JPH0794699A - Solid-state image sensor - Google Patents

Abstract

PURPOSE:To reduce dark current, fluctuation of Qs, and smear components in a solid state image sensor. CONSTITUTION:In a solid state image sensor comprising a light receiving part (photoelectric conversion element) 32 and a charge transfer part 33 formed on single crystal semiconductor substrates 42, 43, a transparent conductive film 53 is formed of ITO, for example, entirely on the positive charge storage region 48 at the light receiving part 32 while touching the the region 48 and the transparent conductive film 53 is connected with an Al shading film 56 being grounded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional CCD solid-state image pickup device. This CCD solid-state imaging device 1 has a first conductivity type, for example, an N-type silicon substrate 2, and a first second conductivity type, that is, P.
An N-type impurity diffusion region 4, an N-type transfer channel region 6 forming a vertical transfer register 5 and a P-type channel stop region 7 are formed in the N-type well region 3.
A P-type positive charge accumulation region 8 is formed on the P-type impurity diffusion region 4,
The second P-type well regions 9 are formed immediately below the N-type transfer channel regions 6, respectively.

Here, a photodiode PD is formed by the PN junction j of the N type impurity diffusion region 4 and the P type well region 3.
The light receiving section (photoelectric conversion element) 10 is constituted by. The light receiving unit 10 is formed corresponding to each pixel.

Then, the vertical transfer including on the light receiving section 10 is performed.
Transfer channel area 6 and channel block that make up register 5
S is formed on the top region 7 and the read gate portion 11 described later.
iO ₂Is polycrystalline silicon on the gate insulating film 15 made of a film?
A transfer electrode 16 composed of the transfer channel region 6,
The gate insulating film 15 and the transfer electrode 16 form a CCD structure.
The vertical transfer register 5 is configured.

A SiO ₂ film 14 is formed on the surface of the transfer electrode 16, and PSG (phosphorus / phosphorus) which is a reflow film is formed on the entire surface including the transfer electrode 16 and the positive charge storage region 8 of the light receiving portion.
An interlayer insulating film 17 made of silicate glass is laminated, and an Al light-shielding film 18 is selectively formed on the transfer electrode 16 via the interlayer insulating film 17.

In the illustrated example, the Al light-shielding film 18 has a two-layer film structure and extends over the vertical transfer register 5 in a strip shape.
Light shielding film 19 and the light receiving portion 10 for covering the first Al light shielding film 19 and blocking the light (light obliquely incident) directly incident on the vertical transfer register 5 from the light receiving portion 10.
The second Al light-shielding film 20 is integrally provided with a protruding portion 20a that partially extends to the side.

Then, for example, a plasma SiN film 21 and a planarizing film 22 are sequentially formed on the entire surface including the Al light shielding film 18. The color filter layer 2 is formed on the flattening film 22.
3 is formed, and the on-chip microlens 24 is further formed on the color filter layer 21 at a position corresponding to the light receiving portion 10.

The transfer electrode 16 is formed so as to extend between the vertical transfer register 5 and the light receiving portion 10, and the read gate portion 11 is formed here.

[0009]

By the way, the above-mentioned solid-state image pickup device 1 has the following problems.

(I) In the light receiving portion 10, as shown in FIG. 4, a phosphorus silicate glass film 17 which is an interlayer insulating film.
Impurity ions (positive ions) 25 and the like existing inside expand the depletion layer 26 at the interface between the insulating film 15 and the positive charge storage region 8, and this causes the increase of dark current. This dark current is due to electron-hole pairs generated by the action of recrystallization centers in the depletion layer 26.

(Ii) The channel stop region 7 is used as a so-called hole drain for sweeping out the holes accumulated in the positive charge accumulation region 8 of the light receiving portion 10, and the positive charge accumulation is performed through this channel stop region 7. The holes accumulated in the area 8 are swept out. However, since the channel stop region 7 extending in the vertical direction has resistance, the amount of holes swept out in the upper and lower light receiving portions 10 in the vertical direction is different, which causes unevenness of the signal charge amount Qs when the same light is applied. Was there.

(Iii) In recent years, in solid-state image pickup devices,
Miniaturization has been promoted. With this miniaturization, even if the curvature of the on-chip microlens 24 and the film thickness of the flattening film 22 are adjusted, it is difficult to focus on the light receiving unit 10 as shown in FIG. Therefore, since the light L that has passed through the on-chip microlens 24 is not completely condensed, the amount of light leaking from the lower portion of the protruding portion 20a of the Al light-shielding film 18 into the vertical transfer register 5 increases, and the smear component increases.

In view of the above points, the present invention has a dark current, Qs.
The present invention provides a solid-state image sensor capable of reducing unevenness and smear components.

[0014]

The present invention provides a solid-state image pickup device comprising a single crystal semiconductor substrate 42, 43 provided with a photoelectric conversion element 32 and a charge transfer section 33.
A transparent conductive film 53 that is in contact with the photoelectric conversion element 32 and is grounded is formed immediately above the element 2.

[0015]

In the present invention, since the transparent conductive film 53 which is grounded is formed in direct contact with the photoelectric conversion element 32, this transparent conductive film 53 acts as a drain of one photoelectrically converted charge, and the Qs unevenness. Can be reduced.

Further, since the surface of the photoelectric conversion element 32 is at the ground potential through the transparent conductive film 53, the photoelectric conversion element 32 is
The depletion at the interface of is prevented and the dark current can be reduced.

Further, depending on the refractive index of the transparent conductive film 53,
The protruding portion 55 of the light shielding film 56 that passes through the photoelectric conversion element 32.
The light L incident from below a is refracted inward (to the photoelectric conversion element side), and it is possible to improve the sensitivity and reduce the smear component.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 (overall view) and FIG. 2 (cross section taken along the line AA) show an example of a CCD solid-state image pickup device according to the present invention. The CCD solid-state imaging device 31 shown in FIG. 1 has a plurality of light receiving portions (photoelectric conversion elements) 32 arranged in a matrix.
A vertical transfer register 33 having a CCD structure for vertically transferring the signal charges from the light receiving section 32 to one side of each light receiving section row.
Further, a horizontal transfer register 34 having a CCD structure for transferring signal charges in the horizontal direction is formed by being connected to an end of each vertical transfer register 33, and an output section 37 is connected to a final stage of the horizontal transfer register 34. Consists of A channel stop region 35 is formed between each light receiving unit row and the adjacent vertical transfer register 33, and is connected at each end. The channel stop region 35 can be grounded.

In the CCD solid-state image pickup device 31 of this embodiment, as shown in the cross section of FIG. 2, a well region 43 of a first conductivity type, for example, N type, on a silicon substrate 42 of a first second conductivity type, that is, P type. An N-type impurity diffusion region 44, an N-type transfer channel region 46 that constitutes the vertical transfer register 33, and a P-type channel stop region 35 are formed therein, and a P-type impurity diffusion region 44 is formed on the N-type impurity diffusion region 44. Positive charge storage area 4
8 and a second P-type well region 49 is formed just below the N-type transfer channel region 46.

Here, the light receiving portion (photoelectric conversion element) 32 is constituted by the photodiode PD formed by the PN junction j of the N type impurity diffusion region 44 and the P type well region 43.

Transfer charts that constitute the vertical transfer register 33
The channel region 46, the channel stop region 35, and the readout
On the gate part 36, for example, SiO₂Gate insulating film 5 by
0 is formed. Polycrystalline silicon is formed on the gate insulating film 50.
A transfer electrode 51 composed of a capacitor is formed, and a transfer channel region is formed.
CC by the region 46, the gate insulating film 50 and the transfer electrode 51
A vertical transfer register 33 having a D structure is configured. Transfer electrode
The surface of 51 is SiO ₂The film 52 is formed.

In the present example, the light receiving section 3 is directly contacted with the entire area of the positive charge storage region 48 of the light receiving section 32.
2 and the vertical transfer register 33, for example, ITO on the entire surface
A transparent conductive film 53 such as a (indium tin oxide) film is formed. Further, a metal light-shielding film, for example, the first Al light-shielding film 5 is formed on the transparent conductive film 53 in a portion corresponding to the vertical transfer register 33 so as to be electrically connected to the transparent conductive film 53.
4 is formed.

An interlayer insulating film 57 made of PSG (phosphorus silicate glass), which is a reflow film, is laminated on the entire surface excluding the first Al light shielding film 54, and further, a metal light shielding film, for example, a second light shielding film is formed on the transfer electrode 51. The Al light-shielding film 55 is selectively formed. In the interlayer insulating film 57 made of PSG, hydrogen contained therein diffuses during annealing and is useful for recovery of crystal defects. The second Al light shielding film 55 is the first Al light shielding film 54.
The projection portion 55 is connected to the light receiving portion 32 and is partially extended to the light receiving portion 32 side in order to block the light directly entering the vertical transfer register 33 from the light receiving portion 32 (light incident obliquely).
a is integrally provided.

The first and second Al light shielding films 54 and 55 constitute an Al light shielding film 56 as a whole.
The Al light shielding film 56 is grounded. Thereafter, similar to the above, for example, plasma Si is formed on the entire surface including the Al light shielding film 56.
An N film 59 and a flattening film 60 are sequentially formed, a color filter layer 61 is formed on the flattening film 60, and the incident light is received on the color filter layer 61 at a position corresponding to the light receiving unit 32. An on-chip microlens 62 for condensing the light is formed.

According to this embodiment described above, the transparent conductive film 53 is formed so as to be in direct contact with the surface of the positive charge storage region 48 of the light receiving portion 33, and the transparent conductive film 53 is grounded.
By being connected to the light-shielding film 56, the transparent conductive film 53 functions as a so-called hole drain, and the holes (holes) accumulated in the positive charge accumulation region 48 in each light receiving portion 32 are transparent conductive films 53. It is swept through the Al light shielding film 56 having a lower resistance. Therefore, the amount of signal charges Qs when receiving the same amount of light becomes approximately the same in the upper and lower light receiving portions 32 in the vertical direction, and so-called Qs unevenness can be reduced.

Further, since the grounded transparent conductive film 53 is directly formed on the entire area of the positive charge storage region 48, the surface of the positive charge storage region 48 is at the ground potential. Therefore, in the positive charge storage region 48, depletion of the interface of the positive charge storage region 48 can be prevented without being affected by the positive impurity ions existing in the interlayer insulating film 57, and the dark current can be reduced. .

Further, since the ITO film, which is the transparent conductive film 53, has a refractive index of 2.0, the light L incident below the protruding portion 55a of the Al light-shielding film 56 is refracted inward (to the light receiving portion side). It will be. As a result, the light L can be concentrated on the light receiving portion 32 to improve the sensitivity, and the smear component due to the light incident under the protruding portion 55a can be reduced.

[0029]

According to the present invention, in a solid-state imaging device, a transparent photoelectric film is formed directly on the photoelectric conversion device to reduce dark current generation and Qs unevenness between the photoelectric conversion devices. It is possible to reduce the smear component due to the leakage of light. Therefore, a highly reliable solid-state image sensor can be provided.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an example of a solid-state image sensor according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a cross-sectional view showing a conventional solid-state image sensor.

FIG. 4 is a cross-sectional view of a main part for explaining a conventional example.

[Explanation of symbols]

 1,31 Solid-state imaging device 10,32 Light receiving part 5,33 Vertical transfer register 34 Horizontal transfer register 7,35 Channel stop region 11,36 Read gate part 37 Output part 2,42 Silicon substrate 3,43 First well region 4 , 44 N-type impurity diffusion region 6,46 Transfer channel region 8, 48 Positive charge storage region 9,49 Second well region 15,50 Gate insulating film 16,51 Transfer electrode 14,52 Insulating film 53 Transparent conductive film 18, 19, 20, 54, 55, 56 Al light-shielding film 21, 59 Plasma SiN film 22, 60 Flattening film 23, 61 Color filter layer 24, 62 On-chip microlens

Claims (1)

[Claims] 1. A solid-state imaging device comprising a single crystal semiconductor substrate provided with a photoelectric conversion element and a charge transfer section, wherein a transparent conductive film grounded in contact with the photoelectric conversion element is formed immediately above the photoelectric conversion element. A solid-state image sensor, comprising: