JPS62145867A - image sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a line-reading image sensor that reads document information with high resolution and has a plurality of columns of pixels and an output line in each column.

BACKGROUND ART In a photodiode or phototransistor in which each pixel has a Pn-junction as a light-receiving part, when a light-receiving element consisting of a pixel row having the structure shown in FIG. Because crosstalk occurs, Figure 3 (b)
It is customary to separate each pixel by using a P-type semiconductor region 11 as shown in FIG.
Generally, elements are separated so that the Pn junction is reverse biased as shown in FIG. Such separation is performed for all elements on the same semiconductor substrate.

Problems to be Solved by the Invention As shown in Figure 3, in the normal bipolar IC process using a reverse-biased Pn junction, acceptor impurities are generally diffused after forming an n-type semiconductor 3 having a relatively low impurity concentration. A P-type semiconductor portion 11 is then formed to perform element isolation, but it is necessary to provide a sufficient margin on the mask to prevent short circuit with the P-type semiconductor region 9 that will be formed in a subsequent step. As described above, securing a sufficiently large margin is disadvantageous in integrating pixels at high density.

Further, when driving the buried n-type semiconductor portion shown in 12 at the same potential, it is necessary to conduct wiring using metal or other low resistance material on the surface, which further reduces the degree of integration.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention aims to reduce the difference between the optical information elements when driving them at the same potential as the adjacent light-receiving elements forming the n-type semiconductor region on the substrate side. Separation is achieved by diffusing a high-density n-type semiconductor region into a low-concentration n-type semiconductor region to reach a buried diffusion low-concentration n-type semiconductor region.

Function Since each photodetector is surrounded by a low-resistance n-type semiconductor region, carriers generated in one photodetector will not flow into other adjacent photodetectors, which is normally achieved using a bipolar IC process. reverse bias P
By forming an n-junction around each element, crosstalk of optical signals between each light receiving element can be prevented, similar to when element isolation is performed.

In addition, even though the impurity concentration is inherently low, part of the n-type semiconductor region remains the same n-type and has a lower resistance, so compared to converting to a P-type semiconductor for general device isolation, Since there is no need to provide a large margin with respect to the P-type semiconductor region formed within, the process can be easily formed and finely formed.

Furthermore, since this low-resistance n-type semiconductor layer exists up to the surface, an electric field is applied in the horizontal direction even to the low impurity concentration region extending to the surface, making it possible to capture and utilize more photoexcited carriers.

Embodiment FIG. 1 shows +al, and FIG. 1(b) shows an embodiment of the light receiving element of the image sensor of the present invention. (81 is a mountain representing a structural example) is a circuit symbol. Three light-receiving elements are shown, each consisting of a photodiode consisting of a Pn junction.
1 is a P-type semiconductor layer forming an anode, and 3 is a low impurity concentration N-type semiconductor layer forming a cathode. 2 and 4
are both made of low-resistance n-type semiconductors, connect the cathodes 3 of the three photodiodes in the figure, and form a common cathode electrode 7.
Among them, the low-resistance n-type semiconductor layer 2 surrounds each light-receiving element, so the photoexcited carriers generated in one light-receiving element do not flow into the adjacent light-receiving element. . In other words, instead of forming this low-resistance n-type semiconductor 2, a P-type semiconductor 11 is formed as shown in FIG. It has the effect of preventing crosstalk of optical signals between elements.If there is no low resistance n-type semiconductor region 2 as shown in FIG. It will leak.

In FIG. 1, the P-type semiconductor region 1 forming the anode and the N-type semiconductor region 2 for crosstalk prevention are semiconductors of different shapes, so even if these two-head regions are somewhat close together due to mask design, A type semiconductor region 2 which has a low risk of short-circuiting and which is a part of the cathode 3 which is originally a semiconductor with a low impurity concentration and the same shape, and which is further diffused with the same type of impurity to lower the resistance and prevent cross-crossing. Therefore, there is no need to provide a large margin on the mask.

Furthermore, since the n-type semiconductor region 2 is electrically connected within the substrate by the buried n-type semiconductor layer 4, there is no need for surface wiring, which also contributes to higher density of the light-receiving elements.

Furthermore, an electric field is created in the horizontal direction on the surface of the low impurity concentration n-type semiconductor region 3 which is narrowed between the P-type semiconductor region 1 and the low-resistance n-type semiconductor region 2. Excited carriers caused by the emitted light are also efficiently collected.

In the sensor shown in FIG. 1, optical information signals can be simultaneously read from each photodiode to each anode terminal 6 by accessing the common cathode side terminal 7, and the anode terminal 6 for one photodiode can be read out simultaneously. Then, the optical information signal of the photodiode is transmitted to the common cathode side terminal 7.
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FIG. 2 shows an example in which an n-type semiconductor region 8 serving as an emitter is further formed in the P-type semiconductor region 1 serving as an anode shown in FIG. 1, and the light-receiving element is changed from a photodiode to a phototransistor. (Al is a structural diagram, and To is a diagram symbolically representing the circuit. In the figure, 10 is an emitter terminal, and 13 is a common collector terminal, which correspond to the anode terminal 6 and common cathode terminal 7 in FIG. 1, respectively, and there is no difference in usage.

In the examples shown in FIGS. 1 and 2 above, the problem of cross !-- which occurs in FIG.
) The light-receiving elements can be arranged closer together than in the case where the elements are separated by Pn junctions.

FIG. 4 (al shows a plan view of a further developed configuration example of the image sensor shown in FIG. 1).

Figure 4 (bl is the circuit symbol. Figure 1 (
The sectional view a) corresponds to the case where the element is cut at a point as shown by a dashed line 14 in FIG. 4(a).

In Figure 4 fat, 1 is a P-type semiconductor region, 2 is a low resistance n
In this figure, three of the islands 15 consisting of each low-concentration impurity n-type semiconductor region separated by a Pn junction are
It prevents crosstalk between the photodiodes and is connected to the common cathode side terminal 7 via a low resistance buried n-type semiconductor layer. A window 19 indicated by a broken line is a window through which the surface wirings 16.17, 18.7 indicated by diagonal lines are in contact with the semiconductor. An image sensor consisting of three rows of light-receiving elements as shown in this figure, one row of light-receiving elements whose anodes are connected to a common anode line 16, one row of light-receiving elements whose anodes are connected to a common anode line 17, and a common anode line. By adding different color filters to the light-receiving element rows to which the anodes are connected to 18, three different output lines 16 for each color are created.
．． A color line image sensor capable of outputting video from i7°18 can be realized. If the image sensor shown in FIG. 4 is further increased in number of light-receiving elements both vertically and horizontally, an area sensor is also possible.

Effects of the Invention As described above, according to the present invention, it is possible to reduce the margin between light-receiving elements sharing one terminal and to arrange the light-receiving elements in high density using an extremely simple method.
There is no crosstalk between the light-receiving elements, and photo-excited carriers generated in the portion exposed to the semiconductor surface of the low impurity concentration n-type semiconductor region where photo-excited carriers are generated can be effectively captured, making it extremely practical.

[Brief explanation of drawings]

Figure 1 (al is a cross-sectional view showing an embodiment of the present invention in which a photodiode is used as a light-receiving element, Figure 1 (b) is a symbol diagram of the same circuit, Figure 2 (al is a cross-sectional view in which a phototransistor is used as a light-receiving element) A sectional view showing an embodiment of the present invention, FIG. 2 fbl is a symbol diagram of the same circuit, FIG.
FIG. 2 is a cross-sectional view of an image sensor in which elements are separated by bonding. FIG. 4+al is a plan view showing a further developed embodiment of the image sensor shown in FIG. 1, and FIG. 4(1)) is a symbol diagram of the same circuit. 4...Low resistance buried n-type semiconductor layer, 5...
- P-type semiconductor substrate, 9...P-type semiconductor region. Name of agent: Patent attorney Toshio Nakao
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Claims (1)

[Claims] A reading pixel is a photodiode or a phototransistor having a buried layer serving as one terminal, and a plurality of consecutive pixels constitute one pixel group, and the pixels included in each pixel group have a buried layer. A common terminal for the pixel sets is formed, and a low resistance semiconductor region of the same type as the buried layer is formed between the pixels in each pixel set, and this is made to reach the buried layer, so that the optical signal current between the pixels is Image sensor that prevents mixing.