WO2021245756A1 - 端面入射型半導体受光素子 - Google Patents

端面入射型半導体受光素子 Download PDF

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Publication number
WO2021245756A1
WO2021245756A1 PCT/JP2020/021628 JP2020021628W WO2021245756A1 WO 2021245756 A1 WO2021245756 A1 WO 2021245756A1 JP 2020021628 W JP2020021628 W JP 2020021628W WO 2021245756 A1 WO2021245756 A1 WO 2021245756A1
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Prior art keywords
light
light receiving
incident
absorption region
receiving element
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PCT/JP2020/021628
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English (en)
French (fr)
Inventor
尚友 磯村
悦司 大村
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株式会社京都セミコンダクター
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Priority to JP2021519177A priority Critical patent/JP6918398B1/ja
Priority to PCT/JP2020/021628 priority patent/WO2021245756A1/ja
Publication of WO2021245756A1 publication Critical patent/WO2021245756A1/ja
Priority to US17/979,777 priority patent/US20230049438A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/10—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a light reflecting structure, e.g. semiconductor Bragg reflector
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0232—Optical elements or arrangements associated with the device
    • H01L31/02327—Optical elements or arrangements associated with the device the optical elements being integrated or being directly associated to the device, e.g. back reflectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022416—Electrodes for devices characterised by at least one potential jump barrier or surface barrier comprising ring electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
    • H01L31/035272—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions characterised by at least one potential jump barrier or surface barrier
    • H01L31/035281—Shape of the body

Definitions

  • the present invention relates to an end face incident type semiconductor light receiving element having increased sensitivity to light in a wavelength range called the L band used in an optical communication system.
  • optical communication In the field of optical communication, development is being carried out to increase the transmission speed in order to respond to the rapid increase in communication volume.
  • an optical signal is transmitted from the transmitting side via an optical fiber cable or the like, and on the receiving side, the optical signal received by the semiconductor light receiving element of the light receiving module is converted into an electric signal.
  • the alignment between the optical fiber cable and the semiconductor light receiving element is accurate and easy, and a plane-mounted light receiving module capable of realizing accurate and easy alignment is useful.
  • the plane-mounted light receiving module is configured so that the incident light from the optical fiber cable is parallel to the mounting substrate of the semiconductor light receiving element.
  • a semiconductor light receiving element suitable for a plane-mounted light receiving module for example, as in Patent Documents 1 and 2, a light absorbing region is provided on the surface side of the semiconductor substrate, and incident light incident from the end surface of the semiconductor substrate is reflected or refracted.
  • an end face incident type semiconductor light receiving element that is made to enter the light absorption region. Since the end face incident type semiconductor light receiving element can be fixed to the mounting substrate without using a sub-board for fixing the surface of the semiconductor substrate toward the incident side of light, it is easy to manufacture a plane mount type light receiving module and the manufacturing cost is reduced. It is possible.
  • optical signal for optical communication light in a wavelength range of 1530 nm to 1565 nm, which is called a C band, which has a small loss in an optical fiber cable, has been mainly used.
  • light in the wavelength range of 1565 nm to 1625 nm, which is called the L band has come to be used in order to cope with the increasing amount of communication.
  • a compound semiconductor having an InGaAs layer is often used as a light absorption region, and the upper limit of the wavelength of a receivable optical signal based on the bandgap energy is about 1670 nm. Therefore, in the L band, the light-receiving sensitivity of the semiconductor light-receiving element to the optical signal tends to decrease as it approaches 1670 nm (the longer the wavelength) (see FIG. 3). Moreover, in principle of the semiconductor light receiving element, it is known that the lower the temperature in the usage environment, the more the light receiving sensitivity spectrum shifts to the short wavelength side, and the light receiving sensitivity in the L band decreases. Therefore, there is a demand for improvement in the light receiving sensitivity of the semiconductor light receiving element.
  • the thicker the light absorption region the more likely it is that crystal defects will occur, and there is a risk that the dark current due to the crystal defects will increase.
  • it takes time to form the light absorption region which increases the manufacturing cost of the semiconductor light receiving element.
  • the light transmitted through the light absorption region 101 is reflected by the reflecting portion 102 formed on the back surface of the semiconductor substrate and is made to enter the light absorption region 101 again.
  • a technique for substantially doubling the thickness of the light absorption region 101 is known (see FIG. 13).
  • the surface-mounting semiconductor light-receiving element needs to be fixed to the mounting board with the surface facing the incident side by using a sub-board, which is not suitable for a plane-mounted light-receiving module.
  • the end face incident type semiconductor light receiving element suitable for the plane-mounted light receiving module as in Patent Documents 1 and 2 has a structure in which the reflected or refracted incident light is incident on the light absorption region once, so that the light absorption region is formed. It is not easy to improve the light receiving sensitivity without making it thicker.
  • An object of the present invention is to provide an end face incident type semiconductor light receiving element having improved light receiving sensitivity.
  • the end face incident type semiconductor light receiving element according to claim 1 has a first light absorption region on the main surface side of the semiconductor substrate, and reflects or refracts the light incident from the end face side of the semiconductor substrate to absorb the first light.
  • the end face incident type semiconductor light receiving element incident on the region is characterized by having a first reflecting portion on the main surface side for incident the light transmitted through the first light absorption region on the first light absorption region. There is.
  • the light incident from the end face side of the semiconductor substrate and transmitted through the first light absorption region on the main surface side is reflected by the first reflection portion on the main surface side of the semiconductor substrate and is reflected in the first light absorption region. Is incident again. Since there is a first reflecting portion on the main surface side where the first light absorbing region is located and the distance between them is short, the spread of light reciprocating between the first light absorbing region and the first reflecting portion is small. Therefore, since all the light transmitted through the first light absorption region can be incident on the first light absorption region, the light reception sensitivity of the end face incident type semiconductor light receiving element can be improved.
  • the end face incident type semiconductor light receiving element of the invention of claim 2 causes the light reflected by the first reflecting portion and transmitted through the first light absorption region to be incident on the first light absorption region. It is characterized by having a second reflective portion for the purpose. According to the above configuration, the light reflected by the first reflecting unit and transmitted through the first light absorbing region can be reflected by the second reflecting unit and incident on the first light absorbing region. Therefore, since the incident light can be incidented on the first light absorption region four times in total by the first and second reflecting portions, the light receiving sensitivity of the end face incident type semiconductor light receiving element can be improved.
  • the end face incident type semiconductor light receiving element of the invention of claim 3 has a second light absorption region separated from the first light absorption region on the main surface side, and the first reflection unit. It is characterized by having a third reflecting portion for incident the light reflected by the light absorbing region and transmitted through the first light absorbing region into the second light absorbing region. According to the above configuration, the light reflected by the first reflecting unit and transmitted through the first light absorbing region can be reflected by the third reflecting unit and incident on the second light absorbing region. Therefore, the incident light can be incidented twice on the first light absorption region by the first reflecting portion, and the light transmitted through the first light absorbing region can be incident on the second light absorbing region by the third reflecting portion. It is possible to improve the light receiving sensitivity of the incident type semiconductor light receiving element.
  • the end face incident type semiconductor light receiving element of the invention of claim 4 has an annular electrode formed on the main surface side so as to border the first light absorption region.
  • the first reflective portion is characterized in that it is formed by laminating a dielectric film and a plurality of metal films inside the annular electrode. According to the above configuration, a first reflective portion in which a dielectric film and a plurality of metal films are laminated is formed inside an annular electrode formed on the main surface side of the semiconductor substrate so as to border the first light absorption region. Has been done.
  • the junction surface of the annular electrode has low reflectance because fine irregularities are generated by alloying.
  • a first reflective portion is formed in which a dielectric film that prevents alloying and provides a smooth surface and a plurality of metal films that provide high reflectance are laminated. .. Therefore, since the light transmitted through the first light absorption region can be reflected by the first reflection unit and incident on the first light absorption region, the light reception sensitivity of the end face incident type semiconductor light receiving element can be improved.
  • the light receiving sensitivity can be improved.
  • the end face incident type light receiving element 1A absorbs light in the InGaAs layer 11 formed on the main surface 10a side with the (100) surface of the semiconductor substrate 10 which is an n-InP substrate as the main surface 10a.
  • a first light receiving unit 15 photodiode having a region 11a and a p-type diffusion region 12a formed in the n-InP layer 12 formed on the InGaAs layer 11 is provided. Since the semiconductor substrate 10 is transparent to infrared light having a wavelength longer than 1000 nm, infrared light having a wavelength longer than 1000 nm incident on the semiconductor substrate 10 travels in the semiconductor substrate 10.
  • the p-type diffusion region 12a is formed by doping a predetermined region of the n-InP layer 12 on the InGaAs layer 11 with, for example, Zn, and although not shown, it includes a circular shape or a rectangle when viewed from the main surface 10a side. It is formed in a polygonal shape.
  • the region of the InGaAs layer 11 in contact with the p-type diffusion region 12a corresponds to the first light absorption region 11a.
  • An annular electrode 16 (p electrode) is provided on the p-type diffusion region 12a so as to border the p-type diffusion region 12a, that is, to border the first light absorption region 11a.
  • the junction surface between the annular electrode 16 and the p-type diffusion region 12a has fine irregularities due to alloying, so that the reflectance of light is low.
  • the region other than the first light receiving portion 15 is covered with, for example, a SiO2 film as the dielectric film 13.
  • the end face incident type semiconductor light receiving element 1A is provided with a substrate electrode 17 (n electrode) on the back surface 10b of the semiconductor substrate 10 facing the main surface 10a.
  • a substrate electrode 17 (n electrode) on the back surface 10b of the semiconductor substrate 10 facing the main surface 10a.
  • One of the substrate electrode 17 or the annular electrode 16 (for example, the substrate electrode 17) is joined in a state of being placed on a predetermined wiring of a mounting substrate (not shown), and the other (for example, the annular electrode 16) is a mounting substrate. It is connected to a predetermined wiring by wire bonding.
  • the back surface 10b of the semiconductor substrate 10 has a groove portion 18 (recessed portion) whose cross section is formed into an isosceles triangle or trapezoidal shape by the first inclined surface 18a and the second inclined surface 18b which are connected to the back surface 10b at obtuse angles.
  • the inclined surface of the groove portion 18 near the first light receiving portion 15 is referred to as the first inclined surface 18a.
  • the groove 18 is formed by a known etching means using a known etching solution having anisotropy depending on the crystal plane orientation (for example, a mixed solution of hydrogen bromide and methanol having a slow etching rate on the ⁇ 111 ⁇ plane). ..
  • the end face substantially perpendicular to the main surface 10a and the back surface 10b of the semiconductor substrate 10 is formed parallel to the direction in which the groove portion 18 extends, and the light emitted from the optical fiber is incident on the end surface 10c on the first inclined surface 18a side. Let P be this emission point.
  • the end face 10c is formed flat in order to prevent scattering of incident light on the end face 10c. Further, the end face 10c may be provided with an antireflection film such as a SiN film in order to suppress the reflection of the incident light.
  • the first inclined surface 18a includes a dielectric film (for example, SiN film, SiO2 film, etc.) and a metal film (for example, Ag film, Au film, etc.) for reflecting incident light, and constitutes a groove reflecting portion 20. ..
  • a dielectric film for example, SiN film, SiO2 film, etc.
  • a metal film for example, Ag film, Au film, etc.
  • the critical angle is 37.3 according to Snell's law. It will be about °.
  • the incident light incident on the end surface 10c from the emission point P and traveling parallel to the main surface 10a and the back surface 10b has an incident angle of 35.3 ° whose optical axis is close to the critical angle with respect to the groove reflecting portion 20. Most of the incident light is reflected toward the first light receiving unit 15.
  • the critical angle is reduced and the incident light is reflected by the groove. It is also possible to configure the unit 20 to totally reflect.
  • the first reflection portion 21 is formed in the vicinity of the first light absorption region 11a and in the region inside the annular electrode 16 on the p-type diffusion region 12a.
  • the first reflective portion 21 is formed of a dielectric film 13 that covers the p-type diffusion region 12a and a plurality of metal films laminated on the dielectric film 13.
  • the dielectric film 13 is, for example, a SiO2 film, and the plurality of laminated metal films are a Cr film 22, a Ni film 23, and an Au film 24 in this order from the dielectric film 13 side.
  • the dielectric film 13 prevents alloying of these metal films with the p-type diffusion region 12a, maintains the smoothness of the interface, and enhances the reflectance of the first reflecting portion 21.
  • the light emitted from the emission point P and incident on the semiconductor substrate 10 from the end face 10c side is reflected toward the first light receiving unit 15 by the groove reflecting unit 20 and incident on the first light absorbing region 11a of the first light receiving unit 15. Then, a part of it is converted into an electric signal.
  • the light transmitted through the first light absorption region 11a is reflected by the first reflection unit 21 in the vicinity of the first light absorption region 11a, and is again incident on the first light absorption region 11a.
  • the first reflecting portion 21 is in the vicinity of the first light absorbing region 11a, the spread of light reciprocating between the first light absorbing region 11a and the first reflecting portion 21 is negligibly small, and the first reflecting portion 21 All the light reflected by is incident on the first light absorption region 11a. Therefore, since the incident light passes through the first light absorption region 11a twice, the thickness of the first light absorption region 11a is substantially doubled, and the light receiving sensitivity of the end face incident type semiconductor light receiving element 1 is improved.
  • FIG. 2 shows the light receiving sensitivity spectrum of the end face incident type light receiving element 1A having the first reflecting unit 21 on the curve L1, and shows the light receiving sensitivity spectrum when the first reflecting unit 21 is not present on the curve L0.
  • the upper limit of the wavelength of the receivable optical signal is about 1670 nm, which is the same, but in the L band (wavelength range of 1565 nm to 1625 nm), the thickness of the first light absorption region 11a is substantially 2 due to the first reflecting unit 21.
  • the light receiving sensitivity is improved by doubling. Further, the light receiving sensitivity is similarly improved in the C band (wavelength range of 1530 nm to 1565 nm).
  • the dielectric film 13 (for example, a SiO2 film having a thickness of 200 nm) covering the semiconductor substrate 10 on which the first light receiving portion 15 is formed on the main surface 10a side is dielectriced by a known photo and etching means.
  • the body film 13 is selectively removed to form a groove 13a for forming the annular electrode 16 (groove forming step). At the bottom of the groove 13a, the p-type diffusion region 12a is exposed.
  • a metal electrode material having a Cr film, a Ni film, or the like as an adhesion layer with the p-type diffusion region 12a is laminated so as to cover the dielectric film 13, and the metal is formed in the groove 13a.
  • the electrode material is deposited, and the metal electrode material outside the groove 13a is selectively removed by a known photo-etching means to form the annular electrode 16 (annular electrode forming step).
  • the alloying of the joint surface between the p-type diffusion region 12a and the annular electrode 16 may be promoted by heat treatment.
  • the dielectric film 13 is exposed at the portion where the metal electrode material is removed.
  • a metal film is formed in the order of Cr film 22, Ni film 23, and Au film 24 with thicknesses of 50 nm, 200 nm, and 200 nm, respectively, so as to cover the dielectric film 13 and the annular electrode 16. (Metal film laminating process). Then, as shown in FIG. 6, the laminated metal film is selectively removed by a known photo-etching means to form the first reflective portion 21 (metal laminated film removing step).
  • the groove reflecting portion 20 is formed, and the metal electrode material is selectively deposited on the back surface 10b of the semiconductor substrate 10 to form the substrate electrode 17, and the end face incident type semiconductor light receiving element 1 of FIG. 1 is obtained (substrate electrode). Formation process).
  • the groove portion 18 may be formed after the formation of the first light receiving portion 15. It may be formed after the metal laminated film removing step.
  • FIG. 7 shows the first reflective portion 21 when the film thicknesses of the Ni film 23 are changed when the film thicknesses of the dielectric film 13 (SiO2 film), the Cr film 22, and the Au film 24 are 200 nm, 50 nm, and 200 nm, respectively. It shows the change of the reflectance of. According to this, the reflectance periodically fluctuates in the range of about 92% to 98% according to the film thickness of the Ni film 23. This is because the reflections at each interface of the laminated film constituting the first reflective portion 21 interfere with each other. Since the thinner Ni film 23 is advantageous for reducing the manufacturing cost, the first reflective portion 21 having a high reflectance of about 98% is formed by adopting the Ni film 23 having a thickness of about 180 nm to 340 nm.
  • the end face incident type semiconductor light receiving element 1B in which the end face incident type semiconductor light receiving element 1A of the first embodiment is modified and equipped with the second reflecting portion 25 will be described.
  • the light incident from the emission point P on the end face 10c side is reflected by the groove reflecting unit 20 toward the first light receiving unit 15, and the first light receiving unit 15
  • the light transmitted through the first light absorption region 11a is reflected by the first reflection unit 21 and re-entered into the first light absorption region 11a.
  • the light transmitted through the first light absorption region 11a is reflected toward the first light receiving unit 15 by the second reflecting unit 25 formed on the back surface 10b side of the semiconductor substrate 10.
  • the light reflected by the second reflecting unit 25 is incident on the first light absorption region 11a, and the light transmitted through the first light absorption region 11a is reflected by the first reflection unit 21 and is reflected on the first light absorption region 11a. It will be incident once more. Therefore, since the light incident from the end face 10c is incident on the first light absorption region 11a four times in total, the light receiving sensitivity of the end face incident type semiconductor light receiving element 1B is improved. Since the light reflected by the second reflection unit 25 spreads and is incident on the first light absorption region 11a, a part of the light reflected by the second reflection unit 25 is incident on the first light absorption region 11a. However, the improvement of the light receiving sensitivity by the second reflecting unit 25 may be limited.
  • the second reflection portion 25 is processed so that the corner portion extending from the back surface 10b of the semiconductor substrate 10 to the end surface 10c becomes a flat surface portion 25a connected to the back surface 10b at a predetermined angle, and the first reflection portion 25a has a flat surface portion 25a. It is formed by forming a laminated film having the same structure as that of the portion 21.
  • the predetermined angle ⁇ 2 of the flat surface portion 25a is 160.6 ° so as to be vertically incident on the second reflecting portion 25 in order to improve the light receiving sensitivity. Is set to.
  • the flat surface portion 25a is processed by cutting, grinding, polishing, or the like.
  • the end face incident type semiconductor light receiving element 1C refracts the light incident from the emission point P on the end face 10c side toward the first light receiving unit 15 by the refracting surface 10d, and the first light receiving unit 15 is the first.
  • the light transmitted through the 1 light absorption region 11a is reflected by the first reflection unit 21 and re-entered into the first light absorption region 11a. Since the incident light passes through the first light absorption region 11a twice, the thickness of the first light absorption region 11a is substantially doubled, and the light receiving sensitivity of the end face incident type semiconductor light receiving element 1C is improved.
  • the corner portion extending from the back surface 10b of the semiconductor substrate 10 to the end surface 10c becomes a flat refracting surface 10d connected to the back surface 10b at a predetermined angle. It has been processed.
  • the predetermined angle ⁇ 3 is, for example, 135 °, and the refraction surface 10d is formed by cutting, grinding, polishing, or the like. Since the first reflecting unit 21 has the same structure as that of the first and second embodiments, the description thereof will be omitted.
  • the end face incident type semiconductor light receiving element 1D in which the end face incident type semiconductor light receiving element 1C of the third embodiment is modified and equipped with the second reflecting portion 26 will be described.
  • the end face incident type semiconductor light receiving element 1D refracts the light incident from the emission point P on the end face 10c side toward the first light receiving unit 15 on the refracting surface 10d, and the first light receiving unit 15 is the first.
  • the light transmitted through the 1 light absorption region 11a is reflected by the first reflection unit 21 and re-entered into the first light absorption region 11a.
  • the light transmitted through the first light absorption region 11a is reflected toward the first light receiving unit 15 by the second reflecting unit 26 formed on the back surface 10b side of the semiconductor substrate 10.
  • the light reflected by the second reflection unit 26 is incident on the first light absorption region 11a, and the light transmitted through the first light absorption region 11a is reflected by the first reflection unit 21 and is reflected on the first light absorption region 11a. It will be incident once more. Therefore, since the incident light is incident on the first light absorption region 11a four times in total, the light receiving sensitivity of the end face incident type semiconductor light receiving element 1D is improved. Since the light reflected by the second reflection unit 26 spreads and is incident on the first light absorption region 11a, a part of the light reflected by the second reflection unit 26 is incident on the first light absorption region 11a. However, the improvement of the light receiving sensitivity by the second reflecting unit 26 may be limited.
  • the second reflecting portion 26 is processed so that the corner portion extending from the back surface 10b of the semiconductor substrate 10 to the end surface 10e on the opposite side of the end surface 10c is formed into a flat surface portion 10f connected to the back surface 10b at a predetermined angle.
  • a laminated film having the same structure as that of the first reflecting portion 21 is formed on the portion 10f to form a film.
  • the predetermined angle ⁇ 4 is 147 ° when the refractive index of the semiconductor substrate 10 with respect to air is 3.4.
  • the flat surface portion 10f is processed by cutting, grinding, polishing, or the like.
  • the end face incident type semiconductor light receiving element 1E in which the end face incident type semiconductor light receiving element 1A of the first embodiment is provided with a second light receiving unit 30 and a third reflecting unit 31 for reflecting light toward the second light receiving unit 30 will be described. ..
  • the end face incident type semiconductor light receiving element 1E has a first light receiving portion 15 and a second light receiving portion 30 formed apart from the first light receiving portion 15 on the main surface 10a side of the semiconductor substrate 10.
  • the groove reflecting portion 20 is provided on the back surface 10b side.
  • the back surface 10b has a third reflecting portion 31 at a portion intermediate between the first light receiving portion 15 and the second light receiving portion 30.
  • the second light receiving unit 30 is a photodiode having a second light absorption region 11b and a p-type diffusion region 12b and having the same structure as the first light receiving unit 15.
  • the end face incident type semiconductor light receiving element 1E reflects the light incident from the emission point P on the end face 10c side toward the first light receiving unit 15 by the groove reflecting unit 20, and forms the first light absorbing region 11a of the first light receiving unit 15.
  • the transmitted light is reflected by the first reflecting unit 21 and re-entered into the first light absorbing region 11a.
  • the light transmitted through the first light absorption region 11a is reflected toward the second light receiving unit 30 by the third reflecting unit 31 formed on the back surface 10b of the semiconductor substrate 10, and the second light of the second light receiving unit 30 is reflected. It is incident on the absorption region 11b.
  • the second light receiving unit 30 has a fourth reflecting unit 35 inside the annular electrode 32, and light is incident on the second light absorbing region 11b twice.
  • the third reflecting portion 31 and the fourth reflecting portion have the same laminated structure as 35 and the first reflecting portion 21.
  • the fourth reflecting unit 35 may be omitted.
  • the second light receiving unit 30 is separated from the first light receiving unit 15 so that the light reflected by the third reflecting unit 31 is incident on the second light receiving unit 30, but the first light receiving unit 15 and the second light receiving unit 15 are separated. 30 are electrically connected in parallel, and the sum of the outputs of the first and second light receiving units 15 and 30 is output from the end face incident type semiconductor light receiving element 1E. Therefore, the light incident from the end face 10c is incident on the first and second light absorption regions 11a and 11b twice, respectively, so that the light receiving sensitivity of the end face incident type semiconductor light receiving element 1E is improved.
  • the third reflection unit 31 Since the light reflected by the third reflection unit 31 spreads and is incident on the second light absorption region 11b, a part of the light reflected by the third reflection unit 31 is not incident on the second light absorption region 11b.
  • the improvement of the light receiving sensitivity by the third reflecting unit 31 may be limited. Further, when the fourth reflection unit 35 is omitted, the light is incident on the second light absorption region 11b only once, so that the improvement of the light receiving sensitivity is limited by that amount.
  • the end face incident type semiconductor light receiving element 1F provided with a second light receiving unit 30 and a third reflecting unit 31 for reflecting light toward the second light receiving unit 30 by deforming the end face incident type semiconductor light receiving element 1C of the third embodiment.
  • the end face incident type semiconductor light receiving element 1F has a first light receiving portion 15 and a second light receiving portion 30 formed apart from the first light receiving portion 15 on the main surface 10a side of the semiconductor substrate 10.
  • a third reflecting portion 31 is provided at a portion intermediate between the first light receiving portion 15 and the second light receiving portion 30 on the back surface 10b.
  • the second light receiving unit 30 is a photodiode having a second light absorption region 11b and a p-type diffusion region 12b and having the same structure as the first light receiving unit 15.
  • the end face incident type semiconductor light receiving element 1F refracts the light incident from the emission point P on the end face 10c side toward the first light receiving unit 15 on the refracting surface 10d, and transmits the light through the first light absorption region 11a of the first light receiving unit 15.
  • the light is reflected by the first reflecting unit 21 and re-entered into the first light absorbing region 11a.
  • the light transmitted through the first light absorption region 11a is reflected toward the second light receiving unit 30 by the third reflecting unit 31 formed on the back surface 10b of the semiconductor substrate 10, and the second light absorption of the second light absorbing unit 30 is performed. It is incident on the region 11b.
  • the second light receiving unit 30 has a fourth reflecting unit 35 inside the annular electrode 32, and light is incident on the second light absorbing region 11b twice.
  • the third reflecting portion 31 and the fourth reflecting portion 35 have the same laminated structure as the first reflecting portion 15.
  • the fourth reflecting unit 35 may be omitted.
  • the second light receiving unit 30 is separated from the first light receiving unit 15 so that the light reflected by the third reflecting unit 31 is incident on the second light receiving unit 30, but the first light receiving unit 15 and the second light receiving unit 15 are separated. 30 are electrically connected in parallel, and the sum of the outputs of the first and second light receiving units 15 and 30 is output from the end face incident type semiconductor light receiving element 1F. Therefore, the light incident from the emission point P is incident on the first and second light absorption regions 11a and 11b twice, respectively, so that the light receiving sensitivity of the end face incident type semiconductor light receiving element 1F is improved.
  • the third reflection unit 31 Since the light reflected by the third reflection unit 31 spreads and is incident on the second light absorption region 11b, a part of the light reflected by the third reflection unit 31 is not incident on the second light absorption region 11b.
  • the improvement of the light receiving sensitivity by the third reflecting unit 31 may be limited. Further, when the fourth reflection unit 35 is omitted, the light is incident on the second light absorption region 11b only once, so that the improvement of the light receiving sensitivity is limited by that amount.
  • the actions and effects of the end face incident type semiconductor light receiving elements 1A to 1F will be described.
  • the end face incident type semiconductor light receiving elements 1A to 1F have a first light absorption region 11a on the main surface 10a side of the semiconductor substrate 10, and the light incident from the emission point P on the end face 10c side is reflected or refracted by the groove reflecting portion 20. By refraction by the surface 10d, the light is incident on the first light absorption region 11a.
  • the end face incident type semiconductor light receiving elements 1A to 1F have a first reflecting portion 21 in the vicinity of the first light absorbing region 11a on the main surface 10a side, and the light transmitted through the first light absorbing region 11a is the first reflecting portion 21.
  • the first reflecting portion 21 is located in the vicinity of the first light absorbing region 11a, the spread of the reflected light is small. Therefore, since all the light reflected by the first reflecting unit 21 can be incident on the first light absorption region 11a, the light receiving sensitivity of the end face incident type semiconductor light receiving elements 1A to 1F can be improved.
  • the end face incident type semiconductor light receiving elements 1B and 1D have second reflecting portions 25 and 26, and the light reflected by the first reflecting portion 21 and transmitted through the first light absorption region 11a is transmitted by the second reflecting portions 25 and 26. It can be reflected and incident on the first light absorption region 11a. Therefore, the incident light can be incidented on the first light absorption region 11a four times in total by the first and second reflecting portions 21, 25, 26, so that the light receiving sensitivity of the end face incident type semiconductor light receiving elements 1B and 1D is improved. be able to.
  • the end face incident type semiconductor light receiving elements 1E and 1F have a second light absorption region 11b separated from the first light absorption region 11a on the main surface 10a side of the semiconductor substrate 10 and a third reflection portion 31 on the back surface 10b. Then, the light reflected by the first reflecting unit 21 and transmitted through the first light absorbing region 11a is reflected by the third reflecting unit and incident on the second light absorbing region 11b. Therefore, the incident light can be incidented twice on the first light absorption region 11a by the first reflection unit 21, and the light transmitted through the first light absorption region 11a by the third reflection unit 31 is transmitted to the second light absorption region 11b. Since the light can be made incident, the light receiving sensitivity of the end face incident type semiconductor light receiving elements 1E and 1F can be improved.
  • the end face incident type semiconductor light receiving elements 1A to 1F have an annular electrode 16 formed on the main surface 10a side of the semiconductor substrate 10 so as to border the first light absorption region 11a, and a dielectric material is provided inside the annular electrode 16.
  • the first reflective portion 21 in which the film 13 and the plurality of metal films 22 to 24 are laminated is formed.
  • the interface between the annular electrode 16 and the p-type diffusion region 12a of the first light receiving portion 15 has low reflectance because fine irregularities are generated by alloying.
  • the dielectric film 13 that prevents alloying and maintains the flatness of the interface, and the plurality of metal films 22 to 24 for providing high reflectance are laminated first.
  • the reflective portion 21 is formed.
  • the light transmitted through the first light absorption region 11a can be reflected by the first reflection unit 21 and incident on the first light absorption region 11a, so that the light reception sensitivity of the end face incident type semiconductor light receiving elements 1A to 1F is improved. Can be made to.
  • End face incident type semiconductor light receiving element 10 Semiconductor substrate 10a: Main surface 10b: Back surface 10c: End face 10d: Refractive surface 10e: End face 10f: Flat surface portion 11: InGaAs layer 11a: First light absorption region 11b: Second Light absorption region 12: n-InP layer 12a, 12b: p-type diffusion region 13: Dielectric film 15: First light receiving portion 16: Circular electrode 17: Substrate electrode 18: Groove portion 18a: First inclined surface 18b: Second inclined Surface 20: Groove reflecting part 21: First reflecting part 22: Cr film 23: Ni film 24: Au film 25, 26: Second reflecting part 30: Second light receiving part 31: Third reflecting part 32: Circular electrode 35: 4th reflector

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Abstract

【課題】受光感度を向上させた端面入射型半導体受光素子を提供すること。 【解決手段】端面入射型半導体受光素子（１Ａ）は、半導体基板（１０）の主面側に第１光吸収領域（１１ａ）を有し、半導体基板（１０）の端面側から入射する光を反射又は屈折によって第１光吸収領域（１１ａ）に入射させ、半導体基板（１０）の主面側に、第１光吸収領域（１１ａ）を透過した光を第１光吸収領域（１１ａ）に入射させるための第１反射部（２１）を有する。

Description

端面入射型半導体受光素子
　本発明は、光通信システムで用いられるＬバンドと呼ばれる波長域の光に対して感度を高めた端面入射型半導体受光素子に関する。
　光通信の分野では、通信量の急激な増加に対応するため、伝送速度を高速化する開発が行われている。光通信は、送信側から光ファイバケーブル等を介して光信号を送信し、受信側では受光モジュールの半導体受光素子が受信した光信号を電気信号に変換している。受光モジュールは、光ファイバケーブルと半導体受光素子との位置合わせが正確且つ容易であることが好ましく、正確且つ容易な位置合わせを実現可能な平面実装式の受光モジュールが有用である。平面実装式の受光モジュールは、光ファイバケーブルからの入射光が半導体受光素子の実装基板に平行になるように構成されている。
　平面実装式の受光モジュールに適した半導体受光素子として、例えば特許文献１，２のように、半導体基板の表面側に光吸収領域を有し、半導体基板の端面から入射した入射光を反射又は屈折させて光吸収領域に入射させる端面入射型半導体受光素子が知られている。端面入射型半導体受光素子は、半導体基板の表面を光の入射側に向けて固定するサブ基板を用いることなく実装基板に固定できるので、平面実装式の受光モジュールの製造が容易且つ製造コストを低減可能である。
　ところで、光通信の光信号には、光ファイバケーブルにおける損失が小さいＣバンドと呼ばれる１５３０ｎｍ～１５６５ｎｍの波長域の光が主に使用されてきた。そして近年は、増加する通信量に対応するために、Ｌバンドと呼ばれる１５６５ｎｍ～１６２５ｎｍの波長域の光も用いられるようになってきている。
　光通信に使用される半導体受光素子は、光吸収領域としてＩｎＧａＡｓ層を有する化合物半導体が用いられる場合が多く、そのバンドギャップエネルギに基づく受信可能な光信号の波長の上限は、１６７０ｎｍ程度である。それ故、Ｌバンドでは、１６７０ｎｍに近づく程（波長が長い程）光信号に対する半導体受光素子の受光感度が低下する傾向がある（図３参照）。その上、半導体受光素子の原理上、使用環境における温度が低くなる程、受光感度スペクトルが短波長側にシフトして、Ｌバンドにおける受光感度が低下することが知られている。それ故、半導体受光素子の受光感度の向上が要望されている。
　受光感度を向上させるためには、光吸収領域のＩｎＧａＡｓ層を厚くして、光信号を電気信号に変換する機会を増加させることが有効である。しかし、光吸収領域は、厚くする程結晶欠陥が発生し易くなり、結晶欠陥に起因する暗電流が増加する虞がある。また、光吸収領域の形成に時間がかかるようになり、半導体受光素子の製造コストを上昇させる。
　そのため、例えば一般的な表面入射型の半導体受光素子１００では、光吸収領域１０１を透過した光を、半導体基板裏面に形成された反射部１０２で反射させて再度光吸収領域に１０１入射させることにより、光吸収領域１０１の厚さを実質的に２倍にする技術が知られている（図１３参照）。
特許第３１５２９０７号公報 特開平１１－３０７８０６号公報
　しかし、表面入射型の半導体受光素子の光吸収領域と反射部の間を往復する間に、入射光が広がってしまうので、反射させた入射光を十分に光吸収領域に再入射させることが困難であり、受光感度の向上は限定的である。そして、表面入射型の半導体受光素子は、サブ基板を用いて表面を入射側に向けて実装基板に固定する必要があり、平面実装式の受光モジュールに不向きである。
　一方、特許文献１，２のような平面実装式の受光モジュールに適した端面入射型半導体受光素子は、反射又は屈折させた入射光を光吸収領域に１回入射させる構造なので、光吸収領域を厚くせずに受光感度を向上させることは容易ではない。
　本発明の目的は、受光感度を向上させた端面入射型半導体受光素子を提供することである。
　請求項１の発明の端面入射型半導体受光素子は、半導体基板の主面側に第１光吸収領域を有し、前記半導体基板の端面側から入射する光を反射又は屈折によって前記第１光吸収領域に入射させる端面入射型半導体受光素子において、前記主面側に、前記第１光吸収領域を透過した光を前記第１光吸収領域に入射させるための第１反射部を有することを特徴としている。
　上記構成によれば、半導体基板の端面側から入射して主面側の第１光吸収領域を透過した光は、半導体基板の主面側の第１反射部によって反射されて第１光吸収領域に再び入射される。第１光吸収領域がある主面側に第１反射部があり、これらの距離が近いので、第１光吸収領域と第１反射部の間を往復する光の広がりは僅かである。従って、第１光吸収領域を透過した光の全てを第１光吸収領域に入射させることができるので、端面入射型半導体受光素子の受光感度を向上させることができる。
　請求項２の発明の端面入射型半導体受光素子は、請求項１の発明において、前記第１反射部によって反射されて前記第１光吸収領域を透過した光を前記第１光吸収領域に入射させるための第２反射部を有することを特徴としている。
　上記構成によれば、第１反射部で反射されて第１光吸収領域を透過した光を、第２反射部によって反射させて第１光吸収領域に入射させることができる。従って、第１、第２反射部によって入射光を第１光吸収領域に通算４回入射させることができるので、端面入射型半導体受光素子の受光感度を向上させることができる。
　請求項３の発明の端面入射型半導体受光素子は、請求項１の発明において、前記主面側に、前記第１光吸収領域から離隔した第２光吸収領域を有し、前記第１反射部によって反射されて前記第１光吸収領域を透過した光を前記第２光吸収領域に入射させるための第３反射部を有することを特徴としている。
　上記構成によれば、第１反射部で反射されて第１光吸収領域を透過した光を、第３反射部によって反射させて第２光吸収領域に入射させることができる。従って、第１反射部によって入射光を第１光吸収領域に２回入射させ、第３反射部によって第１光吸収領域を透過した光を第２光吸収領域に入射させることができるので、端面入射型半導体受光素子の受光感度を向上させることができる。
　請求項４の発明の端面入射型半導体受光素子は、請求項１～３の何れか１項の発明において、前記主面側に前記第１光吸収領域を縁取るように形成された環状電極を有し、前記第１反射部は、前記環状電極の内側において、誘電体膜と複数の金属膜を積層して形成されたことを特徴としている。
　上記構成によれば、第１光吸収領域を縁取るように半導体基板の主面側に形成された環状電極の内側に、誘電体膜と複数の金属膜が積層された第１反射部が形成されている。環状電極の接合面は、合金化によって細かい凹凸が生じるため反射率が低い。しかし、環状電極の内側には、合金化を防いで平滑面を提供する誘電体膜と、高い反射率を提供するための複数の金属膜とが積層された第１反射部が形成されている。従って、第１光吸収領域を透過した光を第１反射部で反射させて第１光吸収領域に入射させることができるので、端面入射型半導体受光素子の受光感度を向上させることができる。
　本発明の端面入射型半導体受光素子によれば、受光感度を向上させることができる。
本発明の実施例１に係る端面入射型半導体受光素子の要部断面図である。 端面入射型半導体受光素子の感度スペクトルを示す図である。 環状電極形成用の溝形成工程を示す図である。 環状電極形成工程を示す図である。 第１反射部形成用の金属膜積層工程を示す図である。 第１反射部形成工程を示す図である。 第１反射部のＮｉ膜厚と反射率の関係を示す図である。 本発明の実施例２に係る端面入射型半導体受光素子の要部断面図である。 本発明の実施例３に係る端面入射型半導体受光素子の要部断面図である。 本発明の実施例４に係る端面入射型半導体受光素子の要部断面図である。 本発明の実施例５に係る端面入射型半導体受光素子の要部断面図である。 本発明の実施例６に係る端面入射型半導体受光素子の要部断面図である。 表面入射型の半導体受光素子を例示する図である。
　以下、本発明を実施するための形態について実施例に基づいて説明する。
　図１に示すように、端面入射型受光素子１Ａは、ｎ－ＩｎＰ基板である半導体基板１０の（１００）面を主面１０ａとして、主面１０ａ側に形成されたＩｎＧａＡｓ層１１内の光吸収領域１１ａと、ＩｎＧａＡｓ層１１上に形成されたｎ－ＩｎＰ層１２内に形成されたｐ型拡散領域１２ａを有する第１受光部１５（フォトダイオード）を備えている。半導体基板１０は、波長が１０００ｎｍより長い赤外光に対して透明であるため、半導体基板１０に入射した１０００ｎｍより長波長の赤外光は半導体基板１０内を進行する。
　ｐ型拡散領域１２ａは、ＩｎＧａＡｓ層１１上のｎ－ＩｎＰ層１２の所定の領域に例えばＺｎをドープして形成され、図示を省略するが、主面１０ａ側から見て円形状又は矩形を含む多角形状に形成されている。このｐ型拡散領域１２ａに接するＩｎＧａＡｓ層１１の領域が第１光吸収領域１１ａに相当する。ｐ型拡散領域１２ａ上には、ｐ型拡散領域１２ａを縁取るように、即ち第１光吸収領域１１ａを縁取るように環状電極１６（ｐ電極）を備えている。環状電極１６とｐ型拡散領域１２ａの接合面は、合金化によって細かい凹凸ができるため、光の反射率が低い。ｎ－ＩｎＰ層１２は、第１受光部１５以外の領域が誘電体膜１３として例えばＳｉＯ２膜に覆われている。
　端面入射型半導体受光素子１Ａは、主面１０ａに対向する半導体基板１０の裏面１０ｂに、基板電極１７（ｎ電極）を備えている。この基板電極１７又は環状電極１６のうちの一方（例えば基板電極１７）が図示外の実装基板の所定の配線上に載置された状態で接合され、他方（例えば環状電極１６）が実装基板の所定の配線にワイヤボンディングによって接続される。
　半導体基板１０の裏面１０ｂには、この裏面１０ｂに夫々鈍角に連なる第１傾斜面１８ａ及び第２傾斜面１８ｂにより断面が二等辺三角形状又は台形状に形成された溝部１８（凹部）を有する。ここでは、溝部１８の第１受光部１５に近い傾斜面を第１傾斜面１８ａとしている。
　第１傾斜面１８ａ及び第２傾斜面１８ｂは半導体基板１０の｛１１１｝面であり、半導体基板１０の（１００）面と｛１１１｝面は５４．７°の角度で交差する。それ故、第１傾斜面１８ａは、裏面１０ｂにθ１＝１２５．３°の鈍角に連なる。この溝部１８は、結晶面方位に依存する異方性を有する公知のエッチング液（例えば｛１１１｝面のエッチング速度が遅い臭化水素とメタノールの混合液）を用いる公知のエッチング手段によって形成される。
　半導体基板１０の主面１０ａと裏面１０ｂに略垂直な端面は、溝部１８が延びる方向に平行に形成され、この第１傾斜面１８ａ側の端面１０ｃに光ファイバから出射される光が入射する。この出射点をＰとする。入射光の端面１０ｃにおける散乱を防ぐため、端面１０ｃは平坦に形成されている。また、この端面１０ｃは、入射光の反射を抑えるために、例えばＳｉＮ膜等の反射防止膜を備えていてもよい。
　第１傾斜面１８ａは、入射光を反射するための誘電体膜（例えばＳｉＮ膜、ＳｉＯ２膜等）及び金属膜（例えばＡｇ膜、Ａｕ膜等）を備えて溝反射部２０を構成している。ここで、例えばＬバンドに属する波長が１６００ｎｍの入射光に対して、ｎ－ＩｎＰ基板及びＳｉＮ膜の屈折率を夫々３．２及び２．０とすると、スネルの法則により臨界角は３７．３°程度になる。
　出射点Ｐから端面１０ｃに入射して主面１０ａ及び裏面１０ｂに平行に進行する入射光は、その光軸が溝反射部２０に対して臨界角に近い３５．３°の入射角になるので、入射光の大部分が第１受光部１５に向かって反射される。屈折率が小さい誘電体膜を選択することにより、又は金属膜及び誘電体膜を備えていない第１傾斜面１８ａを溝反射部２０とすることにより、臨界角を小さくして入射光が溝反射部２０で全反射するように構成することも可能である。
　第１光吸収領域１１ａ近傍であって、ｐ型拡散領域１２ａ上の環状電極１６の内側の領域には、第１反射部２１が形成されている。第１反射部２１は、ｐ型拡散領域１２ａを覆う誘電体膜１３と、この誘電体膜１３上に積層された複数の金属膜により形成されている。誘電体膜１３は例えばＳｉＯ２膜であり、積層された複数の金属膜は誘電体膜１３側から順にＣｒ膜２２、Ｎｉ膜２３、Ａｕ膜２４である。誘電体膜１３は、これら金属膜とｐ型拡散領域１２ａの合金化を防いで界面の平滑性を維持し、第１反射部２１の反射率を高める。
　出射点Ｐから出射されて端面１０ｃ側から半導体基板１０に入射する光は、溝反射部２０によって第１受光部１５に向けて反射され、第１受光部１５の第１光吸収領域１１ａに入射して一部が電気信号に変換される。第１光吸収領域１１ａを透過した光は、第１光吸収領域１１ａ近傍の第１反射部２１で反射され、第１光吸収領域１１ａに再び入射する。
　第１反射部２１は、第１光吸収領域１１ａの近傍にあるので、第１光吸収領域１１ａと第１反射部２１の間を往復する光の広がりは無視できるほど小さく、第１反射部２１で反射された光は全て第１光吸収領域１１ａに入射する。従って、入射した光が第１光吸収領域１１ａを２回通るので、第１光吸収領域１１ａの厚さが実質的に２倍になり、端面入射型半導体受光素子１の受光感度が向上する。
　図２は、第１反射部２１を有する端面入射型受光素子１Ａの受光感度スペクトルを曲線Ｌ１で示し、第１反射部２１がない場合の受光感度スペクトルを曲線Ｌ０で示している。受信可能な光信号の波長の上限は１６７０ｎｍ程度で同じであるが、Ｌバンド（１５６５ｎｍ～１６２５ｎｍの波長域）では、第１反射部２１によって第１光吸収領域１１ａの厚さが実質的に２倍になったことにより受光感度が向上している。また、Ｃバンド（１５３０ｎｍ～１５６５ｎｍの波長域）においても同様に受光感度が向上している。
　次に、第１反射部２１の形成方法について説明する。
　図３に示すように、主面１０ａ側に第１受光部１５が形成された半導体基板１０を覆う誘電体膜１３（例えば２００ｎｍの厚さのＳｉＯ２膜）を、公知のフォト、エッチング手段によって誘電体膜１３を選択的に除去して、環状電極１６を形成するための溝１３ａを形成する（溝形成工程）。溝１３ａの底部では、ｐ型拡散領域１２ａを露出させる。
　次に、図４に示すように、誘電体膜１３を覆うように、ｐ型拡散領域１２ａとの密着層となるＣｒ膜やＮｉ膜等を有する金属電極材料を積層して溝１３ａ内に金属電極材料を堆積し、公知のフォト、エッチング手段によって溝１３ａ外の金属電極材料を選択的に除去して環状電極１６を形成する（環状電極形成工程）。低抵抗化のために熱処理によりｐ型拡散領域１２ａと環状電極１６の接合面の合金化を促進させてもよい。金属電極材料が除去された部分は誘電体膜１３が露出する。
　次に、図５に示すように、誘電体膜１３と環状電極１６を覆うようにＣｒ膜２２、Ｎｉ膜２３、Ａｕ膜２４の順に夫々５０ｎｍ、２００ｎｍ、２００ｎｍの厚さに金属膜を成膜する（金属膜積層工程）。そして図６に示すように、公知のフォト、エッチング手段によって、積層した金属膜を選択的に除去して第１反射部２１を形成する（金属積層膜除去工程）。
　最後に、溝反射部２０を形成し、半導体基板１０の裏面１０ｂに金属電極材料を選択的に堆積して基板電極１７を形成し、図１の端面入射型半導体受光素子１を得る（基板電極形成工程）。尚、溝部１８は第１受光部１５の形成後に形成してもよく。上記金属積層膜除去工程後に形成してもよい。
　図７は、誘電体膜１３（ＳｉＯ２膜）、Ｃｒ膜２２、Ａｕ膜２４の膜厚が夫々２００ｎｍ、５０ｎｍ、２００ｎｍの場合に、Ｎｉ膜２３の膜厚を変えたときの第１反射部２１の反射率の変化を示している。これによると、反射率は概ね９２％～９８％の範囲をＮｉ膜２３の膜厚に応じて周期的に変動する。これは、第１反射部２１を構成する積層膜の各界面における反射が、相互に干渉するためである。Ｎｉ膜２３が薄い方が製造コストの低減に有利なので、１８０ｎｍ～３４０ｎｍ程度のＮｉ膜２３を採用することにより９８％程度の高い反射率を有する第１反射部２１が形成される。
　実施例１の端面入射型半導体受光素子１Ａを変形して、第２反射部２５を装備させた端面入射型半導体受光素子１Ｂについて説明する。
　図８に示すように、端面入射型半導体受光素子１Ｂは、端面１０ｃ側の出射点Ｐから入射する光を溝反射部２０で第１受光部１５に向けて反射させ、第１受光部１５の第１光吸収領域１１ａを透過した光を第１反射部２１で反射させて第１光吸収領域１１ａに再び入射させる。そして、第１光吸収領域１１ａを透過した光を、半導体基板１０の裏面１０ｂ側に形成された第２反射部２５によって第１受光部１５に向けて反射させる。
　第２反射部２５によって反射された光は、第１光吸収領域１１ａに入射し、第１光吸収領域１１ａを透過した光は、第１反射部２１によって反射されて第１光吸収領域１１ａにもう１回入射する。従って、端面１０ｃから入射した光は、第１光吸収領域１１ａに通算４回入射するので、端面入射型半導体受光素子１Ｂの受光感度が向上する。尚、第２反射部２５で反射された光は、広がって第１光吸収領域１１ａに入射するので、第２反射部２５で反射された光の一部が第１光吸収領域１１ａに入射されず、第２反射部２５による受光感度の向上は限定的になる場合がある。
　第２反射部２５は、半導体基板１０の裏面１０ｂから端面１０ｃに連なる角部を、裏面１０ｂに対して所定の角度で連なる平面部２５ａとなるように加工し、この平面部２５ａに第１反射部２１と同じ構造の積層膜を成膜して形成される。第１傾斜面１８ａが裏面１０ｂに１２５．３°の鈍角に連なる場合、受光感度向上のため第２反射部２５に垂直に入射させるように、平面部２５ａの所定の角度θ２は１６０．６°に設定される。尚、平面部２５ａの加工は、切削、研削、研磨等によって行われる。
　図９に示すように、端面入射型半導体受光素子１Ｃは、端面１０ｃ側の出射点Ｐから入射する光を屈折面１０ｄにより第１受光部１５に向けて屈折させ、第１受光部１５の第１光吸収領域１１ａを透過した光を第１反射部２１で反射させて第１光吸収領域１１ａに再び入射させる。入射した光は、第１光吸収領域１１ａを２回通るので、第１光吸収領域１１ａの厚さが実質的に２倍になり、端面入射型半導体受光素子１Ｃの受光感度が向上する。
　入射光を第１受光部１５に向けて屈折させるために、半導体基板１０の裏面１０ｂから端面１０ｃに連なる角部が、裏面１０ｂに対して所定の角度で連なる平坦な屈折面１０ｄとなるように加工されている。所定の角度θ３は、例えば１３５°であり、切削、研削、研磨等によって屈折面１０ｄを形成する。第１反射部２１は、上記実施例１，２と同じ構造なので説明を省略する。
　実施例３の端面入射型半導体受光素子１Ｃを変形して、第２反射部２６を装備させた端面入射型半導体受光素子１Ｄについて説明する。
　図１０に示すように、端面入射型半導体受光素子１Ｄは、端面１０ｃ側の出射点Ｐから入射する光を屈折面１０ｄで第１受光部１５に向けて屈折させ、第１受光部１５の第１光吸収領域１１ａを透過した光を第１反射部２１で反射させて第１光吸収領域１１ａに再び入射させる。そして第１光吸収領域１１ａを透過した光を、半導体基板１０の裏面１０ｂ側に形成された第２反射部２６によって第１受光部１５に向けて反射させる。
　第２反射部２６によって反射された光は、第１光吸収領域１１ａに入射し、第１光吸収領域１１ａを透過した光は、第１反射部２１によって反射されて第１光吸収領域１１ａにもう１回入射する。従って、入射した光は、第１光吸収領域１１ａに通算４回入射するので、端面入射型半導体受光素子１Ｄの受光感度が向上する。尚、第２反射部２６で反射された光は、広がって第１光吸収領域１１ａに入射するので、第２反射部２６で反射された光の一部が第１光吸収領域１１ａに入射されず、第２反射部２６による受光感度の向上は限定的になる場合がある。
　第２反射部２６は、半導体基板１０の裏面１０ｂから端面１０ｃと反対側の端面１０ｅに連なる角部を、裏面１０ｂに対して所定の角度で連なる平面部１０ｆとなるように加工し、この平面部１０ｆに第１反射部２１と同じ構造の積層膜を成膜して形成される。屈折面１０ｄが裏面１０ｂにθ３＝１３５°の鈍角に連なる場合、所定の角度θ４は、空気に対する半導体基板１０の屈折率を３．４とした場合に１４７°である。尚、平面部１０ｆの加工は、切削、研削、研磨等によって行われる。
　実施例１の端面入射型半導体受光素子１Ａに、第２受光部３０と光を第２受光部３０に向けて反射させる第３反射部３１を備備させた端面入射型半導体受光素子１Ｅについて説明する。
　図１１に示すように、端面入射型半導体受光素子１Ｅは、半導体基板１０の主面１０ａ側に第１受光部１５及び第１受光部１５から離隔して形成された第２受光部３０を有し、裏面１０ｂ側に溝反射部２０を有する。また、裏面１０ｂにおける第１受光部１５と第２受光部３０の中間の部位に第３反射部３１を有する。第２受光部３０は、第２光吸収領域１１ｂとｐ型拡散領域１２ｂを有し、第１受光部１５と同じ構造のフォトダイオードである。
　端面入射型半導体受光素子１Ｅは、端面１０ｃ側の出射点Ｐから入射する光を溝反射部２０で第１受光部１５に向けて反射させ、第１受光部１５の第１光吸収領域１１ａを透過した光を第１反射部２１で反射させて第１光吸収領域１１ａに再び入射させる。そして、第１光吸収領域１１ａを透過した光を、半導体基板１０の裏面１０ｂに形成された第３反射部３１によって第２受光部３０に向けて反射させ、第２受光部３０の第２光吸収領域１１ｂに入射させる。
　第２受光部３０は環状電極３２の内側に第４反射部３５を有し、光が第２光吸収領域１１ｂに２回入射する。第３反射部３１と第４反射部は３５、第１反射部２１と同じ積層構造を有する。尚、第４反射部３５を省略することもできる。
　第３反射部３１で反射された光が第２受光部３０に入射するように、第２受光部３０は第１受光部１５から離隔させているが、第１受光部１５と第２受光部３０は電気的に並列接続され、第１、第２受光部１５，３０の出力の和が端面入射型半導体受光素子１Ｅから出力される。従って、端面１０ｃから入射した光は、第１、第２光吸収領域１１ａ，１１ｂに夫々２回入射するので、端面入射型半導体受光素子１Ｅの受光感度が向上する。
　尚、第３反射部３１で反射された光は広がって第２光吸収領域１１ｂに入射するので、第３反射部３１で反射された光の一部が第２光吸収領域１１ｂに入射されず、第３反射部３１による受光感度の向上は限定的になる場合がある。また、第４反射部３５を省略した場合には、第２光吸収領域１１ｂへの光の入射は１回になるので、その分だけ受光感度の向上が制限される。
　実施例３の端面入射型半導体受光素子１Ｃを変形して、第２受光部３０と光を第２受光部３０に向けて反射させる第３反射部３１を備備させた端面入射型半導体受光素子１Ｆについて説明する。
　図１２に示すように、端面入射型半導体受光素子１Ｆは、半導体基板１０の主面１０ａ側に第１受光部１５及び第１受光部１５から離隔して形成された第２受光部３０を有し、裏面１０ｂの第１受光部１５と第２受光部３０の中間の部位に第３反射部３１を有する。第２受光部３０は、第２光吸収領域１１ｂとｐ型拡散領域１２ｂを有し、第１受光部１５と同じ構造のフォトダイオードである。
　端面入射型半導体受光素子１Ｆは、端面１０ｃ側の出射点Ｐから入射する光を屈折面１０ｄで第１受光部１５に向けて屈折させ、第１受光部１５の第１光吸収領域１１ａを透過した光を第１反射部２１で反射させて第１光吸収領域１１ａに再び入射させる。そして第１光吸収領域１１ａを透過した光を、半導体基板１０の裏面１０ｂに形成された第３反射部３１によって第２受光部３０に向けて反射させ、第２受光部３０の第２光吸収領域１１ｂに入射させる。
　第２受光部３０は環状電極３２の内側に第４反射部３５を有し、光が第２光吸収領域１１ｂに２回入射する。第３反射部３１と第４反射部３５は、第１反射部１５と同じ積層構造を有する。尚、第４反射部３５を省略することもできる。
　第３反射部３１で反射された光が第２受光部３０に入射するように、第２受光部３０は第１受光部１５から離隔させているが、第１受光部１５と第２受光部３０は電気的に並列接続され、第１、第２受光部１５，３０の出力の和が端面入射型半導体受光素子１Ｆから出力される。従って、出射点Ｐから入射する光は、第１、第２光吸収領域１１ａ，１１ｂに夫々２回入射するので、端面入射型半導体受光素子１Ｆの受光感度が向上する。
　尚、第３反射部３１で反射された光は広がって第２光吸収領域１１ｂに入射するので、第３反射部３１で反射された光の一部が第２光吸収領域１１ｂに入射されず、第３反射部３１による受光感度の向上は限定的になる場合がある。また、第４反射部３５を省略した場合には、第２光吸収領域１１ｂへの光の入射は１回になるので、その分だけ受光感度の向上が制限される。
　上記端面入射型半導体受光素子１Ａ～１Ｆの作用、効果について説明する。
　端面入射型半導体受光素子１Ａ～１Ｆは、半導体基板１０の主面１０ａ側に第１光吸収領域１１ａを有し、端面１０ｃ側の出射点Ｐから入射する光を溝反射部２０による反射又は屈折面１０ｄによる屈折によって、第１光吸収領域１１ａに入射させる。そして、端面入射型半導体受光素子１Ａ～１Ｆは主面１０ａ側の第１光吸収領域１１ａ近傍に第１反射部２１を有し、第１光吸収領域１１ａを透過した光が第１反射部２１で反射され、第１光吸収領域１１ａに再び入射される。第１光吸収領域１１ａの近傍に第１反射部２１があるので、反射された光の広がりは僅かである。従って、第１反射部２１で反射された光の全てを第１光吸収領域１１ａに入射させることができるので、端面入射型半導体受光素子１Ａ～１Ｆの受光感度を向上させることができる。
　端面入射型半導体受光素子１Ｂ，１Ｄは第２反射部２５，２６を有し、第１反射部２１によって反射されて第１光吸収領域１１ａを透過した光を、第２反射部２５，２６によって反射させて第１光吸収領域１１ａに入射させることができる。従って、第１、第２反射部２１，２５，２６によって入射光を第１光吸収領域１１ａに通算４回入射させることができるので、端面入射型半導体受光素子１Ｂ，１Ｄの受光感度を向上させることができる。
　端面入射型半導体受光素子１Ｅ，１Ｆは、半導体基板１０の主面１０ａ側の第１光吸収領域１１ａから離隔した第２光吸収領域１１ｂと、裏面１０ｂの第３反射部３１を有する。そして、第１反射部２１によって反射されて第１光吸収領域１１ａを透過した光を第３反射部で反射させて第２光吸収領域１１ｂに入射させる。従って、第１反射部２１によって入射光を第１光吸収領域１１ａに２回入射させることができ、第３反射部３１によって第１光吸収領域１１ａを透過した光を第２光吸収領域１１ｂに入射させることができるので、端面入射型半導体受光素子１Ｅ，１Ｆの受光感度を向上させることができる。
　端面入射型半導体受光素子１Ａ～１Ｆは、半導体基板１０の主面１０ａ側に第１光吸収領域１１ａを縁取るように形成された環状電極１６を有し、環状電極１６の内側に、誘電体膜１３と複数の金属膜２２～２４が積層された第１反射部２１が形成されている。環状電極１６と第１受光部１５のｐ型拡散領域１２ａの界面は、合金化によって細かい凹凸が生じるため反射率が低い。しかし、環状電極１６の内側には、合金化を防いで界面の平坦性を維持する誘電体膜１３と、高い反射率を提供するための複数の金属膜２２～２４とが積層された第１反射部２１が形成されている。従って、第１光吸収領域１１ａを透過した光を第１反射部２１で反射させて第１光吸収領域１１ａに入射させることができるので、端面入射型半導体受光素子１Ａ～１Ｆの受光感度を向上させることができる。
　その他、当業者であれば、本発明の趣旨を逸脱することなく、前記実施形態に種々の変更を付加した形態で実施可能であり、本発明はそのような変更形態も包含するものである。
１Ａ～１Ｆ　：端面入射型半導体受光素子
１０　　：半導体基板
１０ａ　：主面
１０ｂ　：裏面
１０ｃ　：端面
１０ｄ　：屈折面
１０ｅ　：端面
１０ｆ　：平面部
１１　　：ＩｎＧａＡｓ層
１１ａ　：第１光吸収領域
１１ｂ　：第２光吸収領域
１２　　：ｎ－ＩｎＰ層
１２ａ，１２ｂ　：ｐ型拡散領域
１３　　：誘電体膜
１５　　：第１受光部
１６　　：環状電極
１７　　：基板電極
１８　　：溝部
１８ａ　：第１傾斜面
１８ｂ　：第２傾斜面
２０　　：溝反射部
２１　　：第１反射部
２２　　：Ｃｒ膜
２３　　：Ｎｉ膜
２４　　：Ａｕ膜
２５，２６　　：第２反射部
３０　　：第２受光部
３１　　：第３反射部
３２　　：環状電極
３５　　：第４反射部

Claims (4)

  1. 　半導体基板の主面側に第１光吸収領域を有し、前記半導体基板の端面側から入射する光を反射又は屈折によって前記第１光吸収領域に入射させる端面入射型半導体受光素子において、
    　前記主面側に、前記第１光吸収領域を透過した光を前記第１光吸収領域に入射させるための第１反射部を有することを特徴とする端面入射型半導体受光素子。
  2. 　前記第１反射部によって反射されて前記第１光吸収領域を透過した光を前記第１光吸収領域に入射させるための第２反射部を有することを特徴とする請求項１に記載の端面入射型半導体受光素子。
  3. 　前記主面側に、前記第１光吸収領域から離隔した第２光吸収領域を有し、前記第１反射部によって反射されて前記第１光吸収領域を透過した光を前記第２光吸収領域に入射させるための第３反射部を有することを特徴とする請求項１に記載の端面入射型半導体受光素子。
  4. 　前記主面側に前記第１光吸収領域を縁取るように形成された環状電極を有し、前記第１反射部は、前記環状電極の内側において、誘電体膜と複数の金属膜を積層して形成されたことを特徴とする請求項１～３の何れか１項に記載の端面入射型半導体受光素子。
PCT/JP2020/021628 2020-06-01 2020-06-01 端面入射型半導体受光素子 WO2021245756A1 (ja)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004241681A (ja) * 2003-02-07 2004-08-26 Toshiba Corp 半導体受光装置及びその製造方法
JP2005165254A (ja) * 2003-11-28 2005-06-23 Korea Electronics Telecommun 光検出器が集積可能な光結合装置
JP2011003638A (ja) * 2009-06-17 2011-01-06 Opnext Japan Inc 受光素子
JP2011187607A (ja) * 2010-03-08 2011-09-22 Nippon Telegr & Teleph Corp <Ntt> 半導体受光素子

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004241681A (ja) * 2003-02-07 2004-08-26 Toshiba Corp 半導体受光装置及びその製造方法
JP2005165254A (ja) * 2003-11-28 2005-06-23 Korea Electronics Telecommun 光検出器が集積可能な光結合装置
JP2011003638A (ja) * 2009-06-17 2011-01-06 Opnext Japan Inc 受光素子
JP2011187607A (ja) * 2010-03-08 2011-09-22 Nippon Telegr & Teleph Corp <Ntt> 半導体受光素子

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