JP2008083509A - Photomask fogging suppression method - Google Patents

Abstract

A photomask having a light-shielding film on the surface of a glass substrate, and a method for suppressing the fogging of the photomask generated on a photomask substrate in which the surface after cleaning or after exposure is activated is provided. With the goal.
After cleaning a photomask provided with a light-shielding film on the surface of a glass substrate, the formation of an oxide film is suppressed by placing it in an inert gas atmosphere for a certain period of time, and an inert film is generated to form a metal film. A photomask fogging suppression method by dry cleaning that suppresses the generation of acid by catalysis and thus suppresses the occurrence of fogging on the surface, after cleaning a photomask having a light shielding film on the surface of a glass substrate Or a photomask that is dried within 12 hours after using the photomask and is subjected to dry cleaning for at least 10 minutes in an inert gas atmosphere having an oxygen concentration of 10% or less and a humidity of 30% or less. How to suppress fogging.
[Selection] Figure 1

Description

  The present invention relates to a photomask fogging suppression method capable of efficiently suppressing fogging of a photomask.

  Currently, when manufacturing a semiconductor device using a wafer or the like, a projection exposure method is used in which a pattern formed on a photomask is exposed on a substrate coated with a photosensitive agent such as a photoresist by a projection optical system. Yes. In recent years, with the miniaturization of the pattern shape, the exposure light used tends to be shortened, and an exposure apparatus using KrF (wavelength 248 nm) or ArF (wavelength 193 nm) has been put into practical use. On the other hand, several tens of photomasks are used.

  These photomasks adhere to foreign matters floating in the surrounding space during exposure, storage, or transportation. The foreign matter on the photomask hinders image formation at the time of exposure, so that a defect appears in the product. In order to prevent such poor resolution due to foreign matters adhering to the photomask surface, the photomask is equipped with a pellicle as a dust-proof cover having translucency on the surface.

  Even in a photomask with a pellicle mounted, defects have recently occurred depending on the usage environment. It is estimated that in addition to foreign matter floating around, the exposure and storage are repeated to cause fogging substances inside the members constituting the pellicle to be adsorbed on the photomask and become a foreign matter due to a light reaction due to exposure. .

  When exposure is performed after a certain amount or more of foreign matter is generated on the photomask, the photomask is fogged and defects appear in the product. For this reason, it is necessary to clean the photomask in order to remove fogging. However, the cleaning increases the cost for manufacturing the product or wears the pattern of the photomask.

  As shown in Japanese Patent Application Laid-Open No. 2003-260, clouding is caused by adsorption of residues such as sulfuric acid existing on the photomask, gas generated from the case or pellicle member, gas from the manufacturing environment, usage environment, and storage environment to the photomask. However, it is expected to be generated as a crystal product by exposure.

  Therefore, suppression of fogging generated on the photomask has become an indispensable technique for supplying and using a stable photomask.

The known literature is described below.
JP 2006-208924 A

  However, as a result of various studies by the inventors, it has been found that it is difficult to completely suppress the fogging of the photomask even if these fogging factors are suppressed as much as possible.

  For example, it is known that a metal oxide film such as Cr used for a photomask has a catalytic action and thus easily reacts with an alcohol having a low boiling point in the atmosphere. These low-boiling alcohols are used in photomask manufacturing processes, photomask exposure processes, storage locations, and the like, and are present in a wide range. Therefore, it is difficult to completely suppress the use of chemical filters.

  For example, the surface of the Cr film becomes a radical state by washing or exposure. Organic substances such as aliphatic alcohol adsorbed thereon are oxidized by oxygen on the Cr film, and aldehyde is generated.

  The aldehyde produced here is further oxidized by oxygen on the Cr film and converted into an acid. Furthermore, it is being understood that the acid and aldehyde produced here react to form a product through steps.

  Here, searching for a new material that does not oxidize a metal film such as Cr may lead to a review of the conditions of all the processes, and a significant development cost is considered necessary.

  It is very difficult from the viewpoint of the cost occupied by the photomask in the current semiconductor device. Even if a new material is developed and fogging can be suppressed, it becomes a very expensive product and does not meet the cost.

  FIGS. 1A to 1E are explanatory views of an example of occurrence of fogging when a metal oxide film of a conventional photomask is used as a catalyst. Hereinafter, the occurrence of fogging of the photomask will be described with reference to FIG.

  In FIG. 1A, the photomask has a light shielding film 2 made of a metal oxide film such as Cr formed on a synthetic quartz glass 1. It is in a state immediately after cleaning the photomask, and the surfaces of the synthetic quartz glass 1 and the light shielding film 2 are in a clean state.

  In FIG. 1B, the pellicle film 4 is bonded to the synthetic quartz glass 1 via the pellicle frame 3 and the pellicle adhesive 5 on one side of the photomask. In this state, the photomask is used as an exposure photomask. It is used. In the photomask in this state, the organic substance 10b and the like are deposited on the surface with time.

  In FIG. 1C, the organic substance, for example, alcohol oxidizes the alcohol using chrome oxide as a component of the light-shielding film 2 as a catalyst to generate an aldehyde 10c. The chemical formula is shown in Formula 1.

この生成は、図１（ｃ）である。

This generation is shown in FIG.

  In FIG. 1 (d), the aldehyde 10c is accelerated in oxidation to produce formic acid 10d. Its chemical formula is shown in Chemical Formula 2.

この生成は、図１（ｄ）である。

This generation is shown in FIG.

  In FIG. 1 (e), with the passage of time, the aldehyde 10c and the formic acid 10d are accelerated in oxidation to produce a carboxylic acid 10e. The chemical formula is shown in Chemical Formula 3.

この生成は、図１（ｅ）である。

This generation is shown in FIG.

The organic matter deposited mainly in the vicinity of the light-shielding film of the photomask accelerates oxidation over time, and photomask fogging related to the formic acid 10d and the carboxylic acid 10e occurs.

  Therefore, an object of the present invention is devised in view of the above problems, and is to provide a photomask fogging suppression method for suppressing oxidation of a metal film after cleaning or after exposure.

The present invention according to claim 1 of the present invention is a photomask fogging suppression method in dry cleaning, which is performed after cleaning a photomask provided with a light-shielding film on the surface of a glass substrate,
A method for suppressing fogging of a photomask, comprising: cleaning a photomask having a light-shielding film on a surface of a glass substrate, and then performing dry cleaning in an inert gas atmosphere having an oxygen concentration of 10% or less and a humidity of 30% or less. .

The present invention according to claim 2 of the present invention is a photomask fogging suppression method in dry cleaning, which is performed after cleaning a photomask provided with a light-shielding film on the surface of a glass substrate,
A photomask fogging suppression method comprising performing dry cleaning in an inert gas atmosphere having an oxygen concentration of 10% or less and a humidity of 30% or less after using a photomask having a light-shielding film on the surface of a glass substrate. .

  The present invention according to claim 3 of the present invention is the photomask fogging suppression method according to claim 1 or 2, wherein the dry cleaning is performed within 12 hours after the cleaning or after the use. .

  In order to satisfy this condition, it is desirable to use nitrogen or argon gas.

  Further, the oxygen concentration at this time is more preferably 1% or less so as not to form an oxide film on the Cr film.

  The present invention according to claim 4 of the present invention is the photomask fogging suppression method according to any one of claims 1 to 3, wherein the dry cleaning is performed for at least 10 minutes.

  In order to satisfy this condition, it is desirable to use nitrogen or argon gas. At this time, if there is no such inert gas, dry air may be used.

  It is more desirable that the humidity be 10% or less because water is also considered to cause clouding. In this case, it is necessary to fully consider the influence of electrostatic breakdown due to low humidity.

  According to the photomask fogging suppression method of the present invention, the metal film surface such as Cr radicalized by cleaning with ozone or the like is subjected to an inert treatment by performing dry cleaning with an inert gas, and the metal film Can prevent oxidation.

  For this reason, even if a component that can be oxidized and become cloudy is adsorbed to the photomask, the metal oxide film is treated inactive, so that the generation of aldehyde can be suppressed, and the occurrence of clouding of the photomask can also be suppressed. Connected.

  Furthermore, by suppressing the occurrence of photomask fogging, the risk of re-cleaning due to the occurrence of photomask fogging and the risk of changes in line width, etc. are reduced, and stable use of photomasks at lower costs. Is possible.

  According to the photomask fogging suppression method according to claim 2, the inert treatment is performed by performing dry cleaning with an inert gas on the surface of a more radicalized metal film such as Cr at the time of exposure to the wafer. To prevent oxidation of the metal film.

  For this reason, even if a component that can be oxidized and become a photomask fogging component is adsorbed on the photomask, the metal oxide is treated inactive, so that the generation of aldehyde can be suppressed and also the generation of photomask fogging can be suppressed. Connected.

  In addition, by suppressing the occurrence of fogging of the photomask, the risk of re-cleaning due to the occurrence of fogging and the risk of changes in line width are reduced, enabling stable use of the photomask at a lower cost. It becomes.

  If a photomask provided with a light-shielding film using the method for suppressing fogging of the photomask of the present invention is used, even if it is a photomask in which the surface after cleaning or after exposure is activated, it is in an inert gas atmosphere. Oxide film formation is suppressed by leaving it for a certain period of time, and by generating an inactive film, acid generation due to metal catalysis is suppressed for a longer time than before, and fogging generated on the photomask surface is suppressed. Occurrence can be suppressed.

  Hereinafter, embodiments of the present invention will be described. The photomask used in the present invention is a member formed by patterning a metal film of about 1000 mm on a glass substrate by a known method such as dry etching, and is used on a silicon wafer used for a semiconductor device. In the exposure process for forming a circuit, the circuit is used as an original plate of the circuit.

  A photomask needs to have very high definition and high quality depending on the application to be used, and is a member that requires countermeasures against contamination and foreign matters among related members of semiconductor devices. In addition, it has been found that by shortening the wavelength used for exposure in recent miniaturization, even components that have not been affected until now can become photomask fogging generation components. It has been a major issue in the field.

  In order to improve this problem, the present inventors have suppressed the intermediate product that can cause photomask fogging by suppressing the catalytic action of metal oxide, and can suppress the photomask fogging substance. I found it.

  In the invention according to claim 1, the surface of a metal film such as Cr radicalized by sulfuric acid cleaning or functional water cleaning such as ozone for the purpose of removing residual contaminants such as resist is subjected to dry cleaning with an inert gas. By carrying out the above, it is possible to perform an inert treatment and prevent the metal film from being oxidized.

  The dry cleaning is more preferably performed within 30 minutes immediately after the cleaning, and the dry cleaning with an inert gas is preferably performed for 60 minutes or more.

  The term “cleaning” as used herein refers to cleaning performed before shipment or cleaning performed when the pellicle is replaced again. Dry cleaning means aging the photomask in an inert gas atmosphere. The purpose of the dry cleaning is to prevent the metal surface from being oxidized as much as possible by not leaving the metal film in a radical state after the cleaning in an atmosphere containing oxygen.

The invention according to claim 2 is characterized in that, in the wafer exposure process using a photomask, the photomask is dried and cleaned in an inert gas atmosphere for at least 10 minutes after exposure for at least 12 hours. This is a fogging suppression method.

  The dry cleaning is more preferably performed within 30 minutes immediately after the cleaning, and is preferably performed for 60 minutes or more.

  Dry cleaning refers to aging the photomask in an inert gas atmosphere. The object is to prevent the metal surface from being oxidized as much as possible by not placing the metal film in a radical state after exposure in an atmosphere containing oxygen.

  A third aspect of the invention is a photomask fogging prevention method characterized in that the oxygen concentration is 10% or less in the inert gas atmosphere of the first and second aspects. In order to satisfy this condition, it is desirable to use nitrogen, helium, or argon gas.

  Further, it is more desirable that the oxygen concentration at this time be 1% or less so as not to form an oxide film on the Cr film. Furthermore, it is more desirable to use inexpensive nitrogen for the inert gas.

  A fourth aspect of the invention is a photomask fogging suppression method characterized in that the humidity during dry cleaning is 30% or less in the inert gas atmosphere of the first and second aspects. In order to satisfy this condition, it is desirable to use nitrogen or argon gas. At this time, if there is no such inert gas, dry air may be used.

  It is more desirable that the humidity be 10% or less because water is also considered to cause clouding.

  Examples of the glass substrate used in the present invention include synthetic quartz glass, and examples of the light shielding film include metals or resins such as Cr and MoSi alloys having a single-layer or multi-layer structure on the glass substrate. It is not limited to.

  Examples of the inert gas used in the present invention include nitrogen, helium, and argon gas.

  Hereinafter, Examples 1 to 10 and Comparative Examples 1 to 4 of the present invention will be described in detail. The present invention is not limited to these examples.

  In Example 1, a photomask obtained by patterning a 1000 Ｃｒ Cr film on a synthetic quartz glass substrate was cleaned with a functional water cleaning machine using ozone, and after 12 hours in an inert gas atmosphere (oxygen concentration of 1 %, Humidity 30%) for 10 minutes.

  A photomask obtained in the same manner as in Example 1 was cleaned in the same manner as that used in Example 1, and then 12 hours later in an inert gas atmosphere (oxygen concentration 10%, humidity 10%). Left for 10 minutes.

  The photomask obtained in the same manner as in Example 1 was washed in the same manner as that used in Example 1, and then 30 minutes later in an inert gas atmosphere (oxygen concentration 10%, humidity 30%). Left for 10 minutes.

  The photomask obtained in the same manner as in Example 1 was cleaned in the same cleaning machine as used in Example 1, and then 12 hours later in an inert gas atmosphere (oxygen concentration 10%, humidity 30%). Left for 60 minutes.

  The photomask obtained in the same manner as in Example 1 was cleaned in the same cleaning machine as used in Example 1, and then 12 hours later in an inert gas atmosphere (oxygen concentration 10%, humidity 30%). Left for 10 minutes.

  Example 11 was carried out as a comparative example of the present invention. In Example 11, the photomask obtained in the same manner as in Example 1 was washed in the same washing machine as used in Example 1, and then mixed with an oxygen / nitrogen ratio of 1: 4 after 12 hours. It was left for 10 minutes in a gas atmosphere (oxygen concentration 20%, humidity 30%).

  Example 12 was carried out as a comparative example of the present invention. In Example 12, the photomask obtained in the same manner as in Example 1 was washed in the same manner as that used in Example 1, and then in a mixed gas atmosphere (oxygen concentration 10%, humidity) after 12 hours. 40%) for 10 minutes.

  The photomasks of Examples 1 to 5 were exposed to a test exposure machine using ArF (wavelength: 193 nm) as a light source for a certain period of time, and were left for a predetermined period of time after washing with functional water using ozone, and then an inert gas atmosphere. The sample was left for a predetermined time under an oxygen concentration of about 10% or less and a humidity of about 30% or less. Then, after storing for a fixed time, the above operation was repeated again up to 10 times.

  The photomasks of Comparative Examples 1 and 2 were exposed to a test exposure machine using ArF (wavelength: 193 nm) as a light source for a certain period of time, and after use, left for a predetermined time after washing with functional water using ozone, and then oxygen and nitrogen The mixture was allowed to stand for 10 minutes in an atmosphere of a mixed gas (oxygen concentration of about 20% or humidity of 40%) with a ratio of 1: 4. Then, after storing for a fixed time, the above operation was repeated again up to 10 times.

  When the photomasks of Examples 1 to 5 and Comparative Examples 1 and 2 were stored in each environment and washing, drying washing and storage were repeated 10 times, the results shown in Table 1 were obtained.

注：◎は、曇りが全くないことを示し、
○は、曇りがほとんどないことを示し、
×は、曇りがあることをしめしている。

Note: ◎ indicates no cloudiness,
○ indicates that there is almost no cloudiness,
X indicates that there is cloudiness.

  Using a test exposure machine using ArF (wavelength: 193 nm) as a light source, a blank mask is exposed for a fixed time within a range of 1 cm □ to a photomask formed by patterning a 1000 Ｃｒ Cr film on a synthetic quartz glass substrate for 12 hours. Later, it was allowed to stand for 10 minutes in an inert gas atmosphere (oxygen concentration 1%, humidity 30%).

  The photomask obtained in the same manner as in Example 6 was exposed using the same exposure machine as that used in Example 1, that is, after use, in an inert gas atmosphere (oxygen concentration 10%, humidity 10%) after 12 hours. ) For 10 minutes.

  A photomask obtained in the same manner as in Example 6 was exposed in the same manner using the same exposure machine as that used in Example 1, and then 30 minutes later in an inert gas atmosphere (oxygen concentration 10%, humidity 30%). Left for 10 minutes.

  The photomask obtained in the same manner as in Example 6 was exposed in the same manner using the same exposure machine as that used in Example 1, and then 12 hours later in an inert gas atmosphere (oxygen concentration 10%, humidity 30%). Left for 60 minutes.

  The photomask obtained in the same manner as in Example 6 was exposed in the same manner using the same exposure machine as that used in Example 1, and then 12 hours later in an inert gas atmosphere (oxygen concentration 10%, humidity 30%). Left for 10 minutes.

  Example 13 was carried out as a comparative example of the present invention. In Example 13, a photomask obtained in the same manner as in Example 6 was exposed using the same exposure machine as that used in Example 1, and after 12 hours, the oxygen / nitrogen ratio was 1: 4. It was left for 10 minutes in a gas atmosphere (oxygen concentration 20%, humidity 30%).

  Example 14 was carried out as a comparative example of the present invention. In Example 14, the photomask obtained in the same manner as in Example 6 was exposed in the same manner using the same exposure machine as that used in Example 1, and then in an inert gas atmosphere (oxygen concentration: 10%, 12 hours later). (Humidity 40%) for 10 minutes.

  The photomasks of Examples 6 to 10 were exposed for a fixed time with a test exposure machine using ArF (wavelength 193 nm) as a light source, and after a predetermined time, in an inert gas atmosphere (oxygen concentration of about 10% or less and humidity of about (30% or less) for a predetermined time. Then, after storing for a fixed time, the above operation was repeated again up to 10 times.

  The photomasks of Comparative Examples 3 to 4 were exposed to a test exposure machine using ArF (wavelength 193 nm) as a light source for a certain period of time, and after use, a mixed gas having an oxygen to nitrogen ratio of 1: 4 (oxygen concentration about 20%) Or in an atmosphere at a humidity of about 40%). Then, after storing for a fixed time, the above operation was repeated again up to 10 times.

  Examples 6 to 10 and Comparative Examples 3 and 4 were stored in each environment, and exposure, drying washing and storage were repeated 10 times. The results shown in Table 2 were obtained.

注：◎は、曇りが全くないことを示し、
○は、曇りがほとんどないことを示し、
×は、曇りがあることをしめしている。

Note: ◎ indicates no cloudiness,
○ indicates that there is almost no cloudiness,
X indicates that there is cloudiness.

(A)-(e) is explanatory drawing of the example of generation | occurrence | production of the clouding in the case of using the metal oxide film of the conventional photomask as a catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Synthetic quartz glass 2 ... Light shielding film (Cr, MoSi, etc.)
3 ... Pellicle frame 4 ... Pellicle film 5 ... Pellicle adhesive 10b ... (deposited) organic substance 10c ... Aldehyde 10d ... Formic acid 10e ... Carboxylic acid

Claims (4)

It is a photomask fogging suppression method in dry cleaning, which is performed after cleaning a photomask having a light shielding film on the surface of a glass substrate,
A method for suppressing fogging of a photomask, comprising: cleaning a photomask having a light-shielding film on a surface of a glass substrate, and then performing dry cleaning in an inert gas atmosphere having an oxygen concentration of 10% or less and a humidity of 30% or less. It is a photomask fogging suppression method in dry cleaning, which is performed after cleaning a photomask having a light shielding film on the surface of a glass substrate,
A method for suppressing fogging of a photomask, comprising using a photomask provided with a light-shielding film on a surface of a glass substrate and then performing dry cleaning in an inert gas atmosphere having an oxygen concentration of 10% or less and a humidity of 30% or less.   The photomask fogging suppression method according to claim 1 or 2, wherein the dry cleaning is performed within 12 hours after the cleaning or after the use.   The photomask fogging suppression method according to any one of claims 1 to 3, wherein the dry cleaning is performed for at least 10 minutes.

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