JPH05181257A - Mask for optical exposure - Google Patents

Abstract

PURPOSE:To improve the resolution on a photographing surface by constituting a phase shift film of a translucent material which generates absorption to exposure light. CONSTITUTION:This phase shift mask is constituted of the translucent phase shift film which generates the absorption to the exposure light on a transparent quartz substrate 11 which is transparent to the exposure light, such as KrF excimer laser. SOG(spin on glass), silicon phosphorus glass, silicon phosphorus boron glass, org. high-polymer film, etc., are used as the essential material of the phase shift film 12. These films can be constituted by a vapor growth method. The transmittance of the phase shift film to the exposure light is set at 40 to 90%, by which the resolution rate is additionally improved. Fine working down to a min. line width of 0.2mum is possible if such mask for optical exposure is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask for photoexposure, and more particularly to a phase shift mask capable of performing fine pattern processing by adding a phase shift to exposure light to enhance resolution.

[0002]

2. Description of the Related Art In the field of semiconductor memory manufacturing, there is a strong demand for fine pattern processing in order to improve the degree of integration. For example, 1-megabit DRAM (dynamic random access memory) currently in mass production
Therefore, a minimum line width of 1.2 μm is required for a 4-megabit DRAM, and a minimum line width of 0.8 μm is required. In addition, 64 to be mass-produced in the future
A minimum line width of 0.3 μm is required for a megabit DRAM and a minimum line width of 0.2 μm is required for a 256 megabit DRAM. In order to form such a fine pattern, a reduction projection exposure technique is generally adopted. Reduction projection exposure is g-line
(436 nm), i-line (365 nm) or KrF (krypton / fluorine) excimer laser (248 nm) or other exposure light is used to reduce and transfer the mask pattern to the photosensitive resin (resist) coated on the semiconductor substrate (usually (1/5 times).

Conventionally, a phase shift mask 30 as shown in FIG. 3 is known as a mask used for reduction projection exposure. The phase shift mask 30 is a transparent quartz substrate 31 (meaning that it is transparent to exposure light).
Chrome film 32 that can completely block exposure light on one side of
Are provided at a predetermined interval, and the transparent phase shift film 33 is provided on one of the adjacent openings 34 and 35. The film thickness Ts of the phase shift film 33 is Ts = λ / {2 (n−1)} with respect to the wavelength λ of the exposure light, where n represents the refractive index. … (1) It is set so that the following relation holds. In this phase shift mask 30, the phase of the light transmitted through the opening 34 and the phase of the light transmitted through the opening 35 are shifted by 180 °.
The two transmitted lights cancel each other, and as a result, it is possible to substantially prevent light from seeping out from both openings to the surroundings. Therefore, the resolution (contrast) of the projected image can be increased.

However, the above phase shift mask 30
Has the problem that it is difficult to make. That is, in order to manufacture the phase shift mask 30, a resist is applied to pattern the chromium film 32 and electron beam drawing is performed, and then a resist is applied again to define the phase shift film 33. Electron beam drawing must be performed. It is technically very difficult to overlap the pattern of the chrome film 32 with the pattern of the phase shift film 33. Moreover, the cost is high.

In order to improve this point, a phase shift mask 40 as shown in FIG. 4 has been proposed. In this phase shift mask 40, a chrome film 42 capable of completely blocking exposure light is provided at a predetermined interval on one surface of a transparent quartz substrate 41, and a phase shift film (made of a transparent resist) is provided on the chrome film 42. 43 is provided. The end of the phase shift film 43 is in a state of protruding outside the end of the chromium film 42. The film thickness of the phase shift film 43 is set so that the relationship of the above expression (1) is established. In this phase shift mask 40, the light transmitted through the region 45 in which the phase shift film 43 protrudes and the light transmitted through the original opening 44 cancel each other, and as a result, the opening 4 is formed.
It is possible to substantially prevent light from seeping from the surroundings to the surroundings. Therefore, the resolution (contrast) of the projected image can be increased. Moreover, it can be manufactured without technical difficulty as compared with the phase shift mask 30. That is, when manufacturing this phase shift mask 40, first, a chromium film 42 is provided on the entire surface of a quartz substrate 41, and a resist (not shown) is applied. Next, electron beam drawing is performed to pattern the resist (to form the same pattern as the phase shift film 43 to be formed), and the chromium film 42 is etched using this resist as a mask (this causes the openings 4
4 is formed). After removing the resist, a phase shift film (transparent resist) 43 is applied on the chrome film 42, and exposure is performed from the quartz substrate 41 side to form the phase shift film 4
The portion of 3 which is present in the opening 43 is removed. After this,
The edge of the chrome film 42 under the phase shift film 43 is etched and set back to form a region 45 where the phase shift film 43 protrudes. As described above, since the electron beam drawing only has to be performed once, the phase shift mask 40 can be manufactured without technical difficulty.

However, the above phase shift mask 40
Because the phase shift film 43 is made of a fragile resist, and the end portion of the phase shift film 43 is floated from the quartz substrate 41, the phase shift film 43 is damaged during cleaning (which must be regularly performed to remove dust on the mask). Easy to receive. Therefore, there is a problem of poor durability. In addition, the manufacturing process is long and complicated.

Therefore, the above two types of phase shift masks 3
In order to solve the problems of 0 and 40, as shown in FIG. 5B, a phase shift mask 50 in which a transparent phase shift film 53 is provided on a quartz substrate 51 with a predetermined width and interval.
Is proposed. In order to manufacture this phase shift mask 50, as shown in FIG. 4A, a phase shift film 53 is provided on the entire surface of a quartz substrate 51, and a resist 56 is applied to the entire surface. Then, electron beam writing is performed to pattern the resist 56, and the phase shift film 53 is processed according to the pattern of the resist 56 as shown in FIG.
In this way, it can be easily manufactured without technical difficulties.

The phase shift mask 50 operates as follows. As shown in FIG. 6A, one phase shift film 5
The case where 3 is provided is assumed. In this case, the phase shift film 5
The light passing through the region A provided with 3 and the light passing through the region B not provided with the phase shift film are out of phase by 180 °. That is, the phase is inverted at the boundary between the areas A and B as shown in FIG. As a result, as shown in FIG. 7C, the light intensity on the projection surface drops at the position corresponding to the boundary between the areas A and B, while it is high at the position corresponding to the inside of the areas A and B. Become. Further, as shown in (d) of the same figure, when a plurality of phase shift films 53 are provided with a predetermined width and interval, the phase of light transmitted through the mask is shown by a broken line φ ₂ in (e) of the same figure. It becomes a state. Accordingly, as indicated by a broken line I ₂ in FIG. 6F, light is projected on the projection surface in the same manner as the phase shift films (those provided with a chrome film that completely blocks exposure light) 30 and 40 described above. Intensity contrast can be shown. The width of the phase shift film 53 is set according to the wavelength of the exposure light. For example, when a KrF excimer laser (wavelength 248 nm) is used, the width of the phase shift film 53 is 0.75 μm on the mask surface.
(It corresponds to 0.15 μm on the projection surface at a reduction ratio of 1/5). The interval of the phase shift film 53 is set according to the resist pattern to be processed. For example, when trying to resolve a line-and-space pattern with a pitch of 0.4 μm, the phase shift film 53
Is set to 1.25 μm on the mask surface (corresponding to 0.25 μm on the projection surface at a reduction ratio of 1/5).

[0009]

However, when the interval of the phase shift film 53 is set to 0.25 μm in terms of projection plane, this interval is approximately the same as the wavelength of exposure light of 248 nm, and therefore the projection plane is It is expected that the contrast will not be easily applied (in the numerical calculation, the ratio between the maximum and the minimum of the light intensity is less than twice as shown by the broken line I ₂₀ in FIG. 2). And, actually, in the phase shift mask 50, 0.4
It is difficult to resolve a line-and-space pattern having a μm pitch (this situation is the same for the phase shift masks 30 and 40 shown in FIGS. 3 and 4).

Therefore, an object of the present invention is to provide an optical exposure mask which can be easily manufactured and can perform fine processing to a minimum line width of 0.2 μm required for a 256 megabit DRAM. ..

[0011]

In order to achieve the above object, the present invention provides a light exposure mask having a phase shift film on a substrate transparent to exposure light, wherein the phase shift film is the exposure light. It is characterized by being made of a semitransparent material that absorbs light.

It is desirable that the phase shift film has a transmittance of 40% to 90% with respect to the exposure light.

[0013]

In the photoexposure mask of the present invention, the phase shift film is made of a semitransparent material that absorbs the exposure light, so that the resolution (contrast) on the projection surface is enhanced. This is based on the idea of the present inventor, and it was confirmed that the numerical calculation improves the resolution. In particular, when the transmittance of the phase shift film is set to 40 to 90%, the improvement effect is remarkable. For example, as shown by the solid line I ₁₀ in FIG. 2, the ratio of the maximum and the minimum of the light intensity can be increased about 20 times on the projection surface (on the resist). In this example, the exposure light has a wavelength of 2
A 48 nm KrF excimer laser is used, the transmittance of the phase shift film is 90%, and the width and interval of the phase shift film are 0.75 μm and 1.25 μm on the mask surface (reduction of 1/5 times). The ratio is 0.15μ on the projection plane.
This corresponds to m and 0.25 μm. ). As a result, the minimum line width is 0.
Fine processing up to 2 μm has become possible (described later).

[0014]

EXAMPLES The photoexposure mask of the present invention will be described in detail below with reference to examples.

FIG. 1B shows the structure of the phase shift mask of one embodiment. This phase shift mask
A semitransparent phase shift film 12 that absorbs the exposure light is provided on a quartz substrate 11 that is transparent (using a KrF excimer laser having a wavelength of 248 nm).

This phase shift mask is manufactured as follows. First, as shown in FIG. 3A, the phase shift film 12 is provided on the entire surface of the quartz substrate 11. The material of the phase shift film 12 is SOG (spin on.
Adopt a light absorbing material (pigment) added to glass).
Then, the film thickness is set to 275 nm by the spin coating method so as to satisfy the above-described formula (1). With this film thickness, the transmittance of exposure light (the ratio of the emission intensity to the incident intensity) is set to about 90%. Next, a resist 16 for electron beam is applied on the phase shift film 12. The resist 16 is a positive type and has a film thickness of 500 nm. The phase shift film 12 and the resist 16 must not be materials that dissolve each other. Next, electron beam drawing and development are performed to form the resist 16
Is patterned, and then RIE (reactive ion etching) is performed to process the phase shift film 12 in accordance with the pattern of the resist 16 as shown in FIG. Here, the width and interval of the phase shift film 12 are 0.75 μm and 1.25 μm, respectively, on the mask surface (corresponding to 0.15 μm and 0.25 μm on the projection surface, respectively, at a reduction ratio of 1/5). .. It is desirable that the end of the phase shift film 12 be vertically finished. After that, the resist 16 is removed and the mask fabrication is completed. In this way, it can be easily manufactured without technical difficulties.

This phase shift mask comprises a phase shift film 1
Since 2 is a semitransparent material that absorbs exposure light, the resolution (contrast) on the projection surface can be increased. Actually, when the exposure amount is optimized by a reduction projection exposure apparatus (stepper) with a numerical aperture of 0.45, the phase and the light intensity of the transmitted light on the projection surface are shown in FIGS. 6 (e) and 6 (f), respectively. The state is shown by the solid lines φ ₁ and I ₁ . As can be seen from FIG. 6 (f),
The light intensity could be reduced in the region A provided with the phase shift film, and the resolution could be increased. As a result, 25
Minimum line width 0.2 μm required for 6 Mbit DRAM
It was possible to perform fine processing up to.

As the exposure light, not the KrF excimer laser (wavelength 248 nm) but, for example, i-line (wavelength 365 nm) can be used. In this case, the film thickness of the phase shift film 12 is set to 405 nm so that the above expression (1) is satisfied. Further, the width and interval of the phase shift film 12 are respectively set to 1.00 μm and 1.75 μm on the mask surface (corresponding to 0.20 μm and 0.35 μm on the projection surface at a reduction ratio of ⅕). As a result, fine processing up to a minimum line width of 0.3 μm required for a 64-Mbit DRAM can be performed.

Further, in this embodiment, the phase shift film 12
Although SOG was used as the main material of the above, it is not limited to this. In addition to SOG, silicon-phosphorus-glass, silicon-phosphorus-boron-glass, organic polymer film, etc. can be used. Further, as a matter of course, the phase shift film can be provided by a vapor phase growth method.

[0020]

As is apparent from the above, the photoexposure mask of the present invention is provided with the phase shift film made of a semitransparent material that absorbs the exposure light, so that the photoexposure mask can be easily manufactured and the resolution is high. The minimum line width can be increased to 0.2
Fine processing up to μm can be performed.

By setting the transmittance of the phase shift film with respect to the exposure light to 40 to 90%, the resolution can be further increased and the processing accuracy can be further increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a phase shift mask according to an embodiment of the present invention.

FIG. 2 is a diagram showing calculation results of light intensity of a phase shift mask having a semitransparent phase shift film.

FIG. 3 is a diagram showing a conventional phase shift mask.

FIG. 4 is a diagram showing a conventional phase shift mask.

FIG. 5 is a diagram showing a manufacturing process of a conventional phase shift mask.

FIG. 6 is a diagram for explaining the operation of the conventional phase shift mask shown in FIG.

[Explanation of symbols]

 11 Quartz Substrate 12 Phase Shift Film 16 Electron Beam Resist

Claims (2)

[Claims] 1. A photoexposure mask having a phase shift film on a substrate transparent to exposure light, wherein the phase shift film is made of a semitransparent material that absorbs the exposure light. A mask for light exposure. 2. The photoexposure mask according to claim 1, wherein the phase shift film has a transmittance for the exposure light set to 40% to 90%.