JP2000284053A - Radiation detector element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector element having a uniform protective film easy to produce for moisture proof of a scintillator. SOLUTION: The radiation detector element comprises photo detector elements 2 arranged two-dimensionally on a board 1 and a scintillator 7 of CsI columnar crystals deposited on the detector elements 2. A parylene organic film 9 is formed, covering the top and side face of the scintillator 7 and extending to a board 1 part outside it, and the film 9 intrudes into at least top gaps among gaps of the columnar crystals of the scintillator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a radiation detecting element,
In particular, the present invention relates to a radiation detection element having a large-area light receiving unit used for medical X-ray photography and the like.

[0002]

2. Description of the Related Art In medical and industrial X-ray photography, conventionally, X-rays are used.
Although a line-sensitive film has been used, a radiation imaging system using a radiation detecting element has become widespread in terms of convenience and preservation of a photographed result. In such a radiation imaging system, two-dimensional image data due to radiation is acquired as an electric signal using a radiation detecting element having a plurality of pixels, and this signal is processed by a processing device and displayed on a monitor. . A typical radiation detecting element has a structure in which a scintillator is arranged on a photodetector arranged one-dimensionally or two-dimensionally, and incident radiation is converted into light by the scintillator and detected.

A typical scintillator material, CsI
Is a hygroscopic material, which absorbs and dissolves water vapor (moisture) in the air. As a result, there is a problem that the characteristics of the scintillator, particularly the resolution, are deteriorated.

[0004] As a radiation detecting element having a structure for protecting a scintillator from moisture, a technique disclosed in Japanese Patent Application Laid-Open No. 5-196742 is known. With this technology,
The scintillator is protected from moisture by forming a moisture-impermeable moisture barrier above the scintillator layer.

[0005]

However, in this technique, it is difficult to make the moisture-proof barrier on the outer peripheral portion of the scintillator layer adhere to the substrate of the radiation detecting element, and in particular, a large-area radiation detecting element used for chest X-ray photography or the like. However, since the length of the outer peripheral portion is long, the moisture-proof barrier is easily peeled off, so that the scintillator layer is not completely sealed, and moisture penetrates into the scintillator layer to deteriorate its characteristics.

Further, in this technique, the moisture seal layer is formed after the thin film layer and the light reflection layer are formed. However, since the thin film layer and the light reflection layer are formed only on the upper surface, each layer is formed. No consideration is given to moisture prevention on the side of the scintillator during the process.

In this technique, the moisture sealing layer of the moisture barrier is coated with a silicone potting material or the like in a liquid state on the scintillator layer, or the moisture sealing layer is provided inside a window material provided on the light receiving surface side of the radiation detecting element. A method of fixing the moisture sealing layer by disposing a window material on the scintillator layer after applying a silicone potting material or the like and before drying the moisture sealing layer is disclosed. In this manufacturing method, it is difficult to uniformly form the moisture seal layer on the scintillator layer having an irregular surface shape, and there is a possibility that the adhesiveness is reduced. This point is particularly likely to occur in a radiation detection element having a large area.

In view of the above problems, an object of the present invention is to provide a radiation detecting element having a uniform and easy-to-manufacture protective film for moisture prevention of a scintillator.

[0009]

Means for Solving the Problems In order to solve the above problems, a radiation detecting element according to the present invention has the following features. (1) A plurality of light receiving elements are arranged one-dimensionally or two-dimensionally on a substrate to form a light-receiving part. A light-receiving element array, (2) a scintillator layer that converts radiation deposited as columnar crystals on the light-receiving element into light, and (3) an upper part and a side surface of the scintillator layer and an outer peripheral part of the scintillator layer of the substrate, and have a columnar shape. And an organic film formed by penetrating at least the upper gap of the crystal.

According to the present invention, the organic film is formed so as to cover from the upper and side surfaces of the scintillator layer to the outer peripheral portion of the scintillator layer of the substrate, and the organic film enters the upper gap of the columnar crystal of the scintillator layer. The organic film adheres to the scintillator layer, and durability is secured.

It is preferable that the organic film is fixedly adhered to the substrate outside the scintillator layer. In this case, peeling from the periphery of the organic film is suitably prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. In addition, in order to facilitate understanding, the same components are denoted by the same reference numerals as much as possible in each of the drawings, and redundant description will be omitted. Further, dimensions and shapes in the drawings are not necessarily the same as actual ones, and some parts are exaggerated for easy understanding.

FIG. 1 is a top view of an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view taken along line AA of an outer peripheral portion thereof.

First, the configuration of the present embodiment will be described with reference to FIGS. Light receiving elements 2 that perform photoelectric conversion are two-dimensionally arranged on an insulating, for example, glass substrate 1 to form a light receiving section. The light receiving element 2 is composed of a photodiode (PD) and a thin film transistor (TFT) made of amorphous silicon. Each of the light receiving elements 2 in each row or each column is electrically connected by a signal line 3 for signal reading. A plurality of bonding pads 4 for extracting a signal to an external circuit (not shown) are arranged along the outer periphery of the substrate 1, for example, along two adjacent sides, and a plurality of bonding pads 4 are provided via the signal line 3. Are electrically connected to the light receiving element 2. An insulating passivation film 5 is formed on the light receiving element 2 and the signal line 3. This passivation film 5 is preferably made of silicon nitride or silicon oxide. on the other hand,
The bonding pad 4 is exposed for connection with an external circuit. Hereinafter, the substrate and the circuit portion on the substrate are referred to as a light receiving element array 6.

On the light receiving portion of the light receiving element array 6, a scintillator 7 having a columnar structure for converting incident radiation into visible light is provided.
Are formed. Although various materials can be used for the scintillator 7, Tl-doped C
sI and the like are preferred. In addition, a resin frame 8 made of a resin and formed in an elongated frame shape is arranged at an inner position of the bonding pad, surrounding the outer periphery of the light receiving portion of the light receiving element array 6. The resin frame 8 is preferably made of silicon resin such as KJR651 or KE4897 manufactured by Shin-Etsu Chemical, TSE397 manufactured by Toshiba Silicon, DYMAX625T manufactured by Sumitomo 3M, or the like. These are widely used for surface treatment for mechanical and electrical protection of a semiconductor element, and have high adhesion to a protective film 12 formed on an upper portion described later.

On the scintillator 7 in the frame of the resin frame 8,
In each case, a first organic film 9 that transmits X-rays and blocks water vapor, an inorganic film 10, and a second organic film 11 are respectively laminated to form a protective film 12.

The first organic film 9 and the second organic film 11 include:
It is preferable to use a polyparaxylylene resin (trade name: Parylene, manufactured by Three Bond Co., Ltd.), particularly, polyparachloroxylylene (trade name: Parylene C, manufactured by the company). The parylene coating film has very low water vapor and gas permeability, high water repellency, high chemical resistance, has excellent electrical insulation even in a thin film, and is transparent to radiation and visible light. , 11 have excellent characteristics. For more information on parylene coating,
Three Bond Technical News (September 23, 1992
This issue is described here.

Parylene can be coated by chemical vapor deposition (CVD), which is deposited on a support in a vacuum, similar to vacuum deposition of metals. This is a process of thermally decomposing diparaxylylene monomer as a raw material, rapidly cooling the product in an organic solvent such as toluene and benzene to obtain diparaxylylene called a dimer, and thermally decomposing the dimer to be stable. It comprises a step of generating a radical paraxylylene gas, and a step of polymerizing and forming a polyparaxylylene film having a molecular weight of about 500,000 by adsorbing and polymerizing the generated gas on a material.

There are two major differences between parylene deposition and metal vacuum deposition. First, the pressure during parylene deposition is
The pressure is 0.1 to 0.2 Torr, which is higher than the pressure of 0.001 Torr in the case of metal vacuum deposition, and the adaptation coefficient of parylene deposition is 2 to 4 digits compared to the adaptation coefficient 1 of metal deposition. It is low. For this reason, at the time of vapor deposition, after the monomolecular film covers the entire adherend, parylene is vapor-deposited thereon. Therefore, a thin film with a thickness of 0.2 μm can be formed to a uniform thickness without pinholes, and it is possible to coat sharp corners, edges, and narrow gaps on the order of microns, which were impossible with liquids. It is. Further, since heat treatment or the like is not required at the time of coating and coating can be performed at a temperature close to room temperature, no mechanical stress or thermal distortion due to curing occurs, and the coating has excellent stability. In addition, coatings on most solid materials are possible.

As long as the inorganic film 10 is transparent to X-rays, various materials such as transparent, opaque, and reflective materials can be used for visible light, and oxide films of Si, Ti, and Cr can be used. Metal films such as gold, silver, and aluminum can be used. In particular, it is preferable to use a film that reflects visible light, because it has the effect of preventing the fluorescence generated by the scintillator 7 from leaking outside and increasing the sensitivity. Here, an example using Al which is easy to mold will be described. Al itself is easily corroded in the air, but the inorganic film 10 is protected from corrosion because it is sandwiched between the first organic film 9 and the second organic film 11.

The protective film 12 is formed by the above-described parylene coating, but is formed by the CVD method, so that it is formed so as to cover the entire surface of the light receiving element array 6. Therefore, in order to expose the bonding pad 4, it is necessary to cut the protective film 12 formed of the parylene coating inside the bonding pad 4 and remove the external protective film 12. As will be described later, by cutting the protective film 12 near the center of the frame portion of the resin frame 8, the outer peripheral portion of the protective film 12 is fixed by the resin frame 8, so that the protective film 12 comes off from the outer peripheral portion. Can be prevented. Further, the outer peripheral portion of the protective film 12 is coated with a coating resin 13 together with the resin frame 8 thereunder. The coating resin 13 is a resin having good adhesion to the protective film 12 and the resin frame 8, for example, an acrylic adhesive such as WO
RLD ROCK No. 801-SET2 (70,0
00cP type). This resin adhesive is irradiated with ultraviolet rays of 100 mW / cm ² for about 20 minutes.
Cures in seconds, the effect film is flexible and has sufficient strength, excellent in moisture resistance, water resistance, electric contact resistance, migration resistance, good adhesion to various materials, especially glass, plastic, etc., coating The resin 13 has preferable characteristics.
Alternatively, the same silicon resin as the resin frame 8 may be used. Alternatively, the same acrylic adhesive as that of the coating resin 13 may be used for the resin frame 8.

Next, the manufacturing process of this embodiment will be described with reference to FIGS. As shown in FIG. 4, a columnar crystal of CsI doped with Tl is grown by a vapor deposition method to a thickness of 600 μm on the light receiving surface of the light receiving element array 6 as shown in FIG. 3 to form a scintillator 7 layer. .

On the other hand, as shown in FIG. 5, a resin frame 8 is formed on the passivation film 5 inside the bonding pad 4 along the outer periphery of the light receiving portion between the respective outer circumferences of the light receiving portion and the light receiving element array. It is formed in an elongated frame shape of 1 mm and height of 0.6 mm. For this frame formation, for example, an automatic XY coating apparatus such as an AutoShooter-3 type manufactured by Iwashita Engineering may be used. At this time, it is more preferable to roughen the surface of the resin frame 8 in order to further improve the adhesion with the first organic film 9 formed on the upper portion. As the rough surface treatment, there is a treatment for forming a streak or forming many small depressions on the surface.

CsI, which forms the scintillator 7 layer, has high hygroscopicity and, if left exposed, absorbs and dissolves water vapor in the air. Therefore, in order to prevent this, as shown in FIG.
The first organic film 9 is formed by wrapping the entire substrate with
To form Although there is a gap in the columnar crystal of CsI, parylene enters the narrow gap to some extent, so that the first organic film 9 adheres to the scintillator 7 layer. Furthermore, the parylene coating provides a precise thin film coating with a uniform thickness on the surface of the seven-layer scintillator having irregularities.
In addition, as described above, the parylene is formed by CVD at a lower degree of vacuum than at the time of metal deposition and can be performed at room temperature, so that processing is easy.

Further, as shown in FIG. 7, an inorganic film 10 is formed by stacking an Al film having a thickness of 0.2 μm on the surface of the first organic film 9 on the incident surface side by a vapor deposition method. Then, parylene was again applied to the surface of the entire substrate by 10 μm by the CVD method.
The second organic film 11 is formed by covering with a thickness (see FIG. 8). The second organic film 11 prevents the inorganic film 10 from being deteriorated by corrosion.

The protective film 12 thus formed is cut by a cutter 14 along the longitudinal direction of the resin frame 8 (see FIG. 9). Since the convex portion is formed in the resin frame 8, it is easy to confirm the cut portion, and since there is a margin for inserting the cutter 14 by the thickness of the resin frame 8, the signal under the resin frame 8 is provided. There is no danger of damaging the wire 3, processing is simplified, and product yield is improved. Then, the protective film 12 on the outside and the back side of the incident surface is removed from the cut portion to expose the bonding pad 4 for connection to an external circuit (see FIG. 10). Thereafter, a coating resin 13 made of an acrylic resin is coated so as to cover the outer peripheral portion of the protective film 12 and the exposed resin frame 8, and the coating resin 1 is irradiated with ultraviolet rays.
3 is cured (see FIG. 11).

Here, the passivation film 5 and the first organic film 9 generally have poor adhesion. However, according to the structure of the present embodiment, the first organic film 9 and the passivation film 5
The first organic film 9 is in close contact with the passivation film 5 by the resin frame 8 because the resin frame 8 is in close contact with both. The protective film 12 adheres to the light receiving element array 12 via the resin frame 8 without providing the coating resin 13. However, if the coating resin 13 is formed, the protective film 12 including the first organic film 9 can be formed. Since it is sandwiched and fixed between the resin frame 8 and the coating resin 13, the adhesion of the protective film 12 to the light receiving element array 6 is further improved, which is preferable. Therefore, since the scintillator 7 is hermetically sealed by the protective film 12, it is possible to reliably prevent moisture from entering the scintillator 7, and to prevent a decrease in the resolution of the element due to deterioration of the scintillator 7 due to moisture absorption.

Next, the operation of this embodiment will be described with reference to FIGS. X-rays (radiation) incident from the incident surface side
Passes through all of the first organic film 9, the inorganic film 10, and the second organic film 11, and reaches the scintillator 7. This X-ray
Visible light is absorbed by the scintillator 7 and emitted in proportion to the amount of X-rays. Of the emitted visible light, visible light that has traveled in the opposite direction to the X-ray incident direction passes through the first organic film 9 and
The light is reflected by the inorganic film 10. Therefore, almost all of the visible light generated by the scintillator 7 enters the light receiving element 2 via the passivation film 5. Therefore, efficient and highly sensitive measurement can be performed.

Each light receiving element 2 performs photoelectric conversion by:
An electric signal corresponding to the amount of visible light is generated and stored for a certain period of time. Since the amount of visible light corresponds to the amount of incident X-rays, that is, the electric signal accumulated in each light receiving element 2 corresponds to the amount of incident X-rays. An image signal corresponding to the image is obtained. This image signal stored in the light receiving element 2 is sequentially read out from the bonding pad 4 via the signal line 3, transferred to the outside, and processed by a predetermined processing circuit to display an X-ray image. Can be.

In the above description, the structure in which the inorganic film 10 is interposed between the first organic films 9 and 11 made of parylene as the protective film 12 has been described. The material of the organic film 11 may be different. Also,
When a material that is resistant to corrosion is used as the inorganic film 10, the second organic film 11 may not be provided.

Here, the resin frame 8 and the coating resin 13 are used.
Is formed on the passivation film 5 outside the light receiving element 2 portion of the light receiving element array 6, but when the light receiving element 2 and the bonding pad 4 are close to each other, a resin frame 8 is difficult to form. In order to surely expose the bonding pad 4 and reliably coat the periphery of the protective film 12 with the coating resin 13, it is preferable to shift the positions of the resin frame 8 and the coating resin 13 toward the light receiving element 2. For this purpose, instead of forming the scintillator 7 on the entire surface of the light receiving element 2,
It is formed on the light receiving element 2 in an effective screen area excluding pixels near the bonding pad 4. Then, after forming the resin frame 8 outside the effective screen area, that is, on the invalid pixels, the protective film 12 is formed so as to cover the entire layer of the formed scintillator 7 and reach the resin frame 8. Thereafter, the protective film 12 is cut along the longitudinal direction of the resin frame 8, the protective film 12 outside the effective screen area is removed, and the edge of the protective film 12 may be coated with the coating resin 13 along the resin frame 8. . In this case, the pixels near the bonding pad 4 are covered with the resin frame 8 and the covering resin 13 or the scintillator 7 does not exist on the front surface, so that the sensitivity to the radiation is reduced. 2 effective pixels,
Although the effective screen area is reduced, when the light receiving element 2 has a large screen and a large number of all pixels, the ratio of invalid pixels is small, and there is an advantage that manufacture is easy depending on the element configuration.

Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 12 is a top view of the radiation detecting element of this embodiment, and FIG.
It is a line expanded sectional view. The basic configuration of this element is shown in FIG.
2 are the same as those of the embodiment shown in FIG. 2, and only the differences will be described below.

In this embodiment shown in FIGS. 12 and 13, the protective film 12 is formed on the light receiving surface side and the rear surface side of the light receiving element array 6, and only the bonding array 4 is exposed. A resin frame 8 is formed so as to surround the exposed bonding array 4, and a coating resin 13 is coated on the resin frame 8 along a boundary (edge) of the protective film 12. Also in the present embodiment, the bonding pad 4 is reliably exposed, and the protective film 12 is securely adhered to the light receiving element array 6 by the resin frame 8 and the coating resin 13, so that the scintillator 7 layer is hermetically sealed and absorbed by moisture. Deterioration can be prevented.

This is particularly effective in the case of a CCD or MOS type image pickup device having a small bonding pad 4 because the length of the edge portion which may cause the peeling of the protective film can be reduced.

[0035]

As described above, according to the present invention,
In order to protect the highly hygroscopic scintillator, an organic film made of parylene or the like is formed so as to cover the scintillator, and serves as a protective film. Since this organic film is formed by penetrating into the upper gap of the columnar crystal of the scintillator layer made of the columnar crystal, the organic film adheres to the scintillator layer and the moisture resistance is improved. Since the organic film covering the upper portion of the scintillator layer further covers the side surface of the scintillator layer, even when the inorganic film is formed in the next step, the scintillator layer is suitably protected from moisture, and the reliability of the radiation detecting element is improved. Performance can be improved.

[Brief description of the drawings]

FIG. 1 is a top view of one embodiment of the present invention.

FIG. 2 is an enlarged sectional view taken along line AA of FIG.

FIG. 3 is a view showing a manufacturing process of the embodiment of FIG. 1;

FIG. 4 is a view showing a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 5 is a view showing a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 6 is a view illustrating a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 7 is a view showing a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 8 is a view showing a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 9 is a view illustrating a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 10 is a view illustrating a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 11 is a view illustrating a continuation of the manufacturing process of the embodiment in FIG. 1;

FIG. 12 is a top view of another embodiment of the present invention.

FIG. 13 is an enlarged sectional view taken along line BB of FIG. 12;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Light receiving element, 3 ... Signal line, 4 ... Bonding pad, 5 ... Passivation film, 6 ... Light receiving element array, 7 ... Scintillator, 8 ... Resin frame, 9, 11 ... Organic film, 10 ... Inorganic film , 12 ... Protective film.

Claims (2)

[Claims] 1. A light-receiving element array in which a plurality of light-receiving elements are arranged one-dimensionally or two-dimensionally on a substrate to form a light-receiving portion, and a scintillator for converting radiation deposited as columnar crystals on the light-receiving elements into light. A radiation detection element comprising: a layer; and an organic film that covers an upper portion and a side surface of the scintillator layer and an outer peripheral portion of the scintillator layer of the substrate, and is formed to enter at least a gap between the columnar crystals. 2. The radiation detecting element according to claim 1, wherein the organic film is fixedly attached to the substrate outside the scintillator layer.