JP2754657B2 - High light-transmitting dust-proof coating with anti-reflection layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high light transmission having an antireflection layer for preventing foreign matter such as dust from adhering to a photomask or a reticle in a semiconductor manufacturing process. The present invention relates to a dustproof film, particularly a dustproof film that can be used for two types of irradiation light.

[Conventional technology]

In the manufacture of semiconductors such as LSIs, in the lithography process of transferring the mask pattern of a photomask to a photoresist, it is necessary to prevent foreign substances from adhering to the photomask or reticle. For this reason, the photomask or reticle is called a pellicle. Protected with a dustproof film.

Exposure apparatuses (steppers) used in photolithography include those having an irradiation light wavelength of 365 nm (i-line) (i-line stepper) and those of 436 nm (g-line) (g-line stepper). We use both. In this case, the dustproof film has high translucency with respect to i-line but does not have high translucency with respect to g-line.
Some have high translucency for lines but not high for i-lines. For each i-line stepper and g-line stepper, a suitable dustproof film must be prepared and used. There is complexity that must be done.

In order to solve such complexity, one dustproof film can
A dust-proof film having high transmittance to both light of the g-line and the g-line has been proposed (Japanese Patent Application No. 62-290882). This dust-proof film, using the fact that the light transmittance curve with respect to the film thickness draws a sine curve, a film thickness such that both the transmittance of 365 nm light and the transmittance of 436 nm light increase, for example, 1.45 to 1.48 μ
m is selected.

However, in the above-described conventional dustproof film, since the range of the film thickness showing a high transmittance for both the i-line and the g-line is narrow, the transmittance greatly varies with a slight change in the film thickness. Further, it is difficult to control the film thickness in a narrow range, and it is practically difficult to obtain a dustproof film having a high transmittance for both the i-line and the g-line.

On the other hand, as a means for enlarging a region of the dustproof film having a high transmittance, an antireflection layer is formed on one or both surfaces of the dustproof film. However, when the antireflection layer is formed on the dust-proof film that exhibits high transmittance for both the i-line and the g-line as described above, the region that exhibits high transmittance for both the i-line and the g-line is narrowed. There is a problem.

[Problems to be solved by the invention]

An object of the present invention is to provide an anti-reflection layer having a high transmittance for both of the two types of irradiation light and a wide range of film thickness showing a high transmittance in order to solve the above-described problems. An object of the present invention is to provide a high light-transmitting dustproof film.

[Means for solving the problem]

The present invention is a highly light-transmitting dustproof film having the following antireflection layer.

(1) A dustproof film which is formed by laminating antireflection layers on both sides of a base layer made of a cellulose derivative and is shared by two types of irradiation light,
The thickness of the base layer is d ₁ (μm), the average value of the refractive index of the base layer with respect to the above two types of irradiation light is n ₁ , the thickness of each antireflection layer is d ₂ (nm), and the above two types of irradiation light If the average value of the refractive index of the antireflection layer was n ₂ with respect to, d _1, d ₂ is ^{_{7.909n 1 2 -22.92n 1 + 18.14 ≧}} d 1 ≧ -1.935n 1 3 + 13.08n 1 2 -27.04 n ₁ +18.82 ... in the range of [I] and _{-105.2n 2 + 281.9 ≧ d 2 ≧} -441.4n 2 2 + 1184n 2 -731.8 ... [II], the two irradiation light 98% Highly light-transmitting dustproof film characterized by transmission.

(2) The highly light-permeable dustproof film according to the above (1), wherein the cellulose derivative is cellulose propionate.

(3) The thickness of the base layer is 1.29 to 1.34 μm, the thickness of the anti-reflection layer is 62 to 99 nm, and the irradiation light having wavelengths of 365 nm and 436 nm is 98%.
The highly light-transmitting dustproof film according to the above (2), which transmits the above.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing an example of a dustproof film. In the figure, 1 is a dustproof film,
Antireflection layers 3 are formed on both sides of the base layer 2.

In the present invention, examples of the cellulose derivative used as the base layer 2 include ethyl cellulose, cellulose acetate, cellulose sulfate, cellulose phosphate, and fatty acid cellulose such as cellulose propionate. Cellulose propionate is preferred from the viewpoints of strength and ease of film formation.

Range thickness d ₁ of the base layer 2 is represented by the formula [I] wherein preferably the range indicated by _{-0.9136n 1 + 2.720 ≧ d 1 ≧} -1.036n 1 + 2.854 ... (III), shared When the irradiation light is i-line and g-line, those having a range of 1.29 to 1.34 μm are used. The film thickness in the range represented by the above formula [III] is preferable because it can be easily produced by a usual method. In the case of the cellulose propionate monolayer film, the film thickness showing a high transmittance for both the i-line and the g-line is 1.45 to 1.48 μm as described later, and 1.29 to 1.
A film having a thickness of 34 μm does not show a high transmittance for both the i-line and the g-line, but by selecting a film thickness in this range, when the antireflection layer 3 is formed, a transmittance of 98% or more is obtained. Rate can be obtained.

The antireflection layer 3 of FIG. 1, to use a mean value n ₂ of the average value n ₁ is smaller than the refractive index of the refractive index of the base layer 2 with respect to two irradiation light. For example, when a thin film of cellulose propionate is used for the base layer 2, the average value n ₁ of the refractive index for the i-line and the g-line of the base layer 2 is 1.51, and the average value n ₂ of the refractive index for the antireflection layer 3 is Those smaller than 1.51, preferably 1.
It is preferable to use one having a low refractive index of 37 or less. Commonly used low refractive index materials include, for example, tetrafluoroethylene / vinylidene fluoride copolymer,
Tetrafluoroethylene / vinylidene fluoride / hexafluoropropylene copolymer or acrylic fluoropolymer such as CH ₂ CHCOOR ¹ or CH ₂ ＣC
(CH ₃ ) COOR ² [where R ¹ and R ² are fluoroalkyl groups which may contain an ether oxygen atom therebetween] Polyfluoro (meth) comprising at least one monomer selected from
Fluorine-based polymers such as acrylates can be used.

Range thickness d ₂ of each of the antireflection layer 3 is represented by [II] wherein preferably _{-20.03n 2 + 126.7 ≧ d 2 ≧} -441.4n 2 2 + 1184n 2 -731.8 ... shown in (IV) In the case where the shared irradiation light is i-line and g-line, the light having a range of 62 to 99 nm is used. Above [IV]
The film thickness in the range shown by the formula is preferable because it can be easily produced by a usual method.

The transmittance of light of a specific wavelength varies depending on the film thickness, and the transmittance curve for the film thickness draws a sine curve. Therefore, when a transmittance curve is drawn for two types of shared irradiation light, for example, i-line and g-line, different sine curves are obtained. The two types of irradiation light, for example, the i-line and g-line shared dustproof film have a film thickness at which the peaks of both transmittance curves coincide with each other, that is, a high transmission for the two types of irradiation light, for example, both the i-line and the g-line. A light-transmitting film having a film thickness exhibiting a specific ratio is used. When such a light-transmitting film is used as a base layer 2 and an anti-reflection layer 3 is formed thereon,
On the contrary, the range of the film thickness that shows high transparency to various kinds of irradiation light, for example, both the i-line and the g-line is narrowed.

FIG. 2 (b) is a transmittance curve diagram of the i-line (365 nm) and the g-line (436 nm) with respect to the film thickness of the cellulose propionate film on which the antireflection layer 3 is not laminated, and shows the peak A, ie, 1.45 to 1.48 μm. It can be seen that the transmittance for both the i-line and the g-line is high in the range of the film thickness.

FIG. 2 (a) shows a high-light-transmitting dustproof layer in which a 79 nm-thick fluoropolymer antireflection layer 3 (average refractive index for i-line and g-line 1.37) is laminated on both surfaces of a cellulose propionate film (base layer). For the film, i-line (365 nm) and g-line (4 nm) with respect to a change in the thickness of the base layer 2 (the thickness of the antireflection layer is constant).
FIG. 2 (b) shows a peak curve A in FIG. 2 (b), which is divided into two peaks as shown by a peak B in FIG. 2 (a), and shows high transmittance in both i-line and g-line. The range is narrow. On the other hand, the peak C, which was separated into two in FIG. 2B, that is, the film thickness of the base layer 2 is 1.29 to 1.
In the range of 34 μm, the peak coincides as shown by the peak D in (a), shows a high transmittance for both the i-line and the g-line, and the range of the film thickness having a transmittance of 98% or more is widened. I have.

In the state where the antireflection layer 3 is not laminated as described above, the film thickness of 1.29 to 1.34 μm in which the transmittance of both the i-line and the g-line is not high.
By forming the above-described anti-reflection layer 3 on the base layer 2 in the range of, high light transmittance having both the i-line and the g-line and high transmittance and having a wide range of high transmittance is obtained. A dustproof film is obtained.

Hereinafter, the process of deriving the formulas [I] to [IV] will be described.

In general, the transmittance T of the thin film is d, the thickness of the thin film is n, the refractive index of the thin film is n, the refractive index of the incident side phase is n ₁₁ , the refractive index of the transmission side phase is n ₁₂ , and the wavelength of the transmitted light is λ. When the incident angle is 0 (normal incidence), it is expressed by the following equation [V] (for example, published by Fuji Techno System Co., Ltd., 1984, supervised by Shunichi Tateda, "Evaluation and Application Technology Handbook", No. 134 Pp. 146, "Preparation of thin film", written by Sadao Yoshida.

T = 8n ₁₁ n ² n ₁₂ ｛(n ₁₁ ² + n ² ) (n ² + n ₁₂ ² ) + 4n ₁₁ n ² n
₁₂ + While ^{_{(n 11 2 -n 2) (}} n 2 -n 12 2) cos (4πnd / λ)} ... (V) above [V] formula is the calculation formula of the transmittance of the thin film of single-layer, 3 In the case of a layer, the total transmittance can be obtained by repeating the calculation of the equation [V] for each layer. That is, the first
In the case of the figure, the transmittance of the upper antireflection layer 3 is calculated with the incident light as 1, and the transmittance of the base layer 2 is calculated for the incident light multiplied by the transmittance thus obtained, and the transmittance obtained by this is calculated. By calculating the transmittance of the lower antireflection layer with respect to the incident light multiplied by the ratio, the overall transmittance can be obtained. In this case, the transmittance of the upper antireflection layer 3 is n
And _11, performs the calculation of the refractive index of the base layer 2 as n _12. The transmittance of the substrate 2 is the refractive index of the antireflection layer 3 of the upper and n _11,
Performing the calculation of the refractive index of the antireflection layer 3 of the lower as n _12.
Refractive index of the antireflection layer 3 on the lower side and the refractive index of the base layer 2 and n _11, performs calculation of the refractive index of air as n _12. The following calculation is performed for the wavelengths of the i-line and the g-line by changing the refractive index and the film thickness of the base layer 2 and each antireflection layer 3 based on the calculation of the entire transmittance. Ask.

As an initial setting, the thickness of the base layer 2 is fixed at 1200 nm, the refractive index is fixed at 1.494 at a wavelength of 365 nm, and 1.484 at a wavelength of 436 nm.
The incident angle was set to 0 degree (normal incidence), the thickness of each antireflection layer 3 was set to 60 nm, and the refractive index was set to 1.34.
The substrate film thickness at which the transmittance at a wavelength of 436 nm is both 98% or more is plotted.

The calculation was performed by adding the thickness of the antireflection layer 3 to 2 nm, and the calculation was repeated until the thickness of the antireflection layer 3 became 150 nm.

The calculation is performed by adding the refractive index of the anti-reflection layer 3 to 0.5, and the calculation is repeated until the refractive index of the anti-reflection layer 3 becomes 1.40.

The calculation is performed by adding the thickness of the base layer 2 to 5 nm, and the calculation is repeated until the thickness of the base layer 2 becomes 1800 nm.

When the plot of the transmittance of 98% or more obtained in the above is represented on the coordinates of the base layer refractive index on the horizontal axis and the base layer thickness on the vertical axis, the plot is dispersed in a band-like region extending to the right and diverging almost horizontally. Therefore, by obtaining a function by the least squares method on the upper contour line of the portion where the film thickness is widened, the expression on the left side of the inequality sign of the expression [I] was obtained as the upper limit value of the base layer 2. In this case, the refractive indices of the base layer and the antireflection layer were represented as the average of the refractive indices for two types of irradiation light. Similarly, by calculating the function of the lower contour line where the film thickness is the largest, the equation on the right side of the inequality sign of the equation [I] was obtained as the equation of the lower limit value of the base layer 2.

If the horizontal axis represents the refractive index of the antireflection layer and the vertical axis represents the coordinates of the thickness of the antireflection layer, and the plot of the transmittance of 98% or more obtained in the above is represented by the coordinates of the antireflection layer thickness, the belt-shaped region extends to the right and extends substantially in the horizontal direction. As the upper limit of the antireflection layer is obtained by calculating the function by the least square method in the same manner as the upper contour line of the portion where the film thickness is widened, The formula was obtained. Similarly, by calculating the function of the lower contour line where the film thickness is the widest,
The expression on the right side of the inequality sign of the expression [II] was obtained as the expression of the lower limit value of the antireflection layer.

In the above description, if the thickness of the anti-reflection layer in which the film is easily formed is plotted in the range of 60 to 100 nm similarly to the coordinates of the base layer, it is dispersed in a band-like region extending substantially in the horizontal direction, so that the film thickness is the widest. By calculating the function of the upper contour line, the equation on the left side of the inequality sign of the equation [III] was obtained as the equation of the upper limit of the preferable range. Similarly, by calculating the function of the lower contour line where the film thickness is the widest, the equation on the right side of the inequality sign of the equation [III] was obtained as the equation of the lower limit of the preferable range.

In the above, if the plot of the film thickness of the anti-reflection layer for which the film formation is easy is 60 to 100 nm is similarly represented in the coordinates of the anti-reflection layer, it is dispersed in a band-like region extending substantially in the lateral direction, and the most film thickness is obtained. By calculating the function of the expanded upper contour line, the formula of the upper limit of the preferred range [IV]
The expression to the left of the expression inequality was obtained. The contour on the lower side is the same as that of [IV], and the equation on the right side of the inequality sign of equation [IV] is the same as that of equation [II].

The method for producing a highly light-transmitting dustproof film having the antireflection layer 3 according to the present invention comprises the steps of: supplying a low-refractive-index polymer solution to both surfaces of the base layer 2 formed by a spinning method using a spinner; The antireflection layer 3 is formed by laminating a film by a method.

Specifically, first, a cellulose derivative solution is supplied onto a smooth substrate such as glass attached to a spinner, and the spinner is rotated to form a base layer 2 made of a transparent thin film of the cellulose derivative by a rotary film forming method. The cellulose derivative is dissolved in a solvent, and a purified solution such as filtration is used.
As the solvent, ketones such as methyl ethyl ketone, methyl isobutyl ketone and acetone, lower fatty acid esters such as butyl acetate and isobutyl acetate, and a mixed solvent of the aforementioned ketone or ester and isopropyl alcohol are used. The thickness within the above range is obtained by changing the thickness of the base layer 2 to be formed, the viscosity of the solution, and the rotation speed of the substrate.

The base layer 2 formed of a transparent thin film of cellulose derivative formed on the substrate is dried by means of hot air or irradiation with an infrared lamp to remove the residual solvent.

Next, a solution of a low-refractive-index polymer is supplied onto the dried base layer 2, and the antireflection layer 3 is formed so as to have a thickness within the above-described range by a rotary film forming method. The solvent that dissolves the low refractive index polymer is a solvent that can dissolve the low refractive index polymer and does not dissolve or swell the base layer 2 and has a boiling point of 40 to 220.
C, preferably in the range of 60 to 150C. For example, xylene hexafluoride, benzotrifluoride, propanol pentafluoride, etc. can be used. The concentration of the low refractive index polymer solution is preferably from 0.3 to 3% by weight.

Next, the dustproof film 1 obtained above is turned upside down and attached to a spinner, and the antireflection layer 3 is laminated on the other side of the base layer 2 by the same operation as described above.

The high light-transmitting dustproof film manufactured as described above is
Attached to a frame in the same manner as a conventional dustproof film, used as a dustproof body such as a mask or a reticle, and used with two types of irradiation light, for example, i.
It shows high transmission for both the g-line and the g-line. Further, since the width of the film thickness through which the two types of irradiation light, for example, both the i-line and the g-line, transmit at least 98% is wide, a high transmittance can be obtained even if there is a slight variation in the film thickness. It will be easier.

〔The invention's effect〕

As described above, according to the present invention, in the base layer having a specific thickness,
Since a specific anti-reflection layer is laminated, a high light-transmitting dust-proof film having a high transmittance for both of the two types of irradiation light and a wide range of film thickness showing a high transmittance is obtained. be able to.

〔Example〕

 Next, examples of the present invention will be described.

Example 1 An antireflection layer (refractive index) of 79 nm fluoropolymer (polytrifluorooctyl acrylate) was formed on a base layer having a thickness of 1.25 to 1.4 μm comprising a cellulose propionate film formed by a rotary film forming method. The average value of 1.37) of the dustproof film was measured for the i-line (365 nm) and the g-line (436
nm) was measured. The results are shown in FIG.

As can be seen from FIG. 3 (a), by laminating the antireflection layer on the base layer, the peaks of the transmittance of 100% for the i-line and the g-line almost overlap, and the variation range of the transmittance is 94 to 100.
%, And the range of the film thickness at which both the i-line and the g-line have a transmittance of 98% or more is about 43 nm, and the film thickness of the base layer at this time is 1.29 to 1.34 μm.

Comparative Example 1 The base layer of Example 1 (film thickness 1.25 to 1.
The transmittance was measured in the same manner as in Example 1 for a 4 μm thin film of cellulose propionate). The results are shown in FIG.

In FIG. 3 (b), the peaks of the transmittance of 100% for the i-line and the g-line are shifted by about 21 nm.
The range of the film thickness transmitting 98% or more is about 15 nm.

Comparative Example 2 Film thickness having a transmittance curve as shown in FIG.
The transmittance of i-line and g-line was measured for the dustproof film having an antireflection layer formed on a base layer of cellulose propionate having a thickness of 4 to 1.55 μm in the same manner as in Example 1. The results are shown in FIG.

In FIG. 4 (b), the peaks of the transmittance of 100% for the i-line and the g-line almost coincide with each other near the film thickness of 1.46 μm. Is about 28
When an anti-reflection layer is laminated on this, as shown in FIG. 4 (a), although the fluctuation width of the transmittance becomes small,
Since the peak of the transmittance of 100% for the i-line and the g-line is shifted by about 35 nm, the range of the film thickness for transmitting the 98% or more of the i-line and the g-line narrows from about 28 nm to about 19 nm.

From the results of Example 1 and Comparative Examples 1-2, 1.29-1.34
When a specific antireflection layer is laminated on a base layer having a thickness of μm, both the i-line and the g-line are 98% in the widest range.
It can be seen that a transparent dustproof film can be obtained.

Further, it can be seen that even if an antireflection layer is laminated on a film having a thickness near the overlap of the transmittances of the i-line and the g-line, the transmittances of the i-line and the g-line cannot be further improved.

Examples 2 and 3 In Example 1, the thickness of the base layer was set to 1.29 μm (Example 2) or 1.34 μm (Example 3).
The transmittance of the dustproof film having the 50 to 100 nm antireflection layer laminated thereon was measured in the same manner as in Example 1. The results are shown in FIG. 5 (a) (Example 2) and FIG. 5 (b) (Example 3).

From the above results, when an antireflection layer having a thickness of 62 to 99 nm is laminated on a base layer of cellulose propionate having a thickness of 1.29 to 1.34 μm, a dustproof film that transmits 98% or more of both i-line and g-line is obtained. It can be seen that it can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of the dust-proof film, FIGS. 2 (a) and (b) are transmittance curve diagrams with respect to the thickness of the dust-proof film, FIG.
(B), FIGS. 4 (a), (b) and 5 (a),
(B) is a transmittance curve diagram in each Example. 1: dustproof film, 2: base layer, 3: anti-reflective layer

Claims (3)

(57) [Claims] An antireflection layer laminated on both sides of a base layer made of a cellulose derivative and used for two types of irradiation light, wherein the base layer has a thickness of d ₁ (μm), When the average value of the refractive index of the base layer with respect to light is n ₁ , the thickness of each antireflection layer is d ₂ (nm), and the average value of the refractive index of the antireflection layer with respect to the above two types of irradiation light is n ₂ , d _1, d ₂ is ^{_{7.909n 1 2 -22.92n 1 + 18.14 ≧}} d 1 ≧ -1.935n 1 3 + 13.08n 1 2 -27.04n 1 +18.82 ... [I] and -105.2n ₂ +281. 9 ≧ d ₂ ≧ −441.4n ₂ ² + 1184n ₂ −731.8 A highly light-transmitting dustproof film which is in the range of [II] and transmits 98% or more of the above two types of irradiation light. 2. The highly light-permeable dustproof film according to claim 1, wherein the cellulose derivative is cellulose propionate. 3. The high light beam according to claim 2, wherein the base layer has a thickness of 1.29 to 1.34 μm and the antireflection layer has a thickness of 62 to 99 nm, and transmits at least 98% of irradiation light having wavelengths of 365 nm and 436 nm. Permeable dustproof membrane.