JPS6381354A - Photomask - Google Patents

Abstract

PURPOSE:To prevent a defective wafer due to the transfer of the shadow of a flaw or a foreign matters from being manufactured, by covering the rear plane of a photomask substrate with a protecting film. CONSTITUTION:A light shielding film by a chrome is formed over the entire surface of a prescribed quadrangular fused quartz consisting of a reticle substrate 2, by evaporation or sputtering. Nearly at a time when the light shielding film is formed, a transparent protecting film 5 is formed on a plane on the opposite side of the forming plane of the light shielding film, that is the plane which forms the rear plane side of the reticle. In this way, it is possible to prevent the flaw on the rear plane of a photomask from being generated in the process of manufacturing the photomask, and to remove the foreign matters attached on the rear plane side by peeling the protecting film just before an exposure process, and as result, the defective wafer due to the transfer of the shadow of the flaw or the foreign matters can be prevented from being manufactured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a technology that is effective when used in photomasks for forming resist patterns on semiconductor wafers (hereinafter simply referred to as "wafers") in the manufacture of semiconductor devices. It is related to.

[Conventional technology]

Regarding the exposure technique using a photomask, for example, there is "Electronic Materials 1985 Separate Volume, VLSI Manufacturing/Testing Equipment Guidebook" published by Kogyo Kenkyukai Co., Ltd., November 20, 1985, pages 95 to 102. Various exposure techniques are introduced here.

The present inventor has studied photomasks used in the above exposure technique. Note that, unless otherwise noted, the word photomask includes a so-called reticle for predetermined reduction exposure as well as one for 1:1 isostatic exposure.

Although the following is not a publicly known technique, it is a technique studied by the present inventor, and its outline is as follows.

That is, in the projection exposure process, it is known that a predetermined circuit pattern is transferred onto a resist film on a wafer using a light-shielding film such as chromium (Cr) on a transparent quartz substrate to form a predetermined resist pattern. .

By the way, in the photomask manufacturing process, first - a transparent mask substrate with a light-shielding film coated on the entire main surface is coated with
It is known that a photomask is manufactured by drawing a predetermined shape using means such as an electron beam, and then performing baking, visual inspection, and the like.

Between each processing step of such photomask manufacturing, the back side of the mask substrate is transferred while being sucked with a vacuum chuck, or the back side of the mask substrate is placed in contact with the stage surface of the processing stage. It is possible to do this.

Since the back side of the photomask is often in contact with devices and the like, there is a higher possibility of foreign matter adhering to the back side of the photomask than on the front side, which increases the probability of scratches.

Therefore, in order to reduce the effect of such scratches on the back side, the thickness of the mask substrate is increased so that the scratches on the back side are defocused during transfer to the wafer. The idea is to prevent the effects.

[Problem that the invention seeks to solve]

However, as semiconductor devices become more highly integrated and circuit patterns on photomasks become finer, even finer shadows are often transferred to wafers during exposure equipment.

For this reason, even if the thickness of the quartz glass plate is increased as described above, if the depth of the scratch on the back side exceeds a certain value, it will be transferred as a shadow on the wafer, which is one of the causes of surface cracks. The inventor has revealed that

Particularly, when this photomask is a reticle for reduction projection exposure, all the circuit sections formed on the wafer are often defective, and the occurrence of scratches on the back side of the photomask is a big problem.

Furthermore, the inventors have also discovered that scratches on the back side of the mask substrate are difficult to detect during visual inspection when the photomask is completed, and that mask defects are often discovered only after the wafer is exposed. .

The present invention has been made focusing on the above problems,
The purpose is to realize a highly reliable photolithography process.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a protective film is attached to the back side of the photomask substrate.

[Effect]

According to the above-mentioned means, it is possible to prevent scratches on the back side of the photomask during the photomask manufacturing stage due to the action of the protective film attached to the back side, and by peeling off this protective film just before the exposure process, the back side It is also possible to remove foreign matter, and as a result, it is possible to prevent splatter defects caused by scratches or transfer of shadows of foreign matter, and to realize a highly reliable photolithography process.

〔Example〕

FIG. 1 is a schematic sectional view of a reticle according to an embodiment of the present invention, and FIG. 2 is a perspective view of this reticle.

The photomask of this example is a so-called reticle l,
The circuit pattern 3 formed on the surface of the reticle substrate 2 (transparent substrate) is placed on a wafer (not shown) at lo:1, for example.
This is because it is transferred at a reduction rate of .

The reticle substrate 2 is a transparent substrate made of, for example, quartz glass, and on the surface of the reticle substrate 2, a circuit pattern 3 is formed by processing a chromium (C'') film into a predetermined shape in the central portion thereof. A left portion 4 is formed around the entire area.

On the other hand, on the back side of the reticle substrate 2, a transparent protective film 5 made of, for example, polyimide resin is adhered.

The reticle 1 having such a structure is formed, for example, as follows.

First, a light-shielding film of chromium is formed over the entire surface of a predetermined rectangular quartz glass constituting the reticle substrate 2 by means such as vapor deposition or sputtering.

Before and after the formation of this light-shielding film, a transparent protective film 5 is formed on the surface opposite to the surface on which the light-shielding film is formed, that is, on the surface that will be the back side of the reticle.

The transparent protective film 5 is formed by, for example, placing the reticle substrate 2 on a rotating stage (not shown) and dropping a predetermined amount of molten polyimide resin onto the center of the rotating reticle substrate 2. The polyimide resin dropped in this way spreads over the entire surface of the reticle substrate 2 by centrifugal force, forming a transparent protective film with a uniform thickness.

In this way, a light-shielding film is formed on one surface of the reticle substrate 2, and a transparent protective film 5 is formed on the entire surface of the reticle substrate 2, respectively.

Next, a resist material made of polymer or the like is applied onto the light shielding film. When applying this resist material, it is necessary to form a uniform resist layer over the entire surface by spin coating or the like, similar to the formation of the transparent protective film 5 described above.

An electron beam of a predetermined wavelength is irradiated onto the resist layer thus formed along a predetermined shape. As the electron beam irradiates, the characteristics of the resist layer in the irradiated portion are chemically changed.

Next, for example, the resist material in the area where this chemical change has occurred is removed, exposing the light-shielding film below the resist layer in a predetermined shape, and the exposed area of the light-shielding film is etched away, and then the layer underneath it is etched away. The surface of the reticle substrate 2 becomes exposed.

Finally, all the resist material is removed and a circuit pattern 3 of a predetermined shape is formed on the reticle substrate 2.

Incidentally, in the manufacturing process of the reticle 1, the reticle substrate 2 is sequentially transferred to an electron beam drawing device, a resist coating device or a cleaning device, an appearance inspection device, etc., and the reticle 1 is manufactured. At this time, the back side of the reticle substrate 2 comes into contact with a handling device, a vacuum chuck, etc., and if there is a foreign object between these device parts and the back side of the reticle substrate 2, this foreign object may damage the back side of the reticle substrate 2. may cause scratches. This is a problem that often occurs especially in visual inspection equipment, etc., which are not maintained at a high level of cleanliness.

However, according to this embodiment, since the transparent protective film 5 made of polyimide resin as described above is adhered to the back side of the reticle substrate 2, the elasticity of the transparent protective film 50 causes direct scratches on the back surface of the reticle substrate 2. is prevented from occurring.

Further, although foreign matter may adhere to the surface of the transparent protective film 5, such foreign matter is also removed when the transparent protective film 5 is peeled off, so that the back surface of the reticle substrate 2 is kept in a highly clean state. .

Therefore, it is desirable that such transparent protective film 5 be peeled off, for example, immediately before performing an exposure process using this reticle 1. At this time, the transparent protective film 5 is attached to the reticle substrate 2.
As for the method of peeling off the film, it is possible to physically peel it off, but it is also possible to perform chemical removal using a predetermined reactive gas.

As described above, according to this embodiment, the following effects can be obtained.

(1) By coating the transparent protective film 5 on the back surface of the reticle substrate 2, it is possible to prevent scratches from occurring on the back surface side of the reticle substrate 5 during the reticle manufacturing process, which would otherwise be caused by the transfer of such scratches. Wafer defects can be prevented.

(2) According to (1) above, by removing the transparent protective film 5 immediately before the exposure process, it is possible to remove foreign matter on the back side of the reticle substrate 2, and it is also possible to prevent splatter defects due to transfer of shadows of foreign matter. .

(3), due to (1) and (2) above, highly reliable e)
Since it is possible to realize the IJ sogelahue level, it is possible to improve the yield of wafers.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. Nor.

For example, although a case has been described in which the transparent protective film 5 is made of polyimide resin, any protective film may be used as long as it can withstand processing temperatures during processes and has characteristics that allow it to be easily peeled and removed.

Furthermore, although the reticle substrate 2 has been described as being made of quartz, it may be any transparent substrate made of low expansion glass or the like.

In the above description, the invention made by the present inventor was mainly applied to a reticle I for reduction projection exposure, which is the field of application of the invention, but the invention is not limited to this, for example, 1:1 etc. It can also be applied to photomasks for optical use.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, a transparent substrate having a predetermined thickness, a light-shielding circuit pattern formed in a predetermined shape on one main surface of the transparent substrate, and a light-shielding circuit pattern attached to at least the main surface of the transparent substrate opposite to the light-shielding circuit pattern. By creating a photomask structure consisting of a protective film, it is possible to prevent scratches on the back side of the photomask during the photomask manufacturing stage, and this protective film is removed immediately before the exposure process.
By separating M, it is also possible to remove foreign matter on the back side, and as a result, it is possible to prevent scratches or scratches caused by the transfer of shadows of foreign matter, and to achieve highly reliable IJ soger cleaning.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic cross-sectional view of a reticle according to an embodiment of the present invention. 1 is a perspective view showing the entire reticle of this embodiment. 1... Reticle (photomask), 2... Reticle substrate (transparent substrate), 3... Light shielding circuit pattern, 4...
Left part, 5...Transparent protective film (protective film).

Claims (1)

[Claims] 1. A transparent substrate, a light-shielding circuit pattern formed in a predetermined shape on one main surface of the transparent substrate, and a protective film deposited on at least the surface opposite to the light-shielding circuit pattern. A photomask consisting of 2. The photomask according to claim 1, wherein the transparent substrate is made of quartz glass, and the protective film is a transparent film made of polyimide resin.