U.S. patent application number 10/746798 was filed with the patent office on 2004-07-22 for substrate treating apparatus.
This patent application is currently assigned to Dainippon Screen Mfg. Co., Ltd.. Invention is credited to Izuta, Takashi.
Application Number | 20040140365 10/746798 |
Document ID | / |
Family ID | 32718764 |
Filed Date | 2004-07-22 |
United States Patent
Application |
20040140365 |
Kind Code |
A1 |
Izuta, Takashi |
July 22, 2004 |
Substrate treating apparatus
Abstract
A substrate treating apparatus for heating a treating solution
formed of a chemical and a diluent, and immersing substrates in the
treating solution for treatment. The apparatus includes a treating
tank for storing the treating solution, a heater for heating the
treating solution, a temperature detector for detecting temperature
of the treating solution, a temperature controller for controlling
the heater so that a detected temperature of the treating solution
reaches a set temperature, a supplementing device for supplement
the treating tank with the diluent, a concentration detector for
detecting concentration of the treating solution, and a
concentration controller, operable only when the temperature
detector detects the treating solution being in a temperature range
close to the set temperature, for controlling the supplementing
device to adjust an amount of the diluent supplemented so that the
concentration of the treating solution detected by the
concentration detector becomes slightly higher than a boiling-point
concentration corresponding to the set temperature of the treating
solution.
Inventors: |
Izuta, Takashi; (Kyoto,
JP) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Assignee: |
Dainippon Screen Mfg. Co.,
Ltd.
|
Family ID: |
32718764 |
Appl. No.: |
10/746798 |
Filed: |
December 24, 2003 |
Current U.S.
Class: |
237/12 |
Current CPC
Class: |
H01L 21/67248 20130101;
H01L 21/67086 20130101 |
Class at
Publication: |
237/012 |
International
Class: |
F24D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2002 |
JP |
2002-377535 |
May 29, 2003 |
JP |
2003-152642 |
Nov 14, 2003 |
JP |
2003-384953 |
Claims
What is claimed is:
1. A substrate treating apparatus for heating a treating solution
formed of a chemical and a diluent, and immersing substrates in the
treating solution for treatment, comprising: a treating tank for
storing the treating solution; heating device for heating the
treating solution; temperature detecting device for detecting
temperature of the treating solution; temperature control device
for controlling the heating device so that a detected temperature
of the treating solution reaches a set temperature; supplementing
device for supplement the treating tank with the diluent;
concentration detecting device for detecting concentration of the
treating solution; and concentration control device, operable only
when the temperature detecting device detects the treating solution
being in a temperature range close to the set temperature, for
controlling the supplementing device to adjust an amount of the
diluent supplemented so that the concentration of the treating
solution detected by the concentration detecting device becomes
slightly higher than a boiling-point concentration corresponding to
the set temperature of the treating solution.
2. An apparatus as defined in claim 1, further comprising: a
collecting tank for collecting the treating solution overflowing
the treating tank; and a circulating system for returning the
treating solution collected in the collecting tank to the treating
tank.
3. An apparatus as defined in claim 2, wherein said heating device
includes a tank heater attached to the treating tank for heating
the treating solution in the treating tank, and a circulating
system heater for heating the treating solution circulating through
the circulating system.
4. An apparatus as defined in claim 1, wherein said concentration
detecting device is arranged to detect the concentration of the
treating solution by substantially detecting specific gravity of
the treating solution.
5. An apparatus as defined in claim 4, wherein said concentration
detecting device has a detecting element disposed at a
predetermined depth in the treating tank for detecting a pressure
of the treating solution applied to the detecting element.
6. An apparatus as defined in claim 1, wherein said concentration
control device is arranged to supplement the diluent when a
detected concentration of the treating solution exceeds a target
concentration, and stop supplementing the diluent when the detected
concentration of the treating solution is less than the target
concentration.
7. An apparatus as defined in claim 1, wherein said treating
solution is a phosphoric acid solution formed of phosphoric acid
acting as the chemical and deionized water acting as the
diluent.
8. An apparatus as defined in claim 2, wherein said treating
solution is a phosphoric acid solution formed of phosphoric acid
acting as the chemical and deionized water acting as the
diluent.
9. An apparatus as defined in claim 3, wherein said treating
solution is a phosphoric acid solution formed of phosphoric acid
acting as the chemical and deionized water acting as the
diluent.
10. A substrate treating apparatus for heating a treating solution
formed of a chemical and a diluent, and immersing substrates in the
treating solution for treatment, comprising: a treating tank for
storing the treating solution; heating device for heating the
treating solution; piping including an air control valve for
supplementing the diluent to the treating solution heated by the
heating device; an electropneumatic converter for applying an
output pressure to the air control valve; concentration detecting
device for detecting concentration of the treating solution; and
concentration control device operable based on a result of
detection by said concentration detecting device, for adjusting the
output pressure of the electropneumatic converter to control the
air control valve and adjust an amount of the diluent
supplemented.
11. An apparatus as defined in claim 10, further comprising:
temperature detecting device for detecting temperature of the
treating solution; and temperature control device for controlling
the heating device so that a detected temperature of the treating
solution reaches a set temperature; wherein said concentration
control device is arranged to adjust the output pressure of the
electropneumatic converter so that the concentration of the
treating solution detected by the concentration detecting device
becomes slightly higher than a boiling-point concentration
corresponding to the set temperature of the treating solution.
12. An apparatus as defined in claim 10, further comprising: a
collecting tank for collecting the treating solution overflowing
said treating tank; and a circulating system for returning the
treating solution collected in the collecting tank to the treating
tank.
13. An apparatus as defined in claim 12, wherein said heating
device includes a tank heater attached to the treating tank for
heating the treating solution in the treating tank, and a
circulating system heater for heating the treating solution
circulating through the circulating system.
14. An apparatus as defined in claim 10, wherein said concentration
detecting device is arranged to detect the concentration of the
treating solution by substantially detecting specific gravity of
the treating solution.
15. An apparatus as defined in claim 14, wherein said concentration
detecting device has a detecting element disposed at a
predetermined depth in the treating tank for detecting pressure of
the treating solution applied to the detecting element.
16. An apparatus as defined in claim 10, further comprising:
temperature detecting device for detecting temperature of the
treating solution; and temperature control device for controlling
the heating device so that a detected temperature of the treating
solution reaches a set temperature; wherein said concentration
control device is operable only when the treating solution is in a
temperature range close to the set temperature.
17. An apparatus as defined in claim 10, wherein said concentration
control device is arranged to supplement the diluent when a
detected concentration of the treating solution exceeds a target
concentration, and stop supplementing the diluent when the detected
concentration of the treating solution is less than the target
concentration.
18. An apparatus as defined in claim 16, wherein said concentration
control device is arranged to supplement the diluent when a
detected concentration of the treating solution exceeds a target
concentration, and stop supplementing the diluent when the detected
concentration of the treating solution is less than the target
concentration.
19. An apparatus as defined in claim 10, wherein said treating
solution is a phosphoric acid solution formed of phosphoric acid
acting as the chemical and deionized water acting as the
diluent.
20. An apparatus as defined in claim 11, wherein said treating
solution is a phosphoric acid solution formed of phosphoric acid
acting as the chemical and deionized water acting as the diluent.
Description
BACKGROUND OF THE INVENTION
[0001] (1) Field of the Invention
[0002] This invention relates to a substrate treating apparatus for
treating, with a treating solution, substrates such as
semiconductor wafers, glass substrates for liquid crystal displays,
glass substrates for photomasks and the like (hereinafter called
simply "substrates").
[0003] (2) Description of the Related Art
[0004] Known apparatus of this type include, for example, an
apparatus for etching a silicon nitride film on substrate surfaces
with a high-temperature phosphoric acid solution (H.sub.3PO.sub.4)
(see Japanese Unexamined Patent Publication No. 9-181041 (1997),
page 3 and FIG. 1, for example).
[0005] The concentration of the solution may be controlled
simultaneously with and independently of its temperature (see
Japanese Unexamined Patent Publication No. 11-154665 (1999),
paragraphs [0015] to [0017] and FIG. 1, for example).
[0006] A known apparatus will be described hereinafter with
reference to FIG. 1. This apparatus includes a treating tank 101
for storing a phosphoric acid solution, a collecting tank 102 for
collecting the phosphoric acid solution overflowing the treating
tank 101, a circulating system 103 for returning the phosphoric
acid solution collected in the collecting tank 102 to the treating
tank 101, a heater 104 for constantly heating the phosphoric acid
solution in the treating tank 101, a phosphoric acid supply device
105, and a supplementing device 106 for supplementing the treating
tank 101 with deionized water for controlling the temperature of
the phosphoric acid solution.
[0007] In order to maintain a high etching rate for silicon oxide
film, the phosphoric acid solution adjusted to a predetermined
concentration is maintained at a high temperature (120 to
170.degree. C.) just below a boiling point corresponding to that
concentration. When the phosphoric acid solution is above the
predetermined temperature, the solution is cooled by supplying
deionized water from the supplementing device 106 into the treating
tank 101. Conversely, when the phosphoric acid solution is below
the predetermined temperature, the solution is heated by the heater
104 without supplementing deionized water.
[0008] Wafers W to undergo etching treatment are placed in the
treating tank 101 as arranged in vertical posture and equidistantly
on a horizontal guide 107a of an approximately L-shaped holding arm
107. The treating tank 101 has an openable cover 108 for covering
an upper opening thereof through which the group of wafers W held
by the holding arm 107 is loaded into and unloaded from the tank
101. The cover 108 is closed when the holding arm 107 is outside
the treating tank 101. The cover 108 is opened for allowing the
group of wafers W to be loaded into the treating tank 101. After
the group of wafers W is loaded into the treating tank 101, the
cover 108 is closed again and etching treatment is carried out in
the state shown in FIG. 1. In this state, a suspension arm 107b of
the holding arm 107 extends out of the tank 101 through an opening
108a formed in the cover 108.
[0009] The conventional apparatus described above has the following
drawback.
[0010] When the group of wafers W in a "lot-out" state outside the
treating tank 101 is moved to a "lot-in" state inside the treating
tank 101, the concentration of the phosphoric acid solution in the
treating tank 101 undergoes a marked change. Such a change in the
concentration of the phosphoric acid solution lowers the quality of
etching treatment. Further, the lot-in state may entail a sudden
boiling (bumping) of the phosphoric acid solution. The bumping of
the phosphoric acid solution results in violent movements thereof,
which vibrate and adversely influence the wafers W.
[0011] The method of controlling concentration and temperature
simultaneously with and independently of each other can easily
control the concentration with high precision when there is no
disturbance and the temperature is stable. However, since the
temperature is seldom maintained stable, this method has the
problem of taking a long time for the concentration to reach a set
value.
[0012] Such a problem will be described by referring to a specific
example of variations in the temperature and concentration
(specific gravity) shown in FIG. 2.
[0013] In this example, as shown in FIG. 2A, heating is started at
time t=0 to increase temperature from tm0 toward a set temperature
tm1. In parallel therewith, as shown in FIG. 2B, concentration is
controlled from cn0 toward a set concentration cn1, and deionized
water is supplied for this purpose. Then, the concentration is
lowered by the deionized water supply and heating. While heating is
continued to increase the temperature toward the set temperature
tm1, the concentration falls below the set concentration cn1 once
before the temperature reaches the set temperature tm1. The
concentration reaches the set concentration cn1 after time t2 when
the temperature reaches the set temperature tm1. That is, by
controlling the temperature and concentration simultaneously, the
concentration undergoes variations under the influence of the
temperature. The variations in the concentration are greatly
influenced also by the deionized water supplied for concentration
control. This results in the problem noted above.
[0014] In the above apparatus, the supplementing device or switch
valve 106 can take either an open position or a closed
position.
[0015] Thus, the time of the switch valve 106 being kept open is
adjusted to control an amount of deionized water supplemented. It
is difficult for the conventional apparatus to supply an accurately
adjusted amount of deionized water.
[0016] In the above conventional example, in order to maintain a
high etching rate, the phosphoric acid solution adjusted to a
predetermined concentration is maintained at a high temperature
just below the boiling point corresponding to that concentration.
The problem noted above occurs also with a different type of
substrate treating apparatus in which the switch valve 106 is
operated to supplement deionized water or other diluent for a
chemical solution to the treating tank 101.
SUMMARY OF THE INVENTION
[0017] This invention has been made having regard to the state of
the art noted above, and its object is to provide a substrate
treating apparatus for maintaining a treating solution in a
treating tank at a fixed concentration to preclude the possibility
of bumping of the treating solution, and for controlling the
concentration in a relatively short time.
[0018] Another object of this invention is to provide a substrate
treating apparatus constructed for linearly adjusting a flow rate
of a diluent to adjust, with high precision, an amount of the
diluent supplemented.
[0019] To solve the above-noted problem of the prior art, Inventor
has made intensive research and attained the following
findings.
[0020] The cover 108 is closed when the group of wafers W is
outside the tank (in the lot-out state). Since the holding arm 107
is above the cover 108, the opening 108a of the cover 108 remains
open. Consequently, part of the heat of the phosphoric acid
solution in the treating tank 101 escapes through the opening 108a.
The heater 104 is adjusted so that, in this lot-out state, the
phosphoric acid solution in the treating tank 101 is maintained at
the high temperature just below the boiling point, and is thermally
balanced.
[0021] Next, when the group of wafers W is loaded into the tank
(lot-in state), the cover 108 is closed as in time of the lot-out
state. Since the suspension arm 107b of the holding arm 107 extends
outward through the opening 108a of the cover 108, the opening 108a
is stopped up by the arm 107b. Consequently, the heat of the
phosphoric acid solution which escaped outside through this opening
108a in time of the lot-out state now loses its outlet. That is,
the thermal balance in the treating tank 101 is lost to raise the
temperature-sustaining effect. As a result, the temperature of the
phosphoric acid solution increases sharply. This temperature
increase is detected by a temperature detector not shown, whereupon
deionized water is supplemented from the supplementing device 106
into the tank, thereby lowering the temperature of the phosphoric
acid solution. The deionized water supplemented lowers the
concentration of the phosphoric acid solution to cause
concentration variations. When the concentration of the phosphoric
acid solution lowers, the boiling point corresponding to the
concentration will also fall sharply. As a result of the boiling
point falling below the temperature of the phosphoric acid solution
in the tank, bumping of the phosphoric acid solution takes place
although the temperature is lowered by the supplement of deionized
water.
[0022] Regarding the concentration control, it has been found that,
rather than controlling concentration simultaneously with
temperature, a concentration control carried out after bringing the
temperature into a fixed range including the set temperature can
attain the set value of concentration within a shorter time than in
the prior art.
[0023] Based on the above findings, this invention provides a
substrate treating apparatus for heating a treating solution formed
of a chemical and a diluent, and immersing substrates in the
treating solution for treatment, comprising:
[0024] a treating tank for storing the treating solution;
[0025] a heating device for heating the treating solution;
[0026] a temperature detecting device for detecting temperature of
the treating solution;
[0027] a temperature control device for controlling the heating
device so that a detected temperature of the treating solution
reaches a set temperature;
[0028] a supplementing device for supplement the treating tank with
the diluent;
[0029] a concentration detecting device for detecting concentration
of the treating solution; and
[0030] a concentration control device, operable only when the
temperature detecting device detects the treating solution being in
a temperature range close to the set temperature, for controlling
the supplementing device to adjust an amount of the diluent
supplemented so that the concentration of the treating solution
detected by the concentration detecting device becomes slightly
higher than a boiling-point concentration corresponding to the set
temperature of the treating solution.
[0031] The temperature control of the treating solution and the
concentration control of the treating solution are performed
independently of each other. When, for example, a temperature
increase occurs for some reason to the treating solution in the
treating tank with substrates placed therein, the temperature
control device controls the heating device to suppress the
temperature increase of the treating solution. That is, this
apparatus does not resort to the temperature control practiced in
the prior art in which the temperature of the treating solution is
lowered by supplementing diluent water. The temperature control of
the treating solution does not result in variations in the
concentration of the treating solution. This precludes the
possibility of bumping of the treating solution. Further, the
concentration control device controls the supplementing device to
adjust an amount of the diluent supplemented so that the detected
concentration of the treating solution becomes slightly higher than
a boiling-point concentration corresponding to the set temperature
of the treating solution. This is effective for maintaining a high
etching rate of the treating solution. Furthermore, a concentration
control performed when the temperature of the treating solution is
far from the set temperature could cause bumping due to lowering of
the concentration of the treating solution. It is necessary to be
aware of the range of concentration variations. However, the
concentration control device of this invention performs the
concentration control only when the treating solution is in a
temperature range close to the set temperature. This requires only
the boiling-point concentration corresponding to the set
temperature to be taken into consideration, which further reduces
the possibility of bumping. In addition, concentration and
temperature may be controlled in a relatively short time.
[0032] In this invention, preferably, the apparatus comprises a
collecting tank for collecting the treating solution overflowing
the treating tank, and a circulating system for returning the
treating solution collected in the collecting tank to the treating
tank.
[0033] The apparatus further comprising such a collecting tank and
a circulating system has the advantage of promoting use efficiency
of the treating solution.
[0034] The heating device, preferably, includes a tank heater
attached to the treating tank for heating the treating solution in
the treating tank, and a circulating system heater for heating the
treating solution circulating through the circulating system.
[0035] This construction further promotes use efficiency of the
treating solution.
[0036] Preferably, the concentration detecting device is arranged
to detect the concentration of the treating solution by
substantially detecting specific gravity of the treating
solution.
[0037] This construction can detect the concentration of the
treating solution relatively easily.
[0038] Preferably, the concentration detecting device has a
detecting element disposed at a predetermined depth in the treating
tank for detecting a pressure of the treating solution applied to
the detecting element.
[0039] The pressure of the treating solution at a predetermined
depth in the treating tank is proportional to the specific gravity
of the treating solution. Thus, the specific gravity of the
treating solution may be determined by detecting the pressure of
the treating solution, and the concentration of the treating
solution may be known from the specific gravity.
[0040] Preferably, the concentration control device is arranged to
supplement the diluent when a detected concentration of the
treating solution exceeds a target concentration, and stop
supplementing the diluent when the detected concentration of the
treating solution is less than the target concentration.
[0041] With this construction, the concentration of the treating
solution is lowered by supplementing the diluent. When the
supplementing of the diluent is stopped, the concentration of the
treating solution is automatically increased by evaporation of the
diluent from the treating solution heated. Thus, the concentration
of the treating solution is easily maintained at the target
concentration.
[0042] Preferably, the treating solution is a phosphoric acid
solution formed of phosphoric acid acting as the chemical and
deionized water acting as the diluent.
[0043] Since a phosphoric acid solution of fixed concentration may
be maintained at a temperature close to the boiling point, nitride
film or the like may be treated at a high etching rate.
[0044] In another aspect of the invention, a substrate treating
apparatus for heating a treating solution formed of a chemical and
a diluent, and immersing substrates in the treating solution for
treatment, comprises:
[0045] a treating tank for storing the treating solution;
[0046] a heating device for heating the treating solution;
[0047] piping including an air control valve for supplementing the
diluent to the treating solution heated by the heating device;
[0048] an electropneumatic converter for applying an output
pressure to the air control valve;
[0049] a concentration detecting device for detecting concentration
of the treating solution; and
[0050] a concentration control device operable based on a result of
detection by the concentration detecting device, for adjusting the
output pressure of the electropneumatic converter to control the
air control valve and adjust an amount of the diluent
supplemented.
[0051] In this invention, the temperature control of the treating
solution and the concentration control of the treating solution are
performed independently of each other. When, for example, a
temperature increase occurs for some reason to the treating
solution in the treating tank with substrates placed therein, the
heating device is controlled to suppress the temperature increase
of the treating solution. That is, this apparatus does not resort
to the temperature control practiced in the prior art in which the
temperature of the treating solution is lowered by supplementing
diluent water. The temperature control of the treating solution
does not result in variations in the concentration of the treating
solution. The concentration control device, based on a result of
detection by the concentration detecting device, adjusts the output
pressure of the electropneumatic converter to control the air
control valve and adjust an amount of diluent supplemented. The
electropneumatic converter can vary the output pressure linearly
according to an electric signal, and operate the air control valve
based on the electric signal. As a result, the amount of diluent
supplemented may be adjusted linearly in response to the output
pressure from the electropneumatic converter to the air control
valve. Thus, the diluent may be supplemented accurately according
to the detected concentration.
[0052] Preferably, the apparatus comprises a temperature detecting
device for detecting temperature of the treating solution, and a
temperature control device for controlling the heating device so
that a detected temperature of the treating solution reaches a set
temperature, wherein the concentration control device is arranged
to adjust the output pressure of the electropneumatic converter so
that the concentration of the treating solution detected by the
concentration detecting device becomes slightly higher than a
boiling-point concentration corresponding to the set temperature of
the treating solution.
[0053] The concentration control device controls the amount of
diluent supplemented by controlling the electropneumatic converter
so that the detected concentration of the treating solution becomes
slightly higher than a boiling-point concentration corresponding to
the set temperature of the treating solution. This is effective to
maintain a high etching rate of the treating solution
accurately.
[0054] In the conventional apparatus shown in FIG. 1, when
treatment is performed with the phosphoric acid solution adjusted
to a predetermined concentration and maintained at a high
temperature (120 to 170.degree. C.) just below a boiling point
corresponding to that concentration, wafers W to undergo etching
treatment are placed in the treating tank 101 as arranged in
vertical posture and equidistantly on the horizontal guide 107a of
the approximately L-shaped holding arm 107. The treating tank 101
has an openable cover 108 for covering an upper opening thereof
through which the group of wafers W held by the holding arm 107 is
loaded into and unloaded from the tank 101. The cover 108 is closed
when the holding arm 107 is outside the treating tank 101. The
cover 108 is opened for allowing the group of wafers W to be loaded
into the treating tank 101. After the group of wafers W is loaded
into the treating tank 101, the cover 108 is closed again and
etching treatment is carried out in the state shown in FIG. 1. In
this state, the suspension arm 107b of the holding arm 107 extends
out of the tank 101 through the opening 108a formed in the cover
108.
[0055] With the conventional apparatus having the above
construction, when the group of wafers W in a "lot-out" state
outside the treating tank 101 is moved to a "lot-in" state inside
the treating tank 101, the concentration of the phosphoric acid
solution in the treating tank 101 undergoes a marked change. Such a
change in the concentration of the phosphoric acid solution lowers
the quality of etching treatment. Further, the lot-in state may
entail a sudden boiling (bumping) of the phosphoric acid solution.
The bumping of the phosphoric acid solution results in violent
movements thereof, which vibrate and adversely influence the wafers
W on the horizontal guide 107a.
[0056] As noted in the foregoing description of the result of the
research, the above inconvenience is caused by the loss of the
thermal balance in times of the lot-out state and lot-in state,
which raises the temperature-sustaining effect to increase the
temperature of the phosphoric acid solution rapidly.
[0057] The additional features of this invention noted hereinbefore
allow the treating solution in the treating tank to be accurately
maintained constant to preclude the possibility of bumping.
[0058] Preferably, the apparatus further comprises a temperature
detecting device for detecting temperature of the treating
solution, and a temperature control device for controlling the
heating device so that a detected temperature of the treating
solution reaches a set temperature, wherein the concentration
control device is operable only when the treating solution is in a
temperature range close to the set temperature.
[0059] A concentration control performed when the temperature of
the treating solution is far from the set temperature could cause
bumping due to lowering of the concentration of the treating
solution. It is necessary to be aware of the range of concentration
variations. In the above construction, however, the concentration
control is carried out only when the treating solution is in a
temperature range close to the set temperature. This requires only
the boiling-point concentration corresponding to the set
temperature to be taken into consideration, which further reduces
the possibility of bumping.
[0060] Preferably, the concentration control device is arranged to
supplement the diluent when a detected concentration of the
treating solution exceeds a target concentration, and stop
supplementing the diluent when the detected concentration of the
treating solution is less than the target concentration.
[0061] With this construction, the concentration of the treating
solution is lowered by supplementing the diluent. When the
supplementing of the diluent is stopped, the concentration of the
treating solution is automatically increased by evaporation of the
diluent from the treating solution heated. Thus, the concentration
of the treating solution is easily maintained at the target
concentration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] For the purpose of illustrating the invention, there are
shown in the drawings several forms which are presently preferred,
it being understood, however, that the invention is not limited to
the precise arrangement and instrumentalities shown.
[0063] FIG. 1 is an explanatory view of a conventional
apparatus;
[0064] FIG. 2 is a graph showing a specific example of variations
in temperature and concentration (specific gravity) occurring with
a conventional control, in which FIG. 2A shows temperature
variations and FIG. 2B shows concentration variations;
[0065] FIG. 3 is a block diagram showing an outline of a substrate
treating apparatus in Embodiment 1;
[0066] FIG. 4 is a flow chart showing a sequence of treatment;
[0067] FIG. 5 is a graph showing a relationship between the
concentration and temperature of a phosphoric acid solution, and a
silicon nitride film etching rate;
[0068] FIG. 6 is a graph showing a specific example of variations
in temperature and concentration (specific gravity), in which FIG.
6A shows temperature variations and FIG. 6B shows concentration
variations;
[0069] FIG. 7 is a block diagram showing an outline of a substrate
treating apparatus in Embodiment 2; and
[0070] FIG. 8 is a graph showing flow rate characteristics of an
air control valve.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] Preferred embodiments of this invention will be described in
detail hereinafter with reference to the drawings.
[0072] Embodiment 1
[0073] FIG. 3 is a block diagram showing an outline of a substrate
treating apparatus in Embodiment 1. A treating solution used in
this apparatus is a phosphoric acid solution obtained by mixing
phosphoric acid acting as a chemical and deionized water acting as
a diluent. The phosphoric acid solution is heated, and substrates
(e.g. semiconductor wafers) are immersed in the solution for
etching treatment.
[0074] This substrate treating apparatus includes a treating tank 1
for storing the phosphoric acid solution. Around the treating tank
1 is a collecting tank 2 for collecting the phosphoric acid
solution overflowing the treating tank 1. The phosphoric acid
solution collected in the collecting tank 2 is returned to the
treating tank 1 through a circulating system 3. The circulating
system 3 includes piping 4 for communicating the collecting tank 2
to injection pipes 1a disposed adjacent the bottom of the treating
tank 1. The piping 4 has, arranged thereon, a pump 5 for feeding
the solution, a circulating system heater 6 and a filter 7. The
circulating system heater 6 is used for heating the phosphoric acid
solution returned to the treating tank 1. The filter 7 is provided
to remove particles from the phosphoric acid solution returned to
the treating tank 1. A tank heater 8 is disposed around the
treating tank 1 and collecting tank 2 for heating the phosphoric
acid solution in the tanks. The circulating system heater 6 and
tank heater 8 correspond to the heating device in this
invention.
[0075] An openable cover 9 is disposed above the treating tank 1. A
plurality of wafers W under treatment are held by a vertically
movable holding arm 10 as arranged in vertical posture and
equidistantly thereon. The cover 9 is closed when the holding arm
10 is outside the treating tank 1. The cover 9 is opened for
allowing the holding arm 10 to load the group of wafers W into the
treating tank 1. While the group of wafers W undergoes etching
treatment in the tank 1, the cover 9 remains closed again. These
features are the same as in the conventional apparatus shown in
FIG. 1.
[0076] A phosphoric acid supply device 11 is provided for supplying
phosphoric acid to the collecting tank 2. The phosphoric acid
supply device 11 includes a nozzle 12 disposed above the collecting
tank 2, piping 13 for connecting the nozzle 12 to a phosphoric acid
source, and a flow regulating valve 14 mounted on the piping 13. A
deionized water supplementing device 15 is provided for
supplementing deionized water to the treating tank 1. The deionized
water supplementing device 15 includes a nozzle 16 disposed
adjacent an edge of the treating tank 1, piping 17 for connecting
the nozzle 16 to a deionized water source, and a flow regulating
valve 18 mounted on the piping 17. The deionized water
supplementing device 15 corresponds to the supplementing device in
this invention.
[0077] The treating tank 1 includes a temperature sensor 19 for
detecting the temperature of the phosphoric acid solution stored
therein. A detection signal of the temperature sensor 19 is applied
to a temperature controller 20. Based on this detection signal, the
temperature controller 20 carries out a PID (proportional, integral
and differential) control of the circulating system heater 6 and an
ON/OFF control of the tank heater 8. Specifically, the temperature
controller 20 controls the circulating system heater 6 so that the
temperature of the phosphoric acid solution is maintained in the
range of 159.7 to 160.3.degree. C. When the temperature of the
phosphoric acid solution is at or below 160.3.degree. C., the
temperature controller 20 maintains the tank heater 6 in ON state.
When the temperature of the solution exceeds 160.3.degree. C., the
temperature controller 20 turns off the tank heater 6. The
temperature sensor 19 corresponds to the temperature detecting
device in this invention. The temperature controller 20 corresponds
to the temperature control device in this invention.
[0078] Further, a concentration detecting device 21 is provided for
the treating tank 1 for detecting the concentration of the
phosphoric acid solution therein. Noting the fact that a
correlation exists between the concentration of the phosphoric acid
solution and the specific gravity thereof, the concentration
detecting device 21 is arranged to detect the concentration of the
phosphoric acid solution by substantially detecting the specific
gravity of the solution. Since the specific gravity of the
phosphoric acid solution has a correlation with a pressure at a
predetermined depth in the treating tank 1, the concentration
detecting device 21 has a detecting element at the predetermined
depth in the treating tank 1, and detects the concentration of the
phosphoric acid solution by detecting a pressure of the treating
solution applied to this element. A specific construction of the
concentration detecting device 21 will be described
hereinafter.
[0079] The concentration detecting device 21 includes a detection
pipe 22, a regulator 23, a pressure detector 24 and a concentration
calculator 25. The detecting pipe 22 is formed of a fluororesin
resistant to the phosphoric acid solution, and has a tip end
thereof acting as the detecting element located at the
predetermined depth in the treating tank 1. The regulator 23
supplies nitrogen gas from a nitrogen gas source at a constant flow
rate into the detection pipe 22. In a normal state, a nitrogen gas
discharge pressure may be considered nearly equal to the liquid
pressure at the predetermined depth from the liquid surface in the
treating tank 1. The pressure detector 24 has a pressure sensor for
measuring a nitrogen gas pressure in the detection pipe 22. Thus,
an output signal from the pressure detector 24 may be regarded as
the liquid pressure at the predetermined depth from the liquid
surface in the treating tank 1. The concentration calculator 25
has, stored therein in advance, working curve data showing a
correspondence between voltage and concentration according to a
pressure from the pressure detector 24. The concentration
calculator 25 derives a concentration of the phosphoric acid
solution in the treating tank 1 from the detection signal (voltage)
received from the pressure detector 24.
[0080] A specific concentration calculating method is described in
detail in Japanese Unexamined Patent Publication No.
11-219931(1999), which, briefly, is as follows.
[0081] The detection signal (voltage) from the pressure detector 24
and the liquid pressure have a fixed functional relationship
therebetween. The liquid pressure may be expressed as a sum of
atmospheric pressure and a value proportional to the product of a
distance (depth) from the liquid surface to the detecting element
of the detection pipe 22 and the specific gravity of the phosphoric
acid solution. Therefore, the liquid pressure acting on the
detecting element may be expressed by a function having variables
consisting in the concentration of the phosphoric acid solution and
the depth of the detecting element. Thus, the concentration and
depth are in a fixed relationship with the voltage outputted from
the pressure detector 24. Based on this relationship, a
concentration of the phosphoric acid solution may be derived from
the voltage outputted from the pressure detector 24 by determining
beforehand a relationship between concentration and voltage for the
predetermined depth.
[0082] The above concentration detecting device 21 corresponds to
the concentration detecting device in this invention.
[0083] Concentration data of the phosphoric acid solution provided
by the concentration detecting device 21 is applied from the
concentration calculator 25 to the concentration controller 26. The
concentration controller 26 controls the deionized water flow
regulating valve 18 to adjust the amount of deionized water
supplemented, so that a detected concentration of the phosphoric
acid solution becomes slightly higher than a boiling-point
concentration corresponding to a set temperature of the phosphoric
acid solution. Specifically, the concentration controller 26
controls the flow regulating valve 18 by PID (proportional,
integral and differential) control, based on a detected
concentration of the phosphoric acid solution.
[0084] A main controller 27 is provided to perform an overall
control of the substrate treating apparatus. Specifically, the main
controller 27 gives a command of a set temperature of the
phosphoric acid solution to the temperature controller 20, a
command of a target concentration of the phosphoric acid solution
to the concentration controller 26, a control command to the
phosphoric acid flow regulating valve 14, and so on.
[0085] Next, operation of this substrate treating apparatus will be
described with reference to the flow chart shown in FIG. 4.
[0086] Steps S1 and S2 First, the phosphoric acid flow regulating
valve 14 is opened to supply phosphoric acid to the collecting tank
2. The phosphoric acid supplied to the collecting tank 2 is heated
by the circulating system heater 6 while being transmitted to the
treating tank 1 through the circulating system 3. The phosphoric
acid introduced into the treating tank 1 is heated also by the tank
heater 8.
[0087] Steps S3, S4 and S5
[0088] The temperature of the phosphoric acid in the treating tank
1 is detected by the temperature sensor 19, and a corresponding
signal is applied to the temperature controller 20. The temperature
controller 20 controls the temperature of the phosphoric acid to be
within .+-.0.3.degree. C. of a predetermined temperature of
160.degree. C. Specifically, when the solution temperature is below
159.7.degree. C., the heating by the circulating system heater 6
and tank heater 8 is continued. When the solution temperature
exceeds 160.3.degree. C., the heating by the circulating system
heater 6 and tank heater 8 is stopped to allow the solution
temperature to lower by natural cooling. It should be noted that no
deionized water is supplemented for lowering the solution
temperature. This point is described in detail hereinafter. When
the solution temperature is brought within the range of 159.7 to
160.3.degree. C., the operation proceeds to step S6.
[0089] Step S6
[0090] The concentration of the solution in the treating tank 1 is
detected from time to time by the concentration detecting device
21. The concentration controller 26 controls the flow regulating
valve 18 by PID control to supplement the treating tank 1 with
deionized water so that the detected concentration agrees with a
target concentration set beforehand. This target concentration is
set to be slightly higher than the boiling-point concentration
corresponding to the set temperature of the phosphoric acid
solution. When the detected concentration of the phosphoric acid
solution in the treating tank 1 exceeds a target concentration
range, the supplementing of deionized water is continued. When the
detected concentration is less than the target concentration range,
the supplementing of deionized water is stopped. When the
supplementing of deionized water is stopped, the deionized water in
the phosphoric acid solution evaporates by the heating of the
phosphoric acid solution, whereby the concentration of the
phosphoric acid solution increases automatically.
[0091] Steps S7, S8 and S9
[0092] When the phosphoric acid solution in the treating tank 1 is
brought into and stabilizes in the target concentration range, the
group of wafers W held by the holding arm 10 is loaded into the
treating tank 1, and etching treatment of the wafers W is started.
The temperature control and concentration control in steps S2-S6
are repeated until a predetermined treating time elapses. After the
treating time, the group of wafers W is withdrawn upward from
inside the tank 1 and transferred to a next treating tank.
[0093] Next, a relationship between the temperature control and
concentration control of the phosphoric acid solution in this
embodiment will be described with reference to FIG. 5.
[0094] FIG. 5 is a graph showing a relationship between the
concentration and temperature of the phosphoric acid solution, and
a silicon nitride film etching rate. As shown in FIG. 5, boiling
point BP has a property of becoming higher with an increase in the
concentration of the phosphoric acid solution. Since, in this
embodiment, the temperature controller 20 performs a control to
maintain the temperature of the phosphoric acid solution constant,
a selected rate in time of etching silicon nitride film (etching
rate) will move along an etching rate curve ERC for each
temperature with variations in the concentration. Here, the
temperature of 150.degree. C. is assumed to provide curve ERC1, the
temperature of 160.degree. C. curve ERC2 and the temperature of
170.degree. C. curve ERC3. In this embodiment, the set temperature
of the phosphoric acid solution is 160.degree. C., the
concentration is variable along the curve ERC2. A concentration
region slightly higher than the boiling-point concentration BP on
the curve ERC2 is sub-boiling point SBP. The etching rate may be
maintained highest by maintaining the concentration of the
phosphoric acid solution at the sub-boiling point SBP located in a
turbulence zone TZ on one side of a boundary of boiling point BP.
The target concentration of the phosphoric acid solution in this
embodiment is set to this sub-boiling point region.
[0095] In this embodiment, as described above, when the temperature
of the phosphoric acid solution exceeds the set temperature range,
the temperature of the solution is lowered by stopping the heating
without supplying deionized water (step S5 in FIG. 4). Further, the
concentration control is performed only when the temperature of the
phosphoric acid solution is in the range of 159.7 to 160.3.degree.
C. (step S6). The reason is as follows. If deionized water is
supplied in order to lower the temperature of the phosphoric acid
solution having risen to 170.degree. C., for example, the
concentration of the phosphoric acid solution will vary leftward
along the curve ERC3 in FIG. 5 (in the direction in which the
concentration lowers). Then, the phosphoric acid solution could
reach the boiling point BP to cause bumping before reaching the
target concentration (sub-boiling point SBP on the curve ERC2 in
FIG. 5) corresponding to the set temperature. In order to avoid
bumping, it is necessary to supplement deionized water gradually.
Then, a long time will be taken to bring the phosphoric acid
solution to the set temperature.
[0096] In this embodiment, however, since the temperature of the
phosphoric acid solution is controlled only by operation of the
circulating system heater 6 and the tank heater 8, the
concentration of the phosphoric acid solution remains unchanged
even if the temperature of the phosphoric acid solution is varied.
This precludes the possibility of bumping of the phosphoric acid
solution. The supplementing of deionized water for adjusting the
concentration of the phosphoric acid solution is performed only
when the temperature of the phosphoric acid solution is in the set
temperature range. Thus, this embodiment is free from bumping due
to the supplementing of deionized water.
[0097] According to this embodiment, as described above, when the
concentration of the phosphoric acid solution is higher than the
target concentration, deionized water is supplemented to lower the
concentration along the curve ERC2 corresponding to the set
temperature of the phosphoric acid solution. Conversely, when the
concentration of the phosphoric acid solution is lower than the
target concentration, no deionized water is supplemented and the
concentration is increased by evaporation of the deionized water
from the phosphoric acid solution heated. In this way, the
concentration of the phosphoric acid solution is maintained at the
sub-boiling point with high precision, thereby maintaining a high
etching rate of the phosphoric acid solution.
[0098] As described above, the concentration control in steps S3-S6
is carried out only when the solution temperature is in the
predetermined range. A specific example of variations in the
temperature and concentration (specific gravity) occurring in time
of the concentration control will be described with reference to
FIG. 6.
[0099] In this example, as shown in FIG. 6A, heating is started at
time t=0 when the temperature is tm0, to raise the temperature to
tm1. On the other hand, as shown in a dotted line in FIG. 6B, the
concentration, in a non-control state with no deionized water
supplemented, lowers from cn0 with the temperature increase. Assume
the temperature reaches the predetermined range at time t3. Then,
the concentration control is started to attain a set concentration
cn1. By starting the concentration control after the temperature
reaches the predetermined range, it is possible to avoid adverse
influences of variations in the concentration due to the
temperature control and to consume a less time than in the prior
art before time t4 when the set concentration is attained.
[0100] Embodiment 2
[0101] FIG. 7 is a block diagram showing an outline of a substrate
treating apparatus in Embodiment 2 of this invention. Like
reference numerals are used to identify like parts in this
embodiment which are the same as in Embodiment 1, and will not be
described again.
[0102] As in Embodiment 1, this substrate treating apparatus
includes a treating tank 1 for storing the phosphoric acid
solution, a collecting tank 2 for collecting the overflowing
phosphoric acid solution, a circulating system 3 and so on.
[0103] A deionized water supplementing device 15 includes a nozzle
16 disposed adjacent an edge of the treating tank 1, piping 17 for
connecting the nozzle 16 to a deionized water source, and an air
control valve 37 mounted on the piping 17.
[0104] An electropneumatic converter 39 applies an output pressure
P.sub.out to the air control valve 37 to adjust a cross-sectional
passage area thereof, thereby to adjust a deionized water flow rate
through the piping 35 with high precision. The electropneumatic
converter 39 is also called an electropneumatic regulator, and
converts compressed air of predetermined pressure applied thereto
into the output pressure P.sub.out according to an input signal
S.sub.in. As the input signal S.sub.in n, for example, 4 to 20 [mA]
are applied, and the output pressure P.sub.out is adjusted to 0-1.0
[MPa] in response thereto. Upon receipt of the output pressure
P.sub.out, the air control valve 37 adjusts the deionized water
flow rate through the piping 17 to 0 to 400 [L/min]. FIG. 8 is a
flow rate characteristic diagram showing such characteristic of the
air control valve 37. As seen from this characteristic diagram, the
deionized water flow rate is linearly adjusted by the air control
valve 37 according to the output pressure P.sub.out from the
electropneumatic converter 39. The input signal S.sub.in n is
applied to the electropneumatic converter 39 from a concentration
controller 55 described hereinafter.
[0105] Concentration data of the phosphoric acid solution obtained
with a concentration detecting device 21 is applied to the
concentration controller 55. The concentration controller 55
controls the electropneumatic converter 39 to adjust the air
control valve 37 so that the detected concentration of the
phosphoric acid solution is slightly higher than the boiling-point
concentration corresponding to the set temperature of the
phosphoric acid solution. As a result, the amount of deionized
water supplied from the nozzle 16 to the treating tank 1 is
adjusted. Specifically, the concentration controller 55 controls
the electropneumatic converter 39 by PID (proportional, integral
and differential) control, based on the detected concentration of
the phosphoric acid solution.
[0106] Operation of this substrate treating apparatus is different
from the operation in Embodiment 1 in the control executed in step
S6.
[0107] That is, the concentration of the solution in the treating
tank 1 is detected from time to time by the concentration detecting
device 21. The concentration controller 55 controls the air control
valve 37 by adjusting the input signal S.sub.in, to the
electropneumatic converter 39 by PID control to supplement
deionized water to the treating tank 1, so that the detected
concentration agrees with a predetermined target concentration.
This target concentration is set to be slightly higher than the
boiling-point concentration corresponding to the set temperature of
the phosphoric acid solution. When the detected concentration of
the phosphoric acid solution in the treating tank 1 exceeds a
target concentration range, the supplementing of deionized water is
continued. When the detected concentration is less than the target
concentration range, the supplementing of deionized water is
stopped. When the supplementing of deionized water is stopped, the
deionized water in the phosphoric acid solution evaporates by the
heating of the phosphoric acid solution, whereby the concentration
of the phosphoric acid solution increases automatically.
[0108] In this way, the electropneumatic converter 39 can vary the
output pressure P.sub.out linearly according to the input signal
S.sub.in received from the concentration controller 55. By
operating the air control valve 37 based on the input signal
S.sub.in., the amount of deionized water supplemented may be
adjusted linearly. Thus, deionized water may be supplemented
accurately according to the concentration detected by the
concentration detecting device 21.
[0109] The relationship between the temperature control and
concentration control of the phosphoric acid solution in Embodiment
2 is the same as in Embodiment 1 described above.
[0110] Deionized water is supplemented for adjusting the
concentration of the phosphoric acid solution only when the
temperature of the phosphoric acid solution is in the set
temperature range. Thus, the supplementing of the deionized water
never causes bumping. Moreover, deionized water is supplemented by
adjusting the output pressure P.sub.out of the electropneumatic
converter 39 to control the air control valve 37. This realizes a
high etching rate of the treating solution maintained accurately
while preventing bumping.
[0111] According to this embodiment, as described above, when the
concentration of the phosphoric acid solution is higher than target
concentration, deionized water is supplemented to lower the
concentration along the curve (ERC2) corresponding to the set
temperature of the phosphoric acid solution. Conversely, when the
concentration of the phosphoric acid solution is lower than the
target concentration, no deionized water is supplemented and the
concentration is increased by evaporation of the deionized water
from the phosphoric acid solution heated. In this way, the
concentration of the phosphoric acid solution is maintained at the
sub-boiling point with high precision, thereby maintaining a high
etching rate of the phosphoric acid solution.
[0112] This invention is not limited to the foregoing embodiments,
but may be modified as follows:
[0113] (1) Embodiments 1 and 2 have been described by taking the
phosphoric acid solution as an example of treating solution. This
invention is applicable also where a different treating solution
such as a sulfuric acid solution is used.
[0114] (2) In Embodiments 1 and 2 described above, the
concentration of the treating solution is adjusted to be slightly
higher than the boiling-point concentration corresponding to the
set temperature of the treating solution. This invention is
applicable to any substrate treating apparatus that supplies a
chemical solution and deionized water to a treating tank without
such a control.
[0115] (3) This invention is applicable also to an apparatus not
having a circulating pipe system as described hereinbefore for
circulating a treating solution.
[0116] This invention may be embodied in other specific forms
without departing from the spirit or essential attributes thereof
and, accordingly, reference should be made to the appended claims,
rather than to the foregoing specification, as indicating the scope
of the invention.
* * * * *