KR100766675B1 - A fabricating method of image sensor with decreased dark signal - Google Patents

Abstract

The present invention relates to an image sensor, and more particularly, to provide a method for manufacturing an image sensor suitable for suppressing the inflow of a dark signal from a silicon lattice defect at an STI interface due to STI formation. Selectively etching the conductive semiconductor layer to form a trench for forming a field insulating film; Forming a field insulating film filled with the trench and containing impurities of a first conductivity type; Diffusing the impurities of the field insulating layer into the semiconductor layers on the sidewalls and the bottom of the trench through heat treatment to form a charge inflow blocking region; Forming a gate electrode on the semiconductor layer away from the field insulating film; And forming a photodiode in the semiconductor layer between the gate electrode and the field insulating layer.

Dark signal, trench, image sensor, photodiode, trench, STI.

Description

A fabricating method of image sensor with decreased dark signal             

1 is a schematic diagram of an image sensor having a conventional trench type field insulating film,

2A through 2D are cross-sectional views illustrating an image sensor manufacturing process according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

20: semiconductor layer 25: charge inflow blocking region

26: field insulating film 27: gate insulating film

28: conductive film for gate electrode 30: spacer

32: sensing diffusion area

29 N-type impurity region for photodiode

31: P-type impurity region for photodiode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly, to a method of manufacturing an image sensor, and more particularly, to an image using a trench trench isolation (STI) to reduce dark signals. It relates to a sensor manufacturing method.

In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. In a double charge coupled device (CCD), individual metal-oxide-silicon (MOS) capacitors are very different from each other. A device in which charge carriers are stored and transported in a capacitor while being located in close proximity, and CMOS (Complementary MOS) image sensor is a CMOS technology that uses a control circuit and a signal processing circuit as peripheral circuits. Is a device that employs a switching method that creates MOS transistors by the number of pixels and sequentially detects the output using them.

In the manufacture of such various image sensors, efforts are being made to increase the photo sensitivity of the image sensor, one of which is a condensing technology. For example, a CMOS image sensor is composed of a photodiode for detecting light and a portion of a CMOS logic circuit for processing the detected light into an electrical signal to make data. To increase light sensitivity, the ratio of the photodiode to the total image sensor area is increased. Efforts have been made to increase (usually referred to as Fill Factor).

Fig. 1 shows a schematic diagram of an image sensor having a conventional trench type field insulating film.

Referring to FIG. 1, a semiconductor layer in which a high concentration of P ++ layer 10 and P-Epi layer 11 are stacked in a conventional image sensor is described below. P ++ layer 10 and P-Epi layer 11 It is called a semiconductor layer.

A trench type field insulating film 12 is formed locally in the semiconductor layer, and a gate electrode including the gate insulating film 13, the conductive film 14 for the gate electrode 14, and the spacer 15 in a region away from the field insulating film 12, for example. A transfer gate is disposed, the n-type impurity region (hereinafter referred to as n-region) and n- for photodiode formed in a predetermined depth inside the semiconductor layer while being in contact with the gate electrode and the field insulating film 12; A shallow P-type impurity region (hereinafter referred to as P0 region) for photodiode is disposed at an interface in contact with the semiconductor layer above the region, and a sensing diffusion region (hereinafter referred to as n + region) is disposed.

On the other hand, the conventional image sensor described above takes the form of a photodiode in which the field insulating film 12 is a simple trench type and extends only a Bird's beak portion in the LOCOS method. For this reason, the field insulating film 12 is formed of STI rather than the conventional LOCOS method.

However, in the case of STI, due to the process characteristics in which the silicon lattice is more damaged by the trench etching at the STI interface than the conventional LOCOS method, the excess electrons are trapped from the defects of the damaged silicon lattice, thereby trapping the image sensor. It generates a representative dark signal of the characteristic deterioration.

In other words, the dark signal is not caused by the photoelectric reaction, and the generated charge is accumulated and accumulated in the photodiode. There are various sources of the dark signal charge, among which, at the interface between the silicon interface of the semiconductor layer and the field insulating film 12. Components due to crystal incompleteness, such as dislocation, are accumulated in the area of the photodiode PD as shown by X as the main cause.

On the other hand, the STI method, which is used as an element isolation method of 0.25 μm or less, has a larger length of the active / field interface than the LOCOS method as described above. The suppression of the dark signal generation by the will have a greater influence on the characteristics of the image sensor.

The present invention proposed to solve the above problems of the prior art, to provide an image sensor manufacturing method suitable for suppressing the inflow of the dark signal from the silicon lattice defect at the STI interface due to the formation of the STI have.

In order to achieve the above object, the present invention provides a method of forming a trench for forming a field insulating film by selectively etching a semiconductor layer of a first conductive type, and a field insulating film containing impurities of a first conductive type to fill the trench. Forming a charge inflow blocking region by diffusing the impurities of the field insulating film to the semiconductor layers on the sidewalls and the bottom of the trench through heat treatment; and forming a gate on the semiconductor layer away from the field insulating film. And forming a photodiode in the semiconductor layer between the gate electrode and the field insulating layer, wherein the photodiode comprises a first region of a second conductive type and an upper portion of the first region. It provides a method for manufacturing an image sensor consisting of a second region of the first conductivity type formed in the.

The present invention is a method for suppressing an increase in dark signal components due to an increase in active / field interface when forming a field insulating film by STI, and thermal diffusion after embedding an insulating film containing P-type impurities such as BSG (Borophospho Silicate) in a trench. P-type impurities are doped at the active / field interface to prevent inflow of dark signal components generated at the interface into the photodiode. In the case of a PNP structure photodiode, P-type impurities are used to prevent the inflow of electrons. The diffusion and separation of the active / field interface by the N-type and P-type impurity doping of the photodiode and the n-region of the photodiode prevents the inflow of charge.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. 2A to 2D are cross-sectional views illustrating an image sensor manufacturing process according to an embodiment of the present invention.

First, as shown in FIG. 2A, the pad oxide film 21/500 Å to 2000 Å having a thickness of 50 μs to 200 μs is thereafter used to distinguish the field insulating region from the active region. After the buffer polysilicon film or the buffer nitride film 22 having a thickness is continuously applied, the photoresist pattern 23 for forming the trench is formed.

Here, in the conventional image sensor, a semiconductor layer in which a high concentration of P ++ layer and P-Epi layer are stacked is used, and reference numeral '20' denotes a semiconductor layer in which such P ++ layer and P-Epi layer are stacked.

Next, as shown in FIG. 2B, the STI in which the pad nitride film 21 and the buffer nitride film 22 are stacked by etching the buffer nitride film 22 and the pad oxide film 21 by using the photoresist pattern 23 as an etching mask. After the formation mask is formed, the photoresist pattern 23 is removed, and then the semiconductor layer is selectively etched using the mask of the pad oxide film 21 / buffer nitride film 22 to form the trench 24.

At this time, the width w of the trench 24 is defined according to the design rule, and the depth d is set to be 3000 kPa to 10000 kPa.

Subsequently, if there is an edge at the bottom of the trench 24, a heat treatment process for rounding the corner is further performed to prevent unevenness of the profile during ion implantation.

Next, as shown in FIG. 2C, an insulating layer doped with P-type impurities, such as BSG, is buried in the trench 24, and then the semiconductor layer around the trench 24 is filled with P-type impurities of the BSG through a heat treatment process. (20) A charge inflow blocking region 26 extending to a portion of the region is formed, which is generated by the silicon lattice discontinuity of the semiconductor layer 20 along its profile according to the trench etching as the trench 24 is formed. Is applied to the n- region of the subsequent photodiode to generate a dark signal, and the heat treatment temperature is appropriately adjusted to form a depth of 100 kV to 1000 kV in the semiconductor layer 20 of the bottom and sidewalls of the trench 24. do.

Subsequently, surface etching or chemical mechanical polishing (hereinafter referred to as CMP) is performed until the surface of the semiconductor layer 20 is exposed to form a field insulating film 25 having an STI structure.

Here, the above heat treatment is preferably carried out for 1 second to 60 minutes at a temperature of 600 ℃ to 1000 ℃.

Next, as shown in FIG. 2D, to form the gate electrodes of the four NMOS transistors in the unit pixel, a polysilicon film and a tungsten silicide film are successively coated, and a photoresist (not shown) is used to form the gate electrode. Exposure and development are performed using a mask. At this time, since the doping profile of the low voltage buried photodiode on one side of the gate electrode formed later determines the charge transfer efficiency, the thickness of the gate electrode is made thick enough so that the low voltage buried photodiode High-energy N-type ion implantation and low-energy P-type ion implantation to form a self-alignment can be performed on one side of the gate electrode (Thick Polycide process).

If the thickness of the gate electrode is not thick enough, dopant phosphorus (P31) penetrates through the gate electrode during high-energy N-type ion implantation. Self alignment is not possible at, resulting in low charge transfer efficiency.                     

Subsequently, a gate electrode, for example, a transfer gate Tx, formed of the gate insulating film 27, the gate electrode conductive film 28, and the spacer 30 is formed through dry etching, and then, between the gate electrode and the field insulating film 26. After forming the photodiode PD consisting of the P0 region 29 and the n-region 31, the sensing diffusion region FD, which is a high concentration n + region, is formed.

In the above-described invention, the P-type charge inflow blocking region is formed along the trench sidewalls and the lower portion of the field insulating film in the STI structure, thereby forming a P-type charge inflow blocking region at the interface with the N-type impurity region of the photodiode. By forming the internal potential of the junction by means of the embodiment that the charge to the photodiode of the charge generating a dark signal can be prevented through the embodiment.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

The present invention described above can be expected to have an excellent effect of ultimately improving the performance of the image sensor by preventing the inflow of the dark current component into the photodiode due to the lattice defect at the contact interface between the field insulating film and the semiconductor layer.

Claims (8)

Selectively etching the first conductive semiconductor layer to form a trench for forming a field insulating film; Forming a field insulating film containing impurities of a first conductivity type to fill the trench; Diffusing the impurities of the field insulating layer into the semiconductor layers on the sidewalls and the bottom of the trench through heat treatment to form a charge inflow blocking region; Forming a gate electrode on the semiconductor layer away from the field insulating film; And Forming a photodiode in the semiconductor layer between the gate electrode and the field insulating film; The photodiode, A method of manufacturing an image sensor comprising a first region of a second conductive type and a second region of a first conductive type formed on the first region. The method of claim 1, In the forming of the charge inflow blocking region, an image sensor manufacturing method, characterized in that formed on the bottom and sidewalls of the trench to a depth of 100 ~ 1000Å. The method of claim 1, The field insulating film is a manufacturing method of an image sensor comprising a BSG. The method of claim 1, The heat treatment is an image sensor manufacturing method, characterized in that performed for 1 second to 60 minutes at a temperature of 600 ℃ to 1000 ℃. The method of claim 1, And forming the trench at a depth of 3000 Pa to 10,000 Pa. The method of claim 1, Forming the trench, Sequentially forming a buffer nitride film and a pad oxide film on the semiconductor layer; Forming a trench forming photoresist pattern on the pad oxide film; Etching the pad oxide film and the buffer nitride film by using the photoresist pattern as an etching mask to form a trench forming mask of the pad oxide film / buffer nitride film; And Etching the semiconductor layer by using the trench forming mask as an etching mask to form the trench Image sensor manufacturing method comprising a. The method of claim 6, The pad oxide film is formed to a thickness of 50 ~ 200 kHz, the image sensor manufacturing method characterized in that. The method of claim 6, The buffer nitride film is formed to have a thickness of 500 kPa to 2000 kPa.

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