US20010022681A1 - Light Modulator - Google Patents
Light Modulator Download PDFInfo
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- US20010022681A1 US20010022681A1 US09/839,120 US83912001A US2001022681A1 US 20010022681 A1 US20010022681 A1 US 20010022681A1 US 83912001 A US83912001 A US 83912001A US 2001022681 A1 US2001022681 A1 US 2001022681A1
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- insulating film
- bonding pad
- section
- layer
- mesa
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction
- G02F1/025—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements with at least one potential jump barrier, e.g. PN, PIN junction in an optical waveguide structure
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
- G02F2201/06—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 integrated waveguide
- G02F2201/066—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 integrated waveguide channel; buried
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
- G02F2201/12—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode
- G02F2201/122—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 electrode having a particular pattern
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- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
- Semiconductor Lasers (AREA)
Abstract
A light modulator having a reduced parasitic static capacitance includes a semiconductor substrate having a mesa section and a bonding pad forming section formed thereon. A primary insulating film is formed on the substrate so as to continuously cover the mesa section and the bonding pad forming section. After a mask has been formed on a portion of the primary insulating film that is above the bonding pad forming section, the remaining portion of the primary insulating film is etched off, followed by removal of the mask. After the removal of the mask, a secondary insulating film is formed so as to continuously cover that portion of the primary insulating film above the bonding pad forming section and the mesa section so that a relatively thick insulating layer can be formed only above the bonding pad forming section.
Description
- 1. Field of the Invention
- The present invention generally relates to a light modulator for modulating a laser beam and, more particularly, to a high speed light modulator of a kind used in a high speed optical fiber communication system. The present invention also relates to a method of manufacturing such light modulator.
- 2. Description of the Prior Art
- In the high speed optical fiber communication system, a considerable amount of data are transmitted by the use of semiconductor laser beams and optical fibers. In order to cope with this feature, the semiconductor laser beams are required to be modulated at a high speed. With the conventional direct modulation system in which the electric current injected to a single-mode semiconductor laser is modulated to provide the modulated output laser beam, change in wavelength resulting from change in density of injected carriers (i.e., wavelength chirping) is so substantial that the conventional direct modulation system cannot be used in high-speed modulation of 10 Gbps or higher.
- In view of the foregoing, as an alternative to the direct modulation system, the external modulation system has come to be the cynosure of those concerned, in which a light modulator having a low chirping and disposed externally of a semiconductor laser is utilized to modulate the laser beam while the current injected to the semiconductor laser is fixed. The combined modulator and laser assembly in which a light modulator, a single-mode semiconductor laser and an isolator separating the light modulator and the semiconductor laser from each other are integrated together on a single chip is shown by60 in FIG. 7. Since no circuit is required between the modulator and the laser, the combined modulator and
laser assembly 60 shown therein has a high practical utility and is extremely important as a key device for optical fiber communication of a large amount of data. - The light modulator will now be described. As shown in FIG. 8A, the
light modulator 70 includes anInP semiconductor substrate 52 on which asemiconductor mesa layer 56 of a predetermined width containing alight absorption layer 51 and a semiconductorbonding pad layer 55 are formed. The laser beam inputted to thelight modulator 70 is modulated by thelight absorption layer 51. More specifically, by applying a voltage to thebonding pad electrode 55 a, an electric field is applied from anelectrode 54, covering thesemiconductor mesa layer 56, to thelight absorbing layer 51, and by shifting the absorption wavelength of thelight absorbing layer 51, the input laser beam is modulated. - As shown in FIG. 8B, a
groove 57 is formed between thesemiconductor mesa layer 56 and the semiconductorbonding pad layer 55 for separating thesemiconductor layers semiconductor mesa layer 56, the semiconductorbonding pad layer 55 and thegroove 57 has their respective surfaces covered by a continuousinsulating film 53. Thebonding pad electrode 55 a and theelectrode 54 are formed by a metallic film continuously covering theinsulating film 53 while theelectrode 54 is held in ohmic contact with thesemiconductor mesa layer 56 through an opening defined in theinsulating film 53. - The conventional method of manufacturing the conventional light modulator is shown in FIGS. 9A to9C. Referring first to FIG. 9A, a predetermined crystalline layer is epitaxially grown on the
InP substrate 52 to form thesemiconductor mesa layer 56 of the predetermined width including thelight absorption layer 51, thegroove 57 and the semiconductorbonding pad layer 55. Then, as shown in FIG. 9B, theinsulating film 53 of SiO2 having a film thickness of about 4000 Åis formed so as to cover the entire surface of theInP substrate 52. After a window for the ohmic contact has been formed in an upper surface of thesemiconductor mesa layer 54 including thelight absorption layer 51, the metallic film is formed at a predetermined location as shown in FIG. 9C to complete thebonding pad electrode 55 a and theelectrode 54. - In order for the light modulator to be used for high-speed modulation, it is necessary to reduce the static capacitance (hereinafter referred to as a “parasitic static capacitance”) formed between surface electrodes (the
bonding pad electrode 55 a and the electrode 54) and a rear surface electrode. The parasitic static capacitance of the light modulator is expressed by the sum of the parasitic static capacitance of themesa layer 56 plus the parasitic static capacitance of thebonding pad layer 55. In order to reduce the parasitic static capacitance of the light modulator, attempts have currently been made to minimize the surface area of each of themesa layer 54 and thebonding pad layer 55 by forming thegroove 57 therebetween. - It has, however, been found that considering the chirping of light that is propagated by the
light absorption layer 51, the width of themesa layer 56 can only be reduced to a certain limited dimension. Also, considering the bonding surface area of the bonding wire, the size of thebonding pad layer 55 is limited to about 50×50 μm. Thus, the approach to reduce the surface area of themesa layer 56 and thebonding pad layer 55 in an attempt to reduce the parasitic static capacitance is limited and, therefore, a sufficiently high-speed modulation characteristic has been difficult to accomplish. - The present invention has therefore been developed in view of the foregoing problems and is intended to provide an improved light modulator capable of accomplishing a high-speed light modulation in which the parasitic static capacitance is reduced and also to provide an improved method of manufacturing such light modulator.
- The light modulator of the present invention is such that the parasitic static capacitance of the bonding pad section has been reduced to substantially eliminate the above discussed problems, and is therefore effective to achieve the high-speed modulation. More specifically, the light modulator of the present invention includes a semiconductor substrate having first and second surfaces opposite to each other with a grounding conductor formed on the second surface thereof. A mesa section of a predetermined width laminated with a semiconductor layer including a light absorption layer and a bonding pad forming section adjacent the mesa section are formed on the semiconductor substrate. An insulating layer continuing from the mesa section to the bonding pad section is formed with an opening defined in a portion of the insulating film above the mesa section, and an electrode contacting an upper surface of the mesa section through the opening and extending to the bonding pad forming section is formed over the insulating layer. Accordance with the present invention, the light modulator is featured in that a portion of the insulating layer the bonding pad forming section has a thickness greater than that of the remaining portion of the insulating layer to reduce the parasitic static capacitance of the bonding pad section.
- The portion of the insulating layer immediately above the bonding pad forming section comprises a multi layered structure containing at least insulating films laminated one above other. The remaining portion of the insulating layer comprises a single or multi layered structure containing a insulating films, in which a number of the insulating film is less than that of the bonding pad forming section.
- The insulating films are two insulating films, one of the two insulating films is made of SiO2 and the other is made of SiN.
- The upper-layer insulating film of remaining portion of the insulating layer is same as the 2nd upper-layer insulating film of the bonding pad forming section.
- The first method of manufacturing the light modulator according to the present invention is such that the parasitic static capacitance of the bonding pad section has been reduced to substantially eliminate the above discussed problems. More specifically, this first method is utilized to manufacture the light modulator which includes a semiconductor substrate having first and second surfaces opposite to each other with a grounding conductor formed on the second surface thereof, which substrate is formed with a mesa section of a predetermined width, laminated with a semiconductor layer including a light absorption layer, and a bonding pad forming section adjacent the mesa section, an insulating layer continuing from the mesa section to the bonding pad section and formed with an opening defined in a portion of the insulating layer above the mesa section, and a one-piece electrode formed over the insulating film and contacting an upper surface of the mesa section through the opening, the one-piece electrode forming a bonding pad electrode. This first method is featured in that it comprises forming a primary insulating film continuing from the mesa section to the bonding pad forming section, forming a mask so as to cover a portion of the primary insulating film formed above the bonding pad forming section, etching the primary insulating film to remove another portion of the primary insulating film other than that portion of the primary insulating film above the bonding pad forming section, removing the mask forming a secondary insulating film continuing from that portion of the primary insulating film above the bonding pad forming section and the mesa section and completing the insulating whereby that portion of the insulating layer above the bonding pad forming section has a thickness greater than that of the remaining portion of the insulating layer to reduce the parasitic static capacitance of the bonding pad section.
- The second method of manufacturing the light modulator according to the present invention is such that the parasitic static capacitance of the bonding pad section has been reduced to substantially eliminate the above discussed problems. More specifically, this second method is utilized to manufacture the light modulator which includes a semiconductor substrate having first and second surfaces opposite to each other with a grounding conductor formed on the second surface thereof, which substrate is formed with a mesa section of a predetermined width, laminated with a semiconductor layer including a light absorption layer, and a bonding pad forming section adjacent the mesa section, an insulating layer continuing from the mesa section to the bonding pad section and formed with an opening defined in a portion of the insulating layer above the mesa section, and a one-piece electrode formed over the insulating film and contacting an upper surface of the mesa section through the opening, the one-piece electrode forming a bonding pad electrode. This second method is featured in that it comprises forming a primary insulating film continuing from the mesa section to the bonding pad forming section, forming a mask so as to cover a portion of the primary insulating film other than a portion of the primary insulating film that is formed above the bonding pad forming section, forming a secondary insulating film over the mask and that portion of the primary insulating film above the bonding pad forming section, removing the mask to allow that portion of the secondary insulating film above the bonding pad section to continue to that portion of the primary insulating film above the mesa section to thereby complete the insulating layer so that that portion of the insulating layer above the bonding pad forming section has a thickness greater than that of the remaining portion of the insulating layer to reduce the parasitic static capacitance of the bonding pad section.
- The third method of manufacturing the light modulator according to the present invention is such that the parasitic static capacitance of the bonding pad section has been reduced to substantially eliminate the above discussed problems. More specifically, this third method is utilized to manufacture the light modulator which includes a semiconductor substrate having first and second surfaces opposite to each other with a grounding conductor formed on the second surface thereof, which substrate is formed with a mesa section of a predetermined width, laminated with a semiconductor layer including a light absorption layer, and a bonding pad forming section adjacent the mesa section, an insulating layer continuing from the mesa section to the bonding pad section and formed with an opening defined in a portion of the insulating layer above the mesa section, and a one-piece electrode formed over the insulating layer and contacting an upper surface of the mesa section through the opening, the one-piece electrode forming a bonding pad electrode. This third method is featured in that it comprises a primary insulating film forming step of forming a primary insulating film continuing from the mesa section to the bonding pad forming section, forming a mask so as to cover a portion of the primary insulating film above the bonding pad forming section, etching another portion of the primary insulating film other than that portion of the primary insulating film above the bonding pad forming section to a predetermined thickness, removing the mask so as to leave the insulating film having a thick film portion above the bonding pad forming section and a thin film portion above the mesa section, the thick and thin film portion being continued together, and completing the insulating layer whereby that portion of the insulating layer above the bonding pad forming section has a thickness greater than the remaining portion of the insulating layer to thereby reduce the parasitic static capacitance of the bonding pad section.
- The primary insulating film forming step of the third method of the present invention discussed above may include forming an under-layer insulating film continuing from the mesa section to the bonding pad forming section, forming over the under-layer insulating film an intermediate-layer insulating film of a material different from that of the under-layer insulating film, and forming over the intermediate-layer insulating film an upper-layer insulating film of the same material as that of the under-layer insulating film. In such case, the etching step may be carried out for selectively etching only a portion the upper-layer other than that formed above the bonding pad section, and completing the insulating layer.
- Preferably, in any of the first to third method, the insulating film is made of SiO2 or SiN.
- In the practice of the third method, one of the primary insulating film and the secondary insulating film is preferably made of SiO2 while the other thereof is preferably made of SiN.
- Also, in the practice of any one of the first to third methods of the present invention, the insulating film is preferably formed by the use of a CVD technique, a sputtering technique or a vacuum evaporation technique.
- FIG. 1A is a fragmentary perspective view of a light modulator according to a first preferred embodiment of the present invention;
- FIG. 1B is a cross-sectional view taken along the line IB-IB in FIG. 1A;
- FIGS. 2A to2D are respective views similar to FIG. 1B, showing a method of manufacture of the light modulator according to the first embodiment of the present invention;
- FIGS. 3A to3D are respective views similar to FIG. 1B, showing the modified method of manufacture of the light modulator according to the first embodiment of the present invention;
- FIGS. 4A to4D are respective views similar to FIG. 1B, showing the further modified method of manufacture of the light modulator according to the first embodiment of the present invention;
- FIG. 5A is a fragmentary perspective view of a light modulator according to a second preferred embodiment of the present invention;
- FIG. 5B is a cross-sectional view taken along the line VB-VB in FIG. 5A;
- FIGS. 6A to6D are respective views similar to FIG. 5B, showing the method of manufacture of the light modulator according to the second embodiment of the present invention;
- FIG. 7 is a perspective view of the prior art combined modulator and laser assembly;
- FIG. 8A is a perspective view of the prior art modulator;
- FIG. 8B is a cross-sectional view taken along the line VIIIB-VIIIB in FIG. 8A; and
- FIGS. 9A to9C are view similar to FIG. 8B, showing the prior art method of manufacturing the prior art light modulator.
- A light modulator according to a first embodiment of the present invention is shown by50 in FIGS. 1A to 4D. Referring particularly to FIGS. 1A and 1B, the
light modulator 50 includes amesa section 9 and a bondingpad forming section 6 both protruding outwardly from anInP semiconductor substrate 2. More specifically, themesa section 9 is delimited by and between a pair ofparallel grooves 3 formed at a predetermined position in thesemiconductor substrate 2. The bondingpad forming section 6 is positioned on one side of one of thegrooves 3 opposite to themesa section 9 and is delimited by such one of thegrooves 3 and a generallyU-shaped groove 3 a defined in thesemiconductor substrate 2. Themesa section 9 includes anelectrode 5 formed thereon through a SiO2 insulating layer 4 and has alight absorption layer 1 embedded therein, whichlayer 1 is operable to receive and transmit a laser beam therethrough. On the other hand, the bondingpad forming section 6 includes abonding pad electrode 6 a formed thereon through a SiO2 insulating thick-layer 40 intervening between it and thebonding pad electrode 6 a. Thebonding pad electrode 6 a and theelectrode 5 form and are served respectively by different parts of a metallic layer. It is to be noted that thelight modulator 50 has a rear surface formed with arear surface electrode 10. - In the illustrated light modulator50, the insulating
layer 4 and the insulating thick-layer 40 are integral parts of a single insulating layer that are formed above themesa section 9 and above the bondingpad forming section 6, respectively. However, as best shown in FIG. 1B, a portion of the insulating layer overlaying the bondingpad forming section 6, that is, the insulating thick-layer 40 has a thickness greater than the remaining portion of the insulating layer, for example, the insulatinglayer 4 overlaying themesa section 9. In addition as discussed hereinabove, the insulatinglayer 4 and the insulating thick-layer 40 are covered by the metallic layer and a portion of the metallic layer immediately above the bondingpad forming section 6 serves as thebonding pad electrode 6 a while another portion of the metallic layer immediately above themesa section 9 serves theelectrode 5. Theelectrode 5 is held in contact with an upper surface of themesa section 9 through an opening defined in the insulatinglayer 4. - Since the insulating thick-
layer 40 is formed only immediately below thebonding pad electrode 6 a, the parasitic static capacitance between thebonding pad electrode 6 a and therear surface electrode 10 can be reduced. In detail, by increasing the thickness of thick-layer 40 around the bondingpad forming section 6 from 4000 Åto 8000 Å,the parasitic static capacitance around the bondingpad forming section 6 is half of the parasitic static capacitance around themesa section 9,becase the capacitance is inverse proportion to the thickness of the insulating layer. Also, since the insulating thick-layer 40 is formed on a relatively narrow portion of the bondingpad forming section 6, there is no possibility that thesubstrate 2 may warp. Furthermore, since that portion of the insulating layer overlaying themesa section 9 has a relatively small thickness as is the case with that in the conventional light modulator, there is no difficulty forming the opening in the insulating layer. - The method of manufacturing the
light modulator 50 of the structure discussed above will now be described with particular reference to FIGS. 2A to 2D. At the outset, as shown in FIG. 2A, after a predetermined crystalline layer has been epitaxially grown on theInP semiconductor substrate 2, a pair ofgrooves 3 are formed at a predetermined location in thesemiconductor substrate 2 so that themesa section 9 of a predetermined width having thelight absorption layer 1 can be eventually formed between thesegrooves 3. The generallyU-shaped groove 3 a continued to one of thegrooves 3 is also formed to define the bondingpad forming section 6. Then, as shown in FIG. 2B, a SiO2 insulating film 41 having a thickness of about 4000 Åis formed on thesemiconductor substrate 2 so as to overlay themesa section 9 and the bondingpad forming section 6 continuously. Thereafter, as shown in FIG. 2C, only a portion of the insulatingfilm 41 overlaying the bondingpad forming section 6 is covered by a photo-resist 7 that is utilized as a mask, followed by removal of the remaining portion of the insulatingfilm 41 other than that portion of the insulatingfilm 41 overlaying the bondingpad forming section 6. After the subsequent removal of the photo-resist 7, as shown in FIG. 2D, another SiO2 insulating film 42 having a thickness of about 4000 Åis again formed on thesemiconductor substrate 2 so as to overlay themesa section 9 and the bondingpad forming section 6 continuously. In this way, the bondingpad forming section 6 is covered by the insulating thick-layer 40 of a thickness of about 8000 Å, i.e., that portion of the insulatingfilm 41 overlapped by the insulatingfilm 42, while a portion other than the bonding pad forming section, for example, themesa section 9 is covered only by the insulatingfilm 42 of about 4000 Å. - Thus, the
bonding pad electrode 6 a and theelectrode 2 are formed immediately above the bondingpad forming section 6 and themesa section 2, respectively. More specifically, while the opening is formed in the portion of the insulating layer overlaying an upper surface of the mesa section and the metallic layer connected in part with the upper surface of the mesa section through the opening and in part overlaying the bonding pad forming section. Therear surface electrode 10 is formed in any known manner as shown in FIG. 1A, thereby completing thelight modulator 50 of the present invention. - Since as discussed above the insulating thick-
layer 40 is formed only immediately below thebonding pad electrode 6 a, the parasitic static capacitance between thebonding pad electrode 6 a and therear surface electrode 10 can be reduced. Also, since the insulating thick-layer 40 is formed on that relatively narrow portion of the bondingpad forming section 6, there is no possibility that thesubstrate 2 may warp. Furthermore, since that portion of the insulating layer overlaying themesa section 9 has a relatively small thickness as is the case with that in the conventional light modulator, there is no difficulty forming the opening in the insulating layer. - The
light modulator 50 of the present invention can also be manufactured by an alternative method which will now be described with reference to FIGS. 3A to 3D. Referring to FIG. 3A, after a predetermined crystalline layer has been epitaxially grown on theInP semiconductor substrate 2, a pair ofgrooves 3 are formed at a predetermined location in thesemiconductor substrate 2 so that themesa section 9 of a predetermined width having thelight absorption layer 1 can be eventually formed between thesegrooves 3. The generallyU-shaped groove 3 a continued to one of thegrooves 3 is also formed to define the bondingpad forming section 6. Then, as shown in FIG. 3B, a SiO2 insulating film 40 a having a thickness of about 8000 Åis formed on thesemiconductor substrate 2 so as to overlay themesa section 9 and the bondingpad forming section 6 continuously. Thereafter, as shown in FIG. 3C, only a portion of the insulatingfilm 41 overlaying the bondingpad forming section 6 is covered by a photo-resist 7 that is utilized as a mask, followed by etching of the remaining portion of the insulatingfilm 40 a other than that portion of the insulatingfilm 40 a overlaying the bondingpad forming section 6 to render that remaining portion of the insulatingfilm 40 a to have a film thickness of about 4000 Å. After the subsequent removal of the photo-resist 7, as shown in FIG. 3D, the insulating layer continuously covering the semiconductor surface including the bondingpad forming section 6 and themesa section 9 can be obtained. A portion of the insulating layer overlying the bondingpad forming section 6 and its vicinity has a film thickness of about 8000 Å(the insulating thick-film 40) while the other portion of the insulating film, for example, a portion of the insulating film overlaying the mesa section has a thickness of about 4000 Å(the insulating film 4). - Thus, the
bonding pad electrode 6 a and theelectrode 2 are formed immediately above the bondingpad forming section 6 and themesa section 2, respectively. More specifically, while the opening is formed in the portion of the insulating layer overlaying an upper surface of the mesa section and the metallic layer connected in part with the upper surface of the mesa section through the opening and in part overlaying the bonding pad forming section. Therear surface electrode 10 is formed in any known manner as shown in FIG. 1A, thereby completing thelight modulator 50 of the present invention. - Since as discussed above the insulating thick-
layer 40 is formed only immediately below thebonding pad electrode 6 a, the parasitic static capacitance between thebonding pad electrode 6 a and therear surface electrode 10 can be reduced. Also, since the insulating thick-film 40 is formed on that relatively narrow portion of the bondingpad forming section 6, there is no possibility that thesubstrate 2 may warp. Furthermore, since that portion of the insulating layer overlaying themesa section 9 has a relatively small thickness as is the case with that in the conventional light modulator, there is no difficulty forming the opening in the insulating layer. - A further modified method of manufacturing the
light modulator 50 of the present will now be described with reference to FIGS. 4A to 4D. At the outset, as shown in FIG. 4A, after a predetermined crystalline layer has been epitaxially grown on theInP semiconductor substrate 2, a pair ofgrooves 3 are formed at a predetermined location in thesemiconductor substrate 2 so that themesa section 9 of a predetermined width having thelight absorption layer 1 can be eventually formed between thesegrooves 3. The generallyU-shaped groove 3 a continued to one of thegrooves 3 is also formed to define the bondingpad forming section 6. Then, as shown in FIG. 4B, a SiO2 insulating film 41 having a thickness of about 4000 Åis formed on thesemiconductor substrate 2 so as to overlay themesa section 9 and the bondingpad forming section 6 continuously. Thereafter, as shown in FIG. 4C, only a portion of the insulatingfilm 41 other than that overlaying the bondingpad forming section 6, for example, only a portion of the insulatingfilm 41 overlaying themesa section 9 is covered by a photo-resist 7 that is utilized as a mask, followed by deposition of a SiO2 insulating film 42 of about 4000 Åin thickness so as to continuously cover themesa section 9 and the bondingpad forming section 6. Accordingly, the insulatingfilm 42 is in part formed over themask 7 and the bondingpad forming section 6 is covered by not only the insulatingfilm 41, but also the insulatingfilm 42 overlaying the insulatingfilm 41. Subsequent removal of the photo-resist 7 is accompanied by removal of that portion of the insulatingfilm 42 overlaying the photo-resist 7, allowing that portion of the insulatingfilm 41 overlaying themesa section 9 to be exposed to the outside. Consequently, as shown in FIG. 4D, the insulating layer continuously overlaying themesa section 9 and the bondingpad forming section 6 can be obtained. Since that portion of the insulatingfilm 41 overlaying the bondingpad forming section 6 is laminated with a corresponding portion of the insulatingfilm 42, that portion of the insulating layer above the bondingpad forming section 6 has a thickness of about 8000 Å(the insulating thick-layer 40), but the remaining portion of the insulating layer other than that over the bondingpad forming section 6, for example, that overlaying the mesa section has a film thickness of about 4000 Å(the insulating film 41). - Thus, the
bonding pad electrode 6 a and theelectrode 2 are formed immediately above the bondingpad forming section 6 and themesa section 2, respectively. More specifically, while the opening is formed in the portion of the insulating layer overlaying an upper surface of the mesa section and the metallic layer connected in part with the upper surface of the mesa section through the opening and in part overlaying the bonding pad forming section. Therear surface electrode 10 is formed in any known manner as shown in FIG. 1A, thereby completing thelight modulator 50 of the present invention. - Since as discussed above the insulating thick-
layer 40 is formed only immediately below thebonding pad electrode 6 a, the parasitic static capacitance between thebonding pad electrode 6 a and therear surface electrode 10 can be reduced. Also, since the insulating thick-layer 40 is formed on that relatively narrow portion of the bondingpad forming section 6, there is no possibility that thesubstrate 2 may warp. Furthermore, since that portion of the insulatingfilm 42 overlaying themesa section 9 has a relatively small thickness as is the case with that in the conventional light modulator, there is no difficulty forming the opening in the insulating layer. - It is to be noted in any one of the foregoing methods, the insulating
layer 40 has been described as made of SiO2, the present invention can be equally applied where SiN or any other insulating layer is employed therefor. - Also, formation of the insulating layer may be carried out any known method such as, for example, by the use of the CVD, sputtering or vacuum evaporation technique.
- The light modulator50 a according to a second preferred embodiment of the present invention is shown in FIGS. 5A and 5B. In this embodiment, the
light modulator 50 a includes, as shown in FIG. 5A, amesa section 9 and a bondingpad forming section 6 both protruding outwardly from anInP semiconductor substrate 2. More specifically, themesa section 9 is delimited by and between a pair ofparallel grooves 3 formed at a predetermined position in thesemiconductor substrate 2. The bondingpad forming section 6 is positioned on one side of one of thegrooves 3 opposite to themesa section 9 and is delimited by such one of thegrooves 3 and a generallyU-shaped groove 3 a defined in thesemiconductor substrate 2. Themesa section 9 includes anelectrode 5 formed thereon through a SiO2 insulating film 44 and has alight absorption layer 1 embedded therein, whichlayer 1 is operable to receive and transmit a laser beam therethrough. On the other hand, the bondingpad forming section 6 includes abonding pad electrode 6 a formed thereon through a SiO2 insulating film 45 intervening between it and thebonding pad electrode 6 a. Thebonding pad electrode 6 a and theelectrode 5 form and are served respectively by different parts of a metallic layer. It is to be noted that thelight modulator 50 has a rear surface formed with arear surface electrode 10. - In the illustrated
light modulator 50 a, as shown in FIG. 5B, a double layered structure including a SiO2 insulating film 43 and aSiN insulating film 44 is formed on thesemiconductor substrate 2 so as to continuously cover themesa section 9, the bondingpad forming section 6 and the generallyU-shaped groove 3 a. The SiO2 insulating film 45 referred to above is formed over a portion of theSiN insulating film 44 overlaying the bondingpad forming section 6. In other words, the bondingpad forming section 6 is covered by an insulating thick-film of a three layered structure including respective portions of the insulatingfilms film 4 and the insulating thick-film so that a portion of the metallic layer overlaying the bonding pad forming section and another portion of the metallic layer overlaying themesa section 9 form thebonding electrode 6 a and theelectrode 5, respectively. Theelectrode 5 is held in contact with themesa section 4 through an opening formed above an upper surface of themesa section 4. - Since the insulating thick-film is formed only immediately below the
bonding pad electrode 6 a, the parasitic static capacitance between thebonding pad electrode 6 a and therear surface electrode 10 can be reduced. In detail, by increasing the thickness of thick-layer 40 around the bondingpad forming section 6 from 4000 Åto 8000 Å, the parasitic static capacitance around the bondingpad forming section 6 is half of the parasitic static capacitance around the mesa section 9.Becase the capacitance is inverse proportion to the thickness of the insulating layer. Also, since the insulating thick-film 40 is formed on a relatively narrow portion of the bondingpad forming section 6, there is no possibility that thesubstrate 2 may warp. Furthermore, since that portion of the insulating layer overlaying themesa section 9 has a relatively small thickness as is the case with that in the conventional light modulator, there is no difficulty forming the opening in the insulating layer. - The light modulator50 a according to the second embodiment of the present invention can be manufactured by the following method which will be described with particular reference to FIGS. 6A to 6D. At the outset, as shown in FIG. 6A, after a predetermined crystalline layer has been epitaxially grown on the
InP semiconductor substrate 2, a pair ofgrooves 3 are formed at a predetermined location in thesemiconductor substrate 2 so that themesa section 9 of a predetermined width having thelight absorption layer 1 can be eventually formed between thesegrooves 3. The generallyU-shaped groove 3 a continued to one of thegrooves 3 is also formed to define the bondingpad forming section 6. Then, as shown in FIG. 6B, a SiO2 insulating film 43 of 2000 Åin thickness, aSiN insulating film 44 of 2000 Åin thickness and a SiO2 insulating film 45 of 4000 Åin thickness are successively formed on thesemiconductor substrate 2 so as to cover themesa section 9 and the bondingpad forming section 6 continuously. Thereafter, as shown in FIG. 6C, only the bondingpad forming section 6 is covered by a photo-resist 7 that is utilized as a mask, followed by removal by etching of a portion of the outermost insulatingfilm 45 overlaying thesubstrate 2, for example, themesa section 9 and thegrooves 3, other than the bonding pad forming section. - Since the insulating
film 45 so removed is made of SiO2 and the insulatingfilm 44 beneath the insulatingfilm 45 is made of SiN, the use of an etching solution capable of selectively etching SiO2 only while the insulatingfilm 44 in the form of the SiN film serves as an etching stopper layer is effective to controllably remove only the outermost SiO2 film. For example, the etching soluitin is a hydrofluoric acid, because the etching rate for SiO2 is as 3-5 times as for SiN. After the subsequent removal of the photo-resist 7, as shown in FIG. 6D, the insulating thick-film, about 8000 Åin thickness, of the three layered structure including the insulatingfilms pad forming section 6, while the other area, for example, themesa section 9 and thegrooves 3 are covered by the insulating film, about 4000 Åin thickness, of the double layered structure including the insulatinglayers - Thus, the
bonding pad electrode 6 a and theelectrode 2 are formed immediately above the bondingpad forming section 6 and themesa section 2, respectively. More specifically, while the opening is formed in the portion of the insulating layer overlaying an upper surface of the mesa section and the metallic layer connected in part with the upper surface of the mesa section through the opening and in part overlaying the bonding pad forming section. Therear surface electrode 10 is formed in any known manner as shown in FIG. 5A, thereby completing thelight modulator 50 of the present invention. - It is to be noted in any one of the foregoing methods, the insulating
films film 44 has been described as made of SiN, the present invention may not be always limited thereto and the insulatingfilms film 44 maybe made of SiO2. In this case, For example, the etching method is a plasma etching by CF4 gas, because the etching rate for SiN is over 5 times than for SiO2. - In the practice of the method of manufacturing the
light modulator 50 a, the insulating films or layers are preferably made by the use of any known method such as, for example, by the use of the CVD, sputtering or vacuum evaporation technique. - Since as discussed above the insulating thick-
film 45 is formed only immediately below thebonding pad electrode 6 a, the parasitic static capacitance between thebonding pad electrode 6 a and therear surface electrode 10 can be reduced. Also, since the insulating thick-layer 40 is formed on that relatively narrow portion of the bondingpad forming section 6, there is no possibility that thesubstrate 2 may warp. Furthermore, since that portion of the insulating layer overlaying themesa section 9 has a relatively small thickness as is the case with that in the conventional light modulator, there is no difficulty forming the opening in the insulating layer. - Thus, in the light modulator of the present invention, that portion of the insulating layer immediately below the bonding pad electrode has a thickness greater than the remaining portion thereof to reduce the parasitic static capacitance of the bonding pad electrode. Accordingly, the light modulator so manufactured can be used for a high-speed modulation.
- The parasitic static capacitance of the bonding pad electrode can effectively be reduced as a result that that portion of the insulating layer immediately below the bonding pad electrode is made of SiO2 or SiN. Accordingly, the light modulator so manufactured can be used for a high-speed modulation.
- Since the light modulator of the present invention is such that the laminated structure of two or more insulating films is formed immediately below the bonding pad electrode, the selective etching method for forming the insulating layer immediately below the bonding pad electrode is effective to controllably form the insulating layer to a desired thickness.
- According to the method of manufacturing the light modulator of the present invention, after the primary insulating film continuously covering the mesa section and the bonding pad forming section has been formed, a portion of the primary insulating film other than that covering the bonding pad forming section is removed, followed by formation of a secondary insulating film continuously covering the mesa section and the bonding pad forming section. In this way, the insulating layer having a great thickness can be formed immediately below the bonding pad electrode.
- Also, according to the method of manufacturing the light modulator of the present invention, after the primary insulating film continuously covering the mesa section and the bonding pad forming section has been formed, a mask is formed on a portion other than the bonding pad forming section, followed by formation of a secondary insulating film before the removal of the mask. In this way, the insulating layer is formed in two stages only over the bonding pad section. In this way, the insulating layer having a great thickness can be formed immediately below the bonding pad electrode.
- Furthermore, according to the method of manufacturing the light modulator of the present invention, after the primary insulating film continuously covering the mesa section and the bonding pad forming section has been formed, a mask is formed on the bonding pad forming section, followed by etching of a portion of the insulating film other than the bonding pad forming section to a predetermined film thickness. In this way, the insulating layer is formed in two stages only over the bonding pad section. In this way, the insulating layer having a great thickness can be formed immediately below the bonding pad electrode at one step, not two step. Yet, according to the method of manufacturing the light modulator of the present invention, the selective etching technique is used to etch the primary insulating film covering the mesa section and the bonding pad forming section continuously. By this reason, the film thickness of the insulating film can be accurately controlled.
- In the practice of the method of manufacturing the light modulator of the present invention, the insulating film or films are made of SiO2 or SiN and, accordingly the parasitic static capacitance of the light modulator can effectively be reduced.
- Also, in the practice of the method of manufacturing the light modulator of the present invention, the insulating film or films are made of SiO2 and SiN and, accordingly the parasitic static capacitance of the light modulator can effectively be reduced.
- The use of the CVD, sputtering or vacuum evaporation technique to form the insulating film or films is effective to facilitate formation of the insulating film or films.
- Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.
Claims (14)
1. A light modulator comprising;
a semiconductor substrate having a rear surface formed with a grounding conductor;
a mesa section of a predetermined width formed on said semiconductor substrate, said mesa section including a laminated layer structure having a light absorbing layer;
a bonding pad forming section formed on said semiconductor substrate at a location adjacent said mesa section;
an insulating layer formed on said semiconductor substrate so as to continuously cover said mesa section and said bonding pad forming section, a portion of said insulating layer immediately above said mesa section having an opening defined therein; and
an electrode formed over said bonding pad forming section and electrically connected with said mesa section through said opening, a portion of said insulating layer immediately above said bonding pad forming section having a film thickness greater than the remaining portion of said insulating layer to reduce the parasitic static capacitance of said remaining portion.
2. The light modulator according to , wherein the portion of said insulating layer immediately above said bonding pad forming section comprises a multi layered structure containing at least insulating films laminated one above other, the remaining portion of said insulating layer comprises a single or multi layered structure containing a insulating films, in which a number of said insulating film is less than that of said bonding pad forming section.
claim 1
3. The light modulator according to , wherein, said insulating films are two insulating films, one of said two insulating films is made of SiO2 and the other is made of SiN.
claim 2
4. The light modulator according to , wherein the upper-layer insulating film of remaining portion of said insulating layer is same as the 2nd upper-layer insulating film of said bonding pad forming section.
claim 2
5. A method of manufacturing a light modulator comprising the steps of;
forming a mesa section of a predetermined width including a laminated layer structure having a light absorbing layer on a semiconductor substrate having a rear surface formed with a grounding conductor;
forming a bonding pad forming section on said semiconductor substrate at a location adjacent said mesa section;
forming a primary insulating film so as to continuously cover said mesa section and said bonding pad forming section;
forming a secondary insulating film over a portion of said primary insulating film above said bonding pad forming section so that said mesa section has a number of said insulating film is less than that of said bonding pad forming section;
forming an opening in a portion of said primary insulating film immediately above said mesa section; and
forming an electrode over said bonding pad forming section and electrically connected with said mesa section through said opening.
6. The method according to , wherein said step of forming said secondary insulating film comprising;
claim 5
forming mask over said primary insulating film other than said primary insulating film above said bonding pad forming section;
forming said secondary insulating film over said mask and said primary insulating film above said bonding pad forming section; and
removing said mask so as to allow a portion of said secondary insulating film above said bonding pad section to continue to a portion of said primary insulating film above said mesa section to thereby complete said insulating layer in which a double layered structure of insulating films are formed over said bonding pad forming section and a single layered structure of insulating film is formed over said mesa section.
7. The method according to , wherein said step of forming said secondary insulating film comprising;
claim 5
forming a mask above a portion of said primary insulating film above said bonding pad forming section;
removing by etching said primary insulating film other than a portion of said insulating film above said bonding pad forming section; and,
forming a secondary insulating film over said a portion of said insulating film above said bonding pad forming section and above said masa section, whereby a double layered structure including said primary and secondary insulating film is formed above said bonding pad forming section and a single layered structure of said primary insulating film is formed above said mesa section.
8. The method according to , wherein said insulating film is made of a material selected from said group consisting of SiO2 and SiN.
claim 5
9. The method according to , wherein said insulating film is formed by the use of a CVD technique, a sputtering technique or a vacuum evaporation technique.
claim 5
10. A method of manufacturing a light modulator comprising the steps of:
forming a mesa section of a predetermined width including a laminated layer structure having a light absorbing layer on a semiconductor substrate having a rear surface formed with a grounding conductor;
forming a bonding pad forming section on said semiconductor substrate at a location adjacent said mesa section;
forming a primary insulating film so as to continuously cover said mesa section and said bonding pad forming section;
forming a mask so as to cover a portion of said primary insulating film that is formed above said bonding pad forming section,
etching to a predetermined thickness another portion of said primary insulating film other than that portion thereof above said bonding pad forming section; and,
removing said mask thereby leave said insulating layer having a first portion overlaying said bonding pad forming section and a second portion overlaying said mesa section, said first portion of said insulating layer having a thickness greater than said second portion of said insulating layer;
forming an opening said primary insulating film immediately above said mesa section; and
forming an electrode over said bonding pad forming section and electrically connected with said mesa section through said opening.
11. The method according to , wherein said insulating layer is made of a material selected from said group consisting of SiO2 and SiN.
claim 10
12. The method according to , wherein said step of forming said primary insulating film comprising the steps of forming an under-layer insulating film continuing from said mesa section to said bonding pad forming section, forming over said under-layer insulating film anintermediate-layer insulating film of a material different from that of said under-layer insulating film, and forming over said intermediate-layer insulating film an upper-layer insulating film of said same material as that of said under-layer insulating film, and said said step of etchig comprising the step of selectively etching only a portion said upper-layer other than that formed above said bonding pad section.
claim 10
13. The method according to , wherein one of said primary and secondary insulating films is made of SiO2 and said other thereof is made of SiN.
claim 12
14. The method according to , wherein said insulating film is formed by the use of a CVD technique, a sputtering technique or a vacuum evaporation technique.
claim 10
Priority Applications (1)
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US09/839,120 US6384955B2 (en) | 1998-08-07 | 2001-04-23 | Light modulator |
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JP10-224241 | 1998-08-07 | ||
JP10224241A JP2000056281A (en) | 1998-08-07 | 1998-08-07 | Optical modulator and its production |
US09/245,838 US6282009B1 (en) | 1998-08-07 | 1999-02-08 | Light modulator and method of manufacturing the light modulator |
US09/839,120 US6384955B2 (en) | 1998-08-07 | 2001-04-23 | Light modulator |
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US09/245,838 Continuation US6282009B1 (en) | 1998-08-07 | 1999-02-08 | Light modulator and method of manufacturing the light modulator |
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US20010022681A1 true US20010022681A1 (en) | 2001-09-20 |
US6384955B2 US6384955B2 (en) | 2002-05-07 |
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US09/245,838 Expired - Fee Related US6282009B1 (en) | 1998-08-07 | 1999-02-08 | Light modulator and method of manufacturing the light modulator |
US09/839,120 Expired - Fee Related US6384955B2 (en) | 1998-08-07 | 2001-04-23 | Light modulator |
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US09/245,838 Expired - Fee Related US6282009B1 (en) | 1998-08-07 | 1999-02-08 | Light modulator and method of manufacturing the light modulator |
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US (2) | US6282009B1 (en) |
JP (1) | JP2000056281A (en) |
DE (1) | DE19915898B4 (en) |
Cited By (1)
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US20080070411A1 (en) * | 2006-09-20 | 2008-03-20 | John Ghekiere | Methods for uniformly etching films on a semiconductor wafer |
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JP2000056281A (en) * | 1998-08-07 | 2000-02-25 | Mitsubishi Electric Corp | Optical modulator and its production |
SG102589A1 (en) * | 2000-08-16 | 2004-03-26 | Inst Materials Research & Eng | Buried hetero-structure opto-electronic device |
US6580843B2 (en) | 2001-04-05 | 2003-06-17 | Fujitsu Limited | Optical device |
US7449354B2 (en) | 2006-01-05 | 2008-11-11 | Fairchild Semiconductor Corporation | Trench-gated FET for power device with active gate trenches and gate runner trench utilizing one-mask etch |
US7446374B2 (en) | 2006-03-24 | 2008-11-04 | Fairchild Semiconductor Corporation | High density trench FET with integrated Schottky diode and method of manufacture |
US8174067B2 (en) | 2008-12-08 | 2012-05-08 | Fairchild Semiconductor Corporation | Trench-based power semiconductor devices with increased breakdown voltage characteristics |
US8304829B2 (en) | 2008-12-08 | 2012-11-06 | Fairchild Semiconductor Corporation | Trench-based power semiconductor devices with increased breakdown voltage characteristics |
US8227855B2 (en) * | 2009-02-09 | 2012-07-24 | Fairchild Semiconductor Corporation | Semiconductor devices with stable and controlled avalanche characteristics and methods of fabricating the same |
US8148749B2 (en) * | 2009-02-19 | 2012-04-03 | Fairchild Semiconductor Corporation | Trench-shielded semiconductor device |
US8049276B2 (en) | 2009-06-12 | 2011-11-01 | Fairchild Semiconductor Corporation | Reduced process sensitivity of electrode-semiconductor rectifiers |
TW201426151A (en) * | 2012-12-19 | 2014-07-01 | Hon Hai Prec Ind Co Ltd | Electro-optical modulator |
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JP2710171B2 (en) * | 1991-02-28 | 1998-02-10 | 日本電気株式会社 | Surface input / output photoelectric fusion device |
JP2754957B2 (en) * | 1991-07-10 | 1998-05-20 | 日本電気株式会社 | Semiconductor light control element and method of manufacturing the same |
JP3484543B2 (en) * | 1993-03-24 | 2004-01-06 | 富士通株式会社 | Method of manufacturing optical coupling member and optical device |
US5543957A (en) * | 1993-12-20 | 1996-08-06 | Nec Corporation | Optical modulator and method of producing the same |
US5889913A (en) * | 1995-03-15 | 1999-03-30 | Kabushiki Kaisha Toshiba | Optical semiconductor device and method of fabricating the same |
JPH08316579A (en) | 1995-05-18 | 1996-11-29 | Toshiba Corp | Optical semiconductor element and fabrication thereof |
FR2748129B1 (en) | 1996-04-29 | 1998-06-12 | Alsthom Cge Alcatel | ELECTRO-OPTICAL MODULATOR WITH QUANTUM WELLS |
JPH1075009A (en) * | 1996-08-30 | 1998-03-17 | Nec Corp | Optical semiconductor device and its manufacture |
JP2000056281A (en) * | 1998-08-07 | 2000-02-25 | Mitsubishi Electric Corp | Optical modulator and its production |
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1998
- 1998-08-07 JP JP10224241A patent/JP2000056281A/en active Pending
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1999
- 1999-02-08 US US09/245,838 patent/US6282009B1/en not_active Expired - Fee Related
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Cited By (1)
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US20080070411A1 (en) * | 2006-09-20 | 2008-03-20 | John Ghekiere | Methods for uniformly etching films on a semiconductor wafer |
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DE19915898B4 (en) | 2008-04-10 |
US6384955B2 (en) | 2002-05-07 |
DE19915898A1 (en) | 2000-02-17 |
US6282009B1 (en) | 2001-08-28 |
JP2000056281A (en) | 2000-02-25 |
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