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Description  |
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TECHNICAL FIELD
The present invention relates to a cleaning apparatus and a cleaning method
used for cleaning a semiconductor substrate or the like with chemical
solutions, particularly to a cleaning apparatus and a cleaning method for
safely performing accurate continuous cleaning at a low cost in a short
time by cleaning an object to be cleaned (e.g. a silicon wafer) in a
cleaning bath while rotating the object.
BACKGROUND ART
The background of the invention is described below by using a silicon wafer
as an object to be cleaned.
Cleaning of a silicon wafer in the semiconductor industry is one of the
most-important semiconductor producing processes.
That is, a lot of impurity particles are attached on a silicon wafer.
Therefore, if a device is formed on the silicon wafer without removing the
particles, only a device having bad characteristics can be obtained.
Therefore, a silicon wafer is generally cleaned with demineralized water
to remove impurities.
The following are objects particularly affecting a semiconductor device on
the surface of a wafer.
(1) Particles
(2) Organic contaminants
(3) Metallic impurities
(4) Native oxides
(5) Surface micro roughness
(6) Molecules adsorbed on the surface
However, only particles can be removed by demineralized water but native
oxides formed on the surface cannot be removed. Moreover, it is difficult
to remove fine particles among particles by demineralized water.
Therefore, cleaning is performed by using various types of chemical
solutions. One of them is RCA cleaning.
However, the RCA cleaning is not greatly improved compared with the RCA
cleaning in its early stages. Therefore, in fact, cleaning is performed in
many processes for a long time.
The RCA cleaning removes organic contaminants from the substrate surface by
oxidizing them. Its treatment processes are roughly shown below.
Cleaning with H.sub.2 SO.sub.4, H.sub.2 O.sub.2, and ultrapure water
Cleaning with ultrapure water
Cleaning with HF, H.sub.2 O.sub.2, and ultrapure water
Cleaning with ultrapure water
Cleaning with NH.sub.4 OH, H.sub.2 O.sub.2, and ultrapure water
Cleaning with ultrapure water
Cleaning with hot ultrapure water
Cleaning with ultrapure water
Cleaning with HF, H.sub.2 O, and ultrapure water
Cleaning with ultrapure water
Cleaning with HCl, H.sub.2 O.sub.2, ultrapure water
Cleaning with hot ultrapure water
Cleaning with HF, H.sub.2 O.sub.2, ultrapure water
Cleaning with ultrapure water
Drying
However, because these cleaning processes are performed by using an
independent cleaning apparatus or cleaning bath for each chemical solution
and successively soaking a silicon wafer in a cleaning bath storing each
chemical solution and ultrapure water, it cannot be avoided that a
chemical solution used in a previous process remains on the wafer and
thereby mutual contamination occurs between chemical solutions in cleaning
baths.
Moreover, because a wafer is transferred to the next cleaning bath through
the air, it is contaminated by the air or causes native oxides to be
produced in the air. Furthermore, because contaminated chemical solutions
are used several times or a plurality of silicon wafers are cleaned at the
same time, impurities removed from a silicon wafer easily attach to other
silicon wafer.
These contaminants during cleaning cause the yield to decrease and the cost
to increase. Moreover, because the present cleaning processes require a
long time, it is a problem that the cost is increased due to the long-time
cleaning.
Because a cleaning apparatus used for cleaning performs only one type of
cleaning in one bath, it is impossible to perform continuous cleaning in
the same bath. Therefore, many cleaning apparatuses and cleaning spaces
are necessary, causing the investment of equipment to increase.
Moreover, higher cleanliness of wafer surface is required because
integration level has been improved in recent years. However, the above
cleaning method cannot correspond to the requirement.
Therefore, a cleaning method and a cleaning apparatus are desired which
realize higher-cleanliness cleaning in a short time.
It is an object of the present invention to provide a cleaning method and a
cleaning apparatus for decreasing the total cost due to production of
high-performance semiconductor by using cleaner silicon-wafer surface,
decrease of the cost for semiconductor production, decrease of the
consumption of chemical solutions by using a new cleaning method and a new
cleaning apparatus, decrease of the cleaning time, decrease of the number
of types of chemical solutions used, easiness of waste liquid, and
decrease of investment on equipment.
DISCLOSURE OF THE INVENTION
The cleaning method of the present invention including a plurality of
chemical-solution-cleaning processes is characterized by performing a
chemical-solution-cleaning process of horizontally arranging objects to be
cleaned in a cleaning bath and closing the cleaning bath, and thereafter
continuously supplying a chemical solution onto the surface of the objects
to be cleaned and an ultrapure-water-cleaning process of supplying
ultrapure water in order in the same cleaning bath for each chemical
solution and then drying the objects.
The cleaning apparatus of the present invention comprises at least:
a cleaning bath having a movable cover at its top so that the apparatus can
be sealed when closing the cover;
object-to-be-cleaned holding means for holding an object to be cleaned in
the cleaning bath;
rotating means for rotating the object-to-be-cleaned holding means;
gas introducing means for introducing a gas into the cleaning bath;
a first nozzle for spraying a first chemical solution onto the surface of
the object to be cleaned held by the object-to-be-cleaned holding means;
a second nozzle for spraying a second chemical solution onto the surface of
the object to be cleaned held by the object-to-be-cleaned holding means;
a third nozzle for spraying the first chemical solution onto the back of
the object to be cleaned held by the object-to-be-cleaned holding means;
a fourth nozzle for spraying the second chemical solution onto the back of
the object to be cleaned held by the object-to-be-cleaned holding means;
a fifth nozzle for spraying ultrapure water onto the surface of the object
to be leaned held by the object-to-be-cleaned holding means;
a sixth nozzle for spraying ultrapure water onto the back of the object to
be cleaned held by the object-to-be-cleaned holding means;
a chemical-solution feed line connected to the first to the fourth nozzles
respectively;
an external chemical-solution feeder for feeding a chemical solution,
connected to each chemical-solution feed line;
an ultrapure water feed line connected to the fifth and sixth nozzles;
ozone adding means for selectively adding ozone to ultrapure water; and
a drainage system for perfectly separating waste liquids after cleaning.
The holding means of the present invention for a wafer having an
orientation flat comprises a spindle, at least three arms extending from
the top of the spindle in the radius direction, and a protrusion having a
terraced portion and formed at the tip of each arm; wherein the
protrusions are arranged so that the inside of at least one protrusion
contacts the lateral of the orientation flat of the wafer and the insides
of other protrusions contact the periphery of the circular arc portion of
the object to be cleaned.
Functions
Functions of the present invention are described below together with the
knowledge obtained in making the present invention.
Cleaning method
An art of cleaning a substrate while rotating it is hitherto known.
However, the art is a cleaning technique using demineralized water. An art
of cleaning a substrate with a chemical solution while rotating it is not
known at present. An art of cleaning a substrate with a plurality of
chemical solutions while rotating it is not known either.
The inventor of the present invention thought that the improvement of
cleanliness is limited in the cleaning by the soaking method and therefore
attempted rotary cleaning.
Particles slightly attached to a surface can be removed by rotary cleaning
using demineralized water. However, it is completely unknown whether other
contamination sources, particularly, native oxides formed on the surface
can be removed by the rotary cleaning with chemical solutions.
The inventor of the present invention performed various types of cleaning
with chemical solutions by using the apparatus shown in FIG. 10 (disclosed
in the official gazette of Japanese Patent Application Laid-Open No.
SHO-52-58458/1977) and spraying ozone-added ultrapure water, a mixture of
HF, H.sub.2 O.sub.2, and ultrapure water, and a mixture of NH.sub.4 OH,
H.sub.2 O.sub.2, and ultrapure water through a nozzle in order while
rotating a substrate.
As the result of measuring the surface cleanliness after ending the above
types of cleaning, native oxides remained on the surface. This was far
from perfect cleaning. Moreover, the surface after cleaned was rough.
Though the cause was unknown, the inventor of the present invention
attempted dropping feed of feeding every several drops of a chemical
solution onto the surface instead of spraying the chemical solution onto
the surface. As a result, it was found that the number of contamination
sources in the case of dropping feed was less than the number of
contamination sources in the case of spraying. However, a satisfactory
cleanliness was not obtained.
Therefore, as the result of repeating the experiment, it was found that it
was very important to continuously feed a chemical solution or ultrapure
water not in the form of a drop but in the form of a fluid. That is, it is
important to feed a chemical solution or ultrapure water not
intermittently but continuously like city water coming out of a faucet.
The cleaning mechanism in the rotary cleaning when continuously feeding a
chemical flow is not clarified. However, the following mechanism is
considered. That is, when a chemical solution is fed to the surface of an
object to be cleaned in accordance with continuous flow of the chemical
solution, the chemical solution extends in the radius direction due to the
centrifugal force to cover the surface and it reacts on contamination
sources on the surface to produce reaction products. The reaction products
is immediately removed from the surface together with the chemical
solution due to a centrifugal force and a new surface is exposed. Because
the chemical solution is continuously fed, the newly-exposed surface of
the object to be cleaned reacts on a fresh chemical solution. Thus, it is
considered that cleaning can be performed at a high cleanliness because a
new surface continuously contacts a fresh chemical solution.
It is preferable to set a chemical-solution feed position to the rotational
center of an object to be cleaned in order to further uniformly clean the
surface.
As described above, the present invention realizes high-cleanliness
cleaning. However, it is more marvelous that the high-cleanliness cleaning
can be performed in a very short time.
For example, to remove a noble metal impurities (e.g. Cu) with an
HF-H.sub.2 O.sub.2 cleaning solution, it takes approx. 60 min to realize
the level of 10 atoms/cm.sup.2 when using the soaking method. However, the
rotary cleaning method of the present invention realizes the level in a
very short time of approx. 30 sec.
The inventor of the present invention did not forecast that the high
cleanliness can be achieved in a short time and the true reason why the
unexpected effect could be achieved is not definite.
In the case of spraying, it is estimated that a chemical solution does not
uniformly cover an object to be cleaned because it is fed in the form of
fog and therefore cleaning at a high cleanliness cannot be achieved.
In the case of the present invention, various types of
chemical-solution-cleaning are performed in the same cleaning bath. When
various types of cleaning are performed in different cleaning baths, an
object to be cleaned is exposed to the air during transfer to cause native
oxides to be formed on the surface and the cleanliness to lower. However,
it is possible to prevent the cleanliness from lowering by performing
various types of cleaning in the same bath.
(Water sprinkling process)
In the present invention, it is preferable to sprinkle water an object to
be cleaned by rotating the object at 100 to 400 rpm before cleaning it
with a chemical solution. The feed rate of ultrapure water depends on the
surface area of an object to be cleaned. In the case of a wafer with a
diameter of 3 to 8 inches, it is preferable to feed ultrapure water of 2.5
to 10 cc to the surface of the object to be cleaned.
An art of decreasing the number of particles attached on the surface of a
wafer by soaking the wafer in demineralized water and thereafter soaking
it in a cleaning chemical solution is disclosed in the official gazette of
Japanese Patent Application Laid-Open No. HEI-3-240229.
In the case of the rotary cleaning, however, it is found that the particles
attached on the surface of a wafer cannot always be decreased only by
feeding demineralized water to the surface.
Therefore, as the result of eagerly following up factors for constantly
decreasing the attached particles, it is found that the factors include
the feed rate of demineralized water and the rotational speed of an object
to be cleaned.
That is, demineralized water of less than 2.5 cc cannot completely cover
the wafer surface. For demineralized water of more than 10 cc, however,
only some ultrapure water flows to form a channel. Thereafter, when a
chemical solution is fed, the chemical solution preferentially flows
through the channel and this prevents uniform cleaning.
Of course, the above phenomenon is first found by the inventor of the
present invention.
When the rotational speed is less than 100 rpm, it may not possible to
entirely cover the wafer surface with sprinkled water. That is, a dry
portion may occur. When the rotational speed exceeds 400 rpm, part of a
sprinkled water layer formed on the surface may be destroyed and the
chemical solution preferentially enters the destroyed portion to cause the
surface to be unevenly cleaned.
(Atmosphere of inert gas)
For the present invention, it is preferable to continuously flow an inert
gas in the way of downflow. By using the atmosphere of an inert gas, it is
possible to prevent an object to be cleaned from being exposed to the air
and an oxide film from being formed. In a practical manner, because water
(ultrapure water) is always present in the cleaning process, it is
considered that native oxides are formed even if the atmosphere of an
inert gas is used. Therefore, it is nonsense to use the atmosphere of an
inert gas in the cleaning process. However, it is found from the knowledge
of the inventor of the present invention that both water and oxygen are
indispensable to form native oxides. That is, it is found that native
oxides are not formed when water or oxygen is independently present.
Therefore, it is possible to prevent native oxides from being formed by
using the atmosphere of an inter gas. From this point of view, it is
preferable to keep the oxygen content in an inert gas at 100 ppb or less,
more preferable to keep it at 100 ppb or less, and most preferable to keep
it at 1 ppb or less.
Nitrogen is particularly preferable as an inert gas. At present, nitrogen
is used to generate an internal pressure, a downflow atmosphere is
generated, and a cleaning bath is completely closed so that a silicon
wafer under the cleaning process is not exposed to the air. As a result, a
cleanliness which cannot be realized by an existing cleaning apparatus is
achieved.
Moreover, it is preferable to introduce a gas so that the pressure in the
cleaning bath gets higher than the external pressure. By making the
pressure in the cleaning bath higher than the external pressure, it is
possible to prevent the air from leaking into the cleaning bath and more
effectively prevent native oxides from being formed.
It is preferable to introduce an inert gas into the cleaning bath in the
way of downflow. In the case of downflow, it is possible to prevent
reaction products from attaching to an object to be cleaned and perform
higher-cleanliness cleaning because the products removed from the surface
fall along the flow of the gas.
Moreover, it is preferable to set the flow rate of the inert gas to a value
which does not disturb a chemical solution layer formed on the surface of
the object to be cleaned.
Furthermore, it is preferable to prevent the external air from leaking by
introducing the inert gas and thereby making the pressure in the cleaning
bath higher than the pressure outside the cleaning bath.
Furthermore, it is preferable to continuously flow the inert gas not only
in cleaning the object to be cleaned in the cleaning bath but also in
introducing the object to be cleaned into the cleaning bath. Though the
object to be cleaned contacts the air when it is brought in or out, the
frequency for the object surface to contact the air decreases by
continuously flowing the inert gas.
(Chemical solution)
The cleaning process includes:
<1> Ozone-added cleaning with ultrapure water
Cleaning with ultrapure water
<2> Cleaning with HF, H.sub.2 O.sub.2, and ultrapure water
Cleaning with ultrapure water
<3> Cleaning with NH.sub.4 OH, H.sub.2 O.sub.2, and ultrapure water
Cleaning with ultrapure water
Cleaning with hot ultrapure water
Cleaning with ultrapure water
<4> Cleaning with HF, H.sub.2 O.sub.2, and ultrapure water
Cleaning with ultrapure water
In the process <1>, organic contaminants on the surface are oxidized with
ozone-added ultrapure water and at the same time, an oxide film is formed
on the surface of a silicon wafer, and then the wafer surface is rinsed
with ultrapure water to wash ozone-added ultrapure water and impurities
away.
In the process <2>, native oxides on the surface are separated by a mixture
of hydrofluoric acid, hydrogen peroxide, and ultrapure water and then the
surface is rinsed with ultrapure water to wash chemical solutions and
impurities away.
In the process <3>, particulates on the surface are removed by a mixture of
ammonium hydroxide, hydrogen peroxide, and ultrapure water and the surface
is rinsed with ultrapure water to wash chemical solutions and impurities
away.
In the process <4>, native oxides are separated again by a mixture of
hydrofluoric acid, hydrogen peroxide, and ultrapure water similarly to the
process <1> to wash chemical solutions and impurities away will ultrapure
water.
Finally, an object to be cleaned is rotated and dried to complete all
processes. All of the above processes are continuously performed in one
cleaning bath.
It is preferable to set the rotational speed of the object to be cleaned to
a value most suitable for each process.
(Ozone concentration)
It is preferable to set the ozone concentration to 2 to 10 ppm.
When the ozone concentration is less than 2 ppm, organic contaminants may
insufficiently be oxidized. When the ozone concentration exceeds 10 ppm,
the oxide film formed on the surface of the object to be cleaned may
become too thick, it may take a lot of time to remove the film, and the
surface roughness may be degraded.
(Rotational speed and feed rate of chemical solution)
The rotational speed of an object to be cleaned is an important factor for
high-cleanliness cleaning when the object is cleaned with a chemical
solution. Therefore, it is preferable to set the rotational speed to 100
to 3,000 rpm, more preferably to set it to 200 to 1,500 rpm.
When the rotational speed is less than 100 rpm, it is impossible to
entirely cover the surface of an object to be cleaned with a chemical
solution if the chemical solution is too little, small. Thus, a dry
portion is produced and the cleaning efficiency may lower. However, if the
chemical solution is too much, it may overflow from the surface before it
is expanded due a centrifugal force. Therefore, when the rotational speed
is less than 100 rpm, it is difficult to keep the feed rate of the
chemical solution at the optimum value.
When the rotational speed exceeds 3,000 rpm, some of the chemical solution
is transformed into mist, collides with the inner wall of a cleaning bath,
and attaches to the surface of an object to be cleaned to probably
contaminate the cleaned surface. Moreover, an object to be cleaned may
float while it is cleaned though depending on the weight of the object.
It is preferable to set the feed rate of a chemical solution to 100 ml/min
to 500 ml/min. Because cleaning is instantaneously completed, the
consumption of the chemical solution greatly decreases compared with the
case of the existing cleaning method.
(Back cleaning)
It is preferable to spray a chemical solution onto both the surface and the
back of an object to be cleaned because the back may unevenly be cleaned
due to the chemical solution incoming from the surface of the object.
(Inner-wall surface cleaning)
In the case of rotary cleaning, a chemical solution splashes from the
surface of an object to be cleaned due to a centrifugal force. In this
case, it is found that the splashed chemical solution attaches to the
inner wall of a cleaning bath. It is also found that the chemical solution
attached to the inner wall separates from the inner wall and attaches to
the surface of the object to be cleaned. Therefore, it is preferable to
remove the attached chemical solution from the inner wall of the cleaning
bath by continuously cleaning the inner wall in the
chemical-solution-cleaning process and the ultrapure-water-cleaning
process in order to realize high-cleanliness cleaning.
Cleaning apparatus
The operation of the apparatus of the present invention is described below
by referring to FIG. 1.
The apparatus of the present invention has a cleaning bath which has a
movable cover at its top.
(Cleaning bath)
FIG. 3 is a schematic view of a cleaning bath.
* Material
Though the material of the cleaning bath of the present invention is not
restricted, it is preferable to use a material having conductivity, heat
resistance, and chemical resistance.
The inventor of the present invention found that a cleaning bath was
electrified with static electricity while eagerly following up causes in
which impurities such as particulates are produced in the cleaning
process. Moreover, the inventor found that, when a cleaning bath was
electrified, impurities such as particulates attached to the inner wall of
the cleaning bath and the attached impurities such as particulates
attached to a wafer again. Therefore, it is possible to control generation
of static electricity by using a material having conductivity for the
cleaning bath and prevent impurities such as particulates from attaching
to the cleaning bath and a wafer from being contaminated.
For example, conductive fluorocarbon resin is preferable as a material
having conductivity, heat resistance, and chemical resistance.
* Cover
The cleaning bath of the present invention has a movable cover at its top.
When the cover is closed, the cleaning bath is sealed. Therefore, it is
possible to completely isolate an object to be cleaned from the air and
minimize the exposure of a silicon wafer to the air. As a result,
prevention of an oxide film from being formed in the cleaning process is
realized which is not realized by the prior art.
It is preferable to set the cover so that it is opened or closed by moving
it upward or downward. When the cover can be opened or closed by moving it
upward or downward and a gas introduction port serving as gas introducing
means to be described later is formed on the cover, it is possible to
minimize the exposure of an object to be cleaned to the air because an
inert gas is continuously flown through the introduction port when the
cover is opened and therefore the gas enters a cleaning bath.
By using the cleaning bath, it is possible to use all chemicals in one
cleaning bath.
(Rotating means)
It is preferable that the rotating means of the present invention has an
automatic control system using, for example, a microprocessor for
realizing smooth and continuous control from stationary state to
high-speed rotation and vice versa. This is because, in the present
invention, ozone-cleaning, ultrapure-water-cleaning, and chemical-cleaning
are performed in the same bath and each type of cleaning has a suitable
rotational speed range.
(Gas introducing means)
It is one of the greatest features of the present invention to use gas
introducing means. It is preferable to form a gas introduction port at the
top of a cleaning bath. That is, by forming the port at the top, it is
possible to make a downflow atmosphere for continuously flowing gas from
the top to the bottom. In this case, because gas is continuously blown
onto the surface of an object to be cleaned, it is possible to remove
impurities from the surface of the object, prevent the impurities from
attaching to the object again, and realize higher-cleanliness cleaning.
(Object-to-be-cleaned holding means)
The object-to-be-cleaned holding means comprises a spindle, at least three
arms extending in the radius direction from the top of the spindle, and a
protrusion having a terraced portion and formed at the tip of each arm. It
is preferable to use object-to-be-cleaned holding means in which
protrusions are arranged so that, when a wafer having an orientation flat
is horizontally mounted on the holding means, the inside of at least one
protrusion contacts the lateral of the orientation flat of the wafer and
the insides of other protrusions contact the periphery of the circular arc
of the wafer.
FIG. 4 shows the shape of the above object-to-be-cleaned holding means. The
object-to-be-cleaned holding means minimizes the area for contacting the
object to be cleaned.
That is, the holding means realizes three-point holding using a centrifugal
force according to rotation, unlike vacuum holding or mechanical holding,
and one of the three points is set to a position for supporting the
orientation flat of the wafer. By using the object-to-be-cleaned holding
means, it is possible to hold an object to be cleaned by only three points
without causing deflection or distortion due to vacuum holding or
mechanical holding. Thus, the object to be cleaned has a clean and flat
surface free from deflection or distortion.
It is important in view of achieving higher-cleanliness cleaning that the
periphery of an object to be cleaned is released except three points. That
is, it is important that a uniform chemical solution film is formed on the
surface of the object to be cleaned in order to perform uniform cleaning.
However, if something is present on the periphery of the object to be
cleaned, solution moved to the periphery by a centrifugal force due to
rotation collides with the thing and reflects to cause a turbulent flow in
the vicinity of the periphery. That is, formation of a uniform solution
film is prevented and uniform cleaning is not realized. It is found by the
inventor of the present invention for the first time that formation of the
above uniform solution film is important to clean an object to be cleaned
by rotating it.
(External chemical solution feeder)
FIG. 5 is a flow chart of an external chemical solution feeder. It is
preferable to use an external chemical solution feeder having a tank at a
high place without using a pump when feeding a chemical solution to a
silicon wafer. By using no mixed chemical solution pump, it is possible to
prevent contamination by the pump and elution of impurities into a
chemical solution and feed the chemical solution at a low pressure.
Moreover, though the type of a chemical solution and the quantity of the
chemical solution are not restricted, it is preferable to use an external
chemical solution feeder having two independent chemical solution feed
lines such as a line for hydrofluoric acid, hydrogen peroxide, and
ultrapure water and a line for ammonium hydroxide, hydrogen peroxide, and
ultrapure water and an automatic chemical solution mixer for automatically
mixing chemical solutions by controlling the flow rate. This makes it
possible to feed chemical solutions with a constantly same mixture ratio
only by replenishing stock solutions without contaminating the chemical
solutions each other. As a result, high-cleanliness cleaning with chemical
solutions free from secondary contamination of an object to be cleaned is
realized.
(Nozzle)
FIG. 6 is a positional schematic view of nozzles in a cleaning bath. The
nozzle mode example shown in FIG. 6 is the mobile type in which a
plurality of nozzles are integrated by a nozzle rack and all the nozzles
move together. Because the nozzle rack is the mobile type, it is possible
to feed a chemical solution and ultrapure water from any position on an
object to be cleaned. Moreover, because this is not the spraying type such
as an existing shower nozzle, it is possible to smoothly and continuously
feed a chemical solution and ultrapure water at a constant flow rate.
Setting every nozzle to one nozzle rack has an important meaning in
achieving high-cleanliness cleaning. That is, it is possible to feed
another type of chemical solution while feeding one type of chemical
solution. For example, it is possible to start feeding the chemical
solution of hydrofluoric acid, hydrogen peroxide and ultrapure water
immediately before rising with ultrapure water is completed. Thus, it is
possible to decrease the time for exposing an object to be cleaned to the
air and control the generation of native oxides.
It is preferable to use a straight nozzle whose inside diameter is the same
up to the solution exit as shown in FIG. 7(a). Moreover, it is preferable
to arrange the cross section of the solution exit so that it is horizontal
to an object to be cleaned. When using the above nozzle, it is possible to
uniformly clean the surface of the object by dropping a chemical solution
or ultrapure water just under the solution exit as a continuous fluid so
that a dropping point comes to the rotational center of the object because
the dropped chemical solution or ultrapure water is uniformly expanded in
the surface due to a centrifugal force. That is, in the case of the nozzle
whose solution exit is narrowed as shown in FIG. 7(b), a chemical solution
coming out of the solution exit becomes fog and therefore the chemical
solution cannot be fed as a continuous fluid. Moreover, in the case of the
nozzle whose solution exit face is not horizontal as shown in FIG. 7(c),
it is impossible to uniformly feed a chemical solution onto the surface
because the quantity of the chemical solution fed from the solution exit
varies or the chemical solution does not drop just under the solution
exit.
(Back-cleaning spray nozzle)
It is preferable to use back-cleaning spray nozzles each of which is
independently used for a chemical solution line and an ultrapure water
line as the back-cleaning nozzles of the present invention. Because every
spray nozzle has an independent line, it is possible to clean the back
with a chemical solution and ultrapure water, which is impossible by an
existing cleaning apparatus. Moreover, because every nozzle has an
independent line, it is possible to simultaneously clean the surface and
the back with different chemical solutions. For example, it is possible to
clean the surface with hydrofluoric acid, hydrogen peroxide, and ultrapure
water and the back with ultrapure water at the same time. As a result, a
clean surface can be obtained which is not contaminated by contaminants
coming from the back.
(Ultrapure water feed line)
It is preferable that the ultrapure water feed line of the present
invention must resist ozone because ozone is added to ultrapure water.
Therefore, it is preferable to use a line made of a stainless steel pipe
provided with surface treatment (e.g. passive-state making treatment) or
fluorocarbon resin. A line extended from an ozone generator is connected
to the vicinity of the end of the ultrapure water feed line through an
automatic valve, which makes it possible to add ozone. Therefore, it is
possible to have the ultrapure water feed line and the ozone-added
ultrapure water line for common use and simplify the pipe arrangement in
the apparatus.
(Ozone adding means)
FIG. 8 is a flow chart of an ultrapure water line and an ozone adding line.
It is preferable that the cleaning apparatus of the present invention
includes a small ozone generator using ultrapure water as a material
because the ozone adding means of the present invention is able to
minimize decomposition of ozone by adding ozone at a position closest to
the use point. That is, the cleaning apparatus of the present invention
controls addition of ozone generated by an ozonizer by changing automatic
valves.
Moreover, by incorporating the ozonizer into the cleaning apparatus, it is
possible to downsize the apparatus and disuse peripheral units.
It is preferable to provide the ultrapure water feed line with a bypass
line through a valve and set an ozone generator on the bypass line.
Moreover, it is preferable to set the bypass line in the cleaning bath. By
setting the ozone generator in the cleaning bath, it is possible to
decrease the distance between the ozone generating source and an ozone
feed destination. That is, it is possible to improve the cleaning
efficiency because generated ozone can be fed to the feed destination
before zone decreases.
(Cleaning-bath inner-wall cleaning means)
The cleaning-bath inner-wall cleaning means of the present invention makes
it possible to wash a used contaminated chemical solution on the inner
wall away with ultrapure water and keep a cleaning bath clean. Thus, a
clean silicon wafer surface is obtained because secondary contamination of
a silicon wafer due to a contaminated chemical solution is preve | | |
