JPH053148A - X-ray mask, manufacture of x-ray mask and exposure method using x-ray mask - Google Patents

Abstract

PURPOSE:To provide an X-ray mask, from which an alignment signal of a sufficient intensity is obtained and which makes the improvement of an alignment accuracy possible. CONSTITUTION:In an X-ray mask, a circuit pattern 3b, which is an X-ray absorber pattern and consists of a 0.7mum thick tantalum film, and patterns 3a for alignment use are formed on the surface of a 2mum thick SiN film 2, which is an X-ray transmitting film. Moreover, alignment marks 6, which are patterns for alignment use to oppose to the patterns 3a and consist of a photosensitive resin, are formed on the rear of the film 2 via the film 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray mask used in an X-ray exposure apparatus, a method for manufacturing the X-ray mask, and an X-ray mask.
The present invention relates to an exposure method using a line mask.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have been remarkably miniaturized and highly integrated, development of fine pattern forming technology has been vigorously carried out in terms of manufacturing equipment and manufacturing technology. In the field of lithography technology development, optical reduction projection exposure technology, which has supported LSI mass production technology, has significantly improved the resolution by efforts to shorten the wavelength of the light source and increase the NA of the lens. The boundaries are approaching the limit.

Electron beam exposure technology or X-ray exposure technology is considered to be promising for the next-generation exposure technology of the 0.25 μm level required for the next-generation devices after 256 MDRAM.

X-ray exposure requires an X-ray mask made of a combination of X-ray absorbing materials and X-ray transmitting materials.

A cross-sectional structure of a conventional X-ray mask is shown in FIG. In FIG. 5, 1 is a silicon support frame made of a Si substrate, 2 is a silicon nitride (SiN) film used as an X-ray transparent film (membrane), 3 is a tantalum film used as an X-ray absorber pattern, and 3a is The alignment pattern 3b is a circuit pattern.

The circuit pattern 3b of the X-ray mask 11 is formed on the back side of the SiN film 2 with respect to the X-ray light source. In a conventional silicon LSI lithography mask, the circuit pattern is formed on the back side of the mask with respect to the light source. The pattern is formed on the back surface because the mask pattern can be transferred onto the semiconductor wafer cleanly even after exposure. This is because if a fine pattern is formed on the light source side with respect to the mask, the pattern will be out of focus because it is out of focus on the semiconductor wafer and cannot be transferred onto the semiconductor wafer cleanly.

Further, since the alignment pattern 3a is formed simultaneously with the circuit pattern 3b, the alignment pattern 3a is formed.
Was always on the same side of the circuit pattern 3b and the X-ray transparent film, and there was no idea to form the alignment pattern 3a and the circuit pattern 3b on different sides.

A silicon carbide film is used as the X-ray transparent film,
A combination of a tungsten film as an X-ray absorber pattern is also being developed.

Materials for the X-ray exposure apparatus, such as mirrors and lenses, which have sufficient performance in the soft X-ray wavelength region, have not yet been developed. The wafer uses a proximity exposure method in which the wafer has a minute gap and is held in parallel facing each other to perform exposure.

On the other hand, when forming a fine pattern of 0.25 μm level, a highly accurate X-ray mask of 0.1 μm or less and inter-wafer positioning accuracy are required. For this reason, a method of continuously performing highly accurate positioning even during exposure is adopted.

FIG. 6 shows a typical alignment configuration during proximity gap exposure. In FIG. 6, 11 is the X-ray mask shown in FIG. 5, 12 is a wafer, 13 is a highly accurate wafer stage, 14 is an alignment optical system, 15 is a laser beam,
16 is diffracted light, 17 is a photodetector, and 18 is an X-ray. Alignment optical system 14 and photo detector 17
Are arranged outside the area of the exposure X-ray 18 so that the position can be detected even during X-ray exposure. After the X-ray mask 11 and the wafer 12 are made to face each other in close proximity, the alignment mark formed on the X-ray mask 11 and the wafer 12 is irradiated with a laser beam 15 for position detection. The diffracted light 16 diffracted by the alignment mark has relative misalignment information between the X-ray mask 11 and the wafer 12. Highly accurate alignment is achieved by feeding back relative misalignment information between the X-ray mask 11 and the wafer 12 to the wafer stage 13 and correcting the stage position, which is obtained from the signal detected by the photodetector 17.

This will be described in more detail with reference to FIG. When the X-ray mask 11 and the semiconductor wafer 12 are aligned with each other, a method for detecting the amount of deviation between them is to align the alignment pattern 3a formed on the X-ray mask 11 with the alignment pattern 3c formed on the semiconductor wafer 12. The method of irradiating the laser light 15, which is light, and comparing the generated diffracted light is used as one of the most accurate methods (Optical technology contact vo1.28 No.7 p.3 (1990). ).
The method will be described in more detail.

In FIG. 7, laser light 15 is an X-ray mask.
The alignment pattern 3a of 11 is irradiated, and of the diffracted light generated at that time, the first-order reflected diffracted light 16 is detected by the photodetector 17. On the other hand, the wafer 12 is transmitted through the X-ray mask 11.
Similarly, the first-order reflected diffracted light 16a generated by the laser beam irradiating the alignment pattern 3c of FIG.
Detected by.

The diffracted light 16, 16a thus detected
X-ray mask 11 and semiconductor wafer 12
The positional deviation of is detected.

[0015]

As the factors that influence the alignment accuracy, the stage positioning accuracy, the alignment signal detection accuracy, and the like can be increased. Among them, the alignment signal strength (S / N) is an important factor in the latter. .

According to the above-mentioned conventional structure, as shown in FIG. 8, when the photodetector 17 detects the alignment signal, the X-ray mask in which the laser beam 15 has a transmittance of about 70%.
The light quantity of the diffracted light 16 is reduced to about 1/2 because it reciprocates through the X-ray transmission film made of the silicon nitride film 2 of 11. Moreover, the transmittance of the SiN film 2 changes periodically depending on its thickness, and there is a possibility that the light amount of the diffracted light 16 may be further reduced depending on the conditions.

The diffraction efficiency of the alignment mark is
In this case, X that constitutes the X-ray mask 11 regardless of the mark shape
Since it depends on the effective refractive index that is determined by the combination of the material of the radiation transparent film and the X-ray absorption pair pattern, the value is usually small, and the optimum value cannot be set arbitrarily.

For these reasons, the alignment signal strength becomes less than the ideal signal strength of about 1/5,
This has been a major obstacle in performing highly accurate alignment.

An object of the present invention is to provide an X-ray mask, an X-ray mask manufacturing method and an exposure method using the X-ray mask, which can obtain an alignment signal with sufficient intensity and improve the alignment accuracy. It is to be.

[0020]

In order to solve the above problems, an X-ray mask of the present invention comprises an X-ray absorber pattern serving as a circuit pattern and a positioning pattern on one main surface of an X-ray transparent film, On the other main surface of the X-ray transparent film, alignment marks of the same pattern facing the alignment pattern are provided.

The method of manufacturing an X-ray mask of the present invention is
The step of coating a photosensitive material for forming an alignment mark on the other main surface of the X-ray transmissive film, and the photosensitive material using the alignment pattern formed on the one main surface of the X-ray transmissive film as a mask Is exposed to light on the entire surface and is transferred to the other main surface of the X-ray transmission film at the same size to form the alignment mark in a self-aligned manner.

Further, in the exposure method using the X-ray mask of the present invention, the step of placing the semiconductor wafer on the wafer stage and the X-ray mask according to claim 1 having a circuit pattern and an alignment pattern, A step of setting at opposite positions; a step of irradiating the alignment marks of the X-ray mask and the semiconductor wafer with a laser beam to detect positional deviation; and a step of exposing the X-ray mask to X-rays to expose the X-ray mask. And transferring the circuit pattern formed on the semiconductor wafer to the semiconductor wafer.

[0023]

According to the structure of the X-ray mask of the present invention, the laser beam is irradiated to the alignment mark formed on the other surface of the X-ray transmission film without being attenuated, and the height of the alignment mark is increased. By selecting the optimum height, it is possible to obtain an alignment signal with sufficient strength.

According to the method of manufacturing an X-ray mask of the present invention, the mask alignment mark is formed on the other surface of the X-ray transmissive film by performing the same size transfer by the self-alignment method using the alignment pattern of the mask and the substrate. Since it is simply provided, the X-ray mask can be manufactured with a high yield by a simple process.

Further, according to the X-ray exposure method, an alignment signal having a sufficient intensity can be obtained, alignment accuracy can be remarkably improved, and the circuit pattern of the mask can be accurately transferred onto the semiconductor semiconductor wafer. It also has excellent productivity.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An X-ray mask according to the present invention will be described with reference to the drawings.

2 (e) and 2 (f) are sectional views of an X-ray mask according to an embodiment of the present invention, in which 1 is a silicon support frame, 2 is a silicon nitride film (SiN film), and 3 is a tantalum film. And 3
Reference symbol a is an alignment pattern, and reference symbol 3b is a circuit pattern. Further, 6 is an alignment mark made of a photosensitive resin.

The X-ray mask of this embodiment has an X-ray absorber pattern of 0.7 μm thick on the surface of the SiN film 2 of 2 μm thick, which is an X-ray transparent film, as shown in the cross section of FIG. 2 (e). Circuit pattern 3b made of tantalum film and alignment pattern 3a
Are formed. Furthermore, the SiN film 2
An alignment mark 6 made of a photosensitive resin and having the same pattern as the alignment pattern 3a is formed on the back surface of the.

As shown in FIGS. 2E and 2F, by forming the alignment mark 6 on the laser light source side with respect to the conventional X-ray mask, the laser beam 15 emitted from the alignment optical system is Si.
Since the light does not pass through the N film 2 but directly hits the alignment mark 6 and diffracts, there is almost no attenuation of the light amount of the laser light 15.

The manufacturing method of the X-ray mask of this embodiment will be briefly described below with reference to the manufacturing process sectional views of FIGS.

First, as shown in FIG. 1 (a), a conventional X-ray mask 11 comprising a silicon supporting frame 1, a SiN film 2 serving as an X-ray transmitting film, and a tantalum film 3 serving as an X-ray absorber pattern.
(FIG. 5) is produced. 3a is a conventional alignment pattern, and 3b is a circuit pattern.

Next, the silicon nitride film 2 is uniformly coated with a photosensitive material 4 (for example, a positive photoresist) by a spinner or the like as shown in FIG. 1 (b). At this time, the film thickness of the photosensitive material 4 is set so that the diffraction efficiency determined by the configuration of the alignment optical system is maximized. Here, the setting of the film thickness of the photosensitive material 4 will be described with reference to FIGS. 3 and 4.

FIG. 3 is a sectional view of the lamellar diffraction grating. As shown in FIG. 3, assuming that the wavelength of the incident laser light is λ, the incident angle is α, the diffraction angle is β, the pitch of the diffraction grating is d, and the height of the diffraction grating is h, the diffraction efficiency is calculated from the theory of the lamellar diffraction grating. η is expressed by the following equation.

Η = (400 / m ² π ² ) · cos ² [(δ ′ + mπ) / 2] where δ ′ = 2πh / λ (cosα + cosβ) mλ = d (sinα−sinβ), where m is the diffraction It is the order of light.

The diffraction efficiency η changes periodically depending on the height h of the diffraction grating, and has a condition of having a maximum value and a minimum value.

In FIG. 4, a helium neon laser (λ = 633 nm) as a laser beam, a diffraction grating with a pitch d = 4 μm is used, and the zero-order diffracted light (ZERO order di
The relationship between the diffraction efficiency η ₀ of the ffracted beam) and the diffraction efficiency η _{1 of the first-} order diffracted light and the height h of the diffraction grating is shown. Since the first-order diffracted light is normally used as the alignment light, it can be seen from FIG. 4 that the maximum diffraction efficiency η ₁ of about 40% can be obtained by setting the height h of the diffraction grating to 0.16 μm, 0.48 μm, etc. . The height h of the diffraction grating thus set is the film thickness of the photosensitive material 4.

In this way, the height of the diffraction grating can be freely selected so as to increase the diffraction efficiency, and since the alignment pattern is formed on the laser light side of the SiN film, the attenuation of the alignment light is small. , Diffracted light with sufficient intensity can be obtained.

Next, as shown in FIG. 1 (c), the tantalum film 3 serving as the X-ray absorber pattern is masked by using light 5 (for example, light from a mercury lamp) which the photosensitive material 4 is sensitive to. Then, the whole surface exposure is performed. Since the film thickness of the silicon nitride film 2 serving as an X-ray transmission film is usually about 2 μm, the same method as contact exposure is used, and the X-ray absorber pattern is accurately transferred to the photosensitive material 4 on the back surface at the same size. . Of course, X
The alignment pattern 3a composed of the line absorber pattern is also accurately transferred without causing positional deviation.

Next, development processing is performed to form the alignment mark 6 for the mask (FIG. 2 (d)). Finally, the X-ray mask is completed by selectively removing unnecessary patterns (FIG. 2 (e)).

It is possible to transfer only the alignment pattern 3a by shielding the circuit pattern 3b from light when performing the above-mentioned collective whole surface exposure 2.

As described above, according to the X-ray mask of this embodiment, by using the alignment mark 6 as a diffraction grating, as shown in FIG. 2 (f), when the laser beam 15 is irradiated, a sufficient intensity is obtained. Diffracted light 16 is generated, and thus high detection resolution can be obtained. That is, this X-ray mask has the alignment mark 6 having an optimized shape that maximizes the diffraction efficiency with respect to the alignment optical system, and as a result, sufficient alignment signal strength is obtained.
It becomes possible to achieve high alignment accuracy.

Further, the process of forming the alignment mark 6 can be carried out simply by uniformly coating the photosensitive material 4 and carrying out collective whole surface exposure, and can be carried out very easily without requiring a special device. Moreover, the transfer of the X-ray absorber pattern is, in principle, the same as the contact exposure.
The pattern position distortion and the like due to the transfer of the linear absorber pattern is at a low level such that it hardly causes a problem and has no influence as a factor of the alignment error. Therefore, as a mask for X-ray exposure that requires highly accurate alignment, it is possible to realize a high-performance X-ray mask provided with alignment marks having sufficiently high optical characteristics.

[0043]

According to the X-ray mask of the present invention, the mask alignment mark is provided on the other surface of the X-ray transparent film by performing the same size transfer by the self-alignment method using the alignment pattern of the mask and the substrate. As a result, it is possible to obtain an alignment signal having a sufficient strength, and it is possible to dramatically improve the alignment accuracy, and it is also excellent in industrial productivity.

Further, since the alignment mark is formed on the laser light source side at a height at which the diffraction efficiency is increased, an alignment signal having a sufficient intensity can be obtained. Further, when a semiconductor wafer is exposed with a circuit pattern formed on the mask using the X-ray mask of the present invention, a desired fine pattern can be easily exposed because there is almost no positional deviation between the mask and the wafer.

[Brief description of drawings]

FIG. 1 is a process sectional view of an X-ray mask manufacturing method according to an embodiment of the present invention.

FIG. 2 is a process sectional view of an X-ray mask manufacturing method according to an embodiment of the present invention.

FIG. 3 is a sectional view of a lamellar diffraction grating.

FIG. 4 is a diagram showing the relationship between the diffraction efficiency and the height of the diffraction grating.

FIG. 5 is a sectional view of a conventional X-ray mask.

FIG. 6 is a diagram for explaining an alignment method at the time of proximity gap exposure.

FIG. 7 is a sectional view for explaining a method of aligning an X-ray mask and a semiconductor wafer.

FIG. 8 is a sectional view for explaining a laser beam incident on an alignment pattern of an X-ray mask.

[Explanation of symbols] 1 Silicon support frame 2 Silicon nitride film 3 Tantalum film 3a Alignment pattern 3b circuit pattern 3c alignment pattern 6 alignment mark 11 X-ray mask 12 Semiconductor wafer 13 Wafer stage 15 Laser light 16 diffracted light 18 X-ray

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03F 7/20 521 7818-2H

Claims (3)

[Claims] 1. An X-ray transparent film is provided on one main surface thereof with an X-ray absorber pattern serving as a circuit pattern and a positioning pattern, and the other main surface of the X-ray transparent film is opposed to the alignment pattern. An X-ray mask provided with alignment marks having the same pattern. 2. A step of coating a photosensitive material for forming an alignment mark on the other main surface of the X-ray transmissive film, and using the alignment pattern formed on the one main surface of the X-ray transmissive film as a mask. , The entire surface of the photosensitive material is exposed to light having sensitivity, X
And a step of forming an alignment mark in a self-aligned manner by transferring the same size to the other main surface of the line-transmissive film. 3. A step of setting a semiconductor wafer on a wafer stage, a step of setting an X-ray mask having a circuit pattern and an alignment pattern at a position facing the semiconductor wafer, and the X-ray mask. And a step of irradiating the alignment mark of the semiconductor wafer with a laser beam to detect a positional deviation, and exposing the X-ray mask to an X-ray to transfer the circuit pattern formed on the X-ray mask to the semiconductor wafer. And an exposure method using an X-ray mask.