Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state
Reexamination Certificate
1997-09-15
2001-05-01
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
C438S267000, C438S289000, C438S293000
Reexamination Certificate
active
06224667
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for fabricating a semiconductor photonic integrated circuit, especially to an improved method of a MOVPE (Metalorganic Vapor Phase Epitaxy) for performing epitaxial growth.
BACKGROUND OF THE INVENTION
Recently, in semiconductor fabrication technology, growth preventing masks are arranged on both sides of a stripe-shaped aperture, and a semiconductor layer is selectively epitaxial-grown on the aperture by MOVPE (Metalorganic Vapor Phase Epitaxy), which is called selective MOVPE. By this technology, a light waveguide device can be formed without an etching technique, therefore the fabrication can be simplified and the yield gets better. When the selective MOVPE technology is applied to epitaxial growth of a quantum well structure of III-V family of compound semiconductor, diffusion of growth species (mainly III family of organic metal material) in vapor phase depends on the width of masks by which the solid phase composition of the growth species varies, and the growth velocity depends on the width of the mask by which the width of the quantum well structure layer varies. Based on the synergistic effect of the above mentioned theory, bandgap energy (transmission energy in the first energy level between valence electron band and conduction band) on the same substrate can be changed by a single MOVPE growth process using a mask with different width partially. This kind of technology is good for fabrication of a semiconductor photonic integrated circuit which is required monolithic integration of optical function devices having different bandgap energy. The inventor has proposed an integrated light source and a tunable DBR (Distributed Bragg Reflection) laser each of which is fabricated by monolithic integration of an electro absorption type of optical modulator and a distributed feedback laser.
The solid phase composition and the thickness of the grown layer would be varied in response to the difference of width of the mask, even if the growth conditions are the same. This means that the thickness of the selectively grown layer varies when the mask is changed in width for control of bandgap energy, even if it is not preferable.
Practically, such a quantum well structure layer is sandwiched with doped clay layers, and current is injected or electric field is applied to the well structure for providing optical function with the well layer. In this processing, there is disadvantage in that electric characteristics, such as device resistance and reverse breakdown voltage, are changing in response to the width variation of the mask and, therefore, important parameters for reliability of the optical functional device cannot be fixed. If the thicknesses of layers are not even on each portion of the substrate, that may cause the quality of photolithography processing to deteriorate.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an improved method for fabricating a semiconductor photonic integrated circuit by which stable electrical characteristics can be provided.
Another object of the invention is to provide an improved method for fabricating a semiconductor photonic integrated circuit by which photolithography processing can be carried out precisely.
According to the invention, a method for fabricating a semiconductor photonic integrated circuit, comprises the steps of:
providing a growth preventing mask on a semiconductor substrate, the growth preventing mask being shaped with a first portion of a first width and a second portion of a second width wider than the first width, the first and second portions having a non-masking stripe aperture extending through the second portion to nearly edge of the first portion;
selectively growing a light waveguide layer on the non-masking stripe aperture of the semiconductor substrate by epitaxial growth technique using a low growth pressure, in which a thickness ratio d/do of the light waveguide layer to the second width of the growth preventing mask is smaller than 1.2;
increasing a growth pressure above the low growth pressure, such that the thickness ratio d/do is greater than 1.2;
selectively growing a multiple quantum well structure layer on the light waveguide layer by epitaxial growth techniques using a high growth pressure, in which a thickness ratio d/do of the multiple quantum well structure layer to the second width of the growth preventing mask is greater than 1.2;
decreasing the growth pressure below the high growth pressure, such that the thickness ratio d/do is smaller than 1.2; and
selectively growing a clad layer on the multiple quantum well structure layer by epitaxial ground technique using a low growth pressure, in which a thickness ratio d/do of the clad layer to the second width of the growth preventing mask is smaller than 1.2;
wherein the light waveguide layer-growing step, the growth pressure-increasing step, the multiple quantum well structure pressure-decreasing step, and the clad layer-growing step are successively carried out in one MOVPE (Metalorganic Vapor Phase Epitaxy) process.
In the fabricating method as specified above, the thickness ratio is defined “normalized thickness” in the art, and “the low growth pressure” is a pressure in which the normalized thickness d/do of a selectively grown layer to a growth preventing mask width W is smaller than 1.2, while “the high growth pressure” is a pressure in which the normalized thickness d/do of a selectively grown layer to a growth preventing mask width W is greater than 1.2.
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T. Kato et al., “Novel MQW DFB Laser Diode/Modulator Intergrated Light Source Using Bandgap Energy Control Epitaxial Growth Technique”, 17th European Conference on Optical Communication/Integrated Optics and Optical Fiber Communication, Paris, France, 1991.
S. Takano, et al., “1.55&mgr;m Wavelength-Tunable MQW-DBR-LDs Employing Bandgap Energy Control In All Selective MOVPE Growth”, 18th European Conference on Optical Communication, Berlin, Germany, 1992.
G. Coudenys, et al., “Lateral Bandgap Engineering for InP-Based Photonic Integrated Circuits,” Fourth Annual Conference on Indium Phosphide and Related Materials, Apr. 1992, pp. 202-205.
Sasaki, et al., “Selective MOVPE Growth and Its Application to Semiconductor Photonic Integrated Circuits,” Electronics and Communications in Japan, Part II: Electronics, vol. 76, No. 4, Apr. 1993, pp. 1-11.
IBM Technical Disclosure Bull 34(5), Oct. 1991.
Foley & Lardner
Kunemund Robert
NEC Corporation
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