KR100431749B1 - Image sensor - Google Patents

Abstract

The present invention relates to an image sensor, and in particular to provide an image sensor that can improve the charge transport efficiency, the present invention for this purpose, the photodiode formed on the substrate; A sensing diffusion region formed on the substrate at a position spaced apart from the photodiode; And a gate electrode overlapping one end of the photodiode and one end of the sensing diffusion region to transfer the optical signal to the sensing diffusion region through an on-off operation, wherein the gate electrode overlaps the sensing diffusion region. It provides an image sensor with a groove formed in a portion of the portion.

Description

Image sensor

The present invention relates to semiconductor devices, and more particularly to an image sensor.

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).

Figure 1 (a) is a plan view showing an image sensor according to the prior art, Figure 1 (b) is a cross-sectional view.

Referring to FIGS. 1A and 1B, in the conventional image sensor, a photodiode (hereinafter referred to as PD) is formed on a substrate (not shown), and the substrate (not shown) is spaced apart from the PD. Sensing diffusion region (hereinafter referred to as FD) and overlaps at one end of the PD and FD, respectively, and transfers an optical signal from the PD to the FD through an on-off operation (transfer gate, hereinafter). Tx) is formed.

The PD includes an N-type photodiode region (hereinafter referred to as n-region) formed under the P-type substrate, and a P-type photodiode region (hereinafter referred to as P0) formed to extend from the substrate surface to the n-region. , FD is a high concentration N-type (n +) formed to extend from the substrate surface to the bottom, Tx is formed using a conductive material mainly containing polysilicon and the like.

On the other hand, in the conventional image sensor having the above-described configuration, the structure of Tx for transmitting the light collected from the PD to the FD is in the form of a bar, thereby spreading the electric field evenly under the Tx. Therefore, when Tx is turned on, a problem may occur in which data does not pass to the sensing region for a predetermined time.

In addition, when the Tx is positioned between the PD and the FD and the PD and the FD are separated as in the above-described structure, the power supply voltage VDD gradually decreases toward the high integration or low voltage, thereby lowering the voltage applied to the Tx. Therefore, the electrons generated in the PD are not completely transferred to the FD, which degrades the image characteristics at low illumination.

That is, at the lower end of Fig. 1 (b), the potential distribution in PD, Tx, and FD is schematically shown based on the maximum potential region X in the PD of Fig. 1 (a). The region is far from the boundary region of Tx and PD, making it difficult to turn on Tx.

The conventional image sensor as described above forms a potential barrier, a P-type barrier, in the charge transport path from the PD to the TD through the Tx due to the diffusion of the P0 region on the PD to hinder charge transport. The impurity concentration of the n-region of the PD formed through ion implantation is lower than that of the inside of the PD, so that the n-region of the surface closer to Tx is closer to the Tx than the point having the highest concentration of the n-region. Since the depletion is faster than the inside of the transistor, when the transfer gate is operated for charge transport, a fringing field for assisting charge transport in the n-region does not develop, which hinders full charge transport. Therefore, the n- region cannot be deepened in order to sufficiently secure the capacity of the PD.

On the other hand, as shown in Figure 2 in order to improve the charge transport efficiency as described above, a low concentration n-region may be additionally implanted into the FD region, in this case, the capacitance between Tx and FD is increased The conversion gain for converting the optical signal into an electrical signal is reduced.

The present invention proposed to solve the problems of the prior art as described above, an object thereof is to provide an image sensor that can improve the charge transport efficiency.

1 is a view showing an image sensor according to the prior art,

2 is a cross-sectional view showing an image sensor according to the improved prior art;

3 is a view showing an image sensor according to an embodiment of the present invention;

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

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

Explanation of symbols on the main parts of the drawings

PD: Photodiode

Tx: Gate electrode (transfer gate)

FD: Sensing Diffusion Area

In order to achieve the above object, the present invention, a photodiode formed on the substrate; A sensing diffusion region formed on the substrate at a position spaced apart from the photodiode; And a gate electrode overlapping one end of the photodiode and one end of the sensing diffusion region to transfer the optical signal to the sensing diffusion region through an on-off operation, wherein the gate electrode overlaps the sensing diffusion region. It provides an image sensor with a groove formed in a portion of the portion.

Preferably, the present invention is characterized in that it further comprises an impurity region which is formed in the semiconductor substrate of the portion overlapping with the partial region, the concentration is lower than the sensing diffusion region,

The partial region may be formed at the center of a portion overlapping with the sensing diffusion region.

The present invention changes the maximum potential point by modifying the shape of Tx in the region overlapping with the PD or FD, or by changing the impurity concentration in the lower region to improve the charge transport efficiency without reducing the capacitance of the PD. Or using a short channel effect.

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 view showing an image sensor according to an embodiment of the present invention, Figure 3 (a) is a plan view showing an image sensor including a Tx having a groove in a portion in the portion overlapping with the FD, 3 (b) is a cross-sectional view of Figure 3 (a), Figure 3 (c) is a cross-sectional view showing the structure of the image sensor is a separate ion implantation in the groove.

3 (a) and 3 (b), the PD is formed on the substrate, the FD is formed on the substrate at a position spaced apart from the PD, and overlapped on one end of the PD and one end of the FD, respectively. Tx is formed to transfer the optical signal from the PD to the FD through the off operation, and a groove is formed in the partial region A at the portion where the Tx overlaps with the FD.

Here, the partial region A is preferably formed at the center of the portion overlapping the FD, and PD is formed from an N-type photodiode region (hereinafter referred to as n-region) formed under the P-type substrate and from the substrate surface. P-type photodiode region (hereinafter referred to as P0 region) formed to extend into the n- region, and FD is a high concentration N-type impurity region (n +) formed to extend downward from the substrate surface, and Tx is polysilicon or the like. It includes a conductive material of.

It looks at the operation of the image sensor having the above configuration.

In the pixel structure of the image sensor, the Tx (gate electrode of Tx) structure is formed in the shape of a groove (A) in the portion overlapping with the FD rather than the conventional bar shape, thereby changing the electric field of this portion (A) Make it higher than the part. Therefore, when the optical signals collected from the PD are transferred to the FD, the data is concentrated in the high portion A of the Tx, and the data is correctly passed to the FD, and the groove A is centered at the portion overlapping the FD of the Tx. It is preferable to be located at. This is because the electric field is the strongest at the center of Tx.

In other words, in the above-described embodiment of the present invention, the short channel effect is used to strengthen the electric field by narrowing the gate of Tx. When the electrons (optical signal) integrated in the PD are transferred to the FD, the FD Because of the faster and concentrated transfer to the center of the charge transport efficiency can be increased, which shows an excellent effect on the low-light transfer characteristics.

Meanwhile, reference numeral 'B' in FIGS. 3 (a) and 3 (b) shows a region in which no groove is formed. In the 'B' region, although the FD and Tx overlap or contact each other, the groove is formed. In the 'A' area, they are arranged as if they are spaced apart by the depth of the groove. Therefore, the n + region of the FD is to be ion-implanted in the lower portion by Tx, as shown by the dotted line and solid line in Figure 3 (b).

Meanwhile, a low concentration of N-type impurities may be ion-implanted only in a portion where the groove is formed to further improve charge transport efficiency. FIG. 3 (c) is formed on the semiconductor substrate at a portion overlapping with the partial region A. In addition, it forms a structure further comprising a low concentration impurity region (n-) compared to the FD.

In this case, even if the capacitance between Tx and FD is increased, reducing the size of the groove can be manufactured without significantly affecting the conversion gain, and the conversion gain is not reduced because the transportation efficiency is increased.

4 is a view showing an image sensor according to another embodiment of the present invention, Figure 4 (a) is a plan view showing an image sensor including a Tx having a protrusion in a portion in the portion overlapping with the PD, 4 (b) is a sectional view of FIG. 4 (a).

4 (a) and 4 (b), the PD is formed on the substrate, the FD is formed on the substrate at a position spaced apart from the PD, and overlapped on one end of the PD and one end of the FD, respectively. The Tx is formed to transfer the optical signal from the PD to the FD through the off operation. The protrusion C is formed at a portion of the Tx at a portion overlapping with the PD.

Herein, the protrusion C is preferably formed at the center of the portion overlapping with the PD, and the PD has an N-type photodiode region (hereinafter referred to as n-region) formed under the P-type substrate and n from the substrate surface. A P-type photodiode region (hereinafter referred to as P0 region) formed to extend into the region, FD is a high concentration N-type impurity region (n +) formed extending from the substrate surface to the bottom, and Tx is a polysilicon It includes a conductive material.

It looks at the operation of the image sensor having the above configuration.

In the lower part of Tx, as described above, the electric field at the central part X is the strongest. Therefore, it is most preferable to form a protrusion at the center thereof, and in the conventional case, the location of the maximum potential is far from the boundary between the PD and the Tx, and as the voltage for driving the Tx becomes smaller, it becomes more difficult to turn on the Tx. If the Tx has a protrusion at the center where the maximum potential point is located, the distance between the PD maximum potential point and the projected Tx is closer, making Tx on easier at low voltage. As shown in the potential distribution along the center portion, the distance between the maximum potential point of the PD region and the boundary of the Tx of the PD gradually becomes shorter, and the on of Tx becomes easier.

Like 'D', the maximum point under the Tx moves near the PD, making it easier to turn on the Tx.

In addition, since the electric field E in the protruding portion C becomes stronger than the non-protruding portion, the electrons collected in the PD are quickly gathered in the protruding portion C and transferred to the FD, so that the charge from the PD to the FD is increased. Transportation efficiency is increased.

5 is a diagram illustrating an image sensor according to another exemplary embodiment of the present invention. FIG. 5A illustrates an image sensor having an n + region having a relatively higher concentration than an n− region of a PD at a portion overlapping with the PD. It is a top view shown, and FIG. 5 (b) is sectional drawing of FIG.

Referring to FIGS. 5A and 5B, an N-type PD region (n-region) is formed under the P-type substrate, and extends from the surface of the substrate to the n-region to form the P-type PD region (P0 region). ) Is formed to form a PD, and an N-type FD (n +) is formed on a substrate spaced apart from the PD, and the optical signal from the PD is overlapped at one end of the PD and one end of the FD through on-off operation. Tx is formed to transfer F to the FD, and a higher concentration n + region (F) than the n- region is formed in a portion of the n- region where Tx and PD overlap.

Herein, the n + region F is preferably formed at the center of the portion overlapping with the PD, and the FD is a high concentration N-type impurity region n + formed extending from the substrate surface downward, and Tx is a conductive material such as polysilicon. Contains substances.

It looks at the operation of the image sensor having the above configuration.

In the lower part of Tx, as described above, the electric field at the central part X appears to be the strongest. Therefore, it is most preferable to form a protrusion at the center thereof. In the conventional case, the position where the maximum potential of the PD is located is far from the boundary between the PD and the Tx, and as the voltage for driving the Tx becomes smaller, it becomes more difficult to turn on the Tx. Bars have a high concentration n + region at the center of the Tx and PD boundary where the maximum potential point is located, which becomes the maximum potential in the n + region, so that the distance between the Tx and PD maximum potential points is close and Tx can be turned on very easily. have. As shown in the dislocation distribution along the center portion, the distance of the maximum potential point of the PD region and the boundary between the PD and Tx gradually becomes shorter, so that the on of Tx becomes easier.

In addition, since the electric field E in the n + region F becomes stronger than the non-protruding portion, the electrons collected in the PD are quickly collected in the n + region F and transferred to the FD, so that the charge from the PD to the FD is increased. Transportation efficiency is increased.

The ion implantation energy used to form the n-region at the portion where PD and Tx overlap is used, for example, by using ion implantation energy of about 160KeV to 200KeV and N-type impurities of 1.0E11 / cm 2 to 9.0E13 / cm 2 concentration. As a result, additional ion implantation is applied to the n- region so that the 'F' region has n + concentration.

This requires a separate ion implantation mask to perform ion implantation in the 'F' region when manufacturing the image sensor, but the point where the potential is significant to improve the potential gradient in the n-region through tilt ion implantation. In order to focus on this, excellent effects can be expected compared to gradient ion implantation.

According to the present invention made as described above, by changing the potential at the boundary overlapping PD or FD in the structure of Tx or the lower substrate of Tx, the electrons can be concentrated in one place to increase the charge transport efficiency. Learned through

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 improve the charge transport efficiency, and ultimately can expect an excellent effect that can greatly improve the performance of the image sensor.

Claims (10)

In the image sensor, A photodiode formed on the substrate; A sensing diffusion region formed on the substrate at a position spaced apart from the photodiode; And A gate electrode overlapping one end of the photodiode and one end of the sensing diffusion region to transfer the optical signal to the sensing diffusion region through an on-off operation; The gate electrode has an image sensor having a groove formed in a portion of the gate electrode overlapping the sensing diffusion region. The method of claim 1, And an impurity region formed on the semiconductor substrate at a portion overlapping with the partial region, the impurity region having a lower concentration than the sensing diffusion region. The method of claim 1, And the partial region is formed at the center of a portion overlapping with the sensing diffusion region. The method of claim 1, The photodiode, A first photodiode region of a second conductive type formed under the substrate of a first conductive type; And A second photodiode region of a first conductivity type formed extending from the substrate surface to the first photodiode region; The sensing diffusion region, It is a high concentration second conductive type formed extending from the surface of the substrate, The gate electrode, An image sensor comprising polysilicon. delete delete delete delete delete delete