Controlling gas in a multichamber processing system

A wafer processing system comprises a container-housing chamber for housing the conveying container conveyed from the common area, a cleaning chamber disposed adjacent to the container-housing chamber, and a load-lock chamber disposed adjacent to the cleaning chamber. The cleaning chamber has an inlet line for introducing a clean gas into the cleaning chamber and a pressure control means for controlling the pressure in the cleaning chamber. The load-lock chamber has a conveying unit capable of extending to the container-housing chamber through the cleaning chamber, in order to take out the object from the conveying container housed in the container-housing chamber to the load-lock chamber through the cleaning chamber.

FIELD OF THE INVENTION
 This invention relates to a processing system and a method of controlling a
 gas in a processing system for processing an object such as a wafer as
 part of a step for processing semiconductor devices.
 BACKGROUND OF THE INVENTION
 In the process to manufacture semiconductor devices, there is a trend that
 semiconductor wafers to be processed change from the current 6 or 8 inch
 wafers directly to 300 mm wafers. Thus, semiconductor manufacturing
 systems which can deal with 300 mm wafers have been developed. In 300 mm
 wafers, not only the diameter and the weight of the wafers have increased,
 but the width of lines in integrated circuits formed on the wafer have
 become ultraminute to not more than a sub-quarter-micron. Therefore, in
 semiconductor manufacturing plants, ultracleaning technology for clean
 rooms and automatic conveying technology for the wafers has become more
 important.
 In the case of wafers up to 8 inches, the carrier for the wafers is
 conveyed usually with the wafers in upright attitude when conveying the
 wafers from one step to another, while the wafers are usually kept
 horizontal when conveying them into and out of processing units of the
 semiconductor production equipment. The operation of conveying the
 carriers into and out of the units is achieved by an operator or AGV
 (automatic guided vehicle). However, in the case of wafers of 300 mm, if
 the wafers are conveyed in an upright stance, the lower edges of the
 wafers may be damaged by the weight of the wafers, vibrations during
 conveying or the like. Therefore, the carrier is conveyed with the wafers
 kept horizontal. The operation of conveying into and out of the unit is
 difficult for the operator to achieve because of the weight of the wafers
 and the problem of generation of particles. Therefore an automatic
 operation is being promoted.
 In the case of wafers up to 8 inches, after the load-lock chamber in which
 the carrier is placed is brought to a certain degree of vacuum, the wafers
 are conveyed one after another through a conveying chamber to a certain
 processing chamber. However, in the case of 300 mm wafers, the carrier
 capacity is large so that it takes much time to bring the load-lock
 chamber to a vacuum state. In addition, the vacuum causes, organic
 compound gases and the like are withdrawn from the plastic parts of the
 carrier, thereby polluting the inside of the unit with impurity gases.
 Therefore, in processing systems which deal with 300 mm wafers, a cleaning
 chamber is provided between a carrier-housing chamber and a load-lock
 chamber so that the wafers are first conveyed into the load-lock chamber
 from the carrier positioned in the carrier-housing chamber by a conveying
 unit placed in the load-lock chamber. The wafers are then conveyed through
 a conveying chamber into each processing chamber one by one. Thus carriers
 adapted for 300 mm wafers are required. At the present time, carriers can
 be roughly classified into an open-type carrier and a closed-type pod (for
 example, an unified pod) which is closed with a lid after putting the
 carrier therein.
 For example, as shown in FIG. 4, the above processing system comprises a
 tray 1 for receiving a pod P which houses 13 or 25 wafers, a
 carrier-housing chamber 2 for housing the retracted tray 1 on which the
 pod P is put, and a load-lock chamber 3 having a wafer conveying unit (not
 shown) which conveys wafers in a bunch into and out of the pod P in the
 carrier-housing chamber 2. Furthermore, a cleaning chamber 5 is provided
 between the carrier-housing chamber 2 and the load-lock chamber 3 to clean
 the atmosphere of the wafer passage line. To the load-lock chamber 3 is
 connected a conveying chamber 4 via a gate-valve so that the wafers in the
 load-lock chamber 3 are conveyed into the processing chamber for wafers
 (not shown) through the conveying chamber 4 one by one. This processing
 system is provided in a unit area R2 which is divided from a common area
 R1 by a front panel 6 in a clean room R.
 At the ceiling of the clean room R, a high-performance filter F such as a
 ULPA filter or a HEPA filter is placed so that air cleaned by the
 high-performance filter F flows downward in the clean room R. This
 processing system introduces air in the unit area R2 into the cleaning
 chamber 5 by a suction fan (not shown) provided in the cleaning chamber 5;
 cleans the air with a high-performance filter provided on a downstream
 side of the suction fan, similar to the above high-performance filter;
 causes the air to flow downward in the cleaning chamber 5 as shown by
 arrows in FIG. 4; and discharges the air from the bottom to the outside.
 In the cleaning chamber 5, an opener 7 is arranged as shown in FIG. 4.
 This processing system opens the lid of the pod P by the opener 7, conveys
 wafers W in the pod P in a lump through the cleaning chamber 5 into the
 load-lock chamber 3 by the wafer conveying unit in the load-lock chamber
 3, keeps all the wafers W horizontal in the load-lock chamber 3, and
 conveys the wafers held by the conveying unit through the conveying
 chamber 4 into the processing chamber. At each transfer port of the wafers
 in the load-lock chamber 3 and in the conveying chamber 4, a gate-valve
 (not shown) is arranged.
 In the case of the above described conventional processing system, there
 are some problems owing to introducing the air in the unit area R2 into
 the cleaning chamber 5. In the unit area R2, unlike the common area R1,
 various units are ordinarily provided. Consequently, particles may be
 produced from these units or organic gases such as an organic solvents
 consisting by of hydrocarbons may be produced as impurity gases from the
 painted portions of these units. Because of this, the air in the unit area
 R2 becomes polluted by these impurities, and the air in the unit area R2
 is inferior in cleanliness to that in the common area R1. If the air in
 the unit area R2 is introduced into the cleaning chamber 5 as it is, even
 though the particles can be removed by a high-performance filter in the
 cleaning chamber 5, the impurity gases can not be removed, so that the
 impurity gases may adhere to the surfaces of the wafers W, thereby
 disturbing the processing of the wafers W and reducing the yield in the
 process. The more ultraminute the processing of wafers W is, the greater
 influence of particles and the impurity gases. In addition, if air is
 introduced, oxygen in the air produces oxidation films on the surfaces of
 the wafers W and moisture in the air flows through the cleaning chamber 5
 into the load-lock chamber 3 to adhere to the walls of the load-lock
 chamber 3. This brings about an adverse influence in that the length of
 time needed to bring the load-lock chamber 3 to a vacuum state becomes
 long.
 SUMMARY OF THE INVENTION
 Therefore, an object of this invention is to provide a processing system
 and a method of controlling a gas in a processing system which can prevent
 drop of the yield by preventing impure gases from adhering to the object
 to be processed therein.
 In this invention, a processing system provided in a unit area which is
 divided from a common area by a partition, for processing an object to be
 processed which is conveyed by a conveying container for an object from
 the common area, comprising; a container-housing chamber for housing the
 conveying container conveyed from the common area; a cleaning chamber
 provided adjacent to the container-housing chamber; and a load-lock
 chamber provided adjacent to the cleaning chamber; wherein the cleaning
 chamber has an inlet line for introducing clean gas into the cleaning
 chamber and a pressure control means for controlling a pressure in the
 cleaning chamber; and the load-lock chamber has a conveying unit capable
 of extending to the container-housing chamber through the cleaning
 chamber, in order to take out the object from the conveying container
 housed in the container-housing chamber to the load-lock chamber through
 the cleaning chamber.
 This invention is characterized by another feature that the pressure
 control means comprises; a valve for adjusting a flow rate of the gas in
 the inlet line, a differential pressure gauge for detecting a differential
 pressure between a pressure in the cleaning chamber and the atmospheric
 pressure, and a valve-controller for adjusting an opening degree of the
 valve so that the pressure in the cleaning chamber is a positive pressure,
 based on a result of the detecting by the differential pressure gauge.
 This invention is characterized by another feature that the cleaning
 chamber is provided at a portion close to an edge on the side of a
 cleaning chamber of the inlet line, and has a ventilating means for
 ventilating the clean gas introduced by the inlet line into the cleaning
 chamber. Further the cleaning chamber preferably comprises; a circulation
 line for circulating the gas ventilated by the ventilating means in the
 cleaning chamber; and a filter provided in the circulation line, for
 removing particles or an impurity gas from the gas circulating in the
 circulation line.
 This invention is characterized by another feature that the inlet line
 connects the cleaning chamber with the common area to introduce the clean
 gas into the cleaning chamber from the common area, or by another feature
 that the system comprises an inert gas supplier, and the inlet line
 connects the cleaning chamber with the inert gas supplier to introduce the
 clean gas into the cleaning chamber from the inlet gas supplier.
 On the other hand, in this invention, a method of controlling a gas in a
 processing system provided in a unit area which is divided from a common
 area by a partition, for processing an object to be processed which is
 conveyed by a conveying container for an object from the common area,
 comprising, a container-housing chamber for housing the conveying
 container conveyed from the common area, a cleaning chamber provided
 adjacent to the container-housing chamber, and a load-lock chamber
 provided adjacent to the cleaning chamber, wherein the cleaning chamber
 has an inlet line for introducing clean gas into the cleaning chamber and
 a pressure control means for controlling a pressure in the cleaning
 chamber, the load-lock chamber has a conveying unit capable of extending
 to the container-housing chamber through the cleaning chamber, in order to
 take out the object from the conveying container housed in the
 container-housing chamber to the load-lock chamber through the cleaning
 chamber, said method comprises the steps of: introducing the clean gas
 from the common area through the inlet line into the cleaning chamber; and
 maintaining a pressure in the cleaning chamber positive by the pressure
 control means.
 This invention is characterized by another feature that the method further
 comprises the steps of: discharging the gas introduced into the cleaning
 chamber; and introducing again the discharged gas into the cleaning
 chamber thorough a filter.
 Further, in this invention, another method of controlling a gas in a
 processing system provided in a unit area which is divided from a common
 area by a partition, for processing an object to be processed which is
 conveyed by a conveying container for an object from the common area,
 comprising, a container-housing chamber for housing the conveying
 container conveyed from the common area, a cleaning chamber provided
 adjacent to the container-housing chamber, a load-lock chamber provided
 adjacent to the cleaning chamber, and an inert gas supplier, wherein the
 cleaning chamber has an inlet line for introducing clean gas into the
 cleaning chamber and a pressure control means for controlling a pressure
 in the cleaning chamber, the load-lock chamber has a conveying unit
 capable of extending to the container-housing chamber through the cleaning
 chamber, in order to take out the object from the conveying container
 housed in the container-housing chamber to the load-lock chamber through
 the cleaning chamber, said method comprises the steps of: introducing the
 inert gas from the inert gas supplier through the inlet line into the
 cleaning chamber, and maintaining a pressure in the cleaning chamber
 positive by the pressure control means.
 This invention is characterized by another feature that the method further
 comprises the steps of: discharging the inert gas introduced into the
 cleaning chamber; and introducing again the discharged inert gas into the
 cleaning chamber thorough a filter.

BEST MODE FOR CARRYING OUT THE INVENTION
 An embodiment of the invention will now be described in more detail with
 reference to FIG. 1 and FIG. 2.
 The embodiment of the processing system 10 according to the invention
 comprises, as shown in FIG. 1, a tray 11 for supporting a pod P which
 houses wafers (objects to be processed), a carrier-housing chamber 12
 (container-housing chamber) for housing a retracted tray 11 on which the
 pod P is put, and a load-lock chamber 13 having a wafer conveying unit 13A
 which conveys wafers in a bunch into and out of the pod P in the
 carrier-housing chamber 12. A cleaning chamber 14 is arranged between the
 carrier-housing chamber 12 and the load-lock chamber 13. To the load-lock
 chamber 13 is openly connected a conveying chamber 15 so that wafers in
 the load-lock chamber 13 can be conveyed into a wafer processing chamber
 (not shown) through the conveying chamber 15 one by one. The conveying
 chamber 15, plural processing chambers are openly connected to each other
 so that wafers W in the load-lock chamber 13 can be conveyed one by one
 into each processing chamber, for example through the conveying unit (not
 shown) in the conveying chamber 15. The reference sign 13B in FIG. 1
 indicates a drive mechanism for the wafer conveying unit 13A.
 As shown in FIG. 2, the pod P comprises a main body P1 and a lid P2 for
 closing the opening in the main body P1. The pod P is adapted to house 13
 or 25 wafers of 300 mm and to be closed tightly by a synthetic resin such
 as PEEK (Poly-Ether-Ether-Keton). When the wafers are transported,
 nitrogen or other such gas is introduced into the pod P to keep its inside
 clean and to seal the inside from the outside thus preventing the wafers
 from being oxidized naturally as much as possible. On the upper surface of
 the pod P, a holding part P3 is attached. The carrier conveying unit which
 moves along a rail arranged on the ceiling of the clean room R, holds onto
 the holding part P3 and conveys the pod P between processing units. The
 reference sign F in FIG. 1 indicates the high-performance filter.
 On the front surface of this embodiment of the processing unit 10, a front
 panel 16 is arranged. The front panel 16 divides the clean room R into a
 common area R1 and a unit area R2. In the front panel 16, a transfer port
 16A is formed for conveying the pod P into and out of the carrier-housing
 room 12. The tray 11 moves through the transfer port 16A between a forward
 position shown by the solid line in FIG. 1 and a backward position shown
 by the chain line in FIG. 1. The plural trays 11 are provided vertically
 so that each tray 11 stops at the transfer port 16A by an elevator
 mechanism 17. At the front panel 16, an opening/closing door 16B is
 arranged. The opening/closing door 16B opens and closes the transfer port
 16A by sliding in the direction of the arrows in FIG. 1 and is driven by
 drive mechanism 16C. The common area R1 is formed as an area for the
 operator to operate the processing unit 10 and is an area for the AGV to
 convey the pod P.
 A wafer transfer port (not shown) is formed in the wall on the side of the
 carrier-housing chamber 12 of the cleaning chamber 14 for conveying
 wafers. The wafer transfer port is fitted with the lid P2 of the pod P.
 Below the wafer transfer port, a lid opener 18 is arranged. This opener 18
 can open/close the lid P2 of the pod P as shown in FIG. 2. On the wall on
 the opposite side to the opener 18, a gate-valve 19 driven by a drive
 mechanism 19 A is mounted. The gate-valve 19 is opened when conveying the
 wafers, and closed after conveying the wafers in order to seal the
 load-lock chamber 18. Accordingly, after the lid P2 of the pod P is opened
 by the opener 18 and the gate-valve 19 is opened, the wafer conveying unit
 13A is driven to convey in a bunch 13 or 25 wafers from the pod P into the
 load-lock chamber 13 where they are held horizontally. Next the opener 18
 and the gate-valve 19 are closed and the transfer port 15A of the
 conveying chamber 15 is opened. The conveying unit in the conveying
 chamber 15 is then driven to take out wafers one by one from the wafer
 conveying unit 13A and to convey them through the conveying chamber 15
 into various processing units. In the processing units, etching, film
 forming or the like is conducted on the wafers.
 In the upper portion of the above cleaning chamber 14, a ventilating fan
 20, a high-performance filter 21 and a chemical filter 22 are arranged
 vertically in this order from top to bottom. The high-performance filter
 21 is an ULPA filter or a HEPA filter or the like. The chemical filter 22
 consists of an absorbent substance such as an active carbon in a
 particulate or fibrous state to absorb impurity gases chemically. At the
 lower portion of the cleaning chamber 14, a floor 23 having a number of
 dispersed holes is arranged horizontally, so that the gas flowing downward
 by the ventilating fan 20 goes though the floor 23, returns through a
 circulating duct 24 to an upper space 14B above the ventilating fan 20 in
 the cleaning chamber 14, and the gas flow circulates through the cleaning
 chamber 14 as shown by arrows in FIG. 1. An inert gas supplier 31 for
 supplying an inert gas such as nitrogen or argon or the like is connected
 to the cleaning chamber 14 through a connecting duct 25. The edge of the
 connecting duct 25 on the side of the cleaning chamber 14 is disposed
 between the ventilating fan 20 and the high-performance filter 21 to
 disperse the inert gas wholly between the ventilating fan 20 and the
 high-performance filter 21. Accordingly the inert gas flows downward in
 the cleaning chamber 14 through both the high-performance filter 21 and
 the chemical filter 22 without turbulence and circulates back to the
 cleaning chamber 14 through the above line as a laminar flow.
 The pressure of the inert gas in the cleaning chamber 14 at this stage can
 be set to any pressure higher than the atmospheric pressure. This is
 achieved by a pressure control valve 26 having a valve-controller 32
 attached to the above connecting duct 25, and a differential pressure
 gauge 27 attached in the cleaning chamber to detect the difference between
 the inside pressure of the cleaning chamber 14 and the atmospheric
 pressure. The differential pressure gauge 27 continually detects the
 pressure of the inert gas in the cleaning chamber 14 detects the
 difference from the atmospheric pressure. The differential pressure gauge
 27 is connected to the valve-controller 32 which continually keeps the
 pressure of the inert gas in the cleaning chamber 14 positive, that is,
 higher than the atmospheric pressure. Therefore, if the pressure of the
 inert gas in the cleaning chamber 14 becomes close to or lower than the
 atmospheric pressure, the valve-controller 32 enlarges the opening degree
 of the pressure control valve 26 in accordance with the value detected by
 the differential pressure gauge 27 to increase the flow rate of the inert
 gas thereby keeping the pressure of the inert gas positive. By keeping the
 pressure of the inert gas in the cleaning chamber 14 positive, the air in
 the unit area R2 is prevented from flowing into the cleaning chamber 14.
 The method for controlling gas and the operation of the processing system
 according to this invention will be described below. When processing
 wafers with the processing unit 10, the opening/closing door 16B of the
 front panel 16 is opened, the tray 11 is drawn out from the transfer port
 16A, and the pod P is placed on the tray 11. Then the tray 11 moves back
 into the carrier-housing chamber 12 and the drive mechanism 16C operates
 to close the opening/closing door 16B thereby sealing off the transfer
 port 16A. Next, the opener 18 in the cleaning chamber 14 operates to open
 the lid P2 of the pod P as shown in FIG. 2, and the gate-valve 19 of the
 load-lock chamber 13, driven by the drive mechanism 19A, operates to open
 the transfer port. As a result, the pod P, the cleaning chamber 14 and the
 load-lock chamber 13 are linked together to make a single space. An inert
 gas such as nitrogen is supplied from the supplier 31 into the cleaning
 chamber 14, thereby filling the pod P, the cleaning chamber 14 and the
 load-lock chamber 13 with very clean nitrogen gas. At this stage, the
 cleaning chamber 14 is the only space having a positive pressure so
 pressure is reduced when the pod P, the cleaning chamber 14 and the
 load-lock chamber 13 are connected together. However, when the pressure
 falls below a certain value, the valve-controller 32 opens or enlarges the
 opening of the pressure control valve 26 in accordance with a signal based
 on the readings detected by the differential pressure gauge 27, thereby
 letting extra nitrogen gas into the space. Consequently, the pressure of
 the unified space is maintained at certain positive pressure.
 Under the above positive pressure, the wafer conveying unit 13A in the
 load-lock chamber 13 is driven by the drive mechanism 13B to convey the
 wafers in the pod P into the load-lock chamber 13 in a bunch. At this
 point, the wafers pass through the cleaning chamber 14. If particles are
 produced from the opener 18 or a moving part of the wafer conveying unit
 13A, or if an organic impurity gases are produced from the lubricating oil
 of the drive mechanism or the like, the impurities will not adhere to the
 surfaces of the wafers resulting in a reduction in the processing yield.
 This is because the unified space is always filled with circulating
 nitrogen gas and when this gas flows through the cleaning chamber 14,
 impurities are removed by the high-performance filter 21 or the chemical
 filter 22.
 The wafer conveying unit 13A horizontally supports 13 or 25 wafers in such
 a way that the gap between two adjacent wafers is very small, thereby
 preventing inert gas from flowing between the wafers. This enables all
 wafers to pass through the cleaning chamber 14, while staying as clean as
 they were when in the pod P. Furthermore, there is no fear of impure air
 from the unit area R2 flowing into the cleaning chamber 14 and
 contaminating the wafers with impurities as the cleaning chamber 14 is
 always maintained at a positive pressure and kept in a clean state, even
 if the cleaning chamber 14 is not closed fully.
 After the wafers are conveyed into the load-lock chamber 13 as mentioned
 above, the opener 18 operates the lid P2 to tightly seal the pod P in the
 cleaning chamber 14, and the drive mechanism 19A operates gate-valve 19 to
 close the transfer port of the load-lock chamber 13. As a result, the
 cleaning chamber 14 and the load-lock chamber 13 are shut off from each
 other. The load-lock chamber 13 is then made into a vacuum state. After
 that, the gate-valve 15A of the conveying chamber 15 opens and the
 gate-valve for the conveying chamber 15 on the side of the processing
 chamber opens thereby connecting the load-lock chamber 13 and the
 conveying chamber 15. The conveying unit of the conveying chamber 15 is
 then driven to carry one by one the wafers held in the wafer conveying
 unit 13A into the appropriate processing chamber where they receive
 certain processes. When the wafers have finished being processed, they are
 taken out of the processing chamber and carried back to their original
 positions in the wafer conveying unit 13A in the load-lock chamber 13.
 When all the wafers have finished being processed, they are moved from the
 load-lock chamber 13 back into the pod P. The pod P is then moved back to
 the next step.
 As above described, according to this embodiment, the processing system 10
 comprises: an inert gas supplier 31; an inlet line 25 introducing clean
 inert gas into the cleaning chamber 14; a pressure control valve 26 having
 a valve-controller 32 for adjusting the flow rate of the inert gas in the
 inlet line 25; a differential pressure gauge 27 for detecting the
 difference in pressure between the cleaning chamber 14 and the atmosphere.
 The valve-controller 32 adjusts the opening of the pressure control valve
 26 in accordance with the value detected by the differential gauge 27. The
 inert gas is also passed through a high performance filter 21 and a
 chemical filter 22. Thus highly pure inert gas is circulated through the
 cleaning chamber 14 while keeping the pressure positive. Under this
 system, when conveying wafers from the pod P to the load-lock chamber 13
 by the wafer conveying unit 13A, there is no fear of particles or
 impurities polluting the wafers, even when they are passed through the
 cleaning chamber 14. And reductions in the wafer yield can be prevented,
 even if wafer processing systems become even more minute than they are
 now. In addition, no moisture can be introduced from the outside area and
 adhere to the inside walls of the load-lock chamber 13 as there is no
 moisture in the inert gas supplied from the inert gas supplier. Because of
 this the time required to bring the chamber in vacuum state is not long,
 and adverse influences caused by the moisture are prevented.
 FIG. 3 shows another embodiment of the invention. While the inert gas is
 introduced into the cleaning chamber 14 in the above embodiment, clean air
 from the common area R1 is introduced into the cleaning chamber 14 in this
 embodiment. All other configurations are the same as those in the above
 embodiment. This embodiment uses the same numeral references as those in
 the above embodiment on identical or similar portions of the invention.
 The features of this embodiment are as follows:.
 Instead of an inert gas supply, an air inlet opening 16D is formed in a
 front panel 16, and an end of an introducing duct 25 is connected to the
 air inlet opening 16D. A suction fan 28 is mounted within this introducing
 duct 25. The suction fan 28 sucks in clean air from the common area R1 and
 conveys it to the cleaning chamber 14 thereby keeping the cleaning chamber
 14 pressure positive. The other end of the connecting duct 25 is inserted
 between the ventilating fan 20 and the high-performance filter 21 as in
 the above embodiment. As in the above embodiment, a pressure control valve
 26 having a valve-controller 32 is connected to the connecting duct 25,
 and a differential pressure gauge 27 is installed in the cleaning chamber
 14. It is preferable to introduce air from the common area R1 into the
 cleaning chamber 14 when possibility that the air in the common area R1
 being polluted by organic impurity gases such as hydrocarbon gas as is
 low, like the air in the unit area R2. When the possibility is low, there
 is no fear that the wafers is polluted by the impurity gases in the
 cleaning chamber 14, even when the air in the common area R1 is introduced
 into the cleaning chamber 14. If there is a possibility that the impure
 gases will mix mixed with the air in the common area R1, it is preferable
 to attach a chemical filter F1 below the high-performance filter F on the
 ceiling of the common area R1. However, as a certain amount of natural
 oxidation films may be formed on the wafers, if slight natural oxidation
 on films disturbs the following process, it is preferable to arrange the
 processing unit 10 according to the former embodiment.
 According to the method for controlling gas in the processing unit 10A in
 this embodiment, clean air is introduced from the common area R1 in the
 clean room R into the cleaning chamber 14, and this air circulates through
 the filters while the pressure in the cleaning chamber 14 is kept
 positive. Because of this, any particles or impurity gases introduced in
 the air for any reason are removed reliably by the high-performance filter
 21 and the chemical filter 22, thereby removing any fear of a reduction in
 the wafer processing yield. The other effects of the features are the same
 as those in the previous embodiment.
 This invention is not limited by the above embodiments. The invention
 includes various techniques for introducing any type of clean gas into the
 cleaning chamber 14 and to circulate the introduced gas through filters
 while keeping the gas pressure positive. The objects to be processed are
 not limited to semiconductor wafers, but could be, for example, glass
 substrates.