JPS6120329A - Mask for x-ray exposure - Google Patents

Abstract

PURPOSE:To decrease the number of patterns for adjustment which are to be formed on a water by forming a pattern for adjustment which is transparent to the used X-ray as well as pattern for forming the desired circuit consisting of the thin film which is opaque to the used X-ray on a mask substrate. CONSTITUTION:On a mask substrate 1, a pattern 3 for adjustment is formed together with a pattern 2 for forming a circuit consisting of an Au thin film of about 1mum thick which is opaque to the used X-ray by using an electron beam lithography technique, electroplating technique and etc., for example. Nextly, after a photoresist 9 is spread over the whole surface of that mask for X-ray exposure, only the adjustment pattern region is removed selectively by a usual photolithography technque. The exposed adjustment patter 3 is etched by ion milling to make a film thickness of the pattern about 0.01-0.1mum. Lastly, the unnecessary resist 9 is removed. Consequently, a density of permeating X-ray becomes 50% or over that of an incident X-ray and the resist enters into a usual sensitized reaction. Then a shadow of the adjustment pattern 3 is not transferred on the wafer.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an X-ray transfer technology that uses soft X-rays instead of ultraviolet rays to transfer fine patterns. The present invention relates to an X-ray exposure mask suitable for manufacturing semiconductor devices that require pattern alignment.

[Background of the invention]

As semiconductor integrated circuits become more highly integrated, pattern transfer using X-ray exposure is attracting attention. When making integrated circuits, multiple exposures are required for a single semiconductor substrate, and each step requires matching the circuit pattern on the wafer surface with the circuit formation pattern on the X-ray exposure mask surface. .

In order to easily and accurately perform this mask alignment, it is common to provide an alignment pattern on the surface of the X-ray exposure mask substrate.

Furthermore, it is necessary to form a matching pattern corresponding to the mask matching pattern on the wafer surface as well.

The alignment is performed by detecting the positions of the pattern on the mask surface and the pattern on the wafer surface.

This detection is important in order to achieve highly accurate alignment.

Detection methods include one using electron beam scanning and one using light interference double diffraction.
nd Prob Q ems of X-Ray Li
thogrphy”;Adv, 5solidState
Phys, XX 259 (1980).

Among these methods, the method using an electron beam requires a vacuum, and has many limitations such as the need for two sets of electron beam scanning to separately detect the alignment patterns of the mask and wafer. It is the mainstream that uses .

An outline of a method for optically detecting the position of a pattern will be explained using FIG.

FIG. 1 shows a detector 7 detecting light reflected by the alignment pattern 3 on the mask substrate while detecting the alignment pattern 5 on the wafer 6 through the mask substrate (pattern support film) 4, and detecting the alignment between the wafer and the mask. This is to find the positional relationship between.

In order to improve the accuracy of alignment using this method, we have added a device to the alignment pattern that utilizes light interference and single diffraction.
formicroscopy objectives
;Appl, 0ptics, 16(3), 549(19
77), which uses a bifocal lens to detect a pattern for aligning a wafer and a mask, has been proposed.

In order to use these optical alignment methods, it is necessary for the detection light of the wafer alignment pattern to pass through the X-ray mask substrate 4, and for the alignment pattern 3 on the mask surface to reflect this light.

In the conventional X-ray exposure mask, this alignment pattern was formed in the same process as the circuit formation pattern. Therefore, the circuit forming pattern and the matching pattern are made of the same material and have the same film thickness.

Therefore, like the circuit pattern, it was opaque to the X-rays used, so the matching pattern was transferred onto the wafer.

In particular, since the mask alignment pattern is transferred onto the alignment pattern on the wafer surface, the same alignment pattern cannot be used again for subsequent exposure.

For this reason, when making an integrated circuit, it is necessary to provide alignment patterns on the wafer surface in a number equal to the number of exposure steps.

By the way, the matching pattern has no function in operating the integrated circuit.

Therefore, as more alignment patterns are created on the wafer surface, the effective area in which elements can be manufactured tends to become narrower.

That is, the number of elements that can be obtained on one wafer is reduced, and economic efficiency becomes a problem.

This problem can be solved by using a mating pattern that is transparent to the X-rays used.

That is, if it is opaque to the one-aligned pattern detection light but transparent to exposure X-rays, the pattern will not be transferred to the wafer.

As an invention of this type, as described in Japanese Patent Laid-Open No. 56-60019, an X
There is one in which an identification mark made of a transparent or semi-transparent thin film is formed on the line.

However, the identification mark is used to visually read the type of X-ray mask, and no consideration has been given to its function as a matching pattern during X-ray exposure.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide an X-ray exposure mask having a matching pattern that is not transferred onto the wafer surface.

[Summary of the invention]

The X-ray exposure mask according to the present invention includes a desired circuit forming pattern made of a thin film that is opaque to the X-rays used on the mask substrate, and a pattern that is transparent to the X-rays used and that is transparent to visible light for alignment. ultraviolet light.

It is characterized by forming a matching pattern made of a thin film that is opaque to laser light.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIG.

Figure 2 (a) is a schematic external view of the same, and Figure 2 (b) is the same figure (
It is an enlarged sectional view of a).

Reference numeral 1 denotes a support ring made of Si, glass, or metal, and a boron nitride (BN) thin film 4 having a thickness of 3 μm is attached to this to constitute a mask substrate.

For example, electron beam lithography technology is applied to this mask substrate 1.
A matching pattern 3 is formed together with a circuit forming pattern 2 made of a thin Au film with a thickness of about 1 μm that is opaque to X-rays using electrolytic plating technology or the like.

Next, a resist is applied to the circuit forming pattern area using a conventional photolithography method.

Next, the exposed pattern area for alignment is selectively etched by ion milling to reduce the thickness of the pattern to 0.1
It should be about the size of a μ intestine. The process will be specifically explained below.

The mask substrate 1 is coated with an Au thin film with a thickness of about 1 μm that is opaque to X-rays used using, for example, electron beam lithography or electrolytic plating technology (the X-ray density I that passes through the material is B).
According to eer's law, it is expressed by the following equation. I =
: I o6XP (-p x) However, ■. : incident X-ray density, μ: X-ray absorption rate of material, X: thickness of material. Here, μ is determined from the wavelength of the X-ray used, and is μ+57 μm for Mll's L-ray (5.4 people). Therefore, from the above formula, if X is 0.7 μm or more, I/I. It can be seen that <1/10.

In other words, the density of X-rays transmitted through a substance is 1/ of the density of incident X-rays.
It can be seen that it is less than 10. On the other hand, since the γ value (relationship between exposure energy and residual film thickness) of a resist sensitive to X-rays is generally 1 or more, if the X-ray density is set to 1710 or less, no photosensitive reaction due to X-rays will occur. ) together with the circuit forming pattern 2 consisting of the circuit forming pattern 3 shown in FIG.
Form as in b).

At this point, the circuit forming pattern 2 and the matching pattern 3 are
have the same thickness.

Therefore, both are opaque to the X-rays used.

Next, after coating the entire surface of this X-ray exposure mask with photoresist 9, only the alignment pattern area is selectively removed using normal photolithography technology (Figure 3(c)).
.

Next, the exposed alignment pattern 3 is etched by ion milling to reduce the thickness of the pattern (A u ) to 0.01.
~0.1 μm (see figure (d)).

Finally, the unnecessary resist 9 is removed to complete the pattern formation (FIG. 4(a)).

If the Au film thickness is about 0.01 to 0.1 μm, the density of transmitted X-rays will be 50% or more of the incident X-ray density from both equations.

Therefore, the resist undergoes a normal photosensitive reaction and the wafer 6
The shadow of the alignment pattern 3 is not transferred on top.

However, if the Au film thickness is 0.01 μm or less, visible light or ultraviolet light for alignment will be transmitted, and the function as the alignment pattern 3 will be lost.

The above-described processing reduces the X-ray absorption ability of the alignment pattern, allowing most of the X-rays to pass through the pattern.

When a pattern was transferred onto a Si wafer coated with SEL resist (a product of Somar Kogyo Co., Ltd.) using M as the target of an X-ray source using the exposure mask made in this way, it was found that it was possible to form a circuit. Only pattern 2 was transferred, and matching pattern 3 was not transferred.

By the way, when the alignment pattern 5 on the wafer 6 surface and the alignment pattern 3 on the mask surface were optically aligned before this exposure, since the alignment pattern 3 was opaque to light,
Highly accurate alignment was possible, no different from conventional methods.

In this example, X-ray transparency was achieved by reducing the thickness of the alignment pattern 3.

On the other hand, it is possible to obtain the above characteristics by changing the material of the matching pattern 3 and the material of the circuit forming pattern 2.

Specifically, the matching pattern 3 is made of Si and Ti.

Even if a material with high X-ray transparency such as An is used, it is possible to carry out the present invention without any problems.

Next, a process for making alignment marks using a material different from the circuit forming pattern will be described.

A material 8 having a small X-ray absorption coefficient μ, such as AQ or Si, is deposited on the mask substrate 4 (FIG. 4(b)).

Thereafter, the above-mentioned adhesion layer 8 is removed, leaving a region where a pattern for alignment will be formed if necessary (FIG. 4(C)).

Thereafter, using the above-mentioned electron beam lithography technique, electrolytic plating technique, etc., a circuit forming pattern 2 made of an Au thin film (about 1 μm thick) and a matching pattern 3 are formed (FIG. 4(d)).

At this time, AM, Si, etc. are present between at least the alignment pattern 3 and the mask substrate.

Thereafter, in the same manner as described above, resist 9 is deposited on the other circuit forming patterns 2, leaving the alignment pattern 3, using the usual photolithography technique (FIG. 2(e)).

Next, using the exposed Au alignment pattern 3 as a mask, the AM, Si, etc. directly under the alignment pattern 3 are etched by ion milling, 2-reactive sputter etching, etc., and the alignment pattern is transferred (FIG. )).

After that, only the Au alignment pattern was removed using an iodine-based etching solution, and A1. A matching pattern 3 made of Si or the like is obtained. (With the iodine-based etching solution, only Au is selectively etched away) (Figure (g)).

Finally, the defective resist 9 is removed to complete the pattern formation (FIG. 2(h)).

In addition, in this example, the circuit forming pattern 2 was formed of an Au thin film, but if the alignment pattern with the above function is used in other X-ray exposure masks using W + T a r N x, etc., the present invention can be used. It is possible to carry out the invention without any hindrance.

〔Effect of the invention〕

As explained above, according to the present invention, by using a thin film that is transparent to xis and opaque to visible light as the alignment pattern, the alignment pattern is not transferred onto the wafer surface, and the wafer surface The number of matching patterns to be formed thereon could be reduced. For this reason,
It became possible to fabricate many effective elements on a single sheet of Uniper, improving economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a method for optically detecting the position of a pattern, FIGS. 2(a) and (b) are a schematic external view and an enlarged sectional view of an embodiment of the present invention, and FIG. The figure is a process diagram for reducing the film thickness of the mating pattern, and FIG. 4 is a process diagram for changing the material of the mating pattern. 1...Support ring, 2...Circuit formation pattern, 3...
・Pattern for alignment, 4... Pattern support film (mask substrate), 5... Alignment pattern for wafer, 6... Wafer, 7... Optical position detector, 8... Aμ, S
i membrane, 9... Atsushi 1 Figure Z Figure uL) ￥J 3 Figure (H) Figure 4 ((L)

Claims (1)

[Claims] The X used together with the desired circuit forming pattern made of a thin film that is opaque to the X rays used for fine pattern transfer.
An X-ray exposure mask characterized by forming a matching pattern made of a transparent thin film on the line.