JP5088142B2 - Foreign matter removing method and foreign matter removing apparatus for photomask - Google Patents

Description

The present invention relates to a foreign matter removing method and a foreign matter removing device for a photomask, and more particularly, to a foreign matter removing method and a foreign matter removing device for removing a foreign matter by blowing nitrogen (N ₂ ) gas or the like onto a photomask.

  In recent semiconductor device photomasks (including reticles), a film called a pellicle film is applied to the pattern surface in order to prevent foreign matter from adhering to the photomask pattern from the outside. In addition, for example, a technique is known in which a photomask is heated to remove an organic substance that becomes a contamination source attached to the photomask (see, for example, Patent Document 1).

By the way, a foreign substance having a size that may be transferred during photolithography may adhere to the surface of the pellicle film or the back surface (glass surface) of the photomask to which the pellicle film is not attached. In such a case, generally, before being loaded into the exposure apparatus, a foreign substance adhering to the surface is blown off by blowing a gas such as high purity N ₂ or clean air (hereinafter referred to as “purging”). It has been broken.

For example, in the case of N ₂ gas, high purity of 99.9% or more is generally used, and furthermore, a filter for removing foreign matter is installed on the piping so that foreign matter is not sprayed from the periphery of the gas and the outlet. It is done. Further, since the pellicle film is affected, the purge pressure and the gas temperature are not excessively increased.

The following are known as foreign matter removing devices (purge devices).
FIG. 4 is a diagram illustrating an example of a purge device.
Here, a purge mechanism portion of a photomask transfer device (8601 type) manufactured by Tokyo Aviation Instruments Co., Ltd. is shown.

  The photomask 50 is fixed to a photomask holding mechanism 52 on the moving stage 51. The photomask holding mechanism 52 fixes the photomask 50 so as to be sandwiched in the direction perpendicular to the drawing. The moving stage 51 can move leftward along the pedestal 53. The driving mechanism for the moving stage 51 is not shown.

  The central purge nozzle 54 is fixed to the support leg 56 via a fixture 55. There are 20 nozzles in the purge nozzle 54 at intervals of 8 mm, and the purge gas is applied over a wider area than the entire surface of the 152 mm □ photomask. The purge nozzle 54 is fixed at an angle of 45 degrees with respect to the horizontal, and can be swung in the vertical direction of the figure together with the fixture 55 during the purge.

A purge gas is supplied to the purge nozzle 54 through a pipe 57. The pipe 57 is connected to a purge gas pipe of a factory (not shown) through a regulator 58.
The purge operation using such a purge apparatus is as follows.

  First, the photomask 50 is fixed to the photomask holding mechanism 52. Then, the purge gas whose pressure is adjusted by the regulator 58 is supplied to the purge nozzle 54 through the pipe 57 and ejected. At this time, the purge nozzle 54 is swung in the vertical direction. In this state, the moving stage 51 is moved to the left, and the foreign matter is removed by applying the photomask 50 to the purge gas ejected from the purge nozzle 54.

FIG. 5 is a diagram schematically showing how the purge gas ejected from the purge nozzle removes foreign matters.
The pellicle film is not shown.

The purge gas 60 ejected by the purge nozzle 54 is sprayed from above on the surface of the photomask 50 moved by the moving stage 51 shown in FIG.
JP 2005-274770 A

  However, in recent years, when purging is used to remove foreign matter, a phenomenon that growing foreign matter increases on the photomask surface (pellicle film surface in the case of a pellicle film) after purging has been a problem. .

  In view of the above points, the present inventor provides a photomask foreign matter removal method and foreign matter removal apparatus capable of removing foreign matter on the surface of a photomask without inducing generation of growth foreign matter during a purge operation. With the goal.

  In order to achieve the above object, a photomask foreign matter removing method including the following steps is provided. This foreign matter removing method of the photomask includes a step of blowing a gas whose pressure is adjusted from a substantially horizontal direction to the photomask to form a laminar flow by the gas on the photomask surface, and a direction of blowing the gas Or a step of spraying the gas onto the photomask surface by changing a height of the gas blowing portion from the photomask surface, and heating the gas or the photomask surface when the gas is sprayed. To do.

  In order to achieve the above object, the following photomask foreign matter removing apparatus is provided. This foreign matter removing apparatus for a photomask includes a gas blowing part for blowing gas to a photomask, a pressure adjusting part for adjusting the pressure of the gas, and a blowing for adjusting an angle of the gas blowing part with respect to the surface of the photomask. An angle adjusting unit, a spraying height adjusting unit that adjusts the height of the gas blowing unit with respect to the surface of the photomask, and a heating unit that heats the gas or the photomask surface. At the start of spraying, the spray angle adjusting unit or the spray height adjusting unit moves the gas blowing unit so as to be arranged in a substantially horizontal direction with respect to the photomask, and the pressure adjusting unit The pressure is adjusted to form a laminar flow by the gas on the photomask surface.

  Foreign substances on the surface of the photomask can be removed without inducing generation of growth foreign substances during the purging operation.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
Growing foreign matter is foreign matter generated on the surface of a photomask used or stored in a factory. Organic substances, acids, and alkalis contained in the photomask surface, in the atmosphere, and outgas from the member, are caused to react by irradiating with ultraviolet rays at the time of photolithography to be crystallized and deposited on the photomask surface to become defects. . The main component of a typical growth foreign substance is ammonium sulfate, but the growth of the foreign substance is considered to proceed by the following mechanism.

Sulfur dioxide (SO ₂ ) contained in the atmosphere changes to sulfur trioxide (SO ₃ ) by ultraviolet irradiation during photolithography. This SO ₃ reacts with moisture (H ₂ O) in the atmosphere to form sulfuric acid (H ₂ SO ₄ ). Furthermore, it is considered that ammonia NH ₃ supplied from the atmosphere reacts with H ₂ SO ₄ and finally precipitates as ammonium sulfate ((NH ₄ ) ₂ SO ₄ ). However, until now, the cause of the generation of growth foreign substances by purging has not been fully elucidated.

  The present inventor has confirmed that there is a correlation between the occurrence state of the foreign matter and the portion hit with the purge gas during the purging while proceeding with the investigation of the growth foreign matter generated after the purging. Furthermore, it was confirmed that a large number of liquid foreign substances having a size of about 100 nm or less estimated to be moisture adhered to the surface of the photomask after purging. It is conceivable that this moisture promotes the reaction during photolithography in the exposure apparatus and becomes a nucleus when a foreign crystal is generated.

  4 and 5, the purge gas 60 ejected from the purge nozzle 54 expands adiabatically, collides with water vapor molecules in the atmosphere, and deprives the energy of the water vapor. It is considered that water drops are deposited on the surface of the photomask 50 by lowering the temperature. Further, it is considered that the surface of the photomask 50 also comes into contact with the purge gas 60 so that the temperature is lowered and water vapor is easily solidified. Since the purge gas 60 has a high purity and does not contain water vapor, when purging for a relatively long time, the reaction with the water vapor occurs on the surface of the photomask 50 immediately after the start of the purge or at the stage after the end of the purge. Conceivable. Also, during the purge, turbulent flow is generated on the surface portion of the photomask 50, and there is a concern that water droplets adhere when the surrounding atmosphere is involved.

From the above, in order to suppress the generation of growth foreign substances due to purging, precipitation of water vapor molecules in the atmosphere on the photomask surface may be prevented.
FIG. 1 is a schematic diagram showing a foreign matter removing method for a photomask according to the present embodiment.

In the figure, the pellicle film is not shown.
When removing the foreign matter 2 from the photomask 1 as shown in FIG. 1A, in the foreign matter removal method of the present embodiment, the pressure is adjusted from the purge nozzle 3 that is a gas blow-out portion from the horizontal direction with respect to the photomask 1 The purge gas 4 that is, for example, high-purity N ₂ is sprayed to form a laminar flow by the purge gas 4 on the surface of the photomask 1.

The pressure of the purge gas 4 is set under conditions for forming a laminar flow on a flat plate such as the photomask 1. On the flat plate, a laminar flow is formed when the Reynolds number is about 3 × 10 ⁵ or less. A higher pressure while satisfying this condition is desirable for removing the foreign matter 2. However, when purging on the pellicle film surface, considering the pressure resistance of the pellicle film (about 0.2 MPa), for example, the pressure is 0.2 MPa. (At this time, the flow rate is preferably about 20 m / s) or less.

By forming a laminar flow on the surface of the photomask 1, water vapor in the atmosphere and the surface of the photomask 1 are separated by the laminar flow.
Next, as shown in FIGS. 1B and 1C, the direction in which the purge gas 4 is sprayed or the height of the purge nozzle 3 from the surface of the photomask 1 is changed, and the purge gas 4 is applied to the surface of the photomask 1. Spray and remove foreign matter 2. Also at this time, the laminar flow is maintained, and adhesion of water droplets to the photomask 1 is suppressed.

Further, when the purge gas 4 is sprayed in the steps of FIGS. 1A to 1C, the surface of the purge gas 4 or the photomask 1 is heated.
When the purge gas 4 is heated, the water vapor in the atmosphere between the surface of the photomask 1 and the purge nozzle 3 is heated to a temperature at which the saturated water vapor pressure is not reached.

  For example, the case where the room temperature is 21 ° C. and the humidity is 45% is as follows. The saturated water vapor pressure at room temperature of 21 ° C. is 2.44633 kPa, and when the humidity is 45%, the water vapor partial pressure is 2.4463 × 0.45 = 1.1089 kPa. The room temperature at which this pressure becomes the saturated water vapor pressure is about 8 ° C. from the scientific chronology, and 13 ° C. lower than room temperature. Therefore, the purge gas 4 needs to be heated at 13 ° C. so that the water vapor partial pressure does not become the saturated water vapor pressure and the water vapor temperature is about the same as the room temperature. Considering fluctuations in room temperature and humidity, for example, when the room temperature is 21 ° C. ± 3 ° C. and the humidity is 45% ± 5%, the temperature of the purge gas 4 is heated from room temperature to 14 ° C. to 9 ° C. It adjusts with the gas heater mentioned later.

  Further, when the surface of the photomask 1 is heated, it is heated at a temperature at which the water vapor in the atmosphere does not solidify on the surface of the photomask 1. Considering the resistance of the pellicle film and the trouble of cooling the photomask 1 for introduction into the exposure apparatus, the film is heated by a heater which will be described later so as to be about 5 ° C. higher than the room temperature.

The heating of the purge gas 4 and the heating of the surface of the photomask 1 may be used in combination, or one of them.
As described above, according to the foreign matter removal method for a photomask of the present embodiment, after forming a laminar flow on the surface of the photomask 1, the foreign matter 2 is removed by changing the spraying direction and the height of the purge nozzle 3. At the same time, since the purge gas 4 or the surface of the photomask 1 is heated, it is possible to prevent moisture from adhering to the surface of the photomask 1 that causes growth foreign matter from the start to the end of the purge.

Hereinafter, a purge device for realizing the above-described foreign matter removing method for the photomask will be described.
FIG. 2 is a diagram showing the configuration of the photomask purge apparatus of the present embodiment.

  A moving stage 12 is disposed on the pedestal 11 of the purge apparatus 10, and the photomask 1 is fixed to the photomask holding mechanism 13 on the moving stage 12. The photomask holding mechanism 13 fixes the photomask 1 so as to be sandwiched in a direction perpendicular to the drawing. The moving stage 12 can move leftward along the base 11. The driving mechanism for the moving stage 12 is not shown.

  The purge nozzle 3 is fixed to a part of the support leg 15 via a fixture 14. Further, an elevator 16 connects between the ceiling portion of the support leg 15 and the fixture 14. The elevator 16 functions as a spray height adjusting unit that adjusts the height of the purge nozzle 3 via the fixture 14. In the drawing, a part of the support leg 15 to which the fixture 14 is connected can be moved up and down to a height adjusted by the elevator 16. The fixture 14 functions as a spray angle adjustment unit that changes the spray direction of the purge nozzle 3. The fixture 14 and the elevator 16 are controlled by a control mechanism (not shown) such as a computer, for example.

FIG. 3 is a schematic diagram of the purge nozzle portion.
As shown in the figure, a plurality of purge nozzles 3 are provided at regular intervals, and the purge gas is applied over a wider area than the entire surface of the photomask 1. And it adjusts so that purge gas may be sprayed with respect to the photomask 1 from a horizontal direction like FIG. 1 (A) with the fixing tool 14 and the elevator 16. FIG. Further, the fixture 14 may swing in the direction of the arrow in FIG.

  As shown in FIG. 2, purge gas is supplied to the purge nozzle 3 through a pipe 17. The pipe 17 is connected via a regulator 18 to a factory purge gas pipe (not shown). In the purge apparatus 10 of the present embodiment, a gas heater 19 is provided between the pipe 17 and the regulator 18 so that the purge gas can be heated. A heater 20 for heating the surface of the photomask 1 is connected to the moving stage 12 via a support leg 21. For example, a halogen heater is used as the heater 20 in order to uniformly heat the surface of the photomask 1. The heater 20 is disposed away from the moving stage 12 by the support leg 21 so as not to contact the support leg 15 and the purge nozzle 3 when the moving stage 12 moves.

Hereinafter, the operation of the purge apparatus 10 will be described.
First, the photomask 1 to be purged is fixed by the photomask holding mechanism 13 on the moving stage 12. Further, the gas heater 19 heats the purge gas to a temperature at which the water vapor in the atmosphere between the surface of the photomask 1 and the purge nozzle 3 does not reach the saturated water vapor pressure according to the room temperature and humidity.

  Subsequently, the fixture 14 and the elevator 16 are adjusted so that the purge gas can be sprayed from the horizontal direction to the photomask 1, the purge nozzle 3 is moved, and the purge nozzle 3 is arranged as shown in FIG. To do. In this state, the purge gas whose pressure is adjusted by the regulator 18 under the condition that allows laminar flow as described above is supplied to the purge nozzle 3.

  Next, the moving stage 12 is moved to the left in the drawing to bring the photomask 1 closer to the purge nozzle 3, and the purge is started. At this time, the purge nozzle 3 can swing in the vertical direction.

  At the initial stage of purge, as shown in FIG. 1A, purge gas is sprayed from the horizontal direction on the photomask 1, so that a laminar flow is formed on the surface of the photomask 1, and water vapor in the atmosphere and the photomask 1 The surface is separated.

  Subsequently, when the foreign matter 2 existing on the surface of the photomask 1 approaches the purge nozzle 3, the fixing tool 14 and the elevator 16 are adjusted to form an angle as shown in FIGS. 1 (B) and 1 (C). Purge gas is sprayed to remove foreign matter 2. During this time, laminar flow is maintained.

Note that the angle and height suitable for removing the foreign matter 2 are determined by experiment. At this time, in the case of purging the surface of the photomask 1 to which the pellicle film (not shown) is attached, the purge pressure needs to remain constant because the pressure resistance of the pellicle film surface is about 0.2 MPa. However, in the case of a glass surface, the pressure is not limited, so the pressure may be increased to remove foreign matter. In this case, however, the Reynolds number exceeds 3 × 10 ⁵ and the purge gas flow becomes turbulent, and the surface of the photomask 1 may come into contact with water vapor molecules. As described above, the purge gas is heated and purged in advance. Therefore, moisture does not condense.

When the foreign matter 2 is removed and the moving stage 12 passes through the purge nozzle 3, the supply of purge gas is stopped and the purge operation is terminated.
The above operation is for the case where the purge gas is heated by the gas heater 19, but the same effect can be obtained even if the surface of the photomask 1 is heated by the heater 20.

  When the heater 20 is used, heating is started before the purge gas is sprayed, and heating is ended after the supply of the purge gas is stopped. The heating temperature in the case of using the heater 20 only needs to be such that water vapor in the atmosphere does not solidify on the surface of the photomask 1 as described above. Since the surface temperature of the photomask 1 is usually the same as the room temperature, for example, it is set to be about 5 ° C. higher than the room temperature.

The gas heater 19 and the heater 20 may or may not be used together. The optimum conditions for the heating temperature of the gas heater 19 and the heater 20 when used in combination are determined by experiment.
As described above, according to the purge apparatus 10 of the present embodiment, a laminar flow is formed on the surface of the photomask 1 and then the foreign matter 2 is removed by changing the spraying direction and the height of the purge nozzle 3, and the purge gas 4 or the surface of the photomask 1 is heated, so that it is possible to prevent moisture from adhering to the surface of the photomask 1 which causes growth foreign matter from the start to the end of the purge.

(Additional remark 1) The process of spraying the gas by which the pressure was adjusted from the substantially horizontal direction with respect to the photomask, and forming the laminar flow by the said gas on the photomask surface,
Changing the height of the gas blowing direction or the height of the gas blowing portion from the photomask surface and blowing the gas to the photomask surface;
Have
A method for removing foreign matter from a photomask, wherein the gas or the photomask surface is heated when the gas is sprayed.

  (Additional remark 2) The foreign substance removal method of the photomask of Additional remark 1 characterized by heating the said gas to the temperature from which the water vapor | steam in air | atmosphere between the said photomask surface and the said gas blowing part does not become saturated water vapor pressure. .

  (Additional remark 3) The said pressure is adjusted to the pressure lower than the pressure | voltage resistance of the pellicle film affixed on the said photomask, The foreign material removal method of the photomask of Additional remark 1 or 2 characterized by the above-mentioned.

  (Additional remark 4) After forming the said laminar flow, the said pressure is strengthened rather than the time of laminar flow formation, and the said gas is sprayed on the said photomask surface, The foreign material removal method of the photomask of Additional remark 1 or 2 characterized by the above-mentioned .

(Additional remark 5) The foreign matter removal method of the photomask as described in any one of additional marks 1 thru | or 4 which heats the said photomask surface using a halogen heater.
(Appendix 6) A gas blowing part for blowing gas to the photomask;
A pressure adjusting unit for adjusting the pressure of the gas;
A spray angle adjusting unit that adjusts an angle of the gas blowing unit with respect to the surface of the photomask;
A spray height adjusting unit for adjusting the height of the gas blowing unit with respect to the surface of the photomask;
A heating unit for heating the gas or the photomask surface;
Have
At the start of gas spraying, the spray angle adjusting unit or the spray height adjusting unit moves the gas blowing unit so as to be arranged in a substantially horizontal direction with respect to the photomask, and the pressure adjusting unit Adjusts the pressure so as to form a laminar flow due to the gas on the surface of the photomask.

  (Supplementary note 7) After the formation of the laminar flow, the spray angle adjusting unit or the spray height adjusting unit changes the gas spraying direction or the height of the gas blowing unit from the photomask surface. The apparatus for removing foreign matter of a photomask according to appendix 6, wherein the gas is sprayed on the surface of the photomask.

(Additional remark 8) The foreign substance removal apparatus of the photomask of Additional remark 6 or 7 with which the said gas blowing part has several blower outlets arrange | positioned at fixed intervals.
(Additional remark 9) The said heating part has a gas heater which heats the said gas supplied to the said gas blowing part, The foreign material removal apparatus of the photomask as described in any one of Additional remark 6 thru | or 8 characterized by the above-mentioned.

  (Additional remark 10) The said heating part has a halogen heater which heats the said photomask surface, The foreign material removal apparatus of the photomask as described in any one of additional marks 6 thru | or 9 characterized by the above-mentioned.

It is a schematic diagram which shows the foreign material removal method of the photomask of this Embodiment. It is a figure which shows the structure of the purge apparatus of the photomask of this Embodiment. It is a schematic diagram of a purge nozzle part. It is a figure which shows an example of a purge apparatus. It is the figure which showed typically a mode that the purge gas ejected from the purge nozzle removes a foreign material.

Explanation of symbols

1 Photomask 2 Foreign object 3 Purge nozzle 4 Purge gas

Claims (6)

Blowing a gas whose pressure is adjusted from a substantially horizontal direction to the photomask to form a laminar flow by the gas on the surface of the photomask;
While maintaining the laminar flow, and the step blowing blowing direction or a gas blowoff portion the gas the by changing the height from the surface of the photomask of the gas on the surface of the photomask,
Have
A method for removing foreign matter from a photomask, wherein the gas or the surface of the photomask is heated when the gas is sprayed. 2. The method for removing foreign matter from a photomask according to claim 1 , wherein the gas is heated to a temperature at which water vapor in the atmosphere between the surface of the photomask and the gas blowing section does not reach a saturated water vapor pressure.   The method for removing foreign matter from a photomask according to claim 1 or 2, wherein the pressure is adjusted to a pressure lower than a pressure resistance of a pellicle film attached to the photomask. The method for removing foreign matter from a photomask according to any one of claims 1 to 3, wherein the surface of the photomask is heated using a halogen heater. A gas blowing section for blowing gas to the photomask;
A pressure adjusting unit for adjusting the pressure of the gas;
A spray angle adjusting unit that adjusts an angle of the gas blowing unit with respect to the surface of the photomask;
A spray height adjusting unit for adjusting the height of the gas blowing unit with respect to the surface of the photomask;
A heating unit for heating the surface of the gas or the photomask;
Have
At the start of gas spraying, the spray angle adjusting unit or the spray height adjusting unit moves the gas blowing unit so as to be arranged in a substantially horizontal direction with respect to the photomask, and the pressure adjusting unit Adjust the pressure to form a laminar flow due to the gas on the surface of the photomask ,
After the formation of the laminar flow, the spray angle adjusting unit or the spray height adjusting unit maintains the laminar flow while the gas blowing direction or the gas blowing unit from the surface of the photomask. An apparatus for removing foreign matter from a photomask, wherein the height is changed . 6. The foreign matter removing apparatus for a photomask according to claim 5, wherein the heating unit heats the water vapor in the atmosphere between the surface of the photomask and the gas blowing unit to a temperature at which a saturated water vapor pressure is not reached. .

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