JPH10286510A - Resist coating device and resist coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the coating irregularities of a resist so that the uniformity of the coated resist is enhanced. SOLUTION: This resist coating device 1 is made up of a rotary cup 6 which is of a flat cup shape and has a cup discharge aperture 5 allowing the drain of a liquid to be drained and the ventilation of an air, and further, anchores a blank 2 on the bottom part 3 through an opening part 7 provided on the top, a rotary cup hood 8 which is mounted on the opening part 7 and blocks it, a spin motor 9 which is installed under the rotary cup 6 to support the rotary cup 6 in a freely rotating manner, and a drain cup 11 which covers the circumference of the rotary cup 6 and also has an exhaust/liquid drain aperture 16 at the bottom face while forming a drain cup opening part 10 against the opening part 7 of the rotary cup 6 on the upper end part. In addition, the rotary cup hood 8 is air-permeable and the drain cup 11 is of such a construction that the drain cup opening part 10 is blocked with a detachable drain hood 13 with an exhaust mechanism 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resist coating apparatus for applying a resist solution on a substrate, and more particularly to a resist coating apparatus and a resist coating apparatus which can be used for a rectangular substrate used for a photomask or a reticle and which has no coating unevenness. About the method. 2. Description of the Related Art In recent years, as semiconductor devices have become larger chips, more highly integrated, and finer, there has been a demand for extremely high pattern dimensional accuracy of a photomask / reticle serving as a master of the pattern.

For this reason, in forming a mask blank resist film used for manufacturing a photomask and a reticle,
Since the uniformity such as the thickness of the film affects the pattern dimensional accuracy, it is necessary to improve the uniformity.

[0003]

2. Description of the Related Art FIG. 3 is a view for explaining an example of a conventional resist coating apparatus. In particular, FIG. 3 is a cross-sectional view showing the structure of a main part of an apparatus used in a manufacturing process of a reticle mask blank which is a rectangular substrate. This conventional resist coating apparatus uses a so-called substantially closed-type rotating cup, and is one of coating unevenness that occurs on a resist applied when a resist is applied on a square substrate, and the localization of the four corners is This apparatus mainly has a purpose of preventing a so-called fringe that appears as an abnormality in a film thickness (hereinafter, referred to as fringe-free).

[0004] This fringe coating unevenness is one of the major causes of resist uniformity impairment. In the case of fringe, its occurrence is correlated with the air flow near the upper surface of the substrate when the resist is coated on the substrate. It has been. Therefore, the use of this substantially closed type rotation cup in the conventional apparatus aims at suppressing the formation of airflow on the application substrate.

As shown in FIG. 3, a conventional resist coating apparatus 101 has a rotating cup 102 provided with a discharge port 107 on a side wall thereof, a closed-type rotating cup hood 103, and a drain port.
Exhaust port 104, drain cup 105 and spin motor 1
06. The functions and actions of each of the parts 102 to 107 constituting the conventional resist coating apparatus 101 will be described below by describing a method of resist coating performed using the apparatus 101.

FIG. 4 is a view for explaining a conventional resist coating method performed using a conventional resist coating apparatus. Conventionally, the resist coating method is roughly divided into three stages,
It consists of setting the substrate blank and supplying the resist onto the blank, controlling the thickness of the applied resist by rotating the supplied blank at high speed, and removing the supplied resist blank. And drying the applied resist by further rotating at a low speed.

Each step will be described with reference to FIG.
As shown in FIG. 4A, a blank 108 as a substrate to which a resist is to be applied is placed at a predetermined position on the bottom of the rotating cup 102 and fixed. At this time, the blank 108 is fixed to the rotating cup 102 by a so-called mechanical chuck that mechanically presses the blank 108. Then, an appropriate amount of the resist solution 109 is supplied to the central portion of the blank 108 by dropping.

Next, as shown in FIG. 4 (B), a closed-type rotating cup hood 103 is attached to an upper opening of the rotating cup 102, and a blank 108 in the rotating cup 102 is provided.
Completely seal the upper part of. Then, the rotating cup 102 keeps the blank 108 fixed for about 10 seconds for about 150 seconds.
The rotation is performed at a high speed by a spin motor 106 provided at a lower portion of the outside of the rotating cup 102 at a rotation speed of 0 rpm, and the coating is performed on the blank 108 so that the resist is uniform.

At this time, the unnecessary resist solution is discharged from the discharge port 107 toward the drain cup 105, and
The liquid is discharged from the liquid discharge port 104 to the outside of the apparatus 101. Next, as shown in FIG.
2, the rotation of the closed cup hood 103 is stopped.
Remove. Then, as it is, the spin motor 10
6 starts low-speed rotation. This low-speed rotation is performed at a rotation speed of about 50 rpm for about 60 seconds, and the blank 108
The upper resist is dried.

According to the above-described method, a resist film is formed on a blank. In the above example, the blank and the air in the cup are rotated together with the rotary cup by using the above-described substantially closed type rotating cup. The formation of airflow near the resist film surface on the blank is suppressed, and the corner of the blank is prevented from becoming a so-called "cut off the wind" during rotation for adjusting the film thickness after coating. It prevents that from happening.

[0011]

However, even if a resist is applied by such a conventional method, a photomask is required due to the uniformity of the film and the recent increase in size, integration, and miniaturization of semiconductor devices.・ Sufficient sources cannot be said to meet the demand for higher precision of reticle pattern dimensions.

Specifically, the above-described fringe-free resist coating apparatus is applied to a blank by using a novolak-based resist, which is one of resists generally used in the field of semiconductor manufacturing, with a resist coating apparatus having such a structure. It has recently become clear that the so-called wind ripple unevenness whose shape is similar to the wind ripple on sand may occur on the entire surface of the blank.

[0013] The unevenness of the wind pattern eventually indicates an uneven film thickness. The difference between the maximum film thickness and the minimum film thickness at the uneven portion of the wind pattern is determined by the fact that the target film thickness of the resist film is 2000 to 300 mm.
At 0 ° it can reach 100 °. Therefore, it is necessary to eliminate the fringe of the resist film on the blank formed by applying the resist and to improve the uniformity.

At the same time, another problem is the suppression of so-called wind-print unevenness which may occur when a resist is applied to a blank to form a resist film. Incidentally, a method / apparatus for improving the resist film thickness distribution generated when a resist is applied to a coating substrate is disclosed in Toshiba Corporation, JP-A-57-166033.
JP, JP-A-59-208831 by Hitachi, Ltd.
And JP-A-63-229169, JP-A-63-133526 and JP-A-4-96316 by Tokyo Electron, and JP-A-3-178122 by Matsushita Electric Industrial Co., Ltd. I have.

However, these methods / apparatuses are intended for a round substrate such as a wafer, and cannot be directly applied to a rectangular substrate for a mask or a reticle. If the method is applied as it is, the above-mentioned fringes are generated at the corners of the four corners peculiar to the rectangular substrate, and the effective area of the application surface which can be used for patterning is very narrow, so that it cannot be used for a highly accurate reticle.

As described above, the present invention provides a novel resist coating apparatus and a new resist coating method which solve the above-mentioned problems. Another object of the present invention is to eliminate fringes in a resist film on a blank formed by applying a resist solution, particularly in a resist film on a square substrate, to improve the uniformity of the fringe, and to further suppress the unevenness of wind ripples. It is intended to provide a resist coating apparatus and a resist coating method which enable the above.

[0017]

According to the first aspect of the present invention,
A rotating cup that has a flat cup shape with an open top and allows the application substrate to be fixed to the bottom through the opening, and a rotating cup hood that is attached to the opening and closes the opening,
A spin motor installed under the rotary cup and rotatably supported; and a size formed so as to cover the circumference of the rotary cup and capable of entering and leaving the rotary cup hood corresponding to the opening of the rotary cup. A resist coating apparatus comprising: a drain cup having a drain cup opening at an upper part thereof; wherein the rotating cup hood is configured to have air permeability; and the drain cup has a drain cup opening and a detachable with an exhaust mechanism. It is characterized by being closed by a possible drain hood.

According to a second aspect of the present invention, in the resist coating apparatus according to the first aspect, the rotating cup hood is entirely or partially circular in shape including a center portion of the rotating cup hood, and is made of a breathable material. It is characterized by having a characteristic. The invention according to claim 3 is the invention according to claim 2.
The resist coating apparatus according to any one of the preceding claims, wherein the permeable material constituting the rotating cup hood is a sintered body.

According to a fourth aspect of the present invention, in the resist coating apparatus according to the third aspect, the rotary cup hood mounted on the rotary cup opening has a different air permeability due to a difference in porosity of the sintered body constituting the rotary cup hood. , One of which is selected from a plurality of sets of rotating cup hoods and mounted. According to a fifth aspect of the present invention, in the resist coating apparatus according to any one of the first to fourth aspects, an exhaust mechanism provided in the drain hood has an exhaust capability adjusting mechanism.

According to a sixth aspect of the present invention, in the resist coating method, the coated substrate is fixed to a bottom portion of a rotating cup having a flat cup shape to be opened, and a resist solution is supplied onto the coated substrate, and then the opening is formed. The opening is closed by attaching a rotating cup hood having air permeability to it, and the periphery of the rotating cup is further covered with a drain cup having a drain cup opening formed corresponding to the opening of the rotating cup. At the same time, the opening of the drain cup is closed by a detachable drain hood provided with an exhaust mechanism, and a spin motor installed under the rotary cup to support while exhausting from above the application substrate by the exhaust mechanism. The coated substrate is rotated with the rotating cup to apply the supplied resist liquid to the coated substrate.

According to a seventh aspect of the present invention, in the method for applying a resist according to the sixth aspect, after applying the resist, the drain hood is detached from the drain cup, and the exhaust by the exhaust mechanism is stopped. The resist on the coated substrate is dried in accordance with the rotation of the coated substrate at a lower speed, the air permeability of the rotating cup hood, and the exhaust from the drain port of the drain cup.

According to the first, fifth, sixth, and seventh aspects of the present invention, when a resist is applied on a substrate, the resist is located above the application substrate fixed in the rotating cup. The rotating cup hood closing the opening of the rotating cup has air permeability. A drain hood is attached to an opening of the drain cup that covers the rotating cup, and the drain hood has an exhaust mechanism. Accordingly, the exhaust mechanism can control the amount of air flowing in or the flow of air in the drain cup, and thus the rotating cup, particularly the flow of air near the application surface of the application substrate.

Accordingly, in applying the resist to the substrate, it is possible to apply the resist with high uniformity. further,
The rotation at a lower speed than that performed for drying the resist on the application substrate can be performed without the drain hood. At that time, since the rotating cup hood has air permeability, the air permeability of the rotating cup is maintained at an appropriate level, and the resist can be dried at an appropriate speed.

Therefore, a highly uniform resist film can be formed. According to the second aspect of the present invention, it is possible to control the air permeability of the rotating cup hood, in particular, the flow of air passing therethrough by selecting the shape of the portion that is responsible for the air permeability. In other words, it is possible to arbitrarily control the air permeability of the rotary cup hood by selecting the size of the portion of the rotary cup hood above the application substrate fixed to the rotary cup and responsible for the air permeability, and selecting the corresponding position. .

Therefore, in applying the resist to the substrate, it is possible to apply the resist with high uniformity. When the resist is dried by low-speed rotation, the air permeability of the rotating cup is arbitrarily maintained, and the resist can be dried at an appropriate speed suitable for the resist to be used. Therefore, a highly uniform resist coating film can be formed.

According to the third and fourth aspects of the present invention, it is possible to prepare a plurality of rotating cup hoods, each of which has a different air permeability by changing the porosity of the sintered body. It is possible to have Therefore, by selecting the rotating cup hood, it is possible to arbitrarily control the air permeability of the rotating cup hood.

Therefore, in applying the resist to the substrate, it is possible to apply the resist with high uniformity. When the resist is dried by low-speed rotation, the air permeability of the rotating cup is arbitrarily maintained, and the resist can be dried at an appropriate speed suitable for the resist to be used. Therefore, a highly uniform resist coating film can be formed.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a resist film on a blank formed by applying a resist solution, particularly in a resist film on a square substrate, it is possible to eliminate fringes, improve the uniformity, and further suppress the occurrence of wind ripple unevenness. is important.
Various studies by the inventors have revealed that the wind ripple unevenness has a correlation with the resist drying speed at the time of resist drying after resist application.

That is, when the drying speed is too high, the wind ripple unevenness occurs. Therefore, the adjustment of the drying speed is effective for suppressing the unevenness of the wind ripples. Such adjustment of the drying speed can be achieved by making it possible to adjust the characteristics according to the characteristics of the resist solution using the air permeability of the environment where the substrate is placed at the time of drying and the volatile characteristics of the solvent contained in the resist solution. .

Further, in the rotation of the resist-coated substrate for adjusting the film thickness after the resist solution is supplied to the substrate prior to the drying of the resist, as described above, there is a possibility that a rectangular substrate is used. In order to prevent a fringe having a defect, it is necessary to suppress the inflow of air flowing into the vicinity of the substrate by placing the environment in which the substrate is placed in a substantially degassing environment, and to suppress the airflow in the vicinity of the substrate. is there.

Accordingly, there is provided a resist coating method for supplying a resist solution onto a substrate, adjusting the thickness of the applied resist by rotating the substrate, and subsequently drying the applied resist also by rotating the substrate. The resist coating apparatus that is responsible must be an apparatus that can simultaneously suppress airflow near the substrate when adjusting the film thickness and secure a certain amount of airflow when drying the resist.

Based on these findings, the present invention provides a resist coating apparatus and a resist coating method that eliminate fringes of a resist applied on a substrate, improve the uniformity of the fringe, and further suppress unevenness of wind ripples. Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the configuration of a resist coating apparatus according to an embodiment of the present invention.

The resist coating apparatus 1 according to the embodiment of the present invention has a flat cup shape, and a blank 2 which is a rectangular coating substrate on the bottom 3 through an opening 7 provided at the top.
And a rotating cup having a cup discharge port 5 which can be fixed by a mechanical chuck provided with an eight-point support and which can discharge liquid and allow ventilation. And the opening 7
A rotary cup hood 8 mounted on the rotary cup 6 to close the opening; a spin motor 9 installed below the rotary cup 6 to rotatably support the rotary cup 6; A drain cup 11 having a drain cup opening 10 in a size corresponding to the opening 7 of the cup 6 so that the rotating cup hood 8 can enter and exit, and having an exhaust / drain port 16 also serving as an exhaust port on the bottom surface; Consists of

At this time, in the resist coating apparatus 1, the rotating cup hood 8 has air permeability, and the drain cup 11 has the drain cup opening 10 closed by a detachable drain hood 13 having an exhaust mechanism 12. It is characterized by the following. The rotating cup hood 8 is formed of a sintered body 14 having a hole in the circular portion including the center portion of the rotating cup hood 8 and having air holes therein and having air permeability. Ensures air permeability.

Then, in the resist coating apparatus 1,
There are a plurality of rotating cup hoods 8 that can be mounted on the opening 7 of the rotating cup 6, each having a different porosity of the constituting sintered body, and having a different air permeability due to this difference. Therefore, it is possible to select one of the plurality of sets of the rotating cup hoods 8 having different air permeability according to the characteristics of the resist solution applied to the blank 2 to be used and mount it as the rotating cup hood.

Thus, by this mounting, the rotating cup 6 rotates in synchronization with the rotation of the rotating cup 6. The sintered body constituting the rotary cup hood used in the resist coating apparatus according to the present embodiment is manufactured by sintering a mesh-like stainless member using stainless steel as its material. Therefore,
It has a large number of holes, and its porosity is uniform in the plane.

As the other member, a glass sintered body having a uniform air permeability can be used. However, since the rotating cup hood rotates together with the rotating cup, it is necessary that the rotating cup hood has strength enough to withstand the rotating movement. From the viewpoint of strength, a sintered body having a slenderness is desirable. In addition, using a plate-like body made of metal or resin having sufficient strength such as a normal stainless steel plate, a plurality of small vents are formed in a part thereof, particularly in a circular shape including a central portion, and a rotating cup hood is formed. Can also be produced.

The exhaust mechanism 12 of the drain hood 13 is controlled by an automatic damper (not shown) to control the amount of exhaust. The exhaust in the drain cup and, consequently, the rotating cup 6 is performed from the exhaust port 15 provided at the position of (1). And drain cup 1
The drainage collected at 1 when the resist is applied to the blank 2 is discarded outside the apparatus 1 through the exhaust / drainage port 16.

Next, a method for applying a novolak-based resist to the reticle blank 2 which is a square-coated substrate using the resist coating apparatus 1 will be described with reference to the drawings. FIG. 2 is a view for explaining a method of applying a resist to an application substrate using the resist application apparatus according to the embodiment of the present invention.

As shown in FIG. 2A, the rotating cup 6
The blank 2 is transported into the inside, and is fixed to the bottom 3 by a mechanical chuck. With the rotation cup 6 stopped, the resist solution 21 is supplied dropwise by 3 to 5 cc. Next, FIG.
As shown in (B), a rotating cup hood 8 having a central portion formed of a sintered body 14 and having air permeability is mounted on the rotating cup 6, and subsequently, the drain hood 1 having an exhaust mechanism 12 is provided.
3 is attached to the drain cup opening 10 of the drain cup 11. While the air in the apparatus 1 is exhausted by exhausting air from the exhaust port 15, the blank 2 together with the rotating cup 6 is 1500 r.
Spin at a high speed of 10 pm for 10 seconds.

Next, as shown in FIG. 2C, the rotation of the rotary cup 6 is stopped, and the drain hood 13 of the drain cup 11 is removed. With the forcible evacuation by the evacuation mechanism 12 stopped, the blank 2 is rotated at a low rotation speed of 50 rpm for 60 seconds while the evacuation / evacuation port 16 is evacuated, and the resist liquid on the blank 2 is dried. After applying the resist according to the above method, the rotating cup hood 8 is removed, the mechanical chuck is opened, the blank 2 is removed from the resist coating device 1, and the coating process is completed. The resulting resist on the blank, which is the coated substrate, does not have the fringe and wind pattern unevenness described above.

Thus, when the above-described method is used using the above-described resist coating apparatus according to the embodiment of the present invention, it is possible to suppress the fringe and the wind ripple unevenness in the resist film on the rectangular substrate, which is the object of the present invention. Although possible, the mechanism for suppressing fringe and wind ripple unevenness by the above-described apparatus and method will be briefly described below. In the resist film on the blank formed by the application of the resist solution, particularly in the resist film on the square substrate, in order to eliminate the fringe and improve the uniformity, after supplying the resist solution on the blank as described above, It is effective to suppress the airflow near the top of the blank at the time of high-speed rotation.

Therefore, in the conventional resist coating apparatus according to the embodiment of the present invention, the opening of the drain cup is reduced by suppressing the inflow of air into the rotary cup achieved by sealing the rotary cup in the conventional apparatus. With closing
Further, this is achieved by providing a forced exhaust mechanism at a position corresponding to the opening and above the substrate. In other words, the air flow near the substrate, which may be caused by the loss of the airtightness of the rotating cup due to imparting air permeability to the rotating cup hood, causes the drain hood covering the rotating cup to flow under the degassing environment derived from the exhaust mechanism. Secure by placing.

Therefore, the inflow of air into the rotating cup is suppressed as in the conventional apparatus, and the air existing near the substrate and the fringes generated in accordance with the flow of the air, particularly the corners of the rectangular substrate, cut off the so-called "wind". Fringing caused by being placed in the "state" is prevented. Next, the occurrence of wind ripple unevenness is related to the drying step in the above-described resist coating method, and in particular, correlates with the drying speed of the resist during low-speed rotation in the drying step as described above.

In the conventional resist coating apparatus, even if the substrate is rotated at a low speed while the conventional closed-type rotating cup hood 103 is mounted, the resist is difficult to dry and requires a very long drying time. , 4,
Remove the sealed rotating cup hood 103 and rotate the rotating cup 10
2 was opened, the substrate was rotated at a low speed, and the resist was dried.

In this case, the volatilization speed of the solvent or the like is too high, and the resist dries quickly. This phenomenon has caused the generation of wind ripple unevenness. Therefore, it is effective to appropriately adjust the drying speed of the resist, in particular, to reduce the drying speed of the resist as compared with a conventional resist coating apparatus. In other words, by installing a permeable rotating cup hood at a position above the coated substrate of the rotating cup, the air permeability inside and outside the rotating cup is adjusted, and the resist drying speed on the coated substrate inside the rotating cup is reduced. By adjusting the pressure in such a manner and drying the resist in an atmosphere of a certain amount of resist solvent, it is possible to suppress the wind ripple unevenness.

Therefore, by using the resist coating apparatus and the resist coating method according to the embodiment of the present invention,
According to the above-described mechanism, it is possible to suppress fringe and wind pattern unevenness in the resist film on the substrate, especially on the rectangular substrate.

[0048]

According to the first, fifth, sixth, and seventh aspects of the present invention, a highly uniform resist can be applied to a substrate. Further, the air permeability of the rotating cup is maintained at an appropriate level, the resist can be dried at an appropriate speed, and a highly uniform resist coating film can be formed.

According to the second aspect of the present invention, it is possible to apply a highly uniform resist to the substrate. When the resist is dried by low-speed rotation, a highly uniform resist coating can be formed. According to the invention described in claims 3 and 4,
By selecting the rotating cup hood, the air permeability of the rotating cup hood can be arbitrarily controlled.

Therefore, in applying the resist to the substrate, it is possible to apply the resist with high uniformity. When the resist is dried by low-speed rotation, a highly uniform resist coating can be formed.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view of a resist coating apparatus according to an embodiment of the present invention.

FIG. 2 is a view for explaining a method of applying a resist to an application substrate using a resist application apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a conventional resist coating apparatus.

FIG. 4 is a diagram illustrating a conventional resist coating method performed using a conventional resist coating apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 resist coating apparatus 2 blank 3 bottom 5 cup outlet 6 rotating cup 7 opening 8 rotating cup hood 9 spin motor 10 drain opening 11 drain cup 12 exhaust mechanism 13 drain hood 14 sintered body 15 exhaust port 16 exhaust / drain Mouth 21 Resist solution

Claims (7)

[Claims] A rotating cup which is formed in a flat cup shape having an open top and is capable of fixing a coating substrate to a bottom portion through the opening, a rotating cup hood mounted on the opening and closing the opening; A spin motor installed under the rotating cup to rotatably support the rotating cup; formed to cover the periphery of the rotating cup; and having a size such that the rotating cup hood can be moved in and out corresponding to the opening of the rotating cup. A resist coating apparatus comprising: a drain cup having a drain cup opening at an upper part thereof; wherein the rotating cup hood is configured to have air permeability; and the drain cup has a drain cup opening which is detachably provided with an exhaust mechanism. Resist coating apparatus characterized by being blocked by a simple drain hood. 2. The resist coating apparatus according to claim 1, wherein the rotary cup hood has a whole or a part of a circular shape including a center portion of the rotary cup hood made of a gas permeable material, and has a gas permeable property. Resist coating apparatus characterized by being performed. 3. The resist coating apparatus according to claim 2, wherein the permeable material forming the rotating cup hood is a sintered body. 4. The resist coating apparatus according to claim 3, wherein the rotating cup hood attached to the rotating cup opening has a plurality of sets having different air permeability due to a difference in porosity of a sintered body constituting the rotating cup hood. A resist coating apparatus, wherein one of the rotating cup hoods is selected and mounted. 5. The resist coating apparatus according to claim 1, wherein an exhaust mechanism provided in the drain hood has a mechanism for adjusting an exhaust capability. 6. A coating cup is fixed to the bottom of a flat cup-shaped rotating cup that opens, and after supplying a resist solution onto the coating board, a rotating cup hood having air permeability is attached to the opening. Further, the periphery of the rotating cup is covered with a drain cup having a drain cup opening formed corresponding to the opening of the rotating cup, and the drain cup opening is covered with an exhaust mechanism. With a removable drain hood equipped with
A resist coating method in which the applied substrate is rotated with the rotating cup by a spin motor installed and supported below the rotating cup to apply the supplied resist liquid to the coated substrate. 7. The resist coating method according to claim 6, wherein after applying the resist, the drain hood is detached from the drain cup, and the evacuation by the evacuation mechanism is stopped. A resist coating method, comprising drying a resist on the coated substrate according to rotation of the substrate, air permeability of the rotating cup hood, and exhaust from a drain port of the drain cup.