JPH10326746A - Method of forming mask pattern - Google Patents

Abstract

(57) [Problem] In a multi-beam interference type exposure, a resist shape does not become rectangular due to lack of contrast due to fluctuation of an optical system peculiar to the multi-beam interference exposure, or a periodic photoresist pattern is formed. However, there is a problem that it is difficult to precisely control the duty or the size of the device. According to the present invention, in a method of forming a mask pattern for forming a pattern periodically arranged on a substrate, a step of forming a photoresist film on the substrate; A mask having good controllability of resist shape and pattern by adopting a mask pattern forming method having a step of forming a layer having a pattern and a step of exposing the substrate by splitting and interfering a light beam from a coherent light source. A method for forming a pattern is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a mask pattern used for etching or selective growth, and more particularly to a method for forming a periodically arranged pattern of an optical element or an optoelectronic element for realizing functions such as wavelength selectivity. And a method of forming a mask pattern.

[0002]

2. Description of the Related Art Various opto devices have been realized in which patterns arranged periodically are formed on a substrate made of a semiconductor or a dielectric. As a typical example of such an opto-device, there is a distributed feedback laser that can obtain wavelength selectivity by having a diffraction grating inside the device. The manufacturing process of a general diffraction grating will be described below. First, a photoresist is applied on a substrate, and an exposure process and a development process are performed to form a periodically arranged resist pattern. By etching the substrate using this as a mask, a diffraction grating is transferred and imprinted on the substrate. At this time, the pitch 回 折 of the diffraction grating is determined by m / 2n times the wavelength λ of the desired light (m is a positive integer and represents the diffraction order, and n is the equivalent refractive index). For example, a semiconductor having n = 3.5 When a diffraction grating adapted to λ = 780 nm is manufactured using a substrate, the pitch の of the diffraction grating is (0.11 × m) μm.

[0003] As can be seen from the above equation, when the diffraction order is designed to be small, it is necessary to reduce the pitch of the diffraction grating. Conversely, if the diffraction order is designed to be large, the pitch of the diffraction grating can be increased, but the duty (line width / pitch of the diffraction grating) may need to be reduced. This point will be described specifically with respect to what has been reported in a gain-coupled distributed feedback laser using an absorptive diffraction grating. FIG. L. Literature by Cao et al., IEEE Photonics Technology
Fig. 2 of the Letter Letters, 4 (1992) 1099 is shown. The horizontal axis shows the duty, and the vertical axis shows the normalized coupling coefficient. Third order (m = 3) as shown in FIG.
When the duty is around 0.3, the normalized coupling coefficient κL (L is the length of the resonator) approaches zero. At this time, no distributed feedback occurs in the gain-coupled feedback laser.

FIG. 6 shows FIG. 3 of the above document. The horizontal axis shows the duty and the vertical axis shows the additional waveguide loss. As shown in FIG. 6, the additional waveguide loss αo due to the absorptive diffraction grating monotonically increases with an increase in the duty, and when the duty is 0.3 or more, the characteristics of the laser are significantly deteriorated. Therefore, the duty of the third-order absorbing diffraction grating is required to be within the range of about 0.1 to 0.2. Specifically, in the case of an AlGaAs-based distributed feedback laser in the 780 nm band, the pitch of about 3500 ° About 35
It is necessary to form an absorption layer having a width of 0 to 700 °. Thus, there is a demand for an extremely fine pattern processing in which the pitch and duty of the diffraction grating are precisely controlled.

Conventionally, as means for realizing such precise fine processing, there are a two-beam interference type exposure using a photoresist and a direct EB exposure using an electron beam resist. In the two-beam interference type exposure, which is effective for forming a periodic pattern, a resist beam is exposed by splitting and interfering a light beam from a coherent light source into a plurality of light beams, and a photoresist pattern that is periodically arranged is formed through a developing process. Was.

Japanese Patent Laid-Open Publication No. Sho 63-136625 discloses a method of performing precise processing, which is based on an optimum value of each processing time of a developing process and an etching process, which changes due to a slight change in a resist film thickness and an exposure amount. Is disclosed during each step. In other words, by projecting a beam from the top surface of the substrate during each process and monitoring the temporal change in the intensity of the diffracted light, the shape change of the resist pattern on the substrate in the development process or the change in the shape of the diffraction grating transferred and formed in the etching process Can understand.

[0007]

However, in the technique of multi-beam interference type exposure, for example, when the optical system has a very small fluctuation, the contrast of the interference pattern as a time average decreases, and the development time or the subsequent time is reduced. Even if the process is optimized, there is a problem that a target pattern shape and a duty cannot be obtained, or manufacturing cannot be performed with good reproducibility. This not only forms lines and spaces periodically at sub-μm pitches, but especially in devices where the duty plays a decisive role in characteristics, a decrease in exposure light contrast is critical in the manufacturing process. Means to be targeted.

Further, the method disclosed in Japanese Patent Application Laid-Open No. 63-136625 can optimize the developing step and the etching step, but cannot optimize the exposure step. In particular, in a method in which the exposure process is important, such as multi-beam interference exposure, the exposure process needs to be optimized.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-beam interference type exposure device which can improve the contrast insufficiency caused by the fluctuation of the optical system and the like peculiar to the multi-beam interference type exposure, and can improve the duty or size of a periodic photoresist pattern. The object of the present invention is to provide a method for precisely controlling the production of a liquid crystal and stably producing it with good reproducibility.

[0010]

According to the present invention, as a means for solving the problems, in a method of forming a mask pattern for forming a pattern periodically arranged on a substrate, a photoresist film is formed on the substrate. Forming a;
Forming a layer having photobleaching property on the photoresist, in particular, a layer called CEL described below, exposing the substrate by splitting and interfering a light beam from a coherent light source; Provided is a method for forming a mask pattern, comprising a step of removing and drying a bleach layer, and a step of developing an exposed photoresist film.

In the step of splitting a light beam from the coherent light source and exposing the substrate, the projection light is made incident on the substrate and the intensity of the diffracted light of the projection light from the substrate is detected, thereby obtaining the diffraction light. Provided is a method of forming a mask pattern for setting an exposure time based on generation of a peak value of light intensity.

A substance having photobleaching property has a feature that it becomes transparent as the amount of irradiation light increases, and when it is formed on a resist, it behaves like a contact mask during exposure and effectively reduces the contrast of exposure light. The cross section of the resist can be sharpened. A photolithography method using such a material having photobleachability is based on CEL (Contr
ast Enhanced Lithography)
is called.

The exposure light of the multi-beam interference type exposure for causing a plurality of light beams to interfere has an essentially sinusoidal intensity distribution unlike a normal VLSI process or the like.
By not only increasing the resolution and drawing a fine pitch, the degree of freedom in setting the duty is greatly improved.

Here, the same effect can be expected to some extent by providing a low-sensitivity resist having relatively high absorbance and photobleaching property on the layer actually serving as a mask instead of the CEL layer. It is difficult to satisfy the accuracy required for the gain-coupled distributed feedback laser using the absorptive diffraction grating as described above.

Hereinafter, referring to the drawings, the case where a low-sensitivity resist is used as a layer having photobleaching property and the CEL
The respective exposure states when the layers are used will be described.
FIGS. 7A and 7B show latent images after exposure when a low-sensitivity resist is laminated on a photoresist layer, and FIG.
(B) shows a latent image after exposure when a CEL layer is laminated on a photoresist layer.

As shown in FIG. 7 (a) and FIG. 8 (a), even when a mask pattern having a low exposure amount and a high duty is formed, a case where a low-sensitivity resist is used as a layer having photobleaching property. There is a difference in the resist profile after development from the case where the CEL layer is used. In the case of a low-sensitivity resist, although the sensitivity is low, the absorbance is not so large, and the contrast of interference fringes is not so high (in the figure, the maximum intensity Imax = 1 and the minimum intensity Imax).
min = 0.3, and (Imax−Imin) / (Im
(ax + Imin) = 54%. )
This is because at the time when the latent image is formed on the lower resist, the low-sensitivity resist is almost already exposed, and the contrast of the exposure light is only slightly improved substantially.

This becomes more remarkable when forming a low-duty mask pattern, that is, when the exposure amount is large. As shown in FIG. 8B, in the CEL layer having an extremely large initial absorbance, the latent resist is hidden in the lower resist. Even when an image is formed, an opaque area still remains, and a substantially rectangular profile is obtained in the lower resist. On the other hand, in the case of a low-sensitivity resist, as shown in FIG. Most of the volume of the resist itself is also exposed, and as a profile after development, only a profile easily affected by scum (residue after development) having an insufficient height can be obtained.

Further, as a result of conducting various experiments using CEL, it was found that CEL itself functions as a diffraction grating. That is, even during exposure, diffracted light from the CEL can be observed. Diffraction light intensity is CE
It changes according to the progress of the bleaching of L, and reaches a peak value at a certain time. By setting the exposure time based on this, it is possible to obtain a desired duty for the photoresist and to precisely control the duty. Therefore, the allowable degree of the variation of the parameter in the subsequent development processing step and the like (hereinafter, referred to as tolerance) is greatly reduced.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) FIG. 1 is a schematic view of an optical system for multi-beam interference type exposure. In this embodiment, exposure is performed by a two-beam interference method using an Ar laser having a wavelength of 3511 °. First, a single-layer resist is formed on a substrate to a thickness of about 500 to 1500 °.

For example, a high-resolution i-line resist P
Spin coat FI38 (manufactured by Sumitomo Chemical) at 90 ° C
Soft baking on a hot plate for 1 minute to a film thickness of 1100 °. A water-soluble i-line CEL having photobleaching properties (ACEM36 manufactured by Shin-Etsu Chemical Co., Ltd.)
5i) is spin-coated to a thickness of 1700 ° to form a substrate 100.

The pinhole is irradiated with exposure light 101 from an Ar laser through a shutter. The light expanded by passing through the pinhole is split into two light beams by the half mirror. By adjusting the mirror of the split light, the two-beam interference patterns on the surface of the base 100 intersect at an angle of a desired pitch Λ.

After exposure by such a method, the substrate 100 is rinsed in running water to remove and dry the ACEM365i, and then subjected to a standard development process (SOI Sumitomo Chemical Co., Ltd.).
PD, 20 ° C, 20 seconds dip), CEL
With a light exposure of about 2 to 3 times that in the case where no is used, a substantially rectangular cross section of the resist was obtained. The exposure amount is a product of a constant exposure light intensity and an exposure time, and here corresponds to a time change of the diffracted light. FIG. 4B shows a sectional view of the resist shape in this case.

Depending on the type of CEL, various types have been developed, such as one that is stripped with pure water rinse before development and one that is stripped with organic cleaning. However, before the underlying resist is actually developed, A step of once removing the entire CEL layer is performed.

Further, by increasing or decreasing the amount of exposure, the duty can be adjusted to 0.1 to 0.1 while maintaining the cross-sectional shape of the resist.
Control was performed over a range of about 0.7, and the in-plane distribution could be suppressed to within an average value ± 0.025.

For comparison, i-line resist PFI 38
Even if exposure is performed using only the above and the processing conditions of the development process are variously changed, the shape of the resist cross section is reduced in the bottom and the duty is controlled with good reproducibility, or a low duty of 0.2 or less is obtained. Was difficult. FIG. 4A is a cross-sectional view of the formed diffraction grating in this case. this is,
It can be interpreted that the interference fringes of the exposure light are smoothed by the vibration of the optical system, the amplitude of the interference fringes is reduced, and at the same time, a uniform bias component is generated on the entire surface, thereby lowering the contrast.

(Example 2) In the case of a combination of a resist having a high resolution and a high γ value and a CEL, although the resist shape is improved and the in-plane distribution can be suppressed, a wide range of duty can be set. The optimal exposure condition is CEL, such as when the resist pattern may not come off due to variations.
Each time the film thickness of the resist or the resist or the optical system is changed, the tolerance is reduced.

On the other hand, when a resist having a relatively low resolution and a low γ value is used, the tolerance is increased, but the resist shape tends to be narrow. It is desired to appropriately select a combination in consideration of matching of characteristics between the CEL and the resist in consideration of desired duty and line width. It is needless to say that a high-resolution resist is more desirable if a stable optical system that always maintains a high contrast of the exposure light can be constructed.

In the case where a resist having a relatively low sensitivity is provided in expectation of the same effect as CEL on the resist upper layer, various parameters may be set at a duty of 0.4 or less, particularly at about 0.2 to 0.3. However, it was not possible to obtain a rectangular profile after resist development even if the experiment was performed while changing the above.

That is, a low-sensitivity, high-gamma-value resist (for example, Sumitomo Chemical Industries P.
FI38) was applied with varying thickness in the range of 500 to 3000 °, and the resist profile was examined by changing the exposure amount and the developing time variously. As a result, when the duty was 0.5 or less, only a skirted mask could be obtained. However, when the duty was larger than 0.5, the degree of tailing decreased. However, even when the duty is 0.5, the in-plane distribution is
It was not less than 0.5 ± 0.1, and the controllability of the mask line width was insufficient. This is because it is originally desirable for the resist to reduce the absorbance as much as possible, and the resist is not designed to be a close contact type mask.

Here, as in Embodiment 1 of the present invention, C
The inventors have found that when EL is used, diffracted light is observed from the substrate before development. That is, the diffraction grating formed by the transparent and opaque portions of the CEL formed during exposure has a sufficient diffraction efficiency. By providing a means for detecting this diffracted light intensity in real time,
The duty of the photoresist after development can be strictly controlled in correspondence with the exposure processing time and the like. Therefore, a reproducible exposure process that does not depend on the resolution of the resist, fluctuations in the CEL film thickness, or the like can be realized.

In the same manner as in the first embodiment, an i-line CEL and ACE having a thickness of 1700 ° are formed on a resist PFI 38 having a thickness of 1100 °.
The substrate 100 on which M365i is formed is exposed.

FIG. 2 shows an optical system used in the present embodiment. The same members as those in the first embodiment are denoted by the same reference numerals. Apart from the light beam 101 that splits the light from the Ar laser into two and causes interference, the light is split by the beam splitter 105 and n
The intensity of the light was appropriately reduced through an neutral density filter (ND filter) 106, and only a part of the periphery of the substrate was irradiated with the projection light 102 having a beam spot of 1 mm. The irradiation of the exposure light 101 and the projection light 102 was started at the same time.

When the projected light 102 has an angle θp
The diffraction light 104 was measured by the photodetector 103 from the direction of the diffraction angle θd determined by sin θd + sin θp = mλ / Λ (where m is a positive integer).

FIG. 3 shows the correlation between the change in the intensity of the diffracted light 104 and the duty according to the amount of exposure. The exposure amount is a product of a constant exposure light intensity and an exposure time, and here corresponds to a time change of the diffracted light. As the exposure progresses, the intensity of the diffracted light 104 increases, passes through a local maximum, decreases smoothly, and disappears.

Further, ACEM365i was added to a plurality of samples of which exposure was completed at each point in FIG.
Rinsing, drying step, and developing step under standard conditions (Developer SOPD manufactured by Sumitomo Chemical Co., Ltd., 20 ° C., dip for 20 seconds) were uniformly applied to measure the duty of the photoresist. Figure 3 shows the average value and the maximum and minimum values for each sample.
And plotted. The in-plane distribution is ±
Within 0.025, about ± 1 in actual resist mask line width
It was able to fit under 00Å.

In the correlation between the duty and the intensity of the diffracted light shown in FIG. 3, the value of the amount of exposure on the horizontal axis slightly shifts due to a change in the optical system. The change did not always change. Therefore, the exposure time is determined during the exposure from the ratio of the diffracted light intensity to the maximum value of the diffracted light intensity for the desired duty, and the shutter is closed through the control device at an appropriate time to terminate the exposure, thereby reducing the duty. It can be manufactured by controlling.

FIG. 3 shows that the intensity peak value of the diffracted light 104 from the CEL during exposure occurs at an exposure amount slightly smaller than the duty ratio of the resist mask formed after development becomes 0.5. . This is the projection light 1
This is because observing the diffracted light 104 by 02 itself accelerates the bleaching of the CEL, resulting in a difference in the exposure amount from the non-projected portion. When light having the same wavelength as the exposure light 101 is projected as in the present embodiment, this offset is inevitable, but by setting the exposure time based on the peak value of the diffracted light 104, the duty can be precisely adjusted. Control is possible.

In this embodiment, the projection light is projected on a part of the substrate. However, even if the intensity of the projection light 102 is further reduced and the entire surface of the substrate to be exposed is uniformly irradiated, the diffraction light can be observed. Needless to say, in this case, unlike the case where the projection light is applied to a part of the substrate 100, the offset hardly occurs, but the correlation between the exposure amount, the duty, and the intensity of the diffracted light is obtained in advance as in FIG. This allows precise control of the duty.

As the light source of the projection light 102, the exposure light 101 itself may be branched and used as in the second embodiment, or separately from the exposure light 101, the wavelength range in which the CEL exhibits bleaching characteristics. Among them, a light source in a wavelength region where the absorbance is not so large may be appropriately selected and projected onto the base 100. In these cases, it is not always necessary to project the projection light 102 at the same time as the start of the irradiation of the exposure light 101, and it may be performed after the exposure has progressed to some extent.

Further, depending on the relationship between the wavelength λ of the exposure light to be used and the pitch 所 望 of the desired diffraction grating, that is, depending on the crossing angle of the branched luminous flux, the secondary diffracted light of the exposure light itself is closer to the substrate surface ( (d is a large angle). At this time, since no projection light is required, diffracted light can be more easily observed.

In this embodiment, the production of the diffraction grating by the two-beam interference type exposure has been described. However, the present invention is not limited to this. For example, the production of a quantum wire, and the two-dimensional method in which a plurality of light beams interfere with each other. The present invention can be applied to all interference photolithography requiring precise control of the duty, such as production of quantum dots using a periodic dot pattern in a plane. At this time, the dimensional accuracy of the mask can be controlled very precisely, and the masks can be arranged at high density and periodically, so that the quantum effect can be further enhanced. Further, it is also possible to form a photonic band by integrating a three-dimensional periodic structure by using the present invention.

As described above, the present invention can be used in the production of an optical element or an optoelectronic element having a high level of function that requires extremely fine pattern processing.

[0043]

According to the present invention, in the production of a photoresist pattern periodically arranged by multi-beam interference type exposure, a multi-beam interference type material is laminated on a resist to form a multi-beam interference type. This has the effect of improving the contrast of the sinusoidal exposure light intensity distribution peculiar to the exposure and improving the controllability of the duty.

Further, the amount of exposure is adjusted while monitoring the intensity of the diffracted light due to the periodic pattern formed by the CEL during the exposure, and the duty or size of the resist mask is controlled more precisely, so that the line width can be adjusted with high precision. It is also possible to control.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical system according to Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram of an optical system according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating the relationship between the intensity of diffracted light and the duty of a photoresist with respect to the amount of exposure.

FIG. 4 is a diagram showing a cross-sectional shape of a resist according to the embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between duty and coupling coefficient κ in the case of a third-order absorbing diffraction grating.

FIG. 6 is a diagram showing the relationship between duty and averaging loss αo in the case of a third-order absorbing diffraction grating.

FIGS. 7A and 7B show a state of a latent image after exposure for forming a mask pattern having a high duty ratio when a low-sensitivity resist is used as a layer having photobleachability; FIGS. It is a figure for explaining a mode of a latent image after exposure for forming a pattern, respectively.

FIG. 8 shows (a) a state of a latent image after exposure for forming a mask pattern having a high duty ratio when a CEL layer is used as a layer having photobleachability; and (b) a mask pattern having a low duty ratio. FIGS. 6A and 6B are diagrams for explaining the state of a latent image after exposure for forming the image.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 substrate 101 exposure light 102 projection light 103 photodetector 104 diffracted light 105 beam splitter 106 filter

Claims (3)

[Claims] In a method of forming a mask pattern for forming a pattern periodically arranged on a substrate, a step of forming a photoresist film on the substrate, and a layer having photobleachability on the photoresist. Forming a mask pattern and exposing the substrate by splitting and interfering a light beam from a coherent light source. 2. A method of exposing the substrate by splitting a light beam from the coherent light source and causing the light beam to interfere with the substrate, by projecting light onto the substrate and detecting a diffracted light intensity of the projection light from the substrate. 2. The method according to claim 1, wherein an exposure time is set based on a peak value of the diffracted light intensity. 3. In the step of exposing the substrate by splitting and interfering a light beam from the coherent light source, an exposure time is determined based on a peak value of the intensity of the diffracted light by detecting the intensity of the diffracted light from the substrate. 2. The method according to claim 1, wherein the setting is performed.