Single-electrode double-photosensitive-region four-quadrant PIN detector and preparation method thereof

Abstract

The invention relates to a single-electrode double-photosensitive-area four-quadrant PIN detector, and belongs to the field of semiconductor photoelectric sensor chips. The detector comprises a substrate, a buffer layer, an absorption layer, a first PIN type photodiode and a second PIN type photodiode, wherein the first PIN type photodiode and the second PIN type photodiode are located on the surface of the absorption layer and distributed in four quadrants. The first PIN type photodiode in each quadrant is in a sector ring shape, and the second PIN type photodiode in each quadrant is in a sector shape; and the fan-ring-shaped first PIN type photodiodes are distributed on the outer sides of the fan-shaped second PIN type photodiodes. Metal wires are arranged in the quadrant intervals and used for connecting the first PIN type photodiode and the second PIN type photodiode in the same quadrant, the first PIN type photodiode and the second PIN type photodiode in the same quadrant share one P electrode, and meanwhile light blocking of the quadrant intervals and enhancement of the electric field of the central area of the detector are achieved. The system can be compatible with the working mode of large and small double light spots, saves the satellite load and power consumption, and has remarkable advantages in the aspect of satellite load application.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor photoelectric sensor chips, and relates to the design and manufacture of PIN type photodiode detector chips, and in particular to a single-electrode dual-photosensitive-area four-quadrant PIN detector and a preparation method thereof. Background Art

[0002] The existing four-quadrant PIN photodiode detector chip (PIN four-quadrant for short) is usually used in scenarios such as photoelectric capture, spot positioning, and signal transmission. According to the different wavelengths of the incident light, semiconductor materials with corresponding bandgap widths are selected to design and prepare the chip. In the same material system, according to the input requirements such as the signal frequency, optical power, and spot size of the incident light, the surface photosensitive area structure and internal epitaxial structure are designed at the chip end to achieve chip responsivity, response frequency, and other functions that match the input requirements, such as Figure 1 Usually, in a PIN photodiode (PIN unit for short), the large photosensitive area type is used to process large light spot, low power, low frequency signal (hereinafter referred to as large light spot mode); the small photosensitive area type is used to process small light spot, high power, high frequency signal (hereinafter referred to as small light spot mode).

[0003] like Figure 2 As shown, the existing detector is composed of 4 independent PIN units distributed in four quadrants with XY intervals; each quadrant corresponds to an independent PIN unit, each PIN unit is provided with a P electrode to lead out the electrical signal after photoelectric conversion, and the 4 PIN units share one N electrode. There is no light blocking design in the XY quadrant interval area.

[0004] When the incident light is irradiated to the photosensitive area, as the spot area focused in the photosensitive area changes from large to small, and the optical power changes from small to large, the f of the PIN unit in each quadrant -3dB The bandwidth (-3dB cutoff frequency, frequency response half-power point) will deteriorate accordingly, which is manifested as f -3dB Insufficient bandwidth or -3dB The optical power is insufficient under the bandwidth. That is, when the incident light changes, the AC saturation optical power deteriorates.

[0005] Usually, when the incident light spot area changes beyond a certain range, two different types of PIN quadrants need to be used simultaneously to process "large spot / low power / low frequency signal" or "small spot / high power / high frequency signal" respectively, which makes the device structure complicated; in addition, when the incident light power at the center of the PIN quadrant is stronger and the spot is smaller, the electric field in the quadrant spacing area becomes weaker, the drift speed of the photogenerated carriers is slow, the transit time is long, and the bandwidth of the photoelectric signal is reduced. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a single-electrode dual-photosensitive-area four-quadrant PIN detector and a preparation method thereof, which adopts the same internal epitaxial structure design and PIN unit layout design under some given external working constraints (such as the incident light spot size, operating frequency, operating voltage, etc.), and is compatible with both "large spot" and "small spot" modes, to solve the problems of no strong electric field in the central area of ​​the PIN four-quadrant, slow drift velocity of photogenerated carriers, and long transit time, and ultimately achieves the expansion of the application range of a certain large photosensitive-area chip for incident light.

[0007] To achieve the above object, the present invention provides a single-electrode dual-photosensitive-area four-quadrant PIN detector, which includes a substrate, a buffer layer located on the upper surface of the substrate, an absorption layer located on the upper surface of the buffer layer, a cap layer located on the upper surface of the absorption layer, and an N-electrode located on the lower surface of the substrate. As a further improvement of the present invention, the detector also includes a first PIN-type photodiode formed in the cap layer and distributed in four quadrants and a second PIN-type photodiode distributed in four quadrants.

[0008] The first PIN photodiode of each quadrant is in a fan-shaped ring shape, and the second PIN photodiode of each quadrant is in a fan-shaped shape; the fan-shaped first PIN photodiode is distributed outside the fan-shaped second PIN photodiode, and the area of ​​the first PIN photodiode is larger than the area of ​​the second PIN photodiode. A P electrode is arranged outside the first PIN photodiode of each quadrant.

[0009] In addition, metal routing is arranged in each quadrant interval of the four quadrants, and the metal routing is used to connect the first and second PIN-type photodiodes in the same quadrant, wherein the second PIN-type photodiode is connected to the P-electrode corresponding to the quadrant through the first PIN-type photodiode, thereby realizing that the first and second PIN-type photodiodes in a quadrant share a P-electrode.

[0010] Optionally, an anti-reflection film is provided on the surface of the first and second PIN-type photodiodes in each quadrant of the detector.

[0011] Optionally, a passivation film is provided on the surface of the cap layer except for the first and second PIN-type photodiodes, and the P electrode is provided on the upper surface of the passivation film.

[0012] In another aspect, the present invention provides a method for preparing a single-electrode dual-photosensitive-area four-quadrant PIN detector, the method comprising:

[0013] Obtaining a substrate, and sequentially forming a buffer layer, an absorption layer and a cap layer on a surface of the substrate;

[0014] A diffusion barrier layer is deposited on the surface of the cap layer by using a PECVD process, and the diffusion barrier layer is a SiNx or SiO2 passivation film;

[0015] Applying photoresist on the surface of the diffusion barrier layer, and performing photolithography on the photoresist to obtain a first target pattern window; using BOE etching solution to etch the diffusion barrier layer according to the first target pattern window formed by the photolithography, to form diffusion holes corresponding to the inner region and the outer region distributed in four quadrants; wherein each quadrant of the inner region is fan-shaped, and each quadrant of the outer region is fan-shaped;

[0016] Diffusion is performed through the diffusion hole to form a first PIN type photodiode and a second PIN type photodiode with P-type conductive characteristics in the cap layer, wherein the first PIN type photodiode is formed in the outer region and the second PIN type photodiode is formed in the inner region;

[0017] Depositing an anti-reflection film on the surface of the first PIN-type photodiode and the second PIN-type photodiode;

[0018] Apply photoresist on the surface of the anti-reflection film, photolithograph the photoresist on the outer edge of the first PIN-type photodiode in each quadrant to obtain a second target pattern window, and simultaneously photolithograph the two vertices of the fan-shaped second PIN-type photodiode in each quadrant to obtain a third target pattern window; dry-etch the anti-reflection film in the second target pattern window and the third target image window area to form a P-electrode window;

[0019] Applying photoresist on the surface of the detector currently formed, photolithography the photoresist outside the first PIN-type photodiode of each quadrant to obtain a fourth target pattern window, forming a P electrode in the fourth target pattern window by evaporating gold, and then removing all the photoresist;

[0020] The other surface of the substrate is thinned by a grinding process, and then an N electrode is formed on the thinned surface by evaporation and gold plating;

[0021] After the detector passes the photoelectric characteristics test, the chip is de-sliced ​​using a wafer splitting device.

[0022] Furthermore, a metal wiring is formed in the interval between each quadrant, and the P-electrode windows of the first and second PIN-type photodiodes are connected through the metal wiring, and the first and second PIN-type photodiodes are connected to the P-electrode through the P-electrode window.

[0023] The beneficial effect of the present invention is that: under the condition that the area of ​​the overall photosensitive area remains unchanged, the present invention divides the large and small photodiodes to target the light spots of different areas, thereby being compatible with the working modes of large and small dual light spots, replacing the traditional solution of using large-area chips for large light spots and small-area chips for small light spots. In addition, the present invention sets metal wiring in the intervals of each quadrant, and at the same time realizes the purposes of sharing P electrodes, blocking light for different quadrant areas, and enhancing the electric field in the central area of ​​the detector, thereby solving the problem that there is no strong electric field in the central area of ​​the detector, the drift speed of photogenerated carriers is slow, and the transit time is long. The present invention is compatible with the working modes of large and small dual light spots, has the characteristics of "one core for two uses", saves manufacturing costs through technological improvement, saves load and power consumption, and has significant advantages in satellite payload applications that are very concerned about "weight and power consumption".

[0024] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 This is a schematic diagram of the existing detector structure layout;

[0027] Figure 2 This is a schematic diagram of the internal structure of an existing detector;

[0028] Figure 3 A schematic diagram showing a comparison between the arrangement of PIN units in a detector provided in one embodiment of the present invention and an existing detector;

[0029] Figure 4 The light spots of different sizes incident on the photosensitive area of ​​the detector;

[0030] Figure 5 Schematic diagram of the detector photosensitive area structure after the diffusion hole is opened for corrosion;

[0031] Figure 6 A P electrode window is formed on the PIN unit;

[0032] Figure 7 Schematic diagram of the layout of the detector surface after the P electrode is formed. DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0034] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0035] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0036] The purpose of the present invention is to adopt the same internal epitaxial structure design and the same diode arrangement scheme under some given external working constraints (such as the incident light spot size, working frequency, working voltage, etc.), and to be compatible with both the "large spot" and "small spot" modes, thereby solving the problem of no strong electric field in the central area of ​​the PIN four-quadrant, slow drift speed of photogenerated carriers, and long transit time, and ultimately achieve the expansion of the application range of a certain large photosensitive area chip to incident light.

[0037] To achieve the above object, an embodiment of the present invention provides a single-electrode dual-photosensitive-area four-quadrant PIN detector, which is improved based on the existing detector, such as Figure 3 Specifically, based on the existing detector, this embodiment makes the following improvements:

[0038] ① PIN unit layout scheme: Divide the PIN units in each quadrant of the existing detector into two, that is, divide a "PIN unit" into a "large PIN unit" and a "small PIN unit", and form independent PN junctions in the large PIN unit (i.e., the first PIN-type photodiode) and the small PIN unit (i.e., the second PIN-type photodiode) through diffusion process. The specific size of the PIN unit refers to the actual spot size.

[0039] ② In terms of optoelectronic link: After each quadrant is divided into two, the two independent PIN units share a P electrode.

[0040] ③ Spacing area: Set high-precision electrode routing in the XY narrow spacing area of ​​the PIN four quadrants.

[0041] According to the common sense principle of PIN photodiode, the response time t r Including the transit time t T , RC time constant t RC and diffusion time t diff Three parts, the calculation formula is: According to f -3dB The bandwidth is calculated by the simplified formula So to increase f -3dB Then you need to reduce t r .

[0042] According to the above description, in terms of the functional principle of the detector provided in this embodiment, after the photosensitive area of ​​the PIN unit is divided into two, the total capacitance of the PIN unit is equal to the sum of the PN junction capacitance of the large PIN unit and the PN junction capacitance of the small PIN unit. j =ε 0 ε r A / d shows that, compared with the existing detector, the PN junction capacitance of the small PIN unit is reduced in proportion to the active area A; and according to t RC =2.2RC, it can be seen that when the junction capacitance decreases, t RC Then it decreases, and f -3dB The bandwidth is improved. Among them, ε 0 represents the vacuum dielectric constant, ε r represents the relative dielectric constant of the InGaAs depletion region material, ε r =13.8, d represents the thickness of the depletion region; R is the total resistance including the load resistance and the detector's own series resistance; C is the total capacitance of the detector. For a four-quadrant detector, from the equivalent circuit point of view, it is composed of four independent detectors in parallel, and the quadrant junction capacitance is equal to the junction capacitance C of a single detector. j .

[0043] like Figure 4As shown, the detector provided in this embodiment receives a large light spot (such as Figure 4 When receiving a small light spot (such as a black coil with a larger radius), the large PIN unit and the small PIN unit output photoelectric signals through the same P electrode, that is, they work at the same time and still have the basic functions of the four quadrants of PIN; Figure 4 When the small PIN unit is illuminated by light, it can perform photoelectric conversion, while the large PIN unit does not perform photoelectric conversion when there is no light. Therefore, the working channel capacitance of its photoelectric transmission is mainly considered to be the PN junction capacitance of the small PIN unit, and the overall response time of its PIN unit is greatly reduced. Therefore, f -3dB Improved bandwidth.

[0044] The detector provided in this embodiment can realize P electrode extraction (such as Figure 7 As shown, by leading out the P electrode, three purposes are achieved: large and small PIN units share the P electrode), the spacing area blocks light, and the center area enhances the electric field. Among them, the spacing area blocks light to minimize the incident light from penetrating the surface and entering the absorption layer in the internal epitaxial layer to generate photogenerated carriers.

[0045] The performance of the detector proposed in this embodiment is compared with that of the existing detector, and the results are shown in Table 1 below:

[0046] Table 1

[0047] detector Incident light power Incident light spot position bandwidth Existing detectors 1.0mW Detector Center 200MHz Existing detectors 1.3mW Detector Center 200MHz Existing detectors 1.6mW Detector Center 80MHz Detector of the present invention 5.0mW Detector Center 200MHz

[0048] It can be seen from Table 1 that even at an incident light power of 5 mW, the detector of the present invention can still reach an f of 200 MHz. -3dB bandwidth.

[0049] Another embodiment of the present invention provides a method for preparing a single-electrode dual-photosensitive-area four-quadrant PIN detector, the method being specifically as follows:

[0050] Step 1: Thin film growth of the diffusion barrier layer.

[0051] PECVD deposition to grow SiNx or SiO 2 Passivation film, thickness is 0.2~0.25μm.

[0052] Step 2: Photolithography to open the diffusion hole.

[0053] Apply EPG512 photoresist (thickness of about 0.8 μm); use a contact exposure machine to expose, develop to obtain the target pattern window; use BOE etching solution to etch the diffusion barrier layer according to the pattern window formed by photolithography to open the diffusion hole. Figure 5As shown, the white area is the blocking layer, and the purple area is the diffusion hole, through which impurities are injected.

[0054] Step 3: Perform open tube diffusion and dope the diffusion hole area with Zn to form a Zn diffusion zone to form P-type conductive characteristics.

[0055] Step 4: Deposit 210nm thick SiNx as an anti-reflection film on the photosensitive surface of the detector, which allows more light to pass through the photosensitive surface.

[0056] Step 5: Preparation of P electrode window.

[0057] Coat a double layer of EPG516 photoresist (thickness of about 2 μm); use a contact exposure machine to expose and develop to obtain a target pattern window; use RIE to dry-etch the anti-reflection film according to the pattern window formed by photolithography, such as Figure 6 As shown, after etching, Figure 6 The P-electrode window in the green part. It should be noted that the P-electrode window of the inner circle small PIN unit has a smaller aperture and is distributed at the two vertices of the fan.

[0058] Step 6: Preparation of P metal ring.

[0059] Apply LOR+EPG512 photoresist (thickness of about 1.2μm); use a contact exposure machine for exposure, and develop to obtain the target graphic window; use evaporation gold plating to make the TiPtAu metal layer, and use a stripping machine to remove the glue, and finally obtain Figure 7 P metal ring shown.

[0060] Step 7: The wafer is thinned to the thickness required for cleavage through a grinding process.

[0061] Step 8: Use evaporation gold plating technology to make a TiPtAu metal layer and prepare an N electrode.

[0062] Step 9: Chip testing, cleavage and sorting.

[0063] Use a probe-type integrated device to test the photoelectric characteristics of the chip, and use a wafer splitting device to de-segment the detector chip.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A single-electrode dual-photosensitive-area four-quadrant PIN detector, comprising a substrate, a buffer layer located on the upper surface of the substrate, an absorption layer located on the upper surface of the buffer layer, a cap layer located on the upper surface of the absorption layer, and an N electrode located on the lower surface of the substrate, characterized in that: It also includes a first PIN-type photodiode formed in the cap layer and distributed in four quadrants and a second PIN-type photodiode distributed in four quadrants, the first PIN-type photodiode in each quadrant is in a fan-shaped ring shape, and the second PIN-type photodiode in each quadrant is in a fan-shaped shape; the first PIN-type photodiode is distributed outside the second PIN-type photodiode, and the area of ​​the first PIN-type photodiode is larger than the area of ​​the second PIN-type photodiode; a P electrode is provided outside the first PIN-type photodiode in each quadrant; A metal wiring is arranged in each quadrant interval of the four quadrants, and the metal wiring is used to connect the first PIN type photodiode and the second PIN type photodiode in the same quadrant, wherein the second PIN type photodiode is connected to the P electrode corresponding to the quadrant through the first PIN type photodiode.

2. The four-quadrant PIN detector according to claim 1, characterized in that: An anti-reflection film is provided on the surface of the first PIN type photodiode and the second PIN type photodiode in each quadrant of the detector.

3. The four-quadrant PIN detector according to claim 1, characterized in that: A passivation film is disposed on the surface of the cap layer in an area other than the first PIN-type photodiode and the second PIN-type photodiode, and the P electrode is disposed on the upper surface of the passivation film.

4. A method for preparing a single-electrode dual-photosensitive-area four-quadrant PIN detector, characterized in that: The method includes: Obtaining a substrate, and sequentially forming a buffer layer, an absorption layer and a cap layer on a surface of the substrate; A diffusion barrier layer is deposited on the surface of the cap layer by using a PECVD process; Applying photoresist on the surface of the diffusion barrier layer, and performing photolithography on the photoresist to obtain a first target pattern window; using BOE etching solution to etch the diffusion barrier layer according to the first target pattern window formed by the photolithography, to form diffusion holes corresponding to the inner region and the outer region distributed in four quadrants; wherein each quadrant of the inner region is fan-shaped, and each quadrant of the outer region is fan-shaped; Diffusion is performed through the diffusion hole to form a first PIN type photodiode and a second PIN type photodiode with P-type conductive characteristics in the cap layer, wherein the first PIN type photodiode is formed in the outer region and the second PIN type photodiode is formed in the inner region; Depositing an anti-reflection film on the surface of the first PIN-type photodiode and the second PIN-type photodiode; Apply photoresist on the surface of the anti-reflection film, photolithograph the photoresist on the outer edge of the first PIN-type photodiode in each quadrant to obtain a second target pattern window, and simultaneously photolithograph the two vertices of the fan-shaped second PIN-type photodiode in each quadrant to obtain a third target pattern window; dry-etch the anti-reflection film in the second target pattern window and the third target image window area to form a P-electrode window; Applying photoresist on the surface of the detector currently formed, photolithography the photoresist outside the first PIN-type photodiode of each quadrant to obtain a fourth target pattern window, forming a P electrode in the fourth target pattern window by evaporating gold, and then removing all the photoresist; The other surface of the substrate is thinned by a grinding process, and then an N electrode is formed on the thinned surface by evaporation and gold plating; After the detector passes the photoelectric characteristics test, the chip is de-sliced ​​using a wafer splitting device.

5. The method according to claim 4, characterized in that Metal wiring is formed in the intervals of each quadrant, and the P-electrode windows of the first PIN-type photodiode and the second PIN-type photodiode are connected through the metal wiring. The first PIN-type photodiode and the second PIN-type photodiode are connected to the P electrode through the P-electrode window.

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