JP6493158B2 - X-ray detector - Google Patents

Description

  The present invention relates to an x-ray detector having a lithium drift region.

  A detector that detects radiation is used to analyze radiation specific to the material, such as X-rays, gamma rays, ultraviolet rays, infrared rays, visible light, etc. emitted from the substance. For example, an X-ray detector (hereinafter referred to as a "Si (Li) detector") having a lithium drift region in which lithium (Li) is drifted on a silicon (Si) substrate is used for detection of X-rays. (See, for example, Patent Document 1). The Si (Li) detector has a semiconductor stack having a p-i-n junction formed by a p-type semiconductor region, a lithium drift region and an n-type semiconductor region.

  An n-side electrode is disposed on the end face where the n-type semiconductor region of the semiconductor laminate of the Si (Li) detector is exposed. On the other hand, the p-side electrode is disposed on the other end face of the semiconductor laminate in which the lithium drift region and the p-type semiconductor region are exposed. In the Si (Li) detector, etching of the exposed surface of the lithium drift region has been performed to improve the interface state of the Schottky junction formed on the junction surface of the lithium drift region and the p-side electrode. (For example, refer to nonpatent literature 1.).

Patent No. 4356445

T. Aramaki et al., "Antideuterons as an Indirect Dark Matter Signature: Si (Li) Detector Development and a GAPS Balloon Mission", Advances in Space Research 46 (2010), p.

  The spectral characteristics of the sample obtained by the X-ray detector usually show a single peak indicative of the characteristic X-ray of the sample. However, in the spectral characteristics of the sample obtained by the Si (Li) detector, a plurality of peaks sometimes appeared. For this reason, there existed a problem which interferes in accurate measurement.

  In view of the above problems, the present invention aims to provide a Si (Li) detector including a lithium drift region, which can obtain a single characteristic X-ray spectrum.

According to one embodiment of the present invention, (i) a p-i-type semiconductor region, a lithium drift region in which the p-type semiconductor region is in contact with the lower side surface, and an n-type semiconductor region stacked on the lithium drift region A semiconductor stack in which an n-junction is formed, and (i) a p-side electrode arranged continuously to an exposed surface of a p-type semiconductor region exposed adjacent to each other on the lower surface of the semiconductor laminate and an exposed surface of a lithium drift region When, an n-side electrode disposed on the upper surface of the (c) n-type semiconductor region, the lower surface of the semiconductor laminate, Ri flat der over the entire surface of the p-type semiconductor region and the lithium drift region, and, p The surface of the ring electrode which is a p-side electrode disposed in the n-type semiconductor region is opposed to the surface in contact with the p-type semiconductor region and the lithium drift region of the window electrode which is a p-side electrode disposed in a lithium drift region A surface opposite to the surface is, X-rays detector positioned on the same plane level is provided.

  According to the present invention, it is possible to provide a Si (Li) detector including a lithium drift region, which can obtain a single characteristic X-ray spectrum.

It is a typical sectional view showing the composition of the X-ray detector concerning the embodiment of the present invention. It is the top view seen from the p side electrode direction of the X-ray detector which concerns on embodiment of this invention. It is a typical sectional view showing the composition of the X-ray detector of a comparative example. It is a schematic diagram which shows the p side electrode of the X-ray detector of a comparative example. It is a graph which shows the spectral characteristic obtained by the X-ray detector of the comparative example which is not segmented. It is a graph which shows the spectral characteristic obtained by the X-ray detector of the segmented comparative example. It is a schematic diagram which shows the p side electrode of the X-ray detector which concerns on embodiment of this invention. It is a graph which shows the spectral characteristic obtained by the X-ray detector which concerns on embodiment of this invention, and the X-ray detector of the comparative example which is not segmented, respectively. It is a graph which shows the spectrum characteristic at the time of segmenting the X-ray detector which concerns on embodiment of this invention. It is a typical sectional view for explaining the manufacturing method of the X-ray detector concerning the embodiment of the present invention (the 1). It is a typical sectional view for explaining the manufacturing method of the X-ray detector concerning the embodiment of the present invention (the 2). It is a typical sectional view for explaining the manufacturing method of the X-ray detector concerning the embodiment of the present invention (the 3). It is a typical sectional view for explaining the manufacturing method of the X-ray detector concerning the embodiment of the present invention (the 4). It is a typical sectional view for explaining the manufacturing method of the X-ray detector concerning the embodiment of the present invention (the 5). It is a schematic diagram which shows the structure of the p side electrode of the X-ray detector which concerns on the modification of embodiment of this invention. It is a schematic diagram which shows the other structure of the p side electrode of the X-ray detector which concerns on the modification of embodiment of this invention.

  Embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. In addition, the embodiments shown below exemplify apparatuses for embodying the technical concept of the present invention. Various modifications can be made to the embodiments of the present invention within the scope of the claims.

  As shown in FIG. 1, the X-ray detector 1 according to the embodiment of the present invention is a semiconductor stack in which a p-i-n junction is formed by the p-type semiconductor region 11, the lithium drift region 12 and the n-type semiconductor region 13. The body 10 is provided. Furthermore, the X-ray detector 1 includes a p-side electrode 20 continuously disposed on the exposed surface of the p-type semiconductor region 11 exposed adjacent to each other on the lower surface of the semiconductor stack 10 and the exposed surface of the lithium drift region 12. And an n-side electrode 30 disposed on the upper surface of the n-type semiconductor region 13.

  As shown in FIG. 1, the lower side surface of the lithium drift region 12 is in contact with the p-type semiconductor region 11. In addition, an n-type semiconductor region 13 is stacked on the upper surface of the lithium drift region 12. The X-ray detector 1 is circular in plan view, and the exposed surface of the p-type semiconductor region 11 is disposed around the exposed surface of the lithium drift region 12 exposed in the central region of the lower surface of the semiconductor laminate 10 .

The X-ray detector 1 shown in FIG. 1 has a p-type Si layer as the p-type semiconductor region 11, a lithium drift layer in which lithium is drifted to a silicon substrate as the lithium drift region 12, and a high concentration n ⁺ as the n-type semiconductor region 13. It is a Si (Li) detector using a layer Li diffusion layer.

  In the X-ray detector 1, the lower surface of the semiconductor stack 10 is flat over the entire surface of the p-type semiconductor region 11 and the lithium drift region 12. A p-side electrode 20 is disposed continuously with the exposed surface of the p-type semiconductor region 11 and the exposed surface of the lithium drift region 12 in contact with the lower surface of the flat semiconductor laminate 10. The p-side electrode 20 has a window electrode 21 disposed on the exposed surface of the lithium drift region 12 and a ring electrode 22 disposed on the exposed surface of the p-type semiconductor region 11.

  As shown in FIG. 2, a circular window electrode 21 is formed in the central region of the p-side electrode 20, and an annular ring electrode 22 is formed around the window electrode 21. FIG. 1 is a cross-sectional view taken along a line II in FIG. X-rays to be detected are incident from the window electrode 21. The ring electrode 22 is a region not irradiated with X-rays to be detected. For example, the ring electrode 22 is covered with a collimator (not shown) that shields the area other than the irradiation area.

  In the X-ray detector 1, by applying a high voltage between the n-side electrode 30 and the p-side electrode 20, the X-ray incident from the window electrode 21 is absorbed by the lithium drift region 12. The X-ray absorbed in the lithium drift region 12 is extracted by the ring electrode 22 and the n-side electrode 30 in the form of charge as electrons and holes, and is detected as a current pulse externally. Thus, the X-ray detector 1 is a semiconductor detector that converts the energy of the irradiated X-rays into an electrical signal. The X-ray detector 1 shown in FIG. 1 is a top hat type, and most of the lithium drift region 12 continuously formed from the n-side electrode 30, the n-type semiconductor region 13 and the n-type semiconductor region 13. The outer edge of the upper structure is located inside the outer edge of the p-type semiconductor region 11 or the p-side electrode 20.

  Incidentally, as shown in FIG. 1, the semiconductor laminate 10 may be formed so that the outer edge portion is left outside the groove 40 for forming the top hat type. By leaving the outer edge, there is an advantage such as facilitating movement by holding the X-ray detector 1 from the outside of the outer edge.

  Conventionally, as in the X-ray detector 1A of the comparative example shown in FIG. 3, the surface of the exposed region of the lithium drift region 12 is etched on the lower surface of the semiconductor stack 10. This is to improve the interface state of the Schottky junction formed on the junction surface between the lithium drift region 12 and the p-side electrode 20, which are sensitive regions for X-rays to be detected. On the other hand, the exposed surface of the p-type semiconductor region 11 is not etched.

  Therefore, the exposed surface of the lithium drift region 12 is recessed from the exposed surface of the surrounding p-type semiconductor region 11. As described above, in the structure of the comparative example in which the lower surface of the semiconductor stack 10 is etched only in the area where the lithium drift region 12 is exposed, the step on the lower surface of the semiconductor stack 10 between the thinned central area and the area around it. Will occur. In addition to this, the film thickness of the window electrode 21 is formed as very thin as 20 nm to 40 nm so that absorption of X-rays is small. Therefore, for example, as shown in FIG. 4, the p-side electrode 20 is separated by a step that is generated at the boundary between the exposed surface of the lithium drift region and the exposed surface of the p-type semiconductor region 11. That is, the window electrode 21 and the ring electrode 22 are separated. The window electrode 21 is, for example, a nickel (Ni) film 201 with a film thickness of about 20 nm, and the ring electrode 22 is, for example, a structure in which a gold (Au) film 202 with a film thickness of 200 nm and a Ni film 201 with a film thickness of about 20 nm are stacked. is there.

  The separation of the p-side electrode 20 as shown in FIG. 4 is hereinafter referred to as “segmentation”. In the analysis using a segmented X-ray detector, as described below, there arises a problem that a plurality of peaks are generated in the spectrum characteristic that a single peak originally appears.

  Spectral characteristics, which are analysis results of a sample of antimony (Sb) using the X-ray detector 1A of the comparative example shown in FIG. 3, are shown in FIGS. Here, “spectral characteristics” is a characteristic in which the number of detected charges is totaled for each energy size, and the horizontal axis is the energy channel, and the vertical axis is the X-ray intensity corresponding to the total number. is there.

  FIG. 5 shows an analysis result using the non-segmented X-ray detector 1A, in which a single main peak P1 showing a peak of SbKa appears. On the other hand, FIG. 6 shows an analysis result using the segmented X-ray detector 1A. As shown in FIG. 6, as peaks other than the main peak P1, the split peak P2 of the SbKa peak and the split peak P3 appear in the spectral characteristics.

  The inventors of the present invention conducted intensive studies on the phenomenon described above, that is, the phenomenon in which only the main peak appears when the p-side electrode 20 is not segmented and the split peak appears in addition to the main peak when segmented. New findings obtained by Until this new knowledge was obtained, after confirming the results of X-ray analysis using the completed X-ray detector, it was necessary to discard the X-ray detector in which a split peak appears in the spectral characteristics as a defective product . For this reason, the manufacturing cost was high.

  In addition, before the present inventors obtained the above-mentioned new knowledge, it was examined that the normal product from which a single peak is obtained might become a defective product from which a split peak occurs due to a change with time. However, it was found that the cause of generation of the split peak in the spectral characteristics is the segmentation of the p-side electrode 20, so that it is clear that the change is not the cause.

  In the X-ray detector 1 shown in FIG. 1, the lower surface of the semiconductor stack 10 is flat over the entire surface of the p-type semiconductor region 11 and the lithium drift region 12. Therefore, as shown in FIG. 7, no segmentation occurs in which the ring electrode 22 and the window electrode 21 are separated. The example shown in FIG. 7 has a structure in which the ring electrode 22 and the window electrode 21 have the same configuration, and a Ni film 201 having a film thickness of about 20 nm and an Au film 202 having a film thickness of 200 nm are stacked.

  Spectral characteristics that are analysis results of a sample of manganese oxide (MnO) obtained using the X-ray detector 1 are shown as a characteristic S1 in FIG. The single main peak P1 showing the peak of MnO appears in the characteristic S1. For comparison, the spectral characteristics of the same sample obtained using the non-segmented X-ray detector 1A of the comparative example shown in FIG. 3 are shown as characteristic S20 in FIG. The peaks of the characteristic S1 and the characteristic S20 coincide with each other. That is, even by the X-ray detector 1 in which the exposed surface of the lithium drift region 12 is not etched, spectral characteristics equivalent to those of the comparative example are obtained.

  On the other hand, the result of examining the influence of segmentation using the X-ray detector 1 is shown in FIG. Characteristic S1 of FIG. 9 is a spectral characteristic of MnO obtained using the X-ray detector 1. The characteristic S21 of FIG. 9 uses the X-ray detector 1 in which the p-side electrode 20 is divided into a region disposed in the lithium drift region 12 and a region disposed in the p-type semiconductor region 11 and segmented. It is a spectrum characteristic of obtained MnO. This segmentation was performed by removing a part of the p-side electrode 20 continuously formed over the entire lower surface of the semiconductor stack 10 in a ring shape. While a single main peak P1 appears in the characteristic S1, a plurality of peaks appear in the characteristic S21 when segmented. In addition, the present inventors confirmed that the peak which appears in a spectral characteristic becomes single by connecting the segmented p side electrode 20 by a metal film.

  As described above, the present inventors have found that the phenomenon in which a plurality of peaks appear in the spectral characteristics is due to the electrode segmentation. In the X-ray detector 1 shown in FIG. 1, the exposed surface of the p-type semiconductor region 11 and the exposed surface of the lithium drift region 12 are flat over the entire surface without etching only the exposed surface of the lithium drift region 12 is there. For this reason, segmentation does not occur without the ring electrode 22 and the window electrode 21 being separated. As a result, it is possible to prevent the manufacture of an X-ray detector in which spectral peaks are split. Thus, according to the X-ray detector 1 according to the embodiment of the present invention, it is a Si (Li) detector including the lithium drift region 12, and an X-ray detector capable of obtaining a single characteristic X-ray spectrum. Can be provided.

  An example of a method of manufacturing the X-ray detector 1 shown in FIG. 1 will be described below with reference to the drawings. In addition, the manufacturing method of X-ray detector 1 described below is an example, and it is needless to say that it is realizable with various manufacturing methods other than this including this modification.

  First, as shown in FIG. 10, a Li film 200 is deposited on the upper surface of a p-type Si substrate 100. Next, the Li of the Li film 200 is thermally diffused to form an n-type semiconductor region 13 (lithium diffusion layer) as shown in FIG. Thereafter, the Li film 200 is removed, and the n-side electrode 30 is formed on the n-type semiconductor region 13 as shown in FIG. For example, a nickel (Ni) film / gold (Au) film is vapor-deposited on the upper surface of the n-type semiconductor region 13.

  Next, processing for the top hat type is performed. That is, as shown in FIG. 13, grooves 40 are formed in the outer peripheral region of the n-side electrode 30, the n-type semiconductor region 13 and a part of the upper portion of the p-type Si substrate 100 by ultrasonic grinding or the like. In the region outside the groove 40, only the p-type Si substrate 100 is left.

  Thereafter, an electric field is applied between the n-type semiconductor region 13 and the bottom of the p-type Si substrate 100 to drift Li to form a lithium drift region 12. As shown in FIG. 14, Li drifts to the lower surface of the central region of p-type Si substrate 100 to form lithium drift region 12, and the periphery of the lower portion of p-type Si substrate 100 does not drift Li is p-type semiconductor region 11. Remain as. Thus, by adopting the top hat type, the remaining region of the region in which the lithium drift region 12 of the p-type Si substrate 100 is formed is used as the p-type semiconductor region 11.

  The lower surface of the p-type semiconductor region 11 and the lower surface of the lithium drift region 12 are surface-treated by etching. Thereby, the lower surface is finished smoothly, and the interface state of the Schottky junction formed on the junction surface of the lithium drift region 12 and the window electrode 21 is improved. By forming the p-side electrode 20 on the surface-treated lower surface, the X-ray detector 1 shown in FIG. 1 is completed. For the p-side electrode 20, for example, a nickel (Ni) film / gold (Au) film is used.

<Modification>
The ring electrode 22 on which a bonding wire or the like is disposed for electrical connection with the outside requires a certain thickness. On the other hand, it is preferable that the film thickness of the window electrode 21 to which X-rays enter be thin. Therefore, the film thickness of the window electrode 21 may be thinner than the film thickness of the ring electrode 22. For example, as shown in FIG. 15, the window electrode 21 is formed of a Ni film 201 having a film thickness of about 20 nm. On the other hand, the ring electrode 22 is formed by laminating an Au film 202 with a film thickness of about 200 nm on a Ni film 201 with a film thickness of about 20 nm formed in contact with the p-type semiconductor region 11. Thereby, the absorption of X-rays at the window electrode 21 is suppressed, and the detection sensitivity of low energy X-rays can be improved.

  As shown in FIG. 16, the order of forming the Au film 202 and the Ni film 201 may be reversed from the structure shown in FIG. 15. That is, the ring electrode 22 can adopt a structure in which the Ni film 201 is stacked on the Au film 202 formed in contact with the p-type semiconductor region 11.

(Other embodiments)
As mentioned above, although the present invention was described by the embodiment, it should not be understood that the statement and the drawings which form a part of this disclosure limit the present invention. Various alternative embodiments, examples and operation techniques will be apparent to those skilled in the art from this disclosure.

  In the description of the embodiment already described, the structure is shown in which the outer edge is left outside the groove 40 for forming the top hat type, but the lithium drift region 12 or n is left without leaving the semiconductor region outside the groove 40. The side surface of the semiconductor region 13 may be exposed to the outside.

  Thus, it is a matter of course that the present invention includes various embodiments and the like which are not described herein. Accordingly, the technical scope of the present invention is defined only by the invention-specifying matters according to the scope of claims appropriate from the above description.

DESCRIPTION OF SYMBOLS 1 ... X-ray detector 10 ... Semiconductor laminated body 11 ... p-type semiconductor area 12 ... Lithium drift area 13 ... n-type semiconductor area 20 ... p side electrode 21 ... Window electrode 22 ... Ring electrode 30 ... n side electrode

Claims (2)

a semiconductor laminate in which a p-i-n junction is formed by a p-type semiconductor region, a lithium drift region in which the p-type semiconductor region is in contact with the lower side, and an n-type semiconductor region stacked on the top surface of the lithium drift region; ,
An exposed surface of the p-type semiconductor region exposed adjacent to each other on the lower surface of the semiconductor stack and a p-side electrode disposed continuously to the exposed surface of the lithium drift region;
The n-type and an n-side electrode disposed on the upper surface of the semiconductor region, the lower surface of the semiconductor laminate, Ri flat der over the entire surface of the p-type semiconductor region and the lithium drift region, and the The surface of the ring electrode as the p-side electrode disposed in the p-type semiconductor region facing the surface in contact with the p-type semiconductor region, and the lithium as the window electrode as the p-side electrode disposed in the lithium drift region An X-ray detector characterized in that a surface opposite to a surface in contact with a drift region is located on the same plane level . The p-side electrode is circular in plan view,
The p-side electrode is disposed on the exposed surface of the lithium drift region, the window electrode having a circular shape in a plan view, and the planar view disposed on the exposed surface of the p-type semiconductor region around the window electrode The X-ray detector according to claim 1, further comprising: an annular ring electrode.

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