JPS6328076A - Semiconductor radiation detector - Google Patents

Abstract

PURPOSE:To avoid cross-talk and improve energy resolution by providing a shielding grid on a radiation incident surface. CONSTITUTION:A semiconductor substrate 6 is made of Si, GaAs, CdTe, HgI or the like and charge clouds (a) of electron-hole pairs are created in the substrate 6 by an incident radiation. On the radiation incident surface of the semiconductor substrate 6, charge collecting electrodes 8 which collect the charge clouds (a) and a shielding grid 9 between the collecting electrodes 8 are provided. The shielding grid 9 is made of material (such as lead Pb or tungsten W) which has high radiation blocking capability and is composed of a shielding layer 9a and an insulating layer 96 which insulates the shielding layer 9a from the charge collecting electrodes 8. A common electrode 7 is provided so as to face the charge collecting electrodes 8 with the semiconductor substrate 6 between.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor radiation detector used for detecting the amount of transmitted radiation in a diagnostic X-ray transmission imaging device or a non-destructive inspection device.

Conventional technology The sensitive layer (layer that can obtain an output signal when irradiated with radiation) of a semiconductor substrate used in a semiconductor radiation detector needs to be thick enough to sufficiently absorb incident radiation. In a semiconductor radiation detector equipped with a semiconductor substrate having such a sensitive layer thickness, crosstalk occurring between charge collecting electrodes becomes a problem. Crosstalk will be explained with reference to FIG. A voltage is applied between the common electrode 102 and the charge collecting electrode 103 of the semiconductor substrate 101 . Here, in the P-type semiconductor substrate, the common electrode 102
A case will be described in which a negative voltage is applied to the charge collection electrode 103 and a positive voltage is applied to the charge collection electrode 103. When radiation is incident from the front surface of the paper toward the back surface as indicated by arrow a in FIG. 4, the semiconductor substrate 1
In the case of an OP type semiconductor substrate in which a charge cloud of electron-hole pairs is generated by photoelectric absorption in a depletion region within 01, electrons, which are minority carriers, are collected by the charge collection current %103. 1 only 10
By applying a voltage to the common electrodes 1o2 and 103, an electric field E is generated and the charge cloud expands the radius of the charge cloud.
The electric current moves toward the charge collecting electrode 103, is collected by the charge collecting electrode 103, and is output as a pulse current. However, when a charge cloud C is generated in the lower part between the charge collection electrodes 103, the lines of electric force are separated in the direction of the adjacent charge collection electrodes 103a and 103b, and accordingly, the charge cloud C is also affected by the adjacent charge collection electrodes. Collector electrode 103a.

The data is divided and collected in 103b. As a result, this charge collecting electrode 103 outputs a minute pulse current. In other words, the output signal is a pulse current obtained from the charge cloud generated under the charge collection electrode 103a and the charge cloud C generated between the charge collection electrodes 103a and 103t. Of this pulse current, The fluctuation of the minute pulse current obtained by the charge cloud C makes it impossible to produce an output proportional to the energy of the radiation. The generation of minute pulse signals accompanying this division and collection is called crosstalk.

In other words, when crosstalk occurs, a pulse output signal proportional to the incident radiation energy cannot be obtained, leading to a problem in which the energy resolution decreases.

As a structure to prevent this crosstalk, Japanese Patent Laid-Open No. 58-
No. 142283 is known. This configuration will be explained with reference to FIG. The semiconductor substrate 1 has spatially separated unit detection regions 1a, and the unit detection regions 1a are partitioned by a material having a high blocking ability against radiation, such as W (tungsten) spacers 5. The semiconductor substrate 1 is provided with an electrode 2 that collects a charge cloud generated by photoelectric absorption within the semiconductor substrate 1, and an electrode 3 is provided opposite to this electrode 2 with the semiconductor substrate 1 interposed therebetween. , a mount plate 4 is attached to the lower part of this electrode 3. The incident radiation a is guided by the W spacer 5 to the unit detection area 1&, thereby preventing the charge cloud from being split and collected on the adjacent electrode 2, thereby preventing crosstalk.

Problems to be Solved by the Invention However, in the above-mentioned conventional structure, since the semiconductor substrate must be cut or grooved, the following problems arise.

(1) Approximately 5 to 1oO from the machined surface due to mechanical strain
Many trap levels are generated in the μm range, and charges generated in the semiconductor substrate by radiation are trapped in these trap levels, and the charge cloud generated near the processed surface is sufficiently absorbed by the charge collecting electrode 2 ( Figure 6) is not included.

Operation) Due to the existence of a trap level near the machined surface, the electric field distribution near the machined surface changes, and the electric field is no longer sufficiently applied to the charge cloud (charge), so that the charge cloud is sufficiently collected at the electrode 2. Not done.

From the above points, semiconductor radiation detectors that have been cut or grooved can be divided into unit detection areas well, but charge traps occur due to the trap level near the processed surface, and the output (current) signal is This caused variations in current values, causing a decrease in energy resolution.

In addition, in order to increase the energy resolution, it is necessary to increase the sensitive thickness of the semiconductor substrate, and the radiation a is made to enter parallel to the electrode 2.3 from the front surface of the paper toward the back surface, so that the effective incident surface ( surface on which radiation can be effectively incident)
is small, and the required effective incident surface was constructed by laminating layers.

The present invention solves the above problems, and aims to provide a semiconductor radiation detector that prevents crosstalk between charge collecting electrodes, has a large effective incident surface, and has excellent energy resolution.

Means for Solving the Problems In order to achieve this object, the semiconductor radiation detector of the present invention includes a plurality of charge collecting electrodes disposed on the radiation incident surface side of the semiconductor substrate, and the charge collecting electrodes A shielding grid is provided in between, and a common electrode is provided opposite to the charge collecting electrode with the semiconductor substrate interposed therebetween.

Operation With the above configuration, a pseudo-insensitive layer is formed in the shielding grid corresponding portion of the semiconductor substrate, and within this pseudo-insensitive layer,
The incidence of radiation and the generation of electric charges due to radiation are eliminated. As a result, crosstalk between the charge collecting electrodes can be eliminated. Furthermore, by eliminating crosstalk, which is a cause of a decrease in energy resolution, a semiconductor radiation detector with excellent energy resolution can be realized. Furthermore, by receiving radiation vertically on the charge collecting electrode, it is possible to increase the effective incidence surface. Embodiment 1 Below, embodiments of the present invention will be described with reference to FIGS. 1 to 3.

In FIGS. 1 to 3, the semiconductor substrate 6 is made of Si, Ga,
A charge collection electrode 8 is formed from As, CdTe, HgI, etc., and generates an electron-hole pair electric device a by the incident radiation.On the radiation incident surface side of the semiconductor substrate 6, there is a charge collection electrode 8 that collects the electric device a. A shielding grid 9 is provided between the charge collecting electrode 8 and the charge collecting electrode 8.

The shielding grid 9 is made of a material (lead Pb, tungsten W, etc.) that has a high ability to block radiation. The shielding grid 9 is composed of a shielding layer 9a and an insulating layer 9b, and the shielding layer 9a and the charge collecting electrode 8 are insulated by the insulating layer 9b.

A common electrode 7 is provided opposite the charge collecting electrode 8 with a semiconductor substrate 6 interposed therebetween.

The operation of the above configuration will be explained below.

Note that the description will be given for the case where the semiconductor substrates are made of a P-type semiconductor.

Due to the incident radiation, an electric device a is formed inside the semiconductor substrate 6.
occurs. The minority carriers in this semiconductor substrate 6 are electrons, and the movement of the electrical device a is considered as electrons. By applying a positive voltage between the charge collecting electrodes and a negative voltage to the common electrode 7, an electric field E is applied from the charge collecting electrode 8 to the common electrode 7, and the electric device a is connected to the charge collecting electrode. It diffuses and moves in eight directions, is collected by the charge collecting electrode 8, and is output as a pulse current signal.

The radiation irradiated onto the shielding grid 9 is blocked from entering the semiconductor substrate θ, and this shielding grid 9
A pseudo-insensitive layer is formed on the semiconductor substrate 6 under the semiconductor substrate 6, in which no electrical device is formed. Therefore, no electric device is generated between the charge collecting electrodes 8, and crosstalk between the charge collecting electrodes 8 is eliminated.

Next, the movement of the electric device a that occurs at the boundary between the sensitive layer C and the pseudo-insensitive layer under the charge collecting electrode 8 will be explained. This electric device is a semiconductor substrate θ in the direction of the charge collection electrode 8,
Spread and move.

In the vicinity of the charge collecting electrode 8, the point where the charge density is 10% of the charge density at the center of the electric device a is defined as the end of the electric device a, and the distance from the center to the end is defined as the charge cloud major radius R (the third (Fig. 2), when the large radius R of the charge cloud amount and the width L of the shielding grid 9 (Fig. 2) satisfy the relationship L>2R, the The electric device a is not affected by the electric field of adjacent electrodes and is divided into charge collecting electrodes 8=L.

8b will no longer be collected. In other words, no crosstalk occurs.

According to the above-mentioned embodiment, since the shielding grid is provided, no electrical equipment is generated in the pseudo-insensitive layer at the bottom of the shielding grid, and furthermore, the boundary between the sensitive IC and the pseudo-insensitive layer is The resulting electric device is not divided and collected by the charge collecting electrode 8. Crosstalk is therefore prevented.

The shielding grid 9 is made up of a conductive shielding layer 9a and an insulating layer 9b, and has a cubic shape.
The shape of the shielding grid 9 may be as shown in FIG. 3, and the shape of the shielding layer 9 may be cylindrical (for example, wire-shaped) (FIG. 3A). The shape of the grid 9 may be a cube, and the radiation blocking ability may be adjusted by changing the thickness l of the shielding layer 9a (FIG. 3B). Further, the shielding grid 9 may be formed only of an insulating material (FIG. 3C).

Effects of the Invention As is clear from the above description of the embodiments, according to the semiconductor radiation detector of the present invention, since the shielding grid is provided on the radiation incident surface side, radiation does not enter between the charge collecting electrodes, The generation of tortoise devices is prevented and crosstalk is prevented. By preventing crosstalk, it is possible to improve energy resolution.

Furthermore, the radiation enters the charge collecting electrode vertically, making it possible to increase the effective incident surface of the semiconductor substrate. Furthermore, it is possible to realize a semiconductor radiation detector that does not require any mechanical processing on the semiconductor substrate, has no problem such as generation of trap levels, and has excellent radiation detection ability.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the semiconductor radiation detector of the present invention, FIG. 2 is a sectional view of the same essential part, and FIGS. 3A, B, and C are various shielding grids of the same semiconductor radiation detector, respectively. 4 is a sectional view illustrating crosstalk, and FIG. 5 is a sectional view showing the configuration of a conventional semiconductor radiation detector. 06...Semiconductor substrate, 7...・・・
...Common electrode, 8...Charge collection electrode, 9...
...Name of shielding grid 0 agent Patent attorney Toshio Nakao and one other person 6-+ guide sanmaku tentative figure 1 8-charge'' to the Nth power to pole q-i 7 wt figure 3 figure 4 Figure 5 Φ flag M8 Eihachi elbow direction

Claims (2)

[Claims] (1) A semiconductor substrate that causes ionization when radiation is incident, a plurality of charge collection electrodes arranged on the radiation incident surface side of the semiconductor substrate, and transmission of radiation provided between the charge collection electrodes. What is claimed is: 1. A semiconductor radiation detector comprising: a shielding grid that makes it impossible to perform a charge collecting electrode; and a common electrode that faces the charge collecting electrode with the semiconductor substrate interposed therebetween. (2) The semiconductor substrate is made of carbon (Si), gallium arsenide (G
2. The semiconductor radiation detector according to claim 1, wherein the semiconductor radiation detector is constructed using any one of aAs), cadmium telluride (CdTe), and mercury iodide (HgI).