JPS6154211B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a photomask for image projection type transfer used in the manufacture of semiconductor integrated circuits, and in particular, the present invention relates to a photomask for image projection type transfer used in the manufacture of semiconductor integrated circuits. This relates to a photomask for image projection type transfer, which is attached to a photomask using an adhesive to prevent dust from adhering to the mask surface and to prevent defects due to scratches and the like.

[Conventional technology]

In the conventional photolithography technology used in the manufacture of semiconductor integrated circuits, an intermediate mask (reticle) is created from design data using an optical pattern generator, and then a master mask is created by repeatedly exposing a pattern of the same size using an optical photorepeater. A working mask is created by copying the master mask, and this working mask is overlaid on the wafer by contact exposure or close exposure.
Processes have been used to transfer patterns onto wafers.

However, as a lithography technique that has been put into practical use in recent years, a process is adopted in which a master mask or intermediate mask is created using an electron beam from an electron beam exposure device, and the mask is transferred onto a wafer by 1:1 projection or reduction projection. For this projection, image-forming projection transfer technology using reflective mirrors and lenses has been used.

Image projection type transfer using lithography technology, which has been incorporated into recent semiconductor manufacturing, does not make contact between the mask and the wafer compared to conventional contact exposure or close exposure transfer, so there is no risk of scratches on the mask due to contact. This has the advantage that the mask can be used for a long period of time, and the yield of semiconductor products is significantly improved.

In the above-mentioned image projection type transfer, if there is dust or scratches on the pattern, it is inevitable that they will also create an image and cause product defects.

Therefore, the transfer operation is usually performed in a dust-free box from which dust is removed. However, there are limits to how clean the inside of the dust-free box can be, and it is also difficult to completely eliminate dust from adhering to the mask during the inspection process and transportation process from the mask manufacturing process to the transfer process. It is. Therefore, product defects caused by dust adhering to the mask surface have been a considerable cause of reduced product yield. This tendency is particularly noticeable in the transfer process for LSI manufacturing, where elements become smaller as the degree of integration increases, and even the slightest amount of dust attached can immediately lead to the production of defective products. However, the situation is somewhat different in image projection transfer technology. In other words, in the case of image projection type transfer, whether it is a reflection projection method using a reflecting mirror (usually a combination of a concave mirror and a convex mirror) or a step-and-repeat method using a lens, the light from the light source is first condensed. A method is adopted in which the light is focused by a light condensing device such as a lens, a mask pattern is placed at the focal point, and the wafer is placed at a position where the transmitted light is imaged through a reflecting mirror system or lens system. In this case, the depth of focus of the condensing device is generally about several to 15 μm. Therefore, by using some method to prevent dust from adhering to the same surface of the mask pattern, and even if it does, by moving it away from the depth of focus range, it is possible to avoid the influence of such minute dust.

U.S. Patent No. 4,063,812 discloses that a mask pattern is coated on a transparent substrate provided with a mask pattern, transparent glass is bonded via UV cure cement, and the thickness of the transparent glass and the transparent substrate is adjusted to the surface of the transparent material layer. It is disclosed that the thickness is such that the adhered contaminant particles are not transferred onto the photosensitive material layer.

[Problem that the invention seeks to solve]

However, the photomask formed as described above has additional problems that must be solved.

That is, when covering a mask pattern and bonding transparent glass, air bubbles contained in the adhesive layer must be pushed out and removed by some means. As a result, adhesive containing air bubbles is present around the photomask to which transparent glass is adhered. If the adhesive remains attached to the periphery in this way, light scattering will occur, which may reduce resolution or cause ghost images.

Furthermore, it is not easy to bond a transparent thin plate glass of 500 μm or less that provides a practical light transmittance on a glass substrate with good flatness. This is because it is not easy to apply the adhesive to a uniform thickness over the entire surface, and the flatness of the adhesive coating tends to be lower in the peripheral area than in the central area. Furthermore, it is not easy to align and bond the thin glass to the effective portion of the photomask.

Therefore, the problem to be solved by the present invention is to cover a transparent substrate with a mask pattern with a mask pattern so that the transparent thin glass can be efficiently bonded with good flatness and aligned with the effective area of the photomask. It is an object of the present invention to provide a method for manufacturing a photomask that can be carried out.

[Means for solving problems]

The present invention solves the above problems. A mask pattern is provided on a transparent substrate in a dust-free atmosphere, and a photocurable adhesive is applied on the surface containing the mask pattern to form an adhesive layer. After placing a transparent thin glass plate on top of the photomask and fixing the transparent substrate with a mask pattern and the thin glass with good flatness, ultraviolet rays are irradiated through an exposure mask that has a light-shielding part on the periphery to check the effectiveness of the photomask. After curing the adhesive area corresponding to the photomask, a groove is made by mechanical means at the UV-cured border, and then the uncured adhesive is removed, and the thin glass is bonded only to the effective area of the photomask. The gist of the present invention is a method for manufacturing a photomask, which is characterized by obtaining a photomask having a structure similar to the above.

Hereinafter, the present invention will be explained in detail.

First, as a transparent substrate, for example, soda glass,
For example, one with an optically smooth surface of 1.0 to 5.0 mm made of hard glass, quartz, AI ₂ O ₃ , etc. is prepared, and chromium, molybdenum,
Films mainly made of metals such as iron, titanium, silicon, selenium, alumina, etc., or single or laminated layers of oxides or nitrides of these metals, or layers of mixtures of these metals or their oxides, nitrides, etc. A mask pattern 2 is provided, for example, on the entire surface of the substrate 1 with a thickness of, for example,
After providing the above-mentioned metal-based film and electron beam resist with a thickness of 300 to 2500 Å, electron beam imaging and etching are performed using conventional electron beam lithography or a photosensitive resin (photoresist) is appropriately selected. Instead, pattern making is performed using any method such as photolithography using light of various wavelengths to produce the desired photomask. As a photomask, a hard surface pattern having a pattern made of a metal thin film as described above is most suitable for this case, but an emulsion pattern made of an emulsion dry plate using a silver salt emulsion may also be applied to this case.

Next, as shown in FIG. 1a, an uncured transparent adhesive 3A is applied onto the photomask 6 having a mask pattern on a transparent substrate, and a transparent thin plate glass is applied on the adhesive layer 3A as shown in FIG. 1b. 4 are bonded together with good flatness to form an adhesive layer 3A into a uniform film. adhesive 3
As for the coating method of A, usual methods such as calendar coating, spinner coating, spraying, pouring, and dripping can be used.The thinner the thickness of the adhesive layer in the present invention, the better, but the thickness of the adhesive layer 3A and the thin plate glass can be used. The thickness including the thickness of 4 is 20~
The thickness should be 500μm. That is, in the present invention, it is necessary that the distance from the surface of the mask pattern to the surface of the transparent thin glass is 20 to 500 μm. The above lower limit is more than twice the depth of focus by the condenser in the image projection transfer operation, and the thin glass 4
This is required in order to prevent the image from becoming blurred by light diffraction and forming a projected pattern on the wafer surface even if dust adheres thereon or the surface of the thin glass 4 is slightly scratched. The above upper limit is required to provide a practical light transmittance.

The bonding operation of the thin glass sheets 4 is preferably performed in a dust-free box. This is because if dust adheres to or gets mixed in on the pattern of the photomask 6 or on the adhesive layer 3A or the adhesive surface side of the thin glass plate 4, it becomes a common cause of defects during transfer.

Materials for the thin glass 4 include soda glass,
It is possible to use glass with good flatness, such as hard glass or quartz, which is the same as glass normally used for photomasks. The thin glass 4 needs to have a minimum size sufficient to cover the mask pattern 2 provided on the transparent substrate 1.

The material for the adhesive layer 3A is a photo-curable adhesive that adheres well to each other's glasses after curing, has chemical resistance, and has excellent transparency to the light used for exposure during transfer, such as , acrylic, epoxy, urethane, styrene, etc., as the main component, and optionally containing an ultraviolet curing accelerator, a thermosetting accelerator, etc. are preferably used.
More specifically, NOA60 manufactured by Norland,
NOA61, NOA63, NOA65, Photobond 100, 300, 500 manufactured by Myojo Churchill, Sonnebond manufactured by Thick Film Technology Research Institute, UVAC manufactured by Konishi,
Examples include UV03162, Adeka Ultraset manufactured by Asahi Denka Kogyo Co., Ltd., and adhesives based on these adhesive resins and containing a thermosetting accelerator.

The adhesive may be cured using ultraviolet rays depending on the characteristics of the adhesive. This curing means is performed by a conventionally known method.

FIG. 1c shows an example of a curing method using a photocurable adhesive. After fixing the photomask 6 and the thin glass 4 with good flatness, an exposure mask having a light-shielding part 7 on the periphery is attached. Ultraviolet light 8 is irradiated through M to obtain a cured adhesive layer 3.

Next, the uncured adhesive 3A is removed.

Figure 1 d shows a method of mechanically removing the uncured portion of the adhesive, in which a groove 9 is created using a dicing saw at the boundary between the UV-cured portion and the uncured portion, and then the uncured portion is removed. Finally, a photomask for image projection type transfer is obtained as shown in FIG. 1e.

〔Example〕

Example 1 Using a 228 mm x 100 mm x 100 mm (0.09″ x 4″ x 4″) photomask substrate (DN-BC manufactured by Dai Nippon Printing Co., Ltd.), an integrated circuit pattern was printed in close contact with the sub-master mask. A photomask with a chromium thin film pattern with a thickness of 850 Å was obtained by performing prescribed development and etching.After that, in the inspection process, the device dimensions and
A photomask with no defects was obtained by inspecting the total pitch dimension, registration, and appearance for dust, scratches, pinholes, etc. After that, alkaline cleaning, water rinsing, and drying were performed.

Next, after fixing the photomask obtained in the above manner to the spinner head, an ultraviolet curing adhesive Photobond (manufactured by Myojo Churchill Co., Ltd.) was dripped onto the photomask pattern, and a transparent thin plate glass with a thickness of 50 μm was set and rotated at high speed ( 3000 rpm for 3 minutes), and the photomask and thin glass were fixed with good flatness.
Thereafter, the adhesive layer was cured by irradiating ultraviolet light into a predetermined shape through a mask. Thereafter, grooves were made in the ultraviolet-cured boundary using a dicing saw, and the uncured adhesive layer was removed to produce a photomask of the present invention in which a thin glass sheet was bonded only to the effective portion of the photomask.

According to the method of this embodiment, even thin sheets of glass can be bonded together with good flatness.

〔Effect of the invention〕

As described in detail above, according to the present invention, a mask pattern is coated on a transparent substrate provided with a mask pattern, and a transparent thin plate glass is efficiently bonded with good flatness and aligned with the effective portion of the photomask. be able to.

The photomask obtained by the method of the present invention is
It has an extremely simple structure of simply pasting a thin sheet of glass onto a mask pattern, and if dust gets mixed in and adheres to the pattern or between the transparent substrate and the thin glass before the adhesive is cured, it can be remade. has advantages. Furthermore, by laminating thin glass sheets, the surface flatness is maintained, it is easy to clean, and it is mechanically strong and resistant to scratches. Furthermore, it is characterized in that it hardly causes problems with dust adhering to the mask surface during the inspection process, transportation process, or transfer process after photomask manufacturing, and can improve the yield of semiconductor element products. .

The photomask obtained by the method of the present invention is
It is used as a mask in a known image projection type transfer method such as a reflection projection method or a step-and-repeat method.

[Brief explanation of the drawing]

FIGS. 1A to 1E are cross-sectional views showing the manufacturing process of the photomask manufacturing method of the present invention. 6 ... Photomask, 3A... Photo-curing adhesive, 4... Transparent thin glass, 7... Light shielding part, M...
...Exposure mask, 9...groove.

Claims (1)

[Claims] 1. A mask pattern is provided on a transparent substrate in a dust-free atmosphere, a photocurable adhesive is applied on the surface containing the mask pattern, a transparent thin plate glass is placed on the adhesive layer, and a mask is formed. After fixing a transparent substrate with a pattern and a thin glass plate with good flatness, ultraviolet rays are irradiated through an exposure mask having a light-shielding part at the periphery to harden only the adhesive area corresponding to the effective part of the photomask. After that, grooves are formed at the ultraviolet-cured boundary portions by mechanical means, and then the uncured adhesive is removed to obtain a photomask having a structure in which thin glass is bonded only to the effective portion of the photomask. manufacturing method.