JPS58179805A - Exposure device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exposure apparatus that uses a photomask to fabricate a local diffraction grating using a two-beam interference method.

2. Description of the Related Art Optical integrated circuits, in which optical functional elements such as laser light sources, modulators, detectors, and demultiplexing elements, and waveguides are integrated on a semiconductor substrate, are eagerly awaited as devices for optical communication.

Among optical functional devices, diffraction gratings are used in demultiplexing and multiplexing devices, distributed feedback lasers, and the like. In this case, a technique is required that can freely produce a diffraction grating in a limited area on a semiconductor substrate.

Currently, photolithography technology is used as a means for forming functional elements.

Of course, diffraction gratings can also be fabricated using the same technology.

However, when producing a grating on a photoresist, the usual method Ct of stacking a photomask having the cross-sections to be formed on a substrate and exposing it to light cannot be used. This is because a fine lattice pattern cannot be formed on the photomask itself.

Therefore, unlike other methods, two-beam interferometry, which does not use a mask, is used to fabricate a diffraction grating.

FIG. 9 is a configuration diagram of an exposure apparatus for producing a diffraction grating using a conventional two-beam interference method.

The light emitted from the laser 41 is split into two beams by a beam splitter 42. Each luminous flux passes through collimator 4
3. ．． 44, the beam is converted into a parallel light beam with a large beam diameter. The expanded light beam is reflected by mirrors 45 and 46, and is applied to a semiconductor substrate 48 coated with a photoresist 47.
irradiate the surface of

Coherent light from the laser is split into two beams and enters the surface of the photoresist 47 at a certain angle to expose it. It receives exposure energy that varies sinusoidally in the intersecting direction. If this is developed appropriately, the photoresist will remain in the uneven stripes, resulting in a diffraction grating. It can be adjusted arbitrarily by changing the circumferential angle of the grating.

According to this method, an interference pattern of 1 μm or less can be exposed. In the projection exposure method using a photomask as described above, a photomask with a diffraction grating pattern with a submicron period cannot be created, so a grating pattern of 1 μm or less cannot be created, but the two-beam interferometry method does not have such limitations.

However, in the conventional two-beam interferometry method, large-diameter beams are interfered with each other, so although it is possible to create a uniform diffraction grating over a wide area, it is possible to create a diffraction grating of a desired size in a limited area. cannot be formed. With this, it is impossible to create an optical integrated circuit that includes a diffraction grating as a part.

The above methods used light.

A third method is an electron beam exposure method. This method creates a diffraction grating using an electron beam, and since the locus of the electron beam can be specified with an accuracy of 1 μm, submicron diffraction gratings can be manufactured. However, this requires a large and expensive device.

The present invention provides an exposure apparatus that is capable of producing a diffraction grating with an arbitrary grating period at a narrowly defined arbitrary position using the two-beam interference method.

Hereinafter, the configuration, operation, and effects of the present invention will be explained with reference to drawings showing examples.

FIG. 1 is a plan view of an exposure apparatus according to an embodiment of the present invention.

A laser 1 emits coherent light, which is reflected by a mirror 2 and enters a beam splitter 3 (luminous flux a).

As the laser, for example, a He-Cd laser (wavelength λ=4416 A) can be used.

The beam splitter 3 separates the beam into two beams.

C and are guided to collimator 4 and collimator 5, respectively.

The collimator 4 includes a convex lens 6, a light shielding plate 8 having a pinhole 7, and a convex lens 9.

This turns the parallel, small-diameter b light beam into a parallel, large-diameter d light beam.

The collimator 5 includes a convex lens 10, a light shielding plate 12 having a pinhole 11, and a convex lens 13.

This converts a C light beam that is parallel and has a small diameter into a C light beam that is parallel and has a large diameter.

The d light flux is reflected by the mirror 14 and becomes the f light flux. mirror 1
The angle 4 can be adjusted as desired by operating the rotary table 15.

The C light flux is reflected by the mirror 16 and becomes the G light flux.

The angle of the mirror 16 can be adjusted as desired by a rotating table 17.

The f beam further passes through a narrow aperture 19 in the intermediate mask 18 (h beam). The h light flux further passes through the lens 20, is converged (i light flux), and enters the object. The object is
A photoresist 22 is applied onto a semiconductor substrate 21, and a photomask 23 is placed on top of this in close contact. The photomask 23 is used to irradiate only a portion of the g and i beams onto a desired limited area.

That is, the lens 20 is arranged so that the image of the aperture 19 is formed on the photomask 23, and the photomask 2
Apply photomask 2 so that this image is formed on the light-transmitting part of 3.
3. Adjust the positions of the photoresist 22 and the substrate 21.

FIG. 2 is a front view of the intermediate mask 18. In this example, the size of the opening at the center of the intermediate mask is a 50 μm square.

FIG. 3 is a front view of the photomask 23.

In the photomask 23, the shaded portion 24 does not allow light to pass through. A wide area without diagonal lines, that is, a transparent area 25
The central transparent portion 26 is a transparent body that allows light to pass through.

This photomask is used when the photoresist 22 is positive type. Since it is a positive photoresist, areas that do not receive light remain after development and are exposed.

The photoresist in place is removed by development.

FIG. 4 is a front view showing another photomask 23'.

Unlike the example of FIG. 3, this is used when the photoresist is negative type.

Most of the photomask 23' is a light shielding part 24', and there is a transparent part 25' in the center parallel to the sides, and a central transparent part 26' is provided in the middle of this.

A perspective view of the substrate after development is shown.

A case will be described in which the photomask shown in FIG. 3 is brought into close contact with a positive photoresist, and the photoresist is exposed to light using this apparatus.

In FIG. 1, the g luminous flux
The entire surface of the photomask 23 placed on the photomask 23 is irradiated.

The i light beam is a limited light beam having the same area as the aperture 19, but it is incident only on the central transparent portion 26 of the photomask 23.

The light blocking section 24 blocks all light. Therefore, the photoresist under the light-shielding portion 24 is not exposed to light and, when developed, becomes a raised strip remaining on the substrate 21 as the waveguide 28 in FIG.

The entire light flux g enters the photoresist directly under the wide transparent portion 25 on the side and the entire portion is exposed, so when it is developed, the photoresist is washed away and the substrate 2 is exposed as shown in FIG.
The number is changed so that 1 is exposed.

The entire luminous flux g and the limited luminous flux i enter the central transparent portion 26 at a certain angle. Therefore, a region in which the exposure energy spatially varies in a sinusoidal manner is created, and if this region is developed, it will become the diffraction grating 27 shown in FIG. 5.

In this way, a diffraction grating 27 having waveguides 28 on both sides can be formed on the semiconductor substrate 21. The size and position of the diffraction grating can be arbitrarily given by the photomask 23 and the intermediate mask 18.

The same thing can be done with a negative photoresist using the photomask shown in FIG.

The photoresist directly under the light shielding portion 24' of the photomask 23' is not irradiated with light. □Since it is a negative type, this part will be removed when it is developed.

The intermediate horizontal transparent part 25' is exposed by the total luminous flux g. The central transparent portion 26' is exposed to two light beams: the entire light beam g and the limited light beam i.

Therefore, the photoresist directly under the transparent portion 25' remains and becomes the waveguide 28. The photoresist directly under the central transparent portion 26' becomes the diffraction grating 27. The waveguide 28 is preferably a single mode waveguide, and has a width of 4 μm, for example.

Figure 6 is a front perspective view of the mask board mounting jig;
The figure is a rear perspective view.

A presser plate 31 is attached to the four sides of the front side of the ring-shaped holder 30 with set screws 32. Photomask 23
The four corners of the holder 30 are pressed against the surface of the holder 30 using the presser plate 31, and the setscrews 32 are tightened to fix the holder.

There is a presser arm 33 on the back side of the holder 30, which presses and fixes the semiconductor substrate 21 against the photomask 23.

A rotating lever 34 is provided on the front side of the holder.

This is for rotating the front side of the holder, which has a double structure. In order to form a diffraction grating at a certain angle with respect to the waveguide, it is necessary to freely rotate the substrate with respect to the exposure light beam.

In addition to this, various mounting jigs for the photomask and semiconductor substrate are possible.

FIG. 8 illustrates a partial cross-sectional view of the substrate and mask.

A semiconductor substrate 21 on which a photomask 23 is to be placed closely.
GaAl! is deposited on the GaAs substrate layer 35. As
layer 36, GaAs layer 37, GaAl! An As layer 38 is grown on top of which a photoresist 22 is applied.

In Figure 1, the distance between the lens 20 and the intermediate mask is 2f (
f is the focal length of the lens), and the distance between the lens 20 and the photoresist 22 is 2f. Therefore, the i beam irradiates only the area equal to the aperture 19 multiplied by the reciprocal of the cosine θ of the incident angle θ. A diffraction grating is generated in this portion, and the period of the grating is given by λ 2thθ . λ is the wavelength of the laser light.

In this example, a lens with f=50 mm is used.

The image of the aperture is projected onto the photoresist as it is, but it is not necessary to change the lens position and focal length to enlarge or reduce the aperture before projecting it onto the photoresist. . In this way, it is not necessary to prepare many types of intermediate masks.

In this embodiment, a waveguide 28g continuous to the diffraction grating is used to form the waveguide 28. Therefore, the photomask 23
In this case, the diffraction grating and the waveguide region had to be combined into a light-shielding or light-transmitting region. Therefore, an intermediate mask was required to further limit the diffraction grating area from the waveguide.

However, it is simpler if only the diffraction grating is desired to be produced in a fixed area. In this case, no intermediate mask or lens is required. Simply use a photomask. (in the case of a negative photoresist with only the desired area transparent), or with a positive photoresist with a light-shielding area)
A photomask may be placed on the substrate 21 and photoresist 22.

According to the present invention, a submicron-order diffraction grating can be fabricated in a limited area of a semiconductor substrate.

This is a useful invention.

[Brief explanation of drawings]

FIG. 1 is a plan view of an exposure apparatus according to an embodiment of the present invention. FIG. 2 is a front view of the intermediate mask. Figure 3 is a front view of the photomask. FIG. 4 is a front view of another photomask. FIG. 5 is a perspective view of a substrate after being exposed by the exposure apparatus of the present invention. FIG. 6 is a front perspective view of the mask and board mounting jig. FIG. 7 is a rear perspective view of the mask and board mounting jig. FIG. 8 is a partial cross-sectional view of the substrate and mask. FIG. 9 is a configuration diagram of an exposure apparatus using a conventional two-beam interference method. 1... - The 2... Mirror 3... Beam splitter - 4, 5... Collimator 14... Mirror 15... ... Rotating table 16 ... Mirror 17 ... Rotating table 18 ... Intermediate mask 19 ... Opening 20 ...... 21...Substrate 22...Photoresist 23...Photomask 24...Light shielding part 25...Transparent part 26... ... Central transparent part 27 ... Diffraction grating 28 ... Waveguide inventor Yoshikazu Menowaki Haruji Oka Matsuoka Ken Tsukasa Moto Patent applicant Sumitomo Electric Industries, Ltd. Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) A laser light source, a beam splitter that divides the light from the laser light source into two beams, a collimator that converts the beam into parallel beams with expanded diameter, and a mirror that irradiates the two divided beams onto a substrate coated with photoresist. and a photomask which has a transparent part corresponding to the position where a diffraction grating is to be formed and which is to be closely attached onto a substrate and a photoresist. (2) The scope of the patent claims that an intermediate mask having a narrow aperture is provided in the optical path of one of the two light beams to limit the light beam, and a portion other than the diffraction grating is exposed by the other light beam. The exposure apparatus according to item (1). (3) The exposure apparatus according to claim (2), wherein a lens is provided between the intermediate mask and the substrate to form an image of the aperture on the photoresist.