JP2011192873A - Wide-wavelength-band photodetector array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wide-wavelength-band photodetector array that is lightweight and highly reliable, and has sensitivity in a wide wavelength band from ultraviolet rays to infrared rays. <P>SOLUTION: A readout IC (ROIC) and an ultraviolet or blue light-receiving element are formed on silicon sapphire (SOS), a red and infrared light-receiving element is formed on a compound semiconductor substrate, and electrodes of the both are stuck together. Outputs of a plurality of photodetectors on the same optical path corresponding to different wavelengths are detected independently and simultaneously to acquire spectrum information without a position shift or time shift. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a photodetector, a photodetector array, or an imaging device having sensitivity in an extremely wide wavelength band from ultraviolet to infrared wavelengths.

  In order to simultaneously detect an extremely wide wavelength band from ultraviolet to infrared wavelengths, it is necessary to use different photosensitive materials depending on the wavelength to be detected. Therefore, in the prior art, it is necessary to mount a plurality of elements in the same apparatus in addition to optical path switching or mounting of a wavelength selection filter, and the configuration of the device is complicated. The reason why the wavelength range that can be detected by a single photosensitive material is limited is that long-wavelength light with energy smaller than the band gap of the photosensitive material is weak in light absorption and is unlikely to generate carriers by light. This is because, when the wavelength of light is too short with respect to the band gap of the material, most of the incident light is absorbed in the vicinity of the surface having a large crystal defect density, and photoinduced carriers are not easily detected as current.

  A general silicon photodiode (Si-PD) as a light absorption layer for a photodetector or camera has a sensitivity in a wavelength range of approximately 400 nm to 1000 nm, depending on the structure. If sensitivity is required for shorter wavelengths, it is necessary to use a wide band gap semiconductor such as GaN or GaP, or to make the photosensitive layer an extremely thin film.

As a photodetector having sensitivity only to ultraviolet rays, there is a GaN PIN-PD on a sapphire substrate, which achieves a spectral sensitivity of about 0.1 A / W. (Non-Patent Document 1)

In SOI (silicon on insulator) and SOS (silicon on sapphire), which are effective for improving the high speed and low power consumption of CMOS LSI, the silicon layer on the insulating film to be the channel layer is usually 100 nm or less. Ultra-thin laterally-bonded silicon-PD using SOI as the photosensitive layer is sensitive only to UV wavelengths from 280 nm to 400 nm and has a spectral sensitivity of about 0.1 A / W. (Patent Document 1)

  On the other hand, in the infrared region with a wavelength of 1000 nm or more, the photosensitivity of the silicon photodetector decreases, so InGaAs, InAs, or InSb compound semiconductors with low band gap energy are widely used as photosensitive elements for high-sensitivity infrared detectors. Yes.

  In order to realize a photodetector array that does not cause positional shift or time shift in multiple photosensitive wavelength bands, PDs with multiple photosensitive materials are placed close to each other in a planar manner, or a short wavelength photodetector and a long wavelength detector. It is effective to stack the photodetectors in the light traveling direction. As a method for expanding the photosensitive wavelength of a single-element photodetector, a tandem structure in which a photosensitive material sensitive to a short wavelength and a photosensitive material sensitive to a long wavelength are bonded together is employed. (Non-Patent Documents 2 and 3)

  In addition, GaN PD sensitive to short wavelength light and silicon PD sensitive to long wavelength are monolithically grown above and below the GaN substrate, respectively, and a photodetector sensitive to ultraviolet and infrared light has been developed. . Furthermore, it is also possible to intentionally suppress the wavelength sensitivity corresponding to the radiation spectrum of sunlight using an InP or GaAs substrate as a filter (sun blind). (Patent Document 2).

Even when the same semiconductor material is used for the photosensitive material, light with a short wavelength is absorbed by the surface, and light with a long wavelength penetrates relatively deeply, so by stacking multiple PDs with different silicon layer thicknesses Color information can be obtained. In the case of this configuration, it is possible to keep the aperture ratio high by obtaining a plurality of wavelength spectrum information on the same light receiving surface. (Non-Patent Document 4)

The structure in which a PN junction is formed in the vicinity of the surface by epitaxial growth (Patent Document 3) filed by the present inventor has made it possible to expand the wavelength range to visible light even in a semiconductor material having absorption in the infrared wavelength region. . Further, by using the n-type epitaxial layer structure on the p-type substrate, deep p-type diffusion is performed from the periphery of the n-type photosensitive layer to the p-type substrate, thereby providing a planar structure with a wide wavelength range and element isolation. A compound semiconductor PD array with good characteristics was realized.

  In the case of a two-dimensional image sensor with sensitivity in the infrared region, a focal plane array (generally a photodiode (PD) array made of a compound semiconductor and a lead-out IC (ROIC) made of a silicon LSI are bump-connected ( FPA) structure is adopted. When bump bonding a compound semiconductor PD array and ROIC, bumps are formed on both surface electrodes with Au or AuSn, and the two are bonded by thermocompression bonding. In this case, the surface on which the light is incident is the back surface of the compound semiconductor PD. For this reason, after bonding the two, the compound semiconductor substrate is usually mirror-polished to 50 μm or less in order to suppress the light absorption effect by the substrate. In this case, since the substrate functions as a long wavelength transmission filter, light corresponding to a wavelength shorter than the band gap of the substrate cannot be detected.

  Further, as described in Patent Documents 3 and 4, when the photosensitive wavelength range is expanded using a shallow PN junction, it is necessary to make light incident from the electrode surface of the element. First, a deep through hole is formed from the surface of the PD, and once the surface of the PD is adhered to the substrate, the compound semiconductor substrate is polished to 50 μm or less, then bumped to the ROIC, and then the substrate is removed. The process of doing is needed. In either case, since a process of thinning a relatively fragile compound semiconductor substrate is required, the manufacturing yield is poor, and the conventional infrared imaging element has been expensive.

  By forming a semiconductor thin film on a transparent substrate such as optical glass and forming a pixel selecting thin film transistor and a photoelectric conversion element, it is possible to prevent the semiconductor substrate from being thinned and the yield is reduced accordingly. For example, as in Patent Document 5, in a flat panel detector for X-ray detection, amorphous silicon is formed on a glass substrate to realize a thin film transistor and a PIN photoelectric conversion element. In recent years, the density of a switching matrix using a thin film transistor in a liquid crystal display and a driving circuit using an LSI arranged in the periphery of the switching matrix have been increased. In the case of a pixel size of about 30 μm pitch or more in the configuration and mounting method, light detection is performed. It is becoming possible to divert to an array.

Furthermore, in the case of SOS, since the sapphire substrate is transparent to ultraviolet rays, incidence from the substrate side is effective. This has the advantage that a large aperture ratio can be obtained when applied to a two-dimensional image sensor that requires a readout IC (ROIC). (Non-patent document 5, Non-patent document 6)
In addition, by utilizing the fact that the sapphire substrate is transparent to infrared light, a transceiver module in which a surface emitting laser (VCSEL) is flip-chip bonded on a driver circuit chip by SOS and a differential detector circuit chip by SOS are used. There is an example of developing a receiver module equipped with PD and transmitting it in free space or optical fiber. (Non-patent document 7)

Infrared cameras are also important for remote sensing, and many are installed in space satellites. In electronic equipment used in outer space, soft / hard errors due to cosmic rays are a problem. Since SOI and SOS do not form CMOS parasitic thyristors that cause hard errors, hard errors do not occur structurally. Although rewritable, soft errors that cause logic errors also have a smaller transistor volume and a generation probability of about 10 ⁻⁴ than that of bulk CMOS. Therefore, it is recommended that the electronic device mounted on the space satellite is composed of an integrated circuit (LSI) based on SOI or SOS. (Non-patent document 8)

Su-Sir Liu, Pei-Wen Li, W.H. Lanb, Wen-jen Lin, "The improvements of GaN p-i-n UV sensor on 1 ° off-axis sapphire substrate", Materials Science and Engineering B 121 (2005) 86-91 Thorlabs DSD2 "Dual Band Detectors" http://www.thorlabs.com/Thorcat/12400/12408-S01.pdf J Novak and P Elias, "A silicon-InGaAs tandem functions for radiation thermometry", Measurement Science Technology 6 pp.1547-1549, 1995 David L. Gilblom, Sang Keun Yoo, "Infrared and ultraviolet imaging with a CMOS sensor having layered photodiodes", SPIE AeroSense 2003-April 22, 2003-Orlando, Florida, USA Chen Xu, Chao Shen, Wen Wu, and Mansun Chan, "Backside-Illuminated Lateral PIN Photodiode for CMOS Image Sensor on SOS Substrate", IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 52, NO. 6, JUNE 2005 E. Culurciello and A.G. Andreou, "16_16 pixel silicon on sapphire CMOS digital pixel photosensor array", ELECTRONICS LETTERS 8th January 2004 Vol. 40 No. 1 J. Jiang Liu, Zaven Kalayjian, Brian Riely, Wayne Chang, George J. Simonis, Alyssa Apsel, and Andreas Andreou, "Multichannel Ultrathin Silicon-on-Sapphire Optical Interconnects", IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 9 , NO. 2, MARCH / APRIL 2003 Staff Writer, "Single Event Effects in UltraCMOSTM Devices", Technology Briefs Peregrine Semiconductor Corporation, http://www.psemi.com/articles/SEE_in_UltraCMOS.pdf Ja-Myeong KOO, Jung-Lae JO, Jong-Bum LEE, Yu-Na KIM, Jong-Woong KIM, Bo-In NOH, Jeong-Hoon MOON, Dae-Up KIM, and Seung-Boo JUNG, "Effect of Atmospheric Pressure Plasma Treatment on Transverse Ultrasonic Bonding of Gold Flip-Chip Bump on Glass Substrate ", Japanese Journal of Applied Physics Vol. 47, No. 5, 2008, pp. 4309-4313 Z. Fu, P. Weerakoon and E. Culurciello, "Nano-Watt silicon-on-sapphire ADC using 2C-1C capacitor chain", Electronics Letters, 16th March 2006, vol.42 No.6, pp341-343

Japanese Patent Publication No. 2008-251709 "Ultraviolet light receiving element, its manufacturing method, and ultraviolet ray measuring device" US 7381966 B2 "Single-Chip Monolithick Dual-Band Visible- or Solar-Blind Photodetector" PCT / JP2009 / 067689 "Photodetector" Japanese Patent Application No. 2010-12875 “Compound Semiconductor Photodetector Array” JP-A-2007-258332 “Photoelectric Conversion Element, Method for Manufacturing Photoelectric Conversion Element, Imaging Device, Manufacturing Method for Imaging Device, and Radiation Imaging Device”

  A conventional infrared detector (FPA) in which a compound semiconductor photodiode array and a silicon ROIC are bonded together 1) Since light is incident from the back of the compound photodiode, the compound semiconductor substrate acts as a long wavelength transmission filter, and the photosensitive wavelength is It is limited to a wavelength longer than the wavelength corresponding to the energy band cap of the substrate. Therefore, in order to obtain an image with a short wavelength for comparison or aiming, it is necessary to prepare another camera or to separate the optical path with a dichroic mirror or the like, and it is necessary to correct misalignment or the like. 2) Further, it is necessary to thin the compound semiconductor substrate after the compound semiconductors are bonded together, and the manufacturing yield is poor. Further, in remote sensing, particularly space satellite cameras, it is necessary to satisfy requirements such as reduction of total weight, excellent mechanical strength, and resistance to damage from cosmic rays.

  A CMOS LSI (SOS) on a sapphire substrate doubles as an ultraviolet or blue sensor and ROIC, and a compound semiconductor photodetector array is bonded together from the surface electrode side of both. The compound semiconductor photodetector array uses InGaP / GaAs, InGaAs / InP, InGaSb / GaSb, InAsSb / GaSb PDs or phototransistors depending on the required photosensitive wavelength. The SOS sapphire substrate is used as an optical window that can transmit from ultraviolet to infrared wavelengths. An ultraviolet sensor using a silicon thin film on the SOS substrate has a back-surface incident structure, and a visible / infrared sensor using a compound semiconductor has a front-surface incident structure, and it is not necessary to make both substrates thin.

  In the present invention, a plurality of photodetecting element arrays made of silicon and compound semiconductors corresponding to the ultraviolet, visible, and infrared wavelength bands are stacked together with the ROIC on the SOS substrate including the digital signal processing circuit. Since the SOS substrate functions as an optical window of the compound-based photodetector, it is not necessary to make the photodetector-side substrate thin, which causes a decrease in yield, and high-density mounting such as bump connection is facilitated. In addition, since the SOS-CMOS integrated circuit with little stray capacitance and easy element isolation is used as the ROIC, the reading circuit can be increased in speed and power consumption can be reduced. By using a sapphire substrate with excellent optical transmission characteristics as an optical window and forming an ultraviolet or blue light detector on the backside of the sapphire substrate, it is possible to suppress the ultraviolet light absorption effect associated with the spin-on glass constituting the CMOS-LSI. it can. On the other hand, an infrared photodetector made of a compound semiconductor is incident on the surface, and has sensitivity in the visible to infrared wavelength region by using a photodiode having a shallow junction.

  The silicon thin film used for the channel layer of SOS is 100 nm or less and is transparent from yellow to the infrared wavelength region. For this reason, light receiving elements with multiple wavelength bands can be stacked on the same light receiving surface, so a large-scale aperture ratio, small positional shift and time delay, and a very high wavelength band FPA covering a wavelength range of 200 nm to 5 μm are compared. Can be manufactured at low cost. In addition, SOS is highly resistant to cosmic rays and can be improved in reliability as a camera for space satellites.

  In a visible to infrared wavelength detector using a compound semiconductor, photodiodes or the like made of materials with different band gaps can be stacked in tandem from the surface to the substrate side, and each photoresponse current can be detected independently. . Therefore, in the photodetector array according to the present invention, it is possible to detect the output from a plurality of elements arranged on the same optical path and having sensitivity in the ultraviolet, visible, or infrared wavelength region by ROIC, respectively. Wavelength spectrum information can be acquired at the same time without a filter or filter.

FIG. 1 is an explanatory view showing a cross section of a portion corresponding to one pixel of an ultra-wide wavelength band photodetector array in which an SOS integrated circuit and a compound semiconductor light receiving element array are bonded together. (Example 1) FIG. 2 is a schematic plan view of a portion corresponding to one pixel of an ultraviolet or blue light detection unit and readout circuit by SOS. (Example 2) FIG. 3 is a schematic plan view of a portion corresponding to one pixel of the infrared detector 200 made of a compound semiconductor. Example 3 FIG. 4 is a circuit block diagram for explaining the ROIC function by the SOS integrated circuit. Example 4 FIG. 5 is a schematic diagram of an ultra wide wavelength band photodetector array in which an SOS integrated circuit and a compound semiconductor light receiving element array are bonded to each other. (Example 5)

  FIG. 1 shows a cross-sectional structure corresponding to one pixel of an ultra-wide wavelength band FPA that receives light from ultraviolet to infrared according to the present invention. The present invention has a structure in which an ultraviolet light detector / ROIC 100 using SOS and an infrared light detector 200 using a compound semiconductor are bonded together. The SOS ultraviolet light detector / ROIC 100 is connected to the compound semiconductor infrared detector 200 by the SOS side gold bump 107 and the infrared light detector side gold bump 212 for each pixel.

  The UV detector / ROIC 100 includes a CMOS circuit 102 formed of thin film silicon on a transparent sapphire substrate 101, an ultraviolet PD array 104 composed of a lateral PIN junction according to Non-Patent Document 4, and infrared detection using a compound semiconductor. A readout circuit 111 for the instrument 200 is provided. Further, a SOS side gold bump 108 having a width of 5 μm, a length of 20 μm, and a thickness of 15 μm is provided via a ROIC side electrode 110 and a wiring 109 for bump connection.

  An infrared photodetector 200 made of a compound semiconductor is based on an n-type InP substrate 202, an n-type InP buffer 203, an n-InGaAs collector 204, and a p-InGaAs base on an electrode 201 for an n-type compound semiconductor substrate according to Patent Document 3. 205, an n-InP emitter 206, and an n-InGaAs emitter contact 207, which has a phototransistor structure. Further, an isolation groove 208 is formed in the lateral direction, and its side surface is surrounded by a p-type diffusion layer 209. .

  The emitter contact 207 and the p-type diffusion layer 209 are connected to the infrared light detector side gold bump 212 via the infrared light detection electrode 210 and the wiring 211. By providing the base 205 with the infrared light detection electrode 210 through the p-type diffusion layer 209 electrically connected to the base, the phototransistor can be reset and the blooming effect is suppressed.

  In addition, by independently measuring the photoresponse currents induced in the emitter-base junction arranged on the surface side and the base-collector junction arranged on the substrate side, two PDs with different junction depths are used, It can be obtained by separating spectral information from visible to infrared wavelengths. In addition, it is possible to switch between a photodiode mode and a phototransistor mode having an internal amplification function according to the intensity of light and the required frame speed.

  Further, a photodiode (PD) can be used as the infrared detector 200. In this case, a positive applied voltage can be used, and the PD structure on the p-type compound substrate disclosed in Patent Document 4 having excellent element isolation is excellent.

  On the ROIC side electrode 105 and the infrared detection electrode 210, gold bumps 107 and 212 each having a height of about 15 microns are formed by electroplating. After the thermocompression bonding process, the ROIC 100, the infrared detector 200, and the gap are filled with BCB (benzocyclobutene) 213 to reinforce the bonding strength.

  The multi-spectrum light 10 is incident from the sapphire substrate 101 side, the ultraviolet light and the visible light on the blue side are applied to the ultraviolet PD array composed of the ultrathin silicon layer constituting the SOS, and the visible light and the infrared light on the red side are It passes through the SOS structure and is absorbed by the infrared photodetector 200 made of a compound semiconductor.

  FIG. 2 is a schematic plan view of a portion corresponding to one pixel of an ultraviolet or blue light detection unit and readout circuit by SOS formed by a silicon thin film on a transparent sapphire substrate 101. Each pixel has a pitch of 25 μm, and an ultraviolet or blue photodiode (PD) or phototransistor 104 at the center, and an ultraviolet or blue PD and address setting CMOS circuit 102 composed of a CMOSFET 103 around each pixel, an infrared photodiode readout circuit 111 is arranged.

  The ultraviolet or blue photodiode 104 is composed of a lateral PN junction composed of a p-type silicon thin film 105, an i-type silicon thin film 106, and an n-type silicon thin film 107 having a thickness of 100 nm. The ultraviolet or blue photodiode amplification and address setting CMOS circuit 102 is composed of four MOSFETs 103 manufactured according to the 0.25 μm rule. The photocurrent induced by the ultraviolet or blue photodiode 104 is amplified by the CMOS circuit 102 and sent to the signal processing circuit.

  On the other hand, the photocurrent detected from the infrared detector 200 is guided from the gold bump 108 having a width of 5 μm and a length of 20 μm to the infrared detection readout circuit 111 composed of several MOSFETs via the wiring 109 and the ROIC side electrode 110. It is burned.

  FIG. 3 is a schematic plan view of a portion corresponding to one pixel when a phototransistor according to Patent Document 3 is used as the infrared light detector 200 made of a compound semiconductor. The emitter contact 207 and the base contact 214 are connected to the infrared light detector side gold bump 212 having a width of 5 μm and a length of 20 μm via the infrared light detection electrode 210 and the wiring 211. The compound semiconductor phototransistors and photodiodes to be disclosed in Patent Document 3 and Patent Document 4 operate with a positive voltage bias with respect to the substrate, and the voltage operates at about 1 V. Is easy to connect.

  For the connection between SOS-ROIC and compound semiconductor HPT array, a gold ultrasonic and thermal pressure bonding process, which is advantageous for forming fine bumps, was used. The gold thermocompression bonding process is generally around 300 ° C., but the heat treatment temperature could be lowered by adding the plasma cleaning treatment without damaging the adhesive strength. (Non-patent document 9)

  FIG. 4 is a circuit block diagram for explaining the ROIC function in the SOS. On the transparent sapphire substrate 101, 640 × 512 pixels of ultraviolet or blue detector / ROIC 100 corresponding to each pixel are arranged. The infrared light detector 200 made of a compound semiconductor is bonded through the ROIC side gold bump 108. The pixels in each row are sequentially selected by the row selection line 120 selected by the row scanning circuit 124, and the image signal corresponding to each column is sent to the AD converter 122 via the column selection line 121. By providing each pixel with a latch function, the signals of the ultraviolet, visible, and infrared photodetectors stacked on the same opening surface can be sent in order according to the order of row selection. Further, the ADC 122 is attached with a multiplexer, and AD-converts signals from two columns in order. The AD converted signal is sent to the 16-bit data bus 123 according to the timing control circuit 125 connected to the external clock. The AD converter 122 employs a switched capacitor system (Non-patent Document 10) capable of operating with extremely low power consumption.

  FIG. 5 is a schematic diagram of a broadband imaging device in which an infrared detector 200 made of a compound semiconductor is stacked under an ROIC and ultraviolet light detector 100 made of SOS. The circuit side of the sapphire substrate 101 and the surface of the InP substrate 202 on the element side are bonded via gold bumps 108. Therefore, the active part of the device is already mechanically protected by the sapphire substrate 101 and the compound substrate 202, and the gap is filled with BCB. As the package, the peripheral portion and the back surface of the compound semiconductor substrate are protected by silicon resin, and terminals for surface mounting are formed on the sapphire substrate.

  In SOS, it is possible to increase the sensitivity in the visible region by increasing the thickness of the silicon thin film to about 0.5 μm. In this case, a visible camera made of silicon CMOS and an infrared camera made of a compound semiconductor are superposed.

10 Multispectral light 100 Ultraviolet detector and ROIC
101 Transparent sapphire substrate 102 CMOS circuit 103 MOSFET
104 UV or blue PD array 105 p-type silicon thin film 106 i-type silicon thin film 107 n-type silicon thin film 108 gold bump 109 wiring 110 ROIC side electrode 111 compound PD readout circuit 120 row selection line 121 column selection line 122 AD converter 123 data Bus 124 Row scanning circuit 125 Timing control circuit 200 Infrared light detector 201 Electrode for n-type compound semiconductor substrate 202 n-type InP substrate 203 n-type InP buffer 204 n-InGaAs collector 205 p-InGaAs base 206 n-InP emitter 207 n -InGaAs emitter contact 208 Isolation groove 209 P-type diffusion layer 210 Infrared light detection electrode 211 Wiring 212 Infrared detector side gold bump 213 BCB
214 Base contact 205 p-side electrode

Claims (6)

  Focal plane array (FPA) in which a silicon-on-sapphire substrate (SOS) is used for the readout circuit (ROIC) and a photodetector array made of a compound semiconductor is bonded to the circuit side.   2. The FPA according to claim 1, wherein the SOS doubles as ROIC and an ultraviolet or blue light detector.   2. The FPA according to claim 1, wherein the photodetector array made of a compound semiconductor is composed of a photodiode.   2. The FPA according to claim 1, wherein the photodetector array made of a compound semiconductor is composed of a phototransistor.   2. The FPA according to claim 1, comprising a plurality of PN junctions in which a photodetector array made of a compound semiconductor is stacked.   2. The FPA according to claim 1, wherein a plurality of photodetectors made of SOS and a compound semiconductor are stacked on the same optical path, and outputs of the plurality of photodetectors can be detected independently.

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