KR100619408B1 - 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 of manufacturing the same. To this end, the present invention provides a high concentration first conductive substrate; An epitaxial layer of a first conductivity type having a thickness of 3 μm to 5 μm on the substrate; And a photodiode extending from the epi layer surface to the substrate region.

In addition, the present invention, a high concentration first conductive substrate; An epitaxial layer of a first conductivity type on the substrate; A photodiode extending from the epi layer surface to the substrate region; A field insulating film disposed on the epi layer in contact with one side of the photodiode; And a channel stop region of a first conductivity type formed under the field insulation layer and extending to the substrate region with a width of the field insulation layer.

In addition, the present invention comprises the steps of forming an epitaxial layer of the first conductive type having a thickness of 3㎛ to 5㎛ on the substrate of the first conductivity type of high concentration; And performing ion implantation to form a photodiode extended from the epi layer surface to the substrate region.

Potential gradient, epi layer, image sensor, crosstalk, photodiode, channel stop area.

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.

2 is a cross-sectional view showing an image sensor according to an embodiment of the present invention.

3A to 3C 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

20a: high concentration P-type substrate 20b: P-type epi layer

21: field insulating film 22: gate oxide film

23: gate conductive film 24: spacer

P +: channel stop area n +: floating sensing node

PD: Photodiode

The present invention relates to an image sensor, and more particularly, to an image sensor capable of preventing crosstalk between adjacent pixels and a method of manufacturing the same.

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. In other words, efforts are being made to increase the fill factor.

1 is a cross-sectional view illustrating an image sensor according to the related art, in which the semiconductor layer 10 is formed by stacking a high concentration of a P ++ layer 10a and a P-Epi layer 10b, hereinafter referred to as a semiconductor layer 10. do.

Referring to FIG. 1, a field insulating film 11 having a shallow trench structure (hereinafter, referred to as STI) is formed in the semiconductor layer 10, and the gate oxide film ( 12 and a gate electrode, for example, a transfer gate, formed of the conductive film 13 for the gate electrode. This serves to transport the optoelectronics from the photodiode to the floating sensing node (hereinafter referred to as FD).

An impurity region for photodiode (hereinafter referred to as n-region) in contact with the field insulating film 11 and the gate electrode is formed in the semiconductor layer 10 to a predetermined depth, and this impurity has a low concentration of, for example, 160KeV to 180KeV. It is ion implanted using high energy.

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. A high concentration n-type impurity region (source / drain; hereinafter referred to as n + region) is formed by ion implantation of the N-type impurity, and the P-type photodiode contacting the upper portion of the n-region and the surface of the semiconductor layer 10 An impurity region (hereinafter referred to as P0 region) is formed.

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

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). This photoelectric effect occurs most frequently in the charge depletion region, and the more frequently the electrons (eg, the n + region) or the excess holes (eg, the p + region) 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 hole H is absorbed by the lower concentration P-type substrate, that is, the P ++ layer 10a, but the electron e becomes very easy to move to the adjacent pixel region, causing cross talk. .

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 cross talk is to block the photoelectric effect by 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, in the conventional image sensor as described above, a potential barrier, which is a P-type barrier, is formed in the charge transport path from the photodiode to the FD through the transfer gate due to the diffusion of impurities in the P0 region above the photodiode. Impeding charge transport, and the impurity concentration in the n-region of the photodiode formed through ion implantation is lower than that in the photodiode, so the transfer is higher than the point having the highest concentration of the n-region. Since the n-area of the surface close to the gate depletes faster than the inside of the photodiode, when operating the transfer gate for charge transport, no fringing field is developed to help charge transport in the n-area. This prevents complete 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 occurrence of crosstalk due to the photoelectric effect is mainly caused by the red light relatively deeper than the color light having different penetration depth due to its long wavelength, and this is mainly caused between the bottom of the n-region and the P-Epi layer 10b. This is because the distance is about 1 µm to 3 µm, and the penetration depth of red light penetrates deeply from the surface of the semiconductor layer 10 to a depth of 2 µm to 3 µm.

Therefore, there is a need for a fundamental countermeasure that can prevent cross talk between adjacent pixels due to the photoelectric effect.

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 minimize crosstalk between adjacent pixels.

In order to achieve the above object, the present invention, a high concentration of the first conductivity type substrate; An epitaxial layer of a first conductivity type having a thickness of 3 μm to 5 μm on the substrate; And a photodiode extending from the epi layer surface to the substrate region.

In addition, the present invention for achieving the above object, a high concentration of the first conductivity type substrate; An epitaxial layer of a first conductivity type on the substrate; A photodiode extending from the epi layer surface to the substrate region; A field insulating film disposed on the epi layer in contact with one side of the photodiode; And a channel stop region of a first conductivity type formed under the field insulation layer and extending to the substrate region with a width of the field insulation layer.

In addition, the present invention for achieving the above object, forming a first conductive epitaxial layer having a thickness of 3㎛ to 5㎛ on the first conductive substrate of high concentration; And performing ion implantation to form a photodiode extended from the epi layer surface to the substrate region.

According to the present invention, the lower region (n-region) of the photodiode has a high concentration in order to prevent crosstalk caused by light entering the P-type epi layer, not the photodiode region, and electrons generated by the photoelectric effect penetrate into adjacent pixels. The thickness of the P-epi layer (1 μm to 3 μm) is reduced so as to be in contact with the substrate region (P ++ region) of the photodiode, that is, there is no P-epi layer between the lower portion of the photodiode and the P ++ region. Compared to the red light of long wavelength, the P ++ region, which generates less photoelectric effect, can reduce cross talk between adjacent pixels. By forming a channel stop region, it is possible to further reduce cross talk.

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.

2 is a cross-sectional view showing an image sensor according to an embodiment of the present invention.

Referring to FIG. 2, the image sensor includes a high concentration P-type (P ++) substrate 20a, a P-type epi layer (P-Epi, 20b) disposed on the substrate 20a, and an epi layer 20b. P-type channel stops formed to extend to the region of the substrate 20a so as to be in contact with the substrate 20a with the field insulation films Fox and 21 disposed locally and under the field insulation film 21 and having the width of the field insulation film 21. A gate electrode disposed on the region P + and the epi layer 20b and having a gate oxide film 22, a gate conductive film 23, and spacers 24 on the sidewall thereof, for example, a gate Tx of a transfer transistor; The photodiode PD is aligned between the one side of the gate electrode and the field insulating film 21 and extends from the surface of the epi layer 20b to the region of the substrate 20a, and the surface of the epi layer 20b in contact with the other side of the gate electrode. And a high concentration N-type floating sensing node (n +) formed therein.

The photodiode PD is in contact with the surface of the epi layer 20b in the N-type impurity region n- and the N-type impurity region n- in contact with the substrate 20a and is aligned with the spacer 24. Impurity region P0.

On the other hand, the thickness of the normal epitaxial layer 20b is generally 7 μm, but in the present invention, the thickness D of the epitaxial layer 20b is relatively thin (3 μm to 5 μm), so that the photodiode PD The N-type impurity region n- of the photodiode PD is in contact with the substrate 20a region without increasing the depth of the N-type impurity region n− of the photodiode PD, that is, the photodiode PD and the substrate ( By preventing the epi layer 20b from being present between 20a, cross talk due to light having a deep penetration depth, such as red light, can be reduced.

This is possible in the region of the substrate 20a having a higher impurity concentration than that of the epi layer 20b since the electrons generated by the photoelectric effect can be almost trapped through holes caused by P-type impurities.

In addition, the P-type impurity is doped into the trench-shaped field insulating layer 21 by a process such as ion implantation, and then a P-type channel stop region P + is formed through thermal diffusion. At this time, by making the depth of the channel stop region P + substantially the same as the depth of the photodiode PD (the depth 'D' of the epi layer 20b), the electrons generated by the photoelectric effect in the case of Even if almost disappeared by a P-type impurity of the substrate 20a and a part thereof remains, it is possible to almost block the capture by the channel stop region P + and transfer to the adjacent pixel region.

In the image sensor structure of FIG. 2 described above, the P-type substrate 20a, the P-type epitaxial layer 20b, and the PNP-type photodiode PD are one example, and the conductive type is generally used. It would also be possible to have the opposite polarity, i.e., the substrate and the epi layer being N-type and the photodiode having an NPN structure.

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

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

In a typical image sensor, a high concentration of a P-type (P ++) substrate 20a and a P-type epi layer (P-Epi, 20b) are stacked, and thus, epitaxial growth is formed on the P-type substrate 20a. The epi layer 20b is formed through.

On the other hand, as described above, in the present invention, the thickness of the epi layer 20b is set to a thickness D of about 3 μm to about 5 μm, which is thinner than a thickness of about 7 μm.

After the epi layer 20b is formed, for example, when fabricating an image sensor having four transistor structures, a gate of a drive transistor serving as a source follower through lateral diffusion by thermal processes is used. forming a P-well (not shown) to contain a gate of a select transistor (Sx) that allows addressing as a gate, Dx) and a switching role. Carry out the process.

Subsequently, as illustrated in FIG. 3A, a pad oxide film 25 is deposited on the epitaxial layer 20a, and then a trench forming photoresist pattern 26 is formed on the pad oxide film 25.

Subsequently, as illustrated in FIG. 2B, a trench t is formed by selectively etching the pad oxide film 25 and the epi layer 20b using the photoresist pattern 26 as a mask.

At this time, the depth of the trench t is formed to be about 0.2 µm to 0.5 µm, which is a normal depth, so that the field insulating film formed subsequently becomes an STI structure.

Subsequently, a channel stop region P + is formed by ion implanting a high concentration of P-type impurities under the trench t using the photoresist pattern 26 and the pad oxide film 25 as an ion implantation mask. ) And deep channel stop region P + into the epi layer 20b. Accordingly, the channel stop region P + acts as a channel stop 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 includes incident light. This makes it possible to form EHP usefully.

At this time, a P-type impurity such as boron is doped into the lower portion of the trench t through an ion implantation process, and then a P-type channel stop region P + is formed through thermal diffusion. By making the depth of P + substantially equal to the depth of the photodiode PD (the depth 'D' of the epi layer 20b) described above, electrons generated by the photoelectric effect in the case of P-type of the substrate 20a are Even if it is almost extinguished by impurities and some of them remain, it is possible to almost block the capture by the channel stop region P + and transfer to the adjacent pixel region.

Next, as shown in FIG. 2C, the 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 epi layer 20b is exposed. By performing a planarization process such as CMP) or an etching back, a field insulating film 21 having an STI structure is formed locally on the epitaxial layer 20b.

Subsequently, a gate electrode, for example, a gate Tx of the transfer transistor, is formed in a region away from the field insulating layer 21, which serves to transport photoelectrons from the photodiode to the FD.

The gate electrode is formed through the deposition of the gate oxide film 22, the formation of the gate conductive film 23, such as tungsten, polysilicon, or metal silicide, and a patterning process.

Subsequently, an N-type impurity region n- for photodiode in contact with the field insulating film 21 and the gate electrode is formed to the depth of the epi layer 20b by using an ion implantation mask (not shown). Doping to a low concentration, and then removing the ion implantation mask (not shown) through the PAL strip and diffusing the ion implanted impurities through heat treatment so that the N-type impurity region n- is in contact with the substrate 20a. do.

Subsequently, a nitride film or the like is deposited on the entire surface, and then spacers 24 are formed on the sidewalls of the gate electrode through the entire surface etching. Here, the spacer 24 is for forming the LDD through subsequent ion implantation to suppress the hot carrier effect. Subsequently, a high concentration of N-type impurities are implanted to form the FD to form a floating sensing node n + on the epitaxial layer 20b that is in contact with the other side of the gate electrode.

Next, ion implantation for forming a P-type electrode for photodiode is performed to form a P-type impurity region P0 in contact with the top of the N-type impurity region n- and the surface of the epi layer 20b. A photodiode PD having a / P structure is formed.

According to the present invention made as described above, the lower region n- of the photodiode is not the low epi layer P-Epi but the high concentration substrate P ++, that is, the lower region n- of the photodiode By making the thickness of the epi layer thinner than the normal thickness without forming it by the deep ion implantation of the photodiode while making contact with the substrate, electrons generated by photoelectric effect in a region other than the photodiode by red light are generated. By dissipating into holes due to, the possibility of cross talk can be reduced.

Also, by making the depth of the channel stop region substantially the same as the depth of the photodiode described above, even if the electrons generated by the photoelectric effect are almost extinguished by the high concentration impurities of the substrate and some of them remain by the channel stop region, Embodiments have been described that the capture and transfer to adjacent pixel regions can be blocked.

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 cross talk 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 (9)

delete delete A high concentration first conductive substrate; An epitaxial layer of a first conductivity type formed on the substrate and having a thickness of 3 μm to 5 μm; And A photodiode extending from the epi layer surface to the surface of the substrate, The photodiode, A first impurity region of a second conductivity type formed in the epi layer in contact with the surface of the substrate; And A second impurity region of a first conductivity type formed under the epi layer surface in the first impurity region Image sensor comprising a. A high concentration first conductive substrate; An epitaxial layer of a first conductivity type formed on the substrate and having a thickness of 3 μm to 5 μm; And A photodiode extending from the epi layer surface to the surface of the substrate; A field insulating layer disposed on the epi layer in contact with one side of the photodiode; And A channel stop impurity region of a first conductivity type formed under the field insulation layer and extending to the substrate region with a width of the field insulation layer; The photodiode, A first impurity region of a second conductivity type formed in the epi layer in contact with the surface of the substrate; And A second impurity region of a first conductivity type formed under the epi layer surface in the first impurity region Image sensor comprising a. delete The method according to claim 3 or 4, 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 a first conductive type having a thickness of 3 μm to 5 μm on a high concentration of the first conductive type substrate; And Performing ion implantation to form a photodiode extending from the epi layer surface to the surface of the substrate so as to contact the surface of the substrate Image sensor manufacturing method comprising a. The method of claim 7, wherein After forming the epi layer, Forming a trench in the epi layer to a predetermined depth; Performing ion implantation to form a channel stop impurity region of a first conductivity type in contact with the surface of the substrate in the epi layer under the trench; Forming a field insulating film buried in the trench; And Forming a gate electrode on the epi layer at intervals from the field insulating layer Image sensor manufacturing method comprising a further. The method of claim 8, In the step of forming the photodiode, And the photodiode is aligned between the gate electrode and the channel stop impurity region.

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