JPH0473348B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a solid-state imaging device with high sensitivity.

Conventional Structure and Problems In recent years, with advances in semiconductor microfabrication technology, solid-state imaging devices have been manufactured using this semiconductor microfabrication technology, and have been used in place of conventional image pickup tubes.

Hereinafter, a conventional solid-state imaging device will be explained with reference to the drawings.

Figure 1a shows the conventional interline transfer method
1 shows a plan view of the main parts of a solid-state imaging device using a CCD. FIG. 1b shows a sectional view of A and A' in FIG. 1a.
In FIGS. 1a and 1b, 1 is a photoelectric conversion element configured on a semiconductor substrate and converts an optical signal into a signal charge;
2 is a charge transfer gate that transfers the signal charge stored in the photoelectric conversion element 1 to the charge transfer element array 3;
is a charge transfer element array that accumulates and transfers the signal charge transferred from the charge transfer gate 2, and is composed of a charge coupled device (CCD), 4 is a charge absorption region that absorbs unnecessary signal charges, and 5 is a charge absorption region. The excess signal charge in the photoelectric conversion element 1 is transferred to the charge absorption region 4.
This is the excess charge transfer gate that transfers the excess charge to.

The operation of the solid-state imaging device configured as described above will be described below.

First, the signal charge photoelectrically converted by the photoelectric conversion element 1 is accumulated in the photoelectric conversion element 1 until it is transferred to the charge transfer element array 3 through the charge transfer gate 2. If the signal accumulated in this photoelectric conversion element 1 exceeds the maximum signal charge that can be accumulated in the photoelectric conversion element 1 before being transferred to the charge transfer element array 3 through the charge transfer gate 2, this photoelectric conversion element 1 Excess signal charges exceeding the maximum signal charge that can be stored are transferred to the charge absorption region 4 through the excess charge transfer gate 5.

The signal charge accumulated in the photoelectric conversion element 1 is transferred to the charge transfer element array 3 through the charge transfer gate 2, and then transferred to the signal output section through the charge transfer element array 3.

Generally, in the above-mentioned solid-state imaging device, the photoelectric conversion element 1
Sensitivity is determined by the surface area of the photoelectric conversion element 1, and the surface area of the photoelectric conversion element 1 is limited by the charge transfer gate 2, the charge transfer element array 3, the charge absorption region 4, and the excess charge transfer gate 5.

Therefore, if the dimensions of the charge transfer gate 2 are reduced in order to increase the surface area of the photoelectric conversion element 1,
This shortens the gate channel length, making punch-through more likely to occur at low voltages. Furthermore, reducing the dimensions of the charge transfer element array 3 reduces the amount of charge that can be transferred by the charge transfer element array 3, and the narrow channel effect is particularly likely to appear, which not only reduces the amount of transferable charge but also reduces the transfer effect. This will cause significant deterioration.
Furthermore, reducing the size of the charge absorption region 4 means that
This results in a decrease in charge absorption capacity. Further, the dimensions of the excess charge transfer gate 5 cannot be made smaller for the same reason as the charge transfer gate 2.

For these reasons, in conventional solid-state imaging devices, in order to improve the sensitivity characteristics with the current structure,
It has a drawback that the dimensions of the photoelectric conversion element 1 cannot be increased by reducing the dimensions of any one of the charge transfer gate 2, the charge transfer element array 3, the charge absorption region 4, and the excess charge transfer gate 5.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides a highly sensitive solid-state imaging device in which the dimensions of the photoelectric conversion element are increased without causing deterioration of characteristics due to the reduction in the dimensions of the readout means.

Structure of the Invention In order to achieve this object, in the solid-state imaging device of the present invention, the semiconductor substrate around the photoelectric conversion element formed on the semiconductor substrate has an inclined surface. With this configuration, the surface area of the solid-state imaging device is effectively increased under a constant light-receiving area, and a readout means other than the photoelectric conversion element is formed on the inclined surface of the semiconductor substrate.
High sensitivity characteristics can be obtained by increasing the area occupied by the photoelectric conversion element relative to the light receiving area.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2a shows a plan view of essential parts of a solid-state imaging device according to an embodiment of the present invention. Figure 2b is Figure 2a
A, A' cross-sectional view is shown. In Figure 2 a and b,
1 is a photoelectric conversion element configured on a semiconductor substrate and converts an optical signal into a signal charge; 2' is a photoelectric conversion element 1
The signal charge stored in the charge transfer gate 2' is transferred to the charge transfer element array 3 through a charge transfer gate, and 3 is a charge transfer element array that accumulates and transfers the signal charge transferred from the charge transfer gate 2' to a charge coupled device (CCD). )
4 is a charge absorption region that absorbs unnecessary signal charges, and 5' is an excess charge transfer gate that transfers excess signal charges in the photoelectric conversion element 1 to the charge absorption region 4.

Here, the charge transfer gate 2' and the excess charge transfer gate 5' are formed on an inclined portion of the semiconductor substrate around the photoelectric conversion element 1 formed on the semiconductor substrate.

The operation of the solid-state imaging device configured as described above will be described below.

First, the signal charge photoelectrically converted by the photoelectric conversion element 1 is accumulated in the photoelectric conversion element 1 until it is transferred to the charge transfer element array 3 through the charge transfer gate 2' formed on the inclined surface of the semiconductor substrate. If this accumulated signal charge exceeds the maximum signal charge that can be accumulated in the photoelectric conversion element 1 before being transferred to the charge transfer element array 3 through the charge transfer gate 2' formed on the inclined surface of the semiconductor substrate, , the excess signal charge greater than the maximum signal charge that can be accumulated in the photoelectric conversion element 1 is
The excess charge is transferred to the charge absorption region 4 through the excess charge transfer gate 5' formed on the inclined surface of the semiconductor substrate.

Signal charges accumulated in the photoelectric conversion element 1 are transferred to a charge transfer element array 3 through a charge transfer gate 2 formed on an inclined surface of a semiconductor substrate, and then transferred to a signal output section through the charge transfer element array 3.

As described above, according to this embodiment, an inclined surface of the semiconductor substrate in the peripheral area of the photoelectric conversion element 1 configured on the semiconductor substrate is formed, and the charge transfer gate 2' and the excess charge transfer gate are formed on the inclined surface of the semiconductor substrate. By creating the gate 5', the area occupied by the photoelectric conversion element 1 relative to the light receiving area can be reduced without reducing the effective dimensions of the charge transfer gate 2' and excess charge transfer gate 5', which cause punch-through at low voltages. Can be made larger. In addition, reducing the size of the charge transfer element array 3 tends to cause a narrow channel effect, which causes a decrease in the amount of charge that can be transferred and a significant deterioration of the transfer efficiency, and reducing the size of the charge transfer element array 3, which causes a decrease in the charge absorption capacity. Without reducing the size of the absorption region 4, the photoelectric conversion element 1 can be increased in size to provide a highly sensitive image sensor.

In the present invention, the charge transfer gate 2' and the excess charge transfer gate 5' are provided on the inclined surface of the semiconductor substrate in the periphery of the photoelectric conversion element 1 formed on the semiconductor substrate. Conversion element 1
The one provided on the inclined surface of the semiconductor substrate around the periphery of
It may be the charge transfer element array 3 and the charge absorption region 4.

Effects of the Invention As described above, the present invention creates a sloped surface on a semiconductor substrate in the peripheral area of a photoelectric conversion element configured on a semiconductor substrate, and utilizes the sloped surface of the semiconductor substrate to provide a large photoelectric conversion element. It can be made into a highly sensitive image sensor, and its practical effects are great.

[Brief explanation of the drawing]

Figure 1a shows the conventional interline transfer method
FIG. 1b is a sectional view of A and A' in FIG. 1a, and FIG. 2a is a plan view of the main parts of a solid-state imaging device using a CCD. The plan view, FIG. 2b, is a sectional view taken along lines A and A' in FIG. 2a. 1... Photoelectric conversion element array, 2'... Charge transfer gate, 3... Charge transfer element array, 4... Charge absorption region, 5'... Excess charge transfer gate.

Claims (1)

[Claims] 1 comprising photoelectric conversion elements arranged in a matrix on a semiconductor substrate, readout means for reading signal charges accumulated in the photoelectric conversion elements, and a charge coupled element for transferring the signal charges, and around the photoelectric conversion elements, A solid-state imaging device characterized in that a part of the semiconductor substrate is provided with an inclined part that is inclined with respect to a main surface of the semiconductor substrate, and a gate electrode of the readout means is provided on the inclined part.