JPH04139717A - Manufacture of x-ray mask - Google Patents

Abstract

PURPOSE:To manufacture an excellent X-ray mask which can cope with a finely constituted integrated circuit by coating one surface of a mask for X-ray exposure mask with a negative photosensitive film and developing the photosensitive film after irradiating the film with X-rays from the surface of the mask on the opposite side of the film. CONSTITUTION:An X-ray mask substrate material 3 which is an X-ray transmissive material is deposited on an Si substrate 2 by a prescribed thickness by vapor deposition, etc. After a pattern 4 is formed on the mask substrate 3 by plating, etching, etc., the substrate 2 on the rear of the substrate 3 is removed by back etching so that a desired field angle can be obtained. After a negative photosensitive film 5 is formed on one surface of the substrate 3 by applying a negative resist, the film 5 is irradiated with X-rays 6 from the surface of the substrate 3 on the opposite side of the film 5, with the irradiation quantity being controlled to a suitable level. When the film 5 is developed, the film 5 does not remain where the substrate 3 is thick and remains as a thick film where the substrate 3 is thin. As a result, the intensity of the X-rays transmitted through this mask is made uniform since the total thickness of the substrate 3 and film 5 becomes uniform.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a mask used for X-ray exposure, and in particular to an X-ray mask manufacturing method that improves the non-uniformity of X-ray transmittance due to non-uniformity of membrane thickness, etc. The present invention relates to a mask manufacturing method.

(Prior art and problems) In recent years, with the miniaturization of large-capacity integrated circuits such as LSI and VLSI, uniformity of line width of resist after development has become more demanding than ever. ing. In order to achieve uniformity in the absorption pattern line width of the resist after development, not only the uniformity of the line width of the exposure mask but also the uniformity of the exposure amount are important.

On the other hand, with the miniaturization of absorber patterns, it has been proposed to perform X-ray exposure as shown in FIG. 6 instead of visible light.

In this X-ray exposure method, as shown in FIG.
The pattern 4 on the mask substrate 3 is to be transferred onto the silicon wafer 8 by irradiating X116 through the optical mask 1. In this case, in order to achieve the uniformity of the exposure amount described above, it is necessary to control the exposure amount of the X-rays 6 irradiated onto the exposure mask I to a predetermined value, and at the same time It is necessary to make the transmittance uniform and the transmitted light 6° uniform.

By the way, as a method for manufacturing this Xll mask for exposure, 5solid 5tate Technology, No. 9
．． 55f1976), a common method is to remove 5i=N4 on a Si substrate and then remove the Si substrate by pack etching.

However, conventionally, in this manufacturing process, 5is
It is extremely difficult to deposit N4 with a uniform thickness over a wide area, resulting in film thickness unevenness of about ±10%. There was a problem in that the intensity of X-rays transmitted through the mask 1 at 6° was uneven, and uniformity in the line width of the resist 7 after development could not be achieved.

Therefore, an object of the present invention is to provide an XI mask with excellent characteristics in which the X-ray transmittance of the X-ray mask substrate 3 is made uniform.

(Means for solving problems) The above objects are achieved by the present invention as described below.

That is, the present invention provides X! ! ! x&! characterized by including a uniformization step of applying a photosensitive film to one side of the exposure mask, irradiating the exposure light from the opposite side to the applied side, and then developing.
This is a method for making a mask.

(Function) According to the present invention, a negative photosensitive coating is formed on one side of an X-ray exposure mask, and the coating is irradiated with an n-ray beam from the opposite side and then developed, thereby forming a mask substrate. Uniformity of X-ray transmittance is achieved, and as a result, the line width of the pattern 4 transferred to the resist 7 on the silicone wafer 8 becomes uniform.

(Example) Next, the present invention will be described in further detail with reference to examples shown in the drawings.

FIGS. 1 and 3 are diagrams showing each step of a method for manufacturing an X-ray mask according to an embodiment of the present invention.

As shown in FIG. 1(a), first, an X-ray mask substrate material 3 such as 5jsN, which is an X-ray transparent material, is deposited on a Si substrate 2 to a predetermined thickness by vapor deposition or the like.

Next, as shown in FIG. 1(b), after forming a pattern 4 on the mask substrate 3 through processes such as plating and etching,
The Si substrate 2 on the back side is removed by back etching to obtain the desired angle of view (Fig. 1(c)). The steps up to this point are the same as the conventional method of manufacturing an X-ray mask. .

Next, as shown in FIG. 1(d), a negative resist is applied to one side of the X-ray mask substrate 3 to form a negative photosensitive film 5, and then X-rays 6 are irradiated from the opposite side of the film 5. . At this time,
The amount of X-ray irradiation is set to an appropriate amount, for example, the amount of irradiation at the position of the thickest X-ray mask substrate 3 is set to the amount at which the negative photosensitive film begins to remain.

Set it so that it roars.

When this is then developed, as shown in FIG. The type photosensitive film 5 remains, and as a result, the total thickness of the X-ray mask substrate 3 and the negative type photosensitive film 5 becomes uniform throughout, so the intensity of X-ray transmission becomes uniform. will be done.

Next, the above phenomenon will be explained in more detail with reference to FIGS. 2 and 3.

Figure 2 is negative resist (chloromethylated polystyrene)
The vertical axis shows the normalized residual film rate T, and the horizontal axis shows the amount of X-ray irradiation. The irradiation amount is negative photosensitive coating 5
It is normalized by setting the irradiation dose D0 at which the amount of radiation begins to remain as 1.

This characteristic curve is T=yl within the range of irradiation D0 to 2D.
og D= 1, 61og D (can be approximated).

Figure 3 shows the shape of the resist coated on the surface of the XII mask substrate 3. Assuming that the thin point is B, the X-ray intensity that has passed through this point is 1. In such a system, the irradiation amount at point A is D
The remaining film rates at points XA and 'B are 0 and 0.
4, and if a 2 μm negative resist is applied as the initial film thickness, a 0.8 μm negative photosensitive film 5 is applied to point B.
will remain. As a result, the original X-ray mask substrate 3
Comparing the X-ray transmittances of , it is found that the transmittance at point B decreases without changing at point A, and the non-uniformity of the X-ray transmittance is alleviated.

The uniformity of this X-ray transmittance is shown below when calculated under the conditions that, for example, 10 people were irradiated with XM and a negative resist (chloromethylated polystyrene) was applied at 2 μm FJ.

First, the X-ray intensity was transmitted through an X-ray mask substrate 3 of 5iJ4 with a thickness of t μm. (1) is I a(t)=I o(0)・exp(−gy −t
) and the obtained results are shown in Figure 4.
. It was shown in Here, μ2 is the linear absorption coefficient of 5ixN4.

When X-rays are irradiated, the negative resist coated on the back side becomes exposed depending on the X-ray intensity Io (tl) transmitted through the X-ray mask substrate 3.The thickest X-ray mask substrate 3 (film thickness to
) The amount of X-ray irradiation transmitted through If the amount of X-ray irradiation is set in advance to ) is the applied film thickness T,
Then, Tl1(t) = 0.434・γ・T1μ・
It can be expressed as (tO-t).

The transmittance of the X-ray extraction window made in this way is 1t (t)
is the linear absorption coefficient of the resist μ7, then It(t)=
Io(t) −exp(−μs ・”r+t(t))
(2) If this is standardized by I, (2) (transmittance at a position of 2 μm on the mask substrate), the result will be as shown in FIG. 4.

As a result, by comparing Io and 11 in FIG. 4, it is clear that the transmitted X-ray intensity has been made uniform.

However, as shown in FIG. 4, there is still unevenness in the transmitted X-ray intensity by ±7% or more. Therefore, by repeating the homogenization process again on the X-ray extraction window created by the above-described homogenization process, the transmitted X-ray intensity can be made even more uniform. Therefore, by repeating this multiple times, the X-ray intensity can be made uniform to a desired value.

For example, if you want to obtain a mask substrate with a uniformity of X-ray transmission intensity of ±2%, the uniformization process is performed so that the average thickness of the mask substrate 3 is tV and the minimum film thickness is tlo. What is necessary is to determine the number of repetitions n.

Here 1. , (t) is the X-ray transmission intensity at the same position after the tum-thick X-ray mask substrate repeats the uniformization process n times, and can be expressed by the following equation.

ha(t)=Io・exp(-μmt)exp[-(1-(1-k
) lll uuΔt]■Here, Δt and k are Δ1=111, assuming that the maximum X-ray mask substrate thickness is tIII+. -1, k=0.434 ・γ・TI LL+t. Therefore, if we calculate the number of repetitions n from formula 0, we get:

Here, if we consider the case where 2 μm (=T1) of negative resist with γ=1.6 is coated on an Xll mask substrate with a film thickness t0=2±0.2 pm, n=6 can be derived from equation 0.

This is shown as ■6 in FIG. It can be seen that the transmitted X-ray intensity is within ±2% in the range of the film thickness of the mask substrate of 2±0.2 μm, and that the uniformity of the transmitted X-rays is achieved.

It should be noted that the surface on which the resist is applied in the uniformization step in the method of manufacturing an X-ray mask of the present invention does not necessarily have to be the opposite side of the pattern 4 (it may be applied on the surface of the pattern 4, or the resist may be applied multiple times). When the uniformization process is repeated, it may be performed alternately.Furthermore, when the SL substrate is back-etched after evaporating 5idL on the St substrate and before the fabrication of the pattern 4, the process of the present invention may be performed before the fabrication of the pattern 4. A homogenization step may also be performed.

Further, in an exposure apparatus in which the wavelength distribution of X-rays differs depending on the exposure position, for example, an X-ray exposure apparatus with a swinging mirror, the above-described uniformization process may be performed using the X-rays used for exposure. In that case, as shown in FIG. 5, at the same height, that is, at the same position, Xl! at the thickest point of the X-ray mask substrate 3! The swinging speed of the mirror 11 may be determined so that the irradiation amount becomes Do.

(Effects of the Invention) As described above, the present invention applies a negative photosensitive coating to one side of an X-ray exposure mask, irradiates X-rays from the opposite side of the coating, and then develops the mask. Uniform X-ray transmittance of the substrate is achieved, the line width of the resist after development is uniform, and an excellent X-ray mask that can cope with miniaturization of integrated circuits can be obtained.

[Brief explanation of the drawing]

FIGS. 1 and 3 are diagrams showing the manufacturing process of an X-ray mask according to an embodiment of the present invention. FIG. 2 is a diagram showing the characteristics of the negative photosensitive coating used in the present invention. Figure 4 shows the transmitted X before and after the uniformization process of the manufacturing method of the present invention.
It is a figure showing the uniformity of line intensity. FIG. 5 is a diagram in which the present invention is applied to an exposure apparatus that uses synchrotron radiation as an exposure beam. FIG. 6 is a diagram showing an X-ray mask for conventional X-ray exposure. Frame mask substrate composed of mask SL substrate etc. 4: Patterned negative photosensitive coating 6: X-ray resist 8: Silicone wafer SR ring
11: X-ray mirror Figure 2 DOSE [DO] Figure 3 1゜ Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) Coat a photosensitive film on one side of the X-ray exposure mask,
1. A method for producing an X-ray mask, comprising a uniformizing step of irradiating an exposure light beam from the opposite side to the coated surface and then developing. (2) X according to claim 1, wherein the homogenizing step is repeated multiple times.
How to make a line mask. (3) The method for producing an X-ray mask according to Claims 1 and 2, wherein the exposure light is synchrotron radiation. (4) The number of repetitions n of the homogenization process repeated multiple times determines the γ value of the photosensitive resin, the initial film thickness Ti, the linear absorption coefficient μ_R of X-rays, the average thickness t_V of the X-ray mask substrate, and the minimum Thickness t_m_i_n and linear absorption coefficient μ_M of mask substrate
Therefore, n≧[ln0.02−ln{μ_M(t_V−t_m_
i_n)}/{ln(1-0.434×γ×Ti×μ
_R)}. The method for producing an X-ray mask according to claim 2.