JPH03276154A - Production of dustproof body having high light transmittance - Google Patents

Abstract

PURPOSE:To prevent photodisintegration even by irradiation with light having short wavelength over a long period of time by using an inorg. film grown on a substrate by oxidation under heating as a pellicle. CONSTITUTION:A silicon wafer 5 is heated and a silicon oxide layer 6 is grown on both sides of the wafer 5 by oxidation. A photoresist layer 7 is formed on the entire surface of the layer 6, irradiated with UV from the rear side of the wafer 5 through a mask 9 and developed. The disclosed layer 6 is removed with an etching soln. and the disclosed wafer 5 is removed by etching. The remaining resist layer 7 is then removed to form a pellicle.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to a photomask or reticle (hereinafter simply referred to as a mask) used in a photolithography process in the manufacturing process of semiconductor devices such as ICs and LSIs. The present invention relates to a dustproof body used to prevent foreign matter from adhering to the present invention, and a method for manufacturing the same.

[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. The problem of dust adhesion is a serious problem in the reduced-intensity projection exposure process, which uses a reticle as a mask to sequentially transfer circuit patterns onto chip areas on a wafer.

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

[Problem to be solved by the invention]

By the way, as the degree of integration of semiconductor devices improves, the wavelength of the light beam during exposure has changed from the g-line (436nm) to the i-line (365nm).
m), and 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, causing the film to break down. In view of the above points, it has been clarified that the thin film itself becomes opaque, stable light transmittance commensurate with short wavelengths cannot be obtained, and the mechanical strength of the thin film deteriorates. By growing an oxide film on the substrate by thermal oxidation and using this oxide film as a light-transparent film, it does not undergo photodecomposition even when irradiated with 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 any damage.

[Means to solve the problem]

The present invention provides a dustproof body equipped with a holding frame attached to a mask and a transparent light-transmitting film attached to the holding frame, in which an inorganic film is grown on a substrate by thermal oxidation, and then the inorganic film is grown on a substrate by thermal oxidation. The gist of the present invention is a method for manufacturing a highly light-transparent dust-proof body in which a light-transparent film is used as a single substrate from a substrate and a holding frame is provided.

Here, the substrate is, for example, a silicon substrate, that is, a silicon wafer 5, and the shape of such silicon wafer 5 may be a disk shape sliced from an ingot, but it may be used in a reduction projection exposure apparatus. Considering that it is attached to a mask, one side is 50 mm −2
It is desirable that it be a rectangular flat plate of about 00 mm, preferably about 100 mm. Also, the thickness of the substrate is 0.2
~1.0 mm is preferred.

Note that an oxide single crystal substrate such as a sapphire substrate or the like may also be used as the silicon substrate.

The inorganic film grown on the substrate by thermal oxidation treatment is, for example, the silicon oxide layer 6 obtained by heat-treating the silicon wafer using a thermal diffusion device, etc., at a temperature of 900°C to 1400°C. By heat treatment for 5 hours to 400 hours under the conditions, 0.2 μm to 101
A film thickness of 1 m can be obtained. Further, for example, after forming a silicon thin film on a sapphire substrate by a CVD method or the like, a silicon oxide thin film with a thickness of 0.2 μm to 10 μm can be obtained by the heat treatment.

The inorganic film thus obtained is referred to as a light-transmitting film 3.

Here, the thickness of the light transmitting film 3 is preferably 1.0 μm.
less than m, particularly preferably 0.2 to S, 240 μm
It transmits 85% or more of light with an average light transmittance of 500 nm to 500 nm. Here, the average light transmittance is 240
This is the average value of the peaks and valleys of interference waves of light transmittance occurring between 500 nm and 500 nm.

Although it is preferable that the film thickness be even thinner than the above-mentioned 10 pm, 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 pm or more.C Considering the increase in optical aberration during exposure, etc., 1
It is preferably 0 μm or less.

The thickness of the light-transmitting film 3 is selected so that the transmittance is high for the wavelength used for exposure. In the present invention, when growing silicon oxide on a silicon substrate, such film thickness can be controlled by the temperature, time, etc. of the thermal oxidation treatment for the silicon wafer 5, which is the silicon substrate.

Here, the thickness of the light transmitting film 3 is d7, the refractive index is 01,
When the wavelength is λ (where m is an integer of 1 or more), reflection is prevented and transmittance is highest. For example, n
, = 1.5, to increase the transmittance of li and g lines (436 nm), the film thickness d1 is set to 0.87 μm, and to increase the transmittance of 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 to prevent transmittance from becoming unstable due to fluctuations in wavelength, it is necessary to An antireflection layer 11 may be further laminated on the upper layer of 3.

When such an antireflection layer 11 is laminated, the refractive index of the light transmitting film 3 is n3, and the refractive index of the antireflection layer 11 is 0.
2. When the thickness of the antireflection layer 11 is d2, C) V'
If the refractive index and film thickness are selected to satisfy both the equations n+=n2 and @d2=mλ/(4n2), reflection will be prevented and the transmittance will be the highest. Further, the antireflection layer 11 is a light transmitting film 3.
It may be laminated on either one side or both sides.

In this way, when the silicon oxide film formed on the silicon wafer is used as the light transmitting film 3, the refractive index n1 is 1.5.
~1.6. Therefore, n 2 = 7n +
This means that a material having a refractive index of 1.22 to 1.26 may be laminated as the antireflection layer 11. 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.

In addition, when the antireflection layer 118 has a two-layer structure of a high refractive index layer 12a and a low refractive index layer 12b as shown in FIG. Rate layer 1
The refractive index of 2a is n2, its film thickness is d2, and the low refractive index layer 12
If the refractive index of b is nl and its film thickness is d, then ■φ1
If you select a refractive index and film thickness that satisfy the following three formulas: 1 = n 2 / n 3, d2 = mλ/4n2, and d, = mλ/4n3, reflection will be completely prevented and high transmittance will be obtained. can.

Examples of materials for the high refractive index layer 12a include cerium fluoride (CeF3) and cesium bromide (CsBr).
, magnesium oxide (MgO), fluoride film (PbF2)
Inorganic substances such as

Examples of materials for the low refractive index layer 12b include lithium fluoride (LiF) and magnesium fluoride (M
Examples include inorganic substances such as g F2 ) and sodium fluoride (NaF). Further, the high refractive index layer 12a
In order to laminate the low refractive index layer 12b, a sputtering method, a vacuum evaporation method, or the like can be used.

Methods for forming the light-transmitting film 3 into a single film include, for example, a method in which an inorganic film grown on a substrate is peeled off from the substrate by physical means, a method in which the substrate portion is decomposed and removed by heating the substrate, and the like. There is also a method of removing the substrate by etching using a solvent or the like. In particular, when performing etching removal, by leaving the hawk substrate in a frame shape and etching only the central portion, the high light transmittance film 3 and the holding frame 2 can be integrated with the remaining part of the substrate as the holding frame 2. It can be formed into.

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, the protected space S composed of the surface of the mask 40, the inner surface of the holding frame 2, and the inner surface of the light transmitting M3,
The structure prevents dust 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 dust shadow becomes a dead focus, and the dust shadow is transferred onto the wafer. Never.

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

[Effect]

According to the above-mentioned means, by using an inorganic film grown by thermal oxidation treatment of a substrate as a light-transmitting film, the opacity of the film due to photodecomposition ([and thin film No deterioration of mechanical strength occurs.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIGS. 1(a) to 1(f) are cross-sectional views sequentially showing a method for manufacturing a highly light-transmitting dustproof body of the present invention.

First, a silicon wafer 5 constituting a substrate is prepared. This silicon wafer is obtained by slicing an ingot obtained by a single crystal pulling method to a thickness of 0.5 mm, and its negative surface is mirror-finished.

In the following description, for convenience of explanation, the mirror side of the silicon wafer 5 will be referred to as the front surface, and the opposite side to the mirror surface will be referred to as the back surface.

The entire surface of the silicon wafer 5 was heated at 1200° C. for 20 hours using a heat diffusion device, etc., and a 1 μm thick silicon oxide layer 6 was grown on both sides of the silicon wafer (Fig. 1(a)). ).

Subsequently, a photoresist solution was spin coated on the outer surface of the silicon oxide layer 6 using a spin coater and dried with hot air to form a photoresist layer 7 with a thickness of 5 μm (
Figure 1(b)). Note that the photoresist layer 7 formed here uses a so-called decomposable photoresist material, and preferably has a layer thickness of 1 to 1 μm.

Next, a light-shielding mask 9 was positioned on the back side of the silicon wafer 5, and ultraviolet rays were irradiated from outside of the light-shielding mask 9.The decomposable photoresist layer 7 was then irradiated with ultraviolet rays. After changing the chemical properties of the irradiated area, the photoresist layer 7 in the irradiated area was removed in a subsequent development step (FIG. 1(C)).

Then, using the photoresist layer 7 remaining in the step explained in FIG. 1(C) as a mask, the exposed portion of the silicon oxide layer 6 is removed using an etching solution such as hydrogen fluoride at 30°C. , the back side of the silicon wafer 5 was exposed (FIG. 1(d)).

Further, the silicon wafer 5 was etched with an aqueous solution such as potassium hydroxide at 50° C. to remove the exposed portion, that is, the central portion of the silicon wafer 5 (FIG. 1(e)).

Then, by removing all the remaining photoresist layer 7, the remaining part of the silicon wafer 5 becomes the holding frame 2, and the silicon oxide layer 6 becomes a single film to form the light transmitting film 3. A permeable dustproof body 1 was obtained (FIG. 1(f)).

The light transmitting film 3 of the highly light transmitting dustproof body 11 thus obtained has a refractive index of 1.53, a film thickness of 1 μm, and a transmittance of 98.0% at 248 nm.
The average light transmittance in the wavelength range of 0 to 500 nm is 92.0%. It is possible to provide a dustproof body with high light transmittance that does not undergo photodecomposition even when irradiated with light for a long period of time.

[Brief explanation of drawings]

FIGS. 1(a) to (f) are cross-sectional views sequentially illustrating the method for manufacturing a highly light-transparent dust-proof body of the present invention, and FIG. FIG. 3 is a cross-sectional view showing a state in which the mask is attached to a mask, FIG. 3 is a cross-sectional view showing a state in which an antireflection layer is formed on the upper layer of a light-transmitting film, and FIG. 4 is a modified example thereof. 1 ・ ・ ・ 2 ・ ・ ・ 3 ・ ・ 4 ・ ・ ・ 5 ・ ・ 6 ・ ・ 7 ・ ・ ・ 9 ・ ・ 10 ・ ・ 11 ・ ・ 12a ・ 12b ・ Right to retain high light transmittance dustproof body Light-transmitting film (inorganic film), mask, silicon wafer (substrate), silicon oxide layer, photoresist layer, light-shielding mask, S...protective space, ・Double-sided adhesive tape, ・Anti-reflection layer, ・・High refractive index layer...low refractive index layer. v 5 Figure 2 Figure 3 11 ゝ11

Claims (3)

[Claims] (1) In a dustproof body equipped with a holding frame attached to a mask and a transparent light-transmitting film attached to this holding frame, an inorganic film is grown on a substrate by thermal oxidation, and then this inorganic film is A method for manufacturing a highly light-transparent dustproof body, characterized in that a holding frame is provided by forming a single film from a substrate as a light-transparent film. (2) The method for producing a high light transmittance dustproof body according to claim 1, wherein the inorganic film is made of silicon oxide that transmits 85% or more of light in the wavelength range of 240 to 500 nm in average light transmittance. (3) The substrate is a silicon substrate, and the inorganic film is
With a thickness of less than 10 μm grown on a silicon substrate, 24
2. The method for manufacturing a highly light-transmitting dust-proof body according to claim 1, which is made of silicon oxide that transmits 85% or more of light in the wavelength range of 0 to 500 nm in terms of average light transmittance.