JP2008244380A - Manufacturing method of semiconductor radiation detection element, semiconductor detector, and nuclear medicine diagnostic apparatus - Google Patents

Abstract

【Task】
It is not possible to sort out the semiconductor radiation detection element that fails initially by only the characteristic inspection. There is a need for a method of selecting and removing semiconductor radiation detection elements that fail initially.
[Solution]
In order to solve the above-mentioned problem, after cutting out a radiation detection element from a semiconductor crystal wafer, cutting out the radiation detection element, performing a process of applying stress to the radiation detection element, and selecting a pass product after the process of applying stress is completed It was set as the manufacturing method of the radiation detection element which carries out.
[Selection] Figure 1

Description

  The present invention relates to a method of manufacturing a semiconductor crystal as a radiation detection element, a semiconductor radiation detector, and a nuclear medicine diagnostic apparatus.

  Japanese Patent Application Laid-Open No. 5-155699 describes that a CdTe single crystal is subjected to a first heat treatment and then a second heat treatment in order to obtain a radiation detection element with a high yield (summary description). It describes that a radiation detection element is produced from a wafer after two heat treatments (paragraph 0014).

JP-A-5-155699

  Since the radiation detection element is manufactured from the wafer after performing the heat treatment twice, the initial failure of the semiconductor detector due to the growth of minute defects generated when the element is cut out from the wafer is not considered. Only the characteristic inspection cannot sort out the semiconductor radiation detection elements that fail early, and there is a need for a method of sorting out and removing the semiconductor radiation detection elements that fail early.

  In order to solve the above-mentioned problem, after cutting out a radiation detection element from a semiconductor crystal wafer, cutting out the radiation detection element, performing a process of applying stress to the radiation detection element, and selecting a pass product after the process of applying stress is completed It was set as the manufacturing method of the radiation detection element which does.

  It is possible to prevent the initial failure of the semiconductor detector due to the growth of minute defects generated when the element is cut out from the wafer.

  A method for manufacturing a semiconductor radiation detection element, a semiconductor detector, and a nuclear medicine diagnostic apparatus according to the present invention will be described below.

  Radiation measurement technology (semiconductor radiation detection using a semiconductor radiation detection element, etc.) has been actively applied to the medical field in recent years, and is being put to practical use as a nuclear medicine diagnostic apparatus. Examples of nuclear medicine diagnosis apparatuses include a scintillation camera, a single photon emission computed tomography (SPECT) apparatus, and a positron emission tomography (PET) apparatus. All of these measure the distribution of gamma rays emitted by radioactive substances by placing a drug containing radioactive substances in the body of the subject. Since gamma rays have strong penetrating power, their distribution can be measured from the outside even inside the human body. The distribution of drugs can be known from the distribution of gamma rays, and various diagnoses can be made.

  A combination of a scintillator and a photomultiplier tube has been mainly used as a radiation detector in a nuclear medicine diagnostic apparatus. In the scintillator, when a gamma ray is incident, it interacts to emit faint light (scintillation). Weak light is amplified as an electrical signal by a photomultiplier tube to detect the incidence of gamma rays. On the other hand, a method using a semiconductor radiation detector using a semiconductor as a radiation detector is also known. In semiconductors, when gamma rays are incident, charges are generated by interaction, and the incident of gamma rays is detected by collecting the charges. In the scintillator, the gamma ray energy is converted into light and then converted back into an electric signal, whereas in the semiconductor, the gamma ray energy is directly converted into a charge amount, that is, an electric signal. Therefore, if a semiconductor radiation detector is used, the energy of gamma rays can be accurately known. When gamma rays pass through the body or are scattered within the detector, the energy may be attenuated. Such a scattered gamma ray has a smaller energy than the original gamma ray, and can be easily identified as a gamma ray by using a detector having a high energy discrimination capability such as a semiconductor radiation detector. As a result, it is possible to obtain a gamma ray image having a good image quality with little influence of scattered gamma rays.

  Conventionally, silicon containing lithium or high-purity germanium has been used as a semiconductor crystal material used as a radiation detection element. However, since silicon has a small atomic number, the sensitivity of gamma rays is low, and germanium can only be operated after being cooled to a very low temperature. Compound semiconductors such as GaAs, CdTe, and CdZnTe have relatively large effective atomic numbers and high gamma ray sensitivity. However, all of the compound semiconductors are brittle and mechanically weak, and there is a problem that if they are not handled with care, they are easily chipped and cracked and become defective.

  The problem that requires attention in handling can be greatly alleviated by bonding the semiconductor crystal to another member as disclosed in JP-A-2005-257437. This is because the bonded electrode member is in direct contact with the outside, and the semiconductor crystal is protected. However, there are still other problems to be solved even with such a structure.

  A plurality of semiconductor radiation detection elements that passed the characteristic inspection were assembled by bonding them together to produce a radiation detector and mounted on a printed circuit board. However, when these radiation detectors were used on a trial basis, a very small number of initial defective products were produced.

  Although it is necessary to replace a radiation detector that has failed at an early stage after being mounted on a printed circuit board, such an operation is very expensive. Therefore, it is desirable to select and remove radiation detectors that cause initial failure in advance. However, even if the characteristics are measured, it is not possible to distinguish between those that have initial failure and those that do not. I couldn't. In addition, the detector uses a plurality of semiconductor radiation detection elements, but when the failed detector is examined, it is almost always the case that one of the plurality has failed. That is, if the detector fails and is removed, even the normal semiconductor radiation detection element is removed together. Accordingly, it is a problem to select and remove those that may cause an initial failure at the stage of the semiconductor radiation detection element before being assembled as a radiation detector.

  When the semiconductor crystal is heated and cooled twice or more times or mechanical vibration is applied, the semiconductor crystal is subjected to thermal stress or mechanical stress. As a result, minute defects in the semiconductor crystal that could not be discriminated from dark current or spectrum measurement can be revealed by dark current or spectrum measurement after processing.

  It has been found that the identity of such minute defects is mainly due to minute cracks that occur when elements are cut out from the wafer. In order to cut out the element from the wafer, a cutting device having a rotary blade called a dicing device is used. At that time, brittle crystal materials such as GaAs, CdTe, and CdZnTe tend to have minute cracks around the cut portion. In addition, cracks generated in this way are difficult to be manifested by a single heat treatment or vibration for a short time, and may grow due to two or more heat treatments or vibration for a long time, and may eventually manifest by deteriorating device characteristics. all right. Therefore, when a heat or vibration is applied several times to the detector such as mounting on a printed board on the crystal having such a minute defect, the minute defect grows, and as a result, an initial failure occurs. On the other hand, a semiconductor crystal having no microdefects does not grow even if stress due to heating or cooling or vibration is applied, so that no initial failure occurs. A radiation detector manufactured using such a semiconductor detection element has high reliability, and when used in a nuclear medicine diagnostic apparatus, it is a high-quality apparatus with few initial failures. As a result, the operation rate of the nuclear medicine diagnosis apparatus is increased.

  Examples of the process for applying stress to the radiation detection element of the present invention include a process for heating and cooling twice or a process for applying vibration.

  Examples of characteristic inspection for selecting acceptable products of the present invention include dark current and spectrum measurement.

  Next, embodiments of the present invention will be described with reference to the drawings.

The manufacturing method of the semiconductor radiation detection element which is a 1st Example is shown in FIG. A wafer is cut out from the semiconductor crystal ingot to form an electrode film. After the electrode film is formed, the element is cut out from the wafer into a predetermined shape with a dicing apparatus or the like. Thereafter, repeated heating and cooling processes are performed, and the characteristics are inspected to complete. The repeated heating and cooling process was performed in the pattern shown in FIG. That is, the heating temperature T2 was changed from room temperature T1 to + 80 ° C., and the temperature was increased during the heating time 21 at a rate of 10 ° C./min. When the temperature reached the heating temperature T2, the cooling temperature T3 was changed to -10 ° C and the temperature was lowered at a change rate of -10 ° C / min. It took a cooling time 22 to reach the cooling temperature T3 from the heating temperature T2. Further, heating and cooling were repeated between the heating temperature T2 and the cooling temperature T3, and a total of 3 cycles were repeated. On the other hand, FIG. 3 shows a manufacturing method as a comparative example, which does not include repeated heating and cooling processes. A semiconductor radiation detector was manufactured by the manufacturing method of the present embodiment shown in FIG. 1, and the semiconductor radiation detector 40 shown in FIG. 4 was manufactured. The semiconductor radiation detector 40 has a structure in which a semiconductor radiation detection element 41 and a semiconductor radiation detection element 42 are sandwiched between an electrode plate 43, an electrode plate 44, and an electrode plate 45. The semiconductor radiation detection element 41 and the semiconductor radiation detection element 42 are Because it does not come into direct contact with the outside, it is difficult to damage and easy to handle. The semiconductor radiation detection element and the electrode plate are connected by an adhesive. 1000 pieces of radiation detectors 40 were manufactured, mounted on a printed circuit board, and a burn-in test for selecting initial defects was performed. As a result, no initial defects were found. On the other hand, when 1000 semiconductor radiation detecting elements manufactured by a conventional manufacturing method were mounted on a printed circuit board and a burn-in test was performed, two of them were initially defective. The detector is mounted on the printed board by soldering the electrodes to the printed board. Moreover, although it tried also about the semiconductor radiation detection element which implemented heating / cooling only 1 cycle, two pieces became initial failure like the case where heating / cooling was not carried out. When heating and cooling were carried out twice, no initial failure occurred. Even when the heating / cooling cycle was set to 3 in consideration of the margin, no initial failure occurred.

In this embodiment, the temperature in the repeated heating / cooling process is set to + 80 ° C. for the heating temperature T and −10 ° C. for the cooling temperature T 3, but this temperature does not have to be particularly high and may be changed according to the material and shape. . Further, the temperature change rate and the number of repetitions are the same, and it may be changed according to the material and shape to be processed. What is important is to repeat heating and cooling before the characteristic inspection. That is, after the radiation detection element is cut out from the semiconductor crystal wafer and before the connection member is connected to the external circuit, the radiation detection element is heated and cooled once. The process of heating and cooling is performed twice or twice or more, and after all the processes of heating and cooling are completed, a characteristic inspection is performed to select an acceptable product.

  The present invention is effective when implemented on brittle semiconductor crystals such as GaAs, CdTe, CdZnTe. In Si and Ge, no initial failure occurred, and the effect could not be confirmed.

  A method for reducing defects by heating a semiconductor crystal is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-166462. In this case as well, the semiconductor crystal is heated and cooled, which is essentially different from the present embodiment. This is because the present embodiment intends to reveal defects and does not reduce the defects. Therefore, it is different from the present embodiment in that it is not necessary to repeat heating and cooling twice or more as shown in FIG.

  As described above, after cutting out the radiation detection element from the semiconductor crystal wafer, cutting out the radiation detection element, performing the process of applying stress to the radiation detection element, and performing the characteristic inspection for selecting the acceptable product after the process of applying the stress is completed. The manufacturing method of the radiation detection element can prevent the initial failure of the semiconductor detector due to the growth of minute defects.

  A method for manufacturing a semiconductor radiation detection element according to the second embodiment is shown in FIG. In FIG. 5, the repeated heating / cooling process of FIG. 1 is replaced with a vibration process. Similar to the first embodiment, the device was cut out from the semiconductor crystal ingot through a predetermined process. After that, it was subjected to vibration treatment and inspected for completion. As shown in FIG. 6, the vibration treatment was performed by placing semiconductor radiation detection elements 61, 62, 63, 64 on the rubber mat 65 and applying a 40 Hz vibration from the vibration table 65 to the rubber mat 65 for 30 seconds. A semiconductor radiation detection element was manufactured by the manufacturing method of the present embodiment shown in FIG. 5, and the radiation detector 40 shown in FIG. 4 was manufactured. When 1000 pieces of radiation detectors 40 were manufactured and mounted on a printed circuit board and a burn-in test was performed, there was no initial failure. In other words, after cutting out the radiation detection element from the semiconductor crystal wafer, a process for applying mechanical vibration is performed, and thereafter, a characteristic inspection is performed to select an acceptable product.

  The treatments of Example 1 and Example 2 are different treatments of heating and cooling and vibration, but it is effective to implement either one or both. When both are performed, the result is the same regardless of which is performed first, and it is effective for sorting out initial defective products. After cutting out the radiation detection element from the semiconductor crystal wafer and before attaching the connection member to the external circuit, performing the heating and cooling process twice or more times, It may be used in combination with a process that imparts mechanical vibration, and after the process is completed, a characteristic inspection is performed to select an acceptable product. By using the two treatments in combination, a detector that eliminates both thermal and mechanical stress factors can be manufactured.

  A PET apparatus was manufactured using the radiation detector 40 manufactured in Example 1. After 60 hours of use, there was no detector indicating an initial failure and there was no need to replace the detector. When the radiation detector manufactured by the conventional method was used, the detector that failed after 60 hours of use was 0.2% of the total, so that it was necessary to replace the detector. By manufacturing the PET apparatus using the radiation detector 40 manufactured in Example 1, it is not necessary to replace the initial defect of the detector, and the manufacturing cost can be reduced. In addition, it has become possible to have high reliability as a nuclear medicine diagnostic apparatus. Even if a PET apparatus is manufactured using the radiation detector manufactured in Example 2, it is not necessary to replace the initial defect of the detector, and the manufacturing cost can be reduced.

  The present invention is a manufacturing method in which an initial failure in a semiconductor radiation detector element is removed in advance. This is preferably applied to a nuclear medicine diagnostic apparatus such as a gamma camera, a PET apparatus, or a SPECT apparatus. In these nuclear medicine diagnostic apparatuses, in order to administer a radiopharmaceutical to a measurement subject, it is necessary to avoid a situation in which measurement is interrupted due to a failure in the middle. Such a situation will not occur if the highly reliable radiation detector according to the present invention is used.

The figure which showed the manufacture flow of the semiconductor radiation detection element of Example 1. FIG. The figure which showed the time change of heating and cooling. The figure which showed the manufacture flow of the semiconductor radiation detection element of a comparative example. The figure which shows a radiation detector. The figure which showed the manufacturing flow of the semiconductor radiation detection element of Example 2. FIG. The figure which showed the vibration process.

Explanation of symbols

21, 23 Heating time 22 Cooling time 40 Semiconductor radiation detectors 41, 42, 61, 62, 63, 64 Semiconductor radiation detecting elements 43, 44, 45 Electrode plate 65 Rubber mat 66 Shaking table T1 Room temperature T2 Heating temperature T3 Cooling temperature

Claims (7)

Cut out the radiation detection element from the semiconductor crystal wafer,
After the cut out, a process of applying stress to the radiation detection element is performed,
A method for manufacturing a radiation detecting element, comprising performing a characteristic inspection for selecting an acceptable product after the process of applying stress is completed. The process of applying the stress according to claim 1,
A method of manufacturing a radiation detection element, characterized in that the process of heating and cooling is performed twice or more, or the process of applying vibrations. The process of applying the stress according to claim 1,
A method of manufacturing a radiation detection element, characterized in that the process of heating and cooling is performed twice or more and the process of applying vibrations. The manufacturing method according to claim 1,
The method of manufacturing a radiation detecting element, wherein the stress applying process is performed before attaching a connection member connected to an external circuit. A plurality of semiconductor detection elements manufactured by the manufacturing method of claim 1,
A semiconductor detector comprising a connection member connected to the plurality of semiconductor detection elements.   A method of manufacturing a radiation detection element, wherein the semiconductor crystal material according to claim 1 is any one of GaAs, CdTe, and CdZnTe.   A nuclear medicine diagnostic apparatus equipped with a semiconductor radiation detection element manufactured by the manufacturing method according to claim 1.

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