JPH1197334A - Pattern formation method - Google Patents

Abstract

(57) Abstract: Provided is a practical method and apparatus for efficiently processing a fine element pattern used for manufacturing a semiconductor integrated circuit or the like in a short time. A pattern of a quarter wavelength is exposed to light by transferring a pattern in a resist (27) by interfering light from a light source for demodulation (20) to form a second grid pattern (26). The pattern is drawn by electron beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring a pattern of a semiconductor integrated circuit, a liquid crystal element or the like onto a sample substrate.

[0002]

2. Description of the Related Art A method of transferring a pattern drawn on a mask onto a sample substrate, which is called a lithography technique, is widely used for forming a pattern of a semiconductor integrated circuit or a liquid crystal element. In order to perform this pattern transfer, a reduced-projection type projection exposure apparatus for reducing and transferring a pattern on a mask is generally used. In particular, the phase shift method is characterized in that it can resolve a fine pattern of half the exposure wavelength.

[0003] There is a method using electron beam lithography to form a smaller fine pattern. Since electron beams can be easily narrowed down to a fine electron beam having a diameter equal to or smaller than the wavelength by an electron optical system, electron beam drawing has high resolution and is suitable for forming a fine pattern. However, pattern drawing requires a long time, and is not suitable for mass production. To compensate for this drawback, Japanese Patent Application Laid-Open No. 4-155812 discloses a method of simultaneously forming a large pattern and a fine pattern on the same resist, by forming a resist film and then exposing the former large pattern by a phase shift method. Draw a pattern with an electron beam,
A method of forming two types of patterns in the same substrate by developing is disclosed. As described above, the purpose of this method is to efficiently form a large pattern by a phase shift method and a fine pattern by electron beam lithography.

Recently, attempts have been made to transfer a fine pattern exceeding the conventional resolution limit using the current projection exposure apparatus. A modulation step of shifting the spatial frequency by shifting the position of the Fourier transform pattern by a predetermined amount on the surface on which the Fourier transform pattern of the mask pattern is formed; and, on the wafer substrate, the spatial frequency shift in relation to the modulation amount in the modulation step. Japanese Patent Application Laid-Open No. 7-326573 discloses that a pattern forming method having a demodulation step of reproducing a mask pattern, that is, a so-called moire method, is used to provide a resolution exceeding the conventional resolution performance. According to this method, it is possible to perform pattern exposure by light exposure up to a very fine pattern of 1/4 of the exposure wavelength.

[0005]

Japanese Patent Application Laid-Open No. 4-155812 discloses a technique for forming a fine pattern by combining a phase shift method and an electron beam drawing method in order to improve mass productivity. Utilizing the high efficiency and high resolution of electron beam lithography, fine patterns are produced at high throughput. However, as the pattern miniaturization of semiconductor integrated circuits and the like progresses further, if most of the patterns constituting the element are fine patterns, the phase shift method cannot resolve them, and most of the fine patterns are formed using electron beams. Since the drawing is performed, the effect of shortening the time cannot be expected.

An object of the present invention is to provide a practical pattern forming method for efficiently forming a fine element pattern in a short time.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide a lithography process for forming a certain pattern layer in the process of manufacturing an element, in which a pattern transfer to the same resist is performed on a mask pattern drawn on a mask substrate. A modulation step of shifting the spatial frequency by shifting the position of the Fourier transform pattern by a predetermined amount on the surface on which the Fourier transform pattern is formed; and, in the resist, by shifting the spatial frequency in association with the modulation amount in the modulation step. This is achieved by performing light exposure for projecting into the resist through a projection optical system having a demodulation step of reproducing a mask pattern to form a pattern, and electron beam exposure.

[0008]

Embodiments of the present invention will be described below. These embodiments are merely examples of the present application, and the present invention is not limited to these embodiments.

In the projection exposure method, as a modulation step, a pattern having a different spatial frequency, that is, diffracted light constituting a moiré fringe passes through a projection lens by superimposing a first lattice fringe on a mask pattern, so that pattern information is written on a wafer. introduce. Then, pattern transfer is performed by demodulation in a resist on the substrate. In the demodulation step, a material whose transmittance or refractive index changes in response to light for a very short time is applied to the surface of the resist.

The demodulation thin film is irradiated with light from two directions to form two-beam interference fringes in the thin film. This interference fringe acts as a second interference fringe for light for exposure for pattern transfer. In this way, it is possible to transfer a fine pattern of １ ／ of the exposure wavelength. This has the advantage that the resolution is higher than half the exposure wavelength, which is the theoretical limit of the phase shift method. Of course, this moiré method is 1/2
It goes without saying that even in the pattern size of the wavelength, a better exposure shape can be provided than in the phase shift method.

In the pattern transfer by the moiré method, the second demodulation grating is not necessarily a light and dark grating having a changed optical density, but may be a phase shift grating having a changed refractive index. In the case of the phase shift grating, since the energy of the exposure light is not absorbed by the demodulation film, there is an advantage that the exposure time can be shorter than that of the light and dark grating.

In order to increase the demodulation effect, it is desirable that the change in the absorbance of the demodulation film be 1 or more when forming moire fringes of a light and dark lattice. When forming moiré fringes of a phase grating, it is desirable that the change in the phase of the demodulation film be equal to or more than 波長 wavelength.

A demodulation grating may be manufactured by using two-beam interference and three-beam interference in which light is incident from the normal direction of the wafer surface in the demodulation layer film. In this case, since there is no limit on the thickness of the demodulation film, many materials can be used for the demodulation film. For example, for light for producing a demodulation grating,
Even for a material having a small change in optical density per unit length, if the thickness of the demodulation film is increased, the optical density of the entire film is increased, so that the material can be used. Conversely, since the change in the optical density of the demodulation material may be small, there is an advantage that the intensity of the light for demodulation can be weakened and the optical deterioration of the demodulation material can be suppressed. Furthermore, if the fringes due to the three-beam interference are regarded as a kind of diffraction grating, the diffraction efficiency is effective for the entire volume in the thickness direction, so that it can be made 100%, and there is an advantage that a complete demodulation effect can be achieved.

Considering the case of light and dark fringes, in principle, the higher the contrast between light and dark, the greater the demodulation effect. In order to obtain high contrast, it is desirable that the intensity of light for forming the second lattice fringes be high. However, when the exposure is constantly performed at a high intensity, the energy stored in the demodulation material increases, and the demodulation material is thermally damaged, which is a problem. Therefore, as the light source, it is desirable to use pulse excitation in which the intensity is high but the exposure is performed for a short time.

When a second lattice fringe is formed by pulse excitation,
The fringes formed in the demodulation material disappear in a short time and return to the original transparent state. This is because the first grid pattern can be mechanically scanned because the upper and lower grid patterns are synchronously scanned, but the lower second grid pattern is optically scanned with interference fringes.
This is a characteristic desired from the measurement principle that the light forming the interference fringes is scanned, and the light should return to the original transparent state as soon as the light stops being irradiated. When the pattern exposure light is constantly irradiated onto the wafer on the demodulation material, the material is exposed even after the lattice fringes have disappeared, so that the demodulation effect is reduced. Since the second lattice fringe is the sharpest immediately after the fringe is formed, pattern exposure only immediately after the fringe formation is a method for maximizing the demodulation effect. Therefore, it is desirable that the light for pattern exposure is also pulsed, synchronized with the pulse light for forming the second grid pattern, and the pattern exposure is performed only immediately after the second grid pattern is formed.

As the pulsed light source, a continuous light source may be pulsed by a mechanical shutter, or a titanium sapphire
A laser that oscillates from the beginning, such as a laser, a yag laser, and an excimer laser, may be used. In particular, a titanium sapphire laser, a laser utilizing an opto-parametric phenomenon, or the like is particularly suitable because the oscillation wavelength can be continuously set to a desired value.

As the resist used in the present invention, ordinary positive type and negative type resists can be used. Particularly, a chemically amplified resist is more preferable because of its high sensitivity.
In the case of a chemically amplified resist, the demodulation layer serves as a protective film for preventing the resist from deteriorating. Therefore, there is an advantage in that there is no dependence on the storage time after exposure and a stable lithography process can be performed.

Further, by using the multilayer resist method, a fine pattern can be favorably formed even under a condition where the depth of focus is shallow.

First Embodiment First, an outline of a configuration example of a projection exposure apparatus for realizing a pattern forming method of the present invention will be described with reference to FIG. The second harmonic pulse light of the first titanium-sapphire laser 1 was used as light (wavelength: 365 nm) for exposure. This titanium sapphire laser light source 1
Is converted by the beam expander 2 into a beam having a desired uniform light intensity in cross section, and illuminates the mask substrate 3. Hereinafter, the mask substrate 3 is referred to as a reticle 3. Pattern 4 drawn on reticle 3 is 1/5 magnification
Is projected on the wafer 6 through the projection lens 5 of the above. The reticle 3 is placed on a stage 8 controlled by a reticle position control means 7, and its center and projection lens 5
Is accurately aligned with the optical axis.

The wafer 6 is placed on a Z stage 9 which can move in the direction of the optical axis of the projection lens 5, that is, in the z direction. The Z stage 9 and the XY stage 10 are provided with respective driving units 12,
Since it is driven by 13, it can be moved to a desired exposure position with respect to the base 14 of the projection exposure apparatus. The position is accurately monitored by a laser length measuring device 16 as a position of a mirror 15 fixed to the Z stage 9. The surface position of the wafer 6 is measured by a normal focus position measuring means of the projection exposure apparatus. By driving the Z stage 9 according to the measurement result, the surface of the wafer 6 can always be made to coincide with the image forming plane of the projection lens 5.

In this embodiment, a transmissive lattice-like optical element 17 acting as a first lattice fringe is arranged very close to the reticle 3. Here, a phase grating was employed, and the pitch of the phase grating 17 was 0.75 μm. This phase grating 17
Is mounted on a stage 18 and can be scanned in a plane by a driving means 19.

The second harmonic (wavelength: 436 nm) from the second titanium-sapphire laser was used as a light source 20 for forming a demodulation lattice fringe. Light from the light source 20 is applied to the surface of the wafer 6 by beam splitters 21 and 22 and mirrors 23 and 2.
The interference fringes 26 having a pitch of 0.15 μm were formed by causing three beams to interfere with each other in the thin film 28 for demodulation using the samples 4 and 25. This pitch is a value obtained by multiplying the pitch of the first grid pattern (0.75 μm) by the magnification (１ ／) of the projection lens 5.

A positive resist 27 was applied on the wafer 6, and a material having a reversible photochemical reaction was applied on the surface thereof to a thickness of 1 μm to form a demodulation thin film 28.
In this embodiment, a solution of acridine orange and polyvinylpyrrolidone was spin-coated on the resist 27 and dried by heating to produce a demodulation thin film 28.

The demodulation thin film 28 has a time response of less than millisecond to light having a wavelength of 436 nm and reacts reversibly. That is, the complex refractive index changes only when the pulse light of 436 nm is irradiated, the refractive index changes instantaneously at 365 nm, and the phase shift type fringe 2 for demodulation is used.
6 and returns to the original refractive index within a short time with a lifetime of less than milliseconds.

The first titanium-sapphire laser 1 and the second titanium-sapphire laser 20 are controlled by the main control system 11 so that the second titanium-sapphire laser 2 of 436 nm is used.
0 creates the grid fringes 26 for demodulation immediately after the first titanium sapphire laser 1 for pattern exposure
6 is set. Therefore, when the exposure light of the first titanium sapphire laser 1 passes through the demodulation layer 28, the lattice fringes 26 having a sufficient contrast are formed, so that the demodulation is performed efficiently. The second lattice fringe 26 moves in the demodulation thin film 28 by continuously changing the phase of light using the mirror driving means 29 of the mirror 24. The resist 27 was exposed to a fine pattern of 0.15 μm by performing pattern exposure while synchronously scanning the first grating 17 and the second grating fringe 26.

Subsequently, a fine pattern of 0.1 μm was drawn by electron beam drawing. Then, the demodulation thin film 2
8 was removed, the positive resist 27 was developed, and the pattern shape was observed with a scanning electron microscope. As a result, a fine pattern having a good shape with a pitch of 0.15 μm was found by the moire method.
A fine pattern having a good shape of 0.1 μm was formed by electron beam lithography. At this time, the change in the complex refractive index of the demodulation film was 0.5 wavelength.

Similar effects were obtained by using a YAG laser as the pulse laser.

[0028]

According to the present invention, a pattern of a quarter wavelength of a fine pattern exceeding the limit of the phase shift method is performed by efficient light exposure, and a fine pattern of a quarter wavelength or less is produced by electron beam drawing. Thus, a fine pattern can be formed with high throughput.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a projection exposure apparatus used in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Exposure light source, 2 ... Beam expander, 3 ... Reticle, 4 ... Pattern on reticle, 5 ... Projection lens,
Reference numeral 6: wafer, 7: reticle position control means, 8: reticle stage, 9: Z stage, 10: XY stage, 11: system main control system, 12: Z stage drive means, 13: XY stage drive means, 14 ... Projection exposure apparatus base, 15: mirror, 16: laser measuring device, 17: first grating, 18: first grating stage, 19: first grating stage driving means, 20: pulse light source for demodulation ,
Reference numerals 21, 22, beam splitters, 23, 24, 25 mirror, 26 second grid pattern, 27 resist, 28 thin film layer for demodulation, 29 mirror driving means.

Claims (7)

[Claims] In a lithography process for forming a certain pattern layer in a manufacturing process of a device, a pattern transfer to the same resist is performed on a surface on which a Fourier transform pattern of a mask pattern drawn on a mask substrate is formed. A modulation step of shifting the position of the Fourier transform pattern by a predetermined amount to change the spatial frequency, and a demodulation step of reproducing the mask pattern by shifting the spatial frequency in the resist in association with the modulation amount in the modulation step. A pattern formation method, wherein the pattern formation method is performed by using light exposure for projecting into the resist through a projection optical system having a pattern to form a pattern, and electron beam exposure. 2. The pattern forming method according to claim 1, wherein the resist is irradiated with light of three-beam interference in the resist as the demodulation step. 3. The pattern forming method according to claim 1, wherein a pulse light source is used as both the projection light source and the light source for the demodulation step. 4. The pattern forming method according to claim 1, wherein a pulsed light source is used as the light source for the demodulation step, an excited state is formed by the pulsed light source, and projection pulse light is irradiated within the life of the excited state. A pattern forming method. 5. The pattern forming method according to claim 1, wherein an excitation state is formed by the light source for the demodulation step, and the change in absorbance of the thin film on the wafer substrate at the wavelength of the projection light source is one or more. Characteristic pattern formation method. 6. The pattern forming method according to claim 1, wherein an excitation state is formed by the light source for the demodulation step, and a change in the refractive index of the thin film on the wafer substrate at the wavelength of the projection light source causes the light in the thin film to change. The optical path difference is 0.5 of the exposure wavelength.
A pattern formation method characterized by having a wavelength or more. 7. The pattern forming method according to claim 1, wherein the resist is converted into a so-called three-layer resist composed of a flattening layer, an intermediate layer, an upper layer, or the like, or a so-called two-layer resist without an intermediate layer. A pattern forming method characterized by having been replaced.