JPS6386435A - Cleaning of x-ray mask - Google Patents

Abstract

PURPOSE:To prevent any foreign matters from directly bonding to a mask by a method wherein an X-ray mask immediately after exposure is coated with a soblimating protective film to be removed together with any foreign matters. CONSTITUTION:A mask substrate 10 is mounted on a holding ring 9 while X-ray absorbent layers 11 are provided on the mask substrate 10. Then, a sublimating protective film 12 is formed on the X-ray mask by dripping naphthalene ethylalcohol solution on the mask 10 for spincoating process. The X-ray mask 10 is spun round while being irradiated with thermal or photo energy 14 immediately before exposure, and vacuum suction and discharge of sublimated gas together with foreign matters 13 are performed. Next, immediately after cleaning process, the X-ray mask 10 is carried into an X-ray exposure device to be exposed and immediately after exposure, covered with the protective film 12 after making sure of no foreign matters on the mask 10. Through these procedures repeated, the X-ray mask with no foreignmatters bonded thereto can be made serviceable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an X-ray mask cleaning method for removing impurities on an X-ray mask.

[Prior Art] An X-ray mask is required for photolithography using X-rays in the manufacturing process of semiconductor devices.

Originally, soft X-rays were easily transmitted, and it was thought that impurities made of organic compounds on the X-ray mask would not affect transfer. However, organic compound contaminants with a thickness of several tens of microns or more and heavy metal pieces with a thickness of several microns or more affect the transfer by causing blurring. Therefore, in order to prevent the occurrence of blur,
Line masks also require some sort of cleaning before exposure.

Conventionally used methods for cleaning photomasks include high-pressure pure water and brush scrubbing. However, it cannot work on masks made of very thin films such as X-ray masks.

FIG. 2 is a diagram showing a cleaning-exposure-storage cycle of a conventionally used photomask.

(a) Many impurities adhere to the photomask 1 during storage.

(b) Contaminants 2 attached to the photomask substrate
Since these are transferred as defects in the pattern 3, high-pressure pure water 4 is sprayed while rotating the photo mask, and then drying is carried out at high speed while irradiating with an infrared lamp. After drying, the mask is attached to an exposure device and exposed, and after use, the mask is stored again.

If the stain is severe, scrub it with gauze containing detergent (surfactant).

Further, as shown in FIG. 3, a method is also used in which a protective film pellicle 6, which is an organic polymer with a ring, is attached to the photomask to prevent contaminants 8 from directly adhering to the mask substrate 5. When this method is used, since the distance between the mask substrate 5 and the contaminants 8 is large, the mask substrate 5
If the exposure is focused on , the shadow of contaminant 8 will not be reflected. Therefore, in this case, there is no need to wash and remove impurities.

Furthermore, as shown in Japanese Patent Application Laid-Open No. 61-87326, xi
Another method is to perform 02 plasma treatment on the mask to oxidize and remove organic impurities.

[Problems to be solved by the invention] However, the conventional photomask cleaning method (second method)
When cleaning an X-ray mask using high-pressure pure water, the xIm mask, which consists of a thin layer of a few μm of pus, may crack or have a high aspect ratio (0.7 μm to 1.2 μm vertically and 0.5 μm horizontally).
Unfortunately, there was a problem that the X-ray absorbing layer pattern peeled off. Furthermore, when brush scrubbing is performed, there is a problem in that the mask substrate and the X-ray absorbing layer pattern are scratched.

In addition, when using a protective film pellicle (Fig. 3),
This method is simple because there is no need to wash and remove contaminants, but there are problems in that the organic polymer film is expensive and the technique for attaching the film to the photomask is difficult.

Generally speaking, the plasma processing method disclosed in JP-A-61-87326 removes only organic impurities, so there is a problem in that inorganic impurities that affect exposure cannot be removed.

This invention was made to solve the above-mentioned problems, and it prevents contaminants from directly adhering to the mask, and also allows the X-ray mask to be installed without damaging the mask substrate or the X-ray absorbing layer pattern. The purpose is to provide a method for cleaning.

c. Means for Solving Problems] The present invention relates to an X-ray mask cleaning method for removing impurities on an xi mask.

and C. Peeling and removing, including the steps of applying a sublimable protective film on the X-ray mask immediately after exposure, and removing the protective film together with impurities.

[Function] Sublimation retention on the X-ray mask immediately after exposure! Since a film is applied, contaminants do not directly adhere to the X-ray mask.

Furthermore, since the protective film has sublimation properties, it is easy to remove.

When this protective film is removed, impurities are also removed.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 18 to 1C are diagrams showing an embodiment of the method of the present invention using cross-sectional views of an X-ray mask.

FIG. 1A shows a cross-sectional view of the X-ray mask. A mask substrate 10 is placed on the support ring 9, and an X-ray absorption layer 11 is provided on the mask substrate 10. This X
The ray mask is made by forming a gold absorption layer with a thickness of 0.7 µl on an X-ray mask substrate consisting of boron nitride (BN) and a polyimide film, and then a 0.2-2 µm polyimide film on top of it. Formed by coating.

FIG. 1B is an X-ray mask coated with sublimable adhesive *mi2, and shows how contaminants 13 have adhered to it during storage. Formation of the sublimable resin 11912 on the X-ray mask is performed by dropping an ethyl alcohol solution of naphthalene onto the X-ray mask and performing spin coating. By this method, a naphthalene protective film of 500 to 2oo, oooX can be obtained.

Then, the XvA mask on which 1 g of naphthalene has been formed is stored under conditions in which naphthalene is as difficult to sublimate as possible.

FIG. 1C shows the X-ray mask being irradiated with heat or light energy 14 just before exposure to
FIG. 3 is a diagram showing a state in which the gas generated by sublimation by rotation at pm is vacuum-suctioned and discharged together with impurities 13 by a pump. The light used was UV light (HQ clamp was used, and the vacuum level of the pump was 10-'m1iHΩ).

The reason why the photo mask is turned upside down when vacuuming with a pump is to make it easier to remove foreign substances since they have weight.

The X-ray mask is cleaned as described above.

Immediately after cleaning, the X-ray mask is then transported into an X11 exposure device and exposed. Immediately after exposure (immediately after using the X-ray mask), it is confirmed that there are no foreign substances on the mask, and a protective film is coated as shown in FIG. 1B.

By repeating the above process, all of the impurities (unattached
A mask can be used.

In the above embodiment, the protective film is sublimated and removed by evacuation while irradiating heat or light energy. However, the present invention is not limited thereto. Even if the naphthalene retainer 1111 is stripped by spraying a protective film-soluble solvent such as ethyl alcohol gas, impurities can be removed and the object of the present invention can be achieved.

[Effects of the Invention] As explained above, in this invention, a sublimable protective film is applied on the X-ray mask immediately after exposure, so that contaminants are directly removed from the X-ray mask.
Do not adhere to line mask. Furthermore, since the protective film has sublimation properties, it is easy to remove. Therefore, impurities on the mII are easily removed.

Furthermore, in the past, high-pressure pure water was directly sprayed or brushed directly onto the absorption layer pattern or mask substrate of an X-ray mask. However, in the present invention, since the X-ray absorbing layer pattern and the mask substrate are not directly stimulated, the X-ray absorbing layer pattern does not peel off and the mask substrate does not crack. Therefore, the durability of the xIl mask is significantly improved.

[Brief explanation of the drawing]

FIGS. 18 to 1C are diagrams showing an embodiment of the method of the present invention using cross-sectional views of an X-ray mask. FIG. 2 is a diagram showing a cleaning-exposure-storage cycle of a conventionally used photomask. FIG. 3 is a sectional view showing a mask with a pellicle. In the figure, 12 is a sublimable protective film, 13 is a contaminant, and 14 is a sublimable protective film.
15 indicates no irradiation of heat or light energy, and 15 indicates no suction or discharge.

Claims (4)

[Claims] (1) An X-ray mask cleaning method for removing impurities on an X-ray mask, which includes a step of applying a sublimable protective film on the X-ray mask immediately after exposure, and a step of removing the protective film together with the impurities. A method for cleaning an X-ray mask, comprising the steps of: (2) The method for cleaning an X-ray mask according to claim 1, wherein the sublimable protective film is a naphthalene film. (3) The applied protective film is removed by irradiation with heat or light energy, and the gas generated by sublimation is sucked and discharged together with impurities.
Method for cleaning an X-ray mask as described in Section 1. (4) The method for cleaning an X-ray mask according to claim 1 or 2, wherein a protective film-soluble solvent is sprayed onto the applied protective film, and then the impurities are peeled off and removed together with the impurities.