JP2012191030A - Method for manufacturing distribution feedback type semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a distribution feedback type semiconductor laser having a sufficient characteristic by simple technique and process.SOLUTION: Diffraction grating patterns 7a, 7b are exposed to a resist 6 and developed. A diffraction grating layer 5 is etched using the developed resist 6 as a mask, to form diffraction lattices 8a, 8b corresponding to the diffraction grating patterns 7a, 7b. A p-type InP embedded layer 10 is formed on the diffraction lattices 8a, 8b. The p-type InP embedded layer 10 and the diffraction lattices 8a, 8b are etched to form a ridge 11. In a direction perpendicular to a resonator, the diffraction grating pattern 7a is longer than the diffraction grating pattern 7b. Then length of the diffraction lattices 8a, 8b in the ridge 11 perpendicular to the resonator is identical to a width of the ridge 11. In a direction along the resonator, a width of the diffraction lattice 8a in the ridge 11 is narrower than a width of the diffraction lattice 8b in the ridge 11.

Description

  The present invention relates to a method of manufacturing a distributed feedback semiconductor laser used in the field of optical communications.

  As a method of changing the optical coupling constant in the direction along the resonator of the distributed feedback semiconductor laser, a method of changing the volume of the active layer, a method of changing the distance between the active layer and the diffraction grating, A method of changing a ratio (duty) within one cycle of a refractive index material and a low refractive index material has been proposed.

  In the method of changing the volume of the active layer, a selective growth method using a selection mask is used during active layer growth. The volume of the active layer varies depending on the shape of the selection mask. When the volume of the active layer changes, the equivalent refractive index of the light guided in the resonator changes, so that the optical coupling constant also changes. However, technical difficulty such as establishment of a selective crystal growth method is high, and the process is complicated.

  By changing the distance between the active layer and the diffraction grating, the ratio of the distribution of light guided through the waveguide to the diffraction grating changes, and the optical coupling constant also changes. In view of this, the distance between the diffraction grating and the active layer is made closer to the part where the optical coupling constant is desired to be increased, and the distance between the diffraction grating and the active layer is made closer to the part where the optical coupling constant is desired to be made smaller. However, this method is also complicated in process.

  In the method of changing the duty of the diffraction grating, a diffraction grating having a constant duty is first formed, and a part other than the part where the duty of the diffraction grating is to be changed is protected with a resist or the like. Thereafter, the exposed diffraction grating is additionally etched. Thereby, the duty of the diffraction grating can be changed. Since the duty is different between the protected diffraction grating and the additionally etched diffraction grating, the optical coupling constant also changes. This method is also complicated in process such as additional etching.

  Further, there has been proposed a semiconductor laser in which the optical coupling constant is changed by changing the length of the diffraction grating in the direction perpendicular to the resonator on the ridge (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-270789

  In order to obtain a refractive index difference necessary for Bragg reflection, the diffraction grating and the surrounding semiconductor layer are made of materials having different band gaps. Holes are easily trapped in the diffraction grating due to the band gap difference of this material. Therefore, the light guided through the active layer oozes out of the active layer, causing absorption between valence bands that excites holes of the diffraction grating between valence bands. Since the loss of laser light due to this valence band absorption is large, the volume of the diffraction grating is preferably small. However, in Patent Document 1, since the length of the diffraction grating is changed on the ridge, there is a possibility that the volume of the diffraction grating increases and the characteristics deteriorate.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a method capable of manufacturing a distributed feedback semiconductor laser having good characteristics by a simple technique and process. is there.

  The method of manufacturing a distributed feedback semiconductor laser according to the present invention includes a step of sequentially forming a first semiconductor layer, a diffraction grating layer, and a resist on a semiconductor substrate, and the first and second diffraction grating patterns on the resist. Exposing and developing the resist, and etching the diffraction grating layer using the developed resist as a mask, so that the first and second diffraction patterns respectively corresponding to the first and second diffraction grating patterns Forming a grating; forming a second semiconductor layer on the first and second diffraction gratings; and etching the second semiconductor layer and the first and second diffraction gratings to form a ridge The first diffraction grating pattern is longer than the second diffraction grating pattern in a direction perpendicular to the resonator, and the first and second diffraction gratings in the ridge The length in the direction perpendicular to the resonator is the same as the width of the ridge, and in the direction along the resonator, the width of the first diffraction grating in the ridge is It is narrower than the width of the second diffraction grating.

  According to the present invention, a distributed feedback semiconductor laser having good characteristics can be manufactured by a simple technique and process.

It is sectional drawing for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 1 of this invention. It is a figure which shows a part of diffraction grating pattern which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 1 of this invention. It is a top view for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 1 of this invention. FIG. 5 is a diagram (upper side) showing a remaining width of a resist after development, and a top view (lower side) showing the resist after development. It is a figure which shows the duty of the diffraction grating pattern drawn on the resist. It is a figure which shows the relationship between an optical coupling coefficient and the remaining width of a diffraction grating. It is a top view for demonstrating the modification 1 of the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 1 of this invention. It is a top view for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 2 of this invention. It is a top view for demonstrating the modification of the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 2 of this invention. It is a top view for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 3 of this invention. It is a top view for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 4 of this invention. It is a top view for demonstrating the modification of the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 4 of this invention. It is a top view for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 5 of this invention. It is a top view for demonstrating the modification of the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 5 of this invention. It is a top view for demonstrating the manufacturing method of the distributed feedback semiconductor laser which concerns on Embodiment 6 of this invention.

  A method of manufacturing a distributed feedback semiconductor laser according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

Embodiment 1 FIG.
A method of manufacturing the distributed feedback semiconductor laser according to the first embodiment of the present invention will be described with reference to the drawings. 1, 3, 5 and 6 are cross-sectional views for explaining the method of manufacturing the distributed feedback semiconductor laser according to the first embodiment of the present invention, and FIG. 4 is a top view. FIG. 2 is a diagram showing a part of the diffraction grating pattern according to Embodiment 1 of the present invention.

  First, as shown in FIG. 1, an n-type InP clad layer 2, an active layer 3, a p-type InP clad layer 4, and a p-type InGaAsP diffraction grating layer 5 are epitaxially grown on an n-type InP substrate 1 in this order. A resist 6 is formed on the p-type InGaAsP diffraction grating layer 5. The active layer 3 has an MQW (Multiple Quantum Well) structure and an SCH (Separated Confinement Heterostructure) structure. The resist 6 is an electron beam photosensitive positive resist.

  Next, the rectangular diffraction grating patterns 7a and 7b shown in FIG. 2 created by CAD (Computer Aided Design) are exposed to the resist 6 by an EB (Electron Beam) exposure apparatus, and the resist 6 is developed. In a direction perpendicular to the resonator, the diffraction grating pattern 7a is longer than the diffraction grating pattern 7b. In the direction along the resonator, the diffraction grating pattern 7a and the diffraction grating pattern 7b have the same width.

  Next, as shown in FIGS. 3 and 4, the developed resist 6 is used as a mask to etch the p-type InGaAsP diffraction grating layer 5 so that the diffraction gratings 8a and 8b respectively corresponding to the diffraction grating patterns 7a and 7b are obtained. Form. Thereafter, the resist 6 is removed. The cross-sectional shape of the diffraction gratings 8a and 8b is not limited to a rectangle, but may be a triangle or a trapezoid. The vicinity of the center of the diffraction gratings 8a and 8b is disposed in a region 9 to be a ridge later.

  Next, as shown in FIG. 5, a p-type InP buried layer 10 is formed on the diffraction gratings 8a and 8b. At this time, the gap between the diffraction gratings 8 a and 8 b is buried with the p-type InP buried layer 10.

  Next, as shown in FIG. 6, the p-type InP buried layer 10, the diffraction gratings 8a and 8b, the p-type InP cladding layer 4, the active layer 3, and the n-type InP cladding layer 2 are etched to form a ridge that becomes an optical waveguide. 11 is formed. At this time, only the diffraction gratings 8a and 8b in the ridge 11 are left, and the other diffraction gratings 8a and 8b are removed. As a result, the length of the diffraction gratings 8 a and 8 b in the ridge 11 in the direction perpendicular to the resonator is the same as the width of the ridge 11. Next, both sides of the ridge 11 are embedded with the current blocking layer 12. A contact layer 13 is formed on the ridge 11 and the current blocking layer 12. Thereafter, a semiconductor laser is manufactured by forming an electrode or cleaving it.

  FIG. 7 is a diagram (upper side) showing the remaining width of the resist after development, and a top view (lower side) showing the resist after development. When a fine pattern is transferred using an exposure apparatus such as an EB exposure apparatus, a pattern different from the diffraction grating pattern created by CAD is transferred onto the resist 6 (pattern effect). In particular, in a long wavelength distributed feedback semiconductor laser for optical communication, diffraction grating patterns are arranged at intervals of 200 nm to 250 nm, and the pattern effect due to the adjacent pattern shape appears remarkably.

  The diffraction grating patterns 7a and 7b do not exist outside the drawing start point and the drawing end point. Therefore, since the diffraction grating pattern is sparse at the drawing start point and the drawing end point, the energy of the integrated electron beam given to the resist 6 becomes small and the exposure amount is insufficient. On the other hand, in the vicinity of the center, the diffraction grating patterns 7a and 7b are present in the front, back, left and right, and are dense, so that the energy of the accumulated electron beam applied to the resist 6 increases, and the exposure amount becomes sufficient. As a result, the diffraction grating patterns 7a and 7b created by CAD are rectangular, but the remaining width of the resist 6 is wide at the drawing start point and the drawing end point, and the remaining width of the resist 6 is narrow near the center.

  Further, in the long diffraction grating pattern 7a, a region where the diffraction grating pattern near the center is dense is wide, and the exposure amount is sufficient. For this reason, in the vicinity of the center of the diffraction grating pattern 7a, the remaining width of the resist 6 remaining after development is narrowed, and the interval is widened. On the other hand, in the short diffraction grating pattern 7b, the region where the diffraction grating pattern near the center is dense is narrow and the exposure amount is insufficient. For this reason, in the vicinity of the center of the diffraction grating pattern 7b, the remaining width of the resist 6 remaining after development is widened, and the interval is narrowed.

  As a result, even if the amount of DOSE during EB exposure is constant, the remaining width of the resist 6 remaining after development can be changed within one chip. Therefore, the remaining width of the diffraction grating can be changed within one chip. In the present embodiment, the width of the diffraction grating 8 a in the ridge 11 is narrower than the width of the diffraction grating 8 b in the ridge 11 in the direction along the resonator.

  FIG. 8 is a diagram showing the duty of the diffraction grating pattern drawn on the resist. A diffraction grating pattern with a period of 200 nm was drawn by a distance of 10 μm by an EB exposure apparatus. A positive resist was used. The duty is a resist remaining width with respect to the interval of the diffraction grating. The duty is wide at the drawing start point and the end point, and the duty is narrow at the center. As a result of the experiment, it has been found that the duty changes about 20 to 30% between the center and the end. However, this amount of change depends on the sensitivity of the resist and the device used.

  Here, one of the parameters determining the characteristics of the distributed feedback semiconductor laser is an optical coupling constant. The optical coupling constant depends not only on the distance between the active layer 3 and the diffraction gratings 8a and 8b but also on the remaining width of the diffraction gratings 8a and 8b.

  FIG. 9 is a diagram showing the relationship between the optical coupling coefficient and the remaining width of the diffraction grating. This data was calculated (see Dr. H. Ghafouri-Shiraz, Distributed Feedback Laser Diodes and Optical Tunable Filters, Wiley; 2nd revised edition). The vertical axis represents κL obtained by multiplying the optical coupling constant κ by the resonator length L. For example, assuming that the cross section of the diffraction grating is a perfect rectangle, the maximum optical coupling constant can be obtained when the remaining width of the diffraction grating becomes a duty of 50%, which is half the pitch. When the duty deviates from 50%, the optical coupling constant decreases. Since the optical coupling constant depends on the amount of change in the refractive index due to the diffraction grating, when the duty is shifted from 50%, the amount of fluctuation in the refractive index due to the diffraction grating is substantially reduced, and the optical coupling constant is reduced.

  Whether the center duty of the diffraction grating pattern is set to 50% or the end duty is set to 50% can be set by the DOSE amount. In the former case, if DOSE is set so that the center duty is 50%, the duty increases to 60% and 70% toward the end. In the latter case, if DOSE is set so that the end duty is 50%, the duty decreases to 40% and 30% toward the center. In the present embodiment, the former case is used. Even in the latter case, although the arrangement pattern arrangement for obtaining a desired optical coupling constant changes, the optical coupling constant in the direction along the resonator can be changed within one chip.

  In the present embodiment, the diffraction gratings 8a and 8b are formed wider than the region 9 to be a ridge. Then, when forming the ridge 11, only the diffraction gratings 8a and 8b in the ridge 11 are left, and the other diffraction gratings 8a and 8b are removed. Thereby, the volume of the diffraction gratings 8a and 8b can be reduced. Therefore, since absorption between valence bands can be suppressed, the semiconductor laser has good characteristics.

  The length of the diffraction grating patterns 7a and 7b can be easily changed on the CAD. In EB exposure, the DOSE setting may be constant at the time of drawing. Accordingly, since the number of wafer process steps is not increased and there are no complicated processes, a semiconductor laser can be manufactured by a simple technique and process.

  Also, if the optical coupling constant is large, the amount of light coupled to the diffraction gratings 8a and 8b increases, so the amount of light that can be extracted to the outside decreases and the slope efficiency decreases. However, since the amount of light in the resonator necessary for stimulated emission increases, the threshold value decreases. On the other hand, when the optical coupling constant is small, the amount of light coupled to the diffraction gratings 8a and 8b decreases, so the amount of light that can be extracted to the outside increases and the slope efficiency increases. Therefore, in the present embodiment, the diffraction grating 8a having a narrow remaining width is disposed on the front end face 14a side, and the diffraction grating 8b having a large remaining width is disposed on the rear end face 14b side. Thereby, since the optical coupling constant on the front end face 14a side becomes small, high slope efficiency can be obtained. Further, since the optical coupling constant on the rear end face 14b side is increased, the threshold value can be kept low. When the diffraction grating 8b has a smaller optical coupling constant than the diffraction grating 8a, the diffraction grating 8b is disposed on the front end face 14a side.

  FIG. 10 is a top view for explaining the first modification of the method for manufacturing the distributed feedback semiconductor laser according to the first embodiment of the present invention. In the first modification, the remaining width of the diffraction grating 8b is changed stepwise by changing the length of the diffraction grating pattern 7b stepwise. Thereby, an optical coupling constant can be changed in steps.

Embodiment 2. FIG.
FIG. 11 is a top view for explaining the method for manufacturing the distributed feedback semiconductor laser according to the second embodiment of the present invention. This semiconductor laser is a phase shift region type distributed feedback semiconductor laser. This figure shows a state before the ridge 11 is formed after the diffraction gratings 8a and 8b are formed.

  In the phase shift region 15, the optical electric field intensity becomes maximum. Such an increase in the optical electric field intensity causes further stimulated emission, increasing the consumption of electron-hole carriers and causing hole burning in which carriers are locally reduced. That is, a local refractive index change occurs in the phase shift region 15 due to the free carrier plasma effect. Such a local refractive index change in the direction along the resonator makes the guided mode unstable and causes a phenomenon undesirable as a communication laser such as a mode hop.

  Therefore, in the present embodiment, a long diffraction grating pattern 7 a is arranged in the phase shift region 15, thereby forming a diffraction grating 8 a having a narrow remaining width in the phase shift region 15. Thereby, the optical coupling constant can be reduced in the phase shift region 15. Therefore, an increase in the optical electric field intensity in the phase shift region 15 is suppressed, hole burning is suppressed, and a local change in refractive index is also suppressed. As a result, stable oscillation is possible. When the diffraction grating 8b has a smaller optical coupling constant than the diffraction grating 8a, the diffraction grating 8b is disposed in the phase shift region 15.

  FIG. 12 is a top view for explaining a modification of the method for manufacturing the distributed feedback semiconductor laser according to the second embodiment of the present invention. In this modification, the length of the diffraction grating pattern 8 a is the longest in the phase shift region 15, and is shortened stepwise as the distance from the phase shift region 15 increases. Thereby, the optical coupling constant can be made the smallest in the phase shift region 15 with the highest optical electric field strength, and the optical coupling constant can be increased stepwise as the distance from the phase coupling region 15 increases.

Embodiment 3 FIG.
FIG. 13 is a top view for explaining the method for manufacturing the distributed feedback semiconductor laser according to the third embodiment of the present invention. This figure shows a state before the ridge 11 is formed after the diffraction gratings 8a and 8b are formed. In a later step, the low reflection coating 16 is provided on the front end surface 14a, and the high reflection coating 17 is provided on the rear end surface 14b. The high reflection coat 17 has a higher reflectance than the low reflection coat 16.

  On the rear end face 14b provided with the high reflection coating 17, the optical electric field intensity becomes maximum. Therefore, in the present embodiment, the long diffraction grating 8a is disposed in the vicinity of the rear end face 14b. As a result, the optical coupling constant in the vicinity of the rear end surface 14b is reduced, and the optical electric field strength at the rear end surface 14b is relaxed, so that deterioration due to optical breakdown can be suppressed.

  When the diffraction grating 8b has a smaller optical coupling constant than the diffraction grating 8a, the diffraction grating 8b is disposed in the vicinity of the rear end face 14b. The length of the diffraction grating pattern 8 a may be the longest at the rear end face 14 b and may be shortened stepwise as the distance from the phase shift region 15 increases.

Embodiment 4 FIG.
FIG. 14 is a top view for explaining the method for manufacturing the distributed feedback semiconductor laser according to the fourth embodiment of the present invention. This figure shows a state before the ridge 11 is formed after the diffraction gratings 8a and 8b are formed.

  In the direction perpendicular to the resonator, the vicinity of the center of the diffraction grating pattern 7a is disposed in a region 9 serving as a ridge. The diffraction grating pattern 7b is arranged so as to be shifted from the diffraction grating pattern 7a, and the end of the diffraction grating pattern 7b is arranged in a region 9 that becomes a ridge. The lengths of the diffraction grating pattern 7a and the diffraction grating pattern 7b are the same.

  As described above, the remaining width of the resist 6 is wide at the ends of the diffraction grating patterns 7a and 7b, and the remaining width of the resist 6 is narrow at the center. For this reason, the width of the diffraction grating 8 a in the ridge 11 is narrower than the width of the diffraction grating 8 b in the ridge 11. Therefore, the optical coupling constant in the direction along the resonator can be changed within one chip.

  In the present embodiment, the diffraction gratings 8a and 8b are formed wider than the region 9 to be a ridge. Then, when forming the ridge 11, only the diffraction gratings 8a and 8b in the ridge 11 are left, and the other diffraction gratings 8a and 8b are removed. Thereby, the volume of the diffraction gratings 8a and 8b can be reduced. Therefore, since absorption between valence bands can be suppressed, the semiconductor laser has good characteristics.

  Further, it is possible to easily shift the arrangement of the diffraction grating patterns 7a and 7b on the CAD. In EB exposure, the DOSE setting may be constant at the time of drawing. Accordingly, since the number of wafer process steps is not increased and there are no complicated processes, a semiconductor laser can be manufactured by a simple technique and process.

  Further, the diffraction grating 8a having a narrow remaining width is disposed on the front end face 14a side, and the diffraction grating 8b having a large remaining width is disposed on the rear end face 14b side. Thereby, since the optical coupling constant on the front end face 14a side becomes small, high slope efficiency can be obtained. Further, since the optical coupling constant on the rear end face 14b side is increased, the threshold value can be kept low. When the diffraction grating 8b has a smaller optical coupling constant than the diffraction grating 8a, the diffraction grating 8b is disposed on the front end face 14a side.

  FIG. 15 is a top view for explaining a modification of the method for manufacturing the distributed feedback semiconductor laser according to the fourth embodiment of the present invention. In this modification, the remaining width of the diffraction grating 8b is changed stepwise by changing the arrangement of the diffraction grating pattern 7b stepwise. Thereby, an optical coupling constant can be changed in steps.

Embodiment 5 FIG.
FIG. 16 is a top view for explaining the method of manufacturing the distributed feedback semiconductor laser according to the fifth embodiment of the present invention. This figure shows a state before the ridge 11 is formed after the diffraction gratings 8a and 8b are formed. This semiconductor laser is a phase shift region type distributed feedback semiconductor laser.

  In the present embodiment, the diffraction grating pattern 7a in which the vicinity of the center is disposed in the region 9 serving as the ridge is disposed in the phase shift region 15, so that the vicinity of the center of the diffraction grating 8a having a narrow remaining width is formed in the phase shift region 15. To do. Thereby, the optical coupling constant can be reduced in the phase shift region 15. Therefore, an increase in the optical electric field intensity in the phase shift region 15 is suppressed, hole burning is suppressed, and a local change in refractive index is also suppressed. As a result, stable oscillation is possible. When the diffraction grating 8b has a smaller optical coupling constant than the diffraction grating 8a, the diffraction grating 8b is disposed in the phase shift region 15.

  FIG. 17 is a top view for explaining a modification of the manufacturing method of the distributed feedback semiconductor laser according to the fifth embodiment of the present invention. In this modification, the vicinity of the center of the diffraction grating pattern 7 a is arranged in the region 9 in the phase shift region 15, and the arrangement of the diffraction grating pattern 7 a is shifted step by step as the distance from the phase shift region 15 increases. Thereby, the optical coupling constant can be minimized in the phase shift region 15 having the highest optical electric field strength. As the distance from the phase shift region 15 increases, the optical electric field strength decreases, and the optical coupling constant can be increased stepwise.

Embodiment 6 FIG.
FIG. 18 is a top view for explaining the method for manufacturing the distributed feedback semiconductor laser according to the sixth embodiment of the present invention. This figure shows a state before the ridge 11 is formed after the diffraction gratings 8a and 8b are formed. In a later step, the low reflection coating 16 is provided on the front end surface 14a, and the high reflection coating 17 is provided on the rear end surface 14b. The high reflection coat 17 has a higher reflectance than the low reflection coat 16.

  On the rear end face 14b provided with the high reflection coating 17, the optical electric field intensity becomes maximum. Therefore, in the present embodiment, the diffraction grating 8a in which the vicinity of the center is disposed in the ridge region 9 is disposed in the vicinity of the rear end face 14b. As a result, the optical coupling constant in the vicinity of the rear end surface 14b is reduced, and the optical electric field strength at the rear end surface 14b is relaxed, so that deterioration due to optical breakdown can be suppressed.

  When the diffraction grating 8b has a smaller optical coupling constant than the diffraction grating 8a, the diffraction grating 8b is disposed in the vicinity of the rear end face 14b. Alternatively, the vicinity of the center of the diffraction grating pattern 7a may be arranged in the region 9 on the rear end face 14b, and the arrangement of the diffraction grating pattern 7a may be gradually shifted as the distance from the rear end face 14b increases.

  Although the positive resist is used in the above embodiment, the same effect can be obtained even if a negative resist is used. When a negative resist is used, the extracted pattern and the remaining pattern in the bird's-eye view of the diffraction grating pattern in the lower diagram of FIG. 7 are reversed. Therefore, the resist remaining width is narrow at the drawing start point and the drawing end point, and the resist remaining width is wide near the center.

  In the above embodiment, the EB exposure apparatus is used. However, the present invention is not limited to this, and another exposure apparatus such as a stepper may be used. In particular, the stepper cannot change the exposure amount in one shot, but the remaining width of the resist 6 remaining after development can be changed according to the above embodiment, so that the optical coupling constant can be changed in the chip. Can do.

  In the above embodiment, the embedded distributed feedback semiconductor laser in which both sides of the ridge 11 are embedded with the current blocking layer 12 is shown. However, the present invention is not limited to this, and the same effect can be obtained with a ridge distributed feedback semiconductor laser. Can be obtained. The positions of the diffraction gratings 8a and 8b may be on the upper side or the lower side of the active layer 3. The same effect can be obtained regardless of whether the refractive index of the diffraction grating layer is larger or smaller than the refractive index of the surrounding material.

  Further, the lengths of the diffraction grating patterns may be changed and the arrangement of the diffraction grating patterns may be shifted by combining the first embodiment and the fourth embodiment. Thereby, since the width of the diffraction grating in the direction along the resonator can be changed, the same effect as in the first and fourth embodiments can be obtained.

  In the second and fifth embodiments, the single phase shift region structure has been described. However, the present invention is not limited to this, and the present invention can also be applied to a multi-phase shift region type distributed feedback semiconductor laser. Further, the diffraction gratings 8a and 8b may be arranged symmetrically with respect to the phase shift region 15, or may be arranged reflecting the optical electric field intensity distribution.

1 n-type InP substrate (semiconductor substrate)
2 n-type InP cladding layer (first semiconductor layer)
3 Active layer (first semiconductor layer)
4 p-type InP cladding layer (first semiconductor layer)
5 p-type InGaAsP diffraction grating layer (diffraction grating layer)
6 resist 7a diffraction grating pattern (first diffraction grating pattern)
7b Diffraction grating pattern (second diffraction grating pattern)
8a Diffraction grating (first diffraction grating)
8b Diffraction grating (second diffraction grating)
9 Region to be a ridge 10 p-type InP buried layer (second semiconductor layer)
11 Ridge 14a Front end face 14b Rear end face 15 Phase shift area 17 High reflection coating

Claims (5)

Forming a first semiconductor layer, a diffraction grating layer, and a resist in order on a semiconductor substrate;
Exposing the resist to first and second diffraction grating patterns and developing the resist;
Etching the diffraction grating layer using the developed resist as a mask to form first and second diffraction gratings respectively corresponding to the first and second diffraction grating patterns;
Forming a second semiconductor layer on the first and second diffraction gratings;
Etching the second semiconductor layer and the first and second diffraction gratings to form a ridge,
In a direction perpendicular to the resonator, the first diffraction grating pattern is longer than the second diffraction grating pattern,
The length of the first and second diffraction gratings in the ridge in the direction perpendicular to the resonator is the same as the width of the ridge,
In the direction along the resonator, the width of the first diffraction grating in the ridge is narrower than the width of the second diffraction grating in the ridge. Method. Forming a first semiconductor layer, a diffraction grating layer, and a resist in order on a semiconductor substrate;
Exposing the resist to first and second diffraction grating patterns and developing the resist;
Etching the diffraction grating layer using the developed resist as a mask to form first and second diffraction gratings respectively corresponding to the first and second diffraction grating patterns;
Forming a second semiconductor layer on the first and second diffraction gratings;
Etching the second semiconductor layer and the first and second diffraction gratings to form a ridge,
In the direction perpendicular to the resonator, the vicinity of the center of the first diffraction grating pattern is disposed in a region where the ridge is formed, and the second diffraction grating pattern is located with respect to the first diffraction grating pattern. Shifted,
The length of the first and second diffraction gratings in the ridge in the direction perpendicular to the resonator is the same as the width of the ridge,
In the direction along the resonator, the width of the first diffraction grating in the ridge is narrower than the width of the second diffraction grating in the ridge. Method.   3. The distributed feedback semiconductor laser according to claim 1, wherein one of the first diffraction grating and the second diffraction grating having the smaller optical coupling constant is disposed on the front end face side. 4. Production method.   3. The distributed feedback semiconductor laser according to claim 1, wherein one of the first diffraction grating and the second diffraction grating having a smaller optical coupling constant is arranged in a phase shift region. 4. Production method. A step of providing a low-reflection coating on the front end surface, and further providing a high-reflection coating having a higher reflectance than the low reflection coating on the rear end surface;
3. The distributed feedback semiconductor according to claim 1, wherein one of the first diffraction grating and the second diffraction grating having the smaller optical coupling constant is disposed in the vicinity of the rear end face. Laser manufacturing method.

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