JP2013068786A - Photo mask cleaning method - Google Patents

Abstract

The present invention provides a cleaning method for removing foreign matter from a foreign matter adhering to a photomask while suppressing destruction of a minute pattern and preventing new foreign matter from adhering by cleaning.
A cleaning method for removing foreign matter adhering to a pattern surface of a photomask, the step of applying a liquid foreign matter removing material on a foreign matter adhesion surface to form a film surrounding the foreign matter; A step of forming a solidified film of the foreign matter removing material, a foreign matter removing step of removing the solidified film together with the foreign matter, a step of contacting the catalyst with the foreign matter removing material remaining on the photomask after the foreign matter removing step, and a residual And a step of decomposing and removing the foreign material removing material with a catalyst.
[Selection] Figure 1

Description

  The present invention relates to a cleaning method for removing foreign matter adhering to a photomask used in an exposure process of a photolithography method.

In general, photomask cleaning is performed by combining chemical cleaning and physical cleaning. Examples of chemicals used for chemical cleaning include sulfuric acid / hydrogen peroxide mixture of sulfuric acid and hydrogen peroxide solution, and ammonia / hydrogen peroxide mixture of ammonia and hydrogen peroxide solution. Sulfuric acid / hydrogen peroxide dissolves and removes inorganic foreign matters such as metals and metal oxides with a strong oxidizing power. In addition, organic foreign matters such as resist residues are also oxidatively decomposed.
In addition, ammonia overwater separates and decomposes organic foreign substances from the surface of chromium constituting the light-shielding pattern of the photomask and the surface of glass constituting the photomask substrate by the dissolving action of ammonia and the oxidizing action of hydrogen peroxide.
It is difficult to remove foreign substances uniformly in a short time by only chemical cleaning with a chemical solution such as sulfuric acid-hydrogen peroxide or ammonia water, and it is often used in combination with physical cleaning, for example, ultrasonic cleaning.

Physical cleaning is a method that removes foreign matter adhering to the photomask substrate by applying a force greater than the adhesion force to the foreign matter. However, if the applied force is too great, it not only removes the foreign matter but also damages the photomask. Become.
As the pattern line width of the photomask becomes finer, the aspect ratio indicating the ratio of the film thickness / line width of the pattern tends to increase, and the allowable size of foreign matter on the photomask pattern tends to decrease. For this reason, the fineness of the pattern line width reduces the adhesion between the pattern and the substrate, while the difficulty of removal increases with the allowable size of fine foreign matter. As a result, it is difficult to improve the foreign matter removal performance while preventing destruction of minute patterns, and it becomes difficult to apply conventional physical cleaning that relies on impact force.
In contrast to physical cleaning that relies on impact force such as brush cleaning or ultrasonic cleaning, cleaning that does not involve impact physical force as shown in Patent Document 1 has also been proposed.

JP-A-5-107744

  Patent Document 1 proposes a foreign matter removal method using formation of a polymer film. In this proposal, a film surrounding a foreign substance is formed by utilizing an irreversible reaction in which a liquid polymer is applied onto a photomask pattern and then heated to form a solid film. After forming the polymer film surrounding the foreign material, the foreign material surrounded by the polymer film can be removed together with the film by dissolving the film or physically peeling the film. In the proposal, it is important that the polymer film is completely removed in the dissolution and peeling. If even a small amount of the formed polymer film remains on the photomask pattern, new foreign matter is generated, and sufficient cleaning that does not leave foreign matter cannot be achieved.

  The present invention is proposed in view of the above-mentioned problems, and the problem to be solved by the present invention is to remove the foreign matter attached to the photomask while suppressing the destruction of the minute pattern, And it is providing the washing | cleaning method which does not attach the new foreign material by washing | cleaning.

The present invention has been made to solve the above-described problems, and as a method for forming a film for removing foreign matter, film formation is performed after a film forming material is applied on a photomask pattern having foreign matter. A solid film is formed by cooling with air or bringing a coolant into contact so that the material is below the melting point. Thereafter, the film surrounded by the film can be removed by peeling the film from the photomask while the film holds the foreign object.
Even if a minute film material remains by the peeling process in the above steps, it can be completely removed from the photomask by decomposing the film material with a catalyst after peeling the film. Become.
A specific configuration of the above method is shown below.

  As a means for solving the above-mentioned problems, the invention according to claim 1 is a cleaning method for removing foreign matter adhering to the pattern surface of a photomask, wherein a liquid foreign matter removing material is provided on the foreign matter-attached surface. Forming a film surrounding the foreign matter by applying a coating, a step of forming a liquid foreign matter removing material into a solidified film, a foreign matter removing step of removing the solidified film together with the foreign matter, and a photomask after the foreign matter removing step A photomask cleaning method comprising: a step of bringing a catalyst into contact with a foreign matter removing material remaining thereon; and a step of decomposing and removing the remaining foreign matter removing material with a catalyst.

  According to a second aspect of the present invention, in the photomask according to the first aspect, the foreign matter removing material is a paraffin having 20 carbon atoms (melting point 36 ° C.) to 40 carbon atoms (melting point 81 ° C.). This is a cleaning method.

  The invention described in claim 3 is characterized in that the step of forming a liquid foreign substance removing material into a solid film is cooled using a cooling gas that does not react with the foreign substance removing material or the photomask. Item 3. The photomask cleaning method according to Item 1 or 2.

  The invention according to claim 4 is the photomask cleaning method according to claim 3, wherein the cooling gas is selected from air, nitrogen, argon, helium, carbon monoxide, and carbon dioxide. is there.

  The invention according to claim 5 is the photomask cleaning method according to any one of claims 1 to 4, wherein the step of decomposing and removing the remaining foreign matter removing material with a catalyst is performed by heating. It is.

  The invention according to claim 6 is the photomask cleaning method according to claim 5, wherein the heating temperature is 210 ° C. or lower.

  The invention according to claim 7 is the photomask cleaning according to any one of claims 1 to 6, wherein the catalyst is selected from zeolite, platinum, rhodium, palladium, ruthenium, and nickel. Is the method.

  The invention according to claim 8 is the photomask cleaning method according to any one of claims 1 to 7, wherein the catalyst is used while being supported on a carrier.

The present invention applies a liquid foreign substance removing material to a foreign substance adhesion region on the pattern surface of a photomask, solidifies to form a film surrounding the foreign substance, and removes the solidified film together with the foreign substance and then on the photomask. This is a cleaning method that decomposes and removes the foreign material removal material remaining on the photocatalyst, so that the foreign material adhering to the photomask is removed while suppressing the destruction of minute patterns, and no new foreign material is attached by cleaning. A sufficient cleaning method for the mask can be provided.
In addition, the cleaning method of the present invention can process only a portion where foreign matter is attached, and can perform partial cleaning that cannot be realized by conventional wet cleaning. It is possible to prevent the movement and diffusion of the contamination between the environment and the cleaning without adhering new foreign matters due to cross contamination with the outside of the system.

It is a process schematic diagram which shows an example of the washing | cleaning process in this invention from the cross section of the board thickness direction of a photomask in order of a process. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view showing an example of a photomask cleaning method according to an embodiment of the present invention from a pattern surface, where (a) shows a foreign matter adhering state before cleaning, and (b) is a foreign matter being cleaned. The remaining state of the removal material is shown, and (c) shows the state where the cleaning process is completed.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an example of a mode for carrying out the present invention will be described in detail with reference to the drawings. The embodiments described below are specific configuration examples of the present invention and do not limit the present invention unless otherwise specified.

FIGS. 1A to 1G are process schematic diagrams showing an example of a cleaning process in the present invention in the order of processes as viewed from a cross section in the thickness direction of a photomask.
FIG. 1A shows an example in which foreign matter 4 is present on the pattern-side surface of a photomask 3 composed of a photomask substrate 1 and a pattern 2. The photomask substrate 1 is made of a flat transparent plate material such as glass or quartz, has a surface that is free of undulations, scratches and dirt, and does not include optically heterogeneous regions inside the material. It is desirable to have stable characteristics. The pattern 2 is composed of a light-shielding film formed of a metal chromium or its oxide film or a laminated body, and has a workability capable of obtaining a good fine pattern shape, high surface hardness, and adhesion to the substrate 1. And stable properties against heat and chemicals are desired. The foreign matter 4 may be mixed in various types in shape and material depending on the generation factor, and appears at various plane positions.

FIG. 1B shows a process of applying the foreign substance removing material 6 to the pattern side surface of the photomask 3.
Examples of the foreign material removing material 6 include paraffin having 20 or more carbon atoms. The foreign matter removing material 6 is supplied from the foreign matter removing material supply nozzle 5 in a state heated to a temperature equal to or higher than the melting point.
In this step, the photomask 3 is fixed to a spin chuck (not shown) and rotated, so that it can be uniformly applied to the pattern surface to be cleaned.

Further, if the location of the foreign matter 4 is confirmed in advance, it is possible to apply the foreign matter removing material 6 only to the vicinity including the foreign matter 4 without rotating the photomask 3 and perform partial cleaning.
After the foreign material removing material 6 is applied to the pattern surface of the photomask 3, the supply of the foreign material removing material 6 is stopped, and when the substrate is spinning, the rotation of the spin chuck is stopped thereafter. As shown in FIG. 1C, the liquid foreign material removing material 6 is deposited by surface tension at least in a certain region of the photomask pattern surface surrounding the foreign material 4.

Next, in FIG.1 (d), the liquid foreign material removal material 6 can be cooled with air at room temperature, and it can reduce to the temperature below melting | fusing point, and can be set as the solidified foreign material removal material 7. FIG. Other gases that do not react with the foreign material removal material and do not adversely affect the pattern or the photomask components of the substrate may be used for cooling.
Examples of the above gas include inert gas such as nitrogen, argon, helium, carbon monoxide, and carbon dioxide in addition to air.
The gas flow rate and flow rate are not limited, but it is desirable to perform natural cooling by replacing the gas around the spin chuck to such an extent that the photomask pattern is not damaged by the wind pressure.

  Further, a coolant 8 having a temperature equal to or lower than the melting point of the foreign material removing material 6 from above the liquid foreign material removing material 6, for example, pure water cooled to room temperature or lower is lowered from the nozzle and brought into contact with the foreign material removing material 6 to rotate the spin. However, by performing the supply and the subsequent spin drying, it is possible to obtain the solid-state foreign material removing material 7 as described above, and the cooling time can be shortened (FIG. 1 (e)).

Next, as shown in FIG. 1 (f), the foreign matter removing material 7 which has become a melting point or lower and is solidified is peeled off from the photomask 3 using vacuum tweezers (not shown) to be held on the foreign matter removing material 7. The formed foreign matter 4 can be removed together with the solidified foreign matter removing material 7 film.
Although there is no restriction | limiting in the force at the time of peeling off the solidified foreign material removal material 7, It is desirable to peel with the force of 1N / 20mm-3N / 20mm, for example in a 20 mm width strip | belt shape so that a photomask pattern may not be damaged.
In addition, by using a plurality of vacuum tweezers as necessary, it can be peeled off with good working efficiency in accordance with an appropriate position and shape.

In the foreign matter removing step, a part 9 of the minute foreign matter removing material may remain on the photomask 3 in some cases. Therefore, as shown in FIG. 1 (g), by bringing the catalyst 12 into contact, a part 9 of the foreign matter removing material remaining on the photomask 3 is decomposed and removed.
In particular, it is preferable that the step of decomposing and removing the remaining foreign matter removing material with the catalyst brought into contact is performed by heating, and the decomposition in this case includes combustion by the catalyst.

  The amount of catalyst used for decomposing and removing the remaining part 9 of the foreign matter removing material can be appropriately determined from the number of carbons and the remaining amount of the foreign matter removing material used. It is preferable to conduct a preliminary experiment with another photomask in advance.

The catalyst can be selected from materials commonly used for cracking hydrocarbons. Examples include solid catalysts such as zeolite, platinum, rhodium, palladium, ruthenium, and nickel.
Further, the catalyst may be the above substance alone, or may be a catalyst in which a compound or mixture containing the above substance is supported on a substance generally used as a catalyst carrier such as zeolite or alumina.

The temperature condition at the time of decomposition with a catalyst is preferably about 210 ° C. or less, which is the heat resistance temperature of a normal photomask.
The used catalyst can be held and removed with vacuum tweezers.

The hydrocarbon which is a foreign material removing material to be used preferably has a melting point of about 30 to 100 ° C. among paraffins, particularly 20 carbons (melting point 36 ° C.) to 40 carbons (melting point 81 ° C.). preferable.
Paraffin with too few carbon atoms is not preferred because it requires a low temperature for solidification, and paraffin with many carbon atoms has a high melting point and is complicated to handle. When the number of carbon atoms is large, decomposition with a catalyst may be insufficient in addition to the above, and it is not preferable because it tends to remain as a foreign matter removing material on the photomask.
The paraffin is preferably a linear so-called normal paraffin.

  Examples of the present invention will be specifically described below, but this is only an example, and the present invention is not limited to these examples.

The cleaning of the present invention shown in FIG. 1 was performed.
In this example, paraffin having 20 carbon atoms was used as the foreign material removing material, and 1 ml of paraffin liquefied at 50 ° C. was dropped onto the photomask 3 using a micropipette and spin-coated at a rotation speed of 100 rpm. After 30 seconds, the rotation was stopped, and the film of the foreign material removing material solidified by cooling to 30 ° C. with air at a room temperature of 23 ° C. was obtained.

For the evaluation, a photomask 3 for evaluation was used in which a CrO (chromium oxide) pattern 2 was formed on the photomask substrate 1 and a foreign substance 4 having a size that can be visually confirmed adhered on the CrO film on the outer periphery of the pattern.
The evaluation photomask 3 was cleaned, and the presence or absence of foreign matter 4 on the evaluation photomask 3 after cleaning was visually confirmed.

The evaluation results are shown in FIG. FIG. 2 is a schematic plan view showing an example of a photomask cleaning method according to an embodiment of the present invention from a pattern surface, where (a) shows a foreign matter adhesion state before cleaning, and (b) The remaining state of the foreign matter removing material during the cleaning is shown, and (c) shows the state where the cleaning process is completed.
The foreign matter 4 adhering to the evaluation photomask 3 before cleaning was not confirmed after the solidified foreign substance removing material 7 film was peeled off from the photomask.
Since a part 9 of the foreign substance removing material was confirmed on the photomask 3 for evaluation, 1 g of crystals of the catalyst 12 (zeolite) was brought into contact with the part 9 of the foreign substance removing material using the photomask substrate 1 as a carrier, and the temperature was increased to 200 ° C. When it was heated in a set clean oven for 30 minutes and decomposed, it was confirmed that part 9 of the foreign matter removing material had disappeared. The used catalyst was removed by air blowing with N ₂ gas and vacuum suction.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

DESCRIPTION OF SYMBOLS 1 ... Photomask board | substrate 2 ... Pattern 3 ... Photomask 4 ... Foreign material 5 ... Foreign material removal material supply nozzle 6 ... Foreign material removal material (liquid)
7. Foreign material removal material (solid)
8 ... Coolant 9 ... Part of foreign material removal material (solid: remaining on mask)
10 ... Foreign matter removal material remaining defect (solid)
11 ... Part of foreign material removal material (gas)
12 ... Catalyst

Claims (8)

A cleaning method for removing foreign matter adhering to the pattern surface of a photomask,
Forming a film surrounding the foreign matter by applying a liquid foreign matter removing material on the foreign matter adhesion surface;
A step of converting the liquid foreign material removal material into a solidified film;
A foreign matter removing process for removing the solidified film together with the foreign matter;
A step of bringing the catalyst into contact with the foreign matter removing material remaining on the photomask after the foreign matter removing step;
A step of decomposing and removing the remaining foreign material removal material with a catalyst;
A method for cleaning a photomask, comprising:   2. The photomask cleaning method according to claim 1, wherein the foreign matter removing material is paraffin having 20 carbon atoms (melting point: 36 ° C.) to 40 carbon atoms (melting point: 81 ° C.).   The photomask cleaning according to claim 1 or 2, wherein the step of forming the liquid foreign matter removing material into a solidified film is cooled using a cooling gas that does not react with the foreign matter removing material or the photomask. Method.   The photomask cleaning method according to claim 3, wherein the cooling gas is selected from air, nitrogen, argon, helium, carbon monoxide, and carbon dioxide.   The method for cleaning a photomask according to any one of claims 1 to 4, wherein the step of decomposing and removing the remaining foreign material removal material with a catalyst is performed by heating.   The method for cleaning a photomask according to claim 5, wherein the heating temperature is 210 ° C. or lower.   The photomask cleaning method according to claim 1, wherein the catalyst is selected from zeolite, platinum, rhodium, palladium, ruthenium, and nickel.   The method for cleaning a photomask according to claim 1, wherein the catalyst is used while being supported on a carrier.

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