U.S. patent application number 10/927483 was filed with the patent office on 2005-03-31 for semiconductor manufacturing apparatus and manufacturing method of semiconductor device.
This patent application is currently assigned to Trecenti Technologies, Inc.. Invention is credited to Funabashi, Michimasa.
Application Number | 20050067101 10/927483 |
Document ID | / |
Family ID | 34372420 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050067101 |
Kind Code |
A1 |
Funabashi, Michimasa |
March 31, 2005 |
Semiconductor manufacturing apparatus and manufacturing method of
semiconductor device
Abstract
Semiconductor manufacturing apparatus and a manufacturing method
of a semiconductor device capable of applying the single-wafer
processing to the wet etching of a silicon nitride film are
provided. Each one wafer is held by wafer holding means and etching
solution is supplied to a deposited film of the wafer by etching
solution supply means. The supplied etching solution is irradiated
with electromagnetic wave by electromagnetic wave heating means so
as to heat the etching solution to a high temperature and then the
deposited film is wet-etched at a high etching rate. The wet
etching with the process time appropriate for the single-wafer
processing can be achieved. The used etching solution is collected
by recycle means and is reused in the subsequent etching after
adjusting its concentration.
Inventors: |
Funabashi, Michimasa;
(Hachioji, JP) |
Correspondence
Address: |
Stanley P. Fisher
Reed Smith LLP
Suite 1400
3110 Fairview Park Drive
Falls Church
VA
22042-0681
US
|
Assignee: |
Trecenti Technologies, Inc.
|
Family ID: |
34372420 |
Appl. No.: |
10/927483 |
Filed: |
August 27, 2004 |
Current U.S.
Class: |
156/345.18 ;
156/345.11; 257/E21.251 |
Current CPC
Class: |
H01L 21/67109 20130101;
H01L 21/31111 20130101; H01L 21/6708 20130101 |
Class at
Publication: |
156/345.18 ;
156/345.11 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2003 |
JP |
JP2003-305605 |
Claims
What is claimed is:
1. A semiconductor manufacturing apparatus, comprising: wafer
holding means for holding a wafer on which a deposited film is
formed; etching solution supply means for supplying etching
solution for etching said deposited film; electromagnetic wave
heating means for heating said etching solution by irradiating said
solution with electromagnetic wave; and silicon concentration
adjusting means for said etching solution.
2. The semiconductor manufacturing apparatus according to claim 1
further comprising: preliminary heating means for heating said
etching solution before the solution is supplied to said deposited
film.
3. The semiconductor manufacturing apparatus according to claim 1,
wherein said wafer holding means holds said wafer so that said
deposited film faces upward, and said etching solution supplied to
said deposited film is kept on said deposited film by surface
tension.
4. The semiconductor manufacturing apparatus according to claim 1,
wherein said wafer holding means includes an immersion bath to be
filled with said etching solution and holds each of said wafers to
dip said deposited film in said etching solution.
5. The semiconductor manufacturing apparatus according to claim 1
further comprising: recycle means for used etching solution which
has been used for the etching of said deposited film.
6. The semiconductor manufacturing apparatus according to claim 1
further comprising: recycle means for used etching solution which
has been used for the etching of said deposited film, wherein said
recycle means has at least one of concentration adjusting means for
chemicals composing etching solution for said etching solution and
concentration adjusting means for reaction product produced by
etching for said etching solution.
7. The semiconductor manufacturing apparatus according to claim 1
further comprising: recycle means for used etching solution which
has been used for the etching of said deposited film, wherein said
recycle means has phosphoric acid concentration adjusting means for
said etching solution and silicon concentration adjusting means for
said etching solution.
8. The semiconductor manufacturing apparatus according to claim 1,
wherein said electromagnetic wave is microwave.
9. The semiconductor manufacturing apparatus according to claim 1,
wherein said electromagnetic wave is infrared.
10. A manufacturing method of a semiconductor device, comprising
the steps of: supplying etching solution to a deposited film on a
held wafer; heating the etching solution supplied to the deposited
film by irradiating the etching solution with electromagnetic wave;
and etching said deposited film by using said heated etching
solution.
11. The manufacturing method of a semiconductor device according to
claim 10, wherein said deposited film is a silicon nitride film,
and said etching solution is phosphoric acid solution.
12. The manufacturing method of a semiconductor device according to
claim 10, wherein said deposited film is a silicon nitride film,
said etching solution is phosphoric acid solution, and the etching
of said deposited film is performed by using said etching solution
heated to a range of 200.degree. C. and 250.degree. C.
13. The manufacturing method of a semiconductor device according to
claim 10, wherein said deposited film is a silicon nitride film,
said etching solution is phosphoric acid solution containing
silicon, and said deposited film is etched selectively with respect
to a silicon oxide film in contact with said deposited film by
using said etching solution heated to a range of 200.degree. C. and
250.degree. C.
Description
CROSS-REFERANCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese Patent
Application No. JP 2003-305605 filed on Aug. 29, 2003, the content
of which is hereby incorporated by reference into this
application.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to a technique for
manufacturing a semiconductor device. More particularly, it relates
to a technique effectively applied to the wet etching of a
deposited film formed on a wafer by using the single-wafer
processing.
BACKGROUND OF THE INVENTION
[0003] The technique described below has been examined by the
inventor of the present invention in the course of developing the
present invention, and its outline will be shown below.
[0004] In the manufacturing process of a semiconductor device,
various kinds of deposited films are formed on a semiconductor
wafer and those deposited films are etched appropriately so as to
form fine patterns for electrodes, wirings and the like.
[0005] Such an etching technique includes the dry etching using
reactive gas and the wet etching based on chemical treatment. Of
these, the wet etching is an etching technique based on chemical
reaction between an object to be etched and the chemical solution,
and it has an advantage that it can obtain a higher selectivity to
an underlying film more easily than the dry etching.
[0006] For this reason, the wet etching has been employed for the
selective etching of a silicon nitride film to an underlying
silicon oxide film in the shallow-trench device isolation technique
when forming the device isolation. "ULSI Technology" by C. Y. Chang
& S. M. Sze, McGraw-Hill, 1996, p 365 contains a description
about such etching.
[0007] In the conventional wet etching, the batch processing is
used for the etching. For example, in the case of the wet etching
of a silicon nitride film, a plurality of wafers to be processed
are dipped at a time in an immersion bath filled with heated
phosphoric acid as the etching solution.
[0008] In the etching of a silicon nitride film using the batch
processing, the heated phosphoric acid at about 150.degree. C. to
170.degree. C. is used and heating means such as an electric heater
is employed for heating the phosphoric acid. Such batch processing
usually takes about an hour.
[0009] FIG. 6A shows an entire configuration of the apparatus for
performing the wet etching using the batch processing system. In
the configuration adopting the batch processing system, a plurality
of wafers are dipped at a time in etching solution and subjected to
the wet etching. The apparatus is provided with a station 1 for
receiving the wafers and a station 2 for carrying out the processed
wafers. Further, it is provided with a buffer section 3 as a
temporary waiting place for the received wafers and for the
processed wafers.
[0010] Also, the apparatus includes a plurality of processing
sections 4 for performing the wet etching of the wafers and a
drying section 5 for drying the wafers after the wet etching. A
wafer received at the station 1 is transferred to a carrying robot
(not shown) of a carrying section 6 by means of a carrying robot
(not shown) provided in the buffer section 3 and carried to the
processing sections 4. A plurality of wafers are wet-etched at a
time in the processing sections 4.
[0011] The wafers after the wet etching in the processing sections
4 are carried to the drying section 5 by the carrying robot of the
carrying section 6 and dried therein, and then, carried further to
the buffer section 3 and finally sent to a next step from the
station 2.
[0012] As shown in FIG. 6B, the wet etching in the processing
sections 4 is performed by dipping a plurality of the wafers W at a
time in the immersion bath 7 filled with etching solution for a
predetermined time. In the immersion bath 7, the etching solution
is circulated by an etching solution circulation system provided
with a circulating pump 8. More specifically, the etching solution
is supplied from a chemical tank 8a containing the etching solution
to the immersion bath 7 through a supply pipe 8b by the circulating
pump 8. At the same time, the etching solution is returned from the
immersion bath 7 to the chemical tank 8a through a return pipe 8c.
In this way, the etching solution is always circulated.
[0013] Such a circulation system of the etching solution is
provided with a heater-type heat exchanger 8d along the supply pipe
8b as shown in FIG. 6B so as to heat the etching solution to a
predetermined temperature. For example, if phosphoric acid solution
is used as the etching solution for the wet etching of a silicon
nitride film, it is heated to 150.degree. C. to 170.degree. C.
[0014] Further, the supply pipe 8b is provided with a pulsation
prevention damper 8e for stabilizing the amount of supplied etching
solution and a filter 8f for removing foreign matters from the
etching solution so as to ensure a stabilized supply of the etching
solution containing no etching residue to the immersion bath 7.
SUMMARY OF THE INVENTION
[0015] However, the inventor of the present invention has found out
the following subjects in the wet etching technique based on the
above-described batch processing.
[0016] That is, although semiconductor device manufacturing line in
recent years has gradually adopted a line structure for the
single-wafer processing instead of the line structure for the batch
processing, even the line structure for the single-wafer processing
still adopts the batch processing for the wet etching of a silicon
nitride film, and thus, the processing line structure for the
single-wafer processing does not operate smoothly. For this reason,
the inventor of the present invention has thought that development
of single-wafer processing technique for the wet etching of a
silicon nitride film is demanded urgently.
[0017] Accordingly, an object of the present invention is to
provide semiconductor manufacturing apparatus and a manufacturing
method of a semiconductor device capable of applying the
single-wafer processing to the wet etching of a silicon nitride
film.
[0018] The above and other objects and novel characteristics of the
present invention will be apparent from the description and the
accompanying drawings of this specification.
[0019] The representative ones of the inventions disclosed in this
application will be briefly described as follows.
[0020] That is, by heating the etching solution used in the wet
etching by electromagnetic wave in a state where it is supplied to
the deposited film on a wafer to be etched, the etching solution
can be heated to a high temperature in a short time, thereby
reducing the time for the etching process.
[0021] The effect obtained by the representative one of the
inventions disclosed in this application will be briefly described
as follows.
[0022] That is, by heating the etching solution to a high
temperature in a short time, the time for the etching process can
be reduced to such an extent that can perform the wet etching by
using the single-wafer processing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is an explanatory diagram schematically showing the
concept of the entire configuration of the semiconductor
manufacturing apparatus for the wet etching according to an
embodiment of the present invention;
[0024] FIG. 2A is an explanatory diagram schematically showing an
example of the structure of the wafer holding means;
[0025] FIG. 2B is an explanatory diagram schematically showing an
example of the structure of the wafer holding means;
[0026] FIGS. 3A to 3C are explanatory diagrams showing the steps of
device isolation forming process;
[0027] FIGS. 4A to 4C are explanatory diagrams showing the steps of
the device isolation forming process continued from FIG. 3;
[0028] FIG. 5 is a graph showing the temperature dependence of the
etching rate of phosphoric acid solution; and
[0029] FIG. 6A is an explanatory diagram showing the entire
configuration of the wet etching apparatus using the batch
processing; and
[0030] FIG. 6B is an explanatory diagram showing the immersion
process into etching solution in the configuration shown in FIG.
6A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying drawings.
Note that components having the same function are denoted by the
same reference numerals throughout the drawings for describing the
embodiments, and the repetitive description thereof will be
omitted.
[0032] First, the semiconductor manufacturing apparatus that can
perform the wet etching by using the single-wafer processing will
be described in this embodiment. FIG. 1 is an explanatory diagram
schematically showing the entire configuration of the semiconductor
manufacturing apparatus. FIGS. 2A and 2B are explanatory diagrams
schematically showing the structure of the wafer holding means.
[0033] As shown in FIG. 1, the semiconductor manufacturing
apparatus formed in the wet etching apparatus comprises wafer
holding means 10 for holding a wafer W for wet etching, etching
solution supply means 20 for supplying etching solution to the
wafer W, electromagnetic wave heating means 30 for heating the
etching solution by irradiating the etching solution supplied to
the wafer W with electromagnetic wave, and recycle means 40 for
recycling the used etching solution after the etching process.
[0034] The wafer holding means 10 is formed so as to hold each one
wafer W. As shown in FIG. 2A, the wafer holding means 10 is formed
as a wafer holding device 10a(10) provided with a base 11 and pawls
11a which are provided on the periphery of the base 11 and capable
of opening/closing.
[0035] In the case shown in FIG. 2A, the periphery of the wafer W
is fastened by the pawls 11a so that it is held substantially
horizontally with a surface thereof on which a deposited film (not
shown) to be wet-etched is formed facing upward.
[0036] The pawls 11a are formed so as to be opened/closed freely as
indicated by the double-sided arrows in FIG. 2A. A wafer W carried
to a predetermined position by a carrying robot (not shown) is
fastened at the side surface thereof by the pawls 11a moved from
its open standby position to its closed position shown in FIG.
2A.
[0037] The wafer holding device 10a having such a structure is
provided in an etching processing chamber 50 as shown in FIG. 1.
The etching processing chamber 50 surrounds the wafer holding
device 10a to prevent the scattering of the etching solution at the
time of etching process. Also, the topside of the chamber 50 is
opened so that the etching solution can be supplied to the wafer W
held by the wafer holding device 10a through that opening of the
chamber 50.
[0038] The chamber 50 which contains the wafer holding device 10a
is provided within a treatment chamber 60 in which the
electromagnetic wave is irradiated. The electromagnetic wave
heating means 30 is provided above the chamber 50 in the treatment
chamber 60 in order to prevent the leakage of the electromagnetic
wave out of the treatment chamber 60. The electromagnetic wave
heating means 30 can be formed of, for example, a microwave
generating unit composed of magnetron or an infrared generating
unit composed of an infrared ray generating tube.
[0039] The electromagnetic wave, for example, microwave or infrared
generated from the electromagnetic wave heating means 30 goes
through the opening of the chamber 50 and reaches the wafer W. A
reflecting material is provided inside the chamber 50 to reflect
the electromagnetic wave entering the chamber 50 so as to
concentrate the electromagnetic wave onto the wafer W.
[0040] In a state where the irradiated electromagnetic wave is
concentrated onto the wafer W, the etching solution is supplied to
the wafer W from above by the etching solution supply means 20. As
shown in FIG. 1, the etching solution supply means 20 is provided
with a circulating pump 21 to supply the etching solution from a
chemical tank 22 storing the etching solution to the wafer W held
on the wafer holding device 10a in the chamber 50 of the treatment
chamber 60 through a supply pipe 23.
[0041] A pulsation preventing damper 24 is provided along the
supply pipe 23 in order to stabilize the amount of etching solution
supplied to the wafer W.
[0042] Further, the supply pipe 23 is provided with a heat
exchanger unit 25a as preliminary heating means 25 in order to
shorten the heating time by means of electromagnetic wave heating
by pre-heating the etching solution to a predetermined temperature
before it is supplied to the wafer W. Additionally, a filter 26 is
provided along the supply pipe 23 to remove foreign matters
contained in the etching solution.
[0043] In this way, a predetermined amount of the etching solution
is supplied to the wafer W held by the wafer holding device 10a in
the chamber 50. As shown in FIG. 2A, a predetermined amount of the
supplied etching solution E is kept on the deposited film (not
shown) of the wafer W by the surface tension. Before supplying the
etching solution, the amount of etching solution necessary for the
wafer W to be etched is obtained by using a dummy wafer in advance,
and by supplying a slightly larger amount of the etching solution
than the necessary amount, the etching solution is appropriately
kept on the deposited film of the wafer W by the surface
tension.
[0044] When a slightly excessive amount of the etching solution is
supplied to the wafer W in this way, the excessive etching solution
spilt out of the wafer W flows on the base 11 and is discharged
through a discharge hole 12 provided in the base 11.
[0045] The discharge hole 12 is connected to a return pipe 27 so
that the etching solution on the base 11 returns to the chemical
tank 22. Consequently, the excessive etching solution when the
etching solution is supplied to the wafer W and the used etching
solution after the etching process are collected into the chemical
tank 22 without being thrown away and then recycled.
[0046] When recycling the etching solution, the collected etching
solution is mixed with non-used etching solution in the chemical
tank 22. Therefore, the recycle means 40 includes concentration
adjusting means 41 for adjusting the concentration of supplied
etching solution to be constant as shown in FIG. 1.
[0047] As the concentration adjusting means 41, at least any one of
concentration adjusting means for chemicals composing the etching
solution and concentration adjusting means for reaction product
produced by etching and contained in the etching solution is
provided.
[0048] For example, if etching solution containing silicon is
assumed as the etching solution, as the concentration adjusting
means for chemicals composing the etching solution, concentration
adjusting means for phosphoric acid which is a chemical composing
the etching solution is equipped, and as the concentration
adjusting means for reaction product produced by etching,
concentration adjusting means for silicon which is a reaction
product produced by the etching is equipped.
[0049] As for the concentration adjusting means for phosphoric
acid, for example, phosphoric acid concentration in the chemical
tank 22 is checked by concentration detecting means based on the
absorbance method. The check result is compared with the
concentration of the phosphoric acid of supplied etching solution
set in advance and if it is higher, purified water is supplied and
if it is lower, non-used phosphoric acid solution is supplied.
[0050] As for the adjustment of the silicon concentration in the
phosphoric acid solution, the silicon concentration in the chemical
tank 22 is checked according to the absorption spectrometry, and
the check result is compared with the silicon concentration in
phosphoric acid solution of the supplied etching solution set in
advance. If it is higher, the collected etching solution is not
returned to the chemical tank 22 and thrown away, and if it is
lower, the collected etching solution is returned to the chemical
tank 22 to adjust the concentration.
[0051] In the semiconductor manufacturing apparatus for wet etching
described above, as shown in FIG. 1, the etching solution is
circulated for recycle by the circulating pump 21 from the chemical
tank 22 through the supply pipe 23, the wafer W, and the discharge
hole 12 to the return pipe 27.
[0052] Particularly, in the case where the wet etching of the
silicon nitride film is performed with using phosphoric acid
solution as the etching solution, the phosphoric acid concentration
adjusting means and the silicon concentration adjusting means are
provided as the recycle means. By doing so, the selective etching
of the silicon nitride film deposited on a silicon oxide film using
the phosphoric acid can be performed efficiently.
[0053] Since the configuration of the semiconductor manufacturing
apparatus described above adopts the means for supplying etching
solution to the deposited film to be etched of the wafer W and
heating the etching solution by irradiating the supplied etching
solution with electromagnetic wave, the etching solution can be
heated to a high temperature in an extremely short time.
[0054] When the etching solution is heated by electromagnetic wave
in a state where it is held on the deposited film of the wafer W by
the surface tension as shown in FIG. 2A, the amount of the etching
solution to be heated, which is held uniformly and thinly on the
deposited film, is extremely smaller than that in the case of the
batch processing. In addition, since the electromagnetic wave
heating means different from the heater-type heating means is used,
the etching solution can be heated up to a high temperature over
200.degree. C. in the unit of seconds. As a result, the etching
rate by the phosphoric acid is improved and the process time of the
wet etching for a silicon nitride film can be remarkably reduced in
comparison to the conventional wet etching using the heated
phosphoric acid with a temperature of 150.degree. C. to 170.degree.
C.
[0055] The wafer holding means 10 with the structure as shown in
FIG. 2B can be used as a wafer holding device 10b. The structure
shown in FIG. 2B enables the wafer W to be dipped in etching
solution one by one. The wafer holding device 10b is provided with
a sidewall 13a on the periphery of a base 13 to form the immersion
bath 14 as shown in FIG. 2B.
[0056] The immersion bath 14 formed to have a volume capable of
dipping one wafer W, and a plurality of supporting members 15 which
support the wafer W by point contact are provided on the base 13
which corresponds to the bottom of the immersion bath 14. Etching
solution is supplied into the immersion bath 14 with the wafer W
supported on the supporting members 15 so that the etching solution
makes contact with the deposited film to be etched of the wafer
W.
[0057] By irradiating with electromagnetic wave by means of the
electromagnetic wave heating means 30 in a state where the etching
solution is supplied to the deposited film, the etching solution in
which the wafer W is dipped is heated to a high temperature over
200.degree. C. in a short time because the amount of the etching
solution is small and electromagnetic heating is strong heating
means. As a result, the etching rate by the phosphoric acid is
improved, and the process time of the wet etching for a silicon
nitride film can be remarkably shortened in comparison to the
conventional wet etching using the heated phosphoric acid with a
temperature of 150.degree. C. to 170.degree. C.
[0058] In the structure of the wafer holding device 10a shown in
FIG. 2A, the deposited film formed on an upper side of the wafer W
is the object to be etched, and thus, it can be said that this
device is for the etching process of a single side of the wafer W.
On the contrary, because the wafer W is dipped in the etching
solution in the structure of the wafer holding device 10b shown in
FIG. 2B, it can be said that this device is for the etching process
of a both sides of the wafer W, which can perform the wet etching
of not only a single side but also double sides in parallel
depending on the cases.
[0059] Also, similar to the wafer holding device 10a as shown in
FIG. 2A, the base 13 is provided with a discharge hole 12 so that
the used etching solution can be returned through the return pipe
27 to the chemical tank 22 for recycle use after the etching is
finished.
[0060] Since the wafer W is dipped in the etching solution in the
structure of the wafer holding device 10b, the wafer W does not
need to maintain a highly precise horizontal posture different from
the structure of the wafer holding device 10a shown in FIG. 2A
which holds the etching solution by the surface tension. There is
no problem if the horizontality is kept to an extent that the
surface of the wafer W is not exposed over the etching
solution.
[0061] Next, the method of manufacturing a semiconductor device
with using the semiconductor manufacturing apparatus for wet
etching having such a configuration will be described. In the
following description, the case where the phosphoric acid solution
containing silicon is used as the etching solution and a silicon
nitride film formed on a silicon oxide film is selectively
wet-etched in order to form device isolation regions for the
shallow trench isolation (STI) used in such a semiconductor device
as MOS-IC will be described.
[0062] As shown in FIG. 3A, a silicon oxide film 100 is formed on a
P-type silicon wafer W and a silicon nitride film 200 is
sequentially laminated thereon. After that, as shown in FIG. 3B,
the device isolation forming areas of the silicon nitride film 200
and silicon oxide film 100 are etched with using a resist film as a
mask. Further, as shown in FIG. 3C, the wafer W is etched to a
predetermined depth with using the silicon nitride film 200 formed
in FIG. 3B as a mask so as to form the STI trench 300.
[0063] After that, as shown in FIG. 4A, silicon oxide film 400 is
deposited so as to fill the STI trench 300 formed in FIG. 3C with
the silicon oxide film 400. Further, the chemical mechanical
polishing (CMP) is performed with using the silicon nitride film
200 as a stopper film so as to form a flat surface as shown in FIG.
4B.
[0064] In a state where the silicon nitride film 200 is exposed as
described above, the silicon nitride film 200 is subjected to wet
etching by using the above-described semiconductor manufacturing
apparatus having the configuration capable of performing the
single-wafer processing.
[0065] That is, the wafers W processed to the state shown in FIG.
4B in the previous steps are transported to the semiconductor
manufacturing apparatus for wet etching having the configuration
shown in FIG. 1 one by one. The transported wafer W is held by the
wafer holding device 10a as shown in FIG. 2A one by one.
[0066] In a state where the wafer W is held, the etching solution
composed of phosphoric acid solution containing silicon is supplied
to the wafer W by the etching solution supply means 20. A slightly
excessive amount of the etching solution is supplied and then, the
etching solution is held on the deposited film formed on the wafer
W by the surface tension.
[0067] The etching solution composed of phosphoric acid solution
containing silicon held on the wafer W by the surface tension is
irradiated with microwave, infrared ray, or other electromagnetic
wave by the electromagnetic wave heating means 30.
[0068] If the phosphoric acid concentration of the phosphoric acid
solution containing silicon which composes the etching solution is
in a range of 94% and 98%, the phosphoric acid solution containing
silicon is heated to a higher temperature of higher than
200.degree. C. and lower than 230.degree. C. in a short time by the
above-described electromagnetic wave heating. Although the time
required for such heating varies depending on the energy quantity
of the irradiated electromagnetic wave, the amount of the
phosphoric acid solution containing silicon to be heated and the
like, it is heated in the unit of several tens seconds, and thus,
the necessary etching is finished in the unit of minutes.
[0069] The heating temperature of the phosphoric acid solution is
specified by the concentration of phosphoric acid and if the
concentration of phosphoric acid is in a range of 94% and 100%, it
can be heated to the temperature range of 200.degree. and
250.degree. C. in a short time by the electromagnetic wave
heating.
[0070] Although the phosphoric acid solution containing silicon can
be heated to a temperatures over 250.degree. C., heating up to the
temperatures over 250.degree. C. is not preferable because it is
necessary to perform the selective etching of the silicon nitride
film 200 in contact with the silicon oxide film 100 as shown in
FIG. 4B.
[0071] FIG. 5 shows the temperature dependence of the etching rate
of the phosphoric acid to the silicon nitride film and the silicon
oxide film. Etching rates at predetermined temperatures are plotted
according to the Arrhenius plot based on the activation energy.
FIG. 5 indicates the plotting up to 220.degree. C.
[0072] FIG. 5 makes it apparent that a line a indicating the
temperature dependence of the etching rate of the silicon nitride
film has a smaller gradient than a line b indicating the
temperature dependence of the etching rate of the silicon oxide
film. That is, if the temperature of the phosphoric acid solution
rises, an increment of the etching rate of the silicon oxide film
becomes larger than an increment of the etching rate of the silicon
nitride film, and the selectivity between the silicon nitride film
and the silicon oxide film is decreased.
[0073] Thus, as a range of practical selectivity, the temperature
upper limit is determined to be 250.degree. C. As is apparent from
the graph of FIG. 5, as the temperature drops, the etching rate
decreases largely although the selectivity is increased.
[0074] Since the present invention aims at the development of the
technique for the wet etching using the single-wafer processing,
the temperature cannot be reduced more than necessary. To secure
the wet etching process time at least in the unit of minutes
required for the single-wafer processing, it is judged that the
lower limit of the temperature is 200.degree. C. or higher. If the
temperature is lower than 200.degree. C., the short wet etching
process time necessary for the single-wafer processing cannot be
expected.
[0075] The selectivity to the silicon oxide film can be improved by
adding silicon to the phosphoric acid solution. If the Si
concentration in the phosphoric acid solution is kept to be about
100 ppm, an effective selectivity can be obtained in the
temperature range of 200.degree. C. and 250.degree. C.
[0076] By performing the wet etching under the condition that the
solution temperature is in a range of 200.degree. C. to 250.degree.
C. and the phosphoric acid solution containing silicon with the Si
concentration of 100 ppm is used as the etching solution, the
silicon nitride film 200 is removed selectively to the silicon
oxide film 100 as shown in FIG. 4C, and the device isolation by the
STI can be achieved.
[0077] The wet etching of the silicon nitride film 200 shown in
FIGS. 4B and 4C can be performed in a short time, for example, in
the unit of minutes demanded for the single-wafer processing by
using the apparatus shown in FIG. 1.
[0078] Although the phosphoric acid solution containing silicon is
heated instantaneously to a high temperature by irradiating it with
microwave just when it is supplied to the wafer W as described
above, it is preferable that the solution is preliminarily heated
to about 170.degree. C. by the preliminary heating means 25 so as
to further reduce the heating time. However, if this is
unnecessary, such preliminary heating can be omitted.
[0079] When the wet etching ends, the wafer W is carried from the
wafer holding device 10a to a next process by a carrying robot. The
used etching solution containing silicon is returned to the
chemical tank 22 through the return pipe 27 and recycled after
adjusting the phosphoric acid concentration and the silicon
concentration by the concentration adjusting means 41 constituting
the recycle means 40.
[0080] When the apparatus shown in FIG. 1 is operated, by recycling
the used etching solution after several dummy wafers are processed,
a specified amount of silicon can be dissolved into the phosphoric
acid solution. Thus, it is not necessary to prepare any phosphoric
acid solution containing silicon from the beginning.
[0081] Although the wet etching of the silicon nitride film 200 can
be performed by the conventional batch processing, it takes about
an hour for the processing and the short time processing demanded
for the single-wafer processing cannot be achieved.
[0082] The batch processing is superior in the processing
capability because a plurality of wafers can be processed at a time
in a single apparatus. However, from the viewpoint of the facility,
a plurality of apparatus are equipped and one of which is reserved
as a backup for a possible accidental trouble. Therefore, in a
routine line flow without any trouble, the reserved apparatus is
the excessive investment.
[0083] Depending on the cases, it is preferable to provide a
plurality of the processing apparatus from the viewpoint of stable
manufacturing. Further, it is preferable to provide the
single-wafer processing apparatus as the reserved apparatus of the
batch processing system from the viewpoint of the apparatus cost.
Thus, the wet etching using the single-wafer processing has a
larger advantage than the batch processing system, and therefore,
the present invention in which the single-wafer processing is made
technically possible is highly meaningful.
[0084] In the foregoing, the invention made by the inventor of the
present invention has been concretely described based on the
embodiments. However, it is needless to say that the present
invention is not limited to the foregoing embodiments and various
modifications and alterations can be made within the scope of the
present invention.
[0085] For example, an example in which phosphoric acid solution
containing silicon is employed as the etching solution for the wet
etching to remove a silicon nitride film has been described.
However, there is no problem if other chemical solution is applied
to the wet etching and the object to be etched is a deposited film
other than the silicon nitride film.
[0086] In the case of using the phosphoric acid solution containing
silicon, the phosphoric acid is indicated as the chemical whose
concentration is to be adjusted by the concentration adjusting
means for chemicals composing etching solution. However, it is
permissible to adjust the concentration of each of plural chemicals
when plural kinds of chemicals are used as the etching solution
instead of the phosphoric acid solution containing silicon.
[0087] Also, the above-described configuration is formed to achieve
the wet etching using the single-wafer processing. However, a part
of the configuration can be applied to the batch processing. For
example, instead of holding each one wafer by the wafer holding
device, the configuration of the batch processing in which plural
wafers are held is used and the etching solution is kept on each of
the wafers by the surface tension, and in this state, the etching
solution is heated to a high temperature by electromagnetic wave
heating, thereby reducing the etching process time. It can be said
that such a configuration is in the same category as the case where
a plurality of the single-wafer processing systems are
provided.
[0088] The present invention can be effectively applied to the
field of the wet etching in the manufacture of the semiconductor
device.
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