JPS6153601A - Dustproof cover body for photomask reticule having high performance - Google Patents

Abstract

PURPOSE:To provide high film strength and good uniformity of a film and to provide high performance of >=98% ray transmittance to a dustproof cover body by forming the multi-layered films constituting the main part of said body in a manner as to have the thickness of the core part film as large as 6-15mum and disposing antireflecting layers on both sides. CONSTITUTION:The antireflecting films 3 are formed by a casting method in dissolving various polymers in a solvent on both sides of the film 2 in the core part consistint of a polymer such as polyethylene terephthalate and having 6- 15mum thickness. The multi-layered films 1 which allow the passage of the certain predetermined light to be prevented of reflection at >=98% can be obtd. by forming the films having >=500g film strength in a method for testing the film strength to ascertain the load (g) at which the test film of 100mm. diameter fixed at the circumference ruptures when a semisphere of 8mm. radius is plunged at 10mm./min speed perpendicularly to the film as the film strength in the above- mentioned manner.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a dustproof cover for a photomask-reticle, in which the main part of the cover is a multilayer film having antireflection layers on both sides. The thickness of the core of the multilayer film is 6 to 15.
The present invention relates to a dust-proof cover body that is relatively thick (μm) and has strong strength, and is capable of transmitting light of a specific wavelength of 98 inches or more used for exposure.

(Prior art) As semiconductor integrated circuits have become more highly integrated in recent years, the image lines of the circuits have become extremely small, measuring 1 to 3 μm. There is a transition from a single-type stepper type to a single-stepper type.

In this lithography step, if dust is present on the photomask/reticle, the dust is also imaged at the same time, resulting in short circuits and defects in the circuit, reducing the yield of LSI.

Particularly in the case of a step saw, several images on the reticle are sequentially reduced and projected onto the wafer, so one piece of dust on the reticle may cause all I and SI to be defective, so the dust is set to zero. This is becoming extremely important.

Therefore, a method has been proposed in which a transparent film is placed on one or both sides of a photomask reticle (hereinafter simply referred to as "mask") with a certain amount of space between them to prevent shavings from adhering to the mask. (Japanese Patent Publication No. 54-28716). According to this method, dust adheres only to this transparent film, and by focusing the image on the mask during projection, dust is not imaged out of focus on the wafer. It is possible to prevent defects caused by dust. This dust-proof cover body is referred to as a dust-proof cover body here.

The dustproof cover body is attached to the mask and attached to the exposure machine.

A film forming a main part of the dustproof cover body is arranged in the exposure optical path.

Therefore, the film needs to transmit the image without distortion or disturbance, and the film is required to have a uniform thickness, be free of dust and particles, and be free of internal distortion.

Furthermore, the exposure light transmittance of the film is also important. In other words, if the transmittance of one light is low, it is necessary to lengthen the light time for that branch.
Throughput deteriorates. Since LSI manufacturing often involves extremely high volume production, improving throughput is important. In particular, in the case of a stucco saw, one sea urchin may be exposed several hundred times per day, so improving light transmittance greatly contributes to improving throughput.

On the other hand, although the dustproof cover body takes dust out of focus, large dust of 50 to 100 μm or more will be projected onto it, so it is necessary to prevent such dust from entering before, during use, or during storage. If it adheres, it is necessary to remove it by air blowing, washing with water, etc. During this removal work, the strength of the membrane is also an important point because if the membrane is not strong enough, it will break. In particular, the film of the dust-proof cover body that has been used a certain number of times deteriorates and becomes more easily torn because the exposure light is ultraviolet rays. Consider this point when setting the membrane strength 1).

need to be considered.

Conventional techniques regarding such a dustproof cover body are of a lower level.

One type is disclosed in Japanese Patent Publication No. 54-28716, which uses a transparent thin film having a film thickness of 0.2 to 6 μm.

The film thickness is limited to 6 μm because the shift amount of the image position due to the installation of the dustproof cover is negligible, and there is no description of the uniformity of the film or the strength of the film for light transmission.

The other one is shown in Japanese Unexamined Patent Application Publication No. 196501/1988-1
There is a dustproof cover made of nitrocellulose or thermoplastic polymer having a film thickness of 0.5 to 10 pm. The reason for limiting the film thickness to 0.5 to 10 μm is that it has sufficient strength to support itself, and is not limited by the film strength required for handling such as air blowing.

Also, the uniformity of the film thickness is about 2 inches or less, preferably 1 inch or less.
It is stated that it is less than or equal to H. On the other hand, the light transmittance can be set to any value from 84 to 99 inches. This utilizes the interference phenomenon of reflected light on the front and back surfaces of the layer, and provides a light transmittance of 99 times at wavelengths at which the reflected waves on the front and back surfaces cancel each other out. However, in reality, as the film thickness increases, this maximum light transmittance decreases and does not increase to 99%. Additionally, as the film thickness increases, the interference waves caused by this interference phenomenon become sharper, so it is extremely difficult to create a film thick enough to transmit more than 99% or 98% of light of a certain wavelength. It is.
'Also, a dustproof cover body made of nitrocellulose with a thickness of 18 μm and subjected to antireflection treatment is also commercially available.

Although this product has sufficient film uniformity and light transmittance, the film thickness is relatively thin at 18 μm, so it is difficult to handle the film, especially during air blowing to remove dust, washing with water, etc. The disadvantage is that it is low.

(Problems to be Solved by the Invention) As stated above, the dustproof ability of the prior art is integral to one of its necessary characteristics: uniformity of the film and light D transmittance.

It was not possible to obtain a membrane that had all three properties.

(Means for Solving the Problems) The present inventors have completed the present invention as a result of intensive research to create a dustproof cover body that satisfies all of these necessary characteristics.

That is, in the present invention, the film constituting the main part of the dustproof cover body is a multilayer film having an antireflection layer on both sides, and transmits light to be prevented from reflecting at least 9 layers. This is a cover body for a photomask/reticle, characterized in that the thickness of the film forming the core part is 6 to 15 μm, and the film strength is 5001 or more in the following test Ia method.

Renal membrane strength test method: Load at which the membrane breaks when a hemisphere with a radius of 8 mm is pierced perpendicularly to the membrane at a speed of 10 mm/min (2) tl - Membrane ant degree.

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 shows the structure of an embodiment of the membrane of the present invention,
Both sides of the core film 2 (where the antireflection layer 3 is arranged and the multilayer film 1
form. The thickness of the core membrane 2 is 6 to 15 μm.

Polymer is suitable as the material for the core membrane 2 due to its light transmittance, strength, and ease of manufacture. Polymer and Ll-jl,!
? Liethylene terephthalate, cellulose esters 1
．． Polycarnate, polymethyl methacrylate, etc. can be produced. Among them, nitrocellulose is the most sophisticated in terms of light transmittance, film strength, and manufacturing. The nitrocellulose used in the invention is JISK, -6703
It is an industrial nitrocellulose with a nitrogen content of 10.7% by weight to LL2 double layer as defined in the following. Also, 3
One question is 30-5OO1 preferably 50-300 as an average degree of polymerization. If the degree of polymerization is less than 30, the film strength will be low and the object of the present invention cannot be obtained.

However, if the degree of polymerization exceeds 500, membrane production becomes extremely difficult.

The strength of the core membrane is an important characteristic during handling such as the above-mentioned removal of dirt and dust, and the required strength is 500 g or more according to the above test method.

If the strength is lower than this, the membrane may be torn by air blowing or washing with water. +! fI/c If the product has been used for a long period of time, the rupture of the membrane deteriorates. Requires a sphere,
Preferably it is 7 μm or more.

In addition, it is practically meaningless to increase the film thickness to 15 μm or more in order to increase the film strength, and at the same time, it is extremely difficult to manufacture a film having such a thickness with a thickness unevenness of about 1 or less. From a manufacturing standpoint, the preferred upper limit of film thickness is 12 μm.
It is.

The method of manufacturing the core membrane 2 is not limited by any method. For thermoplastic polymers, the melt extrusion method is used, and for non-thermoplastic polymers such as cellulose esters, the solution casting method is used. As the solution casting method, a spin coating method, a coater method, an immersion pulling method, a casting method on a fluid surface, etc. are used, but the spin coating method is recommended from the viewpoint of film thickness accuracy and uniformity.

The antireflection layers 3 disposed on both sides of the core mark 2 are important in order to achieve a light transmittance of nine layers or more.

When the thickness of the film 2 becomes 6 μm or more, the maximum value of transmittance (maximum transmission of interference waves due to interference phenomenon) with only one film 2 becomes less than 9 layers, and the object of the present invention cannot be achieved. do not have.

However, it has been found that even with such a low light transmittance film, when antireflection layers are formed on both sides of the film, the light transmittance becomes 9 layers or more. This is because in the case of HI/-1 marks, minute roughness occurs on the front and back surfaces of the film, reducing the light transmittance, but by forming an antireflection layer, this roughness I lost it. This is considered to be the result.

Furthermore, the dustproof cover body of the present invention is disclosed in Japanese Patent Publication No. 54-2
Picture A2 pointed out in Publication No. 8716! Although the amount of positional shift is quite large, it is almost negligible in practical terms.Also, if necessary, by changing the distance between the projection lens and the mask, the amount of shift caused by the integrated dustproof shield can be reduced. It is possible to correct for focus shift and changes in reduction magnification.

The antireflection layer 3 is composed of one layer or two or more layers of various refractive indexes, but in order to obtain a high light transmittance of 98% or more, which is the objective of the present invention, the antireflection layer is A so-called multilayer antireflection method consisting of two or more layers is required.

In the case of a cover body, it is sufficient to prevent reflection of only a certain wavelength of 200 to 450 pam, so the number of antireflection layers is 2 to 3 layers.

The structure of each antireflection layer is, in the case of two-layer antireflection, the refractive index and thickness of the outer antireflection layer are nl+dl, the inner antireflection layer is 'nzed*, and the refractive index and thickness of the inner antireflection layer are When the refractive index is R9, select a material with a value of nl+n2 such that the second value is R or a close value, and the film thickness of each antireflection layer 'a:
It is necessary to set nt dt = nzdz = 4λ (λ: wavelength of light to be prevented from reflecting).

In addition, in the case of three-layer anti-reflection, the refractive index and thickness of the outer anti-reflection layer are nl g dl;
; When R3hd3 and the refractive index of the film forming the center are xi, 2 is m or a close value, 1ltdt:
! It is necessary to have a thickness that satisfies the following: nz dz = R3d3 = -λ (λ: wavelength of light to prevent anti-IM).

Furthermore, if such an antireflection layer is placed only on one side of the film 2, the antireflection effect will be insufficient and a light transmittance of 98% or more will not be obtained, so it is necessary to place it on both sides. .

As a method for forming the anti-reflection layer, it is also possible to form an inorganic compound such as MgFz a Zr0z * k40s, which is commonly used, by vacuum evaporation, suction ringing, ion blating, etc.; A method of dissolving the polymer in a solvent and forming it by a casting method can also be used.

In the method of forming an antireflection layer using an inorganic compound by vacuum deposition, etc., the performance of the formed antireflection layer may be affected by oxidation, density changes, etc. 1) Since there are many changes, care must be taken when using this method.

On the other hand, forming an antireflection layer by casting a polymer solution is a preferable method since there is no such change. As the casting method, it is preferable to use a spin coating method since it is necessary to form a very thin layer over the top.

The antireflection layer is formed by the spin coating method with a polymer concentration of 0.5 to 2 double fa and a rotation i of 500 to 300.
This is achieved by setting the speed to 0 rpm. Examples of polymers include fluorine polymers and silicone polymers for low refractive index vehicles, and polystyrene, polyethersulfone, polysulfone, and polycarbonate for high refractive index vehicles.

Examples include polyphenylene ether.

In FIG. 2, the structure of the parts other than the multilayer film 1 is basically the same as the conventional one. The dustproof cover body is attached to the support frame 4
The structure is such that the multilayer film 1 is fixed to an adhesive layer 5 or the like without wrinkling or sagging, and the support frame 4 has an adhesive layer 6 on the other surface and a release film 7 thereon. The size of the support frame 4 is approximately 1 to 6 inches or approximately 1 to 6 inches square, depending on the dimensions of the photomask or reticle used. Depending on the width of the support frame 4 and the size of the debris to be taken out of focus, the distance will vary from 2 to IQm-. Further, the material of the support frame 4 is aluminum alloy, hard plastic, etc., as it has less dust adhesion, is light in appearance, and has strength.

The dustproof cover body is stored in a clean case until it is ready for use to prevent dust from adhering to it. Except for use, the second
In order to peel off the separation film 7 shown in the figure and cover the image 9 formed on the photomask or reticle 8 as shown in FIG.
Attach dustproof protection. Since the reticle used in the stepper is extremely sensitive to dust, a dustproof cover is attached not only to the image 9 side of the reticle 8 but also to other surfaces.

(Example) Example 1 Nitrocellulose (manufactured by Mukasei Kogyo Co., Ltd., manufactured by Kiki, H-/) was dissolved in ethyl lactate to make a 25-ply fix m, 72 L. Also, polyether sulfone (manufactured by ICI, P-2000) was dissolved in ethyl lactate.
゜np=L63)'r 1 , L , 2 , It was dissolved in 2-tetrachloroethane to make a 0.75 wt'kk% solution. On the other hand, tetrafluoroethylene (rFE)/hexafluoropropylene (HFP)/vinylidene fluoride (V
dF) copolymer polymer (TFE=37.6 double stitches, I(
FP=17.91i%, vdp=44.5% by weight,
nD=tar) e Par 7 silicon wafer (125 mm plate) was set in a spin coater (rotation Ql, cloth 4 pm), and nitrocellulose solution a (commercially sold) was rotated at 12 Q Orpm, and infrared 11 - A coating film of nitrocellulose was formed on the wafer by drying with a real lamp.A polyether sulfone solution was dropped onto this, and
Rotate at 0 rpm, dry, and then apply T F
E/) (F PlVdF copolymer H51J mai solution t
Apply at 500 rpm and let dry.

Next, an adhesive film (Sumitomo 3M (4'll' 21% Scotch 1?-) 5T was applied to one end of an aluminum ring with an inner diameter of 100 gates, an outer diameter of 105 m1p, and a height of 6 gates.
-416) and? An S-type film (Boriester film) was applied.

Also, apply epoxy resin to the other end face and overlap it with the coating film on the wafer. By curing the coating, the coating film and the aluminum ring were made flush with each other.

This product was immersed in water, and after being left for 30 minutes, the membrane was separated from the aluminum ring, and the membrane fixed to the aluminum ring was recovered from the water. After air-drying, place the film firmly on the spin coater again with the skin side up, set the northern aluminum ring, and form the waist in the order of polyether sulfone and TFE/HFP/VdF copolymer poIJ -+r-. Yoshi, 2nd
A dustproof cover body with the structure shown in the figure was created.

The spectral support of the resulting dust-proof cup ζ (manufactured by Shimadzu Corporation, measured with UV-240) was as shown in Figure 4, and the light transmittance at 436 deafness was 99.7 cm. Ta.

On the other hand, a dust-proof cover body consisting only of a nitrocellulose membrane was created in the same manner as the above method and under the same conditions for forming the nitrocellulose membrane. The thickness of this dust-proof Kaz-integrated TV nitro-7-lulose film was calculated from the measurement of the spectral characteristics of the film using the following formula.

2n (λ turtle - λ engineering) d: Film thickness engineering) λ1: Peak wavelength of interference wave (-ry) near D@ (s 87.6M) To λ: λ1 to si-th peak wavelength (hehe ) 1n: No of nitrocellulose
(=1.51) As a result, the film thickness is 6.30±0.0
A book that is 1 μm and has an anti-reflection layer? It is believed that the thickness of the nitrocellulose membrane in the two examples is also the same.

Then, the film strength was measured using the above method and was found to be 5.
It was a strong 30I.

Comparative Example 1 The concentration of nitrocellulose was 20% by weight, and t4oor
A dustproof cover body was produced in the same manner as in Example 1 except that the coating was performed using pm.

What is the film thickness of this thing? Dust at -95±0.01μm, 4
The light transmittance at 36 nm was 99.8%, and the film strength was weak at 245J7.

Example 2 and Comparative Example 2 The concentration of nitrocellulose was 27% by weight, and polysulfone (Yasan Kagaku (K!
, P-3500, no-L63)) A dustproof cover body was created in the same manner as in Example 1 (Example 2).

Further, a dustproof cover body made of nitrocellulose mono/f5M made only from a solution of nitrocellulose having a concentration of 27% by weight was prepared fc (Comparative Example 2).

From the spectral characteristics of Comparative Example 2, Example 2. The thickness of the nitrocellulose membrane of Comparative Example 2 was approximately 9.5 μm, and the membrane strength was both 800·y and strong.

On the other hand, the spectral characteristics are shown in FIG. 5 for implementation row 2.

For Comparative Example 2, 1tTu) shown in Figure 6 is used.
In Example 2, the light transmittance near 436 mm was 9
9.5 μm, whereas in Comparative Example 2, the multilayer film with It has strong coating properties, good film uniformity, and high performance with a light transmittance of 98% or more.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view showing an example of a multilayer film used in the dust-proof cover body of the present invention, FIG. 2 is a cross-sectional view of the dust-proof cover body of the present invention, and FIG. 3 is a cross-sectional view of an embodiment using unexploded EjA. ,
Figure 4 is a graph showing the relationship between wavelength and light transmittance in Example 1, Figure 5 is a graph showing the relationship between wavelength and light transmittance in Example 2, and Figure 6 is a graph showing the relationship between wavelength and light transmittance in Comparative Example 2. A graph showing the relationship between ratios...Multilayer film with antireflection layers on both sides, 2...
... Core film, 3 ... Antireflection layer, 4 ...
... Frame, 5 ... Adhesive layer, 6 ... Adhesive layer, 7 ... Release film, 8 ... Photomask or reticle, 9 ······image. Patent applicant: Asahi Kasei Industries, Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. The film constituting the main part of the dustproof cover is a multilayer film having antireflection layers on both sides, which transmits 98% or more of a certain light to be prevented from reflecting, and is a multilayer film. A dustproof cover for a photomask/reticle (film strength test method) characterized in that the film forming the core of the film has a thickness of 6 to 15 μm and a film strength of 500 g or more in the following test method. The membrane strength is defined as the load (g) at which the membrane breaks when a hemisphere with a radius of 8 mm is pierced perpendicularly to the membrane at a speed of 10 mm/min to a test membrane with a diameter of 100 mm. 2. The dustproof cover body according to claim 1, wherein the membrane forming the core is a nitrocellulose membrane.