Preparation method of shallow contact layer of light inlet surface of silicon-based photodiode

Abstract

The invention belongs to the technical field of photoelectric detectors, and discloses a silicon-based photodiode light inlet surface shallow contact layer preparation method, which comprises the following steps of: 1, selecting a P-type high-resistance monocrystalline silicon substrate, and forming an oxide layer on the front surface of the P-type high-resistance monocrystalline silicon substrate; 2, coating photoresist on the surface of the oxide layer, defining an injection window through photoetching, and forming a silicon wafer; thirdly, boron ions are injected into the front face of the silicon wafer, and the photoresist is removed; and 4, removing an oxide layer on the surface of the silicon wafer, cleaning the silicon wafer, and activating the injected boron ions by using a laser annealing method to form a shallow contact layer. The preparation method is easy and convenient to operate and low in cost, other impurity ions are not introduced in the technological process, and the preparation method is compatible with an existing silicon-based photodiode manufacturing technology and has wide application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoelectric detectors, and relates to a silicon-based photodiode detector, in particular to a preparation method of a shallow contact layer of a light entrance surface of a silicon-based photodiode. BACKGROUND

[0002] The silicon-based photodiode is a photoelectric conversion device based on silicon material, and realizes a photoelectric conversion function. The photodiode is generally divided into PIN type and APD (avalanche) type. The absorption and gain of the PIN photodiode occur in the depletion layer, i.e. the I layer, while the APD photodiode adopts a multiplication and absorption separation structure, and the obtained gain effect is much higher than that of the PIN photodiode. At present, the silicon-based photodiode has been widely used in laser ranging, laser imaging, laser guidance, quantum communication and biological medical fields as a core device of various detection systems, due to low noise, mature process, low manufacturing cost, compatibility with CMOS circuit and high integration degree. Silicon is an indirect bandgap semiconductor, and the bandgap width is 1.12 eV. In theory, the light response cutoff wavelength of silicon is 1100 nm. In the actual preparation process of the photodiode, due to the wide ohmic contact layer, the quantum efficiency of the device generated in the visible light to near-infrared wavelength band is low, which is difficult to meet the demand of high sensitivity detection.

[0003] In order to further improve the quantum efficiency of the silicon-based photodiode in the response wavelength band and improve the sensitivity of the device, the commonly used methods are: using a single / multi-layer antireflection film system on the light entrance surface to improve the light energy utilization rate; increasing the thickness of the absorption layer of the silicon-based photodiode to improve the photoelectric conversion efficiency, or increasing the resonant cavity structure. However, the above designs are only suitable for a specific wavelength band or a specific wavelength range, and cannot be used for all wavelength bands that can be responded by silicon-based materials.

[0004] In the design of the device structure, the contact layer produces light intensity attenuation to the light absorption, and the contribution to the photoelectric response can be ignored, and the quantum efficiency produces a negative effect. This layer is also called "dead layer". For a near-infrared photodetector, reducing the thickness of the contact layer can effectively increase the thickness of the absorption layer and improve the quantum efficiency of the device. For a visible light photodetector, due to the large absorption coefficient, reducing the thickness of the contact layer on the light entrance surface can effectively reduce the light intensity attenuation and improve the sensitivity of the device.

[0005] Currently, the preparation methods of the shallow contact layer mainly include: low-energy high-dose implantation combined with rapid annealing, multiple diffusion, etc. In the above methods, the shallow contact layer prepared by low-energy high-dose implantation has a smaller width, but if the dose is not appropriate, it may cause irreversible lattice damage to the silicon base, at the same time, when the energy is low, the beam stability is poor, and the related equipment is expensive and not suitable for mass production; the method of multiple diffusion is compatible with the existing process, suitable for mass production, and the prepared shallow contact layer is more stable, but the method needs to wash the film multiple times in the operation process to remove substances such as phosphor-silicon glass in the silicon base, and the multiple diffusion process also increases the risk of introducing various impurities, increases the surface leakage current of the device, and reduces the performance of the device. SUMMARY

[0006] (I) Objectives of the Invention

[0007] The purpose of the present application is to provide a silicon-based photodiode shallow contact layer preparation method, which can realize the preparation of the shallow contact layer by using the blocking effect of the oxide layer on boron and phosphorus ions through the method of implantation combined with laser annealing with an oxide layer; the laser annealing is used for ion activation, and the high instantaneous temperature is used to activate the implanted ions.

[0008] (II) Technical Solutions

[0009] In order to solve the above technical problems, the present application provides a silicon-based photodiode light entrance surface shallow contact layer preparation method, comprising the following steps:

[0010] First step: select a P-type high-resistance single crystal silicon substrate, and form an oxide layer on the front surface thereof;

[0011] Second step: coat photoresist on the surface of the oxide layer, define the implantation window through photolithography, and form a silicon wafer;

[0012] Third step: implant boron ions on the front surface of the silicon wafer, and remove the photoresist;

[0013] Fourth step: remove the oxide layer on the surface of the silicon wafer, clean the silicon wafer, and activate the implanted boron ions by laser annealing to form a shallow contact layer.

[0014] Further, in the first step, a 2-inch P-type high-resistance single crystal silicon wafer is used as the substrate material.

[0015] Further, in the first step, the oxide layer is prepared on the P-type high-resistance single crystal silicon substrate by a dry oxygen atmosphere thermal oxidation method.

[0016] Further, in the first step, the resistivity of the P-type high-resistance single crystal silicon substrate is greater than 10000Ω.

[0017] Further, in the first step, the thickness of the oxide layer is 100 nm ± 10 nm, and the oxidation temperature during the formation of the oxide layer is 1000℃.

[0018] Further, in the third step, boron ions are implanted into the front surface of the silicon wafer by using an ion implantation method, and the photoresist on the surface of the silicon wafer is removed by using a photoresist cleaning solution.

[0019] Further, in the third step, the dose of the boron ions is 1×10 15 ~ 2×10 15 ions, and the energy is 30~40keV.

[0020] Further, in the fourth step, the oxide layer on the surface of the silicon wafer is removed by using a mixed aqueous solution of hydrofluoric acid / ammonium fluoride.

[0021] Further, in the fourth step, the silicon wafer is cleaned by using a mixed aqueous solution of sulfuric acid / hydrogen peroxide.

[0022] Further, in the fourth step, when the implanted boron ions are activated by using a laser annealing method, the laser energy is 1.5J / cm 2 , the laser wavelength is 532nm, and the repetition frequency is 15%.

[0023] (III) Beneficial Effects

[0024] The silicon-based photodiode light entrance surface shallow contact layer preparation method provided by the above technical solution has the following beneficial effects:

[0025] (1) The silicon-based photodiode shallow contact layer preparation technology provided by the present application adopts a method of implantation combined with laser annealing with an oxide layer, which can prepare a shallow contact layer structure on the surface of the silicon light entrance surface without multiple high-temperature processes, has the advantages of simple operation, low equipment requirement, low cost and process damage, is compatible with the traditional manufacturing process of the silicon-based photodiode, and has a wide application prospect.

[0026] (2) For near-infrared wavelengths such as 905nm and 1064nm, the preparation of the shallow contact layer can increase the width of the depletion layer, increase the absorption, and improve the responsivity of the device. For visible wavelengths such as 532nm, the absorption coefficient in silicon is large, and the light intensity is attenuated by 95% at a distance of ~2μm from the light entrance surface, so the light energy utilization rate is poor. Therefore, the preparation of the light entrance surface shallow contact layer can effectively reduce the attenuation of light in silicon and improve the light energy utilization rate and responsivity of the device.

[0027] (3) The shallow contact layer prepared by the method of combining oxidation layer injection with laser annealing has better uniformity. In the case of other conditions unchanged, the oxidation temperature changes by 1000±1℃ and the oxidation layer changes by ±5nm, and the depth of the prepared contact layer almost does not change. In the actual process, it is more convenient to control the temperature change within ±1℃. Therefore, the method for preparing the shallow contact layer has great significance for the preparation of photodiodes, source-drain extension regions and miniaturized devices.

[0028] (4) Since the process belongs to the physical process of melting, dissolving and recrystallizing, the injected ions do not undergo secondary diffusion, the prepared contact layer is very shallow, the preparation method is simple and low in cost, other impurity ions are not introduced in the process, and the method is compatible with the existing silicon-based photodiode manufacturing process, so the method has a broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figures 1 to 4 The figures are schematic diagrams of the preparation process of the method.

[0030] Figure 5 The figure is a schematic diagram of the cross section of the light-incident surface shallow contact layer prepared by the method. DETAILED DESCRIPTION

[0031] In order to make the purpose, content and advantages of the present application clearer, the specific embodiments of the present application are described in further detail below in combination with the drawings and examples.

[0032] In this embodiment, a 2-inch P-type high-resistance single crystal silicon wafer is used as a substrate material, and a light-incident surface shallow contact layer prepared therefrom is used.

[0033] Referring to Figures 1 to 4 , the method for preparing a light-incident surface shallow contact layer of a silicon-based photodiode in this embodiment includes the following steps:

[0034] First step: Select a P-type high-resistance single crystal silicon substrate, and form an oxidation layer on the front surface thereof;

[0035] By a thermal oxidation method in a dry oxygen atmosphere, an oxidation layer 2 with a thickness of 100nm±10nm is prepared on the P-type single crystal silicon substrate 1 with a resistivity greater than 10000Ω, and the oxidation temperature is selected to be 1000℃, as shown in the attached Figure 1 .

[0036] Second step: Coating a photoresist 3 on the surface of the oxidation layer 2, and defining an injection window by photolithography to form a silicon wafer, as shown in the attached Figure 2 .

[0037] Third step: Using an ion implantation method 4 to implant boron ions on the front surface of the above-mentioned silicon wafer, and the boron ion dose is 1×10 15 ~2×1015 ions, energy 30-40 keV, see attached Figure 3 , and the photoresist on the surface of the silicon wafer is removed using a photoresist cleaning solution, see attached Figure 4 .

[0038] Fourth step: the oxide layer on the surface of the silicon wafer is removed using a mixed aqueous solution of hydrofluoric acid / ammonium fluoride, and then the silicon wafer is cleaned using a mixed aqueous solution of sulfuric acid / hydrogen peroxide to ensure that the surface of the wafer is clean and free of contamination, and finally the implanted boron ions are activated using a laser annealing method to form a shallow contact layer 5, see attached Figure 5 .

[0039] The laser energy is selected to be 1.5 J / cm 2 , the laser wavelength is 532 nm, and the repetition frequency is selected to be 15%. During the activation process, the cleanliness of the chamber needs to be ensured to prevent changes in the physical properties of the crystallized silicon-based light-incident surface contact layer due to external interference.

[0040] According to the simulation and experimental results, the light-incident surface contact layer prepared according to the method for preparing a light-incident surface shallow contact layer of a silicon-based photodiode described in the present application can effectively improve the device performance of a near-infrared waveband silicon-based photodiode, and can greatly improve the responsivity of a visible light waveband silicon-based photodiode. In the design of the device structure of the silicon-based photodiode, the front-illuminated / back-illuminated photodiode structure can be flexibly designed according to the actual situation.

[0041] As can be seen from the above technical solution, the present application has the following remarkable features:

[0042] (1) The present application combines oxidation layer implantation with laser annealing technology, and innovatively proposes a method for preparing a light-incident surface shallow contact layer of a silicon-based photodiode, which can prepare a relatively shallow ohmic contact layer on the surface of a silicon device. This preparation method is simple, low in cost, does not introduce other impurity ions, and is compatible with the traditional manufacturing process of a silicon-based photodetector, and has a broad application prospect.

[0043] (2) The light-incident surface shallow contact layer prepared according to the method described in the present application can effectively improve the sensitivity and other performance indicators of a 905 nm, 1064 nm, etc. near-infrared waveband silicon-based photodetector, and can greatly improve the responsivity of a 532 nm, etc. visible light waveband silicon-based photodetector. For weak light detection in complex environments such as underwater environments, it has very important significance.

[0044] The above is only a preferred embodiment of the present application, and it should be noted that for ordinary skilled persons in the technical field, several improvements and modifications can be made without departing from the technical principles of the present application, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a shallow contact layer on a light receiving surface of a silicon-based photodiode, characterized by, The method comprises the following steps: Step 1: P-type high-resistance monocrystalline silicon substrate is selected, and an oxide layer is formed on the front surface of the substrate; Step 2: photoresist is coated on the surface of the oxide layer, and an injection window is defined by photolithography to form a silicon wafer; Step 3: boron ions are injected into the front surface of the silicon wafer, and the photoresist is removed; Step 4: the oxide layer on the surface of the silicon wafer is removed, the silicon wafer is cleaned, the injected boron ions are activated by a laser annealing method, and a shallow contact layer is formed.

2. The method of claim 1, wherein the method further comprises: In step 1, a 2-inch P-type high-resistance monocrystalline silicon wafer is used as the substrate material.

3. The method of claim 2, wherein the method further comprises: In step 1, the oxide layer is prepared on the P-type high-resistance monocrystalline silicon substrate by a thermal oxidation method in a dry oxygen atmosphere.

4. The method of claim 3, wherein the method further comprises: In step 1, the resistivity of the P-type high-resistance monocrystalline silicon substrate is greater than 10,000 Ω.

5. The method of claim 4, wherein the method further comprises: In step 1, the thickness of the oxide layer is 100 nm ± 10 nm, and the oxidation temperature during the formation of the oxide layer is selected to be 1,000 °C.

6. The method of claim 5, wherein the method further comprises: In step 3, the front surface of the silicon wafer is injected with boron ions by an ion implantation method, and the photoresist on the surface of the silicon wafer is removed by using a photoresist cleaning solution.

7. The method of claim 6, wherein the method further comprises: In the third step, boron ions were implanted at a dose of 1 x 1016 ions, at an energy of 30-40 keV. 15 15 ions, at an energy of 30-40 keV.​ 8. The method of claim 7, wherein the method further comprises: In step 4, a hydrogen fluoride / ammonium fluoride mixed aqueous solution is used to remove the oxide layer on the surface of the silicon wafer.

9. The method of claim 8, wherein the method further comprises: In step 4, a sulfuric acid / hydrogen peroxide mixed aqueous solution is used to clean the silicon wafer.

10. The method of claim 9, wherein the method further comprises: In the fourth step, the laser energy is 1.5 J / cm 2 , the laser wavelength is 532 nm, and the repetition frequency is 15%.

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