JPH049061A - 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 precipitating silicon dioxide on a base plate immersed in an aqueous solution of hexafluorosilic acid saturated with silica and separating the obtained thin film and fixing it to a holding frame. CONSTITUTION:The silicon dioxide thin film is deposited and formed on the surface of the base plate, such as a plastic plate, precoated with an aqueous solution of a surfactant and dried by immersing the base into an aqueous solution of hexafluorosilicic acid saturated with the silica, and this film is peeled from the base and fixed to the holding frame 2. Said solution is prepared by dissolving silicon dioxide, such as silica gel or silica glass, in a solution of hexafluorosilicic acid, thus permitting the obtained dust removing body 1 high in light transmittance to prevent opacification of the film 3 due to photodecomposition caused by long time exposure to short wavelength light and deterioration of mechanical strength of the film 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed 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 this.

C. Prior art] As a technique for coating the surface of a glass or plastic molded body with silicon dioxide, Japanese Patent Application Laid-Open No. 57-196744,
There are No. 58-161944, No. 6112734, and No. 63-112632. However, all of these techniques merely inhibit metal deposition or protect the surface from damage by coating the surface of the glass substrate or plastic molded body with silicon dioxide.

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

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 chips.

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.

[Problem to be solved by the invention]

However, 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).
), and as the wavelength shifts further to excimer lasers (248 nm), conventional dustproof bodies using transparent thin films made of organic materials have weak molecular bonding, and light is absorbed during light absorption within the thin film. It was revealed that decomposition occurs and the film itself becomes opaque, making it impossible to obtain stable light transmittance and deteriorating the mechanical strength of the film.

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 short wavelength light such as excimer laser for a long period of time. 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 over a long period of time.

[Means to solve the problem]

The present invention provides a dustproof body comprising a holding frame attached to a mask and a transparent light-transmitting film attached to the holding frame, in which a substrate is immersed in a saturated aqueous solution of silica made of hydrosilicofluoric acid. The gist of this invention is to deposit silicon dioxide to form a thin film, use this thin film as a light-transmissive film to separate the substrate from the substrate, and provide a holding frame.

Here, the substrate may be, for example, a plastic substrate such as an acrylic resin, a silicon substrate such as a silicon wafer, a quartz glass substrate, or a metal substrate such as aluminum.

Here, when using the plastic substrate, for example, after applying an aqueous surfactant solution to the surface of the plastic substrate and drying it, the plastic substrate is placed in a saturated aqueous silica solution made of hydrosilicofluoric acid. By dipping, it is possible to deposit a silicon dioxide thin film.

The surfactant aqueous solution used for this purpose must be of a level that does not form water droplets on the surface of the plastic substrate after application.
f. It may be a dilute aqueous solution. This critical concentration varies depending on the type of surfactant, but it can be diluted to a lower concentration by using a fluorine-based surfactant such as a perfluoroalkylcarboxylic acid derivative.

Further, a silica saturated aqueous solution made of hydrofluorosilicic acid can be obtained, for example, by dissolving a silicon oxide source such as silica gel or silica glass in a hydrofluorosilicic acid solution.

Further, by adding boric acid to the hydrosilicofluoric acid aqueous solution for a certain period of time or continuously, the growth of the silicon dioxide thin film on the substrate can be maintained constant. Forming a uniform film over the entire surface of the substrate I can do it. If the amount of boric acid is too small, silicon dioxide will not be deposited on the substrate, and if it is too large, silicon dioxide will precipitate in the aqueous solution.

The thickness of the thin film, i.e. the light-transparent film, obtained by precipitation of silicon dioxide is preferably less than 10 μm, particularly preferably from 0.2 to 5.0 μm, and from 240 to 500 nm.
It transmits 85% or more of the light of m in average light transmittance. Here, the average light transmittance is 240 to 500n
This is the average value of the peaks and troughs of the interference waves of light transmittance occurring between m.

As for the film thickness, it is preferable that the film is thinner than the above-mentioned 10 Pm, but in general, if it 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, but considering the increase in optical aberration during exposure, etc.
It is preferable that it is less than μm.

The thickness of the light-transmitting film 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 deposition time, the concentration of the hydrosilicic acid aqueous solution, and the like.

Here, when the thickness of the light-transmitting film is d3, the refractive index is no, and the wavelength is λ, reflection is prevented and the transmittance is the highest when (m is an integer of 1 or more). For example n
, = 1.5, to increase the transmittance of the g-line (436 nm), the film thickness d is set to 0.87 μm, and to increase the transmittance of the excimer laser (248 nm), the film thickness d1
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 to prevent the transmittance from becoming too stable due to fluctuations in wavelength, it is necessary to An antireflection layer 5 may be further laminated on the L layer of the film 3.

When such an antireflection layer 5 is laminated, the refractive index of the light transmitting film 3 is n2, the refractive index of the antireflection layer 5 is 02,
When the thickness of the antireflection layer 5 is d2, co v'n
If the refractive index and film thickness are selected to satisfy both the equations +=n2 and d2-mλ/(4n2), reflection will be prevented and the transmittance will be the highest. Further, the antireflection layer 5 is a light transmitting film 3.
It may be laminated on either one side or both sides.

In this way, when the silicon dioxide thin film formed on the substrate is used as the light-transmitting film 3, the refractive index n is 1.4-1.6. Therefore, n 2 = V'n I is 1.
This means that a material having a refractive index of 18 to 1.26 may be laminated as the antireflection layer 5. An example of such a substance is calcium fluoride (CaF2).

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

Further, when the antireflection layer 5 has a two-layer structure of a high refractive index layer 5a and a low refractive index layer 5b as shown in FIG. 3, the refractive index of the light transmitting film 3 is nl, When the refractive index of the high refractive index layer 5a is n2, its film thickness is d2, the refractive index of the low refractive index layer 5b is n3, and its film thickness is d3, ■v'n +
If the refractive index and film thickness are selected to satisfy the following three equations: = 12/na, d2-mλ/4n2, and c13=mλ/4n3, reflection can be completely prevented and high transmittance can be obtained.

For example, cerium fluoride (CeF3), cesium bromide (Cs B
r ), magnesium oxide (MgO), lead fluoride (Pb
Examples include inorganic substances such as F2).

Examples of materials for the low refractive index layer 5b include lithium fluoride (LiF) and magnesium fluoride (Mg
F2), sodium fluoride (NaF), and other inorganic substances. Moreover, sputtering method, vacuum evaporation method, etc. can be used to laminate the high refractive index layer 5a and the low refractive index layer 5b.

As a method for forming the light-transmitting film 3 into a single film, for example, the silicon dioxide thin film grown on the substrate is peeled off from the substrate by physical means.41 The substrate is heated to decompose and remove the substrate portion. There is also a method of removing the substrate by etching using a solvent or the like. In particular, when performing etching removal, the substrate is left in the form of a frame and only the central portion thereof is etched away, so that the light-transmissive film 3 and the holding frame 2 are integrated with the remaining part of the substrate as the holding frame 2. It is also possible to mold it into

The highly light-transmissive dustproof body 1 obtained as described in [2] 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, transfer of shadows of foreign matter such as dust to the wafer 10 is prevented during exposure.

That is, the protected space S constituted by the surface of the mask 4, the inner surface of the holding frame 2, and the inner surface of the light-transmitting film 3,
The structure is such that dust is prevented from directly adhering to the surface of the mask 4. Due to this structure, even if dust adheres to the outer surface of the light-transmitting film 3, the shadow of this dust becomes a dead focus, and the shadow of the dust is not transferred onto the wafer. .

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]

By depositing silicon dioxide, which is an inorganic substance, to form a thin film using the above-mentioned method, and by forming this thin film into a single film to obtain a light-transmitting film, it is possible to obtain a light-transmitting film even when irradiated with short-wavelength light for a long period of time. 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 decomposition.

<Example> [Example 1] 200 mm x 200 m in an aqueous solution of hydrosilicofluoric acid at a concentration of 2 mol/1 in which silica gel powder was dissolved until saturated.
After immersing an acrylic substrate with a size of mX 5 mm,
．． While continuously dropping a 5 mol/1 boric acid aqueous solution,
It was left for 45 hours.

Then, when the acrylic substrate was pulled out of the aqueous solution of hydrosilicic acid, a silicon dioxide thin film having a thickness of 2.2 μm was obtained.

Next, the silicon dioxide thin film is peeled off from the acrylic substrate to form a light-transparent film, and this light-transparent film has a diameter of 15 mm.
A dustproof body was obtained by attaching it to the side surface of a metal holding frame with a diameter of 0 mm and a height of 5 mm.

The light transmittance of the dustproof body thus obtained was 248n
Transmittance at m is 99.0%, 240-500
The average light transmittance in nm was 92.0%.

[Example 2] Both sides of the silicon dioxide thin film obtained in Example 1 were coated with CaF2 to a thickness of 50 nm as an antireflection layer 5 by vacuum evaporation. The permeable membrane 3 has a wavelength of 9 over a range of 230-260 nm
It showed a high light transmittance of 9.8% or more.

〔Effect of the invention〕

According to the present invention, silicon dioxide is deposited on a substrate to form a thin film, and this is made into a single film to obtain a light-transmitting film. It is possible to obtain a dustproof body with high light transmittance without causing opacity or deterioration of the mechanical strength of the film.

[Brief explanation of drawings]

1 to 3 show examples of the present invention, in which FIG. 1 is a sectional view of a highly light transmitting dustproof body obtained by the present invention attached to a mask, and FIGS. 2 and 3 are rays of light. FIG. 2 is a cross-sectional view showing the structure of a permeable membrane. 1 High light transmittance dustproof body 2...holding frame 3 Light transmittance film 4/mask
5. Antireflection layer 5a High refractive index layer 5b Low refractive index layer S Protected space

Claims (3)

[Claims] (1) In a dust-proof body equipped with a holding frame attached to a mask and a transparent light-transmitting film attached to this holding frame, a substrate immersed in a silica-saturated aqueous solution made of hydrosilicic acid 1. A method for manufacturing a highly light-transparent dust-proof body, which comprises depositing silicon to form a thin film, using the thin film as a light-transparent film to form a single film from a substrate, and providing a holding frame. (2) The high light transmittance dustproof body according to claim 1, wherein boric acid is added to an aqueous solution obtained by saturating silica of hydrosilicofluoric acid during precipitation of the silicon dioxide. Production method. (3) High light transmittance according to claim 1, characterized in that after the silicon dioxide is precipitated to obtain a thin film, an antireflection layer is formed on both or one side of the thin film to obtain a light transmitting film. A method of manufacturing a dustproof body.