Silicon carbide photodetector

Abstract

To realize a light receiving element having a photodetector unit and a signal amplification unit integrally formed of SiC.SOLUTION: A silicon carbide light receiving element includes a light detection unit 101 that photoelectrically converts incident light, and a signal amplification unit 102 that amplifies the output of the light detection unit 101. The light detection unit 101 includes a first conductive type silicon carbide semiconductor layer 112, and a second conductive type light receiving region 113 formed on the silicon carbide semiconductor layer 112. The signal amplification unit 102 includes a plurality of second conductive type source / drain regions 115 formed on the silicon carbide semiconductor layer 112, a plurality of ohmic electrodes 121 each of which is in ohmic contact with the light receiving region 113 and the source / drain region 115, and a gate electrode 125 formed through a gate insulating film 131 between the adjacent source / drain regions 115.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a silicon carbide light receiving element and an image sensor using the same. [Background technology]

[0002] Remotely controlled or autonomous robots have been attracting attention as a means of performing various tasks in places where humans cannot approach. In particular, there is growing expectation for robots that can be used in sites exposed to high levels of radiation, such as decommissioning work at nuclear reactors. However, silicon (Si) semiconductor devices currently used to control robots have low resistance to radiation, and can only perform tasks for about several tens of minutes to an hour. For this reason, there is a demand for new semiconductor devices that can be used for long periods of time even under high levels of radiation.

[0003] Silicon carbide (SiC) semiconductors are expected to be semiconductor materials with excellent heat resistance and radiation resistance. However, although SiC semiconductors have been studied as power devices that handle large amounts of electricity, their use in other applications has not progressed. In particular, imaging devices that act as the eyes of robots are essential for controlling robots, but imaging devices using SiC have hardly been studied at all, and it is only known that SiC can be used as a photodetector (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-244496 A Summary of the Invention [Problem to be solved by the invention]

[0005] Even if the photodetector element is made of SiC, if the other parts are made of Si semiconductors, a significant improvement in radiation resistance cannot be expected. To form an image sensor, it is necessary to arrange multiple pixels, each of which includes a photodetector element and a signal amplifier that amplifies the detected signal, in an array. For this reason, a technology that can integrally form the photodetector element and the signal amplifier using SiC is essential.

[0006] An object of the present disclosure is to realize a light receiving element having a light detection section and a signal amplification section integrally formed from SiC. [Means for solving the problem]

[0007] One aspect of the silicon carbide light receiving element of the present disclosure includes a photodetection unit that photoelectrically converts incident light, and a signal amplification unit that amplifies an output of the photodetection unit, wherein the photodetection unit has a silicon carbide semiconductor layer of a first conductivity type and a light receiving region of a second conductivity type formed in the silicon carbide semiconductor layer, and the signal amplification unit has a plurality of source / drain regions of the second conductivity type formed in the silicon carbide semiconductor layer, a plurality of ohmic electrodes each in ohmic contact with the light receiving region and the source / drain regions, and a gate electrode formed between adjacent source / drain regions via a gate insulating film. Effect of the Invention

[0008] According to the silicon carbide light receiving element of the present disclosure, the light detection section and the signal amplification section are integrally formed from a silicon carbide semiconductor, and high radiation resistance can be achieved. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing a circuit configuration of a silicon carbide light receiving element according to an embodiment; [Diagram 2] 1 is a cross-sectional view showing a silicon carbide light receiving element according to one embodiment. [Diagram 3] 1 is a plan view showing an image sensor using a silicon carbide light receiving element according to one embodiment. [Figure 4A]1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4B] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4C] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4D] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4E] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4F] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4G] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. [Figure 4H] 1 is a cross-sectional view showing a process of a method for manufacturing a silicon carbide light receiving element according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 1, a silicon carbide light receiving element 100 according to one embodiment has a light detection section 101 including a photodiode, and a signal amplification section 102 that amplifies the output of the light detection section 101. The signal amplification section 102 has a reset transistor (RST), a source follower transistor (SF), and a row selection transistor (RS). It can be driven as a light receiving element by applying a reset signal to φR and a row selection signal to φX.

[0011] 2, the silicon carbide light receiving element 100 of this embodiment has a p-type silicon carbide (SiC) semiconductor layer 112 formed on an n-type silicon carbide (SiC) substrate 111. In the region of the SiC semiconductor layer 112 where the light detection section 101 is formed, a n-type SiC semiconductor layer 112 is formed. + A p-type light receiving region 113 is formed at an interval from the light receiving region 113. + A potential stabilization region 114 of a type is formed. In the region where the signal amplifier 102 is formed, a plurality of n +In the example shown in FIG. 1, source / drain regions 115 of a type are formed. These source / drain regions 115 constitute the source / drain of a reset transistor (RST), a source follower transistor (SF), and a row select transistor (RS).

[0012] An ohmic electrode 121 is formed on each of the light receiving region 113, the potential stabilization region 114, and the source / drain region 115, which are impurity diffusion layers. The ohmic electrode 121 has a metal silicide layer 122 in ohmic contact with the impurity diffusion layer, and a metal electrode layer 123 formed on the metal silicide layer 122. The metal silicide layer 122 is preferably a niobium-nickel silicide layer. The metal silicide layer 122 may also be a molybdenum-nickel silicide layer, a vanadium-nickel silicide layer, a titanium silicide layer, or the like. The metal electrode layer 123 is preferably an aluminum layer. The gate electrode 125 is formed across the adjacent source / drain regions 115 with a gate insulating film 131 interposed therebetween.

[0013] An interlayer insulating film 133 is formed so as to cover the ohmic electrodes 121 and the gate electrodes 125, and electrode pads 135 and wiring 136 connected to the respective electrodes are formed on the interlayer insulating film 133.

[0014] A back electrode 126 is provided on the back surface of the SiC substrate 111. The back electrode 126 is an ohmic electrode in ohmic contact with the back surface of the SiC substrate 111, and can be made of niobium-nickel silicide or the like. The back electrode 126 quickly discharges electron and hole carriers generated in the SiC substrate, and has the effect of stabilizing device operation.

[0015] In this embodiment, the light receiving region 113 and one of the source / drain regions 115 of the reset transistor are integrally formed. In addition, one of the source / drain regions 115 of the source follower transistor and the row selection transistor are also integrally formed, and since there is no need for external connection, the ohmic electrode 121 is not formed. Note that the light receiving region 113 and the source / drain region 115 may be formed independently. In this case, the light receiving region 113 and the source / drain region 115 may have different impurity concentrations and diffusion depths.

[0016] In this embodiment, the SiC semiconductor layer is p-type and an n-type transistor is formed, but the SiC semiconductor layer can be n-type and a p-type transistor can be formed. In this case, the light receiving region can also be p-type, so there is no need to provide a potential stabilization region. Also, a p-type SiC substrate or an n-type SiC substrate can be used as the SiC semiconductor layer as it is.

[0017] In addition, the p-type SiC semiconductor layer + By providing a p-type potential stabilization region, holes generated under ultraviolet light irradiation or radiation environment are quickly discharged from the SiC semiconductor layer. This makes it possible to stabilize the output potential of the light receiving element. + By type layer is meant that the concentration of p-type impurities is higher than that of the p-type layer.

[0018] The crystal structure of the SiC semiconductor layer 112 can be appropriately selected according to the wavelength of light to be detected. For example, when the SiC semiconductor layer 112 is of 4H type, a light receiving element excellent in detecting light in the ultraviolet region of 350 nm or less can be realized. When the SiC semiconductor layer 112 is of 3C type, a light receiving element excellent in detecting light in the visible light to ultraviolet region of about 450 nm to 350 nm can be realized.

[0019] In the silicon carbide light receiving element 100 of this embodiment, light incident on the light receiving region 113 is photoelectrically converted by the photodetector 101, and the signal obtained thereby is amplified and output by the signal amplifier 102. In addition, by arranging a plurality of silicon carbide light receiving elements 100 of this embodiment in an array as shown in Fig. 3, it is possible to form an image sensor 200 in which one silicon carbide light receiving element 100 serves as one pixel. A vertical selection circuit, a horizontal selection circuit, and the like can be formed on the substrate of the image sensor 200.

[0020] In the silicon carbide light receiving element 100 of this embodiment, both the light detection section 101 and the signal amplification section 102 are integrally formed from a SiC semiconductor. This allows for a significant improvement in radiation resistance, and the photoresponse characteristics do not deteriorate significantly even when the accumulated radiation dose reaches several MGy. Furthermore, the photoresponse characteristics do not change even in an environment of about 200°C.

[0021] The silicon carbide light receiving element of this embodiment can be formed, for example, as follows. First, as shown in Fig. 4A, a p-type SiC semiconductor layer 112 is epitaxially grown on an n-type SiC substrate 111. The SiC substrate 111 is not particularly limited, but can be 4H-SiC. The thickness of the SiC semiconductor layer 112 can be, for example, about 1 µm to 5 µm.

[0022] Next, as shown in Fig. 4B, a first ion implantation mask 141 made of silicon oxide (SiO2) is formed on the SiC semiconductor layer 112 by chemical vapor deposition (CVD) and photolithography, and n-type impurities are implanted into the SiC semiconductor layer 112 to form the light receiving region 113 and the source / drain region 115. Next, as shown in Fig. 4C, a second ion implantation mask 142 is formed and p-type impurities are implanted to form the potential stabilization region 114.

[0023] 4D, the SiC semiconductor layer 112 after ion implantation is covered with a carbon cap film 144, and then heat treatment is performed to activate the impurity implanted region. The heat treatment may be performed at a temperature of about 1700° C., for example, and may be appropriately selected depending on the type and concentration of the impurity.

[0024] As shown in Fig. 4E, after removing the carbon cap film 144, thermal oxidation is performed to form the gate insulating film 131. Furthermore, a resist mask 145 is used to provide openings in the gate insulating film 131 to expose the impurity implanted regions, and then a metal film 146 is formed on the entire surface of the substrate. At this time, a metal film 147 that will become the back surface electrode 126 is also formed on the back surface of the SiC substrate 111. The metal films 146 and 147 can be, for example, niobium-nickel films.

[0025] Next, as shown in FIG. 4F, the metal film 146 on the resist mask 145 is removed by lift-off, and then the metal film 146 and the metal film 147 are silicided by heat treatment to form the metal silicide layer 122 and the back electrode 126.

[0026] Next, as shown in FIG. 4G, a metal film made of aluminum or the like is formed on the entire surface of the substrate, and is selectively etched away to form a metal electrode layer 123 and a gate electrode 125.

[0027] Next, as shown in FIG. 4H, an interlayer insulating film 133 is formed over the entire surface of the substrate, and electrode pads 135 and wiring 136 connected to the respective electrodes are formed on the interlayer insulating film 133. EXAMPLES

[0028] The present invention will be described in more detail below using examples. Note that the following examples are illustrative and are not intended to limit the present invention.

[0029] <Formation of the light receiving element> A p-type SiC semiconductor layer with a thickness of 3 μm was formed on a 3-inch n-type 4H-SiC substrate. The substrate had an off-axis angle of 4° from the (0001) plane. The impurity concentration of the p-type SiC layer was 5×10 16 cm 3 The light receiving region and the source / drain region have an impurity concentration of 5×10 19 cm 3The impurity was implanted under the condition that arsenic ions were uniformly distributed to a depth of 70 nm in the substrate. The potential stabilization layer had an impurity concentration of 4×10 20 cm 3 Aluminum ions were implanted as impurities under conditions that would distribute them uniformly to a depth of 70 nm in the substrate. The size of the light-receiving region was 500 μm square. The thickness of the gate insulating film was 20 nm, and the metal silicide layer was a niobium-nickel silicide layer.

[0030] <Confirmation of light response characteristics> V DD The photodetector was driven by applying a square wave with a frequency of 100 Hz, a high of 0 V, a low of 7.0 V, a row selection signal (φX) of 7.0 V, and a reset signal (φR) of 0 V for High and 7.0 V for Low. The output voltage was 0.4 V in the light-shielded state, and 1.59 V when irradiated with 254 nm ultraviolet light, confirming the operation of the pixel. The measurement was performed at room temperature, and the output voltage was the difference between the maximum and minimum voltages during one drive pulse.

[0031] <Confirmation of radiation resistance> The obtained light-receiving element was irradiated with gamma rays, and the photoelectric conversion output was measured at the cumulative irradiation doses of 0.02MGy, 0.03MGy, 0.06MGy, 0.24MGy, 0.44MGy, and 1.1MGy. The measurement conditions for the photoelectric conversion output were the same as those for the case of no gamma-ray irradiation. The output voltages in the light-shielded state and light-irradiated state were 0.16V and 0.45V for 0.02MGy, 0.10V and 2.7V for 0.03MGy, 0.01V and 0.33V for 0.06MGy, 0.02V and 0.57V for 0.24MGy, 0.14V and 1.2V for 0.44MGy, and 0.19V and 0.85V for 1.1MGy.

[0032] Even at a cumulative irradiation dose of 1.1 MGy, the output voltage increased significantly from the light-shielded state, demonstrating that the pixel functioned satisfactorily. Note that the fluctuation in the absolute value of the output voltage was due to the effect of variations in the light irradiation intensity.

[0033] The SiC semiconductor layer was epitaxially grown on an n-type SiC substrate. 14 cm -3 The light receiving region and the source / drain region are p-type layers containing aluminum as an impurity. + A p-type photodiode was fabricated using a photodiode with a p-type doped layer. Note that no potential stabilization region was formed.

[0034] The photoresponse of the obtained p-type photodiode to 254 nm ultraviolet light was measured in the same manner as for the n-type photodiode. DD The row selection signal (φX) was −10 V, and the reset signal (φR) was a square wave with a high of 0 V and a low of −10 V and a frequency of 100 Hz.

[0035] The output voltage before gamma-ray irradiation was 0.012 V in the dark and 0.50 V in the light. When the cumulative dose of gamma-rays was 3 MGy, the output voltage was 0.0084 V in the dark and 0.45 V in the light. When measurements were performed at 200°C before gamma-ray irradiation, the output voltage was 2.11 V in the dark and 4.06 V in the light. [Industrial Applicability]

[0036] The silicon carbide light receiving element of the present disclosure has a light detection section and a signal amplification section integrally formed from a silicon carbide semiconductor, and is useful as an image sensor or the like in high temperature or high radiation environments. [Explanation of symbols]

[0037] 100 Silicon carbide photodetector 101 Light detection unit 102 Signal amplifier 111 Silicon carbide substrate 112 Silicon carbide semiconductor layer 113 Light receiving area 114 Potential stabilization region 115 Source / Drain Region 121 Ohmic Electrode 122 Metal silicide layer 123 Metal electrode layer 125 Gate electrode 126 Back electrode 131 Gate insulating film 133 Interlayer insulating film 135 Electrode Pads 136 Wiring 141 First ion implantation mask 142 Second ion implantation mask 144 Carbon Cap Film 145 Resist Mask 146 Electrode metal film 147 Electrode metal film 200 Image Sensor

Claims

1. A light detection unit that performs photoelectric conversion on incident light; a signal amplifier that amplifies an output of the light detection unit; the photodetector has a silicon carbide semiconductor layer of a first conductivity type formed on a first surface of a silicon carbide substrate, and a light receiving region of a second conductivity type formed in a photodetector formation region of the silicon carbide semiconductor layer; The signal amplifier includes a plurality of source / drain regions of a second conductivity type formed in a signal amplifier formation region of the silicon carbide semiconductor layer, a plurality of ohmic electrodes each in ohmic contact with the light receiving region and the source / drain regions, and a gate electrode formed between adjacent source / drain regions via a gate insulating film; the first conductivity type is p-type and the second conductivity type is n-type; the light detection unit has a potential stabilization region formed in the silicon carbide semiconductor layer at a distance from the light receiving region, the potential stabilization region containing a first conductivity type impurity at a higher concentration than the silicon carbide semiconductor layer; the silicon carbide substrate having a back surface electrode in ohmic contact with a second surface of the silicon carbide substrate;

2. The silicon carbide light receiving element according to claim 1 , wherein the light detecting portion detects light in an ultraviolet region.

3. An image sensor comprising a plurality of silicon carbide light receiving elements according to claim 1 or 2.

4. A method of manufacturing a semiconductor device comprising epitaxially growing a p-type silicon carbide semiconductor layer on a first surface of a silicon carbide substrate; Selectively injecting an n-type impurity into the silicon carbide semiconductor layer to form a light receiving region which is an impurity diffusion layer in a light detection portion forming region and a source / drain region which is an impurity diffusion layer in a signal amplification portion forming region; selectively injecting p-type impurities into the silicon carbide semiconductor layer to form a potential stabilization region that is an impurity diffusion layer that is spaced from the light receiving region and contains a higher concentration of p-type impurities than the silicon carbide semiconductor layer; forming a gate insulating film on a surface of the silicon carbide semiconductor layer on which the impurity diffusion layer is formed; forming a silicide electrode layer in ohmic contact with the impurity diffusion layer and a back surface electrode in ohmic contact with the silicon carbide substrate on an opening portion provided in the gate insulating film exposing the impurity diffusion layer and on a second surface of the silicon carbide substrate; After forming the silicide electrode layer, a metal film is formed on the entire surface of the silicon carbide substrate and selectively etched to form an ohmic electrode and a gate electrode.

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