KR100364792B1 - Solied state image sensor - Google Patents

Abstract

The present invention provides a solid state image pickup device capable of facilitating a reset operation by smoothing charge transfer to a reset drain region. A solid state image pickup device for achieving the above object includes a second conductivity type well formed in a first conductivity type substrate; An output formed in the upper portion of the mem charge transfer region by partially overlapping with the horizontal charge transfer gate to transfer the charge transferred to the last stage of the meso charge transfer region and the horizontal charge transfer region formed on the surface of the second conductivity type well to the sensing amplifier; A gate, a floating diffusion region formed in the surface of the membranous charge transfer region on one side of the output gate to detect the transferred charges, and transferring the sensed charge to one side of the floating diffusion region to be parallel to the output gate A reset gate for forming the memory charge transfer region so as to overlap the reset gate at one side; A reset drain region formed on a surface thereof, an insulating layer formed on the reset gate and the reset drain region, contacting both sides of the reset gate, and being formed on an upper side of the reset drain region and the reset gate, And a first conductive line formed to have a stepped potential distribution, and a second conductive line contacted to the reset drain region and formed in one line direction.

Description

Solid state imaging device {SOLIED STATE IMAGE SENSOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid state image pickup device, and more particularly, to a solid state image pickup device capable of performing a good reset operation by smoothing charge transfer to a reset drain-in area.

In general, the solid state image pickup device includes a photodiode region PD for converting a signal of light into electrical signal charge, and a signal charge photoelectrically converted by being formed in a direction perpendicular to the photodiode region PD. It consists of a vertical charge transfer region (VCCD) for moving the signal charge and a horizontal charge transfer region (HCCD) for transferring the signal charges transferred through the vertical charge transfer region (VCCD) to the sensing amplifier (SA).

In the solid state image pickup device, the signal charge generated by photoelectric conversion in the photodiode region is moved to the horizontal charge transfer region through the vertical charge transfer region, and the signal charge transferred to the end of the horizontal charge transfer region is transferred to the transfer gate (not shown). The clock signal is applied to the sensing amplifier SA.

Referring to the accompanying drawings, a conventional solid state image pickup device will be described below.

FIG. 2 is a layout view of an end portion of the charge coupling device according to the related art (region A of FIG. 1), FIG. 3 is a cross-sectional view of the structure taken along line II ′ of FIG. 2, and FIG. 4 is a clock of H1 and RG of FIG. 3. A diagram showing a conventional potential change according to the operation.

As shown in FIGS. 2 and 3, a P well 12 is formed in an N-type substrate 11 at the end of a charge coupled device of a conventional solid state image pickup device. A region (Buried Charge Coupled Device: BCCD) 13 is formed and partially overlaps with the first horizontal charge transfer gate 14 to transfer the charge transferred to the final stage of the HCCD, above the BCCD 13. An output gate (OG) 15 is formed, and a floating diffusion region 16 for detecting the transferred charge is formed on the surface of the BCCD 13 and is horizontal to the output gate 15. A reset gate 17 is formed on one side of the floating diffusion region 16 to move the sensed charges to the reset drain region 18 so as to form the same. A reset drain region 18 is formed in the BCCD 13 so as to overlap the reset gate 17 at one side. At this time, the floating diffusion region 16 and the reset drain region 18 are doped with N + type, and the reset gate 17 is formed of polysilicon.

In addition, a first metal 19 is contacted with an upper portion of one side of the reset gate 17, and a second metal 20 is contacted with one side of the reset drain region 18. There is no metal in the upper layer.

The reset operation at the end of the charge coupled device of the conventional solid state imaging device having the above configuration will be described as follows.

In order to transfer charges from the floating diffusion region 16 to the reset drain region 18, as shown in FIG. 4A, the H1 signal is applied to the first horizontal charge transfer gate 14 and the reset gate 17. As shown in FIG. Apply the RG signal.

As shown in (a) and (b) of FIG. 4, when T = t1, H1 is a 'high' signal and RG is transmitted as a potential change at each T = t1, T = t2, and T = t3. Since the 'low' signal is applied to the potential under the reset gate (RG) 17 is higher than the floating diffusion region 16. Therefore, no charge is transferred from the floating diffusion region 16 to the reset drain region 18.

When T = t2, since both H1 and RG are 'high' signals, the potential under the reset gate 17 is lower than the potential of the floating diffusion region 16, so that the charge in the floating diffusion region 16 is reset. 18).

Afterward, when T = t3, since H1 is a 'high' signal and RG is a 'low' signal, the potential of RG becomes higher than that of the floating diffusion region 16 so that no charge is transferred to the reset drain region 18. .

In this case, a problem occurs that the charge remaining under the reset gate 17 is transferred to the floating diffusion region 16 without being transferred to the reset drain region 18.

When patterning the reset gate, which is the weakest part of the layout of the solid state image pickup device, plasma etching the reset gate 17 formed of polysilicon using a photo mask causes the reset gate 17 to be destroyed due to plasma damage, thereby causing a threshold voltage. This can be shifted.

The conventional solid-state imaging device as described above has the following problems.

First, when the reset gate is 'OFF' from 'ON', the signal charge of the RG portion is transferred to the floating diffusion region, and partition noise may be generated.

Second, the plasma damage may damage the reset gate made of polysilicon in a subsequent plasma etching process.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a solid state image pickup device capable of performing a reset operation by smoothing charge transfer to a reset drain-in area.

1 is a layout diagram of a typical solid state image pickup device.

2 is a layout view of an end of a charge coupling device according to the related art (area A of FIG. 1)

3 is a cross-sectional view taken along line II ′ of FIG. 2;

4 is a view showing a conventional potential change according to the clock operation of H1 and RG of FIG.

5 is a layout view of an end of the charge coupling device (region A of FIG. 1) according to the present invention;

6 is a structural cross-sectional view taken along the line II-II 'of FIG. 5.

FIG. 7 illustrates potential changes of the present invention according to the H1 and RG clocks of FIG. 6.

Explanation of symbols for the main parts of the drawings

31: N-type substrate 32: P well

33: embedded charge transfer region (BCCD) 34: first horizontal charge transfer gate

35: output gate (OG) 36: floating diffusion area

37: reset gate 38: reset drain area

39: HLD 40: BPSG

41: first metal line 42: second metal line

In order to achieve the above object, the solid-state imaging device of the present invention comprises a second conductive well formed in a first conductive substrate, a mem charge transfer region formed on the surface of the second conductive well, and a horizontal charge transfer region. An output gate partially overlapping with the horizontal charge transfer region to transfer the transferred charges to the sensing amplifier, and within the surface of the mem charge transfer region on one side of the output gate to detect the transferred charges. A floating diffusion region formed thereon, a reset gate for transferring sensed charges to one side of the floating diffusion region so as to be parallel to the output gate, and a reset drain formed on a surface of the membranous charge transfer region so as to overlap one side with the reset gate An insulating layer formed on a region, the reset gate and the reset drain region, A first conductive line contacted on both sides of the set gate and formed on an upper side of the reset drain region and the reset gate, the first conductive line formed to have a stepped potential distribution under the reset gate, and in contact with the reset drain region; It characterized in that it comprises a second conductive line formed.

The solid-state imaging device of the present invention will be described with reference to the accompanying drawings.

FIG. 5 is a layout view of an end portion of the charge coupling device (region A of FIG. 1) according to the present invention, FIG. 6 is a cross-sectional view of the structure taken along line II-II ′ of FIG. 5, and FIG. 7 is a H1 and RG clock of FIG. Figure shows the potential change of the present invention according to.

In the present invention, as shown in FIGS. 5 and 6, the end of the charge coupled device of the solid state imaging device has a P well 32 formed in the N-type substrate 31, and is embedded in the surface of the P well 32. A charge transfer region (BCCD) 33 is formed, and partially overlaps with the first horizontal charge transfer gate 34 to transfer the charge transferred to the last stage of the HCCD to the sensing amplifier. An output gate (OG) 35 is formed on the upper side of 33. A floating diffusion region 36 for detecting the transferred charge is formed on the surface of the BCCD 33. A reset gate (RG) 37 for moving the sensed charges to the reset drain region RD 38 on one side of the floating diffusion region 36 so as to be parallel to the 35. Formed. A reset drain region 38 is formed in the BCCD 33 so as to overlap the reset gate 37 at one side. In this case, the floating diffusion region 36 and the reset drain region 38 are doped with N + type, and the reset gate 37 is formed of polysilicon.

The first metal line 41 is formed in the same direction as the reset gate 37 so as to overlap the upper portion of the reset gate 37 and the upper portion of the reset drain region 38. At this time, the first metal line 41 is in contact with the upper sides of the reset gate 37. An HLD 39 and a BPSG 40 are stacked between the reset gate 37 and one side of the reset drain region 38 and the first metal line 41.

A second metal line 42 is formed in one line direction to contact the reset drain region 38.

The reset operation at the end of the charge coupled device of the solid state imaging device having the above-described configuration will be described as follows.

When the same bias voltage is applied to the polysilicon and the metal, the potential under the metal is smaller than the potential under the polysilicon. Therefore, when polysilicon and the metal are adjacent to each other, a potential of a stepped shape is achieved.

Thus, as shown in FIGS. 5 and 6, the potential of the reset gate 37 is lower in the lower portion where the HLD 39 and the BPSG 40 are formed.

In order to transfer charges from the floating diffusion region 36 to the reset drain region 38, as shown in FIG. 7A, the H1 signal is applied to the first horizontal charge transfer gate 34 and the reset gate 37. As shown in FIG. Apply the RG signal.

As shown in (b) of FIG. 7, H1 is a high signal and T1 is low when RG is equal to T = t1, T = t2, and T = t3. Since the signal is applied, the potential under the reset gate RG 37 is higher than that of the floating diffusion region 36. Therefore, no charge is transferred from the floating diffusion region 36 to the reset drain region 38.

When T = t2, since both H1 and RG are 'high' signals, the potential under the reset gate 37 is lower than the potential of the floating diffusion region 36, so that the charge in the floating diffusion region 36 is reset. 38).

When T = t3, since H1 is a 'high' signal and RG is a 'low' signal, the potential of RG becomes higher than that of the floating diffusion region 36 so that no charge is transferred to the reset drain region 38. . At this time, since the potential under the RG forms a step, all of the charge remaining under the reset gate 37 is transferred to the reset drain region 38 without passing over to the floating diffusion region 36.

The solid-state imaging device of the present invention as described above has the following effects.

First, since the lower portion of the reset gate forms a stepped potential, partition noise can be removed by preventing signal charge from being transferred to the floating diffusion region.

Second, since the first metal line covering the upper portion of the reset gate prevents plasma damage from occurring during plasma etching in a later process, the reset gate may be destroyed and prevented from malfunctioning.

Claims (5)

A second conductivity type well formed in the first conductivity type substrate, A buried charge transfer region formed on the surface of the second conductivity type well, An output gate formed overlying the mem charge transfer region to partially overlap the horizontal charge transfer gate to transfer charges transferred to the last stage of the horizontal charge transfer region to the sensing amplifier; A floating diffusion region formed in a surface of the membranous charge transfer region on one side of the output gate to detect the transferred charges; A reset gate for transferring sensed charge to one side of the floating diffusion region so as to be parallel to the output gate; A reset drain region formed on a surface of the membranous charge transfer region so as to overlap the reset gate at one side; An insulating layer formed on the reset gate and the reset drain region; First conductive lines contacting both sides of the reset gate and formed on one side of the reset drain region and the reset gate and having a stepped potential distribution under the reset gate; And a second conductive line contacting the reset drain region and formed in one line direction. The solid state image pickup device according to claim 1, wherein the reset gate is made of polysilicon. The solid state image pickup device of claim 1, wherein the first and second conductive lines are formed of a metal. The solid state image pickup device of claim 1, wherein the insulation layer is formed by stacking HLD and BPSG. The solid state image pickup device according to claim 1, wherein the first conductive line covers the entire upper portion of the reset gate and is formed in the same direction as the reset gate.