KR100893054B1 - Imase sensor with improved capability of protection against crosstalk and method for fabricating thereof - Google Patents

Abstract

The present invention relates to an image sensor, and more particularly, to provide an image sensor capable of reducing cross talk between adjacent pixels and a method for manufacturing the same. To this end, the present invention provides a semiconductor layer of a high concentration first conductive type; An epitaxial layer of a high concentration first conductivity type on the semiconductor layer; A field insulating film disposed locally on the epi layer; A channel stop region of a first conductive type having a width of the field insulating layer below the field insulating layer and disposed inside the epitaxial layer at a first depth; A gate electrode on the epi layer; A first impurity region of a second conductive type for photodiode disposed in the epi layer to a second depth substantially the same as the channel stop region and in contact with the gate electrode and the channel stop region; And a second impurity region of a first conductivity type for a photodiode in contact with the epi layer surface in the first impurity region.

In addition, the present invention is a semiconductor layer of a high concentration first conductive type; An epitaxial layer of a first conductivity type on the semiconductor layer; A field insulating film disposed locally on the epitaxial layer and extending to a boundary between the epitaxial layer and the semiconductor layer; A gate electrode on the epi layer; A first impurity region of a second conductive type for photodiode disposed in the epitaxial layer and in contact with the gate electrode and the field insulating layer; And a second impurity region of a first conductivity type for a photodiode in contact with the epi layer surface of the first impurity region.

In addition, an image sensor manufacturing method is provided.

Potential gradient, trench, image sensor, crosstalk, photodiode, channel stop area, field insulation film.

Description

Imaging sensor with improved capability of protection against crosstalk and method for fabricating             

1 is a cross-sectional view showing an image sensor according to the prior art.

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

3 is a cross-sectional view of the image sensor formed by FIGS. 2A to 2C.

4 is a sectional view showing an image sensor according to another embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

20a: high concentration P-type semiconductor layer 20b: high concentration P-type epilayer

23: field insulating film 24: gate oxide film

25 conductive film 26 spacer

The present invention relates to an image sensor, and more particularly, to an image sensor and a method of manufacturing the same that can prevent crosstalk.

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 is a cross-sectional view showing an image sensor according to the prior art.

Referring to FIG. 1, the semiconductor layer 10 is formed by stacking a high concentration of the P ++ layer 10a and the P-Epi layer 10b, hereinafter referred to as a semiconductor layer 10.

The field insulating film 11 having a shallow trench structure (hereinafter referred to as STI) is locally formed in the semiconductor layer 10, and the gate oxide film 12 and the gate electrode are formed in a region away from the field insulating film 11. A gate electrode made of the conductive film 13, for example, a transfer gate is formed. This serves to transport the optoelectronics from the photodiode to the floating sensing node (hereinafter referred to as FD). An impurity region (n−) for photodiode in contact with the field insulating film 11 and the gate electrode is formed in the semiconductor layer 10 to a predetermined depth, which is low concentration using high energy, for example, energy of 160 KeV to 180 KeV. It is doped.

Spacers 14 are formed on the sidewalls of the gate electrodes to form lightly doped drains (LDDs) through subsequent ion implantation to suppress hot carrier effects and the like, and to form high concentrations for FD formation. An n + region (source / drain) is formed by ion implantation of an N-type impurity in an N-type impurity, and an impurity region P0 is formed in contact with the top of the n− region and the surface of the semiconductor layer 10.

As the manufacturing process of the CMOS image sensor is increasingly integrated, there are many problems. One of them is a data mix, or cross-talk, problem between pixels entered by an image sensor encoding data using electrons generated by the photoelectric effect on light energy, which is a problem to be solved.

The photoelectric effect is that light energy penetrates through the silicon lattice to desorb electrons from the silicon lattice by the light energy to generate an electron hole pair (hereinafter referred to as EHP). The photoelectric effect occurs most frequently in the charge depletion region, and the more frequently the electrons (high concentration N-type, n +) or the excess holes (high concentration P-type, p +) occur, the smaller the occurrence frequency is.

On the other hand, the behavior of the EHP in the photodiode of the image sensor by the above-described photoelectric effect as shown in FIG. In the electron (e) is released from the electron (e) to form an empty hole (H), that is, EHP is formed. In this case, the holes H are absorbed by the lower concentration P-type substrate, that is, the P ++ layer 10a, but the electrons e are very easy to move to adjacent pixel regions, causing crosstalk. .

On the other hand, light incident on the n-region of the photodiode, such as 'B', desorbs electrons e 'from the silicon lattice to generate holes H' with empty electrons e, that is, EHP. do. In this case, the holes H 'are absorbed by the lower concentration P-type substrate, that is, the P ++ layer 10a, and the electrons e' are trapped in the photodiode region and thus cannot move to the adjacent pixel region. The main reason for the crosstalk will be to block the photoelectric effect by the light incident on the P-Epi layer 10b or to prevent the electrons generated by the photoelectric effect from moving to the adjacent pixel region. In one of the methods, a method of forming the n-region of the photodiode sufficiently deep can be devised.

However, the conventional image sensor described above has a potential barrier, which is a P-type barrier, in the charge transport path from the photodiode to the FD through the transfer gate due to diffusion of the P0 region on the photodiode. The impurity concentration in the n- region of the PD formed through ion implantation is lower than that in the interior of the photodiode. Since the n- region of the near surface depletes faster than the inside of the photodiode, when the transfer gate is operated for charge transport, a fringing field that assists in the charge transport in the n- region does not develop. This hinders full charge transport. Therefore, in order to sufficiently secure the capacity of the photodiode, the n-region cannot be further deepened, resulting in deterioration of operating characteristics due to cross talk.

The present invention proposed to solve the problems of the prior art as described above, an object thereof is to provide an image sensor and a method of manufacturing the same that can reduce crosstalk between adjacent pixels.

In order to achieve the above object, the present invention provides a semiconductor layer of the first conductive type, an epitaxial layer of the first conductive type formed on the semiconductor layer, a field insulating film disposed locally on the epi layer, and a lower portion of the field insulating film. A channel stop region of a first conductivity type disposed within the epi layer at a first depth, a gate electrode disposed on the epi layer, and a second depth equal to the channel stop region, and disposed inside the epi layer; A first impurity region of the second conductive type for photodiode in contact with the gate electrode and the channel stop region, and a second impurity region of the first conductive type for photodiode in contact with the surface of the epi layer in the first impurity region It provides an image sensor.

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In addition, the present invention for achieving the above object, the step of forming an epitaxial layer of the first conductivity type in the semiconductor layer of the first conductivity type, forming a trench in the epi layer, and the semiconductor under the trench Forming a channel stop region of a first conductivity type in the layer, forming a field insulating film buried in the trench, forming a gate electrode on the epi layer at intervals from the field insulating film; Forming a first impurity region of the second conductive type for photodiode in contact with the gate electrode and the field insulating film, and a second impurity of the first conductive type for photodiode in contact with the surface of the epi layer in the first impurity region It provides a method of manufacturing an image sensor comprising the step of forming an area.

The present invention provides a high concentration of the P-type epilayer to prevent crosstalk caused by light incident on the P-type epilayer, not the photodiode region, and electrons generated by the photoelectric effect penetrate into adjacent pixels. It is characterized by trapping the generated electrons or by extending the field insulating film to the boundary between the epi layer and the semiconductor layer, thereby preventing the movement of electrons to adjacent pixels.

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. do.

3 is a cross-sectional view illustrating an image sensor according to an exemplary embodiment of the present invention.

Referring to FIG. 3, a high concentration P-type (P ++) semiconductor layer 20a, a high concentration P-type epi layer (P + Epi, 20b) on the semiconductor layer 20b, and an epi layer 20b are locally disposed. The P-type channel stop region P + disposed inside the epi layer 20b at a first depth X under the field insulating film 23 and the field insulating film, and on the semiconductor layer 20a. 24 and a gate electrode including the conductive layer 25 and the spacer 25, and are disposed in the epi layer 20b at a second depth X ′ that is substantially the same as the channel stop region P +. N-type impurity region (n-) for photodiode in contact with channel stop region (P +) and P-type impurity region (P0) for photodiode in contact with epitaxial surface (20b) surface in N-type impurity region (n-). It is configured with.

The image sensor of the present invention described above makes it possible to capture almost all electrons generated by the photoelectric effect in the epi layer 20b by setting the concentration of the P-type epi layer 20b to a high concentration (P + Epi). The channel stop region P + is formed deep under the insulating layer 23 to be substantially the same depth as the P0 region of the photodiode, thereby improving element isolation characteristics from neighboring pixels to prevent cross talk.

Meanwhile, the above-described manufacturing process of the image sensor of FIG. 3 will be described in detail with reference to FIGS. 2A to 2C.

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

The semiconductor layer 20 is formed by laminating a high concentration P ++ layer 20a and a high concentration P-type epi layer, that is, a P-Epi layer 20b. Hereinafter, the semiconductor layer 20 will be referred to for simplicity of the drawings.

First of all, the drive gate (Dx) serving as a source follower and the switching gate (addressing) can be addressed by switching as a source follower through lateral diffusion. A step of forming a P-well (not shown) is carried out so as to contain (Select Gate, Sx).

Subsequently, as illustrated in FIG. 2A, a pad oxide film 21 is deposited on the semiconductor layer 20, and then a photoresist pattern 22 for forming trenches is formed on the pad oxide film 21.

Next, as illustrated in FIG. 2B, a trench t is formed by selectively etching the pad oxide film 21 and the semiconductor layer 20 using the photoresist pattern 22 as a mask.                     

At this time, the trenches t are formed to a depth of 0.2 µm to 0.5 µm to form an STI structure.

Subsequently, a P + region is formed by ion implanting a high concentration of P-type impurities into the lower portion of the trench t by using the photoresist pattern 22 and the pad oxide layer 21 as an ion implantation mask. The P + region is formed through the semiconductor layer 20. Accordingly, the P01 region acts as a channel stop region and forms a depletion region by PN junction between the photodiodes P / N / P, and also serves as an electrode of the photodiode, and also by incident light In addition to forming an electron-hole pair (hereinafter referred to as EHP) usefully, device separation between neighboring pixels is almost completely achieved by deep P + formation as described above.

Next, as illustrated in FIG. 2C, an oxide or nitride based material is deposited to sufficiently fill the trench t, and then chemical mechanical polishing (hereinafter, referred to as chemical mechanical polishing) until the surface of the semiconductor layer 20 is exposed. And the field insulating film 23 having an STI structure is formed locally on the semiconductor layer 20 by planarizing using a CMP or the like.

Subsequently, gate electrodes 24 and 25, for example, transfer gates, are formed in a region away from the field insulating film 21, which serves to transport the photoelectrons from the photodiode to the FD. Subsequently, an impurity region n- for photodiode contacting the field insulating film 23 and the gate electrode is formed in the semiconductor layer 20 to a predetermined depth by using an ion implantation mask (not shown). After the doping using a low concentration, the ion implantation mask (not shown) is removed through the PAL strip, and then a nitride film or the like is deposited on the entire surface, and then the spacer 26 is formed on the sidewall of the gate electrode through the entire surface etching. Here, the spacer 26 is for forming the LDD through subsequent ion implantation to suppress the hot carrier effect. Subsequently, ion implantation of a high concentration of N-type impurities for FD formation is performed.

Subsequently, ion implantation for forming a P-type electrode for photodiode is performed to form an impurity region P0 in contact with the top of the n- region and the surface of the semiconductor layer 20, thereby depleting the region by a P / N / P junction. As this is formed, a photodiode is formed.

Meanwhile, in addition to the method described above, the field insulating layer may have a depth, that is, a deep trench structure (hereinafter, referred to as DTI). FIG. 4 is a cross-sectional view illustrating an image sensor according to another exemplary embodiment of the present invention. to be.

Referring to FIG. 4, the semiconductor layer 40a of the high concentration P-type (P ++), the P-type epi layer (P-Epi, 40b) on the semiconductor layer 40a, and the epi layer 40b are locally disposed. The field insulating film 41 formed to extend to the boundary between the epi layer 40b and the semiconductor layer 40a and the gate oxide film 42, the conductive film 43, and the spacer 44 when disposed on the epi layer 40b. An N-type impurity region n- for photodiode disposed in the epitaxial layer 40b and in contact with the gate electrode and the field insulating film 41, and an N-type impurity region n- P-type impurity region P0 for photodiode in contact with the epitaxial layer surface is formed.

That is, in another embodiment as shown in FIG. 4, as described above, by extending the field insulating layer to the boundary between the epi layer and the semiconductor layer, crosstalk can be prevented by perfectly separating the adjacent pixels.

According to the present invention made as described above, when forming a photodiode having an STI structure, a channel stop region that is the same as the P0 region of the photodiode is deeply formed and a high epitaxial layer is formed, or a field insulating film is formed in a DPI structure. Embodiments have shown that crosstalk can be prevented by improving device isolation between neighboring pixels.

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 crosstalk of the photodiode, and can be expected to have an excellent effect that can ultimately greatly improve the performance and yield of the image sensor.

Claims (6)

A first conductive semiconductor layer; An epitaxial layer of a first conductivity type formed in the semiconductor layer; A field insulating film disposed locally on the epi layer; A channel stop region of a first conductivity type disposed in the epi layer at a first depth below the field insulating layer; A gate electrode on the epi layer; A first impurity region of a second conductive type for photodiode disposed in the epi layer to a second depth equal to the channel stop region and in contact with the gate electrode and the channel stop region; And A second impurity region of a first conductive type for a photodiode in contact with the epi layer surface in the first impurity region Image sensor comprising a. delete The method of claim 1, The first conductive type is a P-type, the second conductive type is an image sensor, characterized in that the N-type. Forming an epitaxial layer of the first conductive type in the semiconductor layer of the first conductive type; Forming a trench in the epi layer; Forming a channel stop region of a first conductivity type in the semiconductor layer under the trench; Forming a field insulating film buried in the trench; Forming a gate electrode on the epi layer at intervals from the field insulating film; Forming a first impurity region of a second conductivity type for a photodiode so as to have the same depth as that of the channel stop region, and to contact the gate electrode and the field insulating film; And Forming a second impurity region of a first conductivity type for a photodiode in contact with the epi layer surface in the first impurity region Image sensor manufacturing method comprising a. The method of claim 4, wherein The trench is an image sensor manufacturing method, characterized in that to form a depth of 0.2㎛ 0.5㎛. The method of claim 4, wherein The first conductive type is a P-type, the second conductive type is an image sensor manufacturing method, characterized in that the N-type.

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