Adhesive bonding and miscellaneous chemical manufacture – Delaminating processes adapted for specified product – Delaminating in preparation for post processing recycling step
Patent
1992-02-07
1993-06-22
Powell, William A.
Adhesive bonding and miscellaneous chemical manufacture
Delaminating processes adapted for specified product
Delaminating in preparation for post processing recycling step
156656, 156657, 1566591, 156662, 430321, 430323, H01L 21306, B44C 122, C03C 1500, C23F 100
Patent
active
052214290
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates particularly to a method of manufacturing a phase-shifted diffraction grating having a discontinuous phase portion.
BACKGROUND ART
A conventional method of manufacturing a diffraction grating using a two-beam interference method is mainly employed in a DFB (Distributed FeedBack) laser to be described later.
The DFB laser uses a diffraction grating (periodical projection structure) formed in a waveguide as a reflection mechanism for a laser beam. The DFB laser oscillates in a single mode at or near the Bragg wavelength defined by the period of the diffraction grating. In addition, when the DFB laser is to be modulated at a high speed, since it is operated in the single mode, it is expected as a light source of a long-distance large-capacity optical communication system using optical fibers.
When a DFB laser having a waveguide on which a uniform diffraction grating is formed has both end faces having a small reflectance, since the DFB laser easily oscillates at two wavelengths one of which is shorter than the Bragg wavelength and the other of which is longer than the Bragg wavelength, the DFB laser cannot easily oscillate in a single longitudinal mode. Therefore, there is proposed a .lambda./4-shifted DFB laser which oscillates at a single mode such that the phase of a diffraction grating is shifted by .lambda./4 (a phase amount of .pi./2) in the central portion of a laser resonator. In addition, there is proposed a DFB laser which oscillates at a wavelength equal to the Bragg wavelength by a two-beam interference method using positive and negative photoresists (this DFB laser is described in, e.g., Electronics Letters Vol. 20, NO 24, 1984, PP 1,008-1,010). In specific element performance, it is reported that a high production yield can be obtained by using a .lambda./8-shifted diffraction grating having a shift amount half that of the .lambda./4-shifted diffraction grating (this is described in, e.g., the Institute of Electronics and Communication Engineers of Japan, Technical Report OQE86-150).
FIGS. 1A to 1F show a method of manufacturing a diffraction grating using positive and negative photoresists.
As shown in FIG. 1A, a negative photoresist 22 is formed on an InP substrate 21. An intermediate layer 23 is formed on the negative photoresist 22. A positive photoresist 24 is formed on the intermediate layer 23. As shown in FIG. 1B, the positive photoresist 24 is patterned. Thereafter, the intermediate layer 23 and the negative photoresist 22 are etched using the positive photoresist 24 as a mask. As shown in FIG. 1C, the intermediate layer 23 and the positive photoresist 24 are removed. Thereafter, a positive photoresist 25 is formed on the entire surface of the resultant structure. A two-beam interference exposure operation is performed using first and second laser beams 26A and 26B. As shown in FIG. 1D, the positive photoresist 25 is developed. As shown in FIG. 1E, after the InP substrate 21 is etched using a hydrogen bromide-based etchant, the positive photoresist 25 is removed. A positive photoresist (protection film) 27 is formed on only a portion where the InP substrate 21 is etched. Thereafter, the negative photoresist 22 is developed. As shown in FIG. 1F, the InP substrate 21 is etched using a hydrogen bromide-based etchant, and the negative and positive photoresists 22 and 27 are removed, thereby obtaining a phase-shifted diffraction grating.
In the method using the negative and positive photoresists, the negative and positive photoresists are simultaneously used. For this reason, the thicknesses of the photoresists and an exposure time of two-beam interference cannot easily be adjusted. The shapes of diffraction gratings formed in the regions of the negative and positive photoresists may be different from each other. In addition, when a shift amount of the phase of the diffraction grating is adjusted, the shift amount cannot help being set in an amount of .lambda./4 (i.e., a phase amount of .pi./2).
As a method of obtaining an arbitrary shift amo
REFERENCES:
patent: 4895790 (1990-01-01), Swanson et al.
patent: 4988404 (1991-01-01), Aoyagi
patent: 5024726 (1991-06-01), Fujiwara
Shirasaki et al., Fujitsu Laboratories Ltd., Technical Report OQE85-60, ".lambda./4-Shifted DFB-LD Corrugation Formed by a Novel Spatial Phase Modulating Mask", Institute of Electronics and Communication Engineers of Japan.
Yamaguchi et al., Photoelectronic Laboratory of NEC Corporation, "Manufacture of .lambda./4-Shifted Diffraction Grating Using a Phase Shift Film," Japan Society of Applied Physics, lecture No. 29P-T-8 (1986).
Utaka et al., ".lambda./4-Shifted InGaAsP/InP DFB Lasers by Simultaneous Holographic Exposure of Positive and Negative Photoresists," Electronic Letters, vol. 20, No. 24, pp. 1008-1010, Nov. 22, 1984.
Kabushiki Kaisha Toshiba
Powell William A.
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