U.S. patent application number 09/286008 was filed with the patent office on 2001-12-20 for method for cleaning interior of etching chamber.
Invention is credited to CHENG, W. H., CHI, C.M., CHOW, YU-CHANG, LEE, COBBY, YEH, CHIA-FU.
Application Number | 20010052350 09/286008 |
Document ID | / |
Family ID | 21639799 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052350 |
Kind Code |
A1 |
CHOW, YU-CHANG ; et
al. |
December 20, 2001 |
METHOD FOR CLEANING INTERIOR OF ETCHING CHAMBER
Abstract
A process for cleaning the interior walls of a reaction chamber
after a number of silicon wafers is etched inside the chamber. The
cleaning process includes bombarding the interior walls of the
chamber with a first type of plasma in a dry cleaning operation,
and then bombarding the interior walls of the chamber with a second
type of plasma containing the element hydrogen in a warm-up
operation. No silicon wafers need to be placed inside the chamber
when the dry cleaning operation or the warm-up operation is
conducted.
Inventors: |
CHOW, YU-CHANG; (HSINCHU,
TW) ; CHENG, W. H.; (HSINCHU HSIEN, TW) ; YEH,
CHIA-FU; (TAIPEI, TW) ; CHI, C.M.; (TAICHUNG
HSIEN, TW) ; LEE, COBBY; (HSINCHU, TW) |
Correspondence
Address: |
Jiawei Huang
J.C. PATENTS INC.
4 Venture
Suite 250
Irvine
CA
92618
US
|
Family ID: |
21639799 |
Appl. No.: |
09/286008 |
Filed: |
April 5, 1999 |
Current U.S.
Class: |
134/1.1 ;
134/1.2; 134/22.1; 438/905 |
Current CPC
Class: |
H01J 37/32862 20130101;
Y10S 438/905 20130101 |
Class at
Publication: |
134/1.1 ;
134/1.2; 134/22.1; 438/905; 156/345 |
International
Class: |
B08B 009/00; H01L
021/301 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 1, 1999 |
TW |
88103039 |
Claims
What is claimed is:
1. A method for cleaning a reaction chamber of a silicon wafer
etcher, comprising steps of: performing a dry cleaning operation by
bombarding interior walls of the reaction chamber with a first type
of plasma; and performing a warm-up operation by bombarding the
interior walls of the reaction chamber with a second type of
plasma, wherein no silicon wafers are placed inside the reaction
chamber during the dry cleaning operation and the warm-up
operation.
2. The method of claim 1, wherein the first type of plasma contains
gaseous chlorine, gaseous oxygen and carbon hexafluoride.
3. The method of claim 2, wherein a flow rate of gaseous chlorine
is about 20 sccm, a flow rate of gaseous oxygen is about 50 sccm, a
flow rate of carbon hexafluoride is about 100 sccm and the first
type of plasma has a pressure of about 10 mT at a power of about
800W.
4. The method of claim 3, wherein the dry cleaning operation is
carried out for a period of about 70 seconds.
5. The method of claim 1, wherein the second type of plasma
includes a gaseous mixture that contains an element hydrogen.
6. The method of claim 5, wherein the second type of plasma
includes gaseous chlorine having a flow rate of about 50 sccm and
hydrogen bromide having a flow rate of about 50 sccm, and the
second type of plasma is at a pressure of about 15 mT and a power
of about 800W.
7. The method of claim 6, wherein the warm-up operation is carried
out for a period of about 60 seconds.
8. The method of claim 5, wherein the second type of plasma further
includes gaseous hydrogen with a flow rate of about 50 sccm to 150
sccm, and the second type of plasma is at a pressure of between 10
mT to 100 mT and a power of between 500W to 800W.
9. The method of claim 8, wherein the warm-up operation is carried
out for a period of between 60 to 300 seconds.
10. A process for cleaning an interior of a wafer etching chamber
after a number of wafer etching operations, comprising steps of:
bombarding the interior walls of the chamber with a first type of
plasma that contains gaseous chlorine, gaseous oxygen and carbon
hexafluoride; and bombarding the interior walls of the chamber with
a second type of plasma that contains a gaseous source with an
element hydrogen.
11. The process of claim 10, wherein after the step of bombarding
the interior walls of the chamber with the second type of plasma,
further includes performing an inspection.
12. The process of claim 10, wherein after performing a plurality
of the cleaning operations, further includes performing a wet
cleaning operation.
13. The process of claim 10, wherein the first type of plasma
includes gaseous chlorine at a flow rate of about 20 sccm, gaseous
oxygen at a flow rate of about 50 sccm, and gaseous carbon
hexafluoride at a flow rate of about 100 sccm, and the first type
of plasma is at a pressure of about 10 mT and a power of about
800W.
14. The process of claim 13, wherein the step of bombarding the
interior walls of the chamber with the first type of plasma
continues for a period of about 70 seconds.
15. The process of claim 10, wherein the second type of plasma
includes gaseous chlorine with a flow rate of about 50 sccm and
gaseous hydrogen bromide with a flow rate of about 50 sccm, and the
second type of plasma is at a pressure of about 15 mT and a power
of about 800W.
16. The process of claim 15, wherein the step of bombarding the
interior walls of the chamber with the second type of plasma
continues for a period of about 60 seconds.
17. The process of claim 10, wherein the second type of plasma
further includes gaseous hydrogen with a flow rate of about 50 sccm
to 150 sccm, and the second type of plasma is at a pressure of
between 10 mT to 100 mT and a power of between 500W to 800W.
18. The process of claim 17, wherein the step of bombarding the
interior walls of the chamber with the second type of plasma
continues for a period of about 60 to 300 seconds.
19. The process of claim 10, wherein the cleaning operation is
conducted once after roughly one to 30 silicon wafers are etched
inside the chamber.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Taiwan
application Ser. No. 88103039, filed Mar. 1, 1999, the full
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to a method for cleaning the
interior of an etching chamber. More particularly, the present
invention relates to a method for cleaning the interior walls of an
etching chamber with plasma.
[0004] 2. Description of Related Art
[0005] In the manufacture of semiconductor products, most gate
conductive layers of a MOS transistor are composed of a doped
polysilicon layer and a metallic silicide layer. The metallic
silicide layer/is probably a tungsten silicide (WSi.sub.x) layer.
In general, the transistor gate structure is formed by first
depositing a polysilicon layer and then a metal silicide layer over
a substrate. Next, a photoresist layer is deposited and then
patterned using a photolithographic method. Finally, the metal
silicide layer and the polysilicon layer are sequentially etched
using an anisotropic plasma etching method to form a gate
structure.
[0006] An anisotropic plasma etching operation is a process in
which highly energetic particles within the plasma are deployed to
bombard tungsten silicide and polysilicon of the conductive layer.
Therefore, some reaction products are deposited on the interior
walls of the reaction chamber and gradually accumulate. These
reaction products, composing mainly micro-particles or high
molecular weight compounds, may drop back onto the surface of the
silicon wafer when the wafer is undergoing an etching operation.
Often, this may lead to the deviation of critical dimensions for
some of the devices on the wafer.
[0007] In consequence, after the reaction chamber has been used for
a number of times or the etching station has been left idle for
more than an hour, a dry cleaning process needs to be carried out.
The dry cleaning process tries to remove any deposited reaction
products attached to the interior walls of the chamber, thereby
maintaining a rather constant reaction environment inside the
chamber and reducing product yield problems.
[0008] A dry cleaning process actually comprises a dry cleaning
operation and a warm-up operation. Conventionally, the dry cleaning
operation requires the execution of an etching operation inside the
reaction chamber for about 500 RFmin. In other words, the process
includes powering up at normal working radio frequency (RF) range
for about 500 minutes with three silicon wafers inside the reaction
chamber. Next, a mixture of gases including chlorine (Cl.sub.2) and
carbon hexafluoride (CF.sub.6) are passed into the chamber to form
a plasma that can be used to bombard the interior walls of the
reaction chamber. The bombarding operation lasts for another 5
RFmin. Hence, most of the reaction products deposited on the
interior walls of the reaction chamber are removed.
[0009] Since most reaction products deposited on the interior walls
of the reaction chamber are removed during the dry cleaning phase,
the environment inside the reaction chamber with respect to wafer
etching may change suddenly. Great changes in the etching
environment may lead to instability when etching a conductive
layer. In order to obtain a more stable wafer quality, a warm-up
operation is necessary to stabilize the reaction environment inside
the chamber.
[0010] In a conventional warm-up operation, a dummy wafer is placed
inside the chamber and then a reaction condition similar to a
normal etching operation is applied. Since etching a conductive
layer actually includes etching a photoresist layer, a tungsten
silicide layer and a polysilicon layer, the warm-up operation must
includes several steps. Firstly, a gaseous mixture of oxygen,
hydrogen and hydrogen bromide (HBr) is passed into the chamber to
form a plasma, and then the dummy wafer is bombarded using the
plasma for about 90 seconds. Next, a gaseous mixture of chlorine
and hydrogen bromide is passed into the chamber to form another
plasma, and then the dummy wafer is again bombarded by the plasma
for about 140 seconds. Finally, a gaseous mixture containing
hydrogen bromide, helium and helium dioxide (HeO.sub.2) is passed
into the chamber to form yet another plasma, and then the dummy
wafer is bombarded with the plasma for about 100 seconds. The
warm-up operation requires altogether some 3 to 10 dummy wafers.
After the warm-up operation, a more stable etching environment is
obtained.
[0011] However, in the aforementioned method of cleaning the
reaction chamber, fluoride-containing (F) gaseous mixture is used
as a plasma source. Therefore, a considerable amount of fluorine
radicals is attached to the interior walls of the reaction chamber.
When metal silicide or polysilicon layers are being etched, these
fluorine radicals can react with the chlorine and hydrogen bromide
in the plasma. Consequently, uniformity of wafer surface may worsen
and the etching rate may be reduced, leading to larger deviations
in the critical dimensions of some devices. In some cases, even an
etching selectivity ratio between polysilicon and oxide may be
affected. If the etching selectivity ratio changes, it is rather
difficult to determine the etching end point when polysilicon is
etched. Moreover, the plasma used for etching the polysilicon layer
may etch into the gate oxide layer between the gate conductive
layer and the substrate. Since the gate oxide layer is already a
very thin layer of about 80 .ANG., any further reduction of the
gate oxide layer down to a thickness of about 40 .ANG. or lower by
etching leads to serious problems such as the pitting of the active
area of a device.
[0012] The amount of fluoride radicals on the interior wall of the
chamber is reduced gradually as the number of etching operations
being conducted increases, and hence the etching environment
recovers only after a while. Therefore, etch quality of the first
few silicon wafers immediately after the dry cleaning process may
not be too stable, but improves considerably due to the
stabilization of the chamber environment later on. The phenomenon
of the first batch of a few silicon wafers having a poorer quality
than subsequent batches is called the first wafer effect or memory
effect.
[0013] Furthermore, several pieces of silicon wafers and dummy
wafers are wasted during the dry cleaning operation as well as the
warm-up operation. Moreover, a wet cleaning operation needs to be
carried out after every 8000 RFmin of etching operation despite the
performance of dry cleaning processes from time to time. Hence,
functional time of the reaction chamber is short and wafer
productivity is low.
[0014] In light of the foregoing, there is a need to provide a
better method of cleaning the reaction chamber.
SUMMARY OF THE INVENTION
[0015] Accordingly, the present invention provides a method for
clearing away reaction products accumulated on the interior walls
of an etching chamber after a number of etching operations so that
stable etching operations can be resumed.
[0016] To achieve these and other advantages and in accordance with
the invention, as embodied and broadly described herein, the
invention provides a method for cleaning a silicon wafers etching
chamber. The method includes performing a dry cleaning operation
followed by a warm-up operation. In the dry cleaning operation, a
gaseous mixture containing chlorine, oxygen and carbon hexafluoride
is passed into the reaction chamber to form a first type of plasma.
Next, the plasma is made to bombard against the interior walls of
the reaction chamber. In the warm-up operation, a gaseous mixture
containing the element hydrogen is passed into the reaction chamber
to form a second type of plasma. Then, the plasma is again made to
bombard against the interior walls of the reaction chamber so that
fluoride free radicals inside the reaction chamber are removed.
Ultimately, the etching environment within the etching chamber
returns to normal.
[0017] The dry cleaning process according to this invention does
not require the use of any silicon wafer. The dry cleaning process
includes a dry cleaning operation and a warm-up operation. Hence,
the method is capable not only of reducing first silicon effect and
providing a stable etching environment inside the chamber, but also
capable of minimizing silicon wafer wastes. In the dry cleaning
process, only two types of plasmas are used, thereby having fewer
steps and a shorter cleaning period. Furthermore, the reaction
chamber can be used to etch silicon wafers for a longer period
before cleaning is necessary. Hence, there is considerable increase
in productivity.
[0018] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying drawing is included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawing illustrates
embodiments of the invention and, together with the description,
serves to explain the principles of the invention. In the
drawing,
[0020] FIG. 1 is a flow chart showing the steps involved in
cleaning the etching chamber according to this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0022] FIG. 1 is a flow chart showing the steps involved in
cleaning the etching chamber according to this invention.
[0023] If an etching machine is left in idle for more than an hour
or some 1 to 30 silicon wafers have passed through an etching
operation 18, an environment inside the etching chamber may have
changed considerably. If the etching operation is permitted to
continue, problems related to etching quality may arise. In other
words, the etching rate may be difficult to control, resulting
threshold dimensions may be out of range and the etching end point
may be hard to determine. Therefore, a dry cleaning process that
includes a dry cleaning operation 12 and a warm-up operation 14
need to be conducted.
[0024] First, in a dry cleaning operation 12, a first type of
plasma is produced inside the chamber for bombarding against the
interior walls. The first type of plasma is formed by introducing
gaseous chlorine at a flow rate of about 20 sccm, gaseous oxygen at
a flow rate of about 50 sccm and gaseous carbon hexafluoride at a
flow rate of about 100 sccm. The plasma is at a pressure of about
10 mT and a power of about 800W. The bombardment of interior walls
of the etching chamber continues for about 70 seconds. Note that
there is no need to place silicon wafers inside the reaction
chamber when the dry cleaning operation 12 is performed.
[0025] Since the gaseous mixture used in the dry cleaning operation
12 contains the element fluorine, some fluoride radicals accumulate
on the interior walls of the chamber. These fluoride radicals may
react with gaseous chlorine and hydrogen bromide in the plasma when
polysilicon or metal silicide layer is etched, thereby affecting
surface uniformity, etching rate and etching selectivity ratio
between polysilicon and oxide material. Furthermore, the amount of
fluoride radicals diminishes as more etching operations are
conducted, thereby leading to what is known as the first wafer
effect. To remove the fluoride radicals, a warm-up operation 14 is
conducted next.
[0026] In a warm-up operation 14, a second type of plasma is
produced inside the chamber for bombarding against the interior
walls. The second type of plasma is formed by introducing gaseous
chlorine at a flow rate of about 50 sccm and gaseous hydrogen
bromide at a flow rate of about 50 sccm. The plasma is at a
pressure of about 15 mT and a power of about 800W. The bombardment
of the interior walls of the etching chamber continues for about 60
seconds. In addition, the second type of plasma may also be formed
by introducing gaseous hydrogen at a flow rate of about 50 sccm to
150 sccm. The plasma has a pressure of between 10 mT to 100 mT and
a power of between 500W to 800W. The bombardment of interior walls
of the etching chamber continues for about 60 to 300 seconds. Note
that there is no need to place silicon wafers inside the reaction
chamber when the warm-up operation 14 is performed.
[0027] The element hydrogen in the gaseous source used in forming
the second plasma for the warm-up operation 14 can react with the
fluoride free radicals. Hence, the harmful effects of fluoride
radicals in subsequent etching operations are greatly reduced.
[0028] To ensure stability of etching operations inside the
reaction chamber, an inspection 16 of the cleaning process is
conducted immediately after the warm-up operation 14. If the
results meet the normal operation standard with respect to the
etching rate, the quantity of micro-particles and surface
uniformity of etched silicon wafers, normal etching operations 18
can resume. On the contrary, if the conditions inside the reaction
chamber are unsatisfactory, for example, the number of
micro-particles having a diameter more than 0.02 micro-meter are
more than 30, another dry cleaning process needs to be carried out.
In other words, the dry cleaning operation 12, the warm-up
operation 14 and the inspection operation 16 have to be repeated
again. However, if after repeating the dry cleaning operation 12,
the warm-up operation 14 and the inspection operation 16, the
results are still not up to standard, another round of dry cleaning
operation 12, warm-up operation 14 and inspection operation 16 can
be conducted. After performing the dry cleaning process 20 twice,
if there is still no marked improvement in the etching conditions
of the etching operation, a wet cleaning operation 10 needs to be
conducted.
[0029] In addition, after etching one to 30 silicon wafers inside
an etching chamber, a dry cleaning operation 12 followed by a
warm-up operation 14 are conducted. The wafer etching operations
together with the cleaning operation 12 and the warm-up operation
14 can be considered one operating cycle for the reaction chamber.
After going through some 10 to 20 operating cycles, a dry cleaning
operation 12 and a warm-up operation alone may no longer be able to
remove the deposited reaction products accumulated through many
operating cycles. To resume the original etching state or to act
just as a preventive maintenance measure, a wet cleaning operation
10 is then carried out.
[0030] To perform a wet cleaning operation, the entire etching
machine has to be shut down. The etching chamber has to be opened
up so that various components can be taken apart for manual
cleaning. Any reaction products deposited on the interior walls of
the chamber can be brushed away using chemical agents.
Consequently, a wet cleaning operation is quite time-consuming and
labor intensive. However, using the cleaning method of this
invention, the operable period between two wet cleaning operations
is lengthened to over 30000 RFmin.
[0031] In summary, the cleaning method of this invention is able to
remove reaction products attached to the interior walls of a
reaction chamber without having to place silicon wafers into the
chamber, thereby saving some wafers. Furthermore, the method is
able to reconstitute a stable etching environment inside the
chamber without the first wafer effect. Moreover, suitable etching
conditions are maintained longer after each cleaning process than
the conventional method. Hence, more silicon wafers can be etched
inside the chamber, thereby increasing the productivity of
wafers.
[0032] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention, In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *