Semiconductor detector

Abstract

To provide a semiconductor detector that can improve CPS by reducing a rise time by being operated with higher bias.SOLUTION: A semiconductor detector includes: a semiconductor substrate 2; a first surface-side insulating film 10; a signal detection electrode 3; a plurality of drift electrodes 4; an incident window for radiation; a P-type semiconductor region; a depletion electrode; a plurality of field plate electrodes 13; charge collection electrodes 14 disposed in inter-electrode regions 4a between adjacent drift electrodes; a plurality of drift electrode connection portions 10a electrically connecting come of the plurality of drift electrodes and the field plate electrodes 13; and connection wires 15 electrically connecting the drift electrodes not connected to the field plate electrodes by drift electrode connection portions and the charge collection electrodes through collection electrode connection portions 10c.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a semiconductor detector capable of detecting electromagnetic waves and radiation. [Background technology]

[0002] Silicon drift detectors (hereinafter referred to as SDDs) are used as semiconductor detectors for electromagnetic waves such as X-rays or electron beams, which are applied to XRF (X-ray fluorescence analyzer) products that detect fluorescent X-rays, SEM-EDS (energy dispersive X-ray spectroscopy) products, and X-ray detectors for synchrotron radiation.

[0003] An SDD is a semiconductor detector that measures the energy and amount of electromagnetic waves based on the amount of charge that is collected by moving charge carriers generated when electromagnetic waves enter a depletion layer to which a drift electric field is applied to a signal detection electrode using the drift electric field. In other words, in an SDD, a reverse bias voltage is applied to a pn junction formed in a semiconductor substrate, causing a depletion layer to spread across the entire semiconductor substrate, and then electromagnetic waves are incident on the depletion layer, generating charge carriers that are then transported to a signal detection electrode in a drift electric field.The energy and amount of the electromagnetic waves are then measured based on the amount of charge collected by the signal detection electrode.

[0004] This SDD is often used in X-ray fluorescence analyzers because it has high resolution over a wide range of energies, from low energies of a few tens of eV to high energies of a few tens of keV, and can be cooled using a Peltier element instead of liquid nitrogen. Furthermore, the greatest advantage of SDD is that the size of the signal detection electrodes is extremely small, so the electrostatic capacitance (parasitic capacitance) of the signal detection electrodes can be kept small, independent of the signal detection area.

[0005] This advantage allows the SDD to reduce noise caused by parasitic capacitance, making it possible to measure low-energy electromagnetic waves. Furthermore, if the performance of SDDs can be further improved to enable them to detect a large number of electromagnetic waves in a short period of time, the range of applications for SDDs will expand, further increasing the value of SDDs.

[0006] For example, as shown in Figures 5 to 8, a semiconductor detector 100, which is a conventional field plate type SDD, includes a semiconductor substrate 2, a signal detection electrode 3 formed on a first surface (one side) of the semiconductor substrate 2, a plurality of drift electrodes 4 formed on the first surface of the semiconductor substrate 2 so as to surround the signal detection electrode 3 and for moving carriers in the direction of the signal detection electrode 3, a field plate electrode 113 formed on the first surface of the semiconductor substrate 2 and for suppressing current flowing between the drift electrodes 4, a drift electrode connection portion 10a connecting the drift electrode 4 and the field plate electrode 113, and a detection electrode connection portion 10b connecting the signal detection electrode 3 and the signal detection pad 12.

[0007] The field plate electrode 113 is an electrode provided for the purpose of reducing noise (dark current and leakage current) generated between the drift electrodes 4, and a bias is applied to it so that it has a higher potential than between adjacent drift electrodes 4, and it has the role of suppressing depletion of the SiO2 / Si interface 20 between the first-surface-side insulating film 10 and the semiconductor substrate 2. For example, as an example of such a field plate type, Patent Document 1 describes a semiconductor device provided with first and second conductive plates (FFP14 and 19) that are field plate electrodes. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2019 / 202760 Summary of the Invention [Problem to be solved by the invention]

[0009] The above-mentioned conventional techniques still have the following problems. The full width at half maximum (FWHM) and counts per second (CPS) are well-known indicators of SDD performance. The smaller the FWHM value, the higher the resolution of the detected signal, and the higher the CPS value, the more signals can be detected per unit time. A typical technique for improving CPS is to shorten the signal rise time. This rise time is lengthened by the expansion of the electron cloud, a mass of charge carriers generated by incident electromagnetic waves, as it moves from the outside of the SDD toward its center. Therefore, to shorten the rise time, it is advantageous to have an SDD with a smaller detection area. However, reducing the area also reduces the total number of counts, so it is not easy to increase the CPS while maintaining a short rise time.

[0010] On the other hand, as shown in Figure 5, among the biases applied to operate an SDD (the inner electrode R1, which is the central ring electrode on the ring side; the outer electrode RX, which is the outer ring electrode; and the depleted electrode BC, which is the back contact electrode on the window side), it is known that increasing the bias applied to the outer electrode RX shortens the rise time. This is due to the stronger electric field between the inner electrode R1 and the outer electrode RX, and between the outer electrode RX and the depleted electrode BC. This result suggests that the rise time may be shortened by increasing the operating voltage of the SDD. However, to operate an SDD, three biases must be applied: the inner electrode R1, the outer electrode RX, and the depleted electrode BC. These three biases are interrelated, and increasing the voltage of only one of them does not result in optimal SDD characteristics. For example, it is known to be difficult to obtain bias conditions that simultaneously shorten the rise time while maintaining an optimal FWHM.

[0011] The present invention has been made in view of the above-mentioned problems, and aims to provide a semiconductor detector that can shorten the rise time and improve the CPS by operating at a higher bias. [Means for solving the problem]

[0012] The present invention employs the following configuration to solve the above problems: That is, a semiconductor detector according to a first aspect of the present invention includes an n-type semiconductor substrate, a first-surface-side insulating film formed on a first surface of the semiconductor substrate, a signal detection electrode formed on the first surface and collecting charges generated by incidence of radiation, a plurality of drift electrodes formed on the first surface surrounding the signal detection electrode and moving the charges toward the signal detection electrode by applying a voltage so as to generate a potential gradient in which the potential changes toward the signal detection electrode, a radiation entrance window provided on a second surface of the semiconductor substrate, a P-type semiconductor region formed on the surface side of the second surface within the entrance window, and a depletion gate formed on the second surface and applying a reverse bias between the P-type semiconductor region and an N-type semiconductor region in the semiconductor substrate. a plurality of field plate electrodes formed on the outer surface facing adjacent drift electrodes to suppress current flowing between the drift electrodes; a charge collection electrode disposed in an inter-electrode region sandwiched between adjacent drift electrodes; a plurality of drift electrode connectors formed through the first-surface-side insulating film to electrically connect some of the plurality of drift electrodes to the field plate electrode; and connection wiring formed on the outer surface to electrically connect the drift electrodes not connected to the field plate electrodes by the drift electrode connectors to the charge collection electrodes via collector electrode connectors formed through the first-surface-side insulating film.

[0013] This semiconductor detector includes a connection wiring that electrically connects the drift electrode that is not connected to the field plate electrode by the drift electrode connection part to the charge collection electrode via the collection electrode connection part formed through the first-surface-side insulating film, so that the dark current between adjacent drift electrodes is absorbed via the charge collection electrode and the connection wiring, thereby suppressing the leakage current between the drift electrodes. Therefore, by suppressing the leakage current between the drift electrodes, the optimal bias can be set higher, and the rise time can be shortened.

[0014] The semiconductor detector according to the second invention is characterized in that, in the first invention, at least one of the plurality of field plate electrodes is arranged opposite and covers a space between three or more of the drift electrodes. In other words, in this semiconductor detector, at least one of the multiple field plate electrodes is arranged facing and covering a gap between three or more drift electrodes, making it possible to apply a higher bias between drift electrodes that are further apart. In this way, by generating a higher potential difference between the drift electrodes and adjusting the width of the wiring (ladder) connecting the drift electrodes, it becomes possible to control the voltage distribution between each drift electrode and the potential generated between the drift electrodes.

[0015] The semiconductor detector according to a third invention is the semiconductor detector according to the first or second invention, characterized in that the plurality of charge collection electrodes are provided in different inter-electrode regions and connected to one of the drift electrodes via the collection electrode connection parts and the connection wiring. That is, in this semiconductor detector, multiple charge collection electrodes are provided in different inter-electrode regions and are connected to one drift electrode via collection electrode connectors and connection wiring, so that charges can be collected more effectively. [Effects of the Invention]

[0016] According to the present invention, the following effects are achieved. That is, the semiconductor detector according to the present invention is provided with a connection wiring that electrically connects the drift electrode that is not connected to the field plate electrode by the drift electrode connection portion and the charge collection electrode via the collection electrode connection portion formed through the first-surface-side insulating film, and therefore, by absorbing the dark current between adjacent drift electrodes via the charge collection electrode and the connection wiring, leakage current between the drift electrodes can be suppressed. Therefore, in the semiconductor detector of the present invention, the optimum bias can be set higher, the rise time can be shortened, and the CPS can be improved. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view showing a semiconductor detector according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic cross-sectional view of a main part of the semiconductor detector in the present embodiment. [Figure 3] FIG. 2 is a diagram of the first surface showing the drift electrode and the like in this embodiment. [Figure 4] FIG. 2 is a diagram of the outer surface of the first-surface-side insulating film showing a field plate electrode and the like in this embodiment. [Figure 5] FIG. 1 is a schematic cross-sectional view showing a semiconductor detector in a conventional example of the semiconductor detector according to the present invention. [Figure 6] FIG. 10 is a schematic cross-sectional view of a main part of a semiconductor detector in a conventional example. [Figure 7] FIG. 1 is a diagram of the first surface showing the drift electrode and the like in a conventional example. [Figure 8] FIG. 10 is a diagram of the outer surface of the first-surface-side insulating film showing a field plate electrode and the like in a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of a semiconductor detector according to the present invention will be described below with reference to Figures 1 to 4. In the drawings used in the following description, the scale has been appropriately changed as necessary to make each component recognizable or easily recognizable.

[0019] 1 to 4, the semiconductor detector 1 of this embodiment is a silicon drift detector (SDD), and includes an n-type semiconductor substrate 2, a first-surface-side insulating film 10 formed on a first surface (the lower surface in FIG. 1) of the semiconductor substrate 2, a signal detection electrode 3 formed on the first surface and configured to collect charges generated by incidence of radiation X1, a plurality of drift electrodes 4 formed on the first surface surrounding the signal detection electrode 3 and configured to move the charges toward the signal detection electrode 3 by applying a voltage to the drift electrodes 4 so as to generate a potential gradient in which the potential changes toward the signal detection electrode 3, and a second surface (the upper surface in FIG. 1) of the semiconductor substrate 2. ), an entrance window 5 for radiation X1 provided in the first surface 10a, a P-type semiconductor region 6 formed on the surface side of the second surface within the entrance window 5, a depletion electrode BC formed on the second surface and applying a reverse bias between the P-type semiconductor region 6 and the N-type semiconductor region 2 a in the semiconductor substrate 2, a signal detection pad 12 formed on the outer surface of the first-surface-side insulating film 10 and facing the signal detection electrode 3, and a plurality of field plate electrodes 13 formed in an annular shape on the outer surface of the first-surface-side insulating film 10 surrounding the signal detection pad 12 and facing between adjacent drift electrodes 4, for suppressing current flowing between the drift electrodes 4.

[0020] The semiconductor detector 1 of this embodiment also includes a charge collection electrode 14 arranged in an inter-electrode region 4a sandwiched between adjacent drift electrodes 4, a detection electrode connection portion 10b formed to penetrate the first-surface-side insulating film 10 and electrically connecting the signal detection electrode 3 and the signal detection pad 12, a plurality of drift electrode connection portions 10a formed to penetrate the first-surface-side insulating film 10 and electrically connecting some of the plurality of drift electrodes 4 to the field plate electrode 13, and connection wiring 15 formed on the outer surface and electrically connecting the drift electrodes 4 that are not connected to the field plate electrodes 13 by the drift electrode connection portions 10a to the charge collection electrode 14 via collection electrode connection portions 10c formed to penetrate the first-surface-side insulating film 10.

[0021] At least one of the plurality of field plate electrodes 13 is disposed facing and covering a space between three or more drift electrodes 4. The plurality of charge collection electrodes 14 are formed on the first surface, provided in different inter-electrode regions 4a, and connected to one drift electrode 4 via collection electrode connectors 10c and connection wiring 15.

[0022] That is, as shown in Figures 2 and 4, each connection wiring 15 in this embodiment connects two charge collection electrodes 14 provided in different inter-electrode regions 4a to one drift electrode 4 via three collection electrode connecting parts 10c. 2 is a schematic cross-sectional view of a region surrounded by a virtual line (two-dot chain line) A in FIG. 3 and a virtual line (two-dot chain line) B in FIG.

[0023] The semiconductor substrate 2 is a Si substrate doped with n-type impurities, and is a high resistance substrate of 5 kΩ or more. The signal detection electrode 3 is + It is a signal output electrode made of a semiconductor and functions as an anode electrode. An amplifier 17 is electrically connected to the signal detection electrode 3 . The amplifier 17 includes, for example, a field effect transistor or a CMOS amplifier, and its gate electrode is connected to the signal detection electrode 3 .

[0024] The P-type semiconductor region 6 is doped with, for example, both B (boron) and F (fluorine). + The semiconductor substrate 2 is made of Si, and a pn junction is formed between the semiconductor substrate 2 and the N-type semiconductor region 2a. The P-type semiconductor region 6 functions as a cathode, and the signal detection electrode 3 functions as an anode. On the surface of the P-type semiconductor region 6, an oxide film (SiO2) 6a is formed.

[0025] The depletion electrode BC is a back contact connected to the P-type semiconductor region 6, and by adjusting the voltage applied to this depletion electrode BC, a reverse bias is applied to the pn junction, causing a depletion layer to expand from the pn junction and depleting the semiconductor substrate 2. In addition, a plurality of ring-shaped protective electrodes 8 are formed on the outer periphery of the depletion electrode BC, and are set to a floating potential in order to prevent dielectric breakdown between the edge of the semiconductor substrate 2 and the P-type semiconductor region 6.

[0026] The plurality of drift electrodes 4 are concentric ring electrodes centered on the signal detection electrode 3 and are formed at intervals from one another. Adjacent drift electrodes 4 are connected to one another by connecting portions 4b that are much thinner than the width of the drift electrodes 4. The drift electrodes 4 include an inner electrode R1 formed on the inner periphery and an outer electrode RX formed on the outer periphery. Different voltages are applied to the inner electrode R1 and the outer electrode RX, thereby forming a drift electric field in the semiconductor substrate 2 having a depletion layer. That is, the voltage is applied so that the innermost drift electrode 4 has the highest potential and the outermost drift electrode 4 has the lowest potential. The outermost electrode 4c is a ground electrode.

[0027] The first surface is a surface on which a plurality of ring-shaped drift electrodes 4 are formed, that is, a so-called ring surface. The second surface is a surface on which an entrance window 5 is provided, that is, a so-called window surface. On the outer periphery of the entrance window 5, a second surface side insulating film 9 made of an oxide film (SiO2) is formed as a guard ring. The protection electrode 8 and the depletion electrode BC are connected to the semiconductor substrate 2 and the P-type semiconductor region 6 by metal electrodes 9a made of Al or the like that penetrate the second-surface-side insulating film 9, respectively.

[0028] The first surface-side insulating film 10 is an oxide film (SiO2) formed on the first surface. The signal detection electrode 3 and the plurality of drift electrodes 4 are connected to the N-type semiconductor region 2a of the semiconductor substrate 2 by a drift electrode connection portion 10a and a detection electrode connection portion 10b that penetrate the first surface side insulating film 10, respectively. The detecting electrode connection portion 10b, the drift electrode connection portion 10a, and the collecting electrode connection portion 10c are metal electrodes made of Al or the like that penetrate the first surface side insulating film 10. As the metal electrode, Ti, poly-Si, etc. can be used in addition to Al, and it is preferable to use an element that is as light as possible and has low resistance.

[0029] The drift electrode 4 is formed by implanting B (boron) or Al (aluminum). The charge collection electrodes 14 and the signal detection electrodes 3 are formed by implanting P (phosphorus) or As (arsenic). The signal detection pad 12 and the field plate electrode 13 are patterned and made of Al (aluminum).

[0030] As shown in FIG. 3, a plurality of the connection wirings 15 are provided on the field plate electrode 13. As described above, drift electrode 4 connected to connection wiring 15 via collector electrode connector 10c is not connected to field plate electrode 13 via drift electrode connector 10a.

[0031] The plurality of field plate electrodes 13 are ring electrodes with the signal detection pad 12 at the center, and are formed at intervals from one another. 6, the field plate electrode 113 of the conventional SDD has a structure that covers only the space between two adjacent drift electrodes 4, whereas the field plate electrode 13 of the SDD (semiconductor detector 1) of this embodiment has a structure that covers not only the space between two adjacent drift electrodes 4 but also the space between the adjacent drift electrodes 4. In other words, the field plate electrodes 13 are arranged facing each other and cover the space between three drift electrodes 4.

[0032] The semiconductor detector 1 of this embodiment operates as follows.

[0033] First, when radiation X1 such as X-rays, photons, electron beams, or other charged particle beams is incident on the semiconductor substrate 2 through the entrance window 5, charges (holes H and electrons e) corresponding to the energy of the radiation X1 absorbed in the semiconductor substrate 2 are generated in the semiconductor substrate 2. These charges move due to the electric field in the semiconductor substrate 2, and electrons e flow into and are collected by the central signal detection electrode 3. The electrons e collected by the signal detection electrode 3 in this manner are output as an electric signal via the amplifier 17. Furthermore, dark current and leak current generated between adjacent drift electrodes 4 are absorbed from charge collection electrodes 14 disposed in inter-electrode regions 4a to connection wiring 15 via collection electrode connecting portions 10c.

[0034] As described above, the semiconductor detector 1 of this embodiment includes the connection wiring 15 that electrically connects the drift electrode 4 that is not connected to the field plate electrode 13 by the drift electrode connection portion 10a to the charge collection electrode 14 via the collection electrode connection portion 10c formed through the first-surface-side insulating film 10, so that the dark current between adjacent drift electrodes 4 (inter-electrode region 4a) can be absorbed via the charge collection electrode 14 and the connection wiring 15, thereby suppressing the leakage current between the drift electrodes 4. Therefore, by suppressing the leakage current between the drift electrodes 4, the optimum bias can be set higher, and the rise time can be shortened.

[0035] Furthermore, at least one of the multiple field plate electrodes 13 is disposed facing and covering a gap between three or more drift electrodes 4, making it possible to apply a higher bias between drift electrodes 4 that are further apart. In this way, by generating a higher potential difference between drift electrodes 4 that are further apart and adjusting the width of the wiring (ladder) connecting the drift electrodes 4, it becomes possible to control the voltage distribution between the drift electrodes 4 and to control the potential generated between the drift electrodes 4.

[0036] Furthermore, since multiple charge collection electrodes 14 are provided in different inter-electrode regions 4a and are connected to one drift electrode 4 via collection electrode connecting portions 10c and connecting wiring 15, charges can be collected more effectively. [Example]

[0037] As an example of the present invention, Tables 1 and 2 show the results of measuring the FWHM and rise time when the BC-R1 voltage and the RX-R1 voltage are changed for the SDD (semiconductor detector) of the above embodiment. The measurement results for the large-area SDD (semiconductor detector) are shown in Table 1, and the measurement results for the small-area SDD (semiconductor detector) are shown in Table 2. Furthermore, as a conventional example, the results of similar measurements on the conventional SDD shown in FIGS. 5 to 8 are also shown in Tables 1 and 2. From these results, it is clear that the rise time is shorter in all cases in the present invention than in the conventional example.

[0038] [Table 1]

[0039] [Table 2]

[0040] The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0041] 1,100...semiconductor detector, 2...semiconductor substrate, 3...signal detection electrode, 4...drift electrode, 5...entrance window, 6...p-type semiconductor region, 10...first surface side insulating film, 10a...drift electrode connection portion, 10b...detection electrode connection portion, 10c...collection electrode connection portion, 13,113...field plate electrode, 14...charge collection electrode, 15...connection wiring, BC...depletion electrode, X1...radiation

Claims

1. an n-type semiconductor substrate; a first surface-side insulating film formed on a first surface of the semiconductor substrate; a signal detection electrode formed on the first surface for collecting charges generated by incidence of radiation; a plurality of drift electrodes formed on the first surface surrounding the signal detection electrode, the drift electrodes moving the charges toward the signal detection electrode when a voltage is applied thereto so as to generate a potential gradient in which the potential changes toward the signal detection electrode; a radiation entrance window provided on a second surface of the semiconductor substrate; a P-type semiconductor region formed on the surface side of the second surface within the entrance window; a depletion electrode formed on the second surface for applying a reverse bias between the P-type semiconductor region and an N-type semiconductor region in the semiconductor substrate; a plurality of field plate electrodes formed on the outer surface of the first surface side insulating film so as to face between adjacent drift electrodes and suppress current flowing between the drift electrodes; a charge collection electrode disposed in an inter-electrode region between adjacent drift electrodes; a plurality of drift electrode connection portions formed through the first surface side insulating film and electrically connecting some of the plurality of drift electrodes to the field plate electrode; a connection wiring formed on the outer surface and electrically connecting the drift electrode, which is not connected to the field plate electrode by the drift electrode connection portion, to the charge collection electrode via a collection electrode connection portion formed through the first surface side insulating film.

2. 2. The semiconductor detector according to claim 1, A semiconductor detector, characterized in that at least one of the plurality of field plate electrodes is disposed facing and covering a gap between three or more of the drift electrodes.

3. 3. The semiconductor detector according to claim 1, A semiconductor detector characterized in that a plurality of the charge collection electrodes are provided in different inter-electrode regions and are connected to one of the drift electrodes via the collection electrode connection portion and the connection wiring.

Images