JPS6190185A - Holographic exposure method - Google Patents

Abstract

PURPOSE:To form a minute pattern having varied shapes with one exposure by transmitting a laser light having a certain diameter through a specific medium and irradiating an interference pattern to a medium to be exposed. CONSTITUTION:The diameter of a laser beam 11 generated from a laser light source 10 is expanded by a beam expander 12, and the laser beam is refracted and is made incident on a light-transmissive medium 13. The medium 13 is prismatic, and laser beams 11' and 11'' incident on planes 16 and 17 which are inclined at certain angles theta1 and theta2 to a plane 15 are refracted at angles alpha1 and alpha2. That is, though beams going in directions of arrows 18 and 18' overlap near the lane 15, the interference is caused because the phase difference between two lights is varied in accordance with position/ and a grating image having a certain space cycle is formed near the plane 15, and the interference image of beams is formed on a coating optical medium 14 such as a semiconductor substrate, and the minute pattern is exposed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the field of manufacturing technology for semiconductor devices, optoelectronic devices, etc., and particularly relates to a method for forming fine patterns.

BACKGROUND OF THE INVENTION Conventional configurations and their problems In recent years, along with the remarkable progress of the information society due to the development of electronics and communication technology, more and more advanced semiconductor technology and optical communication technology are required.

Therefore, the development of ultra-LSI is active, and the development of optical 100 systems that integrate semiconductor lasers, guiding waveguides, etc. is still expected.

Under these circumstances, microfabrication technology has become increasingly important, and now machining technology in the submicron region is being established, and mass production is becoming an issue.

In particular, even in semiconductor lasers, there is a technology to form a diffraction grating with a spatial period (0.2 to O.S μm) comparable to the oscillation wavelength in the bulk near the photoactive layer where stimulated emission of light occurs. As an essential step, a diffraction grating is formed using a holographic exposure method.

Therefore, an outline of the conventional holographic exposure method is shown in FIG. 1 is a He-06 laser oscillator, this is it)
The emitted ultraviolet light (approximately 326 degrees) 2 is expanded in beam diameter by a beam expander 3 and then split into beams 5 and 6 by a beam splitter 4. These beams 5 and 6 are configured to be irradiated onto a sample 9 at a constant angle by reflecting mirrors 7 and 8.

However, the conventional holographic exposure method for forming a diffraction grating splits a laser that emits ultraviolet light, such as a He-Cd laser, using a beam splitter 4, and then superimposes the split lights again. Exposure is performed by using an interference image created by the laser beam, which requires a large physical space, a large anti-vibration table, and the optical path and optical axis of invisible ultraviolet laser light. This made it very difficult to set up the device. In addition, sample setting is difficult because the pitch changes in proportion to the cosine of the sample setting angle, and furthermore, when trying to form diffraction gratings with different periods and different directions on the same substrate, it is necessary to expose once. After that, the sample is exposed again by slightly changing the placement angle of the sample, the optical path and optical axis alignment of the laser beam is reset, or the sample is moved to a separately set optical system. mass production was extremely difficult.

OBJECTS OF THE INVENTION The present invention overcomes the drawbacks of the conventional holographic exposure method described above, and allows holographic exposure to be performed with a very simple configuration, and moreover, allows multiple diffraction patterns to be produced on the same substrate in -times of exposure. It enables the formation of a lattice61,
The present invention also makes it possible to easily form a submicron pattern with a relatively large period of several μm in a single exposure.

t7/7 Formation of the Invention The present invention has an extremely simple configuration in which a laser beam having a constant beam diameter is passed through a specific medium and an interference pattern is irradiated onto the medium to be exposed.

DESCRIPTION OF EMBODIMENTS FIG. 2 schematically shows the configuration of the holographic ink exposure method of the present invention. Reference numeral 10 denotes an ultraviolet laser light source such as Ha-Cd, and the generated laser beam 11 is expanded in beam diameter by a beam expander 12, refracted, and incident on a light-transmitting medium 13. . Reference numeral 14 denotes a medium to be exposed such as a semiconductor substrate, and the medium 13 is placed on the surface of the substrate.
This is the principle that an interference image of the light generated by this process is formed, and a fine pattern is exposed. It can be seen that the structure is simpler than the conventional holographic exposure method shown in FIG.

Embodiment 1 The medium 13 in FIG. 2 is a prism-shaped medium as shown in FIG.
5, constant angular variation θ, and θ2 (however, 0 and θ1.
a second plane 16 and a third plane 1 having θ2<90°)
An example will be shown in which a medium having a beam angle 7 is used and the beam is incident on the medium from a direction perpendicular to the plane 16.

For example, a laser beam 11' incident on a plane 16 is refracted in a direction 18 at an angle α with respect to a direction perpendicular to the plane 16. However, α and θ have the following relationship.

sin θ = n sin α1 Here n is the refractive index of the medium.

Similarly, the light ray 11' incident on the plane 17 is refracted in the direction 18' of α2, which satisfies the relationship sin 02=n sin α2 with respect to the direction perpendicular to the plane 17.

The light beams traveling to 18 and 18' are once again on the plane 1.
Although the two light beams overlap in the vicinity of the plane 16, since the phase difference between the two light beams differs depending on the location, interference occurs, and a grating image having a constant spatial period W is formed in the vicinity of the plane 16. FIG. 4 shows an example of the spatial distribution of light intensity. The spatial period is, for example, the distance from the point where the light intensity reaches its maximum to the next maximum point.

As an example, FIG. 5 shows the relationship between θ and the spatial period W when θ=θ, =02. In Figure 5,
The parameter is the refractive index of the medium, n = 1.2
, 1.4, 1.6, 1.8, and 2.0.

The horizontal axis is θ(0), and the vertical axis is the wavelength λ of the laser beam.
It shows the ratio of the spatial period to (W/λ). From FIG. 6, it can be seen that as θ becomes larger, the spatial period of the lattice pattern becomes shorter, and even for the same θ, the larger the refractive index of the medium, the shorter the spatial period becomes.

Therefore, as the laser beams 11' and 11', Hθ-c
d using a laser wavelength of 3250 and using quartz glass (n ~ 1.48) as the medium 13.

If set to θ near 4.0', W=0.1993μ7
A 7L diffraction grating can be obtained, and if θ=44.0', a W=0.3985 μm diffraction grating can be obtained.

The upper diffraction grating is marked by the medium 14.For example, the distribution of the nGaAs P/In) system formed on a semiconductor substrate I@
They serve as the primary and secondary gratings of the distant semiconductor laser (DFB-LD), respectively.

On the other hand, if an acrylic plastic material (n~1.58), which is easy to process and form, is used as the medium 13, θ to obtain the above diffraction grating is 66:6° and 37°, respectively.
．． It becomes 7°.

Next, FIG. 6 shows the relationship between the angle of incidence of the laser beam on the medium and the pitch of the diffraction grating. The refractive index of the medium is assumed to be 1.60. According to this result, it can be seen that even if the incident angle of the laser beam is tilted by 20 to 30', the period of the diffraction grating hardly changes. This means that when performing mass production, alignment accuracy during exposure is not strictly required, and it shows that the present invention is very suitable for mass production.

In the above example, the case where θ1=02 was described.

Also in the case of θ1 and θ2, a constant pitch is determined under each condition, and this pitch hardly changes even with a slight deviation of one angle in the laser beam illumination η.

Embodiment 2 FIG. 7 shows an embodiment in which the shape of the medium 13 in FIG. 2 has a plurality of pairs of planes.

In this example, the plane is 19.19', 20°20'
The incident light interferes with each other on and near the plane 15, forming a more complicated pattern than in the first embodiment.

In FIG. 8, - as an example, θ1=θ2:=so'.

The intensity distribution of light on the plane 16 in the case of θ,=04=30′ is shown. By selecting exposure conditions, it is possible to form a diffraction grating with a spatially varying pitch.

Also, in Fig. 9, θ1=02=60', θ5=θ4=2
The light intensity distribution of the interference image in the case of 4.1° is shown. In this case, a diffraction grating formed with θ=600 and a diffraction grating formed with θ==24.
The pitch of the diffraction grating formed at 1° is 1:3, and due to their interference, the pitch is three times that of the case where θ = 02 = 60°, but the line width is almost the same. It can be seen that a diffraction grating image can be obtained. Similarly, by changing the pitch ratio of the diffraction grating, patterns with similar line widths and larger pitches can be obtained. This is also extremely useful when forming submicron gates in semiconductor integrated circuits and the like.

However, when trying to form a pattern with a large pitch and narrow line width using only two pairs of planes, there is a region that is exposed to some extent between the thin lines that should be exposed to J, so exposure and development Conditions become more restrictive. FIG. 10 shows an example where the pitch of the interference patterns in two pairs of planes is 1:6.

Therefore, in order to prevent this, it is necessary to provide a new pair of planes and use a medium as shown in FIG.
The above problem can be solved by designing the period of the diffraction grating formed by -21', 22-22', and 23-23' to be an integer ratio. Figure 12 shows θ1
=θ, '=60', θ2=θ2'=24°.

It shows the intensity distribution of the diffraction image on the plane 16 when o,=o3r=6.2°.

In the case of FIGS. 7 and 11, there is a disadvantage that the area where the desired diffraction pattern is formed becomes small, but this can be easily solved by forming the medium as shown in FIGS. 13 and 14. It is something that can be solved. Furthermore, by using a medium as shown in FIG.
5-25'.

By setting the diffraction gratings 26-26' to be formed in different regions of the plane 15,
A plurality of diffraction gratings with different periods or directions can be formed on the same substrate by one exposure.

Although the shapes of these media are complex, they can be easily realized at low cost by using acrylic or polycarbonate plastics.

Next, an example will be described in which the first medium 13 has a plurality of curved surfaces.

Embodiment 3 FIG. 16 shows the planes 27 and 27 at an acute angle
An example is shown in which curved surfaces ' are present opposite each other and the angle thereof continuously changes (increases) in 28 directions. In this case, the pitch of the diffraction pattern formed on the plane 15 changes (decreases) in the direction of 28, as shown in FIG.

Embodiment 4 FIG. 18 shows an example in which a pair of curved surfaces is provided in addition to Embodiment 3. Based on the same principle as in Example 3,
Thin lines with varying intervals as shown in FIG. 19 are formed.

If such an exposure method using the medium 13 is used, a pattern of thin lines that gradually spread from a fixed interval can be easily formed, and a modulation element such as a directional coupler can be easily formed in an optical integrated circuit. .

Example 6 In Examples 1 to 5, the case of a plurality of planes or curved surfaces was shown, but it does not necessarily have to be a plurality of planes or curved surfaces, and exactly the same effect can be obtained when both a plane and a curved surface are mounted. The matter is self-evident. Furthermore, there is nothing wrong with a shape having a curved surface that partially includes a curved surface and a flat portion. Furthermore, when a conical wedge as shown in FIG. 20 is used as the first medium, a concentric interference pattern is formed, making it easy to form a Fresnel lens or the like in an optical integrated circuit.

Effects of the Invention As explained in the examples above, the present invention can realize fine patterns with extremely diverse shapes in a single exposure, and can be said to be a method that is excellent in mass production. .

The present invention is an extremely useful method for manufacturing VLSIs, high-performance and multifunctional semiconductor lasers, and practical applications such as optical integrated circuits.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the conventional holographic exposure method, Figure 2
The figure is a schematic diagram of the configuration of the holographic exposure method of the present invention,
Fig. 3 is a cross-sectional view of the prism-shaped medium and the exposed medium used in the holographic exposure of the present invention, and Fig. 4 shows the light intensity of the light pattern formed on the exposed surface when the medium of Fig. 3 is used. Figure 5 is a diagram showing the distribution of θ (=θ,
= θ2) and the pitch of the holographic pattern formed. Figure 6 shows the relationship between the angle of incidence of the laser beam and the diffraction when the medium of Figure 3 is used and the angle of incidence of the laser beam on the medium is tilted. FIG. 7 is a diagram showing the relationship between the pitches of the gratings, and FIG. 7 is a diagram showing an embodiment in which the shape of the medium 13 in FIG. 2 has two pairs of planes. FIG. 8 shows the embodiment of FIG. 7, with θ1=02=60°. A diagram showing the light intensity distribution of the interference pattern formed on the plane 15 in the case of θ3-04-300, FIG. 9 is the embodiment of FIG. 7, θ1-02=60', θ, -04=24.1 10 is a diagram showing the light intensity distribution of the interference image when the pitch is 1:5 in the example of FIG. 11 is a diagram showing an example in which the shape of the medium 13 in FIG. 2 has three pairs of planes, and FIG. 12 is a diagram showing the distribution of θ
1=θ,'=80'. 13th diagram showing the intensity distribution of the diffraction image on the plane 15 when θ2=02′=24°, θ,=θ,′=8.2°
Figures (&) and Φ) are a perspective view, a cross-sectional view, and a 14th
Figures (&) and Φ) are a perspective view and a cross-sectional view of a medium of another embodiment having the same effect as the embodiment in Figure 10, and Figure 15 shows a plurality of exposures on the same substrate with one exposure. Figure 16 shows an example of a medium that realizes a diffraction grating with a continuously changing pitch. Figure 17 shows an example of a medium that realizes a diffraction grating with a continuously changing pitch. FIG. 18 is an explanatory diagram of an example of a medium having two pairs of curved surfaces. FIG. 19 is an illustration of an example of a holographic pattern formed when using FIG. 18. 2CI
31 is a diagram showing a conical medium and a holographic pattern generated thereby. 1o... Laser light source, 14... Exposure medium, 13... First medium, 1B, 16, 17
,19°19/ ,20.20',22.22'
, 23.23'. 24.24', 25.26', 26.26'
...Flat surface, 27.27'...Curved surface. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Fig. 3 Fig. 4 Dtatctnce (X/λ) Fig. 5 8NOL E (+) EGI Fig. 6 ANeLE CDE (r) Dzwtty, nce (X/in) Fig. 13 Fig. 15 fΦ Fig. 17 Fig. 18 Cause Fig. 19

Claims (10)

[Claims] (1) A laser beam is irradiated through a light-transmissive first medium having at least one plane from the side opposite to the first plane of the first medium, and the laser beam is irradiated close to the first plane of the first medium. A holographic exposure method, characterized in that the surface of the second medium is exposed using an interference pattern of the laser beam formed on the second surface of the second medium, which is disposed in the same direction. (2) The first medium has a plurality of planes on the laser beam incident side that make an acute angle with respect to the first plane of the first medium that is arranged in close contact with or near the second medium; A laser beam incident on the plane of the plurality of planes is simultaneously irradiated and passes through the first medium, and a specific pattern is formed on a part or the entire surface of the second plane of the second medium. 2. The holographic exposure method according to claim 1, wherein the exposure is performed using a holographic exposure method. (3) The plurality of planes are composed of third and fourth planes, and an interference pattern is formed on the second plane by a laser beam irradiated on the first medium including a part or all of the third and fourth planes. The holographic exposure method according to claim 2, wherein a diffraction grating is formed by utilizing the holographic exposure method. (4) In addition to the third and fourth planes, the plurality of planes are the fifth plane,
It is composed of a plurality of pairs of planes such as a sixth plane, and the exposure is performed using an interference pattern formed on the second plane by a laser beam including the plurality of pairs of planes. The holographic exposure method according to item 2. (5) The plurality of planes are composed of a plurality of pairs of planes, and each spatial period of the plurality of spatially periodic light intensity patterns formed on the second plane by the refraction and interference effects of light on each of the plurality of pairs of planes is an integer number. Claim 2 characterized in that it is a ratio
The holographic exposure method described in section. (6) The first medium has a plurality of curved surfaces forming an acute angle with respect to the first plane on the incident side, and the laser beam incident on the plurality of curved surfaces is simultaneously irradiated to each curved surface, and the second medium is exposed to the second plane. 2. The holographic exposure method according to claim 1, wherein exposure is performed using an interference pattern formed thereon. (7) The plurality of curved surfaces are composed of a first curved surface and a second curved surface, and the angles formed by these curved surfaces with respect to the first curved surface continuously change in a fixed direction. A holographic exposure method according to claim 6. (8) A plurality of curved surfaces constitute each curved surface pair, and the spatial period of the spatially periodic intensity distribution formed by irradiating the plurality of curved surfaces with a laser beam has an integer ratio. A holographic exposure method according to claim 6, characterized in: (9) Holographic exposure according to claim 1, wherein the shape of the first medium is a shape having a curved surface that forms an acute angle with respect to the first plane and surrounds the first plane. Method. (10) The holographic exposure method according to claim 1, wherein the first medium is made of plastic.