U.S. patent application number 11/147197 was filed with the patent office on 2005-12-08 for etching method.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Igarashi, Yoshiki, Naito, Wakako.
Application Number | 20050269294 11/147197 |
Document ID | / |
Family ID | 35446554 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050269294 |
Kind Code |
A1 |
Igarashi, Yoshiki ; et
al. |
December 8, 2005 |
Etching method
Abstract
In an etching method, multiple etchings are sequentially
performed in a single processing vessel on a laminated film having
a plurality of layers formed on a substrate to be processed,
without unloading the substrate to be processed from the vessel.
Between the etchings, a cleaning processing for removing deposits
from the processing vessel by using a plasma of a cleaning gas is
performed. The cleaning gas is O.sub.2 containing gas, and
preferably, a gaseous mixture of O.sub.2 and N.sub.2 gas. Further,
the cleaning processing is performed under conditions of
50.about.200 mTorr in the processing vessel; 5.about.15 mL/min of
O.sub.2 flow rate; and 100.about.400 mL/min of N.sub.2 flow rate.
The method prevents etching characteristics from being affected due
to a memory effect, while offering the advantages of an all-in-one
etching.
Inventors: |
Igarashi, Yoshiki;
(Nirasaki-shi, JP) ; Naito, Wakako; (Nirasaki-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
35446554 |
Appl. No.: |
11/147197 |
Filed: |
June 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60589791 |
Jul 22, 2004 |
|
|
|
Current U.S.
Class: |
216/67 ; 134/1.1;
257/E21.252; 257/E21.279; 257/E21.293 |
Current CPC
Class: |
H01L 21/3185 20130101;
B08B 7/0035 20130101; H01L 21/31116 20130101; H01L 21/31612
20130101 |
Class at
Publication: |
216/067 ;
134/001.1 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2004 |
JP |
2004-170361 |
Claims
What is claimed is:
1. An etching method for sequentially performing multiple etchings
in a single processing vessel on a laminated film having a
plurality of layers formed on a substrate to be processed, without
unloading the substrate to be processed from the vessel, wherein,
between the etchings, a cleaning processing for removing deposits
from the processing vessel by using a plasma of a cleaning gas is
performed.
2. An etching method for sequentially performing multiple etchings
in a single processing vessel on a laminated film having a
plurality of layers formed on a substrate to be processed in an
order of a first film and a second film from a top, without
unloading the substrate to be processed from the vessel, the method
comprising the steps of: performing a first etching of the first
film by using a plasma of a first etching gas; performing a
cleaning processing for removing deposits from the processing
vessel by using plasma of a cleaning gas after the first etching;
and performing a second etching of the second film by using a
plasma of a second etching gas after the cleaning.
3. The etching method of claim 2, wherein, in the first etching, a
silicon oxide film as the first film is etched by using the plasma
of the first etching gas containing CF based gas; and in the second
etching, a silicon nitride film as the second film is etched by
using the plasma of the second etching gas containing CHF based
gas.
4. The etching method of claim 2, wherein, in the first etching, a
silicon oxide film as the first film is etched by using the plasma
of the first etching gas containing CF based gas; and in the second
etching, an organic film as the second film is etched by using the
plasma of the second etching gas containing N.sub.2 or NH.sub.3
gas.
5. The etching method of claim 2, wherein, in the second etching,
the first film serves as a mask film.
6. The etching method of claim 1 or 2, wherein the cleaning
processing is performed without applying a bias power to the
substrate to be processed.
7. The etching method of claim 1 or 2, wherein the cleaning gas is
O.sub.2 containing gas.
8. The etching method of claim 7, wherein the O.sub.2 containing
gas is a gaseous mixture of O.sub.2 and N.sub.2 gas.
9. The etching method of claim 8, wherein the cleaning processing
is performed under conditions of 50.about.200 mTorr in the
processing vessel; 5.about.15 mL/min of O.sub.2 flow rate; and
100.about.400 mL/min of N.sub.2 flow rate.
10. An etching method for sequentially performing multiple etchings
by using a patterned mask film as a mask in a single processing
vessel on a laminated film having a plurality of layers formed on a
substrate to be processed in an order of a first insulating film
and a second insulating film from a top, without unloading the
substrate to be processed from the vessel, the method comprising
the steps of: performing a first etching of the first insulating
film by using a plasma of a first etching gas; performing a
cleaning processing for removing deposits from the processing
vessel by using a plasma of a cleaning gas after the first etching;
and performing a second etching of the second insulating film by
using a plasma of a second etching gas after the cleaning, wherein,
in the first and the second etchings, bias powers are applied to
the substrate to be processed; and, in the cleaning processing, a
bias power is not applied to the substrate to be processed.
11. The etching method of claim 10, wherein, in the first etching,
a silicon oxide film as the first insulating film is etched by
using the plasma of the first etching gas containing CF based gas;
and in the second etching processing, a silicon nitride film as the
second insulating film is etched by using the plasma of the second
etching gas containing CHF based gas.
12. The etching method of claim 10, wherein, in the first etching,
a silicon oxide film as the first insulating film is etched by
using the plasma of the first etching gas containing CF based gas;
and in the second etching, an organic film as the second insulating
film is etched by using the plasma of the second etching gas
containing N.sub.2 or NH.sub.3 gas.
13. The etching method of claim 10, wherein the cleaning gas is
O.sub.2 containing gas.
14. The etching method of claim 13, wherein the O.sub.2 containing
gas is a gaseous mixture of O.sub.2 and N.sub.2 gas.
15. The etching method of claim 14, wherein the cleaning processing
is performed under conditions of 50.about.200 mTorr in the
processing vessel; 5.about.15 mL/min of O.sub.2 flow rate; and
100.about.400 mL/min of N.sub.2 flow rate.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an etching method for
etching on a substrate, e.g., a semiconductor substrate or the
like, by performing a plasma processing.
BACKGROUND OF THE INVENTION
[0002] When etching a laminated film of an SiN film, SiO.sub.2
film, SiLK film and the like, which is formed on a substrate, e.g.,
a semiconductor substrate or the like, etching process conditions
depend on the type of film being etched. Hence, to perform etching
of different layers, conventional etching demands that each layer
be etched in a different processing vessel (chamber). However,
since this method requires handling of the substrate to different
processing vessels, multiple processing vessels need to be
provided. Further, the overall system size becomes large, and an
improvement of throughput is hard to achieve. To overcome the
disadvantages, there has been proposed an all-in-one etching
processing which allows etchings of different layers to be
performed in one processing vessel, without using multiple
single-purpose processing vessels (e.g., reference 1).
[0003] Reference 1: Japanese Patent Laid-open Application No.
2003-309107 (claim 2 and the like)
[0004] The above all-in-one etching system offers advantages in
that the overall size of the apparatus becomes smaller and the
system's throughput is improved. However, since etchings with
different process conditions are repeatedly performed in one
processing vessel, the vessel is subjected to multiple etching
conditions. As a result, the conditions of an etching processing
affect successive etchings performed in the vessel due to the
memory effect in the vessel. Ultimately, successive etching
characteristics are affected and modified by earlier etchings
performed in the vessel, as compared to cases where etchings with
different process conditions are performed individually in multiple
single-purpose vessels.
SUMMARY OF THE INVENTION
[0005] The present invention has been made under such a background.
It is, therefore, an object of the present invention to provide an
etching method capable of preventing etching characteristics from
being affected due to a memory effect, while offering the
advantages of an all-in-one etching.
[0006] In accordance with a preferred embodiment of the present
invention, there is provided an etching method for sequentially
performing multiple etchings in a single processing vessel on a
laminated film having a plurality of layers formed on a substrate
to be processed, without unloading the substrate to be processed
from the vessel, wherein, between the etchings, a cleaning
processing for removing deposits from the processing vessel by
using a plasma of a cleaning gas is performed.
[0007] In accordance with another preferred embodiment of the
present invention, there is provided an etching method for
sequentially performing multiple etchings in a single processing
vessel on a laminated film having a plurality of layers formed on a
substrate to be processed in an order of a first film and a second
film from a top, without unloading the substrate to be processed
from the vessel, the method including the steps of: performing a
first etching of the first film by using a plasma of a first
etching gas; performing a cleaning processing for removing deposits
from the processing vessel by using plasma of a cleaning gas after
the first etching; and performing a second etching of the second
film by using a plasma of a second etching gas after the
cleaning.
[0008] In accordance with still another preferred embodiment of the
present invention, there is provided an etching method for
sequentially performing multiple etchings by using a patterned mask
film as a mask in a single processing vessel on a laminated film
having a plurality of layers formed on a substrate to be processed
in an order of a first insulating film and a second insulating film
from a top, without unloading the substrate to be processed from
the vessel, the method including the steps of: performing a first
etching of the first insulating film by using a plasma of a first
etching gas; performing a cleaning processing for removing deposits
from the processing vessel by using a plasma of a cleaning gas
after the first etching; and performing a second etching of the
second insulating film by using a plasma of a second etching gas
after the cleaning,
[0009] wherein, in the first and the second etchings, bias powers
are applied to the substrate to be processed; and, in the cleaning
processing, a bias power is not applied to the substrate to be
processed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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:
[0011] FIG. 1 offers a schematic cross sectional view of a plasma
processing apparatus for etching in accordance with the present
invention;
[0012] FIGS. 2A to 2C show schematic diagrams showing the
progressive status of a chamber and a semiconductor wafer as
etching is performed in accordance with a first embodiment of the
present invention; FIG. 2A shows the status before first etching
step; FIG. 2B shows the status after first etching step; and FIG.
2C shows the status after second etching step;
[0013] FIGS. 3A to 3C show schematic diagrams showing the
progressive status of a chamber and a semiconductor wafer as
etching is performed in accordance with a second embodiment of the
present invention; FIG. 3A shows the status before first etching
step; FIG. 3B shows the status after first etching step; and FIG.
3C shows the status after second etching step;
[0014] FIG. 4 shows a graph representing etched amount of a
semiconductor wafer in accordance with a first example;
[0015] FIG. 5 shows a graph representing etched amount of a
semiconductor wafer for reference;
[0016] FIG. 6 shows a graph representing etched amount of a
semiconductor wafer for comparison;
[0017] FIG. 7 shows a graph representing the relationship between
the amount of etched resist and the cleaning time as pressure is
varied;
[0018] FIG. 8 shows a graph representing the relationship between
the amount of etched resist and the cleaning time as flow rate of
N.sub.2 is varied, and
[0019] FIG. 9 shows a graph representing the relationship between
the amount of etched resist and the cleaning time as flow rate of
O.sub.2 is varied.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Hereinafter, preferred embodiments of the present invention
will be described in detail with reference to the accompanying
drawings.
[0021] FIG. 1 is a cross sectional view showing schematically a
preferred plasma processing apparatus for carrying out the method
of the present invention. The plasma processing apparatus 1 is
configured as a capacitively coupled parallel plate type plasma
processing apparatus, wherein upper and lower electrode plates face
each other in parallel, and a power supply for producing a plasma
is connected to one of the electrodes.
[0022] The plasma processing apparatus 1 has a cylindrical chamber
2 made of aluminum whose surface is alumite treated (anodically
oxidized), wherein the chamber 2 is grounded. In a bottom portion
of the chamber 2, there is provided an approximately cylindrical
susceptor support 4 for mounting thereon an object to be processed,
e.g., a semiconductor wafer (hereinafter, referred to as `wafer`),
through an insulating plate 3 such as a ceramic or the like; and a
susceptor 5 forming a lower electrode is installed on the susceptor
support 4. A high pass filter (HPF) 6 is connected to the susceptor
5.
[0023] Inside the susceptor support 4, there is provided a coolant
chamber 7, into which coolant, e.g., liquid nitrogen or the like,
is introduced to circulate therein through a coolant introducing
line 8; and cold heat thereof is thermally transferred to the wafer
W through the susceptor 5, to thereby set the surface temperature
of the wafer W at a desired level.
[0024] The susceptor 5 has a circular plate shape with a protrusion
in an upper central portion, on which an electrostatic chuck 11
having a substantially same shape to the wafer W is installed. The
electrostatic chuck 11 has an electrode 12 intervened between
insulating materials; and a DC voltage of, e.g., 1.5 kV, is applied
to the electrostatic chuck 11 from a DC power supply 13 connected
to the electrode 12, to thereby electrostatically adsorb the wafer
W by, e.g., Columbic force.
[0025] Further, a gas channel 14 runs through the insulating plate
3, susceptor support 4, susceptor 5 and electrostatic chuck 11, to
thereby supply a heat transfer medium, e.g., He gas or the like, to
the rear surface of the wafer W as an object to be processed; and
cold heat of the susceptor 5 is transferred to the wafer W through
the heat transfer medium to maintain the wafer W at a predetermined
temperature.
[0026] At an upper peripheral portion of the susceptor 5, an
annular focus ring 15 is disposed to surround the wafer W mounted
on the electrostatic chuck 11. The focus ring 15 is made of
conductive material such as silicon or the like, and the focus ring
improves etching uniformity.
[0027] Above the susceptor 15, an upper electrode 21 is installed
to face the susceptor 5 in parallel. The upper electrode 21 is
supported at an upper portion of the chamber 2 via an insulating
member 22 to face the susceptor 5. The electrode 21 is composed of
an electrode plate 24 and an electrode support 25. The electrode
plate 24 has multiple injection holes 23 and is made of, e.g.,
silicon, SiC or amorphous carbon. The electrode support 25 is made
of conductive material, e.g., aluminum whose surface is
alumite-treated, for supporting the electrode plate 24. Further,
the susceptor 5 and the upper electrode 21 are set apart by, e.g.,
about 10.about.60 mm. Still further, as for the electrode plate 24,
it is preferable to use a silicon that is capable of scavenging as
for the aforementioned materials.
[0028] At the center of the electrode support 25 in the upper
electrode 21, there is provided a gas inlet port 26, to which a gas
supply line 27 is connected. Further, the gas supply line 27 is
connected to a processing gas supply system through a valve 28. In
the present embodiment, the processing gas supply system is formed
of a C.sub.5F.sub.8/Ar/O.sub.2 supply source 52 as a first etching
gas supply unit; a CH.sub.2F.sub.2/Ar/O.sub.2 supply source 53 as a
second etching gas supply unit; and an N.sub.2/O.sub.2 supply
source 54 as a cleaning gas supply unit, all of which are connected
to valves 30 and mass flow controllers (MFC) 29, respectively.
[0029] As for etching gas, various gases that have been
conventionally used for etching can be used. A gas with halogen,
e.g., a CF based gas (flouorocarbon gas: CxFy), can be properly
used. If wafer W has an SiN film and then an SiO.sub.2 film thereon
and etching is performed on the SiO.sub.2 film, it is preferable to
use a processing gas containing C.sub.4F.sub.8 or C.sub.5F.sub.8.
If C.sub.5F.sub.8 is used, O.sub.2 is preferably added. In that
case, it is preferable that the partial pressure of C.sub.5F.sub.8
is in the range of 0.5.about.2 mTorr, and its ratio, i.e.,
O.sub.2/C.sub.5F.sub.8, is in the range of 5/8.about.7/8. If a
processing gas contains C.sub.4F.sub.8 or otherwise C.sub.5F.sub.8
and O.sub.2, a rare gas species such as Ar, He and the like, or
N.sub.2 may be added. Further, other CF based gas (CxFy) or CHF
based gas (hydrofluorocarbon: CpHqFr) can be added.
[0030] Further, if etching is performed on the SiN film, it is
preferable that CHF based gas, e.g., CH.sub.2F.sub.2 containing gas
or the like, is used. In this case, O.sub.2 is preferably added as
well. Additionally, a rare gas species such as Ar, He and the like,
or N.sub.2 may be added. As for a preferred example of CHF based
gas, a gaseous mixture of CH.sub.2F.sub.2, Ar and O.sub.2 can be
used.
[0031] At the bottom portion of the chamber 2, the chamber is
connected to a gas exhaust line 31, to which a gas exhaust unit 35
is connected. The gas exhaust unit 35 has a vacuum pump such as a
turbo molecular pump or the like, to vacuum-exhaust the inside of
the chamber 2 until it reaches a predetermined depressurized level,
e.g., 1 Pa or less. Further, at a sidewall of the chamber 2, there
is provided a gate valve 32; and the wafer W is allowed to be
transferred to a neighboring load-lock chamber (not shown) while
the gate valve 32 is opened.
[0032] A first high frequency power supply 40 is connected to the
upper electrode 21, and a matching unit 41 is installed in a feeder
line thereof. Further, a low pass filter (LPF) 42 is connected to
the upper electrode 21. The first high frequency power supply 40
has a frequency in the range of 50.about.150 MHz. By applying such
a high frequency, it is possible to generate a high-density plasma
in a preferred dissociation state in the chamber 2, and thus a
plasma processing may be performed at low pressure. It is
preferable that the frequency of the first high frequency power
supply 40 is in the range of 50.about.80 MHz, and typically, it is
set at 60 MHz or so.
[0033] A second high frequency power supply 50 is connected to the
susceptor 5 as a lower electrode, and a matching unit 51 is
installed in a feeder line thereof. The second high frequency power
supply 50 has a frequency in the range of 1.about.4 MHz. By
applying such a range of frequency, it is possible to apply a
proper ionic action to the wafer W as an object to be processed
without damaging it. It is preferable that a frequency of the
second high frequency power supply 50 is in the range of 1.about.3
MHz, and typically, it is set at 2 MHz or so.
[0034] Next, etching such as an oxide film formed on the wafer W,
in the plasma processing apparatus 1 as configured above is
discussed. First, the wafer W as an object to be processed is
loaded into the chamber 2 from the load-lock chamber (not shown) to
be mounted on the electrostatic chuck 11, after the gate valve 32
is opened. Further, a DC voltage is applied from the DC power
supply 13 to electrostatically adsorb the wafer W on the
electrostatic chuck 11. Subsequently, the gate valve 32 is closed,
and the inside of the chamber 2 is vacuum-exhausted at a
predetermined vacuum level by the gas exhaust unit 35.
[0035] Thereafter, the valve 28 is opened, so that a processing
gas, e.g., a gaseous mixture of C.sub.5F.sub.8, Ar and O.sub.2 (Ar
and O.sub.2 are for dilution), is introduced from the processing
gas supply unit into a hollow portion of the upper electrode 21
through the processing gas supply line 27 and the gas inlet port
26, while a flow rate thereof is adjusted by the mass flow
controller 29; and it is uniformly supplied through the injection
holes 23 of the electrode plate 24 towards the wafer W, as
indicated by arrows shown in FIG. 1.
[0036] Further, the pressure of the chamber 2 is maintained at a
predetermined level. In this case, it is preferable that the
pressure is 1.06.about.13.3 Pa. After that, a high frequency power
of 50.about.150 MHz, e.g., 60 MHz, is applied to the upper
electrode 21 from the first high frequency power supply 40.
Accordingly, a high frequency electric field is generated between
the upper electrode 21 and the susceptor 5 as a lower electrode,
and thus, the processing gas is dissociated to form a plasma.
[0037] Meanwhile, a high frequency power of 1.about.4 MHz, e.g., 2
MHz, is applied to the susceptor 5 as a lower electrode from the
second high frequency power supply 50. Accordingly, ions in the
plasma are attracted towards the susceptor 5, and as a result, a
high etching anisotropy is achieved due to ion-assist.
[0038] In the cleaning procedure, cleaning gas instead of etching
gas turns into a plasma in the plasma processing apparatus 1, and
this is preferable. For example, a plasma processing may be
performed in such a manner that the valve 30 connected to the
N.sub.2/O.sub.2 supply source 54 is opened; and an N.sub.2/O.sub.2
as a cleaning gas is introduced into the hollow portion of the
upper electrode 21 through the processing gas supply line 27 and
the gas inlet port 26 while the flow rate thereof is adjusted by
the mass flow controller 29, and thus, it being uniformly supplied
towards the wafer W through the injection holes 23 of the electrode
plate 24, as indicated by arrows shown in FIG. 1.
[0039] Hereinafter, the process conditions of the cleaning
procedure will be discussed. The cleaning procedure is performed
under a zero bias condition where a high frequency power is not
supplied from the second high frequency power supply 50 to the
susceptor 5 as a lower electrode, and a bias power is not applied
to the wafer W. By performing the cleaning procedure under a zero
bias condition, it is possible to keep any effects on a mask film
or a base film to a minimum, and to perform the cleaning without
affecting the wafer W.
[0040] Further, when performing the cleaning procedure, it is
preferable that the gap between the susceptor 5 and the upper
electrode 21 is set large (e.g., about 60 mm), as compared to the
gap during etching, in order to avoid any effects on the wafer
W.
[0041] Preferably, the cleaning gas may be a gas containing at
least O.sub.2 gas (i.e., an O.sub.2 containing gas). For example,
there may be preferably used a gaseous mixture of O.sub.2 and
N.sub.2 gas, a gaseous mixture of O.sub.2 and rare gas (Ar or He or
the like), or a gaseous mixture of O.sub.2 and CO gas, etc. Among
the O.sub.2 containing gases, it is most preferable that the
gaseous mixture of O.sub.2 gas and N.sub.2 gas is employed. If a
first film as an etching target is a silicon oxide film such as
SiO.sub.2 or the like, the etching is commonly performed by using a
halogen containing gas such as C.sub.4F.sub.8, C.sub.5F.sub.8 or
the like, so that a halogen compound is deposited in the chamber.
Such a deposit is readily removed by using a gaseous mixture
containing N.sub.2 and O.sub.2 as cleaning gas.
[0042] If a processing is performed by using a gaseous mixture of
N.sub.2 and O.sub.2, it is preferable that pressure of the
processing vessel is about 50.about.200 mTorr; the flow rate of
O.sub.2 is about 5.about.15 mL/min (=sccm); and the flow rate of
N.sub.2 is about 100.about.400 mL/min, as described below.
[0043] The endpoint of cleaning may be detected by, e.g., a plasma
emission monitor (not shown). Since fluorine has a peak intensity
at 703.8 nm, the cleaning may be performed until the wavelength of
fluorine is not detected while being continuously monitored.
[0044] Next, a preferred embodiment of an etching method in
accordance with the present invention will be explained with
reference to FIGS. 2A.about.2C and 3A.about.3C.
[0045] FIGS. 2A to 2C present views schematically showing cross
sectional status of the chamber 2 and the substrate to be processed
in the etching processing. FIGS. 2A to 2C correspond to a case
where a film to be etched is an insulating film made of an
inorganic material, wherein, on substrate 61 forming the wafer W,
stacked from the top surface are: a photosensitive resist film 64,
a silicon oxide film 63 as a first film to be etched, and a silicon
nitride film 62 as a second film. As described above, the
insulating film as an etching target layer may be a silicon oxide
film, e.g., SiO.sub.2 or the like, or a silicon nitride film such
as SiN or the like. Further, in the present embodiment, the mask
film is the photosensitive resist film 64 made of an organic
material, but it may be a hard mask made of an inorganic
material.
[0046] As described in FIG. 2A, the photosensitive resist film 64,
as the outermost layer, is exposed and developed to have a
predetermined pattern. In a first etching, the silicon oxide film
63 is etched by using the photosensitive resist film 64 as a
mask.
[0047] After the first etching, the deposits 70 remain on the inner
wall surface of the chamber 2, as shown in FIG. 2B. If a second
etching processing is performed in such a state where the deposits
70 are formed in the chamber 2 as above, the conditions of the
second etching processing is affected and therefore changed due to
a memory effect, and thus it is difficult to achieve a satisfactory
etching. For the same reason, cleaning is performed to remove the
deposits 70. By removing the deposits 70 from the chamber by
performing the cleaning, this memory effect can be reduced.
[0048] After the cleaning procedure, a second etching processing is
performed. In the second etching processing, as described in FIG.
2C, the silicon nitride film 62 is etched by using the
photosensitive resist film 64 and the silicon oxide film 63 as a
mask. As mentioned above, in the second etching step, the silicon
oxide film 63 of the first film as well as the photosensitive
resist film 64 can serve as a mask film.
[0049] Etching of the silicon nitride film 62 may be performed
under a stable condition, without being affected by the deposits
70, since the deposits 70 produced by the etching of the silicon
oxide film 63 have been removed from the chamber by performing the
cleaning procedure.
[0050] FIGS. 3A to 3C show cross sectional configurations of the
substrate to be processed in the etching processings, in accordance
with a second embodiment of the present invention. Here,
illustrated therein are cases where a film to be etched is composed
of a silicon oxide film (made of an inorganic material) and an
organic film.
[0051] Namely, on a substrate 61 forming the wafer W, there are
stacked, from the top surface, a photosensitive resist film 67,
silicon oxide film 66 as a first film to be etched, and organic
film 0.65 as a second film. The silicon oxide film as an etching
target layer may be an insulating film such as SiO.sub.2 or the
like, same as above. As for the organic film, it can be used a low
dielectric interlayer insulating film (Low-k film), e.g., SiLK
(trademark name: Dow chemical made); MSQ of SOD-SiOCH (methyl
silsesquioxane); CORAL of CVD-SiOCH (trademark name: Novellus
Systems made); or Black Diamond (trademark name: Applied Materials
made).
[0052] As described in FIG. 3A, the photosensitive resist film 67
as an outermost layer is exposed and developed to have a
predetermined pattern. In a first etching, the silicon oxide film
66 is etched by using the photosensitive resist film 67 as a
mask.
[0053] After the first etching processing, the deposits 70 are
formed on the inner wall surface of the chamber 2, as shown in FIG.
3B. Hence, cleaning of the chamber 2 is performed to remove the
deposits 70.
[0054] After the cleaning processing, a second etching processing
is performed. In the second etching processing, as shown in FIG.
3C, the organic film 65 is etched by using the photosensitive
resist film 67 and the etched silicon oxide film 66 as a mask. As
mentioned above, in the second etching processing, the silicon
oxide film 66 of the first film as well as the photosensitive
resist film 67 can serve as a mask film.
[0055] If the second film is an organic film, it is preferable
that, e.g., a gaseous mixture of N.sub.2 and H.sub.2, an NH.sub.3
gas, a gaseous mixture of N.sub.2 and O.sub.2, or the like may be
used as etching gas. The etching of the organic film 65 can be
performed under a stable condition, without being affected by the
deposits 70, since the deposits 70 produced by the etching of the
silicon oxide film 66 have been removed from the chamber by
performing the earlier cleaning.
[0056] In FIGS. 2A.about.2C and 3A.about.3C, it is illustrated a
case where an etching target layer as an object to be etched is
two-layered. However, even if the etching target layer is composed
of three-layers or more, the same effect may be obtained by
performing a cleaning processing in the processing vessel after
each etching, and then etching in the vessel, in the same
manner.
[0057] Hereinafter, the present invention will be explained more
specifically by illustrating examples, but it is not limited
thereto.
EXAMPLE 1
[0058] Etching processing in accordance with the present
invention:
[0059] In accordance with the present invention, an etching
processing was performed on a wafer W of silicon substrate, on
which, following layers are stacked from the top: a mask film (a
photosensitive resist film); an SiO.sub.2 film (a thermal oxide
film; 300 nm) as first film to be etched; and an SiN film (a plasma
Si.sub.3N.sub.4 film; 50 nm) as second film.
[0060] In first etching processing, high frequency powers of 1500 W
and 1700 W were applied to the upper electrode 21 and the susceptor
5, respectively; pressure in the chamber was set at 30 mTorr, and
the gap between the susceptor 5 and the upper electrode 21 was set
at 30 mm; a gaseous mixture of C.sub.5F.sub.8, Ar and O.sub.2 was
used as etching gas; and gas flow rate (mL/min) ratio was set
C.sub.5F.sub.8:Ar:O.sub.2=1- 5:800:17 to perform etching. Further,
the volume of the chamber used was 80 litters.
[0061] After the first etching, a zero bias cleaning was carried
out. That is, a power was not applied to the susceptor 5 while a
high frequency power of 500 w was applied to the upper electrode
21; pressure in the chamber was set at 100 mTorr and the gap
between the susceptor 5 and the upper electrode 21 was set at and
60 mm; a gaseous mixture of N.sub.2 and O.sub.2 was used as
cleaning gas; and gas flow rate (mL/min) ratio was set
N.sub.2:O.sub.2=100:10 to perform cleaning. The gap between the
susceptor 5 and the upper electrode 21 is set large so as to have
minimal effects on the wafer W. The endpoint of the cleaning was
detected by a plasma emission monitor.
[0062] After the cleaning step was completed second etching
processing was carried out in the same chamber. In the second
etching processing, high frequency powers of 2000 w and 100 W were
applied to the upper electrode 21 and the susceptor 5,
respectively; pressure in the chamber was set at 50 mTorr, and the
gap between the susceptor 5 and the upper electrode 21 was set at
and 55 mm; a gaseous mixture of CH.sub.2F.sub.2, Ar and O.sub.2 was
used as etching gas; and gas flow rate (mL/min) ratio was set
CH.sub.2F.sub.2:Ar:O.sub.2=20:100:15 to perform etching.
[0063] The state of the wafer W after etching is shown in FIG. 4.
The vertical axis in FIG. 4 is etched amount; and the horizontal
axis is distances from the center (zero scale) of the wafer W to
each of end portions in X and Y directions.
[0064] Further, as an example for reference purpose, the state of
the wafer W is shown in FIG. 5 when the second etching was
performed in a different chamber from the first etching.
COMPARATIVE EXAMPLE 1
[0065] An etching was performed under the same conditions as in
Example 1, except that the cleaning was not performed. The state of
the wafer W after the etching processing is shown in FIG. 6.
[0066] As can be seen clearly from the comparison between FIGS. 4
to 6, the wafer W of Example 1, on which the cleaning was
performed, was etched as uniformly as in the reference example
(FIG. 5) wherein etching was performed in different chambers.
Meanwhile, in the all-in-one etching of Comparative example 1 (FIG.
6) wherein the cleaning was not performed, etched amount decreased
in the central portion of the wafer W, and uniform etching was not
achieved. The memory effect of etching the SiO.sub.2 film is
considered to have produced this difference in etching conditions
for the SiN film.
EXAMPLE 2
[0067] Examination on Cleaning Condition (Pressure):
[0068] A cleaning procedure was performed under the same conditions
as in Example 1, except that pressure is changed in the range of
10.about.200 mTorr. The results are shown in FIG. 7. If the
pressure is in the range of 50.about.200 mTorr, the chamber
cleaning time is short, and also the resist etching rate is low.
Therefore, the amount of resist etched during the cleaning
procedure is small and satisfactory. This result can be obtained
stably in the pressure range of 100.about.200 mTorr, specifically.
Accordingly, the above range is found to be most preferable.
EXAMPLE 3
[0069] Examination on Cleaning Condition (Flow Rate of
N.sub.2):
[0070] A cleaning procedure was performed under the same conditions
as in Example 1, except that flow rate of O.sub.2 is fixed at 10
mL/min and that of N.sub.2 is changed in the range of 50.about.400
mL/min. The results are shown in FIG. 8.
[0071] From FIG. 8, if flow rate of N.sub.2 is less than 100
mL/min, the relative fraction of O.sub.2 is increased (e.g., when
the flow rate of N.sub.2 is 50 mL/min,
O.sub.2/(N.sub.2+O.sub.2)=17%). Thus, the chamber cleaning time is
decreased, but the resist etching rate is significantly increased.
As a result, the amount of etched resist is also increased even
though the overall cleaning time is made shorter. On the contrary,
if the flow rate of N.sub.2 is equal to or greater than 200 mL/min,
the chamber cleaning time and the resist etching rate were
decreased in a substantially same manner. As a result, the amounts
of resist etched were substantially constant and satisfactory in
the N.sub.2 flow rate range of 100.about.400 mL/min. When the flow
rate of N.sub.2 are 200 mL/min and 400 mL/min,
O.sub.2/(N.sub.2+O.sub.2) were 4.8% and 2.4%, respectively.
EXAMPLE 4
[0072] Examination on Cleaning Condition (Flow Rate of
O.sub.2):
[0073] A cleaning processing was performed under the same
conditions as in Example 1, except that flow rate of N.sub.2 is
fixed at 100 mL/min and that of O.sub.2 is changed in the range of
5.about.15 mL/min. The results are shown in FIG. 9.
[0074] From FIG. 9, it is understood that if the flow rate of
O.sub.2 is reduced to, e.g., 5 mL/min, so that the ratio of O.sub.2
is decreased [O.sub.2/(N.sub.2+O.sub.2)=4.8%], the resist etching
rate is not significantly decreased. However, since the chamber
cleaning time is increase, the resulting amount of etched resist is
increased.
[0075] Contrary to this, if flow rate of O.sub.2 is increased
(e.g., 10 mL/min, so O.sub.2/(N.sub.2+O.sub.2)=9%; and, 15 mL/min,
so .degree. 2/(N.sub.2+O.sub.2)=13%), the chamber cleaning time is
significantly shortened. Accordingly, even if the etching rate of
the resist is somewhat increased, the etched resist amount is
consequently decreased because the cleaning time became
significantly shorter.
[0076] Further, if the conditions of Example 3 (FIG. 8), wherein
the fractions of O.sub.2 are 4.8% and 2.4%, are compared with those
of FIG. 9, wherein the fraction of O.sub.2 is 4.8%, even though the
O.sub.2 fractions are the same or lower in the former conditions
than the latter, the chamber cleaning time is shortened and the
amounts of etched resist are small and satisfactory. The reason is
believed that since the total amount of gas to be supplied is
large, the cleaning gas is efficiently diffused over the whole
inner wall of the chamber, onto which deposits build up, and
reaction products from the wall surface are efficiently
exhausted.
[0077] From FIGS. 8 and 9, it is shown that a preferred O.sub.2
ratio is about 5.about.15% (preferably, about 9.about.15%) and a
flow rate of total gas is about 200.about.400 mL/min in the
cleaning processing.
[0078] In accordance with an etching method of the present
invention, it is possible to avoid changes in etching
characteristics due to a memory effect while maintaining the
benefits of all-in-one etching.
[0079] The etching method in accordance with the present invention
may be employed in the fabrication of semiconductor devices.
[0080] While the invention has been shown and described with
respect to the preferred embodiments, 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.
* * * * *