Process for manufacturing a photomask

A photomask manufacturing process including step of forming on a transparent silica glass substrate a silicide film in which an alloy comprising two or more metal elements is silicidized. A resist is applied onto the silicide film and then a patterning mask is provided by light or electron beam, followed by developing step. Exposed portion of the silicide film is etched away using a dry etching process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for manufacturing a photomask 
and, more particularly, to a process for manufacturing a photomask for use 
with manufacture of a semiconductor device. 
2. Description of the Prior Art 
FIGS. 1A to 1D show sequential steps of a conventional photomask 
manufacturing process. First of all, a conventional process of 
manufacturing a photomask will be described with reference to FIGS. 1A to 
1D. First, as shown in FIG. 1A, a transparent glass substrate 1 is 
prepared and then a metal mask material 2 such as chromium is formed on 
the transparent glass substrate 1 by means of evaporation process, 
sputtering process or the like, with a thickness of 800-1000.ANG.. Then, 
as shown in FIG. 1B, a resist 3 is applied onto the metal mask material 2, 
a desired pattern is drawn by light or electron beam and then developing 
process is achieved, so that a resist pattern can be formed. Thereafter, 
as shown in FIG. 1C, exposed portion of the metal mask material 2 such as 
chromium is etched away by a gas plasma process and the like and then the 
resist pattern is removed, so that a photomask called a hard mask, is 
formed as shown in FIG. 1D. 
In an earlier time, a mask used for manufacturing a semiconductor device 
included a photography emulsion dry plate using a transparent glass 
substrate. However, with advance of high integration and fining, a hard 
mask including a transparent glass substrate and a metal film such as 
chromium formed on the glass substrate has been widely used. More 
particularly, in case of a hard mask such as chromium, a thinner film of 
chromium can be used, as compared with a conventional emulsion mask and 
hence it becomes possible to obtain a finer pattern and lifetime of mask 
becomes longer. 
However, at the same time, an etching technique of a metal mask material 2 
of a hard mask such as chromium is important. In a case where a metal film 
is made of chromium, a wet chemical etching process is generally used, in 
which a mixture solution of ammonium cerium (V) nitrate and perchloric 
acid is employed. On the other hand, with advance of technique for fining 
a pattern, a dry etching technique has been developed and utilized, in 
which a gas plasma or reactive ion etching is employed. In case of a 
plasma etching of chromium, a chromium is etched by glow-discharging a 
mixed gas containing a halogen element such as chlorine and oxygen, with 
the reaction being considered as follows; 
EQU Cr+20+2Cl.fwdarw.CrO.sub.2 Cl.sub.2 
As described in the foregoing, a hard mask of chromium and the like is 
advantageous for forming a fine pattern, while there is a disadvantage 
that a rate of etching, particularly a dry etching using a gas plasma, is 
low. More particularly, in case of chromium, the etching rate is about 
100.ANG./min is a condition of 300W and 0.2 Torr and 8-10 minutes of 
etching time is required (in case of 800-1000.ANG. in thickness). In 
addition, reduction of thickness of resist film due to a longer time 
required for etching is also a problem. 
Incidentally, Japanese patent application No. 42176/1981, filed Mar. 23, 
1981 and laid open for public inspection Sept. 28, 1982 and Japanese 
patent application No. 42183/1981, filed Mar. 23, 1981 and laid open for 
public inspection Sept. 28, 1982 disclose that a silicon layer and a metal 
layer are deposited on a glass substrate so that a pattern of silicide is 
formed by an electron beam. 
SUMMARY OF THE INVENTION 
Accordingly, a principal object of the present invention is to eliminate 
the above described defects and to provide a process of manufacturing a 
photomask which can be easily etched by a dry etching. 
Briefly stated, the present invention is directed to a process for 
manufacturing a photomask comprising the steps of preparing a transparent 
glass substrate, forming on the transparent glass substrate a silicide 
film in which an alloy comprising two or more metal elements is 
silicidized, applying a resist on the silicide film, providing a mask 
pattern by light or electron beam and developing the pattern so that some 
portion of the applied resist can be removed, and etching away the exposed 
portion of the silicide film by means of dry etching process. 
According to the present invention, an etching rate of mask material 
becomes larger and a good joining ability between the mask material and a 
substrate can be obtained, because a silicide film in which an alloy 
comprising two or more metal elements is silicidized is used as a mask 
material for forming a mask pattern. 
According to a preferred embodiment of the present invention, the 
transparent glass substrate is a silica glass substrate and the alloy for 
silicide film is titanium-molybdenum or titanium-molybdenum-tungsten. 
These objects and other objects, features, aspects and advantages or the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 2A to 2D are cross sectional views showing a process of manufacturing 
a photomask of one embodiment of the present invention. First of all, 
referring to FIG. 2A, a transparent glass substrate 1, such as a silica 
glass, is prepared and then a silicide film 4 in which an alloy of 
molybdenum (Mo) - titanium (Ti) or an alloy of molybdenum (Mo) - titanium 
(Ti) - tungsten (W) is silicidized is formed on the transparent glass 
substrate 1, with about 1000.ANG. in thickness, using a sputtering process 
of electron beam and the like in which molybdenum and titanium or 
molybdenum, titanium and tungsten are used as a target. Then, referring to 
FIG. 2B, a resist 3 is applied onto the silicide film 4. Thereafter, a 
desired pattern is drawn by light or electron beam so that a resist 
pattern 3 is formed, as shown in FIG. 2C. Then, following the processes of 
development and baking, the exposed portion of the silicide 4 is etched 
away using dry etching process and then the resist pattern 3 is removed, 
so that a mask pattern of an alloy silicide is formed, completing the 
formation of a photomask for use in a process of a semiconductor device. 
FIG. 3 is a schematic diagram showing a direct current two-polarity type of 
sputtering apparatus which may be used for manufacturing a photomask of 
the present invention. In this apparatus, a negative voltage of -2 to -5kV 
is applied to a cathode electrode which is a target, while argon with 
10.sup.-2 Torr is being applied. As a result, a glow-discharge occurs in a 
chamber and a positive ions in the plasma are accelerated by a strong 
electric field in a dark portion in front of the cathode to bombard the 
cathode so that atoms are removed from the target. These atoms deposit on 
the surface of the substrate so that a thin film can be formed on the 
substrate. Apart from the above described sputtering process, a high 
frequency sputtering process is also well known in which a plasma is 
generated by using a high frequency. At any rate, in these sputtering 
process, molybdenum and titanium or molybenum, titanium and tungsten are 
used as a target in accordance with the present invention. 
Use of metal (alloy) silicide film 4 as a mask material permits the 
provision of photomask with a good quality, since a dry etching process 
can be easily used and joining ability between a transparent glass 
substrate 1 and a mask material increases. In case where a pattern is 
drawn by light or electron beam after application of a photo resist or an 
electron beam resist onto the transparent glass substrate 1 with thickness 
of 4000-6000.ANG., a value of resistance of the metal (alloy) silicide 
film 4 is about 100 Ohms and hence there is no charge up phenomenon in an 
electron beam drawing. A dry etching process is applied more easily to the 
metal silicide film 4, as compared with a chromium film. For example, in 
case of metal (alloy) silicide film 4 of molybdenum (Mo) and titanium 
(Ti), an etching rate of about 500-1000.ANG./min is obtained, with a mixed 
gas of CF.sub.4 +O.sub.2 (2%), vacuum of 0.3 Torr and 300 W, which rate is 
about 5 to 10 times the conventional dry etching rate for chromium film. 
This sufficiently meets requirement of mass production and to that end, 
size control can be made easier. 
In addition, since the metal silicide film 4 contains a silicon (Si) as a 
main constituent element, the film 4 is much familiar with a silica 
substrate including SiO.sub.2, Al.sub.2 O.sub.3 or the like and hence 
there is no problem in which mask pattern is stripped off the substrate, 
which can produce a photomask with high reliability. 
As described in the foregoing, according to the present invention, a 
transparent glass substrate such as silica glass is used and a metal 
silicide film is formed on the transparent substrate, so that a dry 
etching process can be used with ease, whereby mass production of 
photomask with high accuracy and high reliability becomes possible. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.