JPS60105382A - Solid-state pickup element - Google Patents

Abstract

PURPOSE:To minimize the area needed for separation between light sensitive parts by shutting off the part for accumulating the signal charge of the adjacent light sensitive part with the groove formed at the semiconductor substrate surface and by forming the diffusion area having the conductive type opposite to the semiconductor substrate at the groove bottom part. CONSTITUTION:A groove 14 is formed at P type semiconductor substrate 13. A drain 15 for excess carrier absorption consisting of the N type diffusion layer with high concentration is formed at the bottom part of a groove 14. A surface layer 16 of the flush channel consisting of the impurity diffusion layer is formed at the surface of a substrate 13 between the light sensitive part and a groove 14. A gate electrode 17 is formed on a gate oxidation film 18. When the positive bias is impressed for a substrate 13 to a drain 15, and even when the excess charge occurs at a substrate 13, the charge is absorbed and exhausted to a drain 15 and the blooming can be prevented. Consequently, the flow-in of the excess charge between light sensitive parts can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid-state imaging device used in imaging devices such as video cameras.

Conventional Structure and Its Problems FIG. 1 shows an example of the structure of a solid-state image sensor. This is a charge-coupled two-dimensional solid-state imaging device, and more specifically, it is called a frame transfer solid-state imaging device. That is, the signal charge accumulated in the photosensitive cheek section 1 of the imaging section B is transferred to the corresponding storage element 1' of the storage section B within the vertical erasing time period in the television scanning system. After this,
For each horizontal scan, one stage is vertically transferred, and the horizontal scanning c
Charge is transferred to the an shift register 2. This transfer occurs within the horizontal erase period. The signal charge of the horizontal shift register 2 that performs horizontal scanning is converted into a signal output by the output section 3.

FIG. 2 shows a typical configuration example of an M20 solid-state image sensor.

This method is called an interline transfer method, and the signal charge of the photosensitive cheek portion 1 corresponding to a picture element is transferred to the vertical transfer line 4 within the vertical erasing time.

The vertical transfer line 4 may be a charge transfer line or may be a simple guide. In that case, when the signal charges accumulated in the photodetector 1 are transferred to the vertical transfer line 4, a switch is provided between them, and this switch is opened and closed by the vertical shift register.

Further, a conversion unit 6 is provided for injecting the charges on the vertical transfer line 4 into the horizontal charge transfer line.

By the way, electrical insulation of the photosensitive cheek part 1 where photoelectric conversion is performed has been achieved by a so-called channel stop region as shown in FIG. That is, the imaging section channel stop region 6 in FIG. 1 is provided under a relatively thick oxide film 9 (~1 micron) formed on the surface of the epitaxial layer 8 on the substrate 7, as shown in FIG. The impurity layer 1o of the same conductivity type as the layer 8 is 1017 to 101.
It is often formed with a concentration of about 8 ("F7+") and a thickness of about 1 to 3 microns. In the same figure, 11 is a gate oxide film, and 12 is a gate electrode for charge transfer. This is generally a channel stop. However, with this structure, the purpose of insulation cannot be achieved under general operating conditions, which will be described later.

That is, in order to achieve the necessary resolution, the picture element period needs to be a few microns, but since the width of this channel stop region 6 is large, it is necessary to maintain a large area ratio of the photosensitive cheek region 10. Have difficulty. That is, firstly, the width of the channel stop region 60 is such that it is difficult to form a thick oxide film with a small width, and secondly, it is difficult to form a high concentration diffusion region 7 between adjacent photosensitive cheeks 1. It has become clear that this is insufficient. That is, when the optical input is excessive, the potential barrier provided by the highly concentrated diffusion region becomes ineffective, and a so-called pluming phenomenon occurs. Therefore, a mechanism is required to actively discharge the charge overflowing the potential well of such a picture element portion.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and provides a solid-state imaging device that can narrow the width of the electrically insulating region between photosensitive parts and absorb and discharge excess light input charge and leakage charge. It is.

Structure of the Invention In the solid-state imaging device of the present invention, the signal charge accumulation portion of the adjacent photosensitive cheek is blocked by a groove formed on the surface of the semiconductor substrate, and the bottom of the groove has a conductivity type opposite to that of the semiconductor substrate. A diffusion region is formed and configured.

DESCRIPTION OF EMBODIMENTS FIG. 4 is a sectional view showing a first embodiment of the present invention. First, the semiconductor substrate 13 is made of single crystal silicon having a P type (100) orientation and a specific resistance value of 10 to 2 ohms, and the depth of the groove 14 is 3 to 8 microns. The drain 15 for absorbing excess carriers is a highly concentrated N-type diffusion layer, and is
A positive 6 voltage of 1o volts is applied. The surface layer 16 is the first
In the frame transfer type solid-state image sensor shown in the figure, in order to transfer charge in the direction perpendicular to the page, groove 1 is
5×1 on the surface of the semiconductor substrate 13 which becomes the photosensitive cheek area between 4
The buried channel consists of an impurity diffusion layer with a thickness of 1-2 microns and an impurity concentration of 0.015-2.times.10.sup.16 cm.sup.3. In this case, a gate electrode 17 for charge transfer is formed of low-resistance polycrystalline silicon on a gate oxide film 18 made of silicon dioxide and having a thickness of about 120 oi.

In the solid-state imaging device, it is preferable to remove the gate electrode 17 from the outermost layer of the photosensitive cheek part 1 in order to avoid loss due to absorption of light, and to stabilize the surface potential and protect the surface. It is preferable to provide a silicon nitride film 19 with a thickness of 500 to 1,500 layers, which has a high density and is difficult for surface impurities to pass through.

The film thickness relationship between the gate oxide film 18 and the surface layer 16 is set so as to maximize the transmission characteristics in the visible light range, especially in the blue to green light range. When the thickness of the gate oxide film is 18,500 and the thickness of the silicon nitride film 19 is 1,000, the reflectance in the i'+' region becomes a minimum value. This achieves a balance in terms of spectral sensitivity, which is important for improving the sensitivity of solid-state imaging devices.

Next, the operation of the embodiment shown in FIG. 4 will be explained. A positive bias is applied to the N-type drain 16 with respect to the P-type substrate 13 . Therefore, even if excess charge is generated in the substrate 13, it is absorbed and discharged by the drain 16, thereby preventing blooming. If the drain 15 is formed deeper than the substrate 13 as in this embodiment, excess charges generated in the deeper portion of the substrate 13 can be effectively absorbed. Therefore, excessive charges are prevented from flowing between the photosensitive areas. Here, when the drain is formed on the same plane as the photosensitive cheek as in the past, excess carriers generated in the deep part of the substrate move toward the substrate surface, and before being absorbed by the drain, the adjacent photosensitive Blooming could not be sufficiently prevented due to excessive charge flowing into the cheek area. In this way, the present invention can sufficiently prevent the inflow of excess charges.

FIG. 6 is a sectional view showing a second embodiment of the present invention. In this example, an N-type substrate 2o and a P-type epitaxial layer 21 formed on this N-type substrate 20 form a composite substrate. The substrate 15 used has a specific resistance of about 60 to 2 ohm. A reverse bias is then applied between the epitaxial layer 21 and the substrate 20. In this case, since there is a groove 14 between the adjacent photosensitive cheeks 1, the excited signal charges will not leak to the adjacent photosensitive cheeks 1. When excessive excitation occurs, the excitation simply builds up on the substrate 20 side before overflowing to the adjacent photosensitive cheek 1, resulting in a reverse current. Therefore, leakage signal charges between adjacent picture elements are almost completely blocked.

By the way, this is the case when the substrate 20 is of the same conductivity type as the epitaxial layer 21, that is, the P type and the concentration is ten times or more higher than that of the epitaxial layer 21.

In this case, by performing a heat treatment step that increases the rate of recombination of carriers within the substrate 2o, it is possible to prevent diffusion of carriers generated in the substrate 2o and suppress leakage signal charges.

FIG. 6 is a diagram showing the manufacturing process of the solid-state image sensor of the present invention. First, a silicon dioxide film 22 and a silicon nitride film 23 are formed on the surface of the epitaxial layer 21, and portions of the silicon dioxide film 22 and silicon nitride film 23 that will become isolation regions are removed.

Thereafter, the surface of the epitaxial layer 21 is etched using the silicon nitride film 23 as a mask to form a groove 24 (FIG. 6a).

Next, the surface of the epitaxial layer 21 is oxidized by about 1,000 degrees to form an oxide film 25. Next, the groove 24
Phosphorus or arsenic ions are implanted into the bottom to form a drain 26 for absorbing excess carriers (FIG. 6b).
. After that, polycrystalline silicon 27 is deposited,
Fill the groove 24. A photoresist 28 is poured into the recess above the groove 24 (FIG. 6C). Thereafter, the deposited polycrystalline silicon 27 is removed by plasma etching. Then, the etching is stopped at the point where the polycrystalline silicon 27 of the groove 24 is approximately on the same plane as the photosensitive cheek. Then, an oxide film 29 is formed on the groove portion 24 (FIG. 6d). After that, it is manufactured using almost the same steps as for forming a normal charge transfer element.

Effects of the Invention The solid-state imaging device of the present invention described in detail above requires less area for separating light-sensitive parts, and a high-resolution solid-state imaging device having high-density light-sensitive cheek parts can be obtained.

At the same time, it is possible to completely eliminate operational failures caused by leakage signal charges when a large amount of light is input, which is a particular problem with solid-state image sensors.

[Brief explanation of drawings]

Figure 1 is a two-dimensional layout diagram of a frame transfer type COD solid-state image sensor, and Figure 2 is an interline type ca
n A two-dimensional layout diagram of a solid-state image sensor, FIG. 3 is a cross-sectional view of main parts showing separation between conventional light-sensitive parts, and FIGS. 4 and 6 are cross-sections of a solid-state image sensor according to an embodiment of the present invention. Figure 6a
"-d is a sectional view of the manufacturing process of the solid-state image sensor according to the present invention. 14...Groove portion, 15...Drain for absorbing excess carriers. Name of agent: Patent attorney Satoshi Nakao Man and 1 other judge
1 Figure Crane 2 Figure /, 5 /, 5 S Figure

Claims (2)

[Claims] (1) A plurality of gate electrodes arranged in parallel to each other on the surface of a semiconductor substrate with an insulating layer interposed therebetween, and a plurality of grooves arranged on the surface of the semiconductor substrate perpendicular to the gate electrodes. A solid-state image pickup device, comprising: a region having a conductivity type opposite to that of the semiconductor substrate provided immediately below the bottom of the groove, and a photosensitive cheek portion being formed between adjacent grooves. (2) An epitaxial layer having a conductivity type opposite to that of the substrate is provided on the semiconductor substrate, and a groove extending from the surface of the epitaxial layer to the semiconductor substrate is formed. The solid-state imaging device according to item 1.