JPS60117735A - Pattern transfer method - Google Patents

Abstract

PURPOSE:To offer the transfer of high resolution without light diffraction by irradiating a substance to be exposed with a laser beam combined with a supersaturation absorber. CONSTITUTION:A laser beam source 1 passed through an image forming optical system 2 which is adapted for a wavelength. In the image forming optical system 2, there is a patterned mask the whole surface of which is scanned by a laser beam (LB). A supersaturation absorber 3 is, e.g., a cyanine dye and changes the transmittance keenly to increase it only for the specific wavelength of the incident light. And the transmittance changes rapidly to be increased at a certain limiting value of the light intensity. A resist film 4 has a characteristic that it is exposed to light by a wavelength of about 4,000A. The supersaturation absorber 3 is arranged between the image forming optical system 2 and the substance to be exposed 4 thereby utilizing the property of selective transmission of the absorber 3 to expose the substance to be exposed 4 with the light beam of an acute angled wave form of a peak in a wide zone width.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) 1 Technical Field of the Invention The present invention relates to a pattern transfer method, and more particularly to high-resolution pattern transfer using a combination of a laser beam and a supersaturated absorber.

(b) Background of the Technology In recent years, the field of technology that requires fine and precise patterning of semiconductor wafers has expanded.

Generally, the pattern transfer method is to expose the transferred object coated with a photoresist film with ultraviolet light, but due to scattering due to light diffraction phenomenon, it is difficult to transfer fine and dense patterns. There is a limit to resolution, and a pattern transfer method with higher resolution is desired.

(C), Prior Art and Problems Conventionally, so-called photolithography technology has been adopted as a pattern transfer method, in which a substrate coated with a photoresist film is optically exposed using a patterned mask. There is.

This photolithography is a method in which a photoresist film is applied in advance to the surface of a semiconductor or metal substrate, and ultraviolet rays are irradiated onto the photoresist film through a patterned mask.

For example, in the case of a negative resist film, only the part of the photoresist film that is irradiated with ultraviolet light is exposed to light and becomes polymerized, and this part remains undissolved in the developer and is not exposed to light. A portion of the photoresist film is dissolved in a developer, and a desired pattern can be transferred onto the developed substrate.

However, this photolithography is limited in terms of resolution because of the diffraction phenomenon of exposure light, which causes the light to be diffused.

According to Railejgh's theory, the resolution limit can be expressed as follows.

0.61λ/NA (11 λ; between wavelengths of light; numerical aperture As shown in formula (1), in order to reduce the resolution, increase the numerical aperture NA and decrease the wavelength λ of light. Bye.

In the case of commonly performed ultraviolet light exposure, the numerical aperture NA=0.
3, and since the wavelength of the light at the exposed point is ultraviolet, λ-
0.4 .mu.m, and the resolution limit is about 1 .mu.m.

Therefore, to overcome this resolution limitation, other new transfer methods are needed.

On the other hand, electron beam exposure technology has been put into practical use as a new method to improve the drawbacks of photolithography technology.

The electron beam exposure technology for resist films is characterized by the ability to focus the electron beam narrowly using an electron lens system and the depth of focus is deep, but because the electron beam is sensitive to the aberrations of the electron lens, If the area is scanned, the pattern will be distorted, and the disadvantage is that obtaining a highly accurate pattern is limited to a small area.

(d)0Object of the Invention In view of the above-mentioned drawbacks of the conventional method, an object of the present invention is to provide a high-resolution pattern transfer method by using a laser beam and a saturable absorber.

(e) 9 Structure of the Invention According to the present invention, when a substrate to which a pattern is to be transferred is irradiated with a laser beam in the form of a pulse wave from an imaging optical system including a mask having a predetermined pattern, the laser beam is This can be achieved by providing a pattern transfer method characterized by irradiation through a saturable absorber.

(f) 8 Embodiments of the Invention Hereinafter, embodiments of the present invention will be explained with reference to FIG. 1. FIG. 1 is a schematic diagram illustrating the present invention.

In the figure, laser light source 1 that oscillates pulsed wave laser light
, an imaging optical system 2 that optimally images the emitted laser beam, a saturable absorber 3, and an exposed object 4 coated with a photoresist.

Laser light source 1 has a wavelength of approximately 3, although it varies depending on the type of laser.
Laser light of about 00OA to 5000Δ is oscillated, and this laser light passes through an imaging optical system 2 that matches the wavelength.

Inside the imaging optical system 2 is a patterned mask, the entire surface of which is scanned with a laser beam.

The saturable absorber 3 is a cyanine-based dye, and has the property of sharply changing the transmittance only for a specific wavelength of light incident on the saturable absorber, improving the transmission, and also having the property shown in FIG. As shown in the figure, the saturable absorber is a material that has two types of properties: the transmittance changes rapidly at the limit value (threshold) of the light intensity, and the transmittance improves. be.

The above-mentioned characteristics of such saturable absorbers are due to the fact that the energy level is excited by optical excitation of the saturable absorber and converted through a non-radiative transition process or into optical energy of a completely different wavelength. It is dissipated as energy, which is an important property of saturable absorbers.

The resist film 4 has a characteristic that it is sensitive to a light wavelength of about 4000A.

Generally, the irradiation bandwidth of laser beam exposure becomes a wide irradiation pattern due to light diffraction, as shown in FIG.

Since the pulsed laser beam has a strong output, the present invention originally uses a saturable absorber 3 installed between the imaging optical system 2 and the object 4 to be exposed, as shown in FIG. By inserting a saturable absorber into the optical path of the laser beam irradiation pattern that has a wide bandwidth due to optical diffraction, the saturable absorber becomes opaque to the laser beam with a light intensity of less than a-a shown in Figure 3. , Utilizing the property of selective transmission, which becomes transparent to laser beams of a-3 or higher,
As shown in FIG. 4, the object to be exposed 4 is exposed with a sharp light beam having a peak waveform a-a with a wide bandwidth.

To explain the specific operation here, laser light sources include excimers such as xenon (Xe), chlorine (C1), lasers (Excimer 1.aser), helium, cadmium (lie-Cd) lasers, and argon (8r) lasers.
) ions, lasers, or dyes, lasers (Dye L
a5er) etc., and the wavelength of the laser is approximately 4000.
It is about A.

In addition, there are many types of saturable absorbers 3, and the light absorption, conversion wavelength, energy efficiency, etc. differ depending on the type, but the cyanine dyes mentioned above are the most used. This is an example.

In any case, as a criterion for selecting a saturable absorber,
Of the light energy irradiated to the saturable absorber, for the light energy below the limit value (threshold value) of the saturable absorber, the wavelength of the converted light energy is such that it is not sensitive to the photoresist film. It is necessary to have a light wavelength, which is generally a light wavelength of 4000 to which a photoresist film is sensitive.
Yellow, which has a much longer wavelength than A (wavelength 5500M)
) to 7000 A).

In this way, depending on the wavelength of the laser beam, the saturable absorber has a certain limit (threshold value) of transmittance and is exposed to a sharp laser beam. On the other hand, in the present invention, the resolution can be improved to about 0.5 μm.

(g) 3 Effects of the Invention As explained in detail above, by irradiating the exposed object with a combination of the laser beam of the present invention and the saturable absorber and performing the pattern transfer method, high-resolution transfer without light diffraction can be achieved. It has the great effect of providing the following.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram explaining the present invention in detail, Fig. 2 is an optical characteristic diagram of a saturable absorber, Fig. 3 is a diagram explaining the diffraction of a conventional laser beam without a saturable absorber, and Fig. 4 is a diagram explaining the diffraction of a conventional laser beam without a saturable absorber. The figure shows the peak of a laser beam after the diffraction portion of the laser beam is removed by a saturable absorber. In the drawing, 1 is a pulsed laser light source, 2 is an imaging optical system, 3 is a saturable absorber, and 4 is an exposed object. Figure 1 Figure 3 Support level

Claims (1)

[Claims] A pattern transfer characterized in that when a substrate to which a pattern is to be transferred is irradiated with a pulsed wave output laser beam from an imaging optical system including a mask with a predetermined pattern, the laser beam is irradiated through a saturable absorber. Method.