WO2024057435A1 - Backside incident-type semiconductor light receiving element - Google Patents

Backside incident-type semiconductor light receiving element Download PDF

Info

Publication number
WO2024057435A1
WO2024057435A1 PCT/JP2022/034374 JP2022034374W WO2024057435A1 WO 2024057435 A1 WO2024057435 A1 WO 2024057435A1 JP 2022034374 W JP2022034374 W JP 2022034374W WO 2024057435 A1 WO2024057435 A1 WO 2024057435A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
light
semiconductor
electrode
photodiode
Prior art date
Application number
PCT/JP2022/034374
Other languages
French (fr)
Japanese (ja)
Inventor
尚友 磯村
健 臼井
悦司 大村
Original Assignee
株式会社京都セミコンダクター
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社京都セミコンダクター filed Critical 株式会社京都セミコンダクター
Priority to PCT/JP2022/034374 priority Critical patent/WO2024057435A1/en
Publication of WO2024057435A1 publication Critical patent/WO2024057435A1/en

Links

Images

Classifications

    • 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
    • H01L31/08—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 in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—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 in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors

Definitions

  • the present invention relates to a back-illuminated semiconductor light-receiving device, and particularly to a back-illuminated semiconductor light-receiving device that requires high-speed response.
  • optical communication In the field of optical communications, development is underway to increase transmission speeds in order to cope with the rapid increase in communication traffic in recent years.
  • an optical pulse signal is transmitted from the transmitting side via an optical fiber cable or the like, and on the receiving side, the optical pulse signal received by a semiconductor light receiving element is converted into an electrical signal.
  • Increasing the transmission speed on the receiving side is achieved by increasing the response speed of the semiconductor light-receiving element, but for this purpose it is necessary to increase the upper limit of the response speed determined by the element capacitance and element resistance.
  • the element capacitance In order to increase the response speed of a semiconductor light-receiving element, it is effective to reduce the element capacitance. For example, when a semiconductor light-receiving element has a PIN-type photodiode in which a light absorption layer is sandwiched between two semiconductor layers of different conductivity types, the light absorption layer generates two types of charge carriers by photoelectric conversion upon receiving a light pulse signal. The smaller the area, the smaller the element capacitance. When a response frequency band of about 20 GHz is required, if the light absorption layer is formed into a circle with a diameter of about 20 ⁇ m, the element capacitance can be reduced to an allowable level.
  • a condenser is formed integrally with the semiconductor substrate on the back surface of the semiconductor substrate where the light enters.
  • a back-illuminated semiconductor light-receiving element equipped with an optical lens (convex lens) is known.
  • the drift travel time of charge carriers generated in the light absorption layer in the light absorption layer in order to increase the response speed of a semiconductor light-receiving element, it is also effective to shorten the drift travel time of charge carriers generated in the light absorption layer in the light absorption layer.
  • the drift distance and drift time can be shortened.
  • the light absorption layer is thin, the chances of the incident light being converted into charge carriers are reduced, and the sensitivity of the semiconductor light receiving element is reduced.
  • a mirror electrode is formed on the photodiode through a SiN film, and light is incident from the back side of the semiconductor substrate and transmitted through the InGaAs light absorption layer of the photodiode.
  • a back-illuminated semiconductor light-receiving element in which light is reflected by a mirror electrode and re-enters an InGaAs light absorption layer is known.
  • a mirror electrode formed of a Ti (titanium) film and an Au (gold) film is connected to a semiconductor layer of a photodiode via a ring-shaped contact portion penetrating the SiN film.
  • the reflective area of the mirror electrode is increased, the area of the contact portion becomes smaller, so the resistance of the contact portion, which is one of the components of the element resistance, becomes larger, which impedes an increase in response speed.
  • the reflection area of the mirror electrode will become smaller and less light will be reflected, resulting in a decrease in sensitivity.
  • Patent Document 3 the time it takes for light to travel back and forth between a photodiode on the front side of a semiconductor substrate and a reflective film formed of a Ti film and an Au film on the back side depends on the thickness of the semiconductor substrate. It takes a few microseconds. Therefore, the light reflected by the reflective film on the back side of the first optical pulse signal and the subsequent optical pulse signal overlap and enter the light absorption layer, making it impossible to separate the signals, so a faster response speed is required.
  • This technology cannot be used if
  • the electrodes formed by the Ti film and the Au film are alloyed by mutual diffusion to form ohmic contact. Then, for example, when it is bonded to the outside, it is heated and alloying is promoted, and there is a possibility that high reflectance cannot be obtained due to this alloying. Therefore, when a three-layer structure (see FIG. 13) having a Pt (platinum) film as a barrier film between a Ti film and an Au film is used, as in the barrier electrode of Patent Document 2, a high reflectance as shown in FIG. 14 is obtained. is not obtained.
  • an object of the present invention is to provide a back-illuminated semiconductor light-receiving element having a high reflectance electrode suitable for increasing response speed.
  • the invention of claim 1 has a first semiconductor layer, a light absorption layer, a second semiconductor layer, and a third semiconductor layer stacked in order from the semiconductor substrate side on the front side of a semiconductor substrate that is transparent to incident light.
  • a back-illuminated semiconductor light-receiving element that includes a photodiode and in which light is incident on the photodiode from the back side of the semiconductor substrate, the photodiode is connected to most of the surface of the third semiconductor layer.
  • the electrode includes, in order from the third semiconductor layer side, a complex refractive index having a real part n having a value smaller than the refractive index of the third semiconductor layer and an imaginary part k having a value of 10 or more.
  • a second metal layer connected to the first metal layer on the outer peripheral side of the dielectric layer; The structure is characterized in that the light that has passed through is reflected by the electrode and re-enters the light absorption layer.
  • the electrode of the photodiode Since this electrode has the first metal layer connected to most of the surface of the third semiconductor layer of the photodiode, it is possible to increase the reflective surface of the electrode and increase the contact area to reduce contact resistance. , which is advantageous in increasing response speed.
  • This electrode has a first metal layer in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer and the value of the imaginary part k of the complex refractive index is 10 or more,
  • a structure including a dielectric layer between the first metal layer and the second metal layer can provide a high reflectance. Therefore, most of the light that has passed through the light absorption layer can be reflected by the electrode close to the photodiode and be made to enter the light absorption layer again, so that sensitivity can be improved. Therefore, the light absorption layer can be made thinner while suppressing a decrease in sensitivity, and the response speed can be increased.
  • a back-illuminated semiconductor light-receiving device is characterized in that, in the first aspect of the invention, the first metal layer is formed of a metal selected from the group consisting of Au, Ag, Cr, and Al. It is said that According to the above structure, the first metal layer is made of Au, which is a metal in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer, and the value of the imaginary part k of the complex refractive index is 10 or more. (gold), Ag (silver), Cr (chromium), or Al (aluminum). Since these metals are commonly used as materials for semiconductor devices, electrodes with high reflectance can be easily formed.
  • a back-illuminated semiconductor light-receiving element is characterized in that, in the first aspect of the present invention, an adhesion layer containing Ti as a main component is provided between the dielectric layer and the second metal layer.
  • the adhesion layer prevents film lifting or peeling of the second metal layer, which is a concern when the second metal layer is formed of a metal that does not have good adhesion to the dielectric layer. This makes it possible to prevent deterioration in electrode function due to film lifting or film peeling.
  • the photodiode is formed in a truncated cone shape such that the light absorption layer has a diameter of 20 ⁇ m or less, and the photodiode is formed on the back surface of the semiconductor substrate. , it is characterized by having a condensing lens portion whose lens optical axis is aligned with the central axis of the truncated conical photodiode.
  • the diameter of the light absorption layer is 20 ⁇ m or less, the area of the photodiode can be reduced, the element capacitance can be reduced, and the response speed can be increased.
  • the back-illuminated semiconductor light-receiving device of the present invention it is possible to increase the response speed while suppressing a decrease in sensitivity due to the high reflectance electrode.
  • FIG. 1 is a cross-sectional view of a back-illuminated semiconductor light-receiving device according to an embodiment of the present invention.
  • FIG. 2 is an enlarged cross-sectional view of main parts showing the photodiode and electrodes of FIG. 1.
  • FIG. FIG. 3 is a cross-sectional view showing a process of forming a truncated conical photodiode.
  • FIG. 3 is a cross-sectional view showing a process of forming an electrode of a photodiode.
  • 3 is a graph showing, in contour lines, the calculated results of the reflectance of the electrode with respect to the complex refractive index of the first metal layer of the electrode.
  • 11 is a graph showing the relationship between the thickness of a dielectric layer, the thickness of a first metal layer, and the reflectance of an electrode when the first metal layer of the electrode is made of Ti. It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Ta. It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Ag. It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Al.
  • FIG. 2 is a cross-sectional view showing an example of a photodiode including an electrode having an adhesion layer between a dielectric film and a second metal film.
  • 12 is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode in FIG. 11 is made of Cr.
  • FIG. 2 is a sectional view showing a conventional example of an electrode.
  • 14 is a graph showing the relationship between the Ti thickness and Pt thickness of the electrode of FIG. 13 and the reflectance of this electrode.
  • a back-illuminated semiconductor light-receiving device 1 includes a first semiconductor layer 3, a light absorption layer 4, and a first semiconductor layer 3, which are laminated in order from the semiconductor substrate 2 side on the front surface 2a side of a semiconductor substrate 2.
  • a PIN type photodiode 7 having two semiconductor layers 5 and a third semiconductor layer 6 is provided.
  • the photodiode 7 is formed into a truncated cone shape by a groove 8a formed on the outer periphery of the photodiode 7.
  • the photodiode 7 is formed so that the diameter of the light absorption layer 4 is, for example, 20 ⁇ m or less, and the area is reduced to reduce the element capacitance.
  • the semiconductor substrate 2 is, for example, a semi-insulating InP substrate that is transparent to the emitted light L1 having a wavelength in the infrared region (for example, 1300 to 1600 nm) emitted from the optical fiber cable OC.
  • the first semiconductor layer 3 is a first conductivity type, for example, an n-InP layer.
  • the light absorption layer 4 is, for example, an InGaAs layer.
  • the second semiconductor layer 5 is a p-InP layer of a second conductivity type, for example.
  • the third semiconductor layer 6 is, for example, an InGaAs layer formed thinner than the light absorption layer 4, and is formed for ohmic contact with an electrode (second electrode 12) to be described later.
  • the groove 8a is formed by etching the first semiconductor layer 3 halfway through the third semiconductor layer 6, second semiconductor layer 5, and light absorption layer 4 by, for example, reactive ion etching. At this time, an opening 8b (hole or groove) reaching the first semiconductor layer 3 outside the photodiode 7 is also formed at the same time. Then, as shown in FIG. 3, the insulating film 9 is formed using a known method to cover a region other than most of the surface 6a of the third semiconductor layer 6 of the photodiode 7 and the bottom of the opening 8b (not shown). contact holes 9a and 9b are formed in the insulating film 9. For example, a SiO2 film, a SiN film, or the like is used as the insulating film 9.
  • a first metal layer 12a connected to the third semiconductor layer 6 through the contact hole 9a is selectively formed so as to extend to the outside of the groove 8a, for example, by a known lift-off method. Ru.
  • a dielectric layer 12b is selectively formed on the first metal layer 12a in a region corresponding to the photodiode 7 by a known method (film formation, photolithography, etching).
  • a second metal layer 12c is selectively formed to cover the first metal layer 12a and the dielectric layer 12b by, for example, a known lift-off method, and the second electrode 12 is formed as shown in FIGS. 1 and 2. be done.
  • the second metal layer 12c is connected to the first metal layer 12a on the outer peripheral side of the dielectric layer 12b.
  • the first metal layer 12a and the second metal layer 12c connected to the first semiconductor layer 3 through the contact hole 9b are selectively formed so as to extend outside the opening 8b.
  • the first electrode 11 is formed simultaneously with the second electrode 12.
  • the first and second electrodes 11 and 12 are each connected to an external wiring section of a printed circuit board, for example.
  • the second electrode 12 formed in this manner has a structure in which a first metal layer 12a, a dielectric layer 12b, and a second metal layer 12c are laminated in order from the third semiconductor layer 6 side in a portion corresponding to the photodiode 7. has.
  • the first metal layer 12a has a value of the real part n (refractive index) of the complex refractive index smaller than the refractive index of the third semiconductor layer 6 and a value of the imaginary part k (extinction coefficient) of the complex refractive index of 10 or more. is made of metal.
  • This first metal layer 12a is a thin film of a metal alternatively selected from the group consisting of Au (gold), Ag (silver), Al (aluminum), and Cr (chromium).
  • the second metal layer 12c is often made of Au, which can be easily bonded to the outside and is difficult to oxidize.
  • a condensing lens portion 2c formed integrally with the semiconductor substrate 2 and having a convex lens shape.
  • the condensing lens portion 2c is formed such that the lens optical axis coincides with the central axis 7a of the photodiode 7 having a truncated cone shape.
  • Output light L1 (light pulse signal) emitted from the optical fiber cable OC is emitted so that its optical axis coincides with the central axis 7a, and enters the condenser lens portion 2c while expanding conically.
  • the incident light L2 that enters the condenser lens section 2c and travels through the semiconductor substrate 2 is condensed onto the photodiode 7 by the condensing action of the condenser lens section 2c.
  • incident light L2 enters the photodiode 7, and a portion of it is converted into two types of charge carriers (electrons and holes) in the light absorption layer 4. Then, one charge carrier moves to the first semiconductor layer 3, and the other charge carrier moves to the second semiconductor layer 5, and is output as a photocurrent to the outside via the first and second electrodes 11 and 12. Ru. Further, the configuration is such that reflected light L3 of the incident light L2 that is not photoelectrically converted and is transmitted through the light absorption layer 4 and reflected by the second electrode 12 enters the light absorption layer 4 again. A part of the reflected light L3 re-entering the light absorption layer 4 is photoelectrically converted and outputted to the outside as a photocurrent together with charge carriers photoelectrically converted from the incident light L2 via the first and second electrodes 11 and 12. .
  • the reflected light L3 re-enters the light absorption layer 4, the effective thickness of the light absorption layer 4 increases, and the sensitivity of the back-illuminated semiconductor light receiving element 1 improves. Therefore, it is possible to form the light absorption layer 4 thinly while suppressing a decrease in sensitivity, and it is possible to shorten the transit time of charge carriers and increase the response speed.
  • the second electrode 12 is close to the photodiode 7, the time for light to travel back and forth between the light absorption layer 4 and the second electrode 12 is shortened, and it can be separated from the subsequent optical pulse signal. Therefore, it can support high-speed communication.
  • the area of the photodiode 7 is small, the element capacitance can be reduced and the response speed can be increased.
  • the incident light L2 is made incident on the small area photodiode 7 by the condenser lens section 2c, the incident light L2 can be used without waste to suppress a decrease in sensitivity.
  • the reflectance of the second electrode 12 will be explained using an example in which the wavelength ⁇ of light is 1550 nm.
  • a portion of the incident light L2 passes through the light absorption layer 4, passes through the second semiconductor layer 5 and the third semiconductor layer 6, and reaches the first metal layer 12a of the second electrode 12.
  • the second semiconductor layer 5 is p-InP and the third semiconductor layer 6 is InGaAs
  • the refractive index of the second and third semiconductor layers 5 and 6 is 3.22, respectively.
  • FIG. 5 shows the reflectance of the second electrode 12 using the real part n (refractive index) and imaginary part k (extinction coefficient) of the complex refractive index of the metal of the first metal layer 12a constituting the second electrode 12 as parameters.
  • the calculation results are shown in contour lines.
  • the thickness of the first metal layer 12a is 20 nm
  • the dielectric layer 12b is formed of a SiO2 film with a thickness of 100 nm.
  • the second metal layer 12c is an Au film with a thickness of 600 nm also in the graphs from FIG. 5 onwards.
  • the metals that provide a high reflectance of over 80% are Au (gold), Ag (silver), Cu (copper), and Al (aluminum). and Cr (chromium). These metals have a value of the real part n of the complex refractive index smaller than the refractive index of the third semiconductor layer 6 (InGaAs).
  • Ni nickel
  • Ti titanium
  • Pt platinum
  • Ni nickel
  • Ti titanium
  • Pt platinum
  • Ta tantalum
  • the value of the imaginary part k of the complex refractive index is smaller than that of Ag etc., so that the incident light is It is thought that the reflectance is low because it penetrates deeply from the interface.
  • Cu is difficult to process compared to Au, Ag, Al, and Cr, and has the property of easily diffusing into other materials, so it is difficult to use it as the first metal layer 12a.
  • FIG. 6 shows the reflectance of the second electrode 12 calculated using the thickness of the dielectric layer 12b (SiO2 film) and the thickness of the first metal layer 12a as parameters when the first metal layer 12a is made of Ti. , shown as contour lines.
  • the thinner the first metal layer 12a and the thinner the dielectric layer 12b the higher the reflectance.
  • the thinner the first metal layer 12a is, the more light passes through the first metal layer 12a, and the more light is reflected at the interface between the first metal layer 12a and the dielectric layer 12b and the interface between the dielectric layer 12b and the second metal layer 12c. This is thought to be due to an increase in
  • FIG. 7 shows the reflectance of the second electrode 12 calculated using the thickness of the dielectric layer 12b (SiO2 film) and the thickness of the first metal layer 12a as parameters when the first metal layer 12a is formed of Ta. , shown as contour lines.
  • the thickness of the dielectric layer 12b is, for example, 100 nm and the thickness of the first metal layer 12a is, for example, 20 nm
  • the reflectance is less than 80%. In order to bring the reflectance close to 90%, it is necessary to make at least one of the first metal layer 12a and the dielectric layer 12b thinner, which is not easy.
  • FIG. 8 shows a case where the first metal layer 12a is made of Ag.
  • FIG. 9 shows a case where the first metal layer 12a is made of Al.
  • FIG. 10 shows a case where the first metal layer 12a is made of Cr.
  • the dielectric layer 12b has a thickness of, for example, 100 nm and the first metal layer 12a has a thickness of, for example, 20 nm
  • the reflectance exceeds 85%. Therefore, when the first metal layer 12a is made of Ag, Al, or Cr, high reflectance can be easily obtained.
  • the thickness of the first metal layer 12a thicker than, for example, 25 nm, it is possible to reduce the contact resistance and obtain a reflectance of 90% or more. Further, according to FIG. 3, a high reflectance can be obtained similarly when the first metal layer 12a is made of Au.
  • the second electrode 12 can be formed in the same manner as shown in FIG.
  • the dielectric layer 12b prevents a change in the complex refractive index due to alloying of the first metal layer 12a by preventing alloying between the first metal layer 12a and the second metal layer 12c due to mutual diffusion. Since the first metal layer 12a and the second metal layer 12c are connected on the outer peripheral side of the dielectric layer 12b, the second electrode 12 has conductivity and high reflectance. Note that, when the thickness of the first metal layer 12a is such that the contact resistance is small, the reflection by the second electrode 12 is dominated by reflection at the interface between the third semiconductor layer 6 and the first metal layer 12a, and the dielectric
  • the layer 12b may be formed of, for example, a SiON film, a SiN film, etc. other than the SiO2 film.
  • the second electrode 12 may include an adhesion layer 12d containing Ti as a main component at least between the dielectric layer 12b and the second metal layer 12c. Note that the thickness of the adhesive layer 12d that is generally used is about 10 nm.
  • the second electrode 12 provided with the Ti adhesion layer 12d can obtain a high reflectance.
  • the reflectance exceeds 85%, which is the same level of reflection as the second electrode 12 in FIG. 10 without the adhesive layer 12d. rate is obtained.
  • the adhesion layer 12d can prevent the second metal layer 12c from peeling off or lifting, thereby preventing the function of the second electrode 12A from being impaired.
  • FIG. 13 shows a photodiode 7 in which the second electrode 12 is replaced with a conventional electrode 22 having a conventional structure.
  • the conventional electrode 22 is formed by laminating, in order from the third semiconductor layer 6 side, a Ti layer 22a, a Pt layer 22b as a barrier layer for preventing alloying during bonding with the outside, and an Au layer 22c.
  • the value of the real part n of the complex refractive index of the Ti layer 22a is larger than the refractive index of the third semiconductor layer 6, and the value of the real part n of the complex refractive index of the Pt layer 22b is larger than the value of the complex refractive index of the Ti layer 22a.
  • the second electrode 12 is formed of a metal in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer 6, and the value of the imaginary part k of the complex refractive index is 10 or more. It has a first metal layer 12a. With this structure including the dielectric layer 12b between the first metal layer 12a and the second metal layer 12c, higher reflectance than before can be obtained. Therefore, most of the light transmitted through the light absorption layer 4 can be reflected by the second electrode 12 close to the photodiode 7 and can be made to enter the light absorption layer 4 again. Therefore, the light absorption layer 4 can be made thinner while suppressing a decrease in sensitivity of the back-illuminated semiconductor light-receiving element 1, and the response speed can be increased.
  • the first metal layer 12a is made of a metal such as Au, Ag, or Cr, in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer 6 and the value of the imaginary part k of the complex refractive index is 10 or more. and Al. Since these metals are commonly used as materials for semiconductor devices, the second electrode 12 with high reflectance can be easily formed.
  • the second electrode 12 may have an adhesion layer 12d containing Ti as a main component between the dielectric layer 12b and the second metal layer 12c.
  • the adhesion layer 12d can prevent film lifting or peeling of the second metal layer 12c, which is a concern when the adhesion between the second metal layer 12c and the dielectric layer 12b is not good. Therefore, deterioration in the function of the second electrode 12 due to film lifting or film peeling can be prevented.
  • the photodiode 7 is formed in the shape of a truncated cone such that the diameter of the light absorption layer 4 is 20 ⁇ m or less, and the optical axis of the lens is aligned with the central axis 7a of the truncated cone-shaped photodiode 7 on the back surface 2b of the semiconductor substrate 2. It has a condensing lens section 2c. Since the area of the photodiode 7 is small, the element capacitance can be reduced, and the response speed can be increased.
  • the condenser lens section 2c By condensing the light and making it incident on the photodiode 7, which has a small area, using the condenser lens section 2c, it is possible to suppress a decrease in the sensitivity of the back-illuminated semiconductor light-receiving element 1. Note that the diameter of the light absorption layer 4 can be appropriately set depending on the required response frequency band.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Light Receiving Elements (AREA)

Abstract

[Problem] To provide a backside incident-type semiconductor light receiving element having a high-reflectance electrode suited to an increase in response speed. [Solution] This backside incident-type semiconductor light receiving element (1) comprises a photodiode (7) having a first semiconductor layer (3), a light absorption layer (4), a second semiconductor layer (5), and a third semiconductor layer (6) laminated in this order on a front surface (2a) side of a semiconductor substrate (2) that is transparent to incident light (L1), wherein light enters the photodiode (7) from the rear surface (2b) side of the semiconductor substrate (2). The backside incident-type semiconductor light receiving element comprises an electrode (12) connected to the majority of a front surface (6a) of the third semiconductor layer (6) of the photodiode (7), wherein: the electrode (12) has, in order from the third semiconductor layer (6) side, a first metal layer (12a) for which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer (6) and the value of the imaginary part k is at least 10, a dielectric layer (12b), and a second metal layer (12c) connected to the first metal layer (12a) on the outer peripheral side of the dielectric layer (12b); and light that has entered the photodiode (7) from the rear surface (2b) side and passed through the light absorption layer (4) is reflected at the electrode (12) and re-enters the light absorption layer (4).

Description

裏面入射型半導体受光素子Back-illuminated semiconductor photodetector
　本発明は、裏面入射型半導体受光素子に関し、特に高速応答が要求される裏面入射型半導体受光素子に関する。 The present invention relates to a back-illuminated semiconductor light-receiving device, and particularly to a back-illuminated semiconductor light-receiving device that requires high-speed response.
　光通信分野では、近年の通信量の急増に対応するため、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パルス信号を送信し、受信側では半導体受光素子が受信した光パルス信号を電気信号に変換している。受信側における伝送速度の高速化は、半導体受光素子の応答速度の高速化により実現されるが、そのためには素子容量と素子抵抗で定まる応答速度の上限を向上させる必要がある。 In the field of optical communications, development is underway to increase transmission speeds in order to cope with the rapid increase in communication traffic in recent years. In optical communication, an optical pulse signal is transmitted from the transmitting side via an optical fiber cable or the like, and on the receiving side, the optical pulse signal received by a semiconductor light receiving element is converted into an electrical signal. Increasing the transmission speed on the receiving side is achieved by increasing the response speed of the semiconductor light-receiving element, but for this purpose it is necessary to increase the upper limit of the response speed determined by the element capacitance and element resistance.
　半導体受光素子の応答速度の高速化には、素子容量を小さくすることが有効である。例えば半導体受光素子が異なる導電型の２つの半導体層で光吸収層を挟持したＰＩＮ型のフォトダイオードを有する場合に、光パルス信号を受けて光電変換によって２種類の電荷キャリアを生成する光吸収層の面積が小さいほど素子容量は小さくなる。そして、２０ＧＨｚ程度の応答周波数帯域が要求される場合、光吸収層を直径２０μｍ程度の円形とすれば、素子容量が許容できる程度に小さくなる。 In order to increase the response speed of a semiconductor light-receiving element, it is effective to reduce the element capacitance. For example, when a semiconductor light-receiving element has a PIN-type photodiode in which a light absorption layer is sandwiched between two semiconductor layers of different conductivity types, the light absorption layer generates two types of charge carriers by photoelectric conversion upon receiving a light pulse signal. The smaller the area, the smaller the element capacitance. When a response frequency band of about 20 GHz is required, if the light absorption layer is formed into a circle with a diameter of about 20 μm, the element capacitance can be reduced to an allowable level.
　このような小径のフォトダイオードに光を十分に導入して感度低下を抑制するために、例えば特許文献１のように光が入射する半導体基板の裏面に、半導体基板と一体的に形成された集光レンズ（凸レンズ）を備えた裏面入射型半導体受光素子が知られている。 In order to sufficiently introduce light into such a small-diameter photodiode and suppress a decrease in sensitivity, for example, as disclosed in Patent Document 1, a condenser is formed integrally with the semiconductor substrate on the back surface of the semiconductor substrate where the light enters. A back-illuminated semiconductor light-receiving element equipped with an optical lens (convex lens) is known.
　一方、半導体受光素子の応答速度の高速化には、光吸収層で生成された電荷キャリアの光吸収層におけるドリフト走行時間を短縮することも有効である。例えばＰＩＮ型のフォトダイオードにおいて、２つの半導体層の間の光吸収層を薄くすることによって、ドリフト走行距離を短くしてドリフト走行時間を短縮することができる。しかし、光吸収層が薄い場合には、入射した光が電荷キャリアに変換される機会が減少し、半導体受光素子の感度が低下する。 On the other hand, in order to increase the response speed of a semiconductor light-receiving element, it is also effective to shorten the drift travel time of charge carriers generated in the light absorption layer in the light absorption layer. For example, in a PIN type photodiode, by thinning the light absorption layer between two semiconductor layers, the drift distance and drift time can be shortened. However, if the light absorption layer is thin, the chances of the incident light being converted into charge carriers are reduced, and the sensitivity of the semiconductor light receiving element is reduced.
　このような感度低下を抑えるため、例えば特許文献２のように、フォトダイオードにＳｉＮ膜を介してミラー電極が形成され、半導体基板の裏面側から入射してフォトダイオードのＩｎＧａＡｓ光吸収層を透過した光が、ミラー電極で反射されてＩｎＧａＡｓ光吸収層に再入射する裏面入射型半導体受光素子が知られている。また、感度向上のために、例えば特許文献３のように、ｎ－ＩｎＧａＡｓ層（光吸収層）を２回透過した光が、半導体基板裏面側に形成された反射膜によって反射されて光吸収層に再入射する裏面入射型半導体受光素子が知られている。 In order to suppress such a decrease in sensitivity, for example, as in Patent Document 2, a mirror electrode is formed on the photodiode through a SiN film, and light is incident from the back side of the semiconductor substrate and transmitted through the InGaAs light absorption layer of the photodiode. A back-illuminated semiconductor light-receiving element in which light is reflected by a mirror electrode and re-enters an InGaAs light absorption layer is known. In addition, in order to improve sensitivity, for example, as in Patent Document 3, light that has passed through the n-InGaAs layer (light absorption layer) twice is reflected by a reflective film formed on the back side of the semiconductor substrate, and the light absorption layer A back-illuminated semiconductor light-receiving element that re-enters the light is known.
特開平２－１０５５８５号公報Japanese Patent Application Publication No. 2-105585 特開２０１８－１５２３６９号公報JP 2018-152369 A 特開平６－７７５１８号公報Japanese Patent Application Publication No. 6-77518
　特許文献２では、ＳｉＮ膜を貫通するリング状のコンタクト部を介して、Ｔｉ（チタン）膜とＡｕ（金）膜で形成されたミラー電極がフォトダイオードの半導体層に接続されている。しかし、ミラー電極の反射面積を大きくするとコンタクト部の面積が小さくなるので、素子抵抗の構成要素の１つであるコンタクト部の抵抗が大きくなって、応答速度の高速化が阻害される。また、コンタクト部の抵抗を小さくするためにコンタクト部の面積大きくすると、ミラー電極の反射面積が小さくなって反射される光が少なくなり、感度が低下する。 In Patent Document 2, a mirror electrode formed of a Ti (titanium) film and an Au (gold) film is connected to a semiconductor layer of a photodiode via a ring-shaped contact portion penetrating the SiN film. However, if the reflective area of the mirror electrode is increased, the area of the contact portion becomes smaller, so the resistance of the contact portion, which is one of the components of the element resistance, becomes larger, which impedes an increase in response speed. Furthermore, if the area of the contact portion is increased in order to reduce the resistance of the contact portion, the reflection area of the mirror electrode will become smaller and less light will be reflected, resulting in a decrease in sensitivity.
　一方、特許文献３では、半導体基板の表面側のフォトダイオードと裏面側のＴｉ膜とＡｕ膜で形成された反射膜の間を光が往復するのにかかる時間は、半導体基板の厚さによるが数マイクロ秒になる。それ故、先に入射した光パルス信号の裏面側の反射膜による反射光と後続の光パルス信号とが重なって光吸収層に入射して信号を分離できなくなるので、応答速度の高速化が要求される場合にはこの技術を利用することができない。 On the other hand, in Patent Document 3, the time it takes for light to travel back and forth between a photodiode on the front side of a semiconductor substrate and a reflective film formed of a Ti film and an Au film on the back side depends on the thickness of the semiconductor substrate. It takes a few microseconds. Therefore, the light reflected by the reflective film on the back side of the first optical pulse signal and the subsequent optical pulse signal overlap and enter the light absorption layer, making it impossible to separate the signals, so a faster response speed is required. This technology cannot be used if
　また、Ｔｉ膜とＡｕ膜によって形成された電極は、相互拡散により合金化してオーミック接触になる。そして、例えば外部との接合時に加熱されて合金化が促進され、この合金化によって高い反射率が得られない虞がある。そこで、特許文献２のバリア電極のように、Ｔｉ膜とＡｕ膜の間にバリア膜としてＰｔ（白金）膜を有する３層構造（図１３参照）とした場合、図１４のように高い反射率が得られない。 Furthermore, the electrodes formed by the Ti film and the Au film are alloyed by mutual diffusion to form ohmic contact. Then, for example, when it is bonded to the outside, it is heated and alloying is promoted, and there is a possibility that high reflectance cannot be obtained due to this alloying. Therefore, when a three-layer structure (see FIG. 13) having a Pt (platinum) film as a barrier film between a Ti film and an Au film is used, as in the barrier electrode of Patent Document 2, a high reflectance as shown in FIG. 14 is obtained. is not obtained.
　そこで、本発明は、応答速度の高速化に適した高反射率の電極を有する裏面入射型半導体受光素子を提供することを目的としている。 Therefore, an object of the present invention is to provide a back-illuminated semiconductor light-receiving element having a high reflectance electrode suitable for increasing response speed.
　請求項１の発明は、入射光に対して透明な半導体基板の表面側に、この半導体基板側から順に積層された第１半導体層と光吸収層と第２半導体層と第３半導体層を有するフォトダイオードを備え、前記フォトダイオードに対して前記半導体基板の裏面側から光が入射される裏面入射型半導体受光素子において、前記フォトダイオードは、前記第３半導体層の表面の大部分に接続された電極を備え、前記電極は、前記第３半導体層側から順に、複素屈折率の実部ｎの値が前記第３半導体層の屈折率よりも小さく且つ虚部ｋの値が１０以上である第１金属層と、誘電体層と、前記誘電体層の外周側で前記第１金属層に接続された第２金属層を有し、前記裏面側から前記フォトダイオードに入射されて前記光吸収層を透過した光が、前記電極で反射されて前記光吸収層に再入射するように構成されたことを特徴としている。 The invention of claim 1 has a first semiconductor layer, a light absorption layer, a second semiconductor layer, and a third semiconductor layer stacked in order from the semiconductor substrate side on the front side of a semiconductor substrate that is transparent to incident light. In a back-illuminated semiconductor light-receiving element that includes a photodiode and in which light is incident on the photodiode from the back side of the semiconductor substrate, the photodiode is connected to most of the surface of the third semiconductor layer. The electrode includes, in order from the third semiconductor layer side, a complex refractive index having a real part n having a value smaller than the refractive index of the third semiconductor layer and an imaginary part k having a value of 10 or more. a second metal layer connected to the first metal layer on the outer peripheral side of the dielectric layer; The structure is characterized in that the light that has passed through is reflected by the electrode and re-enters the light absorption layer.
　上記構成によれば、半導体基板の裏面側からフォトダイオードに入射して光吸収層を透過した光が、このフォトダイオードの電極で反射されて光吸収層に再入射する。この電極は、フォトダイオードの第３半導体層の表面の大部分に接続された第１金属層を有するので、電極の反射面を大きくすると共に接触面積を大きくしてコンタクト抵抗を小さくすることができ、応答速度の高速化に有利である。そして、この電極は、複素屈折率の実部ｎの値が第３半導体層の屈折率よりも小さく且つ複素屈折率の虚部ｋの値が１０以上である第１金属層を有し、この第１金属層と第２金属層との間に誘電体層を備えた構造によって、高い反射率を得ることができる。従って、光吸収層を透過した光の大部分をフォトダイオードに近接する電極で反射して光吸収層に再入射させることができるので、感度を向上させることができる。それ故、感度の低下を抑制しながら光吸収層を薄くして、応答速度の高速化を図ることができる。 According to the above configuration, light that enters the photodiode from the back side of the semiconductor substrate and passes through the light absorption layer is reflected by the electrode of the photodiode and re-enters the light absorption layer. Since this electrode has the first metal layer connected to most of the surface of the third semiconductor layer of the photodiode, it is possible to increase the reflective surface of the electrode and increase the contact area to reduce contact resistance. , which is advantageous in increasing response speed. This electrode has a first metal layer in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer and the value of the imaginary part k of the complex refractive index is 10 or more, A structure including a dielectric layer between the first metal layer and the second metal layer can provide a high reflectance. Therefore, most of the light that has passed through the light absorption layer can be reflected by the electrode close to the photodiode and be made to enter the light absorption layer again, so that sensitivity can be improved. Therefore, the light absorption layer can be made thinner while suppressing a decrease in sensitivity, and the response speed can be increased.
　請求項２の発明の裏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金属層は、Ａｕ、Ａｇ、Ｃｒ及びＡｌからなる群から選択される金属によっ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金属層は、複素屈折率の実部ｎの値が第３半導体層の屈折率よりも小さく且つ複素屈折率の虚部ｋの値が１０以上の金属であるＡｕ（金）、Ａｇ（銀）、Ｃｒ（クロム）又はＡｌ（アルミニウム）によって形成される。これらの金属は、半導体素子の材料として一般的に使用されているので、反射率が高い電極を容易に形成することができる。 A back-illuminated semiconductor light-receiving device according to a second aspect of the invention is characterized in that, in the first aspect of the invention, the first metal layer is formed of a metal selected from the group consisting of Au, Ag, Cr, and Al. It is said that
According to the above structure, the first metal layer is made of Au, which is a metal in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer, and the value of the imaginary part k of the complex refractive index is 10 or more. (gold), Ag (silver), Cr (chromium), or Al (aluminum). Since these metals are commonly used as materials for semiconductor devices, electrodes with high reflectance can be easily formed.
　請求項３の発明の裏面入射型半導体受光素子は、請求項１の発明において、前記誘電体層と前記第２金属層の間にＴｉを主成分とする密着層を有することを特徴としている。
　上記構成によれば、誘電体層との密着性が良好ではない金属によって第２金属層が形成された場合に懸念される第２金属層の膜浮き又は膜剥がれを、密着層によって防止することができ、膜浮き又は膜剥がれによる電極の機能の低下を防ぐことができる。 A back-illuminated semiconductor light-receiving element according to a third aspect of the present invention is characterized in that, in the first aspect of the present invention, an adhesion layer containing Ti as a main component is provided between the dielectric layer and the second metal layer.
According to the above configuration, the adhesion layer prevents film lifting or peeling of the second metal layer, which is a concern when the second metal layer is formed of a metal that does not have good adhesion to the dielectric layer. This makes it possible to prevent deterioration in electrode function due to film lifting or film peeling.
　請求項４の発明の裏面入射型半導体受光素子は、請求項１の発明において、前記フォトダイオードは、前記光吸収層の直径が２０μｍ以下となる円錐台状に形成され、前記半導体基板の裏面に、円錐台状の前記フォトダイオードの中心軸線にレンズ光軸を一致させた集光レンズ部を有することを特徴としている。
　上記構成によれば、光吸収層の直径が２０μｍ以下なので、フォトダイオードの面積を小さくして素子容量を小さくすることができ、応答速度を高速化することができる。そして、この面積が小さいフォトダイオードに対して、集光レンズ部によって集光して入射させることによって感度の低下を抑制することができる。 In the back-illuminated semiconductor light-receiving element of the invention according to claim 4, in the invention according to claim 1, the photodiode is formed in a truncated cone shape such that the light absorption layer has a diameter of 20 μm or less, and the photodiode is formed on the back surface of the semiconductor substrate. , it is characterized by having a condensing lens portion whose lens optical axis is aligned with the central axis of the truncated conical photodiode.
According to the above configuration, since the diameter of the light absorption layer is 20 μm or less, the area of the photodiode can be reduced, the element capacitance can be reduced, and the response speed can be increased. By condensing light into the photodiode having a small area using a condensing lens section, it is possible to suppress a decrease in sensitivity.
　本発明の裏面入射型半導体受光素子によれば、高反射率の電極によって感度の低下を抑制しながら応答速度の高速化を図ることができる。 According to the back-illuminated semiconductor light-receiving device of the present invention, it is possible to increase the response speed while suppressing a decrease in sensitivity due to the high reflectance electrode.
本発明の実施例に係る裏面入射型半導体受光素子の断面図である。FIG. 1 is a cross-sectional view of a back-illuminated semiconductor light-receiving device according to an embodiment of the present invention. 図１のフォトダイオードと電極を示す要部拡大断面図である。FIG. 2 is an enlarged cross-sectional view of main parts showing the photodiode and electrodes of FIG. 1. FIG. 円錐台状のフォトダイオードの形成工程を示す断面図である。FIG. 3 is a cross-sectional view showing a process of forming a truncated conical photodiode. フォトダイオードの電極の形成工程を示す断面図である。FIG. 3 is a cross-sectional view showing a process of forming an electrode of a photodiode. 電極の第１金属層の複素屈折率に対するこの電極の反射率の計算結果を等高線状に示すグラフである。3 is a graph showing, in contour lines, the calculated results of the reflectance of the electrode with respect to the complex refractive index of the first metal layer of the electrode. 電極の第１金属層がＴｉである場合に、誘電体層の厚さと第１金属層の厚さと電極の反射率の関係を示すグラフである。11 is a graph showing the relationship between the thickness of a dielectric layer, the thickness of a first metal layer, and the reflectance of an electrode when the first metal layer of the electrode is made of Ti. 電極の第１金属層がＴａである場合に、誘電体層の厚さと第１金属層の厚さと電極の反射率の関係を示すグラフである。It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Ta. 電極の第１金属層がＡｇである場合に、誘電体層の厚さと第１金属層の厚さと電極の反射率の関係を示すグラフである。It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Ag. 電極の第１金属層がＡｌである場合に、誘電体層の厚さと第１金属層の厚さと電極の反射率の関係を示すグラフである。It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Al. 電極の第１金属層がＣｒである場合に、誘電体層の厚さと第１金属層の厚さと電極の反射率の関係を示すグラフである。It is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode is Cr. 誘電体膜と第２金属膜の間に密着層を有する電極を備えたフォトダイオードの例を示す断面図である。FIG. 2 is a cross-sectional view showing an example of a photodiode including an electrode having an adhesion layer between a dielectric film and a second metal film. 図１１の電極の第１金属層がＣｒである場合に、誘電体層の厚さと第１金属層の厚さと電極の反射率の関係を示すグラフである。12 is a graph showing the relationship between the thickness of the dielectric layer, the thickness of the first metal layer, and the reflectance of the electrode when the first metal layer of the electrode in FIG. 11 is made of Cr. 電極の従来例を示す断面図である。FIG. 2 is a sectional view showing a conventional example of an electrode. 図１３の電極のＴｉの厚さとＰｔの厚さとこの電極の反射率の関係を示すグラフである。14 is a graph showing the relationship between the Ti thickness and Pt thickness of the electrode of FIG. 13 and the reflectance of this electrode.
　以下、本発明を実施するための形態について実施例１、２に基づいて説明する。 Hereinafter, embodiments for carrying out the present invention will be described based on Examples 1 and 2.
　図１、図２に示すように、裏面入射型半導体受光素子１は、半導体基板２の表面２ａ側に、この半導体基板２側から順に積層された第１半導体層３と光吸収層４と第２半導体層５と第３半導体層６を有するＰＩＮ型のフォトダイオード７を備えている。フォトダイオード７は、このフォトダイオード７の外周に形成された溝８ａによって円錐台状に形成されている。フォトダイオード７は、光吸収層４の直径が例えば２０μｍ以下となるように形成され、面積を小さくして素子容量を小さくしている。 As shown in FIGS. 1 and 2, a back-illuminated semiconductor light-receiving device 1 includes a first semiconductor layer 3, a light absorption layer 4, and a first semiconductor layer 3, which are laminated in order from the semiconductor substrate 2 side on the front surface 2a side of a semiconductor substrate 2. A PIN type photodiode 7 having two semiconductor layers 5 and a third semiconductor layer 6 is provided. The photodiode 7 is formed into a truncated cone shape by a groove 8a formed on the outer periphery of the photodiode 7. The photodiode 7 is formed so that the diameter of the light absorption layer 4 is, for example, 20 μm or less, and the area is reduced to reduce the element capacitance.
　半導体基板２は、光ファイバケーブルＯＣから出射される赤外線領域（例えば１３００～１６００ｎｍ）の波長の出射光Ｌ１に対して透明な例えば半絶縁性のＩｎＰ基板である。第１半導体層３は第１導電型の例えばｎ－ＩｎＰ層である。光吸収層４は例えばＩｎＧａＡｓ層である。第２半導体層５は第２導電型の例えばｐ－ＩｎＰ層である。第３半導体層６は、光吸収層４よりも薄く形成された例えばＩｎＧａＡｓ層であり、後述する電極（第２電極１２）とのオーミック接触のために形成されている。 The semiconductor substrate 2 is, for example, a semi-insulating InP substrate that is transparent to the emitted light L1 having a wavelength in the infrared region (for example, 1300 to 1600 nm) emitted from the optical fiber cable OC. The first semiconductor layer 3 is a first conductivity type, for example, an n-InP layer. The light absorption layer 4 is, for example, an InGaAs layer. The second semiconductor layer 5 is a p-InP layer of a second conductivity type, for example. The third semiconductor layer 6 is, for example, an InGaAs layer formed thinner than the light absorption layer 4, and is formed for ohmic contact with an electrode (second electrode 12) to be described later.
　溝８ａは、例えば反応性イオンエッチングによって、第３半導体層６と第２半導体層５と光吸収層４を貫通して第１半導体層３の途中までエッチングすることにより形成される。このとき、フォトダイオード７の外側で第１半導体層３に到達する開口部８ｂ（穴又は溝）も同時に形成される。そして、図３に示すように、絶縁膜９が、フォトダイオード７の第３半導体層６の表面６ａの大部分と図示外の開口部８ｂの底部とを除いた領域を覆うように公知の方法によって選択的に形成され、絶縁膜９にコンタクト孔９ａ，９ｂが形成される。絶縁膜９には、例えばＳｉＯ２膜、ＳｉＮ膜等が用いられる。 The groove 8a is formed by etching the first semiconductor layer 3 halfway through the third semiconductor layer 6, second semiconductor layer 5, and light absorption layer 4 by, for example, reactive ion etching. At this time, an opening 8b (hole or groove) reaching the first semiconductor layer 3 outside the photodiode 7 is also formed at the same time. Then, as shown in FIG. 3, the insulating film 9 is formed using a known method to cover a region other than most of the surface 6a of the third semiconductor layer 6 of the photodiode 7 and the bottom of the opening 8b (not shown). contact holes 9a and 9b are formed in the insulating film 9. For example, a SiO2 film, a SiN film, or the like is used as the insulating film 9.
　次に図４に示すように、例えば公知のリフトオフ法によって、コンタクト孔９ａを介して第３半導体層６に接続する第１金属層１２ａが、溝８ａの外側まで延びるように選択的に形成される。そして、この第１金属層１２ａ上のフォトダイオード７に対応する領域に、公知の方法（成膜、フォト、エッチング）によって誘電体層１２ｂが選択的に形成される。 Next, as shown in FIG. 4, a first metal layer 12a connected to the third semiconductor layer 6 through the contact hole 9a is selectively formed so as to extend to the outside of the groove 8a, for example, by a known lift-off method. Ru. Then, a dielectric layer 12b is selectively formed on the first metal layer 12a in a region corresponding to the photodiode 7 by a known method (film formation, photolithography, etching).
　さらに、例えば公知のリフトオフ法によって、第１金属層１２ａと誘電体層１２ｂを覆うように第２金属層１２ｃが選択的に形成されて、図１、図２のように第２電極１２が形成される。第２金属層１２ｃは、誘電体層１２ｂの外周側で第１金属層１２ａに接続されている。開口部８ｂにおいても、コンタクト孔９ｂを介して第１半導体層３に接続する第１金属層１２ａと第２金属層１２ｃが、開口部８ｂの外側に延びるように選択的に形成されて、第２電極１２と同時に第１電極１１が形成される。第１、第２電極１１，１２は、外部の例えばプリント基板の配線部に夫々接合される。 Further, a second metal layer 12c is selectively formed to cover the first metal layer 12a and the dielectric layer 12b by, for example, a known lift-off method, and the second electrode 12 is formed as shown in FIGS. 1 and 2. be done. The second metal layer 12c is connected to the first metal layer 12a on the outer peripheral side of the dielectric layer 12b. Also in the opening 8b, the first metal layer 12a and the second metal layer 12c connected to the first semiconductor layer 3 through the contact hole 9b are selectively formed so as to extend outside the opening 8b. The first electrode 11 is formed simultaneously with the second electrode 12. The first and second electrodes 11 and 12 are each connected to an external wiring section of a printed circuit board, for example.
　このように形成された第２電極１２は、フォトダイオード7に対応する部分に、第３半導体層６側から順に第１金属層１２ａと誘電体層１２ｂと第２金属層１２ｃが積層された構造を有する。第１金属層１２ａは、複素屈折率の実部ｎ（屈折率）の値が第３半導体層６の屈折率よりも小さく且つ複素屈折率の虚部ｋ（消衰係数）の値が１０以上の金属で形成されている。この第１金属層１２ａは、Ａｕ（金）、Ａｇ（銀）、Ａｌ（アルミニウム）及びＣｒ（クロム）からなる群から択一的に選択された金属の薄膜である。第１金属層１２ａは、フォトダイオード７の第３半導体層６の表面６ａの大部分に接続されているので、第２電極１２のコンタクト抵抗を低くすることができる。第２金属層１２ｃには、外部との接合が容易且つ酸化し難いＡｕが用いられる場合が多い。 The second electrode 12 formed in this manner has a structure in which a first metal layer 12a, a dielectric layer 12b, and a second metal layer 12c are laminated in order from the third semiconductor layer 6 side in a portion corresponding to the photodiode 7. has. The first metal layer 12a has a value of the real part n (refractive index) of the complex refractive index smaller than the refractive index of the third semiconductor layer 6 and a value of the imaginary part k (extinction coefficient) of the complex refractive index of 10 or more. is made of metal. This first metal layer 12a is a thin film of a metal alternatively selected from the group consisting of Au (gold), Ag (silver), Al (aluminum), and Cr (chromium). Since the first metal layer 12a is connected to most of the surface 6a of the third semiconductor layer 6 of the photodiode 7, the contact resistance of the second electrode 12 can be lowered. The second metal layer 12c is often made of Au, which can be easily bonded to the outside and is difficult to oxidize.
　半導体基板２の裏面２ｂ側には、半導体基板２と一体的に形成された凸レンズ状の集光レンズ部２ｃを有する。この集光レンズ部２ｃは、レンズ光軸が円錐台状のフォトダイオード７の中心軸線７ａと一致するように形成されている。光ファイバケーブルＯＣから出射された出射光Ｌ１（光パルス信号）は、その光軸が中心軸線７ａと一致するように出射されて円錐状に広がりながら集光レンズ部２ｃに入射する。集光レンズ部２ｃに入射して半導体基板２を進行する入射光Ｌ２は、集光レンズ部２ｃの集光作用によってフォトダイオード７に集光される。 On the rear surface 2b side of the semiconductor substrate 2, there is a condensing lens portion 2c formed integrally with the semiconductor substrate 2 and having a convex lens shape. The condensing lens portion 2c is formed such that the lens optical axis coincides with the central axis 7a of the photodiode 7 having a truncated cone shape. Output light L1 (light pulse signal) emitted from the optical fiber cable OC is emitted so that its optical axis coincides with the central axis 7a, and enters the condenser lens portion 2c while expanding conically. The incident light L2 that enters the condenser lens section 2c and travels through the semiconductor substrate 2 is condensed onto the photodiode 7 by the condensing action of the condenser lens section 2c.
　図２のように、入射光Ｌ２がフォトダイオード７に入射し、その一部が光吸収層４で２種類の電荷キャリア（電子、ホール）に変換される。そして、一方の電荷キャリアが第１半導体層３に移動し、他方の電荷キャリアが第２半導体層５に移動して、光電流として第１、第２電極１１，１２を介して外部に出力される。また、入射光Ｌ２のうち、光電変換されずに光吸収層４を透過して第２電極１２で反射された反射光Ｌ３が、光吸収層４に再入射するように構成されている。光吸収層４に再入射した反射光Ｌ３の一部は光電変換され、入射光Ｌ２から光電変化された電荷キャリアと共に光電流として第１、第２電極１１，１２を介して外部に出力される。 As shown in FIG. 2, incident light L2 enters the photodiode 7, and a portion of it is converted into two types of charge carriers (electrons and holes) in the light absorption layer 4. Then, one charge carrier moves to the first semiconductor layer 3, and the other charge carrier moves to the second semiconductor layer 5, and is output as a photocurrent to the outside via the first and second electrodes 11 and 12. Ru. Further, the configuration is such that reflected light L3 of the incident light L2 that is not photoelectrically converted and is transmitted through the light absorption layer 4 and reflected by the second electrode 12 enters the light absorption layer 4 again. A part of the reflected light L3 re-entering the light absorption layer 4 is photoelectrically converted and outputted to the outside as a photocurrent together with charge carriers photoelectrically converted from the incident light L2 via the first and second electrodes 11 and 12. .
　このように、反射光Ｌ３が光吸収層４に再入射するので、光吸収層４の実効的な厚さが大きくなり、裏面入射型半導体受光素子１の感度が向上する。それ故、感度の低下を抑制しながら光吸収層４を薄く形成することが可能になり、電荷キャリアの走行時間を短縮して応答速度を高速化することができる。そして、第２電極１２は、フォトダイオード７に近接しているので、光が光吸収層４と第２電極１２の間を往復する時間が短くなり、後続の光パルス信号と分離することができるので、高速通信に対応することができる。その上、フォトダイオード７の面積が小さいため、素子容量を小さくして応答速度を高速化できると共に、小さい面積のフォトダイオード７に集光レンズ部２ｃによって入射光Ｌ２を入射させるので、入射光Ｌ２を無駄なく利用して感度の低下を抑制することができる。 In this way, since the reflected light L3 re-enters the light absorption layer 4, the effective thickness of the light absorption layer 4 increases, and the sensitivity of the back-illuminated semiconductor light receiving element 1 improves. Therefore, it is possible to form the light absorption layer 4 thinly while suppressing a decrease in sensitivity, and it is possible to shorten the transit time of charge carriers and increase the response speed. Since the second electrode 12 is close to the photodiode 7, the time for light to travel back and forth between the light absorption layer 4 and the second electrode 12 is shortened, and it can be separated from the subsequent optical pulse signal. Therefore, it can support high-speed communication. Moreover, since the area of the photodiode 7 is small, the element capacitance can be reduced and the response speed can be increased. Furthermore, since the incident light L2 is made incident on the small area photodiode 7 by the condenser lens section 2c, the incident light L2 can be used without waste to suppress a decrease in sensitivity.
　次に、光の波長λが１５５０ｎｍの場合を例に、第２電極１２の反射率について説明する。
　入射光Ｌ２の一部は、光吸収層４を透過し、第２半導体層５と第３半導体層６を通って第２電極１２の第１金属層１２ａに到達する。第２半導体層５がｐ－ＩｎＰ、第３半導体層６がＩｎＧａＡｓである場合に、第２、第３半導体層５，６の屈折率は夫々３．２２である。 Next, the reflectance of the second electrode 12 will be explained using an example in which the wavelength λ of light is 1550 nm.
A portion of the incident light L2 passes through the light absorption layer 4, passes through the second semiconductor layer 5 and the third semiconductor layer 6, and reaches the first metal layer 12a of the second electrode 12. When the second semiconductor layer 5 is p-InP and the third semiconductor layer 6 is InGaAs, the refractive index of the second and third semiconductor layers 5 and 6 is 3.22, respectively.
　図５には、第２電極１２を構成する第１金属層１２ａの金属の複素屈折率の実部ｎ（屈折率）と虚部ｋ（消衰係数）をパラメータとして第２電極１２の反射率の計算結果が等高線状に示されている。第１金属層１２ａの厚さは２０ｎｍであり、誘電体層１２ｂは、厚さが１００ｎｍのＳｉＯ２膜で形成されている。第２金属層１２ｃは、図５以降のグラフにおいても厚さが６００ｎｍのＡｕ膜である。 FIG. 5 shows the reflectance of the second electrode 12 using the real part n (refractive index) and imaginary part k (extinction coefficient) of the complex refractive index of the metal of the first metal layer 12a constituting the second electrode 12 as parameters. The calculation results are shown in contour lines. The thickness of the first metal layer 12a is 20 nm, and the dielectric layer 12b is formed of a SiO2 film with a thickness of 100 nm. The second metal layer 12c is an Au film with a thickness of 600 nm also in the graphs from FIG. 5 onwards.
　図５によれば、第１金属層１２ａの複素屈折率の実部ｎ（屈折率）の値が小さいほど且つ虚部ｋの値が大きいほど、即ちグラフの左上の領域において反射率が高くなる傾向がある。そして、フォトダイオード７に入射する光を有効に利用するためには、第２電極１２の反射率が高いほど好ましい。半導体素子の材料として一般的に使用される金属を図５にプロットすると、８０％を超える高い反射率が得られるのはＡｕ（金）、Ａｇ（銀）、Ｃｕ（銅）、Ａｌ（アルミニウム）及びＣｒ（クロム）である。これらの金属は、第３半導体層６（ＩｎＧａＡｓ）の屈折率よりも複素屈折率の実部ｎの値が小さい。 According to FIG. 5, the smaller the value of the real part n (refractive index) of the complex refractive index of the first metal layer 12a and the larger the value of the imaginary part k, that is, the higher the reflectance in the upper left region of the graph. Tend. In order to effectively utilize the light incident on the photodiode 7, it is preferable that the reflectance of the second electrode 12 is as high as possible. When metals commonly used as materials for semiconductor devices are plotted in Figure 5, the metals that provide a high reflectance of over 80% are Au (gold), Ag (silver), Cu (copper), and Al (aluminum). and Cr (chromium). These metals have a value of the real part n of the complex refractive index smaller than the refractive index of the third semiconductor layer 6 (InGaAs).
　一方、低い反射率になるＮｉ（ニッケル）、Ｔｉ（チタン）、Ｐｔ（白金）は、第３半導体層６の屈折率よりも複素屈折率の実部ｎの値が大きい。Ｔａ（タンタル）は、第３半導体層６の屈折率よりも複素屈折率の実部ｎの値が小さいが、Ａｇ等と比べて複素屈折率の虚部ｋの値が小さいため入射した光が界面から深く進入し、反射率が低くなっていると考えられる。尚、Ｃｕは、Ａｕ、Ａｇ、Ａｌ及びＣｒと比べて加工し難く、他の材料中に拡散し易い性質を有するため、第１金属層１２ａとして使用することが困難である。 On the other hand, Ni (nickel), Ti (titanium), and Pt (platinum), which have low reflectance, have a value of the real part n of the complex refractive index larger than the refractive index of the third semiconductor layer 6. Ta (tantalum) has a value of the real part n of the complex refractive index smaller than the refractive index of the third semiconductor layer 6, but the value of the imaginary part k of the complex refractive index is smaller than that of Ag etc., so that the incident light is It is thought that the reflectance is low because it penetrates deeply from the interface. Note that Cu is difficult to process compared to Au, Ag, Al, and Cr, and has the property of easily diffusing into other materials, so it is difficult to use it as the first metal layer 12a.
　図６には、第１金属層１２ａがＴｉで形成された場合に、誘電体層１２ｂ（ＳｉＯ２膜）の厚さと第１金属層１２ａ厚さをパラメータとして計算した第２電極１２の反射率が、等高線状に示されている。この図６によれば、第１金属層１２ａが薄いほど且つ誘電体層１２ｂが薄いほど反射率が高くなる。第１金属層１２ａが薄いほど、この第１金属層１２ａを透過する光が増え、第１金属層１２ａと誘電体層１２ｂの界面及び誘電体層１２ｂと第２金属層１２ｃの界面での反射が増加するためであると考えられる。 FIG. 6 shows the reflectance of the second electrode 12 calculated using the thickness of the dielectric layer 12b (SiO2 film) and the thickness of the first metal layer 12a as parameters when the first metal layer 12a is made of Ti. , shown as contour lines. According to FIG. 6, the thinner the first metal layer 12a and the thinner the dielectric layer 12b, the higher the reflectance. The thinner the first metal layer 12a is, the more light passes through the first metal layer 12a, and the more light is reflected at the interface between the first metal layer 12a and the dielectric layer 12b and the interface between the dielectric layer 12b and the second metal layer 12c. This is thought to be due to an increase in
　しかし、第１金属層１２ａが薄いほど第２電極１２のコンタクト抵抗が高くなり、応答速度の高速化を阻害する。また、形成する膜が薄いほど、その膜の厚さの制御が困難になる。それ故、コンタクト抵抗を低く且つ厚さの制御が容易なように、例えば誘電体層１２ｂの厚さを１００ｎｍ且つ第１金属層１２ａ厚さを２０ｎｍとした場合には、第２電極１２の反射率は２０％未満の低い値になり、Ｔｉは第１金属層１２ａとして適していない。 However, the thinner the first metal layer 12a is, the higher the contact resistance of the second electrode 12 becomes, which impedes an increase in response speed. Furthermore, the thinner the film is formed, the more difficult it becomes to control the thickness of the film. Therefore, in order to lower the contact resistance and easily control the thickness, for example, when the dielectric layer 12b has a thickness of 100 nm and the first metal layer 12a has a thickness of 20 nm, the reflection of the second electrode 12 is The ratio becomes low, less than 20%, and Ti is not suitable as the first metal layer 12a.
　図７には、第１金属層１２ａがＴａで形成された場合に、誘電体層１２ｂ（ＳｉＯ２膜）の厚さと第１金属層１２ａ厚さをパラメータとして計算した第２電極１２の反射率が、等高線状に示されている。誘電体層１２ｂの厚さが例えば１００ｎｍ、第１金属層１２ａ厚さが例えば２０ｎｍの場合には反射率が８０％未満になる。反射率を９０％に近づけるためには、第１金属層１２ａと誘電体層１２ｂの少なくとも一方を薄くする必要があり、容易ではない。 FIG. 7 shows the reflectance of the second electrode 12 calculated using the thickness of the dielectric layer 12b (SiO2 film) and the thickness of the first metal layer 12a as parameters when the first metal layer 12a is formed of Ta. , shown as contour lines. When the thickness of the dielectric layer 12b is, for example, 100 nm and the thickness of the first metal layer 12a is, for example, 20 nm, the reflectance is less than 80%. In order to bring the reflectance close to 90%, it is necessary to make at least one of the first metal layer 12a and the dielectric layer 12b thinner, which is not easy.
　図８～図１０には、誘電体層１２ｂ（ＳｉＯ２膜）の厚さと第１金属層１２ａ厚さをパラメータとして計算した第２電極１２の反射率が、等高線状に示されている。図８は、第１金属層１２ａがＡｇで形成された場合である。図９は、第１金属層１２ａがＡｌで形成された場合である。図１０は、第１金属層１２ａがＣｒで形成された場合である。 8 to 10, the reflectance of the second electrode 12 calculated using the thickness of the dielectric layer 12b (SiO2 film) and the thickness of the first metal layer 12a as parameters is shown in contour lines. FIG. 8 shows a case where the first metal layer 12a is made of Ag. FIG. 9 shows a case where the first metal layer 12a is made of Al. FIG. 10 shows a case where the first metal layer 12a is made of Cr.
　図８～図１０の何れの場合も、誘電体層１２ｂの厚さが例えば１００ｎｍ且つ第１金属層１２ａ厚さが例えば２０ｎｍのときには、反射率が８５％を超える。従って、第１金属層１２ａがＡｇ又はＡｌ又はＣｒで形成された場合には、高い反射率を容易に得ることができる。第１金属層１２ａの厚さを例えば２５ｎｍよりも厚くすることによって、コンタクト抵抗を小さくすると共に９０％以上の反射率を得ることもできる。また、図３によれば、第１金属層１２ａがＡｕの場合にも同様に高い反射率を得ることができる。これらＡｕ、Ａｇ、Ａｌ、Ｃｒは、複素屈折率の虚部ｋの値が１０以上であり、複素屈折率の実部ｎの値が第３半導体層６の屈折率よりも小さいので、高い反射率の第２電極１２を形成することができる。 In any case of FIGS. 8 to 10, when the dielectric layer 12b has a thickness of, for example, 100 nm and the first metal layer 12a has a thickness of, for example, 20 nm, the reflectance exceeds 85%. Therefore, when the first metal layer 12a is made of Ag, Al, or Cr, high reflectance can be easily obtained. By making the thickness of the first metal layer 12a thicker than, for example, 25 nm, it is possible to reduce the contact resistance and obtain a reflectance of 90% or more. Further, according to FIG. 3, a high reflectance can be obtained similarly when the first metal layer 12a is made of Au. These Au, Ag, Al, and Cr have a value of the imaginary part k of the complex refractive index of 10 or more, and a value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer 6, so they have high reflection. The second electrode 12 can be formed in the same manner as shown in FIG.
　ここで、誘電体層１２ｂは、第１金属層１２ａと第２金属層１２ｃの相互拡散による合金化を防ぐことによって、第１金属層１２ａの合金化による複素屈折率の変化を防止する。そして、誘電体層１２ｂの外周側で第１金属層１２ａと第２金属層１２ｃが接続されているので、第２電極１２は導電性と高い反射率を有する。尚、第２電極１２による反射は、コンタクト抵抗が小さくなる第１金属層１２ａの厚さのときには、第３半導体層６と第１金属層１２ａの界面での反射が支配的であり、誘電体層１２ｂはＳｉＯ２膜以外の例えばＳｉＯＮ膜、ＳｉＮ膜等で形成されてもよい。 Here, the dielectric layer 12b prevents a change in the complex refractive index due to alloying of the first metal layer 12a by preventing alloying between the first metal layer 12a and the second metal layer 12c due to mutual diffusion. Since the first metal layer 12a and the second metal layer 12c are connected on the outer peripheral side of the dielectric layer 12b, the second electrode 12 has conductivity and high reflectance. Note that, when the thickness of the first metal layer 12a is such that the contact resistance is small, the reflection by the second electrode 12 is dominated by reflection at the interface between the third semiconductor layer 6 and the first metal layer 12a, and the dielectric The layer 12b may be formed of, for example, a SiON film, a SiN film, etc. other than the SiO2 film.
　第２金属層１２ｃがＡｕで形成される場合、誘電体層１２ｂ（ＳｉＯ２膜）との密着性が良好ではないので、第２金属層１２ｃが誘電体層１２ｂから浮き上がってしまい、第２電極１２の機能（例えば導電性、外部との接合性）が損なわれる虞がある。そこで、図１１に示すように、第２電極１２は、少なくとも誘電体層１２ｂと第２金属層１２ｃの間にＴｉを主成分とする密着層１２ｄを備えていてもよい。尚、一般的に用いられる密着層１２ｄの厚さは、１０ｎｍ程度である。 When the second metal layer 12c is made of Au, the adhesion with the dielectric layer 12b (SiO2 film) is not good, so the second metal layer 12c rises from the dielectric layer 12b, and the second electrode 12c There is a possibility that the functions (e.g. conductivity, bonding ability with the outside) may be impaired. Therefore, as shown in FIG. 11, the second electrode 12 may include an adhesion layer 12d containing Ti as a main component at least between the dielectric layer 12b and the second metal layer 12c. Note that the thickness of the adhesive layer 12d that is generally used is about 10 nm.
　図１２に示すように、第１金属層１２ａがＣｒである場合に、Ｔｉの密着層１２ｄを備えた第２電極１２は高い反射率を得ることができる。例えば誘電体層１２ｂの厚さが１００ｎｍ、第１金属層１２ａ厚さが２０ｎｍの場合には、反射率が８５％を超え、密着層１２ｄが無い図１０の第２電極１２と同程度の反射率が得られる。そして、密着層１２ｄによって第２金属層１２ｃの膜剥がれ又は膜浮きを防止して、第２電極１２Ａの機能が損なわれないようにすることができる。 As shown in FIG. 12, when the first metal layer 12a is made of Cr, the second electrode 12 provided with the Ti adhesion layer 12d can obtain a high reflectance. For example, when the dielectric layer 12b has a thickness of 100 nm and the first metal layer 12a has a thickness of 20 nm, the reflectance exceeds 85%, which is the same level of reflection as the second electrode 12 in FIG. 10 without the adhesive layer 12d. rate is obtained. The adhesion layer 12d can prevent the second metal layer 12c from peeling off or lifting, thereby preventing the function of the second electrode 12A from being impaired.
　図１３には、第２電極１２を従来の構造を有する従来電極２２に変更したフォトダイオード７を示している。従来電極２２は、第３半導体層６側から順にＴｉ層２２ａと、外部との接合時に合金化を防ぐバリア層としてＰｔ層２２ｂと、Ａｕ層２２ｃが積層されて形成されている。上述のように、Ｔｉ層２２ａの複素屈折率の実部ｎの値は第３半導体層６の屈折率よりも大きく、Ｐｔ層２２ｂの複素屈折率の実部ｎの値はＴｉ層２２ａの複素屈折率の実部ｎの値よりも大きい（図５参照）。そして図１４に示すように、この従来電極２２では、Ｐｔ層２２ｂの厚さとＴｉ層２２ａの厚さを調整しても反射率が低く、本発明の第２電極１２のように高い反射率を得ることができない。 FIG. 13 shows a photodiode 7 in which the second electrode 12 is replaced with a conventional electrode 22 having a conventional structure. The conventional electrode 22 is formed by laminating, in order from the third semiconductor layer 6 side, a Ti layer 22a, a Pt layer 22b as a barrier layer for preventing alloying during bonding with the outside, and an Au layer 22c. As described above, the value of the real part n of the complex refractive index of the Ti layer 22a is larger than the refractive index of the third semiconductor layer 6, and the value of the real part n of the complex refractive index of the Pt layer 22b is larger than the value of the complex refractive index of the Ti layer 22a. It is larger than the value of the real part n of the refractive index (see FIG. 5). As shown in FIG. 14, in this conventional electrode 22, even if the thickness of the Pt layer 22b and the thickness of the Ti layer 22a are adjusted, the reflectance is low, and unlike the second electrode 12 of the present invention, the reflectance is low. can't get it.
　上記の裏面入射型半導体受光素子１の作用、効果について説明する。
　半導体基板２の裏面２ｂ側からフォトダイオード７に入射して光吸収層４を透過した光が、このフォトダイオード７の電極である第２電極１２で反射されて光吸収層４に再入射する。この第２電極１２は、フォトダイオード７の第３半導体層６の表面６ａの大部分に接続された第１金属層１２ａを有するので、第２電極１２の反射面を大きくすると共に第２電極１２のコンタクト部の抵抗を小さくすることができ、応答速度の高速化に有利である。そして、第２電極１２は、複素屈折率の実部ｎの値が第３半導体層６の屈折率よりも小さく、且つ複素屈折率の虚部ｋの値が１０以上である金属によって形成された第１金属層１２ａを有する。この第１金属層１２ａと第２金属層１２ｃの間に誘電体層１２ｂを備えた構造によって、従来よりも高い反射率を得ることができる。従って、光吸収層４を透過した光の大部分をフォトダイオード7に近接する第２電極１２で反射して光吸収層４に再入射させることができる。それ故、裏面入射型半導体受光素子１の感度の低下を抑制しながら光吸収層４を薄くして、応答速度の高速化を図ることができる。 The functions and effects of the above-mentioned back-illuminated semiconductor light-receiving device 1 will be explained.
Light that enters the photodiode 7 from the back surface 2b side of the semiconductor substrate 2 and passes through the light absorption layer 4 is reflected by the second electrode 12, which is the electrode of the photodiode 7, and enters the light absorption layer 4 again. Since this second electrode 12 has a first metal layer 12a connected to most of the surface 6a of the third semiconductor layer 6 of the photodiode 7, the reflective surface of the second electrode 12 is made large and the second electrode 12 The resistance of the contact portion can be reduced, which is advantageous for increasing response speed. The second electrode 12 is formed of a metal in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer 6, and the value of the imaginary part k of the complex refractive index is 10 or more. It has a first metal layer 12a. With this structure including the dielectric layer 12b between the first metal layer 12a and the second metal layer 12c, higher reflectance than before can be obtained. Therefore, most of the light transmitted through the light absorption layer 4 can be reflected by the second electrode 12 close to the photodiode 7 and can be made to enter the light absorption layer 4 again. Therefore, the light absorption layer 4 can be made thinner while suppressing a decrease in sensitivity of the back-illuminated semiconductor light-receiving element 1, and the response speed can be increased.
　第１金属層１２ａは、複素屈折率の実部ｎの値が第３半導体層６の屈折率よりも小さく且つ複素屈折率の虚部ｋの値が１０以上の金属であるＡｕ、Ａｇ、Ｃｒ及びＡｌからなる群から選択された金属によって形成されている。これらの金属は、半導体素子の材料として一般的に使用されているので、反射率が高い第２電極１２を容易に形成することができる。 The first metal layer 12a is made of a metal such as Au, Ag, or Cr, in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer 6 and the value of the imaginary part k of the complex refractive index is 10 or more. and Al. Since these metals are commonly used as materials for semiconductor devices, the second electrode 12 with high reflectance can be easily formed.
　第２電極１２が、誘電体層１２ｂと第２金属層１２ｃの間にＴｉを主成分とする密着層１２ｄを有していてもよい。これにより、第２金属層１２ｃと誘電体層１２ｂとの密着性が良好ではない場合に懸念される第２金属層１２ｃの膜浮き又は膜剥がれを、密着層１２ｄによって防止することができる。従って、膜浮き又は膜剥がれによる第２電極１２の機能の低下を防ぐことができる。 The second electrode 12 may have an adhesion layer 12d containing Ti as a main component between the dielectric layer 12b and the second metal layer 12c. Thereby, the adhesion layer 12d can prevent film lifting or peeling of the second metal layer 12c, which is a concern when the adhesion between the second metal layer 12c and the dielectric layer 12b is not good. Therefore, deterioration in the function of the second electrode 12 due to film lifting or film peeling can be prevented.
　フォトダイオード７は、光吸収層４の直径が２０μｍ以下となる円錐台状に形成され、半導体基板２の裏面２ｂに、円錐台状のフォトダイオード７の中心軸線７ａにレンズ光軸を一致させた集光レンズ部２ｃを有する。フォトダイオード７の面積が小さいため素子容量を小さくすることができるので、応答速度を高速化することができる。そして、この面積が小さいフォトダイオード７に対して、集光レンズ部２ｃによって集光して入射させることによって、裏面入射型半導体受光素子１の感度の低下を抑制することができる。尚、光吸収層４の直径は、要求される応答周波数帯域に応じて適宜設定することができる。 The photodiode 7 is formed in the shape of a truncated cone such that the diameter of the light absorption layer 4 is 20 μm or less, and the optical axis of the lens is aligned with the central axis 7a of the truncated cone-shaped photodiode 7 on the back surface 2b of the semiconductor substrate 2. It has a condensing lens section 2c. Since the area of the photodiode 7 is small, the element capacitance can be reduced, and the response speed can be increased. By condensing the light and making it incident on the photodiode 7, which has a small area, using the condenser lens section 2c, it is possible to suppress a decrease in the sensitivity of the back-illuminated semiconductor light-receiving element 1. Note that the diameter of the light absorption layer 4 can be appropriately set depending on the required response frequency band.
　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、上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、本発明はその種の変更形態も包含するものである。 In addition, those skilled in the art can implement various modifications to the above embodiments without departing from the spirit of the present invention, and the present invention includes such modifications.
１　　：裏面入射型半導体受光素子
２　　：基板
２ａ　：表面
２ｂ　：裏面
２ｃ　：集光レンズ部
３　　：第１半導体層
４　　：光吸収層
５　　：第２半導体層
６　　：第３半導体層
７　　：フォトダイオード
７ａ　：中心軸線
８ａ　：溝
８ｂ　：開口部
９　　：絶縁膜
１１　：第１電極
１２　：第２電極（電極）
１２ａ：第１金属層
１２ｂ：誘電体層
１２ｃ：第２金属層
１２ｄ：密着層
２２　：従来電極
２２ａ：Ｔｉ層
２２ｂ：Ｐｔ層
２２ｃ：Ａｕ層
Ｌ１　：出射光
Ｌ２　：入射光
Ｌ３　：反射光
ＯＣ　：光ファイバケーブル 1: Back-illuminated semiconductor light-receiving element 2: Substrate 2a: Front surface 2b: Back surface 2c: Condensing lens section 3: First semiconductor layer 4: Light absorption layer 5: Second semiconductor layer 6: Third semiconductor layer 7: Photodiode 7a: Central axis 8a: Groove 8b: Opening 9: Insulating film 11: First electrode 12: Second electrode (electrode)
12a: First metal layer 12b: Dielectric layer 12c: Second metal layer 12d: Adhesive layer 22: Conventional electrode 22a: Ti layer 22b: Pt layer 22c: Au layer L1: Outgoing light L2: Incident light L3: Reflected light OC :Optical fiber cable

Claims (4)

  1. 　入射光に対して透明な半導体基板の表面側に、この半導体基板側から順に積層された第１半導体層と光吸収層と第２半導体層と第３半導体層を有するフォトダイオードを備え、前記フォトダイオードに対して前記半導体基板の裏面側から光が入射される裏面入射型半導体受光素子において、
    　前記フォトダイオードは、前記第３半導体層の表面の大部分に接続された電極を備え、
    　前記電極は、前記第３半導体層側から順に、複素屈折率の実部ｎの値が前記第３半導体層の屈折率よりも小さく且つ虚部ｋの値が１０以上である第１金属層と、誘電体層と、前記誘電体層の外周側で前記第１金属層に接続された第２金属層を有し、
    　前記裏面側から前記フォトダイオードに入射されて前記光吸収層を透過した光が、前記電極で反射されて前記光吸収層に再入射するように構成されたことを特徴とする裏面入射型半導体受光素子。     A photodiode having a first semiconductor layer, a light absorption layer, a second semiconductor layer, and a third semiconductor layer stacked in this order from the semiconductor substrate side is provided on the front side of a semiconductor substrate transparent to incident light, In a back-illuminated semiconductor light-receiving element in which light is incident on the diode from the back side of the semiconductor substrate,
    The photodiode includes an electrode connected to most of the surface of the third semiconductor layer,
    The electrode includes, in order from the third semiconductor layer side, a first metal layer in which the value of the real part n of the complex refractive index is smaller than the refractive index of the third semiconductor layer and the value of the imaginary part k is 10 or more; , comprising a dielectric layer and a second metal layer connected to the first metal layer on the outer peripheral side of the dielectric layer,
    A back-illuminated semiconductor light-receiving device, characterized in that the light is incident on the photodiode from the back surface side and transmitted through the light-absorbing layer, and is reflected by the electrode and re-enters the light-absorbing layer. element.
  2. 　前記第１金属層は、Ａｕ、Ａｇ、Ｃｒ及びＡｌからなる群から選択される金属によって形成されたことを特徴とする請求項１に記載の裏面入射型半導体受光素子。 2. The back-illuminated semiconductor light-receiving device according to claim 1, wherein the first metal layer is formed of a metal selected from the group consisting of Au, Ag, Cr, and Al.
  3. 　前記誘電体層と前記第２金属層の間にＴｉを主成分とする密着層を有することを特徴とする請求項１に記載の裏面入射型半導体受光素子。 2. The back-illuminated semiconductor light-receiving device according to claim 1, further comprising an adhesion layer containing Ti as a main component between the dielectric layer and the second metal layer.
  4. 　前記フォトダイオードは、前記光吸収層の直径が２０μｍ以下となる円錐台状に形成され、
    　前記半導体基板の裏面に、円錐台状の前記フォトダイオードの中心軸線にレンズ光軸を一致させた集光レンズ部を有することを特徴とする請求項１に記載の裏面入射型半導体受光素子。     The photodiode is formed in a truncated cone shape in which the light absorption layer has a diameter of 20 μm or less,
    2. The back-illuminated semiconductor light-receiving device according to claim 1, further comprising a condenser lens portion on the back surface of the semiconductor substrate, the lens optical axis of which is aligned with the central axis of the truncated conical photodiode.
PCT/JP2022/034374 2022-09-14 2022-09-14 Backside incident-type semiconductor light receiving element WO2024057435A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/JP2022/034374 WO2024057435A1 (en) 2022-09-14 2022-09-14 Backside incident-type semiconductor light receiving element

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2022/034374 WO2024057435A1 (en) 2022-09-14 2022-09-14 Backside incident-type semiconductor light receiving element

Publications (1)

Publication Number Publication Date
WO2024057435A1 true WO2024057435A1 (en) 2024-03-21

Family

ID=90274596

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2022/034374 WO2024057435A1 (en) 2022-09-14 2022-09-14 Backside incident-type semiconductor light receiving element

Country Status (1)

Country Link
WO (1) WO2024057435A1 (en)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002252366A (en) * 2000-12-19 2002-09-06 Fujitsu Quantum Devices Ltd Semiconductor light-receiving device
JP2006120913A (en) * 2004-10-22 2006-05-11 Toyoda Gosei Co Ltd Semiconductor light emitting element
JP2013131637A (en) * 2011-12-21 2013-07-04 Japan Oclaro Inc Optical module
JP2014007285A (en) * 2012-06-25 2014-01-16 Nippon Telegr & Teleph Corp <Ntt> Photodiode
CN112768550A (en) * 2020-12-18 2021-05-07 中国电子科技集团公司第四十四研究所 Structure for improving responsivity of back-illuminated photodiode and manufacturing method
WO2022149253A1 (en) * 2021-01-08 2022-07-14 株式会社京都セミコンダクター Semiconductor light-receiving element

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002252366A (en) * 2000-12-19 2002-09-06 Fujitsu Quantum Devices Ltd Semiconductor light-receiving device
JP2006120913A (en) * 2004-10-22 2006-05-11 Toyoda Gosei Co Ltd Semiconductor light emitting element
JP2013131637A (en) * 2011-12-21 2013-07-04 Japan Oclaro Inc Optical module
JP2014007285A (en) * 2012-06-25 2014-01-16 Nippon Telegr & Teleph Corp <Ntt> Photodiode
CN112768550A (en) * 2020-12-18 2021-05-07 中国电子科技集团公司第四十四研究所 Structure for improving responsivity of back-illuminated photodiode and manufacturing method
WO2022149253A1 (en) * 2021-01-08 2022-07-14 株式会社京都セミコンダクター Semiconductor light-receiving element

Similar Documents

Publication Publication Date Title
CA2365454C (en) Semiconductor photodetection device
JP3601761B2 (en) Light receiving element and method of manufacturing the same
US20030178636A1 (en) Back illuminated photodiodes
US20020003231A1 (en) Semi-transparent power monitor integrated with a light producing module
JP4291521B2 (en) Semiconductor light receiving element, semiconductor light receiving device, semiconductor device, optical module, and optical transmission device
JPH0888393A (en) Semiconductor photodetection device and its manufacture
JPH05110048A (en) Opto-electronic integrated circuit
WO2024057435A1 (en) Backside incident-type semiconductor light receiving element
US20040056179A1 (en) Semiconductor light-receiving device
JP2014013844A (en) Semiconductor photodetector and manufacturing method of the same
JP2004200202A (en) Semiconductor photodetecting element
JP4048217B2 (en) Semiconductor photo detector
CN114284390B (en) Vertical incidence ultra-wideband integrated photoelectric detector chip and manufacturing method thereof
JP3674255B2 (en) Manufacturing method of light receiving element
JP2952906B2 (en) Photodiode
US5990490A (en) Optical electronic IC capable of photo detection
WO2021019744A1 (en) Light-receiving element unit
JPH05102513A (en) Semiconductor phtodetector
JP3442493B2 (en) Semiconductor light receiving element and method of manufacturing the same
JPH05267708A (en) Electrode structure for optical semiconductor device
US20240044701A1 (en) Light sensor structure and manufacturing method thereof
WO2023199403A1 (en) Light-receiving element
JP2968440B2 (en) Semiconductor light receiving element
KR20010009571A (en) Photo-detector device and method manufacturing thereof
JP4058457B2 (en) Semiconductor photo detector

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 22958763

Country of ref document: EP

Kind code of ref document: A1