JPH02220489A - Manufacture of phase-shift diffraction grating - Google Patents

Abstract

PURPOSE:To prevent a transition width from being produced by a method wherein, after a region used as a first diffraction grating face has been exposed to light by using interference waves, a substrate is moved, by a prescribed distance, in a direction in which interference fringes are arranged and a region used as a second diffraction grating face is exposed to light by using the interference waves. CONSTITUTION:Regions 39a, 39b used as a first diffraction grating face of a photoresist 32 are exposed to light by using interference waves 37a, 37b; after that, a substrate 31 is moved, by a prescribed distance, in a direction in which interference fringes are arranged; regions 39c, 39d used as a second diffraction grating face are exposed to light by using the interference waves 37a, 37b. Accordingly, the photoresist 32 used as a mask when a phase-shift diffraction grating 40 is formed may be either a negative resist or a positive resist. Thereby, when an etching operation is executed by intermingling the negative resist with the positive resist, a transition width by which the diffraction grating is not formed cannot be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a phase shift diffraction grating, and more particularly to a method of manufacturing a phase shift diffraction grating used in a semiconductor laser. [Prior Art] FIG. 4 is a cross-sectional view of a semiconductor laser 1 provided with a λ/4 phase shift diffraction grating. As shown in FIG. 4, this semiconductor laser 1 includes an n-type InP substrate 2 and a p-type InP substrate 3.
It has a structure in which an InGaAsP layer 4a and an InGaAsP layer 4b are sandwiched together. InGaAsP layer 4
Although the elements constituting the layer a and the InGaAsP layer 4b are the same, the mixing ratio of each element is different. InGaAsP
Layer 4a becomes the active layer. λ on the surface of the p-type InP substrate 3
A /4 phase shift diffraction grating 5 is formed. The λ/4 phase shift diffraction grating will be explained using FIG. FIG. 5 is an enlarged view of the λ/4 phase shift diffraction grating surface 5 shown in FIG. The λ/4 phase shift diffraction grating surface 5 selectively reflects light whose wavelength is an integral multiple of the pitch 6 between valleys. In other words, light 7
selectively reflects. In this case, if the pitches of all the valleys are the same, the reflected light and the unreflected light will interfere with each other, canceling out the light 7. So pitch 6
A portion is provided where the pitch 8 is longer by one quarter of the wavelength λ of the light 7 compared to the wavelength λ of the light 7. A conventional method for manufacturing a λ/4 phase shift diffraction grating will be described with reference to FIGS. 6A to 6F. First, as shown in FIG. 6A, a positive resist 12, an intermediate layer 13, and a negative resist 1 are placed on the main surface of an InP substrate 11.
Apply 4. The intermediate layer 13 is for preventing the positive resist 12 and the negative resist 14 from being mixed together. Next, as shown in FIG. 6B, half of the negative resist 14 is removed by exposure and development. Then, half of the intermediate layer 13 and half of the positive resist 12 are etched and removed using a H2SO4 solution. Next, as shown in FIG. 6C, the InP substrate 1 from which the positive resist 12, intermediate layer 13 and negative resist 14 have been removed
1, a negative resist 15 is applied. Furthermore, polyvinyl alcohol 16 is applied onto the negative resists 14 and 15. polyvinyl alcohol 16
is for preventing the negative resists 14 and 15 from being oxidized. Next, as shown in FIG. 6D, interference waves are generated by causing the light 17a and the light 17b to interfere. 18 shows interference fringes of this interference wave. The positive resist 12 and the negative resist 15 are exposed using this interference wave. Only the part of the interference wave whose light intensity exceeds a certain level is used for exposure. Therefore, as shown in FIG. 6D, the hatched area is exposed. When this is developed, exposed portions of the negative resist 15 remain, and unexposed portions of the positive resist 12 remain, as shown in FIG. 6E. Finally, as shown in FIG. 6F, the remaining negative resist 15
and positive resist 12 as a mask, the InP substrate 11 is etched to form a diffraction grating surface 19. Then, the negative resist 174 phase shift 15 and positive resist 12 are removed to complete the λ/4 phase shift diffraction grating. This method utilizes the difference in properties between a negative resist and a positive resist to shift the phase of the resist remaining on the substrate. [Problems to be Solved by the Invention] However, there is a possibility that the negative resist 15 and the positive resist 12 mix together in the portion where the negative resist 15 and the positive resist 12 are in contact with each other. When exposure and development are performed in such a state, a portion 20 where negative resist and positive resist are mixed remains in a wide area as shown in FIG. 7A. When a diffraction grating is formed by etching in this state, the 7B
As shown in the figure, a portion where the diffraction grating is not formed, that is, a transition width 21 is formed. If a diffraction grating as shown in FIG. 7B is used in a semiconductor laser, light of a specific wavelength cannot be selected in the transition width 21 portion. Therefore, the light selectivity of the semiconductor laser becomes weak. Therefore, the present invention has been made to solve these conventional problems, and its purpose is to provide a method for manufacturing a phase shift diffraction grating in which no transition width occurs. [Means for Solving the Problems] The present invention includes a first diffraction grating surface that selects a first light of a specific wavelength from among the emitted light, and a first diffraction grating surface that is out of phase at the same wavelength with respect to the first light. and a second diffraction grating surface that selects a second light beam. This invention includes a step of applying a photoresist on the main surface of a substrate, a step of exposing the photoresist located on a region to become a first diffraction grating surface to interference waves,
After the exposure process, there is a step of moving the substrate a predetermined distance in the direction in which the interference fringes of the interference waves are lined up, and a step of moving the substrate by a predetermined distance in the direction in which the interference fringes of the interference waves are arranged. a step of exposing to light; a step of developing a photoresist to form a predetermined resist pattern; and a step of etching the main surface of the substrate using the resist pattern as a mask to form first and second diffraction grating surfaces. , is equipped with. [Operation] According to the present invention, the phase of the photoresist remaining on the substrate is shifted by moving the substrate. Therefore, as a photoresist, only IFIi can be used between a negative resist and a positive resist. Therefore, negative resist and positive resist are mixed,
No large areas of resist remain on the substrate after development. [Example] A λ/4 phase shift diffraction grating for a semiconductor laser was manufactured using an example of the present invention. This manufacturing process will be explained using FIGS. 1A to 1G. As shown in FIG. 1A, an InP substrate 31 coated with a negative resist 32 was prepared and placed on a piezoelectric element 33. As shown in FIG. A photomask 34 was placed on the negative resist 32. The photoresist located under the light blocking part 35 of the photomask 34 is not exposed, and the photoresist located under the light transmitting part 36 is exposed. In this embodiment, the light blocking section 35 and the light transmitting section 36 are formed so that half of the negative resist 32 is exposed and the other half is unexposed. The photomask 34 is fitted into a mask holder (not shown). The mask holder is connected to a step motor (not shown). Therefore, the photomask 34 is moved by a step motor. A step motor is a motor whose shaft rotates a predetermined angle when a predetermined pulse is sent. The right side of the piezoelectric element 33 when viewed from FIG. 1A is fixed with a piezoelectric element fixing jig (not shown). Therefore, when a voltage is applied from the piezoelectric element power supply, the piezoelectric element 33 expands in the direction of the arrow shown in FIG. 1A. The InP substrate 31 is moved by the piezoelectric element 33. Next, as shown in FIG. 1B, the lights 37a and 37b are caused to interfere with each other to generate an interference wave. 38 shows interference fringes of interference waves. 39a and 3 of the negative resist 32 due to interference waves
Part 9b was exposed. Next, as shown in FIG. 1C, the photomask 34 is placed so that the light transmitting part 36 is placed where the light blocking part 35 was, and the light blocking part 35 is placed where the light transmitting part 36 was. It was moved in the direction of arrow B by a step motor. Next, as shown in FIG. 1D, the piezoelectric cord 33 is connected to the interference pattern 38.
By expanding in the direction of the arrow, which is the same direction as
The InP substrate 31 was moved by λ/4 in the direction of arrow A. λ is the wavelength of light to be reflected by the diffraction grating surface. Next, as shown in FIG. 1E, by causing the lights 37a and 37b to interfere with each other, interference waves were generated, and the portions 39c and 39d of the negative resist 32 were exposed. Next, as shown in FIG. 1F, the negative resist 32 was developed. And the remaining negative resist 39 a, 3
Wet etching was performed using 9b, 39c and 39d as masks to form a λ/4 phase shift diffraction grating surface 40 on the InP substrate 31. Next, as shown in FIG. 1G, negative resist 39a139b is applied.
, 39c and 39d, InPl plate 31 plate surface 1
A four phase-shifted diffraction grating surface was completed on the surface. According to this embodiment, the manufacturing process of the λ/4 phase shift diffraction grating can be shortened compared to the conventional method. Therefore, this embodiment also has the unique effect of improving the productivity of the λ/4 phase shift diffraction grating. In this embodiment, the light blocking section 35 and the light transmitting section 36 are reversed by moving the photomux 34, but the following method may also be used. First, a photomask 41 having a light blocking part 42a and a light transmitting part 42b shown in FIG. 2A is placed on a negative resist and exposed. Next, the photomask 41 is removed from above the negative resist, and the substrate is moved in the same direction as in the previous embodiment. Then, a photomask 43 in which the light blocking portion 42a and the light transmitting portion 42b of the photomask 41 and the like are reversed is placed on the negative resist and exposed. In this example, the photomask 34 was moved by a step motor. When using a normal motor, the method shown in FIG. 3 is used. As shown in FIG. 3, a light blocking section 52a and a light transmitting section 52b
A metal light reflecting film 5 is placed on a photomask 51 having
3a and 53b are provided. The light reflecting film 53a is the light blocking part 5
provided on the photomask 51 located at the end of 2a,
The light reflection 11153b is provided on the photomask 51 located at the end of the light transmission section 52b. Laser generator 54
A half mirror 55 and a condensing lens 56 are provided between the photomask 51 and the photomask 51 . A detector 57 serving as a sensor is installed at a position where the half mirror 55 reflects light. Next, a method of moving the photomask 51 using a normal motor will be explained using FIG. 3. First, the laser 58 is generated from the laser generator 54 . Laser 58 moves in the direction of arrow C. At the same time as the laser 58 is generated, the photomask 51 is moved in the direction of the arrow by the motor. When the light reflection film 53a comes under the laser generator 54, the laser 58 is reflected in the direction of arrow E by the light reflection film 53a. The laser 58 reflected in the direction of arrow E is focused by a condensing lens 56 and reflected in the direction of arrow F by a half mirror 55. The laser 58 reflected in the direction of arrow F is detected by a detector 57, and the motor is stopped by a signal from the detector 57. Therefore, the photomask 51 stops when the light reflecting film 53a comes to a position below the laser generator 54. Next, a laser 58 is generated from the laser generator 54 . At the same time, the photomask 51 is moved in the direction of the arrow by the motor. The light reflecting film 53b is the laser generator 5.
4, the photomask 51 is stopped by the same operation as before. The photomask 51 can be moved by the method described above. In this example, the InP substrate was moved by λ/4 to shift the phase of the diffraction grating by λ/4, but the present invention is not limited to this, and the phase of the diffraction grating can be shifted by the desired amount. All you have to do is move the InP substrate. In this example, a λ/4 phase shift diffraction grating for a semiconductor laser was manufactured, but the present invention is not limited thereto, and phase shift gratings for other uses can also be manufactured. [Effects of the Invention] According to the method of the present invention, by moving the substrate, the phase of the photoresist remaining on the substrate is shifted. Therefore, when forming the phase shift diffraction grating, the photoresist used as a mask may be either a negative resist or a positive resist. Therefore, it is no longer possible to create a transition width where no diffraction grating is formed due to mixing of the negative resist and the positive resist.

[Brief explanation of the drawing]

FIGS. 18 to 1G are cross-sectional views showing an embodiment of the present invention in the order of steps. FIGS. 2A and 2B are cross-sectional views of a photomask used in a modification of one embodiment of the present invention. FIG. 3 is a diagram showing a method of moving a photomask used in a modification of one embodiment of the present invention. FIG. 4 is a sectional view of a semiconductor laser provided with a λ/4 phase shift diffraction grating. FIG. 5 is an enlarged view of the λ/4 phase shift grating. 6A to 6F are cross-sectional views showing a conventional method for manufacturing a λ/4 phase shift diffraction grating in the order of steps. FIGS. 7A and 7B are cross-sectional views sequentially showing the process of creating a transition width. 31 is a 1nP substrate, 32 is a negative resist, 33 is a piezoelectric element, 34 is a photomask, 37a and 37b are lights, and 40 is a λ/4 phase shift diffraction grating surface. Agent Masuo Oiwa Figure 1E Figure 1F Figure 4 Figure 6D Figure 6E Figure 11:l Figure 6F Figure 5 Figure 6A Figure 7A Figure 7B (self-motivated) Yujiri'211B Showa Year Month Day 5. Column 6, Detailed explanation of the invention in the specification to be amended, Contents of amendment (1) "rlnP substrate 2" on page 2, line 16 of the specification
Correct to lnPn double layer. (2) Delete "λ/4 phase shift" on page 5, line 8 of the specification. Above 3. Relationship with the case of the person making the amendment

Claims (1)

[Claims] A first light source that selects a first light beam having a specific wavelength from among the incident light beams.
A method for manufacturing a phase shift diffraction grating comprising a diffraction grating surface and a second diffraction grating surface that selects a second light having the same wavelength and phase shift with respect to the first light, the method comprising: a step of applying a photoresist on the main surface of the substrate; a step of exposing the photoresist located on the region to become the first diffraction grating surface to interference waves; and after the exposure treatment, exposing the substrate to light. , a step of moving the interference wave by a predetermined distance in the direction in which interference fringes are lined up; and after moving the substrate, exposing the photoresist located on the area that is to become the second diffraction grating surface with the interference wave. forming a predetermined resist pattern by developing the photoresist; and forming the first and second diffraction grating planes by etching the main surface of the substrate using the resist pattern as a mask. A method for manufacturing a phase shift diffraction grating, comprising the steps of: