Low cost method of fabrication of a photoelectric sensor and its structure

Abstract

The application discloses a low-cost preparation method of a photoelectric sensor and belongs to the field of semiconductor processes. The application forms a low-doped layer with the same doping type as the substrate on the surface of a silicon wafer by general implantation, replaces the original cutoff ring, and plays a role in reducing the dark current of the device. Meanwhile, the implantation dose and energy of general implantation have a great influence on the performance of the photoelectric device, especially on the breakdown voltage. The photo-sensitive surface adopts an oxidation scheme to prepare a silicon oxide dielectric layer, replaces the original scheme of redepositing a photo-sensitive dielectric layer after photoetching, finally realizes reduction of five photoetching of the photoelectric sensor to only three photoetching, and finally realizes a great reduction of the manufacturing cost of the photoelectric sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor process, in particular to a low-cost preparation method of photoelectric sensor and a structure thereof. BACKGROUND

[0002] The photoelectric sensor is a kind of semiconductor device that converts light energy into electrical energy, and is widely used in industrial sensing, intelligent household appliances, industrial control and other industries, such as remote control, light switch, encoder, photocell and the like. Since the photoelectric sensor has very wide application, the market has very high requirements for low-cost photoelectric sensor chips.

[0003] The conventional photoelectric sensor needs five different functional areas, i.e. cutoff ring, PN junction, photosensitive surface, contact hole and electrode, so the conventional photoelectric sensor chip needs to be prepared by five times of photolithography, and etching and implantation are also needed after each photolithography, so the cost of the photoelectric sensor cannot be further reduced. SUMMARY

[0004] The present application aims to provide a low-cost preparation method of photoelectric sensor and a structure thereof to solve the problem of high cost in preparing the photoelectric sensor.

[0005] To solve the above technical problems, the present application provides a low-cost preparation method of photoelectric sensor, comprising:

[0006] Step 1, providing a substrate, forming a shielding layer on the front surface of the substrate by thin oxidation, and lightly doping the surface with a first dopant to form a first doped region;

[0007] Step 2, preparing a field oxide layer on the surface of the doped substrate;

[0008] Step 3, etching out a second doped window region by first photolithography, and doping the second doped window region with a second dopant to form a second doped region;

[0009] Step 4, oxidizing an oxide layer on the surface of the second doped window region according to light response requirements;

[0010] Step 5, performing second photolithography on the oxide layer on the surface of the second doped window region to prepare a contact hole;

[0011] Step 6, depositing a metal electrode on the front surface and performing third photolithography to etch out a front metal electrode;

[0012] Step 7, depositing a back metal electrode on the back surface of the substrate.

[0013] Optionally, the doping type of the first dopant is the same as the doping type of the substrate, and the doping type of the second dopant is different from the doping type of the first dopant.

[0014] Optionally, the first dopant has an implantation dose of 1 x 1012cm-2~5 x 1012cm-2. 11 cm-2 -3 ~1 x 1012cm-2 13 cm-2 -3 and an implantation energy of 30 keV~100 keV.

[0015] Optionally, the first dopant has an implantation dose of 1 x 1012cm-2~5 x 1012cm-2. 12 cm-2 -3 ~5 x 1012cm-2 12 cm-2 -3 and an implantation energy of 60 keV~80 keV.

[0016] Optionally, the second dopant has an implantation dose of 1 x 1012cm-2~1 x 1012cm-2. 13 cm-2 -3 ~1 x 1012cm-2 16 cm-2 -3 and an implantation energy of 50 keV~120 keV.

[0017] Optionally, the second dopant has an implantation dose of 1 x 1012cm-2~1 x 1012cm-2. 14 cm-2 -3 ~1 x 1012cm-2 15 cm-2 -3 and an implantation energy of 70 keV~100 keV.

[0018] Optionally, the thickness of the oxide layer in step 4 is 130~150 nm or 150~170 nm; when the thickness is 130~150 nm, the peak wavelength of the light responsivity is 800 nm, and when the thickness is 150~170 nm, the peak wavelength of the light responsivity is 900 nm.

[0019] A photoelectric sensor structure, comprising a substrate, a back metal electrode deposited on the bottom outer surface of the substrate, and an oxide layer formed on the top outer surface of the substrate; a first doped region and a second doped region are formed on the top inner surface of the substrate, the first doped region and the second doped region are located below the oxide layer, and the depth of the second doped region is greater than that of the first doped region; a front metal electrode covers the first doped region; the front metal electrode contacts the second doped region through the oxide layer.

[0020] Optionally, the oxide layer comprises a shielding layer and a prepared field oxide layer, and the total thickness of the shielding layer and the field oxide layer is 600 nm~1100 nm.

[0021] In the low-cost preparation method and structure of the photoelectric sensor provided by the application, a low-doped layer of the same doping type as the substrate is formed on the surface of the silicon wafer by general injection, replacing the original cutoff ring, to reduce the dark current of the device; the photosensitive surface is prepared by oxidation to form a silicon oxide dielectric layer, replacing the original scheme of depositing a photosensitive dielectric layer after photolithography, so that the five photolithography steps of the photoelectric sensor are reduced to only three photolithography steps, reducing the preparation cost of the photoelectric sensor by 40% and increasing the production capacity of the photoelectric sensor by 66.66%. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of forming a thin oxide layer on a silicon wafer substrate;

[0023] Figure 2 is a schematic diagram of lightly doping the surface of the silicon wafer substrate with a first dopant to form a first doped region;

[0024] Figure 3 is a schematic diagram of preparing a field oxide layer on the doped surface;

[0025] Figure 4 is a schematic diagram of forming a second doped region at a second doped window;

[0026] Figure 5 is a schematic diagram of performing second photolithography on the surface of the second doped window region to prepare a contact hole;

[0027] Figure 6 is a schematic diagram of depositing metal on the front surface;

[0028] Figure 7 is a schematic diagram of performing third photolithography to etch the surface metal to form a front metal electrode;

[0029] Figure 8 is a schematic diagram of depositing a metal electrode on the back surface to form a back metal electrode. DETAILED DESCRIPTION

[0030] The low-cost preparation method and structure of a photoelectric sensor provided by the application will be further described in detail below in combination with the drawings and specific embodiments. The advantages and features of the application will be more apparent according to the following description and claims. It should be noted that the drawings are greatly simplified and use non-precise proportions, only to facilitate and clarify the purpose of assisting in the description of the embodiments of the application.

[0031] This invention provides a low-cost fabrication method for photoelectric sensors. A low-doped layer with the same doping type as the substrate is formed on the silicon wafer surface using a monolithic injection method, replacing the original cutoff ring and reducing the device's dark current. Simultaneously, the injection dose and energy of the monolithic injection have a significant impact on the performance of the photoelectric device, especially on the breakdown voltage. The photosensitive surface is fabricated using an oxidation method to create a silicon oxide dielectric layer, replacing the original method of re-depositing the photosensitive dielectric layer after photolithography. Ultimately, this reduces the photoelectric sensor fabrication process from five photolithography steps to only three, resulting in a significant reduction in the manufacturing cost of the photoelectric sensor.

[0032] The low-cost fabrication method for the photoelectric sensor provided by this invention has the following specific process flow:

[0033] Step 1: As Figure 1 As shown, a thin oxide layer of less than 100 nm is formed on the silicon substrate 1 to form a masking layer 2 to prevent surface damage in subsequent implantation processes.

[0034] Step 2: As Figure 2 As shown, the surface of the silicon substrate 1 is lightly doped with a first dopant to form a first doped region 3. The doping type of the first dopant is the same as that of the substrate. The implantation dose of the first dopant is 1 × 10⁻⁶. 11 cm -3 ~1×10 13 cm -3 The preferred injection dose is 1×10 12 cm -3 ~5×10 12 cm -3 The injection energy is 30keV to 100keV, with 60keV to 80keV being the preferred range. Higher injection doses result in lower device breakdown voltages; therefore, the injection dose and energy need to be adjusted according to the actual breakdown voltage requirements.

[0035] Step 3: As Figure 3 As shown, oxidation is continued on the doped surface to prepare a field oxide layer, the total thickness of which includes the masking layer 2 and the newly prepared field oxide layer is 600 nm to 1100 nm.

[0036] Step 4: As Figure 4 As shown, a first photolithography step is performed to form a second doped window. A second dopant is then used to dope the second doped window, forming a second doped region 4. The implantation dose of the second dopant is 1 × 10⁻⁶. 13 cm -3 ~1×10 16 cm -3 The preferred injection dose is 1×10 14 cm-3 ~1×10 15 cm -3 The implantation energy is 50keV to 120keV, preferably 70keV to 100keV. The doping type of the second dopant is different from that of the first dopant. Then, according to the photoresponse requirements, an oxide layer of corresponding thickness is oxidized in the second doping window region. The oxide layer thickness is 130 to 150 nm, corresponding to a peak photoresponse wavelength of 800 nm. The oxide layer thickness is 150 to 170 nm, corresponding to a peak photoresponse wavelength of 900 nm.

[0037] Step 5: As Figure 5 As shown, a second photolithography is performed on the oxide layer on the surface of the second doped window region to prepare contact hole 5.

[0038] Step 6: As Figure 6 As shown, metal is deposited on the positive surface.

[0039] Step 7: As Figure 7 As shown, a third photolithography process is performed to etch the metal on the surface to form the front metal electrode 6.

[0040] Step 8: As Figure 8 As shown, a metal electrode is deposited on the back surface to form the back metal electrode 7.

[0041] This invention features a simple process requiring only three photolithography steps. It replaces the cutoff ring method with a generalized surface deposition technique on the entire substrate surface and replaces the photosensitive surface fabrication method with a direct oxidation method. This reduces the number of photolithography steps for the photoelectric sensor from five to three, lowering the fabrication cost by 40% and increasing production efficiency by 66.67%.

[0042] The photoelectric sensor structure prepared by the above method is as follows: Figure 8 As shown, the substrate includes a substrate 1, on which a back metal electrode 7 is deposited on the outer bottom surface, an oxide layer and a first doped region 3 are formed on the outer top surface, and a second doped region 4 is formed on the inner top surface; a front metal electrode 6 is covered on the first doped region 3. The oxide layer includes a shielding layer 2 and a pre-formed oxide layer, with a total thickness of 600 nm to 1100 nm.

[0043] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for low cost fabrication of a photoelectric sensor, characterized in that, The method comprises the following steps: Step 1, providing a substrate, performing a thin oxidation process on the front surface of the substrate to form a shielding layer, and lightly doping the entire surface with a first dopant to form a first doped region; Step 2, preparing a field oxide layer on the surface of the doped substrate; Step 3, performing a first photolithography and etching a second doped window region, and doping the second doped window region with a second dopant to form a second doped region; Step 4, oxidizing an oxide layer on the surface of the second doped window region according to light response requirements; Step 5, performing a second photolithography on the oxide layer on the surface of the second doped window region to prepare a contact hole; Step 6, depositing a front metal electrode on the front surface of the substrate and performing a third photolithography to etch the front metal electrode; Step 7, depositing a back metal electrode on the back surface of the substrate.

2. The method of claim 1, wherein the photoelectric sensor is prepared at a low cost, and The doping type of the first dopant is the same as the doping type of the substrate, and the doping type of the second dopant is different from the doping type of the first dopant.

3. The method of claim 1, wherein the photoelectric sensor is prepared at a low cost, and The implantation dose of the first dopant is 1x1013~1x1014cm-2, and the implantation energy is 30keV~100keV. 11 cm -3 ~1x1013 13 cm -3 , and the implantation energy is 30keV~100keV.

4. A method of low cost production of a photoelectric sensor according to claim 3, characterized in that, The implantation dose of the first dopant is 1 x 10 12 cm -3 ~5 x 10 12 cm -3 ; and the implantation energy is 60 keV ~ 80 keV.

5. The method of claim 1, wherein the photoelectric sensor is prepared at a low cost, and The implantation dose of the second dopant is 1 x 10 13 cm -3 ~1 x 10 16 cm -3 , and the implantation energy is 50 keV~120 keV.

6. The method of claim 1, wherein the photoelectric sensor is prepared at a low cost, and The implantation dose of the second dopant is 1 x 10 14 cm -3 ~1 x 10 15 cm -3 , and the implantation energy is 70 keV~100 keV.

7. The method of claim 1, wherein the photoelectric sensor is prepared at a low cost, and The thickness of the oxide layer in step 4 is 130-150 nm or 150-170 nm; when the thickness is 130-150 nm, the peak wavelength of the light response degree is 800 nm, and when the thickness is 150-170 nm, the peak wavelength of the light response degree is 900 nm.

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