shoulder (edge) 204a of the photoresist layer 208 [the etching
rate of the silicon oxide film layer/the etching rate of the
shoulder part (edge part) of the photoresist layer] was about
6.0.
[0054] Through the above description regarding the conventional
etching and the etching in accordance with the present invention,
it can be seen that in the case of the present invention, N.sub.2
is added to the processing gas to select the desired flow rate
ratio, thereby preventing the etching stop from occurring and at
the same time increasing the etching rate of the silicon oxide film
layer 206, acting as the protective film layer.
[0055] In addition, there improved the etching selectivity of the
silicon oxide film layer 206 over the silicon nitride film layer
204, acting as the protective film layer of the gates 202.
Therefore, the silicon nitride film layer 204, acting as the
protective film layer of the gates 202, is prevented from being
etched, thereby capable of forming the contact hole 210 with an
improved aspect ratio.
[0056] Although, the preferred embodiments in accordance with the
present invention have been described in an illustrative manner
with reference to the drawings, the present invention is not
limited to the embodiments described herein, and it is to be
understood that the terminology used is intended to be in the
nature of description rather than of limitation. Many modifications
and variations of the present invention are possible in light of
the above teachings. Therefore, it is to be understood by those
skilled in the art that within the scope of the claims attached
thereto, the invention may be practiced in different ways from
those specifically described.
[0057] For example, there is disclosed only the silicon oxide film
layer 206 as the silicon-containing oxide film acting as the
insulating film layer in the present invention, however an
inorganic low-k film, such as a carbon-added silicate (SiOC) film,
a hydrogen-added silicate (SIOH) film and a fluorine-added silicate
(SiOF) film, may be used instead of the silicon oxide film.
[0058] Additionally, the silicon oxide film may be exemplified by a
borophosphosilicate glass (BPSG) film, a phosphosilicate glass
(PSG) film, a tetraethoxy orthosilane (TEOS) film, a thermal oxide
(Th-OX) film or a spin on glass (SOG) film.
[0059] Further, in the present invention, only C.sub.4F.sub.6 gas
is used as fluorocarbon-based gas which rendered to be included in
the processing gas, but C.sub.5F.sub.8 gas and the like may be used
as the fluorocarbon-based gas.
[0060] Furthermore, in the present invention, the high frequency
power with the frequency of about 60 Hz is applied to the upper
electrode of the etching apparatus and the high frequency power
with the frequency of about 2 MHz is applied to the lower
electrode, however the present invention is not limited to what is
explained above, and the high frequency power may be applied to the
upper or the lower electrodes of the etching apparatus, or a
magnetic field may be formed around the upper and/or the lower
electrode.
[0061] With respect to this, it is most preferable to use the
etching apparatus, in which the high frequency power with the
frequency of about 60 Hz is applied to the upper electrode and the
high frequency power with the frequency of about 2 MHz is applied
to the lower electrode, because the high frequency power applied to
the upper electrode serves to control a plasma density and the high
frequency power applied to the lower electrode functions to control
an ion energy. Consequently, it is controllable, i.e., to attach
and remove reaction products (deposits), affecting the etching
selectivity.
[0062] As well, the etching apparatus may be embodied by an ECR
plasma etching apparatus, a helicon wave plasma etching apparatus,
a TCP type plasma etching apparatus, and an inductively coupled
plasma etching apparatus.
[0063] In accordance with the present invention as described above,
N.sub.2 is added to the processing gas and the flow rate of N.sub.2
is desirably selected to prevent the etching from stopping, to
increase the etching rate of the silicon oxide film layer, acting
as the insulating film layer, and to improve the etching
selectivity of the silicon oxide film layer over the silicon
nitride film layer, acting as the protective film layer of the
gates. Therefore, the silicon nitride film, acting as the
protective film layer of the gates, is prevented from being etched
and the contact hole with the high aspect ratio may be stably
formed securely while assuring an excellent controllability.
[0064] While the invention has been shown and described with
respect to the preferred embodiment, it will be understood by those
skilled in the art that various changes and modifications may be
made without departing from the spirit and scope of the invention
as defined in the following claims.
* * * * *