KR100841208B1 - 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 the dark signal to the active by the OSF at the field / active interface, the present invention for this purpose, Forming a field insulating film locally on the semiconductor layer of the type; Forming an ion implantation mask to open the field insulating film; Performing a tilt ion implantation using the ion implantation mask to form a first impurity region of a first conductivity type on a lower edge of the field insulating layer; Forming a second impurity region of a first conductivity type under the field insulating layer by performing vertical ion implantation using the ion implantation mask; And diffusing impurities in the first and second impurity regions through heat treatment to form a channel stop region having a structure surrounding the field insulating layer.

Dark signal, image sensor, photodiode, STI, OSF (Oxidation induced Stacking Faults), tilt, channel stop area.

Description

A fabricating method of image sensor with decreased dark signal             

1 is a schematic cross-sectional view of an image sensor having a conventional field insulating film.

FIG. 2 is a schematic cross-sectional view of an image sensor doped with impurities to form a channel stop region. FIG.

3A to 3D are cross-sectional views illustrating an image sensor manufacturing process according to an embodiment of the present invention.

4 is a plan view showing a process step at the time of tilt ion implantation.

Explanation of symbols on the main parts of the drawings

30 semiconductor layer 33 field insulating film

36: channel stop area Y: OSF

The present invention relates to an image sensor, and more particularly, to an image sensor manufacturing method, and more particularly, to an image sensor manufacturing method having a double channel stop region for reducing a dark signal.

In general, an image sensor is a semiconductor device that converts an optical image into an electric signal, and a charge coupled device (CCD) has individual metal-oxide-silicon (MOS) capacitors that are very different from each other. A device in which charge carriers are stored and transported in a capacitor while being in close proximity, and a 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).

1 shows a schematic cross-sectional view of an image sensor with a conventional 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 field insulating film 12 is formed locally in the semiconductor layer, and a gate electrode, for example, a transfer, comprising a gate insulating film 13, a gate electrode conductive film 14, and a spacer 15 in a region away from the field insulating film 12. A gate is disposed, and an N-type impurity region (hereinafter referred to as an n-region) and an n-region upper region for a 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 photodiode P-type impurity region (hereinafter referred to as P0 region) is disposed at an interface in contact with the semiconductor layer of the semiconductor layer, and a sensing diffusion region (hereinafter referred to as n + region) is disposed.

Meanwhile, the above-described conventional image sensor uses a simple trench type (Shallow Trench Isolation) or LOCOS (LOCOS) type for the field insulating layer 12. In the case of the trench type, the LOCOS method is used. It takes the form of a photodiode that extends only the Bird's beak portion of the film, and the field insulating film 12 is formed by STI rather than the LOCOS method for high integration.

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 the interface between the silicon interface of the semiconductor layer and the field insulating film 12 Defective components, such as OSF (Oxidation induced Stacking Faults), such as defects due to incomplete crystallization, such as dislocations, increase in density from the edge to the area of the photodiode Accumulate.

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 has a greater influence on the characteristics of the image sensor.

Accordingly, an N-channel stop region in which a P-type impurity region is formed in the lower portion of the field insulation layer through ion implantation or the like as a method for suppressing an increase in the dark signal component due to the active / field interface attacked when forming the field insulation layer described above ( A method for preventing the inflow of the dark signal component generated at the active / field interface into the photodiode by the P-type channel stop region at the active / field interface has been devised.

For example, in the case of a photodiode having a PNP structure, a P-type channel stop region is formed using a P-type impurity to prevent the inflow of electrons. By separating the field interface from the n-region of the photodiode, the inflow of charge is blocked. The channel stop region also serves to prevent crosstalk between adjacent pixels.

2 is a schematic cross-sectional view of an image sensor doped with impurities to form a channel stop region.                         

In FIG. 2A, the P-type impurity is implanted into the lower portion of the field insulating film 12 using the nitride film mask 16 to form an impurity region before diffusion as shown in FIG. 17. Here, it can be seen that OSF (Y) is concentrated under the field insulating film 12, particularly at the edge.

The impurity region 17 formed by ion implantation forms a profile through thermal diffusion, and FIG. 2 (b) shows an ideal thermal diffusion profile, and surrounds the OSF (Y) by diffusion of the impurity region to form a lower portion of the field insulating film 12. A channel stop region 18 is formed in the groove.

However, in FIG. 2A, the diffusion distance required for the dopant implanted into the impurity region 17 to cover the OSF existing at the edge of the field insulating layer 12 is relatively larger than that of 'a'. , 'b' and 'a' is the difference between the spreading distance by position a <b.

Due to the non-uniformity of the diffusion profile, if the channel stop region is formed so as to be concentrated only on the lower portion of the field insulating film to cover the OSF (Y) as shown in FIG.

The present invention proposed to solve the above problems of the prior art, the object of the present invention is to provide an image sensor manufacturing method suitable for suppressing the inflow of the dark signal to the active by the OSF at the field / active interface.

In order to achieve the above object, the present invention comprises the steps of: forming a field insulating film locally on the semiconductor layer of the first conductivity type; Forming an ion implantation mask to open the field insulating film; Performing a tilt ion implantation using the ion implantation mask to form a first impurity region of a first conductivity type on a lower edge of the field insulating layer; Forming a second impurity region of a first conductivity type under the field insulating layer by performing vertical ion implantation using the ion implantation mask; And diffusing impurities in the first and second impurity regions through heat treatment to form a channel stop region having a structure surrounding the field insulating layer.

In the present invention, since ion implantation is performed twice to form a channel stop region, the ion implantation is concentrated only at the edge of the field insulating layer through tilt ion implantation using low energy to cover the OSF, and relatively high energy is achieved. After the impurity region for forming the channel stop region is formed in the lower portion of the field insulating layer by using a channel process, the channel stop region is formed to sufficiently cover the OSF through diffusion through thermal process to improve the saturation characteristics of the photodiode and to prevent crosstalk. And dark signal generation due to OSF at the edge of the field insulating film.

Hereinafter, in order to explain in detail enough to enable those skilled in the art to easily carry out the technical idea of the present invention, refer to FIGS. 3A to 3D attached to the most preferred embodiment of the present invention. Will be explained.                     

3A to 3D are cross-sectional views illustrating a manufacturing process of an image sensor according to an exemplary embodiment of the present invention.

First, as shown in FIG. 3A, a pad oxide film 31, a buffer polysilicon film (not shown), a nitride film 32, and the like are successively applied to distinguish a field region from an active region. And a photoresist pattern (not shown) are formed by exposure and development using an ISO isolation mask, and then the nitride film 32 is formed by dry etching the photoresist pattern with an etching mask. By etching, the portion where the field insulating film is to be formed, that is, the field region is etched.

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 30 denotes a semiconductor layer in which such P ++ layer and P-Epi layer are stacked.

Next, as shown in FIG. 3B, the field insulating layer 33 is formed through an oxidation process, for example, a thermal oxidation process, and then the pad oxide layer 31 and the nitride layer 32 on the active region are etched. Remove through. 'Y' shown shows OSF, which is one of the defects that appear intensively at the edges of the field insulating film 33 as described above.

Subsequently, a photoresist is applied to the entire surface where the field insulating film 13 is formed, and then an ion implantation mask 34 is formed through an exposure and development process using a field insulating film open mask.

Subsequently, a P-type first impurity region 35a is formed at the edge of the lower portion of the field insulating film 33, specifically, at the portion where the OSF (Y) is concentrated through tilt ion implantation.

Thus, as shown, the first impurity region 35a has a structure surrounding the OSF (Y).

At this time, the energy at the time of ion implantation is relatively low energy, for example, 60KeV to 90KeV when the thickness of the ion implantation mask 34 is 1400 kPa, and the tilt is 5 ° to 10 °, using boron (Bron, B), which is a P-type impurity. Perform 4 rotations.

FIG. 4 is a plan view illustrating a process step during tilt ion implantation. Referring to this, it can be seen that the first impurity region 35a is formed by ion implantation at the edge of the field insulating layer 33 through four rotations. .

On the other hand, in the case of boron, it is preferable to use a dose of 0.5E12 / cm 2 to 2.0E12 / cm 2, and when the ion implantation energy is excessively used, the ion implantation depth increases and the active region decreases, so that the field insulating film 33 Make sure you have a minimum depth to cover the edges of).

Subsequently, as illustrated in FIG. 3C, a second impurity region 35b for the channel stop region is formed under the field insulating layer 33 through vertical ion implantation to improve saturation characteristics of the photodiode and prevent crosstalk. At this time, the ion implantation is carried out in a normal process recipe, and 200KeV to 300KeV, the tilt is 0 ° and the dose is 4.0E12 / cm 2 to 8.0E12 / cm 2 using boron as a P-type impurity.

Next, the ion implantation mask 34 is removed and impurities in the first impurity region 35a and the second impurity region 35b are diffused to each other through a thermal process to sufficiently fill the OSF (Y) at the edge of the field insulating film 33. A P-type N-channel stop region 36 is formed having a good profile that can wrap and suppress iso punch in the field region.

On the other hand, although not shown in the drawing, by forming a metal wiring and a microlens with four NMOS transistors, photodiodes and the like in the unit pixel, the image sensor manufacturing process is completed, the subsequent well annealing process is the first impurity region In order to prevent diffusion of impurities into the active region, it is preferable to use a rapid thermal process (hereinafter referred to as RTP) instead of a tube anneal.

In the present invention described above, the first impurity region is formed to cover the OSF concentrated at the edge of the field insulating film by performing the first tilt ion implantation to form the channel probe region, and the second impurity region under the filter insulating film without the second tilt. And then forming a channel stop region diffused from the first and second impurity regions through a heat treatment process, thereby forming a good profile to effectively prevent dark signal components from entering into the active region by OSF, and It was found through the examples that the saturation characteristics of the diode can be improved and crosstalk can be prevented.

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 prevent the inflow of the dark signal component into the active region by the OSF in the field region and the active region due to the formation of the field insulating film, thereby ultimately improving the performance of the image sensor. You can expect

Claims (7)

Forming a field insulating film locally on the first conductive semiconductor layer; Forming an ion implantation mask to open the field insulating film; Performing a tilt ion implantation using the ion implantation mask to form a first impurity region of a first conductivity type on a lower edge of the field insulating layer; Forming a second impurity region of a first conductivity type under the field insulating layer by performing vertical ion implantation using the ion implantation mask; And Forming a channel stop region having a structure surrounding the field insulating layer by diffusing impurities of the first and second impurity regions through heat treatment. Image sensor manufacturing method comprising a. The method of claim 1, And forming the first impurity region so as to surround the activation induced stacking faults (OSFs) concentrated at the lower edge of the field insulating layer. The method of claim 1, Method of manufacturing an image sensor, characterized in that to have a tilt of 5 ° to 10 ° when the tilt ion implantation. The method of claim 3, wherein Method of manufacturing an image sensor characterized in that carried out while having four rotations when the tilt ion implantation. The method of claim 4, wherein Boron (B) is used as an impurity in the ion implantation to form the first impurity region, the dose is 0.5E12 / ㎠ to 2.0E12 / ㎠, the ion implantation energy of the image of 60KeV to 90KeV Sensor manufacturing method. The method of claim 1, Boron (B) is used as an impurity in the ion implantation to form the second impurity region, the dose is 4.0E12 / ㎠ to 8.0E12 / ㎠, the ion implantation energy 200KeV to 300KeV Sensor manufacturing method. The method of claim 1, The first conductive type is an image sensor manufacturing method, characterized in that the P-type conductive type.

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