JPH0252995B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation measurement element. More specifically, the present invention relates to a radiation measuring element that can detect radiation energy efficiently and with high spatial resolution, and that is integrated, smaller, lighter, and hybridized.

In recent years, with advances in the technology of medical devices that use radiation such as CT and various radiation measurement devices, the measurement of radiation intensity distribution has become an important issue. As a measuring device for measuring the intensity distribution of radiation, there is a device that measures the radiation intensity of each section by combining an ionization chamber composed of a large number of sections, but these are susceptible to vibration and have a complicated structure. It was large and heavy, making it difficult to handle and manufacture.

Therefore, there has been a desire for a radiation measuring element that is smaller and lighter and capable of measuring distribution.

In this regard, the inventors of the present invention focused on semiconductor photodetecting elements. Semiconductor photodetecting elements are conventionally known as visible light detecting elements, but they also have some sensitivity to radiation. Since the sensitive portion can be easily fractionated into an array when manufacturing a semiconductor photodetecting element, it is considered to be suitable as an instrument for measuring intensity distribution. However, the radiation measurement sensitivity obtained when such an array type semiconductor photodetector element is used is still insufficient.

Furthermore, in order to improve the measurement sensitivity of the array type semiconductor photodetecting element, on its radiation incident surface,
A phosphor (scintillator) layer, similar to that used in ordinary scintillation counters, is bonded with adhesive to convert part or most of the radiation into visible light, which is highly sensitive to semiconductor photodetectors, increasing measurement sensitivity. It is also possible to do so. However, when a scintillator is simply combined with an array type semiconductor photodetector like this, the converted visible light from the scintillator is subject to a crosstalking phenomenon (the converted visible light is dispersed laterally from the direction of incidence of the incident radiation). ), the light does not efficiently enter the sensitive part of the photodiode corresponding to the incident position, and as a result, the measurement of the intensity distribution becomes unclear and cannot be put to practical use. In addition, to improve this point, it is possible to prevent the crosstalk phenomenon by inserting a large number of partition plates (for example, heavy metal plates, etc.) into the scintillator layer, but there is a limit to the thinness of the width of the partition plates themselves. There is a large amount of dead space, and even if the resolution increases slightly, the overall detection efficiency is insufficient.
First, it is extremely difficult to manufacture and cannot be put to practical use.

This invention has been made to solve these conventional problems. The inventors of the present invention discovered that it is possible to form a scintillator thin layer having a fine needle-like partition structure in an array type semiconductor photodetector, and furthermore, it is possible to form a scintillator thin layer having a fine needle-like partition structure in an array type semiconductor photodetecting element, and furthermore, it is possible to use a partition plate etc. in a device using such a scintillator thin film. This invention was achieved by discovering the fact that the resolution is significantly improved, and that the radiation measurement element can be made smaller and lighter.

Thus, according to this invention, p-type (or n-type)
A large number of fine needles extend approximately vertically through an electromagnetic wave transparent film onto an array type semiconductor photodetecting element formed by dividing a plurality of n-type (or p-type) semiconductor regions on the surface of a semiconductor substrate. A radiation measuring element is provided, which is characterized in that it is formed by closely forming a scintillator film having a partitioned structure.

The most distinctive feature of this invention lies in the combination of an array type semiconductor photodetector element and a scintillator film having a specific structure. It is known that a scintillator film having the above-mentioned specific structure, that is, a large number of fine needle-like partition structures extending approximately vertically, is used as a luminescent screen in high-quality television picture tubes such as X-ray image tubes ( Special Public Service 1977-
19029) is directly combined with a semiconductor device such as the present invention, which can be said to be novel in itself.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The radiation measuring device of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic structural explanatory diagram showing a radiation measuring element 1 which is a specific example of the present invention. In the figure, a radiation measuring element 1 of the present invention is an array type semiconductor photodetecting element, such as a photodetector, in which four n-type semiconductor regions 3 are formed in sections on the surface of a p-type semiconductor substrate 2 by doping with phosphorus, arsenic, etc. On top of the diode, a SiO ₂ vapor-deposited film 4 with a thickness of about 0.1 μm, which transmits radiation and visible light well, is placed.
A scintillator film 5 made of CsI (Tl) with a thickness of 160 μm is closely formed, and the entire scintillator film 5 is covered with an aluminum vapor-deposited protective film 6 to protect the outer surface of the scintillator film 5 and reflect internally generated fluorescence. It will be done. The scintillator film 5 is
CsI in which a large number of fine acicular sections 51 extending approximately perpendicularly to the array type semiconductor photodetecting element are integrated.
(Tl) It is composed of crystals. Note that each n-type semiconductor region of the array type semiconductor photodetecting element is configured to function as a separate channel for radiation measurement, and is connected to an indicating instrument.

In the radiation measuring element 1 having the above configuration, the radiation such as the X beam that travels in the direction of the arrow passes through the protective film 6 and enters the inside. At this time, a part of the radiation passes through the scintillator film 5 and enters the array type photodiode, and the other part is converted into visible light by scintillation within the scintillator film 5 and is transmitted to the array type semiconductor photodetecting element. Therefore, the array type semiconductor photodetecting element detects both radiation and converted visible light. Therefore, the detection efficiency is improved compared to one without a scintillator film.

Furthermore, since the scintillator film 5 consists of a large number of fine needle-like sections 51 extending approximately vertically, the visible light generated by scintillation is reflected within the sections as shown in FIG. The light is efficiently guided to the sensitive portion (for example, the n-type semiconductor region) of the semiconductor photodetecting element, and no crosstalking phenomenon occurs. Therefore, the radiation intensity distribution with excellent resolution can be measured with almost no interference between the sensitive parts of the photodiodes.

Although a pn junction type is used as the array type semiconductor photodetecting element in this invention, it may be a PIN junction type or a so-called surface barrier type that utilizes metal-semiconductor contact. The semiconductor is not limited to silicon, and other materials such as germanium and various compound semiconductors may also be used. Among these, it is preferable to reduce the impurity concentration of the base as much as possible and to improve the depletion layer generated near the pn junction as much as possible.

A scintillator film is closely formed on the array type semiconductor photodetecting element.

The material of the scintillator film of this invention includes inorganic scintillators used in ordinary scintillation counters, such as NaI (Tl), CsI (Tl),
Examples include KI (Tl), ZnS (Cu), and _CdWO4 , and in some cases, an organic scintillator may be used.

The scintillator film having a specific structure of the present invention can be obtained by forming, for example, an electromagnetic wave-transmitting film such as a SiO ₂ film that can transmit radiation and visible light on the surface of a semiconductor photodetecting element by vapor deposition, and then depositing the desired film on the surface of the semiconductor photodetecting element. It is obtained by forming a film by vapor deposition of a scintillator in a heated state, and then cooling it naturally to generate vertical cracks due to the difference between the coefficient of thermal expansion of the SiO ₂ film and that of the scintillator film. More specifically, for example, an electromagnetic wave detection diode on which a thin SiO ₂ film of about 0.1 to 1 μm is formed is heated to 200°C in advance.
While maintaining this at 200℃ under vacuum, the thickness is 20 ~
A scintillator film of about 500 μm is formed by vapor deposition, and then naturally cooled to form a scintillator film with a width of 5 to 50 μm.
It is obtained by creating a large number of fine needle-like compartment structures of about 20 μm in size by cracking.

The outer surface of the scintillator membrane of the present invention is usually
It is preferable to form a protective film as described above to prevent the influence of moisture, etc., but this protective film must be able to transmit the radiation to be measured.
Furthermore, it is preferable to use a film that reflects visible light from the outside because it can reduce radiation measurement errors. Further, from another point of view, it is preferable to use a visible light reflective protective film in order to prevent the converted visible light from being scattered to the outside due to scintillation within the scintillator film.

From this point of view, on the outer surface of the scintillator membrane,
Most preferably, a deposited thin film of a low density metal such as aluminum as described above is formed.

In radiation measurement, the radiation irradiation surface is usually set on the scintillator film side as shown by the arrow in Figure 1, but it may also be set on the bottom side of the semiconductor photodetector element, and similar radiation measurements can be performed. can be done.

As described above, since the radiation measurement element of the present invention combines an array type semiconductor photodetection element and a scintillator film having a specific structure, the radiation detection efficiency is improved and the resolution is also excellent. Furthermore, like a conventional scintillation counter,
Since it does not require a scintillator layer of 1.5 to 3 mm and is formed integrally with the semiconductor element, it is small, lightweight, and convenient in manufacturing and handling. Arrays of array type electromagnetic wave detection diodes can be easily fractionated and formed in large numbers using phosphorography, thereby making it possible to appropriately increase the resolution. Therefore, CT, which requires high spatial resolution,
It is extremely useful as a measuring element in measuring the intensity distribution of radiation such as in a line image detector.

This invention will be explained below with reference to Examples.

Example 1 CsI with fine acicular compartment structure as shown in Figure 1
Using the radiation measuring instrument of the present invention on which a (Tl) scintillator film (160 μm thick) was formed, X-rays of various energies were measured and the output per channel was investigated. The output of a similar photodiode without a mintilator film was also investigated and compared.

The results are shown in FIG. In the figure, A shows the output from the radiation measuring instrument of this invention, and B shows the CsI
(Tl) Shows the output before crystal bonding (comparative example). Further, FIG. 4 shows changes in the output ratio (A/B) based on the data in FIG. 3.

As shown in these figures, the X-ray tube voltage V
The output at V = 50 kV is 1.35 times that of one without a scintillator film, and at V = 100 kV it is 2.8 times higher, indicating an increase in sensitivity due to improved radiation detection efficiency, especially for hard X A remarkable increase in sensitivity is seen in the lines.

Example 2 Interference between radiation detectors, that is, between adjacent elements of a photodiode array was investigated. first,
As shown in FIG. 5, in order to examine the interference between two n-type semiconductor regions 3a and 3b with an interval of 0.3 mm, a 4 mm thick lead plate 8 is placed on the radiation receiving surface at an interval of about 1 mm to block the radiation, and the blocking position is were set to C and D, and the blocking effect on the blocked n-type semiconductor region 3a was measured using the measuring device 7, and the degree of crosstalking phenomenon within the scintillator film was investigated. As a result, it was found that in any cut-off state, almost no influence was observed on the n-type semiconductor region 3a, and almost no cross-talking phenomenon was observed within the scintillator film.

[Brief explanation of drawings]

FIG. 1 is a schematic structural explanatory diagram showing a specific example of the radiation measuring element of the present invention, FIG. 2 is an enlarged view of the main part of FIG. 1, and FIGS. 3 and 4 are the radiation measuring element of the present invention. FIG. 5 is a graph showing the radiation detection output according to the present invention together with a comparative example. DESCRIPTION OF SYMBOLS 1... Radiation measurement element, 2... P-type semiconductor substrate, 3, 3a, 3b... N-type semiconductor region, 4...
SuO ₂ vapor deposited film, 5... scintillator film, 51...
Fine acicular section, 6... Protective film, 7... Measuring device, 8
……lead plate.

Claims (1)

[Scope of Claims] 1. An electromagnetic wave transmitting layer is formed on an array type semiconductor photodetecting element formed by dividing a plurality of n-type (or p-type) semiconductor regions on the surface of a p-type (or n-type) semiconductor substrate. 1. A radiation measuring element comprising a scintillator film closely formed with a scintillator film having a plurality of fine needle-like compartment structures extending substantially vertically through the film. 2. The measuring element according to claim 1, wherein the outer surface of the scintillator film is coated with a protective film that can transmit radiation to be measured. 3. The measuring element according to claim 1 or 2, wherein the outer surface of the scintillator film is coated with a protective film capable of reflecting visible light due to scintillation.