JP2629671B2 - Holographic exposure method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a fine pattern, particularly in the field of manufacturing a semiconductor device or an optoelectronic device.

Configuration of Conventional Example and Problems Thereof With recent remarkable progress of the information society accompanying the development of electronics and communication technology, more advanced semiconductor technology and optical communication technology are required.

Therefore, the development of super LSIs is also active, and the development of optical ICs integrating a semiconductor laser, an optical waveguide, and the like is also expected.

Under these circumstances, the importance of microfabrication technology has become more and more important. At present, processing technology in the submicron region is being established, and its mass productivity has become a problem.

Especially in semiconductor lasers, it is indispensable to form a diffraction grating near the photoactive layer where stimulated emission of light occurs, having a spatial period (0.2 to 0.5 μm) similar to the oscillation wavelength in the bulk. A diffraction grating is formed using a holographic exposure method.

FIG. 1 schematically shows a conventional holographic exposure method. Reference numeral 1 denotes a He-Cd laser oscillator. Ultraviolet light (about 3250 °) emitted from the beam oscillator 2 is expanded in beam diameter by a beam expander 3 and then beam splitter 4
Divided into 5,6. The beams 5 and 6 are configured to irradiate a sample 9 at a fixed angle by reflecting mirrors 7 and 8.

However, in the conventional holographic exposure method for forming a diffraction grating, a laser that emits ultraviolet light such as a He-Cd laser is split by a beam splitter 4, and the split light is superimposed again and formed there. Exposure is performed by using an interference image, which requires a large physical space as well as a large anti-vibration table, and also adjusts the optical path and optical axis of invisible ultraviolet laser light. This had to be done and setting up the device was very difficult. In addition, it is difficult to set the sample because the pitch changes in proportion to the cosine with respect to the set angle of the sample.Furthermore, when trying to form diffraction gratings with different periods and different directions on the same substrate, it is necessary to perform exposure once After that, a step of slightly changing the arrangement angle of the sample again and exposing again, resetting the optical path and optical axis alignment of the laser beam, or transferring the sample to another optical system set separately Has to be repeated, and mass production has been extremely difficult.

The object of the present invention is to overcome the above-mentioned drawbacks of the conventional holographic exposure method, to perform holographic exposure with a very simple structure, and to perform a plurality of diffraction gratings on the same substrate in one exposure. The present invention also makes it possible to easily form a submicron pattern with a relatively large period of several μm by a single exposure. .

Configuration of the Invention The present invention is an extremely simple configuration in which a laser beam having a constant beam diameter is irradiated onto a medium to be exposed through a specific medium to an interference pattern.

2. Description of the Embodiment FIG. 2 schematically shows the configuration of the holographic exposure method of the present invention. 10 is an ultraviolet laser light source such as He-Cd,
The generated laser beam 11 is expanded in beam diameter by a beam expander 12, refracts the laser beam, and is incident on a medium 13 having optical transparency. Reference numeral 14 denotes a medium to be exposed such as a semiconductor substrate, The principle is that an interference image of the light generated by the medium 13 is formed and the exposure of the fine pattern is performed. It can be seen that the configuration is simpler than the conventional holographic exposure method shown in FIG.

First Embodiment A medium 13 shown in FIG. 2 is a prism-shaped medium as shown in FIG. 3, that is, a first plane 15 which is close to or close to a medium 14 to be exposed.
At constant angles θ ₁ and θ ₂ (where 0 <θ ₁ , θ ₂
An example is shown in which a medium having a second plane 16 having a <90 °), 16 and a third plane 17 is used and the beam is incident on the medium from a direction perpendicular to the plane 15.

For example, the laser beam 11 'incident on the plane 16 is
It is refracted in a direction 18 at an angle α ₁ with respect to the 16 vertical directions.
However, α and θ have the following relationship.

sin θ ₁ = n sin α ₁ where n is the refractive index of the medium.

Similarly beam 11 which is incident on the plane 17 ".18 and is refracted into sinθ _{2 =} n sinα α ₂ in a direction 18 that satisfies the relation of ₂ 'relative to the vertical plane 17
The light traveling to 18 'overlaps again in the vicinity of the plane 15 again, but because the phase difference between the two rays differs depending on the place, interference occurs, and the light has a constant spatial period W in the vicinity of the plane 15. A lattice image is formed. FIG. 4 shows an example of the spatial distribution of light intensity. The spatial period is, for example, from the point at which the light intensity reaches a maximum to the next maximum point.

As an example, FIG. 5 shows the relationship between θ and the spatial period W when θ = θ ₁ = θ ₂ . In FIG.
The parameter is the refractive index of the medium, n = 1.2,1.4,1.6,
1.7, 1.8, and 2.0 have been changed.

The horizontal axis is θ (゜), and the vertical axis is the wavelength λ of the laser beam.
The ratio (W / λ) of the spatial period with respect to is shown. It can be seen from FIG. 5 that the spatial period of the lattice pattern becomes shorter as θ becomes larger, and that the spatial period becomes shorter as the refractive index of the medium becomes larger for the same θ.

Therefore, if a wave of 3250 ° of a He—Cd laser is used as the laser beams 11 ′ and 11 ″ and quartz glass (n to 1.48) is used as the medium 13, W = 74.0 ° and W =
A diffraction grating of 0.993 μm is obtained, and a diffraction grating of W = 0.3985 μm is obtained by setting θ = 44.0 °. The upper diffraction grating is formed on a medium 14, for example a semiconductor substrate
The InGaAsP / InP distributed feedback semiconductor laser (DFB-LD) functions as a primary and secondary grating, respectively.

On the other hand, when an acrylic plastic material (n to 1.58) which is easy to process and form is used as the medium 13, θ for obtaining the above diffraction grating is 66.6 ° and 37.7 °, respectively.

Next, FIG. 6 shows the relationship between the angle of inclination of the laser beam when it is incident 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, even if the incident angle of the laser beam is inclined by 20 to 30 °, the period of the diffraction grating hardly changes. This means that alignment precision at the time of exposure is not strictly required in mass production, and this indicates that the present invention is very suitable for mass production.

In the above example, the case where θ ₁ = θ ₂ has been described, but θ ₁ ≠ θ
Also in the case of ₂ , a constant pitch is determined under each condition, and this pitch hardly changes even with a slight deviation of the irradiation angle of the laser beam.

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 the present embodiment, light incident on the planes 19, 19 ', 20, and 20' interferes on and near the plane 15 to form a more complicated pattern than in the first embodiment.

FIG. 8 shows, as an example, θ ₁ = θ ₂ = 60 °, θ ₃ = θ ₄
5 shows the light intensity distribution on the plane 15 when = 30 °. By selecting the exposure conditions, it is possible to form a diffraction grating having a spatially changed pitch.

FIG. 9 shows that θ ₁ = θ ₂ = 60 ° and θ ₃ = θ ₄ = 2
The light intensity distribution of the interference image in the case of 4.1 ゜ is shown. in this case,
The pitch of the diffraction grating formed at θ = 60 ° and the pitch of the diffraction grating formed at θ = 24.1 ° are 1: 3, and due to their interference, the pitch of θ ₁ = θ ₂ = 60 ° It can be seen that a diffraction grating image having a pitch three times and a line width almost the same can be obtained. Similarly, by changing the pitch ratio of the diffraction grating, a pattern having a similar line width and a large pitch can be obtained. This is extremely useful also when forming a submicron gate in a semiconductor integrated circuit or the like.

However, when a pattern with a large pitch and a small line width is to be formed only by two pairs of planes, there is a region to be exposed to some extent in the middle of a fine line to be exposed, so that the exposure and development conditions are limited. The restrictions become stricter. FIG. 10 shows an example in which the pitch of the interference pattern in the two pairs of planes is 1: 5. Therefore, in order to prevent this, a new pair of planes is provided, and for example, the diffraction formed by each pair of planes 21-21 ', 22-22', 23-23 'using a medium as shown in FIG. The above problem can be solved by designing the period of the lattice to be an integer ratio. FIG. 12 shows θ ₁ = θ ₁ ′ = 60
It shows the intensity distribution of the diffraction image on the plane 15 when ゜, θ ₂ = θ ₂ ′ = 24 ° and θ ₃ = θ ₃ ′ = 8.2 °.

In the case of FIGS. 7 and 11, there is a disadvantage that the area where the desired diffraction pattern is formed is small.
This can be easily solved by forming a medium as shown in FIGS. 13 and 14. Further, by using a medium as shown in FIG. 15, a plane pair 24-24 ', 25-25', 26-2
By setting the diffraction gratings formed at 6 'to be formed in different regions of the plane 15, a plurality of diffraction gratings having different periods or directions can be formed on the same substrate by one exposure. Although the shape of these media is complicated, they can be easily and inexpensively realized by using acrylic or polycarbonate plastic.

Next, an embodiment in the case where the shape of the first medium 13 has a plurality of curved surfaces will be described.

Embodiment 3 FIG. 16 shows a case where curved surfaces 27 and 27 'are present at an acute angle with respect to the plane 15 and the angle continuously changes (increases) in the direction of 28. An example is shown. 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 further provided in Embodiment 3. According to the same principle as in the third embodiment,
As shown in FIG. 19, a thin line whose interval changes is formed.

By using such an exposure method using the medium 13, a fine line pattern gradually spreading from a certain interval can be easily formed, and a modulation element such as a directional coupler can be easily formed in the optical integrated circuit. .

Fifth Embodiment In the first to fifth embodiments, the case of a plurality of planes or curved surfaces has been described. However, it is not always necessary to have a plurality of planes or curved surfaces, and the same effect can be obtained when both a plane and a curved surface are included. Is self-evident. Further, there is no problem even if the shape has one curved surface in which the curved surface and the flat portion are partially included. When a conical medium as shown in Part 20 is used as the first medium, a concentric interference pattern is formed, and it becomes easy to form a Fresnel lens or the like on the optical integrated circuit.

Effects of the Invention As described in the above embodiments, the present invention can realize a fine pattern of extremely various shapes in one exposure, and can be said to be a method excellent in mass productivity. .

The present invention is a very useful method for manufacturing an VLSI, a high-performance and multifunctional semiconductor laser, or a practical application such as an optical integrated circuit.

[Brief description of the drawings]

FIG. 1 is a schematic view of a conventional holographic exposure method, and FIG.
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 a prism-shaped medium and a medium to be exposed used in the holographic exposure of the present invention. FIG. 4 is a diagram showing the light intensity of a light pattern formed on an exposed surface when the medium of FIG. FIG. 5 shows the distribution, and FIG. 5 shows θ (= θ _{1) in} FIG.
= Θ ₂ ) and the pitch of the holographic pattern to be formed. FIG. 6 shows the inclination angle and the inclination angle of the laser beam incident on the medium when the medium of FIG. 3 is used. FIG. 7 is a diagram showing a relationship between pitches of a diffraction grating, and FIG.
FIG. 8 shows an embodiment in which the shape of the medium 13 in FIG. 2 has two pairs of planes, and FIG. 8 shows the embodiment of FIG.
FIG. 9 shows the light intensity distribution of the interference pattern formed on the plane 15 when ₁ = θ ₂ = 60 ° and θ ₃ = θ ₄ = 30 °. FIG. 9 shows the embodiment of FIG. 7, where θ ₁ = θ. ₂ = 60 degrees, θ ₃ = θ ₄ = 24.1
FIG. 10 shows the light intensity distribution of the interference image in the case of ゜, and FIG.
FIG. 11 is a diagram showing a light intensity distribution of an interference image when the pitch ratio of the interference patterns in the two pairs of planes is 1.5 in the embodiment of FIG. 11; It illustrates an embodiment in which a flat, FIG. 12 at a Figure 11, theta _{1 =} theta
₁ ′ = 60 °, θ ₂ = θ ₂ ′ = 24 °, θ ₃ = θ ₃ ′ = 8.2
The figure showing the intensity distribution of the diffraction image on the plane 15 in the case of ゜,
13 (a) and 13 (b) are a perspective view, a sectional view, and a perspective view of a medium showing an example of another embodiment having the same effect as the embodiment of FIG.
14 (a) and 14 (b) are perspective views and sectional views of an example of a medium having another embodiment having the same effect as that of FIG. 10, and FIG. 15 shows a single exposure on the same substrate. FIG. 16 is a diagram showing an example of an embodiment of a medium for realizing a plurality of diffraction gratings, FIG. 16 is a diagram showing an example of a medium for realizing a diffraction grating whose pitch changes continuously, and FIG. Illustration of a continuously changing diffraction grating, FIG. 18 is an illustration of an example of a medium having two pairs of curved surfaces, and FIG. 19 is an illustration of an example of a holographic pattern formed by using FIG. FIG. 20 shows a conical medium and the resulting holographic pattern. 10 laser light source 14 exposure medium 13 first medium 15,16,17,19,19 ', 20,20', 22,22 ', 23,23', 24,2
4 ', 25,25', 26,26 '... plane, 27,27' ... curved surface.

Claims (8)

(57) [Claims] 1. A light-transmitting first medium having at least one plane and a plurality of planes or curved surfaces provided on opposite sides of the first plane transmits one light beam from the plurality of planes or curved surfaces. Irradiating a laser beam, and utilizing the interference pattern of the laser beam formed on a second plane of a second medium placed close to a first plane of the first medium, The surface of the medium is exposed, and an acute angle is formed on the incident side of the first medium laser beam with respect to the first plane of the first medium which is disposed in close contact with or near the second medium. It has a plurality of planes, and a laser beam incident on the plurality of planes is simultaneously irradiated on each of the plurality of planes, passes through the first medium, and is on the second plane of the second medium. Utilize a specific pattern formed on part or all of A holographic exposure method, comprising: 2. The method according to claim 1, wherein the plurality of planes comprises third and fourth planes,
The diffraction grating is formed by utilizing an interference pattern formed on a second plane by a laser beam irradiated on a first medium including a part or all of the third and fourth planes. 2. The holographic exposure method according to claim 1. 3. An interference pattern formed on a second plane by a laser beam irradiating a plurality of planes including a fifth, a sixth, etc. pairs of planes in addition to the third and fourth planes. 2. The holographic exposure method according to claim 1, wherein the holographic exposure is carried out by utilizing the following. 4. A plurality of spaces of a plurality of spatially periodic light intensity patterns formed on a second plane by a refraction and interference effect of light on each of the plurality of planes. 2. The holographic exposure method according to claim 1, wherein the period has an integer ratio. 5. A light-transmitting first medium having at least one plane and a plurality of planes or curved surfaces provided on opposite sides of the first plane. Irradiating a laser beam, and utilizing the interference pattern of the laser beam formed on a second surface of a second medium placed in proximity to a first plane of the first medium, Exposure of the medium surface is performed. On the incident side of the first medium, a plurality of curved surfaces forming an acute angle with respect to the first plane are provided, and the laser beam incident on the plurality of curved surfaces is A holographic exposure method, wherein the exposure is performed using an interference pattern that is simultaneously irradiated on a curved surface and formed on the second plane. 6. The method according to claim 1, wherein the plurality of planes are formed of a plurality of finer curved surfaces, and an angle formed by the fine curved surfaces changes continuously in a fixed direction. 6. The holographic exposure method according to claim 5. 7. A plurality of curved surfaces constitute each curved surface pair, and a spatial periodic distribution formed by irradiating the plurality of curved surfaces with a laser beam has an integer ratio. A holographic exposure method according to claim 5. 8. A light-transmitting first medium having at least one plane and a plurality of planes or curved surfaces provided opposite to the first plane. Irradiating a laser beam, and utilizing the interference pattern of the laser beam formed on a second surface of a second medium placed in proximity to a first plane of the first medium, Holographically exposing a medium surface, wherein the shape of the first medium is a shape that forms an acute angle with respect to the first plane and has a curved surface surrounding the first plane. Exposure method.