RU2541416C1 - METHOD OF PRODUCING SILICON p-i-n PHOTODIODE - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to production of silicon p-i-n photodiodes which are sensitive to radiation with wavelength of 0.9-1.06 mcm. Said silicon p-i-n photodiodes are intended for use in different optoelectronic devices which require detection of short laser pulses (10-40 ns). After performing high-temperature thermodiffusion processes to form the photodiode structure: - thermal oxidation; - phosphorus diffusion to form n+-type regions (photosensitive areas and collar rings); - phosphorus diffusion into the back surface of the wafer to generate impurities; - boron diffusion into the back surface of the water after etching a gettering n+-type layer to form a p+-type layer, after forming ohmic contacts, the method includes etching the dielectric film from the silicon surface and etching silicon by a depth less than 1 mcm, followed by depositing a silicon dioxide film using a low-temperature technique at temperature not higher than 800°C. Ohmic contacts are then formed using known techniques.

EFFECT: reduced dark current of photosensitive areas and the collar ring, reduced values of coupling factors between the photosensitive areas of multielement photodiodes and high output of non-defective devices.

Description

The claimed invention relates to a manufacturing technology of silicon p-i-n photodiodes (PD), sensitive to radiation with wavelengths of 0.9-1.06 microns. They are intended for use in various electron-optical equipment in which registration of short pulses of laser radiation (10-40 ns) is required.

One of the main parameters of such PDs is: the value of the dark current at the operating voltage, which determines the noise level of the PD, and, therefore, its threshold sensitivity, as well as the magnitude of the photoelectric coupling coefficients between the photosensitive areas in multi-element PDs.

Known copyright certificate [a.s. No. 680538 with a priority of February 19, 1976, Klimanov EA, Kulymanov A.V., Liseikin V.P. "A method of manufacturing a pin photodiode"], which describes a method of manufacturing a PD, where gettering of electrically active defects is used to reduce dark currents using a diffusion n ⁺ layer created on passive surfaces of the plate.

Known US patent [US 4127932 with priority from 08/06/1976 A.R. Hartman, H. Melhior, D.P. Schinke, R.G. Smith, “Method of fabricating silicon photodiodes”], which also uses gettering with a diffusion layer of defects in the bulk of samples and annealing structures with a manufactured contact system in forming gas at 300 ° to reduce the density of surface states.

A well-known silicon pin photodiode is a large area [patent for utility model of the Russian Federation No. 56069 U1 with priority November 21, 2005, Filachev AM, Kravchenko N.V., Khakuashev P.E., Ogneva O.V., Chinareva I.V., applicant FSUE NPO Orion], sensitive at wavelengths of 1.06 μm and 0.9 μm, the manufacturing method of which is adopted as the closest analogue. In a substrate of p-type monocrystalline silicon using phosphorus diffusion through a silicon dioxide (SiO ₂ ) film, n ⁺ -type regions are formed: a photosensitive region and a guard ring region. A p-type conductivity layer is formed on the other side of the substrate by boron diffusion. The creation of two-layer ohmic contacts to the photosensitive region, the guard ring region and the p-type contact layer is carried out by applying a gold film with a titanium sublayer.

The disadvantage of these methods for manufacturing PD is the reduction in the percentage of suitable products by the values of the dark currents of the photosensitive sites and the guard ring, as well as the values of the photovoltaic coefficients between the photosensitive sites due to the formation of inversion and conversion layers with a high concentration of minority charge carriers - electrons in the surface regions of silicon p-type with a low concentration of major carriers (of the order of 10 ¹² cm ^-3 ). The formation of these layers leads to a large contribution of surface leakage currents to the dark currents of the photosensitive sites and the guard ring and a decrease in the resistance between them. These layers arise during high-temperature processes due to the formation of a positive built-in charge at the oxide-silicon interface and the diffusion of contaminants, leading to a change in the type of conductivity from p-type to n-type in the surface region of silicon.

The objective of the invention is to reduce the level of dark current of the photosensitive sites and the guard ring, reduce the values of the coefficients of the relationship between the photosensitive areas of multi-element PDs and increase the percentage of suitable devices.

This goal is achieved by eliminating the inversion and conversion layers in the near-surface regions of the PD, which is achieved by the fact that after all high-temperature operations (oxidation, phosphorus diffusion, gettering, boron diffusion), the dielectric silicon dioxide film is etched from the wafer surface and the surface silicon layer is etched to a depth less than one micron, followed by the deposition of a film of silicon dioxide by one of the low-temperature methods (for example, the decomposition of tetraethoxysilane Oxidation monosilane) at a temperature not exceeding 800 ° C. Then, by known methods, the formation of two-layer ohmic contacts to the photosensitive region, the area of the guard ring and the contact layer of the p ⁺ type of conductivity is carried out.

The proposed manufacturing method allows to reduce the current of the guard ring and obtain the resistance values of the surface channels between the photosensitive sites, photosensitive sites and the guard ring at the level of tens of milliohms, which provides low surface leakage currents of the photosensitive sites, the guard ring and the coupling coefficients between the photosensitive sites.

Low values of surface leakage currents and coupling coefficients are achieved due to the fact that large values of the surface channel resistance between the guard ring and photosensitive sites lead to the leakage of peripheral leakage currents along the guard ring circuit, preventing them from branching into the photosensitive area circuit.

At the same time, increasing the resistance of the surface channel between the photosensitive sites reduces the flow of photocurrents between them, which reduces the coefficient of photoelectric interconnection between the sites.

Thus, the technical result is a decrease in the dark current level of the photosensitive sites and the guard ring, a decrease in the correlation coefficients between the photosensitive areas of multi-element PDs and an increase in the percentage of suitable devices, achieved after the high-temperature thermal diffusion processes to create the PD structure:

- thermal oxidation;

- phosphorus diffusion to create areas of n ⁺ type conductivity (photosensitive sites and a guard ring);

- diffusion of phosphorus into the back surface of the plate for gettering contaminants;

- boron diffusion into the back surface of the plate after etching the gettering n ⁺ layer to create a layer of p ⁺ type conductivity,

Before the operation of creating ohmic contacts, the dielectric film is etched from the silicon surface and silicon is etched to a depth of less than one micron, followed by deposition of the silicon dioxide film by one of the low-temperature methods (for example, decomposition of tetraethoxysilane, oxidation of monosilane) at a temperature not exceeding 800 ° C. Then produce the formation of ohmic contacts by known methods.

Claims (1)

A method of manufacturing a silicon photodiode, including thermal diffusion operations of thermal oxidation, diffusion of phosphorus to form regions of n ⁺ type conductivity, diffusion of phosphorus to getter contaminants, boron diffusion to form regions of p ⁺ type conductivity and the operation of creating bilayer ohmic contacts to the photosensitive region, region a protective ring and a contact layer of p ⁺ type conductivity by applying a gold film with a titanium or chromium sublayer, characterized in that to reduce dark the new currents of the photosensitive sites and the guard ring, reduce the values of the coefficients of the relationship between the photosensitive areas of multi-element photodiodes (PD) and increase the percentage of suitable devices after performing thermal diffusion operations before the operation of creating ohmic contacts, the dielectric film is etched from the silicon surface and silicon is etched to a depth of less than one micron followed by deposition of a film of silicon dioxide by one of the low-temperature methods at a temperature not rising to 800 ° C.