PROCESS FOR MANUFACTURING A PHOTOMASK

Abstract: A photomask manufacturing process including a step of forming metal silicide film (4) on a transparent silica glass substrate (1). A resist (3) is applied onto the metal silicide film (4) and then a patterning mask is provided by light or electron beam, followed by developing step. Exposed por­ tions of the metal silicide film is etched away using a dry etching process.

Description: The present invention relates to a photomask and a process for manufacturing a photomask and, more particularly, to a photomask and process for manufacturing thereof for use with the manufacture of a semiconductor device. Figs. 1A to 1D show steps of a conventional photomask manufacturing process. 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 an evaporation process, sputtering process or the like, with a thickness of 800-1000Å. Then, as shown in Fig. 1B, a resist 3 is applied onto the metal mask material 2, a desired pattern is drawn thereon by light or an electron beam followed by a developing process, so that a resist pattern is thereby formed. Thereafter, as shown in Fig. 1C, an exposed portion of the metal mask material 2 is etched away by a gas plasma process or the like and then the resist pattern is removed, so that a photomask (a hard mask), is formed as shown in Fig. 1D. Previously, a mask used for manufacturing a semiconductor device included a photographic emulsion dry plate using a transparent glass substrate. However, with advance of high integration and high resolution, 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 the lifetime of the mask becomes greater. However, at the same time, an etching technique of a metal mask material 2 of a hard mask such as chromium is important. In the 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 (IV) nitrate and perchloric acid is employed. On the other hand, with advances in techniques for refining 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, the chromium is etched by glow-discharging a mixed gas containing a halogen element such as chlorine and oxygen, the reaction being as follows; Cr + 2O + 2Cl→ CrO₂Cl₂ As described in the foregoing, a hard mask of chromium or the like is advantageous for forming a fine pattern, while there is a disadvantage that the rate of etching, particularly with dry etching using a gas plasma, is low. More particularly, in case of chromium, the etching rate is about 100Å/min (0.17nm/sec) in conditions of 300W and 0.2torr, and 8-10 minutes (480-600sec) of etching time is required (in the case of a 800-1000Å thickness). In addition, reduction in the thickness of the resist film due to the longer time required for etching is also a problem. Japanese Patent Application No. 42176/1981, filed March 23, 1981 and laid open for public inspection September 28, 1982 and Japanese Patent Application No. 42183/1981, filed March 23, 1981 and laid open for public inspection September 28, 1982 disclose a system where 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. Accordingly, it would be desirable to eliminate the above-described defects and to provide a photomask which can be easily etched by dry etching, and a process of manufacturing such a photomask involving such dry etching. Accordingly, the present invention provides a method defined by claim 1 hereinbelow. In such a process the etching rate of the mask material is increased and a good adhesion between the mask material and the substrate is obtained, because a metal silicide film is used as a metal mask material for forming a mask pattern. In a preferred embodiment the transparent glass substrate is a silica glass substrate and the metal silicide film is a thin film of about 1000Å in thickness. These features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. Figs. 1A through 1D are drawings for explaining a conventional process of manufacturing a photomask; and Figs. 2A to 2D are drawings for explaining a process of manufacturing a photomask of the present invention. 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 metal silicide film 4 is formed on the transparent glass substrate 1, with about 1000Å in thickness, using a sputtering process or electron beam and the like in which metal such as molybdenum (Mo), tungsten (W) and the like are used as a target. Then, referring to Fig. 2B, a resist 3 is applied onto the metal silicide film 4. Thereafter, a desired pattern is drawn by light or electron beam so that a resist pattern is formed, as shown in Fig. 2C. Then, following the processes of development and baking, the exposed portion of metal silicide film 4 is etched away using a dry etching process and then the resist pattern is removed, so that a mask pattern of a metal silicide is formed, completing the formation of a photomask for use in a process of a semiconductor device. Use of metal silicide film 4 as a mask material permits the provision of a 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 photoresist or an electron beam resist onto the transparent glass substrate 1 with thickness of 4000-6000Å, a value of resistance of the metal silicide film 4 is about 1KΩ 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 a metal silicide film 4 of molybdenum (Mo), an etching rate of about 500-1000Å/min is obtained, with a mixed gas of CF₄ + O₂ (2%), vacuum of 0.2torr and 300W, 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 silicon (Si) as a main constituent element, the film 4 has characteristics in common with a silica substrate including SiO₂, Al₂O₃ or the like and hence there is no problem of the mask pattern being stripped from the substrate, and a photomask with high reliability is therefor produced. As described in the foregoing, a transparent glass substrate such as a 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.

Claims: A method of making a photomask, in which a film (4) is formed on a transparent substrate (1), a resist (3) is applied on the film (4) and patterned in accordance with a mask pattern, and the portions of the film (4) exposed by the patterning of the resist (3) are etched by a dry etching process, characterised in that the film (4) is a metal silicide film. A method according to claim 1 in which the substrate (1) is a glass substrate. A method according to claim 1 or claim 2 in which the dry etching process is a gas plasma etching process. A method of making a photomask according to any one of claims 1 to 3, wherein said metal silicide film is a thin film of about 1000Å in thickness. A photomask made by a method according to any one of claims 1 to 4.

Inventors: MATSUDA, SHUICHI, OKAMOTO, TATSUO MITSUBISHI DENKI K. K. LSI, WATAKABE, YAICHIRO MITSUBISHI DENKI K. K. LSI
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1986
Main classification: G03F1
IPC codes: G03F1, H01L21