GB1577479A

GB1577479A - Optical exposure apparatus

Info

Publication number: GB1577479A
Application number: GB40537/77A
Authority: GB
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1976-10-07
Filing date: 1977-09-29
Publication date: 1980-10-22
Also published as: DE2744837A1; NL7710996A; CA1070855A

Abstract

A mask for optical exposure including a transparent supporting plate, a transparent conformable film having a predetermined opaque pattern formed thereon, and a penetrating hole formed through the transparent supporting plate, in which the transparent conformable film is attached to the transparent supporting plate so that a gas-tight space is formed between them, and the external of the transparent supporting plate is communicated with the gas-tight space through the penetrating hole.

Description

(54) OPTICAL EXPOSURE APPARATUS (71) We, SONY CORPORATION, a corporation organised and existing under the laws of Japan, of 7-35 Kitashinagawa-6, Shinagawa-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical exposure apparatus which can be used for example for manufacturing a highly integrated semiconductor device by the technique of deepultraviolet conformable-contact photolithography.

When manufacturing a semiconductor integrated circuit, a photosensitive resin (a photoresist) is coated on a semiconductor substrate (hereinafter called a "wafer") made of silison or the like and a photomask having a predetermined pattern is closely contacted with the photosensitive resin layer. The photosensitive resin is exposed through the photomask and then treated with a developer for the subsequent etching of the wafer.

A known apparatus for the optical exposure process includes a photomask which is a transparent plate made of glass having a thickness of about 1.2mm and having a opaque pattern thereon. Such a photomask has several serious disadvantages. When the photomask is brought into contact with the wafer, a small gap is liable to be formed between them due to the presence of small imperfections of the surface of the wafer, or due to warping of the wafer. Accordingly, the photomask and the wafer cannot be brought into sufficiently close contact with each other, so that it becomes difficult to transfer the fine pattern of the photomask onto the wafer. Particularly in the case where the optical exposure process is done to form a fine pattern on the wafer in a vacuum using ultraviolet rays (deep-UV) having a shorter wave-length than that of ultraviolet rays hitherto used, the above small gap causes deterioration in the accuracy of the photo etching.

To avoid these disadvantages, the conformable-contact method has been proposed (H.L. Smith, N. Efremow and P. L. Kelly "Photolithographic Contact Printing of 4000 Linewidth Patterns", J. Electrochem.

Soc., 121, 1503 (1974); J. Melngailis, H. L.

Smith, and N. Efremow "Instrumentation for Conformable Photomask Lithography", IEEE Trans. Electron Devices ED-22, 496 (1975). These techniques have been briefly explained and further studied (B. J. Lin "Deep-UV Conformable-Contact Photo Lithogtaphy for Bubble Circuits", IBM J.

Res. Develop, may (1976)). In the conformable-contact method, a photomask of a transparent thin film having a thickness of about 0.2 mm is utilized. The photomask and the wafer can be sufficiently closely contacted with each other because the former is elastically deformed corresponding to the uneven surface of the wafer. However, since the photomask is made of thin film, scars are often left therein when the photomask is moved for example to effect mask alignment. For this reason, a special apparatus for the optical exposure is required when using the thin film. In addition to this, it is difficult to separate the mask and the wafer from each other because of the continuing effect of the vacuum between the contacting surfaces after the exposure process.

According to the present invention there is provided an optical exposure apparatus comprising a supporting means for an object to be exposed, a mask for exposure comprising a transparent supporting plate and a transparent film having a predetermined opaque pattern formed thereon, said transparent supporting plate and said transparent film being combined with each other through a ring shaped spacer means located near a periphery of said transparent film so that a first space is formed between them, an elastic ring means on said supporting means being able to be in contact with said transparent supporting plate so that said supporting means, said transparent supporting plate and said elastic ring means form a second space between them surrounding said transparent film, a first penetrating hole formed in said transparent supporting plate which is connected to a first means to control the gas pressure in said first space, a second penetrating hole formed in said supporting means connected to a second means to control the gas pressure in said second space, and an irradiating beam source to expose said object according to said opaque pattern.

Throughout this specification "transparent" means able to pass the beam used for the optical exposure and "opaque" means not able to pass said beam.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of an embodiment of apparatus for optical exposure according to the present invention; and Figure 2 is a cross-sectional view of the apparatus of Figure 1 in use.

As shown in Figure 1, suction holes 2 and 3 to be connected to a vacuum pump (not shown) are formed in a vacuum chuck 1. A ring-shaped elastic member 4 is arranged on the vacuum chuck 1. A semiconductor substrate of wafer 5 is put on the vacuum chuck 1. A photosensitive agent or resin is coated on the upper surface of the wafer 5.

A mask A for optical exposure includes a transparent supporting plate 6 having a thickness of 1.2 mm, a ring 7 disposed on the inner surface of the supporting plate 6, and a transparent conformable film 8 for effecting too actual meshing and having a thickness of 0.2 mm. The ring 7 is fixed to the supporting plate 6, and the film 8 is fixed to the ring 7 by the use of adhesive material.

The ring 7 has a thickness of 0.5Fm to 30 Fm. The ring 7 can be made of a ring-shaped elastic member or an adhesive layer coated between the plate 6 and the film 8. In the latter case, the adhesive layer is coated on the surface of the film 8, and the supporting plate 6 is fixed to the film 8 through the adhesive layer.

A gas-tight space 11 is formed by the supporting plate 6, the film 8 and the ring 7.

The space 11 has a small thickness corresponding to the thickness of the ring 7. When the ring 7 is formed only by the adhesive layer, the thickness of the space 11 or the gap between the plate 6 and the film 8 is smaller compared with the case where the ring 7 is formed by the ring-shaped elastic material. Accordingly, the accuracy of a mask alignment for the wafer 5 can be further improved.

A predetermined pattern is formed on the lower surface 8a of the film 8, that is, on the surface thereof adjacent to the wafer 5. The pattern is made of opaque material. The opaque material can be photographic emulsion or metal such as chromium which also does not allow visible radiation to pass through, or it can be silicon, germanium, metal oxide or material produced by an ion implantation technique which does not allow light from a light source for the optical exposure to pass through. A small penetrating hole 9 is formed through the supporting plate 6 and a pipe 10 is fixed to the supporting plate 6 in connection with the hole 9. The exterior of the supporting plate 6 is in communication with the gas-tight space 11 through the pipe 10 and the hole 9.

The pipe 10 is connected to a vacuum pump (not shown). The transparent plate 6 can be made of glass, quartz, sapphire or the like.

These materials should be suitably selected dependent on the wave-length of beam from the light source. The hole 9 which is formed through the plate 6 from the back surface to the front surface, however, can be modified to penetrate through the plate 6 from the back surface to the lateral side surface.

Next, the operation of the apparatus described above will be explained.

The wafer 5 is first put on a given part of the chuck 1 and is then drawn by the vacuum through the suction on hole 2 to be held on the chuck 1 as shown in Figure 1.

Air contained in the space 11 is discharged through the hole 9 and the pipe 10 by the vacuum pump so that the space 11 is put in a state of reduced pressure. The supporting plate 6 is lowered down in place on the elastic member 4 as shown in Figure 2. The supporting plate 6 is then slightly moved and adjusted to align the film 8 with the wafer 5 or to set the film 8 on a predetermined part of the wafer 5. Because the pressure in the space 11 is already reduced at that time, the film 8 is elastically deformed to be curved slightly upward as shown by the dot-dash line in Figure 2. When the ring 7 is made of elastic material, it is also elastically deformed to be compressed under the reduced pressure of the space 11, so that the film 8 approaches the supporting plate 6 as a whole. As a result of the above deformation of the film 8, the lower surface 8a or the pattern thereof is not contacted with the wafer 5. Therefore, the pattern of the film 8 and the photosensitive layer of the wafer 5 are prevented from being scarred during the operation of mask alignment.

After the film 8 is thus aligned with the wafer 5, air in a space 12 formed by the supporting plate 6, the elastic member 4 and the chuck 1 is discharged through the suction hole 3 by the vacuum pump. As a result, the space 12 is put under reduced pressure so that the supporting plate 6 is held on the elastic member 4. Air or nitrogen is supplied to the space 11 through the pipe 10 and the hole 9 to put the space 11 in a state of increased pressure. By the increased pressure, the film 8 is elastically returned to the original shape and is further elastically deformed in conformity with the uneveness (concavities and convexities) of the surface of the wafer 5. As a result, the film 8 can be sufficiently closely contacted with the wafer 5 without a gap being formed therebetween as shown by a solid line in Figure 2. Under this condition, the optical exposure for the wafer 5 is effected by irradiating beams, for example, ultraviolet rays 13 on the wafer 5 from the upper side of the supporting plate 6.

To remove or separate the film 8 from the wafer 5 after the completion of the beam irradiation, gas in the space 11 is sucked through the hole 9 and the pipe 10 by the vacuum pump to put the space 11 under the reduced pressure again. As a result, a film 8 is elastically deformed upward again to be easily separated from the wafer 5. To remove or separate the whole of the mask A from the chuck 1, gas is supplied to the space 12 to put it under atmospheric pressure again.

As apparent from the above description, the pattern of the film 8 can be prevented from being scarred because the space 11 is put under reduced pressure to separate the film 8 from the wafer 5 on the mask alignment. The film 8 can be sufficiently closely contacted with the wafer 5 for supplying the space 11 with the gas under pressure in the optical exposure process.

Various modifications can be made. For example, the ring 7 does not necessarily need to be made of elastic material. The wafer 5 is supported by the chuck 1 in the described embodiment, however, the manner of support can be variously modified.

The way of supporting the whole of the mask A is not necessarily limited to that in the embodiment wherein the mask A is held on the chuck 1 due to the reduced pressure.

WHAT WE CLAIM IS: 1. An optical exposure apparatus comprising a supporting means for an object to be exposed, a mask for exposure comprising a transparent supporting plate and a transparent film having a predetermined opaque pattern formed thereon, said transparent supporting plate and said transparent film being combined with each other through a ring-shaped spacer means located near a periphery of said transparent film so that a first space is formed between them, an elastic ring means on said supporting means being able to be in contact with said transparent supporting plate so that said supporting means, said transparent supporting plate and said elastic ring means form a second space between them surrounding said transparent film, a first penetrating hole formed in said transparent supporting plate which is connected to a first means to control the gas pressure in said first space, a second penentrating hole formed in said supporting means connected to a second means to control the gas pressure in said second space, and an irradiating beam source to expose said object according to said opaque pattern.

2. Apparatus according to claim 1 wherein said spacer means is an elastic ring adhered on one of its sides to said transparent supporting plate and on the other of its sides to said transparent film.

3. Apparatus according to claim 1 wherein said spacer means is formed of adhesive material.

4. Apparatus according to claim 1 wherein said transparent film is elastically deformed to be separated from said object by putting said first space under reduced pressure on the alignment of said mask, and said transparent film is elastically deformed towards said object to be closely contacted with said object by supplying said first space with gas under pressure during the optical exposure process.

5. Apparatus according to claim 1 wherein said transparent film is elastically deformed to be separated from said object by putting said first space under reduced pressure after the optical exposure process is completed.

6. Apparatus according to claim 1 wherein said supporting means forms part of a vacuum chuck for holding said mask and said object by putting said second under reduced pressure.

7. An optical exposure apparatus substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the chuck 1 is discharged through the suction hole 3 by the vacuum pump. As a result, the space 12 is put under reduced pressure so that the supporting plate 6 is held on the elastic member 4. Air or nitrogen is supplied to the space 11 through the pipe 10 and the hole 9 to put the space 11 in a state of increased pressure. By the increased pressure, the film 8 is elastically returned to the original shape and is further elastically deformed in conformity with the uneveness (concavities and convexities) of the surface of the wafer 5. As a result, the film 8 can be sufficiently closely contacted with the wafer 5 without a gap being formed therebetween as shown by a solid line in Figure 2. Under this condition, the optical exposure for the wafer 5 is effected by irradiating beams, for example, ultraviolet rays 13 on the wafer 5 from the upper side of the supporting plate 6. To remove or separate the film 8 from the wafer 5 after the completion of the beam irradiation, gas in the space 11 is sucked through the hole 9 and the pipe 10 by the vacuum pump to put the space 11 under the reduced pressure again. As a result, a film 8 is elastically deformed upward again to be easily separated from the wafer 5. To remove or separate the whole of the mask A from the chuck 1, gas is supplied to the space 12 to put it under atmospheric pressure again. As apparent from the above description, the pattern of the film 8 can be prevented from being scarred because the space 11 is put under reduced pressure to separate the film 8 from the wafer 5 on the mask alignment. The film 8 can be sufficiently closely contacted with the wafer 5 for supplying the space 11 with the gas under pressure in the optical exposure process. Various modifications can be made. For example, the ring 7 does not necessarily need to be made of elastic material. The wafer 5 is supported by the chuck 1 in the described embodiment, however, the manner of support can be variously modified. The way of supporting the whole of the mask A is not necessarily limited to that in the embodiment wherein the mask A is held on the chuck 1 due to the reduced pressure. WHAT WE CLAIM IS:

1. An optical exposure apparatus comprising a supporting means for an object to be exposed, a mask for exposure comprising a transparent supporting plate and a transparent film having a predetermined opaque pattern formed thereon, said transparent supporting plate and said transparent film being combined with each other through a ring-shaped spacer means located near a periphery of said transparent film so that a first space is formed between them, an elastic ring means on said supporting means being able to be in contact with said transparent supporting plate so that said supporting means, said transparent supporting plate and said elastic ring means form a second space between them surrounding said transparent film, a first penetrating hole formed in said transparent supporting plate which is connected to a first means to control the gas pressure in said first space, a second penentrating hole formed in said supporting means connected to a second means to control the gas pressure in said second space, and an irradiating beam source to expose said object according to said opaque pattern.