JPH0350522Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to the structure of a photomask.

As is well known, a photomask is used for patterning semiconductor elements.

FIG. 1 shows one of the steps. 1 is a silicon wafer, the upper surface of which is coated with photoresist 2; 3 is a photomask, which has a desired pattern formed on a glass substrate.
The pattern has transparent parts and opaque parts arranged appropriately depending on its shape. 4 is the light source, usually 3650 ~
A xenon lamp is used that emits light with a wavelength of 4358A°. There are three ways to arrange the wafer 1 and the photomask 3: a contact printing method in which the two are placed in complete contact with each other, a proximity printing method in which the two are set apart by several microns to several tens of microns, and a gap printing method in which the two are set with a sufficient separation between them. There is a project print method. In either method, the pattern of the photomask 3 is projected onto the wafer 1 by the light source 4, the resist 2 is exposed to light, and then a pattern of the same type as the pattern of the photomask 3 is formed on the wafer 1 through a resist etching process and a wafer etching process. . Now, the structure of a conventional photomask is shown in FIG. The photomask 3 has a pattern 3b formed on one surface of a glass substrate 3a serving as a transparent substrate. Pattern 3b is transparent part 3
b-1 and an opaque portion 3b-2. Transparent part 3b
-1 sufficiently transmits the light from the light source 4, but the opaque part 3
b-2 does not transmit light. Therefore, the opaque part 3b
-2 is provided by forming, for example, a chromium layer or a chromium oxide layer on the glass substrate 3a. The manufacturing process of such a photomask will be briefly described.
The transparent substrate that serves as the base of a photomask is usually made of soda glass, but the surface of soda glass is not flat but wavy during the manufacturing process. In order to make the wavy shape flat, both sides are removed by a technique called lapping or sanding to obtain a glass substrate with a thickness of 1.5 to 1.6 mm or 2.3 mm. At this point, the surface of the glass substrate is rough but has a so-called ground glass appearance, so polishing is performed. The purpose of this is to make the surface of a glass substrate mirror-finished, and polishing is performed by sandwiching polishing cloths from both sides and supplying water and an abrasive material (for example, cerium oxide) between them. This is done by making the surface of the glass substrate look like water glass, rather than by cutting it to create a mirror surface. Next, a chromium layer is applied to the entire surface of the
A chromium oxide layer is formed and removed by etching according to a desired pattern to form a transparent portion, thereby forming a pattern consisting of a combination of transparent portions and opaque portions. Now, the problem here is in the polishing process, which is intended to create a mirror finish, but because abrasives are used, the surface of the glass substrate may have so-called scratches in lines. or a circular protrusion called a pit. If such defects are left as is and used as a photomask, the light may be bent within the photomask, or reflected diffusely at the scratches or pits, resulting in the exposed area not being the same as the desired pattern, or the resist may be damaged. This results in insufficient exposure to light, resulting in a decrease in the yield of semiconductor devices. Such defects, especially scratches, may also occur during handling during use of the photomask, and once a defective glass substrate or photomask has occurred, it is simply discarded, which is extremely uneconomical. In particular, photomasks using quartz or saphire as a base are expensive, further aggravating the above-mentioned drawbacks. The present invention provides a photomask that eliminates such drawbacks, and is a photomask that has a mask pattern on one side of a glass substrate, in which the unevenness of the glass substrate is substantially removed. This is achieved by providing a coated glass layer that can be seen as FIG. 3 is a sectional view showing a photomask according to the present invention. 31 is a glass substrate as a transparent substrate, 32 is a glass layer provided on both sides of the glass substrate 31, and 33 is a mask pattern. Glass substrate 3
1 is manufactured through wrapping to make it flat and polishing to make it mirror like the conventional example. and,
Glass layer 32 is formed as follows. That is, when the mirrored glass substrate 31 is rotated at high speed, silica glass is dissolved in an organic solvent to form a liquid, and when it is dotted onto the surface of the glass substrate 31, the silica glass is applied to the surface with a uniform thickness. will be done. At this time, a desired value can be selected for the thickness of the glass layer depending on the viscosity of the silica glass, the rotation speed of the glass substrate 31, etc. (This process is called spin coating) After that, heat treatment is performed, dehydration, and oxidation are performed to form the glass layer 32. After the formation of the glass layer 32 on one surface is completed, a glass layer is similarly formed on the other surface.

Note that the present invention is not limited to forming the glass layer after mirror polishing, and the mirror polishing step may be omitted and the glass layer 32 may be directly formed after flattening. This glass layer 32
Even if there are scratches 34 and pits 35 on the surface of the glass substrate, it is applied and formed to cover them, so it can be considered that the scratches and pits have been substantially removed from the glass substrate. can. The pattern 33 is manufactured in exactly the same manner as in the prior art, with the transparent portion 33a being left as is, and the opaque portion 33b being formed with a chromium layer or a chromium oxide layer by etching or the like. In this way, if a scratch occurs on the completed photomask during use, the photomask can be made reusable through the following steps. Now, assuming that a scratch occurs on the pattern side of the photomask, the opaque area 33
The chromium layer and chromium oxide layer of b are removed. Thereafter, by forming another glass layer on the glass layer 32 using the spin coating method in the same manner as described above, the scratches mentioned above can be substantially removed.

As described above, the present invention not only makes it possible to eliminate the step of mirror-finishing the transparent substrate, but also makes it possible to use the photomask because even if there are scratches on the photomask, the scratches can be removed by the glass layer. Therefore,
It becomes possible to shorten the manufacturing time of a photomask and eliminate the uneconomical effects of the conventional method.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the positional relationship between a wafer, a photomask, and a light source, Fig. 2 is a sectional view of a conventional photomask, and Fig. 3 is a sectional view of a photomask according to the present invention. 32 is a glass layer, and 33 is a mask pattern.

Claims (1)

[Claims for Utility Model Registration] A photomask with a mask pattern on one side of a glass substrate, a glass layer coated on the glass substrate so that it can be considered that the unevenness of the glass substrate has been substantially removed. A photomask characterized by being provided with.