JPH0738372B2 - Pattern formation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pattern forming method for forming a pattern of a semiconductor element, a magnetic bubble element, a diffraction grating or the like using a mask.

[Conventional technology]

Conventional pattern formation methods include photolithography using light (ultraviolet rays, far ultraviolet rays, etc.) as a light source, and X-ray lithography using soft X-rays. The principle of these lithography techniques is schematically shown in FIG. That is, a mask 3 is formed on a film formed on the substrate 1 such as a semiconductor wafer and exposed to light or X-rays, for example, a resist film (hereinafter, a case where a resist film is used as an example of a photosensitive film will be described for simplicity). The pattern 6 of the mask 3 is transferred by exposing through light or X-rays 4 through. Here, the conventionally used mask 3 is formed on the mask substrate 5 having a high transmittance of light or X-rays.
Thickness and material that makes it much more opaque to the line (referred to as absorber)
Thus, the pattern 6 is formed. That is, of the light or X-rays that have entered the mask 3, only those that have entered the portion without the absorber pass through the mask 3 and reach the surface of the resist film 2, and the pattern 6 is transferred.

[Problems to be solved by the invention]

In such a pattern transfer method, the influence of the diffraction phenomenon cannot be avoided. That is, light or X-rays is also diffracted to the portion of the resist film 2 facing the absorber portion, which is not supposed to be exposed, and the exposure effect is exerted. As a result, the resolution is lowered. In the case of the proximity exposure method, the influence of diffraction can be reduced by reducing the distance g between the mask 3 and the resist film 2. However, the distance g is at least 10 μm or more in order to protect the mask 3 from mutual movement for alignment and contamination and damage of the mask 3.
Practically, several tens of μm is required. Further, the size of the pattern that can be transferred is also limited by the limit of the fine processing technology of the pattern of the mask 3.

Therefore, the minimum size of a pattern that can be transferred is around 0.4 μm in photolithography, and even in the case of using synchrotron radiation, which is considered to be the most excellent radiation source for lithography in X-ray lithography.
The limit is about 0.1 μm.

The present invention has been made in order to solve the above problems, and by using a mask based on a principle different from the conventional technique, an ultrafine pattern is transferred without the resolution being limited by diffraction. The purpose is to obtain a pattern forming method.

[Means for solving problems]

According to the pattern forming method of the present invention, a mask is constructed by arranging two kinds of films having the same amplitude of transmitted light or transmitted X-rays and having a phase difference of π or an odd multiple thereof side by side in the mask plane. Then, light or X-rays are exposed through this mask, and the pattern corresponding to the intensity distribution generated at the position on the sample surface corresponding to the boundary portion of the two kinds of films due to the phase difference is exposed to light or X-rays. It is formed on a film that is exposed to light.

[Action]

In the present invention, since the mask is formed of two kinds of films in which the amplitude of the transmitted light or the transmitted X-rays is equal and the phase difference is π or an odd multiple thereof, the distance between the mask and the resist film and the mask pattern. Ultra-fine patterns can be formed because high resolution up to the wavelength level can be obtained regardless of the limitations of the microfabrication technology.

〔Example〕

1 (a) to 1 (c) are sectional views showing the principle of the present invention.

First, as shown in FIG. 1 (a), constituent materials of a mask pattern composed of different materials (hereinafter simply referred to as constituent materials) 7,
In the structure of the mask 3 in which 8 have the same width, the transmitted waves (light or X
(B) the amplitudes are equal to each other, while the phases are different from each other by π or an odd multiple thereof, the intensity distribution finally obtained on the resist film 2 surface is shown in FIG. 1 (b).
become that way. That is, the light or the X-ray that passes through each of the constituent substances 7 and 8 and reaches each point X1, X2, X3, ... on the resist film 2 corresponding to the boundary with the constituent substances 7 and 8 is Since the phase difference is π or an odd multiple thereof, they cancel each other out, resulting in zero intensity. Such a phenomenon is independent of the distance g between the mask 3 and the resist film 2 and the pattern size (width of the constituent substances 7 and 8 in the case of FIG. 1).

Therefore, unlike the prior art, there is no reduction in resolution due to an increase in the distance g and no limitation on resolution due to diffraction, and theoretical analysis enables high resolution up to the wavelength level.

The structure of the mask 3 is not limited to that shown in FIG. 1 (a), but as shown in FIG. 1 (c), a mask substrate having a uniform thickness for increasing mechanical strength. Even when 10 is attached, the same effect can be obtained if the conditions regarding the amplitude and the phase difference are satisfied. Further, in the physics of ultrafine structures and research and development of advanced devices, a structure that is not necessarily periodic may be necessary. Even in such a case, the structure as shown in FIG. If the conditions concerning the amplitude and the phase difference in the transmitted waves from the constituent substances 7 and 8 are satisfied, the intensity becomes the minimum at the position corresponding to the boundary between the two, and the same effect can be obtained.

The material and thickness of the pattern portions of the constituent substances 7 and 8 shown in FIG. 1 can be determined based on the following consideration.

First, the conditions for equalizing the amplitudes of the transmitted waves in the two substances a and b are taμa = tbμb (1) where t and μ are the thickness and attenuation coefficient, and the subscripts a and b are Indicates that it belongs to a substance (subscripts a and b are used with the same meaning in the following description). On the other hand, the phase difference is π
2 {(na−a) ta− (nb−1) tb} / λ = 1 (2) where n is the refractive index and λ is the wavelength. It suffices to select a combination of the substances a and b that satisfy the above two expressions at the same time and ta and tb have realistic values in mask fabrication.

Next, as an embodiment of the present invention, a combination of silicon nitride and a gold film will be described below as an example. In order to satisfy the above conditions, the film thicknesses of silicon nitride and gold may be 2.37 μm and 0.16 μm, respectively, when λ = 1 nm.
Such a mask 3 can be manufactured by the method shown in FIG. First, a structure having the structure shown in FIG. 2A is prepared by the same method as that used for manufacturing a conventional X-ray mask. Here, 11 is a substrate such as a silicon wafer, 10 is a mask substrate made of a film such as silicon nitride, boron nitride, or polyimide, 12 is a thin metal film such as gold, and 13 is a 2.37 μm thick silicon nitride film that forms a pattern. It is a film, and the opening 13a is formed by directly processing with a focused ion beam or by processing such as reactive ion etching using a resist pattern formed by a lithography technique using light, electrons, X-rays, etc. as a mask. Form. The gold film 14 is deposited to a thickness of 0.16 μm by a method such as plating through the opening 13a.
By removing from the back side by etching,
A mask 3 having a structure as shown in FIG. 2 (b) can be obtained. Here, the metal film 12 and the mask substrate 10 are not related to the phase difference of the transmitted waves between the silicon nitride film 13 and the metal 14 portion forming the pattern. Therefore, each thickness can be freely selected within a range that meets the respective purposes of improving the adhesion of the metal 14 and increasing the mechanical strength.

As a second embodiment of the present invention, a case of a combination of aluminum (Al) and polymethylmethacrylate (PMMA) will be described with reference to the sectional views shown in FIGS. When the wavelength is 1.5 nm, the respective film thicknesses for satisfying the above conditions regarding the amplitude and the phase difference are
2.16μm, PMMA film is 2.07μm. Such a mask 3
Can be manufactured by the method shown in FIG.

First, a PMMA film 15 having an opening having a thickness of 2.16 μm or more is formed by the same method as described with reference to FIG. 2, and an Al film 16 is deposited to a thickness of 2.16 μm in the opening, The structure is as shown in FIG. Alternatively, a PMMA film 15 having a flat surface is formed by a method such as forming an Al film 16 having a thickness of 2.16 μm having an opening and spin-coating a solution of PMMA on the Al film 16. The structure is as shown in FIG. For the structure shown in FIG. 3 (a) or (b), plasma etching using a gas such as oxygen, which hardly etches the Al film 16,
Alternatively, perform reactive ion etching or the like to remove the PMMA film 15
By reducing the film thickness to 2.07 μm and removing the substrate 11 from the back surface by etching or the like, a mask having a desired structure can be obtained as shown in FIG. 3 (c).

The conditions regarding the amplitude and the phase difference of the transmitted light or the transmitted X-ray do not necessarily have to be strictly satisfied.

According to the results of theoretical studies on the above examples, even if the thickness of each mask constituent material has an error of about ± 10%,
It has almost no effect on the pattern transferred to the resist.
Further, the film thickness, the combination of materials, and the mask manufacturing method shown in the embodiments are some of the possible choices, and the present invention is not limited thereto.

〔The invention's effect〕

As described above, according to the present invention, a mask is composed of two kinds of films having the same amplitude of transmitted light or transmitted X-rays and a phase difference of π or an odd multiple thereof, and the light or the X-ray is transmitted through the mask. Line exposure, and a pattern corresponding to the intensity distribution caused by the phase difference was formed on the film that was exposed to light or X-rays. In principle, it is possible to form an ultrafine pattern up to the same size as the wavelength without any limitation on the resolution due to the limitation of.

Further, since the distance between the mask 3 and the wafer does not affect the formation pattern, it is not necessary to bring the distance close to the limit or precisely control it as in the conventional technique. Therefore, there is an advantage that the device configuration such as holding the mask and the wafer, their moving mechanism, and the alignment mechanism can have a margin and can be simplified.

[Brief description of drawings]

1 (a) to 1 (d) are sectional views showing the principle of the present invention,
2 (a) and 2 (b) are sectional views showing an embodiment of the present invention, FIGS. 3 (a) to 3 (c) are sectional views showing a second embodiment of the present invention, and FIG. It is sectional drawing which shows an example of the conventional pattern formation method. In the figure, 3 is a mask, 7 and 8 are constituent substances of a mask pattern, and 9
Is an absorber, 10 is a mask substrate, 11 is a substrate, 12 is a metal film, 13
Is a silicon nitride film, 13a is an opening, 14 is a gold film, and 15 is PMMA.
The film, 16 is an Al film.

Front Page Continuation (72) Inventor Taku Song Sato 4259 Nagatsuta, Midori Ward, Yokohama City, Kanagawa Prefecture Graduate School of Science and Engineering, Tokyo Institute of Technology (56) Reference JP-A-58-173744 (JP, A)

Claims (1)

[Claims] 1. A mask for optical lithography or X-ray lithography, in which two kinds of first and second films having different refractive indexes and / or thicknesses are arranged next to each other in the mask plane. At least one pair of the above-mentioned structures and the amplitudes are equal to each other and the phase difference is π or an odd multiple thereof in the transmitted wave of light or X-ray from each of the first film and the second film. , The intensity of the pattern is minimized because the transmitted waves from the first film and the second film interfere with each other on the sample surface to which the pattern is to be transferred, at a position corresponding to the boundary portion between the first film and the second film. To produce a light or X-ray intensity distribution that causes exposure to a film or light- or X-ray-sensitive film previously formed on the surface of the sample. Pattern corresponding to And a method of forming a pattern.