JP2848435B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device,
In particular, the present invention relates to a solid-state imaging device having a vertical overflow drain.

[0002]

2. Description of the Related Art A CCD is used as a signal charge transfer section of a solid-state image sensor.
In a CCD solid-state imaging device using a (charge-coupled device), a mechanism for sweeping out excess charges is generally provided for each pixel in order to suppress blooming. The vertical overflow drain is a mechanism for sweeping out excess charges to the substrate. FIG. 4 shows a sectional structure of a unit pixel of a conventional solid-state imaging device having a vertical overflow drain.
5 shows an interline transfer type, and FIG. 5 shows a frame transfer type. The case where the signal charge is an electron will be described below.
When the signal charge is a hole, the same discussion can be made by reversing the polarity.

In FIG. 4, a P-type semiconductor
There is a type semiconductor layer 41, on which an N-type photoelectric conversion unit 42 and an N-type signal charge transfer unit 43 are provided. The N-type photoelectric converter 42 is fixed at a constant potential by the high-concentration P-type semiconductor region 44. The high-concentration P-type semiconductor region 47 prevents punch-through between the N-type signal charge transfer section 43 and the N-type semiconductor substrate 40 and suppresses smear due to diffusion. An electrode 45 is provided on the N-type signal charge transfer section 43, and on the electrode 45,
A light-shielding film 46 is provided. In FIG. 5, a P-type semiconductor layer 51 is provided on an N-type semiconductor substrate 50, and an N-type signal charge transfer unit / photoelectric conversion unit 52 is provided thereon. The high-concentration P-type semiconductor region 54 prevents punch-through between the N-type signal charge transfer unit / photoelectric conversion unit 52 and the N-type semiconductor substrate 50. An electrode 55 is provided on the N-type signal charge transfer / photoelectric conversion unit 52.

[0004]

FIG. 6 shows the photoelectric conversion characteristics of the above-mentioned conventional solid-state imaging device. When the amount of incident light is small, the output increases in proportion to the amount of incident light. Reached I ₆₁ become somewhat the amount of incident light is large, the electric charge of more than the capacity of the N-type photoelectric conversion layer is generated, the excess charge is swept out to the N-type semiconductor substrate, an increase in output with respect to an increase of more light intensity Can be suppressed. This state is called a saturated state.
When the output in the saturated state is also used as the information signal, the amount of increase in the output with respect to the change in the light amount in the saturated state must be increased to some extent, but then blooming occurs with a small light amount.

The present invention aims to increase the amount of increase in output with respect to a change in the amount of light in a saturated state, and to increase the amount of light in which blooming occurs.

[0006]

According to the present invention, a P-type semiconductor layer is provided on an N-type semiconductor substrate, and an N-type photoelectric conversion unit and an N-type signal charge transfer unit (using a charge-coupled device) are provided thereon. In a solid-state imaging device having a mechanism in which excess charge generated in the N-type photoelectric conversion unit is swept out to the N-type semiconductor substrate, the P-type semiconductor layer below each N-type photoelectric conversion unit has an impurity concentration of It is characterized in that it is divided into a P-type semiconductor layer 1 having a small thickness and a large thickness and a P-type semiconductor layer 2 having a large impurity concentration and a large thickness. In addition, a P-type semiconductor layer is provided on an N-type semiconductor substrate, and an N-type signal charge transfer unit (using a charge-coupled device) serving also as a photoelectric conversion unit is provided thereon. In a solid-state imaging device having a mechanism in which excess charge is swept out to an N-type semiconductor substrate, each N
The P-type semiconductor layer below the type photoelectric conversion part is characterized by being divided into a P-type semiconductor layer 1 having a small impurity concentration and a large thickness and a P-type semiconductor layer 2 having a large impurity concentration and a small thickness. .

[0007]

In the saturated state, in order to determine the intensity of light based on the magnitude of the output, it is necessary to increase the ratio of the increase in the output to the increase in the amount of light to some extent. However, in such a case, blooming occurs with a relatively small amount of light.

As shown in FIG. 3A, when a characteristic is provided such that the rate of increase in output with respect to the amount of photoelectric conversion changes in two stages, the increase in output with respect to the increase in light amount is increased, and blooming occurs. The amount of light can be increased.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1A is a sectional view of a unit pixel according to an embodiment of the present invention, and FIG. 1B is a plan view thereof. A first P-type semiconductor layer 11 and a second P-type semiconductor layer 12 are provided on an N-type semiconductor substrate 40, and an N-type photoelectric conversion unit 42 and an N-type signal charge transfer unit 43 are provided thereon.
48 is an output amplifier, and 49 is a horizontal charge transfer unit. FIG.
(A) is a sectional view of a unit pixel according to an embodiment of the present invention, and (b) is a plan view of the same. A first P-type semiconductor layer 21 and a second P-type semiconductor layer 2 on an N-type semiconductor substrate 50;
2, and an N-type signal charge transfer unit / photoelectric conversion unit 52 is provided thereon. 58 is an output amplifier, and 59 is a horizontal charge transfer unit. In each of the embodiments of FIGS. 1 and 2, one of the first P-type semiconductor layer and the second P-type semiconductor layer has a small impurity concentration and a large thickness, and the other has a large impurity concentration and a small thickness. The boundary is below the N-type photoelectric conversion unit. The photoelectric conversion characteristics have such characteristics that the output changes its slope twice with an increase in the amount of incident light. The reason is,
It is explained as follows.

When strong light is incident, the excess charge that cannot be accumulated in the N-type photoelectric conversion portion exceeds the potential barrier formed in the P-type semiconductor layer below the N-type photoelectric conversion portion, and the N-type semiconductor Swept out to the substrate. The amount of light reaching the saturated state and the slope of the increase in output with respect to the amount of light in the saturated state depend on the impurity concentration distribution. That is, when the impurity concentration distribution changes, the amount of light reaching saturation and the case of an increase in output with respect to the amount of light in the saturated state also change.

Therefore, by providing two P-type semiconductor layers having different impurity concentrations and layer thicknesses under the N-type photoelectric conversion layer, as shown by a solid line in FIG. The output slope can be changed in two stages according to the light quantity. In the P-type semiconductor layer, when the impurity concentration is small and the layer thickness is large, the amount of light reaching saturation is small and the output gradient in the saturated state is large. The output slope becomes smaller.

FIGS. 3B and 3C show photoelectric conversion characteristics of a solid-state imaging device having only one P-type semiconductor layer. Figure (b)
If the impurity concentration of the P-type semiconductor layer is small and the layer thickness is large,
FIG. 3C shows the case where the impurity concentration of the P-type semiconductor layer is large and the layer thickness is small. The light quantity reaching the saturation state in (b) is smaller than that in (c), and the ratio of the increase in the output to the increase in the light quantity in the saturation state is larger. When the P-type semiconductor layer having such two impurity concentration distributions is provided under the N-type photoelectric conversion region, when the light amount reaches I ₃₁ , the excess charge passes through the P-type semiconductor layer 1 to the N-type semiconductor substrate. Be swept out. When the light quantity further increases and the light quantity reaches I ₃₃ , the excess charge is transferred to the P-type semiconductor layer 2.
Through the N-type semiconductor substrate.

The photoelectric conversion characteristics in this case are as shown in FIG. That is, the ratio of the output increase to the light amount changes in two stages.

For example, the P-type semiconductor layer has a region 1 having an impurity concentration of 8.0 × 10 ¹⁴ / cm ^{3 and a} thickness of 2.6 μm and a region 1 having an impurity concentration of 1.4 × 10 ¹⁵ / cm ^{3 and a} thickness of 1.8 μm. When divided into two regions, that is, region 2, 7.0 × 10 ¹¹ electrons / cm ²
When the electric charge is accumulated, the excess electric charge is swept out through the region 1, and when the light quantity further increases and the electric charge of 1.0 × 10 ¹⁵ electrons / cm ² is accumulated, the excessive electric charge is passed through the region 2. Be swept out. At this time, the minimum light amount at which blooming occurs is about 1.0 in comparison with the case where the P-type semiconductor layer has only one region with a layer thickness of 1.8 μm and an impurity concentration of 1.4 × 10 ¹⁵ / cm ³ .
5 times.

[0016]

As is apparent from the above description, according to the present invention, it is possible to increase the output with respect to the increase in the amount of light in a saturated state, and to increase the amount of light in which blooming occurs.

[Brief description of the drawings]

FIGS. 1A and 1B show a solid-state imaging device according to an embodiment of the present invention, wherein FIG. 1A is a cross-sectional view and FIG.

FIGS. 2A and 2B show a solid-state imaging device according to an embodiment of the present invention, wherein FIG. 2A is a cross-sectional view and FIG.

FIG. 3 is a diagram showing various photoelectric conversion characteristics of the solid-state imaging device according to the present invention.

FIG. 4 is a cross-sectional view of a conventional interline transfer type solid-state imaging device.

FIG. 5 is a cross-sectional view of a conventional frame transfer type solid-state imaging device.

FIG. 6 is a diagram illustrating a photoelectric conversion characteristic of a conventional solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 1st P-type semiconductor layer 12 2nd P-type semiconductor layer 21 1st P-type semiconductor layer 22 2nd P-type semiconductor layer 40 N-type semiconductor substrate 41 P-type semiconductor layer 42 N-type photoelectric conversion part 43N Type signal charge transfer section 44 High-concentration P-type semiconductor region 45 Electrode 46 Light-shielding film 47 High-concentration P-type semiconductor region 48 Output amplifier 49 Horizontal charge transfer section 50 N-type semiconductor substrate 51 P-type semiconductor layer 52 N-type signal charge transfer section Photoelectric conversion unit 54 high-concentration P-type semiconductor region 55 electrode 58 output amplifier 59 horizontal charge transfer unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 27/148 H04N 5/335

Claims (2)

(57) [Claims] 1. A charge-coupled device is used for a signal charge transfer section.
CCD-type solid-state image sensor with a second conductive semiconductor substrate
A conductive semiconductor layer is provided, and a first conductive photoelectric conversion unit and a first conductive signal charge transfer unit are provided thereon.
In a solid-state imaging device having a mechanism in which excess charge generated in a conductive type photoelectric conversion unit is swept out to a first conductive type semiconductor substrate, the second conductive type semiconductor layer below each photoelectric conversion unit has an impurity concentration. 1. A solid-state imaging device comprising: a second conductive semiconductor layer 1 having a small thickness and a large thickness; and a second conductive semiconductor layer 2 having a large impurity concentration and a small thickness. 2. A charge-coupled device is used for a signal charge transfer section.
CCD-type solid-state image sensor with a second conductive semiconductor substrate
A conductive semiconductor layer is provided, and a first conductive photoelectric conversion unit serving also as a signal charge transfer unit is provided thereon, and excess charges generated in the first conductive photoelectric conversion unit are transferred to the first conductive photoelectric conversion unit. In a solid-state imaging device equipped with a mechanism that is swept to the type semiconductor substrate,
The second conductive semiconductor layer below each photoelectric conversion part has a second conductive semiconductor layer 1 having a small impurity concentration and a large layer thickness and a second conductive semiconductor layer 2 having a large impurity concentration and a small layer thickness. And a solid-state image sensor.