JPH049060A - Manufacture of dustproof body high in light transmittance - Google Patents

Abstract

PURPOSE:To obtain a dustproof body high in light transmittance and not causing photodecomposition even when it is irradiated with short wavelength light for a long time by heat treating a thin gel film obtained by developing sol on the surface of a liquid by the casting method, and forming an inorganic film high in light transmittance. CONSTITUTION:The sol is developed on the surface of the liquid rendered in specific weight and surface tension higher than the sol, the obtained thin gel film is scooped, and dried with hot air or the like, the obtained thin dry gel film is fixed to a holder 2 made of a metal or ceramics, and heat treated to form the inorganic film 3 high in light transmittance. At the time of drying, the gel film may be fixed to another base plate, and after drying the obtained inorganic film may be fixed to another holder 2, thus permitting the obtained dustproof body 1 high in light transmittance to prevent opacification of the film 3 due to photodecomposition caused by long time exposure to short wave- length light and deterioration of mechanical strength.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is intended to prevent foreign matter such as dust from adhering to photomasks, reticles, etc. used in the photolithography process in the manufacturing process of semiconductor devices such as ICs and LSIs. The present invention relates to a method of manufacturing a dustproof body used to prevent dust.

[Conventional technology]

In the exposure process in the manufacturing process of semiconductor devices, a mask is used to pattern a circuit with a vapor-deposited light-shielding film such as chromium on the surface of a glass plate, and this circuit pattern is transferred onto a silicon wafer coated with a photosensitive agent such as resist. Work is being done to

At this time, if exposure processing is performed with foreign matter such as dust attached to the mask, the shadow of this dust will be transferred onto the wafer as it is, resulting in product defects.
This becomes a factor that reduces so-called yield. In particular, in reduction projection exposure processing in which circuit patterns are sequentially transferred onto chip areas on a wafer using a reticle as a mask, the problem of dust adhesion is serious, as it determines the quality of most products.

Therefore, it is known that a transparent dustproof material (pellicle) made of organic material such as nitrocellulose is placed at a predetermined distance above the circuit pattern of the mask to prevent dust from directly adhering to the circuit pattern. ing.

Also, J. Membrane 5science, 3
9 (1988) P213-P220, L, C, KL
“PORE” by EIN, D, GALLAGHER
STRUCTURES OF 5QL-GEL 5IL
In the document entitled ``ICA MEMBRANES'',
It has been reported that the production of a silica gel sheet with a thickness of 100 μm has been reported. This technology is too thick to be used as a light-transmitting film in the pellicle, and furthermore, without heat treatment, the film has a thickness of several tens of μm. There are countless spherical voids with different diameters.

[Problems to be Solved by the Invention] Incidentally, as the degree of integration of semiconductor devices improves, the wavelength of the light beam during exposure has changed from the g-line (436 nm) to the i-line (365 nm).
m), as the wavelength shifts further to excimer lasers (248 nm), the conventional dustproof body using a transparent thin film made of organic matter has weak molecular bonding and photodecomposition occurs within the thin film. It was revealed that the film itself became opaque, making it impossible to obtain stable light transmittance, and that the mechanical strength of the film deteriorated.

The object of the present invention has been made in view of the above points, and by using a thin film formed by depositing an inorganic substance on a substrate as a light-transmitting film, it is possible to transmit not only g# & i-line but also excimer. It is an object of the present invention to provide a dustproof body with high light transmittance that does not cause photodecomposition even when irradiated with short wavelength light such as a laser for a long period of time.

[Means to solve the problem]

The present invention provides a step of obtaining a gel thin film by spreading a sol on a liquid surface formed to have a higher specific gravity and surface tension than the sol when manufacturing a highly light transmitting dustproof body; The gist of the present invention includes the steps of heat-treating the gel thin film to obtain an inorganic film, and stretching the gel thin film or the inorganic film on a holding frame before or after the heat treatment.

The inorganic film obtained above is preferably one containing silicon oxide as a main component (c) In addition to silicon oxide,
Li, Na, K, Cs, Mg.

Ca, Sr, Ba, Y, LaTi
Zr HfV, Nb, Ta, Cr,
Fe, Co, Ni, Pd.

Au, Zn, Cd, B, AI, I
n, C, GeSn, Pb, N, P,
It may contain elements such as As, Sb, O, S, F, etc. or element oxides.

As a method for obtaining a gel thin film from a sol, a so-called sol-gel method can be used.

In the sol-gel method, a sol is prepared by dissolving or dispersing fine particles of an organometallic compound such as a metal alkoxide or a metal oxide as a starting material in an appropriate solvent, and a thin gel film is obtained from this sol, which is then dried. Thereafter, the gel thin film is heated to form a glass-like inorganic film.

In addition, when preparing the above-mentioned sol, a wood catalyst, a deflocculant, etc. may be added as necessary.

Examples of the metal alkoxide include tetramethoxysilane (S i (OCHa) 4), tetraethoxysilane (S I (OC2Hs) 4),
Aluminum isopropoxide (A l (OCR[CH3] 2) 3), titanium isopropoxide (T i (OCR[CH3]
Cop) 4), Zirconium propoxide (Z r
(OC3H7) 4) etc. can be exemplified.

In addition to the metal alkoxides, starting materials include silicon octylate (S i (Cv H+ s COO) 4) and aluminum octylate (AI (Cv HIs Co0)).
Examples include organic acid metals such as 3).

Examples of the metal oxide fine particles include silicon oxide fine particles obtained by hydrolysis of the metal alkoxide and silicon oxide fine particles produced by flame hydrolysis of metal chlorides.

Further, the solvent is not particularly limited, and any solvent that can be used in a normal sol-gel method may be used. Examples of such solvents include alcohols such as tert-butanol, impropatol, ethanol, and methanol, amides such as formamide and dimethylformamide, aromatic hydrocarbons such as benzene, toluene, and xylene, pentane, hexane, Aliphatic hydrocarbons such as heptane and octane, glycols such as ethylene glycol, diethylene glycol and triethylene glycol, jetanolamine,
Examples include amines such as triethanolamine, needles such as ethylene glycol monoethyl ether and ethylene glycol monoethyl ether, ketones such as acetone and methyl ethyl ketone, and β-diketones such as acetylacetone and benzoylacetone.

The amount of the solvent to be used is not particularly limited, but is preferably in the range of 0.1 to 20 moles per mole of metal constituting the inorganic membrane.

Further, when a catalyst is added when preparing a sol, examples of the catalyst include hydrochloric acid, nitric acid, acetic acid, silicon tetrachloride, hydrofluoric acid, titanium tetrachloride, sodium hydroxide, and aqueous ammonia. The amount of catalyst to be added is 1.1 to 1 mole of metal constituting the inorganic membrane. Ox 10-5~1.0
A molar range is preferred.

Furthermore, when a peptizing agent is added when preparing the sol, for example, hydrochloric acid, nitric acid, acetic acid, hydrofluoric acid, aqueous ammonia, polyvinyl alcohol, etc. can be used. The amount of such peptizer added is 20% of the sol to be prepared.
It is best if it is less than % by weight.

In addition, when adding water during the preparation of the sol,
The amount of water added is preferably in the range of 0.1 to 20 moles per mole of metal constituting the inorganic membrane.

A sol can be prepared by adding fine particles of an organometallic compound or metal oxide to a solvent and stirring the mixture at a temperature ranging from usually room temperature to the reflux temperature of the solvent, or by adding fine particles of an organometallic compound or metal oxide to a solvent, usually at room temperature. The solvent is added while stirring at a temperature ranging from 100 to reflux temperature of the solvent.

When adding the NoK catalyst and peptizer in the above process, the method of addition is not particularly limited, but it is preferable to add them to the solvent in advance and mix thoroughly.

A so-called casting method can be used to obtain a gel thin film from the sol obtained as described above.

The casting method is a method in which the sol is spread on a liquid surface to form a liquid film of the sol on the liquid surface.

The liquid surface used in this casting method needs to be a liquid surface formed by a liquid having a higher specific gravity and higher surface tension than the sol.

Suitable liquids for this purpose include, for example, acetylenetetrabu tff phyto(CHB N r 2 CHB r 2
) can be exemplified. At this time, it is preferable that the viscosity of the sol is adjusted in advance using an evaporator or the like so that it can be easily formed into a film.

The sol liquid film developed on the liquid surface -L becomes a thin gel film when left standing for a certain period of time. Then, this gel thin film is scooped off from the liquid surface 1- and dried with hot air or the like to form a dry gel thin film.

The dry gel thin film thus obtained is fixed to a metal or ceramic holder and then heat-treated. The heat treatment is performed continuously for 0.1 to 5 hours at, for example, 300 to 1000°C.High light transmittance film 3 made of an inorganic film
is completed. At this time, the heat treatment atmosphere is preferably in the air or in an oxygen-containing gas.

Note that fixing to the holder may be done at the gel thin film stage before heat treatment as described above. During heating, the gel thin film is attached to another substrate, and the inorganic film obtained after heating is may be attached to a separate holder.

Here, the thickness of the highly light transmitting film 3 is preferably 10 μm.
m, particularly preferably 0.2 to 5.0 p
The average light transmittance for light between 240 and 500 nm is 8.
It transmits 5% or more. Here, the average light transmittance is the average value of peaks and valleys of interference waves of light transmittance occurring between 240 and 500 nm.

It is preferable that the film thickness be even thinner than the above-mentioned 1107J. Generally, if the film thickness is less than 0.2 μm, sufficient strength cannot be obtained in many cases. However, it goes without saying that the film thickness may be less than this value if there is no problem in terms of strength.

On the other hand, the thickness of the film may be 10 μm or more.C Considering the increase in optical aberration during exposure, etc., 1
It is preferably 101I or less.

The thickness of the highly light transmitting film 3 is selected so that the transmittance is high for the wavelength used for exposure. In the present invention,
Such film thickness can be controlled by the viscosity of the sol, the surface tension of the solvent used to prepare the sol, and the like.

Here, the thickness of the highly light transmitting film is d4, the refractive index is n4,
When the wavelength is λ (where m is an integer greater than or equal to 1), reflection is prevented and the transmittance is highest. For example n
, = 1.5, to increase the transmittance of the g-line (436 nm), the film thickness d1 should be 0.87 μm, and to increase the transmittance of the excimer laser (248 nm), the film thickness d, to 0.83 or 2.48 μm.

Here, in order to prevent a decrease in transmittance due to the inability to obtain the desired film thickness or destabilization of transmittance due to wavelength fluctuations, high light transmittance is required as shown in Figure 2. An antireflection layer 7 may be further laminated on top of the film 3.

When such an anti-reflection layer 7 is laminated, the refractive index of the highly light transmitting film 3 is nl, and the refractive index of the anti-reflection layer 7 is n2.
, when the thickness of the antireflection layer 7 is d2, (p v'n + =n2, ■d2=mλ/(4
n2) (7) If the refractive index and film thickness are selected to satisfy both formulas, reflection will be prevented and the transmittance will be the highest. Further, the antireflection layer 7 may be laminated on either one side or both sides of the high light transmittance film 3.

The refractive index n of such a highly light transmitting film 3 is 1.5 to 1.6. Therefore, n 2−V'n
This means that a material having a refractive index of 1.22 to 1.26 (7) may be laminated as the antireflection layer 7.

Examples of such substances include calcium fluoride (
CaF2).

In order to laminate such a compound, a vacuum evaporation method, a sputtering method, etc. can be used.

Also, anti-reflection layer 77! l", as shown in FIG. 3, in the case of a two-layer structure of a high refractive index layer 7a and a low refractive index layer 7b, the refractive index of the high light transmittance film 3 is nl, and the high refractive index layer 7a is When the refractive index of the low refractive index layer 7b is n2, its film thickness is d2, the refractive index of the low refractive index layer 7b is n3, and its film thickness is d3, (D v'n' + -n 2 / n3, ■d2-m
λ/4n2. Reflection can be completely prevented by selecting a refractive index and film thickness that satisfy the following three formulas: and ■d3=mλ/4n3
High transmittance can be obtained.

Examples of materials for the high refractive index layer 7a include cerium fluoride (CeF3), cesium bromide (C8Br),
Examples include inorganic substances such as magnesium oxide (MgO) and lead fluoride (PbF2).

Examples of materials for the low refractive index layer 7b include lithium fluoride (LiF) and magnesium fluoride (MgF).
2), inorganic substances such as sodium fluoride (NaF) can be mentioned. Moreover, sputtering method, vacuum evaporation method, etc. can be used to laminate the high refractive index layer 7a and the low refractive index layer 7b.

The high light transmittance film 3 is stretched over the holding frame 2 to complete a high light transmittance dustproof body.

The high light transmittance dustproof body 1 obtained as described above is attached to a mask 4 with double-sided adhesive tape or the like, as shown in FIG. By using the mask 4 whose surface is protected by such a high light transmittance dustproof body 1, the shadow of foreign matter such as dust is prevented from being transferred onto the wafer during exposure.

That is, a structure in which dust is prevented from directly adhering to the surface of the mask 4 due to the protective space S formed by the surface of the mask 4, the inner surface of the holding frame 2, and the inner surface of the high light transmittance film 3. It becomes. Due to this structure, even if dust falls on the outer surface of the highly transparent gland 3, the shadow of this dust becomes out of focus, that is, it becomes a dead focus, and the shadow of the dust is transferred onto the wafer. Never.

Note that the high light transmittance dustproof body 1 may be attached to the mask 4 not only on one side but also on both sides.

[Effect]

According to the above-mentioned L stage, a thin gel film obtained by spreading a sol on the liquid surface by a casting method is heat-treated to form an inorganic film. It is possible to provide a dustproof body with high light transmittance that does not cause the film to become opaque or deteriorate in mechanical strength due to photodecomposition even when irradiated over a long period of time.

<Example> [Example 1] 10% of tetraethogysilane (Sl(○C2H3)4)
mol, water 100 mol, nitric acid 0.05 mol, ethanol 5
．． The 0 mol mixture was stirred at room temperature for 3 hours and then distilled under reduced pressure until the viscosity was 1. A concentrated solution was obtained by concentrating the mixture to Oc P s.

Next, liquid level 1 formed by acetylene tetrabromide (CHB r2CHBr2):
.

The concentrated solution is developed to form a sol film of the concentrated solution on the acetylene tetrabromide solution.

The sol liquid film was left standing at room temperature I7 to gelate into a gel thin film. This gel thin film was scooped up from above the acetylene tetrabromide liquid surface and dried with hot air at 40° C. for 30 minutes.

The dried gel film obtained by drying in this way was
After pasting and fixing on a 0 mm quartz glass frame, the temperature was raised to 600° C. over 30 hours in an electric furnace, held at this temperature for 2 hours, and then cooled to room temperature over a further 30 hours.

The inorganic membrane (dry gel membrane) obtained as above is
The refractive index is 1.53, the film thickness is 2.20 μm, and 248
Transmittance in nm is 98.9%, 240-500nm
The average light transmittance was 92.0%.

[Example 2] Both surfaces of the inorganic film obtained in Example 1 were coated with CaF2 to a thickness of 50 nm as an antireflection layer 7 by vacuum evaporation.

The inorganic film provided with the antireflection layer 7 thus obtained exhibited a high light transmittance of 99.8% over the range of 230 to 260 nm.

〔Effect of the invention〕

According to the present invention, a thin gel film obtained by spreading a sol on a liquid surface by a casting method is heat-treated to form an inorganic film. Water By making this a highly light-transparent film, a highly light-transparent dustproof material that does not cause the film to become opaque due to photodecomposition or deteriorate its mechanical strength even when irradiated with short wavelength light for a long period of time. can be provided.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a highly light-transparent dustproof body obtained by the present invention attached to a mask, and FIGS. 2 and 3 are cross-sectional views showing the structure of the highly light-transparent film. Body, 2. Holding frame, 3. High light transmittance A

Claims (3)

[Claims] (1) A step of spreading a sol on a liquid surface formed to have a higher specific gravity and surface tension than the sol to obtain a thin gel film, and a step of heat-treating the thin gel film to obtain an inorganic film. . A method for manufacturing a highly light-transmitting dustproof body, including the step of stretching the gel thin film or the inorganic film on a holding frame before or after the heat treatment. (2) The method for producing a high light transmittance dustproof body according to claim 1, wherein the sol is a solution in which fine particles of an organometallic compound or a metal oxide are dissolved or dispersed. (3) The inorganic film has a film thickness of 0.2 μm to 10 μm and an average light transmittance of 85% for light of 240 nm to 500 nm.
2. The method of manufacturing a highly light-transmitting dust-proof body according to claim 1, wherein the dust-proof body has a high light transmittance.