JPS6341855A - Dry cleaning method for photomask - Google Patents

Abstract

PURPOSE:To execute dry cleaning without damaging a mask by spin-coating a sublimatic organic protection film on the surface of a mask immediately after exposure and sublimating the protection film immediately before the succeeding exposure. CONSTITUTION:A naphthalene isopropyl alcohol solution is dropped on the surface of a mask substrate 1 free from dust to spin-coat a naphthalene protection film 4 with 500-200,000Angstrom thickness and the mask is stored under a condition that the protection film 4 does not disappears due to sublimation. Immediately before exposure, the mask is set up vertically downward in a dry cleaning device, the back of the substrate 1 is heated up to 40-80 deg.C by a heater 6 and evacuated to <=10<-3>Torr for 5-30min to remove the protection film 4 and dust 5 on the film 4. The film 4 and dust 5 can be similarly removed by evacuating to <=10<-3>Torr while radiating UV light 8 from a Hg lamp. The removing speed is increased by simultaneously executing the heating based upon the heater 6 and UV light 8 radiation based upon the Hg lamp. The removing speed is also increased by rotating the mask substrate 1 at 100-6,000rpm speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for cleaning a photomask used in a manufacturing process of a semiconductor device.

[Conventional technology]

In the manufacture of semiconductor devices, several masks are required for each device, and if dust adheres to the mask, it will be transferred to the wafer 1 as a defect during exposure. Therefore,
It is important to have a cleaning method that eliminates all dust on the mask. As a conventional cleaning method, washing with water is mainly used. This water washing method includes (a) spraying high-pressure pure water, (b)
l Scrub cleaning with detergent cloth or brush, tc)
! This includes sonic cleaning.

FIG. 3 is a diagram showing the above-mentioned water washing method. In the diagram, 1 is the mask i+, 2 is a pattern made of Cr, 3 is pure water, and 5 is dust.

As shown in FIG. 3(a), a lot of dust 5 adheres to the mask during storage. Therefore, it is necessary to clean this mask, but usually while rotating the mask,
As shown in Figure 3, it is washed by spraying pure water 3, and then dried at high speed while being irradiated with an infrared lamp. After drying, it is attached to an exposure device, exposed, and stored again. If the dirt is severe, scrub it with gauze containing detergent (mama lemon water).

In addition to the water washing method, there is also a method of attaching a protective film pellicle 7 to the mask to prevent dust 5 from directly adhering to the mask substrate 1, as shown in FIG.

[Problem that the invention seeks to solve]

As semiconductor devices become more highly integrated, patterns on masks become finer and are transferred using exposure equipment with high resolution. As resolution improves, even finer dust particles begin to affect transfer. However, the van der Waals force increases with fine dust, making it difficult to remove the dust once adsorbed by washing with pure water alone. Therefore, if you try to forcefully remove the mask material (Cr, M) by scrubbing.

There were problems such as easy peeling of the sL (sl) and the occurrence of other defects.

Further, the method using a pellicle has problems such that the pellicle is expensive and it is difficult to attach the pellicle to a mask from which dust has been completely removed.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for dry cleaning a photomask, which allows dry cleaning to be performed without damaging the mask.

[Means for solving problems]

The dry cleaning method for a photomask according to the present invention includes spin coating a sublimable organic protective film on the mask immediately after exposure, and sublimating and removing the protective film by irradiating the mask with heat or light energy immediately before exposure. It is something.

[Effect]

The sublimable organic protective film of the present invention prevents dust from directly adhering to the mask substrate, and simultaneously removes dust adhering to the protective film through sublimation.

〔Example〕

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

FIG. 1 is a diagram showing a cleaning method according to an embodiment of the present invention. First, before transporting the mask to the exposure device 12, the mask with a protective film is attached to the dry cleaning device 11, and UV light (
Dry cleaning was performed by evacuation using a pump while irradiating the substrate with ultraviolet light or heating the substrate. After cleaning, the mask was transported to the exposure device 12 and exposed. After the exposure was completed, the mask was transferred to the protective film coating device 13, and a protective film was coated with a spin cord. In this method, the dry cleaning device 11 and the protective film coating device 13 are separated, but the same device may have two functions.

FIG. 2 is a diagram showing the process steps of the present invention.

An isopropyl alcohol solution of naphthalene was dropped onto a dust-free mask substrate 1, and a naphthalene protective film 4 of 500 to 200,000 layers was spin-coded (see Fig. 2).
)), and the mask was stored under conditions that would prevent the protective film 4 from sublimating and disappearing (Figure 2)). Immediately before exposure, this mask is installed vertically downward in a dry cleaning device, and the back surface of the substrate 1 is heated to 40 to 80°C with a heater 6.
Evacuate at 10-' Torr or less for 0 minutes and remove the protective film 4.
and the garbage 5 on it were removed. In addition, the UV of the Hg lamp
Even when evacuation was carried out at 10 −3 Torr or less while irradiating the light 8, the same removal was possible. Furthermore, the removal speed was increased by simultaneously performing the heating by the heater 6 and the irradiation of the UV light 8 by the Hg lamp. Furthermore, 10 mask substrates
In order to increase the removal speed even when rotating at a speed of 0 to 6,000 rpm, as shown in FIG. 2 (C1), the dry-cleaned mask is then conveyed to the exposure device 12 shown in FIG. 1 and exposed. After that, the naphthalene protective film was spin-coded again.

In the above example, naphthalene was spin-coded, but a similar protective effect could be obtained by spin-coding camphor (Clo H + h O). However, since camphor tends to sublimate, it was preferable to store it at as low a temperature as possible. Heating during removal was possible up to about 160°C.

Furthermore, in the above embodiment, a Cr mask was described, but M
Even if a mask with an o S iz pattern is used, naphthalene and camphor can be used as a protective film without reacting with M o S t 1.

〔Effect of the invention〕

As described above, according to the dry cleaning method for a photomask according to the present invention, a protective film is formed using a sublimable organic substance,
Since dust is removed by sublimation, complete dry cleaning is possible, the system is inexpensive, and the pattern on the mask substrate does not peel off due to cleaning.
This has the effect of increasing the durability of the mask.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a dry cleaning method for a photomask according to an embodiment of the present invention, FIG. 2 is a process sectional view showing the method of the above-mentioned embodiment, and FIG. 3 is a sectional diagram showing the process of a conventional water rinsing method. FIG. 4 is a sectional view showing a method using a conventional pellicle. 1 is a mask substrate, 2 is a pattern made of Cr, 3 is pure water for cleaning, 4 is a protective film, 5 is dust, 6 is a heater, 7 is a speckled film, and 8 is light. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In a dry cleaning method for photomasks used in the manufacture of semiconductor devices, there is a step of applying a sublimable organic thin film to the photomask immediately after it is used for exposure, and a step of applying light energy to the photomask immediately before it is used for exposure again. Alternatively, a dry cleaning method for a photomask comprising a step of irradiating thermal energy to sublimate and remove the organic thin film. (2) The dry cleaning method for a photomask according to claim 1, wherein the sublimable organic thin film is made of naphthalene or camphor.