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  Semiconductor laser device and method of manufacturing the sameUSPTO Application #: 20080013582Title: Semiconductor laser device and method of manufacturing the same Abstract: A method of manufacturing semiconductor laser device capable of reducing κL, with manufacturing restrictions satisfied, is provided. In a distributed-feedback or distributed-reflective semiconductor laser device, immediately before burying regrowth of a diffraction grating, halogen-based gas is introduced to a reactor, and etching is performed on the diffraction grating so that each side wall has at least two or more crystal faces and a ratio of length of an upper side in a waveguide direction to a bottom side parallel to a (100) surface is 0 to 0.3. And, a reactive product formed on side surfaces of the diffraction grating and in trench portions between stripes of the diffraction grating at an increase of temperature for regrowth is removed. Therefore, the diffraction grating with reduced height and a sine wave shape is obtained, thereby κL of the device is reduced. Thus, an oscillation threshold and optical output efficiency can be improved. (end of abstract) Agent: Mcdermott Will & Emery LLP - Washington, DC, US Inventors: Kaoru Okamoto, Ryu Washino, Kazuhiro Komatsu, Yasushi Sakuma USPTO Applicaton #: 20080013582 - Class: 372050110 (USPTO) Related Patent Categories: Coherent Light Generators, Particular Active Media, Semiconductor, Injection, Monolithic Integrated, With Diffraction Grating (bragg Reflector) The Patent Description & Claims data below is from USPTO Patent Application 20080013582. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application claims priority from Japanese patent application No. JP 2006-122777 filed on Apr. 27, 2006, the content of which is hereby incorporated by reference into this application. TECHNICAL FIELD OF THE INVENTION [0002] The present invention relates to semiconductor laser devices and manufacturing techniques thereof, and particularly relates to techniques effective when applied to distributed-feedback or distributed-reflective semiconductor laser devices for optical transmission apparatuses or information storage apparatuses, and a method of manufacturing thereof. BACKGROUND OF THE INVENTION [0003] For example, as a light source for optical transmission apparatus or information storage apparatus, a distributed feedback (DFB) laser using a refractive-index-modulation diffraction grating, which has narrow spectrum and allows single mode oscillation, is mainly adopted. In a DFB laser, light output and modulation characteristic significantly change according to .kappa.L, product of a coupling coefficient .kappa. of light diffracted in a waveguide direction and an oscillator length L. Therefore, in designing and manufacturing laser devices, it is important to set .kappa.L at a desired value. Here, the coupling coefficient .kappa. is determined by height of the diffraction grating, distance from an active layer, and difference in refractive index between a diffraction grating layer and a buried layer (clad layer). In particular, the coupling coefficient .kappa. largely depends on the height of the diffraction grating. [0004] A conventional process of forming a diffraction grating is described below. On an n-InP substrate, an n-InP first clad layer, an n-InGaAlAs first optical guide layer, an InGaAlAs active layer, a p-InGaAlAs second optical guide layer, a p-InP spacer layer, a p-InGaAsP diffraction grating layer, and a p-InP cap layer are formed through crystal growth, such as metal organic chemical vapor deposition (MOCVD). In order to increase a carrier confinement effect, the InGaAlAs active layer includes a multiple quantum well (MQW) having an InGaAlAs barrier layer and InGaAlAs well layer laminated in a periodic structure. [0005] Furthermore, on the p-InP cap layer, an insulating film, such as a silicon dioxide (SiO.sub.2) film or a silicon nitride (SiN) film, is formed. Then, through photolithography and interference exposure or electron beam (EB) exposure, a striped pattern is formed in a direction perpendicular to a waveguide. The insulating film is removed through dry etching with fluorinated gas or wet etching with hydrofluoric acid solution, using the resist pattern as a mask. Then, the resist pattern is removed with solvent. Using the insulating film as a mask, the p-InP cap layer and the p-InGaAsP diffraction grating layer are removed through dry etching or wet etching to form a rectangular diffraction grating. Next, a p-InP second clad layer regrowth is performed through MOCVD or the like. SUMMARY OF THE INVENTION [0006] Meanwhile, in recent years, achievement of lasers with high outputs staring at its uncooled operation has been desired not only in semiconductor laser devices for information systems but also in those for optical transmission. Lengthening an oscillator and reducing .kappa. in association with the lengthening are took up as technical problems. [0007] As has been described above, .kappa. depends on the height of the diffraction grating. Therefore, in order to reduce .kappa., the height of the diffraction grating has to be lowered. However, if the height of the diffraction grating is too low, large variations in yield of device characteristics, caused by deterioration in etching controllability over the diffraction grating layer or loss due to thermal decomposition at increase in temperature in burying regrowth or the like, may occur. In conventional process, to avoid these problems, the height of the diffraction grating after etching has to be 15 nm or higher. To reduce the .kappa. with the manufacturing restrictions in the height of diffraction grating satisfied, the height of the diffraction grating after etching must be 20 nm to 30 nm which includes sufficient margin in process controllability, and must be lowered immediately before burying regrowth. In one means for this purpose, the height can be lowered by actively using thermal decomposition at increase of temperature. In this case, however, mass transport of the thermally-decomposed layer to trench portions of the diffraction grating produces reaction product. The product is low in crystallinity and may cause deterioration of laser device characteristics. [0008] A theoretical value of .kappa.L is varied depending on whether the diffraction grating has a rectangular shape or a sine wave shape, and value of .kappa. in a diffraction grating having a sine wave shape can be reduced. FIG. 5 depicts simulation results of a relation between the height of the diffraction grating and .kappa.L depending on a difference in shape of the diffraction grating. Note that .kappa.L is relative value. It is assumed herein that a composition wavelength (.lamda.) of the InGaAsP diffraction grating layer is 1.15 .mu.m, and the oscillator length (L) is 500 .mu.m. A primary component in a result of Fourier transform of a cross-section shape of the diffraction grating in the waveguide direction considered as a periodic waveform affects the magnitude of .kappa.L. Therefore, such a phenomenon as depicted in the drawing occurs. According to this result, by forming the diffraction grating in a sine wave shape, .kappa.L can be reduced by 21.5% (.pi./4) compared with the case of a rectangular shape. Usually, a diffraction grating is formed through dry etching or wet etching. In this case, a shape of the diffraction grating become rectangular, and it is difficult to form a sine wave shape through etching. This sine wave shape can be formed through thermal decomposition at increase of temperature in burying regrowth. In this case, however, the above-mentioned problem occurs due to mass transport. [0009] As has been described above, in the conventional semiconductor laser device manufacturing technology, the lower limit of height of the diffraction grating is determined by the restrictions in the diffraction grating forming process, thereby it is difficult to reduce the value of .kappa.. Also, a reactive product is formed on side surfaces and the trench portions of the diffraction grating in a process of an increase of temperature in burying regrowth of the diffraction grating, and causes deterioration of oscillation threshold and optical output efficiency of the device. [0010] An object of the present invention is to overcome the above-described problems, and to provide a semiconductor laser device manufacturing technology capable of reducing .kappa.L with manufacturing restrictions satisfied. [0011] The above and other objects as well as novel features of the present invention will be readily apparent from the description of the specification and accompanying drawings. [0012] The outline of a representative one of the inventions to be disclosed in the present application is briefly explained as below. [0013] The present invention is applied to a distributed-feedback or distributed-reflective semiconductor laser device having diffraction gratings formed in stripes perpendicular to a waveguide direction, and characterized by that each diffraction grating has side walls each having at least two or more crystal faces, and a ratio of length of an upper side to a bottom side of the diffraction grating, in a waveguide direction parallel to a (100) surface, is 0 to 0.3. [0014] Furthermore, the diffraction grating is formed of III-V family compound semiconductor layer including at least one of In, Ga, As, and P elements. [0015] Still further, immediately before burying regrowth of the diffraction grating, halogen-based gas is introduced to a reactor, and etching process is performed to the diffraction grating to have the above-described shape. And a reactive product, formed on side surfaces of the diffraction grating and in trench portions between stripes at an increase of temperature in regrowth, is removed. [0016] The effects achieved by a representative one of the inventions to be disclosed in the present application is briefly explained as below. [0017] According to the present invention, in the semiconductor laser device having the diffraction grating, a value of .kappa.L can be reduced with manufacturing restrictions satisfied. Furthermore, with an effect that the reactive product deteriorated in crystallinity on a regrowth surface is removed, an improvement of the optical output efficiency of the semiconductor laser device and a reduction of oscillation threshold can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS [0018] FIG. 1 is a drawing describing a diffraction grating having a sine wave shape in a semiconductor laser device according to a preferred embodiment of the present invention. [0019] FIG. 2 is a drawing describing a relation between a thickness of diffraction grating layer and L.sub.1/L.sub.0 corresponding to an etching method in the semiconductor laser device according to a preferred embodiment of the present invention. Continue reading... Full patent description for Semiconductor laser device and method of manufacturing the same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Semiconductor laser device and method of manufacturing the same patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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