JPH1138592A - Production of phase shift type diffraction grating transfer mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively produce a phase shift type diffraction grating transfer mask having excellent single mode selectivity with good reproducibility by forming first transfer mask patterns, coating prescribed regions with photoresist patterns, removing the first transfer mask patterns of the non-coated regions and forming second transfer mask patterns. SOLUTION: The photoresist is applied by spinner coating application on a quartz glass substrate 1 having a first light shielding layer 2. Next, the photoresist is subjected to interference exposure by using an Ar ion laser 4 to obtain the photoresist patterns 3. The first transfer mask patterns 5 are formed with the periodic photoresist patterns as a mask. Next, the ordinary photoresist patterns 7 are formed in the prescribed regions and the exposed first transfer mask patterns 5 are peeled from the quartz glass substrate 1 and in succession, the photoresist patterns 7 are peeled. The second transfer mask patterns 9 are then formed and the phase shift type diffraction grating transfer mask is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a method of manufacturing a diffraction grating transfer mask used for manufacturing a semiconductor laser, a semiconductor laser obtained by the method, an optical module using the semiconductor laser, and an optical application system.

[0002]

2. Description of the Related Art A distributed feedback semiconductor laser operating in a single longitudinal mode is a key device for constructing a multiplex optical transmission system corresponding to large-capacity communication. It is effective to form a diffraction grating whose phase is inverted at the center of the vessel. A conventional method of forming a phase-shifting diffraction grating is described in Journal of Applied Physics, Vol. 75, No. 1, 1994, No. 1
It is systematically summarized in the explanatory papers from page to page 29. As described in the above literature, there are several methods for forming a phase shift type diffraction grating, such as a double resist method, an electron beam exposure method, a phase modulation mask method, a phase modulation layer method, and a diffraction grating transfer mask adhesion method. A method is being considered. Among them, a method of closely transferring a phase shift type diffraction grating transfer mask to a sample surface has been studied for practical use due to a simple technique.

[0003]

The phase shift type diffraction grating transfer mask of the diffraction grating transfer mask contact method has the following problems in the prior art.

[0004] The processing dimensions of the diffraction grating are high in accuracy, and there is a problem in mass productivity because a mechanical marking device is used to manufacture this phase shift type diffraction grating transfer mask, and the transfer mask is expensive. there were. Since a large number of semiconductor lasers having different oscillation wavelengths are used in a multiplex optical transmission system, a large number of transfer masks having different diffraction grating pitches are required, and there has been a problem with the problem of cost reduction.

A first object of the present invention is to provide a method of manufacturing a phase shift type diffraction grating transfer mask excellent in single mode selectivity with good reproducibility and at low cost. Also,
A second object of the present invention is to provide a semiconductor laser excellent in single mode selectivity at low cost by using the diffraction grating transfer mask manufactured by the present invention. A third object of the present invention is to provide an optical module mounting the semiconductor laser of the present invention at low cost. A fourth object of the present invention is to provide an inexpensive optical application system such as an optical transmission system or an optical information processing system equipped with the semiconductor laser of the present invention.

[0006]

Means for solving the problems of the prior art are described below. An ordinary distributed feedback semiconductor laser uses a diffraction grating having a uniform period. This is easily obtained by an interference exposure method using a laser beam. The present invention is characterized in that an interference exposure method using this laser light is used for a method of manufacturing a phase shift type diffraction grating transfer mask.

After a diffraction grating having a uniform period is formed on the glass substrate of the transfer mask, the phase shift type diffraction grating transfer mask can be manufactured by a simple process by inverting the diffraction grating phase in an arbitrary region. This can reduce the cost.

The first object of the present invention is to provide a method of manufacturing a phase shift type diffraction grating transfer mask, in which a first light shielding layer is formed on a quartz glass substrate, and a photoresist pattern formed by laser beam interference exposure. Processing the first light-shielding layer to form a first diffraction grating transfer mask pattern, forming a quartz glass groove using the transfer mask pattern as a mask, and covering a predetermined region of the surface with a photoresist pattern And forming a second diffraction grating transfer mask pattern comprising a second light-shielding layer in the quartz glass groove by removing the first diffraction grating transfer mask pattern in an uncovered region. This is achieved by using a method of manufacturing a diffraction grating.

The second object of the present invention is attained by manufacturing a semiconductor laser having a diffraction grating manufactured by using the above manufacturing method. Further, the third object of the present invention is achieved by manufacturing an optical module on which the above-described semiconductor laser is mounted. The fourth object of the present invention is attained by configuring an optical application system equipped with the semiconductor laser.

A feature of the present invention is that a phase shift type diffraction grating transfer mask can be provided at low cost by the technique of a photoresist pattern formed by ordinary laser beam interference exposure. In particular, for a demand for controlling and supplying a semiconductor laser having an oscillation wavelength subdivided by wavelength division multiplexing communication for optical transmission, application of an inexpensive phase shift type diffraction grating transfer mask by this method is effective.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 First, a first embodiment will be described in detail with reference to FIG. Lamination of Ti and Au (thicknesses of 10 nm and 3 respectively)
A photoresist is spin-coated to a thickness of 100 nm on a quartz glass substrate 1 having a first light-shielding layer 2 of 0 nm). Next, Ar ion laser 4 (wavelength 364n)
Using m), interference exposure is performed at a cycle of 202 nm to obtain a photoresist pattern 3 (FIG. 1A). Au, Ti, and quartz glass are sequentially dry-etched by ion milling in which Ar ions are accelerated using the periodic photoresist pattern as a mask to form a first transfer mask pattern 5. The quartz glass groove 6 having a depth of about 50 nm from the surface may be processed by ordinary dry etching mainly using CHF ₃ gas (FIG. 1B).

Next, a normal photoresist pattern 7 is formed in a predetermined area, and a second light shielding layer 8 of Cr and Au (thicknesses 10 nm and 30 nm, respectively) is formed by vapor deposition (FIG. 1C). )). Thereafter, the first transfer mask pattern 5 exposed by being immersed in a dilute HF solution is peeled off the quartz glass, the photoresist pattern 7 is subsequently peeled off, and the second transfer mask pattern 9 and the first transfer mask pattern 5 are removed. A phase shift type diffraction grating transfer mask having a relationship in which the phase is inverted between them is obtained (FIG. 1D). FIG. 1 shows a main part of a transfer mask corresponding to one element, which is periodically arranged to constitute the whole.

In the above manufacturing process, the metal on the surface of the light-shielding layer
The reason for using u is to reduce the adhesive force in the contact transfer method so that the photoresist layer on the sample surface does not adhere to the phase shift diffraction grating transfer mask. For this purpose, the metal on the surface of the light-shielding layer may be a non-oxidizable metal such as Pt. The quartz glass groove 6 is provided to facilitate the formation of the second light-shielding transfer mask pattern 9. Further, the reason why Ti and Cr were used as the lower metals of the first and second light-shielding layers, respectively, is that the former easily melts in rare HF, the latter hardly melts, and both have strong adhesive strength. Other materials satisfying the purpose can also be used.

(Embodiment 2) Next, a second embodiment will be described in detail with reference to FIG. As in the first embodiment, an Ar ion laser 4 (wavelength 364 nm) is used on a quartz glass substrate 21 having a first light-shielding layer 2 made of a stack of Ti and Au (thicknesses 10 nm and 30 nm, respectively). A photoresist pattern is obtained by interference exposure at a cycle of 204 nm, and a first transfer mask pattern 22 is formed by ion milling (FIG. 2A). Next, a normal photoresist pattern 26 is formed on this surface in a predetermined region, and a quartz glass groove 25 having a depth of about 50 nm is processed by normal dry etching mainly using CHF ₃ gas (FIG. 2B). .

Subsequently, Cr and A, which are the second light shielding layers 27, are formed.
A stack of u (thicknesses 10 nm and 30 nm, respectively) is formed by vapor deposition (FIG. 2C). Thereafter, the first transfer mask pattern 22 exposed by being immersed in a dilute HF solution is peeled off the quartz glass, and then the photoresist pattern 2 is removed.
6 is peeled off to obtain a phase-shifting diffraction grating transfer mask having a phase inversion relationship between the second transfer mask pattern 28 and the first transfer mask pattern 22 (FIG. 2).
(D)).

In the above manufacturing steps, the step of forming the second transfer mask pattern 28 can be changed as follows. After the step of FIG. 2C, about 50 n
An m-thick photoresist is applied and lightly etched back to remove the exposed metal layer. In the first and second embodiments, the example in which the groove is formed in the quartz glass substrate is described. However, this is to simplify the manufacturing process. As another method, an insulating film is formed on the quartz glass substrate. The groove may be machined.

(Embodiment 3) Next, a third embodiment will be described in detail with reference to FIG. WSi metal layer 32 (thickness, 100
nm) on a quartz glass substrate 31 having a first light shielding layer 2 as in the first embodiment.
(Wavelength 364 nm) to obtain a photoresist pattern 33 by interference exposure at a cycle of 206 nm (FIG. 3).
(A)). Next, the metal layer 32 of WSi is processed by anisotropic dry etching mainly using SF ₆ gas, and the photoresist pattern 33 is left as it is (FIG. 3B). Subsequently, a second light-shielding layer 27 of Cr and Au (thicknesses of 10 nm and 30 nm, respectively) is formed by vapor deposition (FIG. 3C).

Thereafter, the exposed WSi metal layer 32 is formed.
And the photoresist pattern 33 are shaved by isotropic dry etching mainly using a mixed gas of CF ₄ and O ₂ , the photoresist pattern 34 is peeled off, and the second transfer mask pattern 3 is removed.
A phase shift type diffraction grating transfer mask having a relationship where the phase is inverted between the first transfer mask pattern 32 and the first transfer mask pattern 32 is obtained (FIG. 3D).

In this method, the second transfer mask pattern 3
The WSi metal layer 32 is designed to be thicker than the other metal layers in order to make it easier to fabricate 5, and the second transfer mask pattern 35 can be formed without leaving the photoresist pattern 33 as shown in this embodiment.

In this embodiment, the metal layer 32 of WSi is used. However, it is added that the material used here may be Mo, W, Si or the like which can be easily processed into a vertical sectional shape by dry etching. Au may be superimposed on the surface of the WSi metal layer 32 in order to reduce the adhesive strength with the photoresist.

As described above, it can be understood that the method of manufacturing the phase shift type diffraction grating transfer mask described in Examples 1 to 3 can be manufactured simply and easily as compared with the conventional method. As a result, the transfer mask can be produced in-house, other types corresponding to each oscillation wavelength can be arbitrarily prepared, and a semiconductor laser for multiplex communication can be supplied at low cost.

(Embodiment 4) Next, a fourth embodiment will be described in detail with reference to FIGS. This relates to a method for manufacturing a phase shift type diffraction grating transfer mask for closely transferring a diffraction grating to a sample surface by an X-ray source.

FIG. 4 shows a method of manufacturing another phase shift type diffraction grating transfer mask according to the present invention. Here, instead of a quartz glass substrate, a SiN film 41 is
A first transfer mask pattern 42 and a second transfer mask pattern 45 are formed on a substrate deposited to a thickness of nm in the same manner as in the third embodiment. These are respectively Au / Ti
And Au / Cr layers (FIG. 4A). continue,
An Au layer 46 having a thickness of about 200 nm is formed on the first and second transfer mask patterns by plating (FIG. 4B).

The Si substrate 40 immediately below the transfer mask pattern is entirely removed from the back surface by KOH chemical etching.
A mask is composed of the SiN film 41 transmitting X-rays and the light-shielding Au layer (FIG. 4C). The Si substrate 40 in an area where pattern transfer is unnecessary is left as a frame 48 for mask reinforcement.

FIG. 5 shows a procedure of manufacturing a diffraction grating on a crystal surface using a phase shift type diffraction grating transfer mask formed by the manufacturing method of the present invention. An X-ray resist layer 52 is applied on an InP crystal substrate 51, and a phase shift type diffraction grating transfer mask 53 is adhered to the X-ray resist layer 52 and irradiated with X-rays 59 (FIG.
(A)). Using the developed X-ray resist pattern 54 as a mask, the InP crystal substrate 51 is shaved with an HBr-based chemical etching solution to form a diffraction grating 55 (FIG. 5B). The cross-sectional shape of the resist pattern formed by X-ray exposure with a short wavelength is sharp.

In addition to the above, according to the gist of the present invention, a method of manufacturing a phase shift type diffraction grating transfer mask for X-ray transfer using different materials and procedures is possible. For example, Be or alumina may be used as a thin film that easily transmits X-rays, and a light shielding layer such as Au or W may be formed by dry etching without using plating. The support substrate may be other than Si. The pattern formation of the phase shift type diffraction grating may use an electron beam drawing method.

(Embodiment 5) Next, a fifth embodiment will be described in detail with reference to FIG. FIG. 6 shows a wavelength of 1.3 μm using the present invention.
This is an example in which an m 2 distributed feedback semiconductor laser is manufactured.
As shown in FIG. 6A, the n-type (100) InP substrate 1
01, an n-type InP buffer layer 1.0 μm 115 and an n-type InGaAsP lower guide layer by metal organic chemical vapor deposition
(Composition wavelength 1.10 μm) 0.05 μm, 5 cycles of multiple quantum well layer (6.0% thick 1% compression strained InGaAsP (composition wavelength 1.37 μm) well layer, 10 nm thick InGaAs
P (composition wavelength 1.10 μm) barrier layer), InGaAsP
(Composition wavelength 1.10 μm) Upper light guide layer 0.05 μm
Active layer 116 made of, and the first p-type InP clad layer 0.1.
A 1 μm 117, an undoped InGaAsP (composition wavelength: 1.15 μm) diffraction grating supply layer 0.05 μm 118, and a P-type InP cap layer 0.01 μm 119 are sequentially formed.
The emission wavelength of the multiple quantum well active layer 116 is about 1.31 μm.
It is.

Next, a photoresist pattern was formed on the crystal surface by contact exposure using the phase shift type diffraction grating transfer mask prepared by the manufacturing method of Example 1. Using this as a mask, a diffraction grating 120 whose phase is inverted at the center of the device with a period of 202 nm is formed on the entire surface of the substrate by HBr-based chemical etching as shown in FIG. 6B. Diffraction grating depth is about 8
The thickness is set to 0 nm so that the diffraction grating passes through the diffraction grating supply layer 118 and reaches the first P-type InP cladding layer 117.
Subsequently, a second P-type InP cladding layer 1.7 μm 121 and a high-concentration p-type InGaAs cap layer 0.2 μm 122 are sequentially formed by metal organic chemical vapor deposition (FIG. 6).
(C)).

Subsequently, after forming into a buried type laser structure having a width of about 1.5 μm or a ridge waveguide type laser structure having a width of about 2.2 μm, the upper electrode 123 and the lower electrode 12 are formed.
4 is formed. As shown in FIG. 6 (d), after a device having a device length of 400 μm is cut out by a cleavage step, a low reflection film 125 having a reflectance of about 1% is formed on both end surfaces of the device by a known method.

The fabricated 1.3 μm-band distributed feedback semiconductor laser device has a threshold current of 10 μm at room temperature under continuous conditions.
mA and the oscillation efficiency were 0.45 W / A. 85 ° C
Even at high temperatures, the threshold current is 25 mA, and the oscillation efficiency is
Good oscillation characteristics of 30 W / A were obtained. FIG. 6E shows a spectrum shape when a forward bias is applied below the oscillation threshold. A typical spectrum in which the oscillation dominant mode appears at the center of the stop band reflecting the phase shift type diffraction grating was obtained. Reflecting the excellent mass productivity, reproducibility, and single mode selectivity of the phase shift diffraction grating manufacturing technology according to the present invention, a stable single mode operation with a submode suppression ratio of 40 dB or more even at a high temperature of 85 ° C. is 95% This was achieved with the above high production yield. This structure can be applied not only to the 1.3 μm band, but also to a distributed feedback semiconductor laser in the 1.5 μm band and other wavelength bands.

(Embodiment 6) Next, a sixth embodiment will be described in detail with reference to FIG. FIG. 7 shows the structure of an optical transmission module in which the distributed feedback semiconductor laser 126 according to the fourth embodiment is mounted on a heat sink 127, and an optical lens 128, a photodiode 129 for monitoring the rear end face light output, and an optical fiber 130 are integrated. FIG. Under room temperature and continuous conditions, the threshold current was 10 mA and the oscillation efficiency was 0.20 W / A.
Even at a high temperature of 85 ° C., the threshold current is 25 mA,
Oscillation efficiency of 0.13 W / A and good oscillation characteristics were obtained. Also, reflecting a simple fabrication, a stable single mode operation with a sub-mode suppression ratio of 40 dB or more even at a high temperature of 85 ° C.
Achieved with a high production yield of 5% or more. In this laser, the normalized optical coupling coefficient can be set as high as 2.5 or more.
The deterioration of the oscillation characteristics due to the return light from the fiber end, which is the biggest problem in module mounting, did not occur at all.

(Embodiment 7) Next, a seventh embodiment will be described in detail with reference to FIG. FIG. 8 illustrates a trunk optical communication system using the transmission module according to the sixth embodiment. Transmission device 132
Has a transmission module 131 and a drive system 133 for driving the module 131. Module 131
From the receiving device 135 through the fiber 134
The light is detected by the light receiving unit 136 inside. According to the optical communication system according to the present embodiment, non-repeater optical transmission over 100 km can be easily realized. This is based on the fact that the chirping is significantly reduced, so that the signal degradation due to the dispersion of the fiber 134 is also significantly reduced.

[0033]

According to the present invention, a phase shift type diffraction grating transfer mask can be manufactured at low cost by using a conventional technique, and by using this, a phase shift distribution feedback semiconductor laser having excellent single mode selectivity can be manufactured at low cost. Can be realized. With the present invention,
This not only dramatically improves the productivity of an element having an arbitrary single oscillation wavelength, but also is effective in reducing the cost of an optical module and an optical application system equipped with this element.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a manufacturing process of a diffraction grating transfer mask according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a manufacturing process of a diffraction grating transfer mask according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a manufacturing process of a diffraction grating transfer mask according to a third embodiment of the present invention.

FIG. 4 is a sectional view illustrating a diffraction grating manufacturing process according to a fourth embodiment of the present invention.

FIG. 5 is a sectional view illustrating a diffraction grating manufacturing process according to a fourth embodiment of the present invention.

6A and 6B are a cross-sectional view illustrating a semiconductor laser manufacturing process according to a fifth embodiment of the present invention and a light emission characteristic diagram of the semiconductor laser.

FIG. 7 is a partial cross-sectional perspective view of an optical transmission module according to a sixth embodiment of the present invention.

FIG. 8 is a block diagram showing a model configuration of a trunk optical communication system according to a seventh embodiment of the present invention.

[Explanation of symbols]

1,2,31 ... quartz glass substrate, 2 ... first light shielding layer,
3 ... periodic photoresist pattern, 4 ... laser light,
5, 22, 32 ... first transfer mask pattern, 7, 2
6, 34: Normal photoresist pattern, 9, 28, 3
5 ... second transfer mask pattern, 27 ... second light shielding layer,
53: X-ray transfer mask, 59: X-ray, 101: n-type In
P semiconductor substrate, 115... N-type InP buffer layer, 116
... multiple quantum well active layer, 117 ... first p-type InP cladding layer, 118 ... undoped InGaAsP diffraction grating supply layer, 1
19: Multiple quantum well active layer, 120: p-type InP cap layer, 121: second p-type InP cladding layer, 122: p
Type InGaAs cap layer, 123 ... upper electrode, 124
.., Lower electrode, 125, low reflection film, 126, distributed feedback semiconductor laser, 127, heat sink, 128, optical lens, 129, photodiode, 130, optical fiber,
131: transmission module, 132: transmission device, 133:
Drive system, 134: optical fiber, 135: receiving device, 13
6 ... Light receiving unit.

Claims (8)

[Claims] A step of forming a first light-shielding layer on a quartz glass substrate, and processing the first light-shielding layer with a photoresist pattern formed by laser beam interference exposure to form a first diffraction grating transfer mask pattern. Forming a quartz glass groove using the mask pattern as a mask, covering a predetermined area of the surface with a photoresist pattern, and removing the first diffraction grating transfer mask pattern in an uncovered area. Forming a second diffraction grating transfer mask pattern comprising a second light shielding layer in the quartz glass groove. 2. A step of forming a first light-shielding layer on a quartz glass substrate, and processing the first light-shielding layer with a photoresist pattern formed by laser light interference exposure to form a first diffraction grating transfer mask pattern. A step of covering a predetermined area of the surface with a photoresist pattern, a step of forming a quartz glass groove in an uncovered area, a step of forming a second light-shielding layer on the surface, and Forming a second diffraction grating transfer mask pattern comprising a second light-shielding layer in the quartz glass groove by removing the first diffraction grating transfer mask pattern in the non-existent area. A method for manufacturing a transfer mask. 3. A step of forming a first light-shielding layer made of WSi on a quartz glass substrate, and processing the first light-shielding layer with a photoresist pattern formed by laser beam interference exposure to form a first diffraction grating transfer mask pattern. Forming a;
A step of coating a predetermined area of the surface with a photoresist pattern, a step of forming a second light-shielding layer in an uncoated area, and a step of forming a first diffraction grating transfer mask pattern made of WSi in an uncoated area. Removing and forming a second diffraction grating transfer mask pattern made of a second light-shielding layer on the surface of the quartz glass. 4. A step of forming a thin film that transmits X-rays on a supporting substrate, a step of forming a first light-shielding layer for shielding X-rays, and a photoresist pattern formed by laser beam interference exposure. Processing a first light-shielding layer to form a first diffraction grating transfer mask pattern, covering a predetermined region of the surface with a photoresist pattern, and shielding X-rays in uncovered regions. A step of forming a second light-shielding layer, and a step of removing a first diffraction-grating transfer mask pattern in an uncovered area to form a second diffraction-grating transfer mask pattern including a second light-shielding layer. A method for manufacturing a phase shift type diffraction grating transfer mask, comprising: 5. The method according to claim 1, wherein at least one of the upper surfaces of the first diffraction grating transfer mask pattern and the second diffraction grating transfer mask pattern is made of a noble metal.
A manufacturing method of the phase shift type diffraction grating transfer mask described in the above. 6. A semiconductor laser manufactured using a phase shift type diffraction grating transfer mask manufactured by using the manufacturing method according to claim 1. 7. An optical module comprising the semiconductor laser according to claim 6. 8. An optical application system comprising the semiconductor laser according to claim 6.