JP3963760B2 - Energy line discriminator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an energy beam discriminator, and more particularly, to an energy beam discriminator that detects α rays and has a higher energy than α rays, for example, transmits β rays and γ rays.
[0002]
[Prior art]
Conventionally, as a radiation detection apparatus that discriminates and detects radiation, for example, there is one disclosed in JP-A-5-3337. In this radiation detection apparatus, pn junctions are provided on the front and back sides of a single semiconductor, and a first depletion layer and a second depletion layer are formed by the first pn junction and the second pn junction, respectively. Is. Of these, energy rays having different energies, for example, α rays and β rays are projected onto the first depletion layer, the α rays are detected by the first depletion layer, and the β rays pass through the first depletion layer. The β rays transmitted through the first pn junction reach the second depletion layer and are detected by the second depletion layer.
[0003]
[Problems to be solved by the invention]
By the way, in this type of radiation detector, it is necessary to accurately form a depletion layer that transmits β rays while reliably detecting α rays. In order to transmit energy rays, for example, β rays, it is necessary to reduce the thickness of the substrate to a predetermined thickness.
[0004]
However, since the conventional radiation detector disclosed in the above publication uses a normal high-resistivity semiconductor, it is difficult to accurately adjust the film thickness. Further, there is a problem that it is difficult to ensure the strength of the semiconductor substrate only by thinning the film.
[0005]
Furthermore, in the radiation detector disclosed in the above publication, a first pn junction and a second pn junction are formed on the front and back of one semiconductor. For this reason, since the first depletion layer and the second depletion layer are formed on one semiconductor, it is difficult to reduce the thickness.
[0006]
On the other hand, as a technique for accurately thinning a so-called semiconductor substrate into a desired film thickness, there is one disclosed in JP-A-7-240534. However, the technique disclosed in the above publication is not used for an energy beam discriminator.
[0007]
Therefore, an object of the present invention is to accurately thin the semiconductor substrate and reduce the thickness of the semiconductor substrate so that the radiation detector for detecting the alpha rays can detect the alpha rays and transmit the radiation having higher energy than the alpha rays. It is also possible to have a high strength.
[0008]
[Means for Solving the Problems]
Energy ray discriminator according to the present invention which solves the above problems comprises a first layer through portions by an etching process is formed and a second layer which is laminated on the surface side of definitive to the first layer, the first The portion of the layer where the penetrating portion is formed is a thin portion, the portion where the first layer and the second layer are stacked is the thick portion, and the P-type semiconductor is formed on the surface side of the thin portion of the second layer. A semiconductor substrate having an N-type semiconductor layer formed on the back surface of the first layer and a portion exposed from the penetrating portion formed in the first layer in the second layer. An α-ray detector that detects β-rays and transmits β-rays or γ-rays , and has a stopper surface that serves as a stopper when performing an etching process to form a penetrating portion in the first layer. It is what.
[0009]
The semiconductor substrate of the energy discriminator according to the present invention is formed by laminating a first layer and a second layer, and an α-ray detector is formed in a thin part of the first and second layers. This thin portion is formed by etching the semiconductor substrate. In the energy ray discriminator according to the present invention, a stopper surface is formed between the first layer and the second layer when etching is performed. Yes. When the etching process reaches the stopper surface, the progress of the etching process stops at the stopper surface. For this reason, the thickness of the thin portion can be accurately controlled by forming the stopper surface at a predetermined position. Therefore, for example, the thickness of the thin portion can be controlled with higher precision than when the thickness of the thin portion is controlled by controlling the etching time.
[0010]
Further, by forming the stopper surface, the unevenness of the film thickness due to etching can be reduced. By reducing the unevenness of the film thickness, the α-ray detection accuracy in the α-ray detector can be further increased. Moreover, in addition to the thin portion where the α-ray detection portion is formed, it has a thick portion consisting of a portion where the first layer and the second layer are laminated, so that the strength of the entire semiconductor substrate can be increased. .
[0011]
Here, the semiconductor substrate is configured using a directly bonded wafer in which two wafers having different plane orientations are laminated and bonded, and the stopper surface is formed on the first layer of the wafers forming the second layer. The facing surface is preferred.
[0012]
By using the surface of the wafer forming the second layer facing the first layer as a stopper, the wafer forming the second layer has the thickness of the thin portion as it is, so that the thickness of the thin portion can be surely and easily. Can be controlled.
[0013]
More preferably, the first layer is configured using a silicon wafer having a plane orientation (100), and the second layer is configured using a silicon wafer having a plane orientation (111).
[0014]
By using a silicon wafer having a plane orientation (100) as the first layer, etching can be easily performed. Further, by using a silicon wafer having a plane orientation (111) as the second layer, the thin portion itself can be given higher strength than silicon having the plane orientation (100).
[0015]
Alternatively, the semiconductor substrate is formed using an SOI wafer in which a SiO ₂ film is formed between the first layer and the second layer, and one surface of the SiO ₂ film in the SOI wafer is a stopper surface. You can also
[0016]
Thus, an SOI wafer can be used as the semiconductor substrate. In this case, the SiO ₂ film laminated between the first layer and the second layer in the SOI wafer can be used as a stopper surface.
[0017]
Moreover, it is preferable that an electrode connected to the bonding wire is disposed on the second layer of the thick portion of the semiconductor substrate in which the first layer and the second layer are stacked. As described above, by disposing the electrode connected to the bonding wire in the thick portion, damage given to the detection portion due to an impact during wire bonding can be reduced.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol shall be used for the same element and the overlapping description is abbreviate | omitted.
[0019]
FIG. 1 is a side sectional view showing an energy beam discriminator according to a first embodiment of the present invention.
[0020]
As shown in FIG. 1, the energy beam discriminator 1 according to the present embodiment has a semiconductor substrate 10. The semiconductor substrate 10 includes, for example, a first layer 11 configured using a silicon wafer having a plane orientation (100) and a second layer 12 serving as an active layer configured using a silicon wafer having a plane orientation (111). The first layer 11 and the second layer are formed using a directly bonded wafer that is laminated and adhered. A through portion 11 </ b> A is formed in a part of the first layer 11. The position where the penetrating part 11 </ b> A is formed is the thin part 13 in the semiconductor substrate 10, and the thin part 13 is formed only by the second layer 12. Further, a thick portion 14 is formed around the thin portion 13, and the thick portion 14 is formed by laminating the first layer 11 and the second layer 12. The thickness of the thin portion 13 is, for example, 100 μm, and the thickness of the thick portion 14 is, for example, 300 μm. Further, the surface of the second layer 12 facing the first layer 11, that is, the surface on the first layer side 11 is the stopper surface of the present invention. Of this stopper surface, the position corresponding to the through-hole 11A formed in the first layer 11 functions as a stopper in the etching process.
[0021]
The thin-walled portion 13 is formed with an α-ray detector 15 (hereinafter referred to as a “detector”) 15 that detects α-rays and serves as a depletion layer that transmits energy rays having higher energy than α-rays, such as β-rays and γ-rays Has been. The detection unit 15 includes a P-type semiconductor layer (hereinafter referred to as “P + layer”) 16 formed on the surface side of the thin portion 13 in the second layer 12 and an N-type semiconductor layer (hereinafter referred to as “N”) formed on the back side. + Layer) 17). P + layer 16 is formed, for example, by diffusing P + impurities on the surface of second layer 12 , and N + layer 17 is a portion of second layer 12 exposed from through portion 11 </ b > A formed in first layer 11. The first layer 11 is formed over the entire back surface. These P + layer 16 and N + layer 17 form a PN junction. A channel stopper 18 made of an N + layer is formed around the P + layer 16 on the surface side of the second layer 12.
[0022]
Further, a SiO ₂ film 19 as a protective film is formed on the surface side of the second layer 12 so as to cover the P + layer 16 and the channel stopper 18, and the P + layer 16 and the channel stopper 18 are formed. The entire surface of the second layer 12 is protected. In addition, the SiO ₂ film 19 is partially removed from the position corresponding to the P + layer 16, and the anode electrode 20 made of aluminum is provided at the removed portion. 16 is connected. The anode electrode 20 is disposed on the thick portion so as not to damage the detection portion due to an impact during wire bonding. On the other hand, an aluminum layer 21 is laminated on the N + layer 17 formed on the back surface side of the second layer 12 at a position corresponding to the penetrating portion 11 </ b> A of the first layer 11 in the second layer 12. The cathode electrodes 22 and 22 made of Ni / Au are attached to the end of the aluminum layer 21.
[0023]
In the energy ray discriminator 1 according to the present embodiment having such a configuration, when the energy rays are α rays when the energy rays pass through the detector 15, the detector 15 detects the α rays. Further, when β rays and γ rays having higher energy than α rays are transmitted, β rays and γ rays are transmitted as they are. Transmitted β-rays and γ-rays transmitted through the detector 15 can be detected by an energy ray detector provided separately.
[0024]
Here, in order to detect α-rays and transmit β-rays and γ-rays to increase the detection accuracy, it is necessary to accurately control the thickness of the thin portion 13 in which the detection portion 15 is formed. Is done. In this regard, in the energy beam discriminator 1 according to the present embodiment, a directly bonded wafer obtained by directly bonding silicon wafers having different plane orientations is used as the semiconductor substrate 10. For this reason, the thickness of the thin portion 13 can be appropriately controlled to a desired thickness by performing an etching process described later.
[0025]
In addition, a thick portion 14 formed by laminating the first layer 11 and the second layer 12 is formed around the thin portion 13. By forming the thick portion 14, the strength of the entire semiconductor substrate 10 can be suitably increased. Moreover, since the second layer 12 constituting the thin portion 13 is made of a silicon wafer having a plane orientation (111), its strength can be fully expressed, so that the energy beam discriminator 1 can be increased in size. It can also respond.
[0026]
Next, the manufacturing method of the energy beam discriminator 1 which concerns on this embodiment is demonstrated.
[0027]
FIG. 2 is a process diagram showing a procedure for manufacturing the energy beam discriminator 1 according to the present embodiment.
[0028]
In manufacturing the energy beam discriminator 1 shown in FIG. 1, first, a directly bonded wafer formed by attaching the first layer 11 and the second layer 12 is prepared. Next, as shown in FIG. 2A, a P + layer 16 is formed by diffusing P + impurities on the surface side of the second layer 12 in the directly bonded wafer. A channel stopper 18 is formed around the P + layer 16 by diffusing N + impurities. Further, an SiO ₂ film 19 is formed on the surface side of the second layer 12. Then, for the etching process, the back surface of the semiconductor substrate 10 is covered with the SiN film 23, and as shown in FIG. 2A, a portion where the through portion 11A is formed in the first layer 11 is removed. Next, etching processing by Si wet etching using KOH is performed to form a penetrating portion 11A in the first layer 11 as shown in FIG. By forming the through portion 11A, the thin portion 13 in the semiconductor substrate 10 is formed.
[0029]
Here, the film thickness can be suitably controlled by forming the thin portion 13 by etching the first layer 11 to form the through portion 11A. This point will be described. For example, when an ordinary semiconductor substrate is etched to control the film thickness, the etching process time is controlled to control the film thickness. That is, as the etching progresses, the film thickness gradually decreases. Therefore, when a predetermined time elapses, the etching process is terminated and the film thickness is determined as a desired film thickness is reached.
[0030]
However, for example, when the etching time is shortened, the film thickness becomes too thick as desired, and conversely, when the etching time is long, the film thickness becomes too thin, and its control is relatively difficult. Even if the time control is performed reliably and the desired film thickness is obtained, the etching control time is long, so bubbles are generated from the scraped portion, and the time for contact with KOH varies from place to place. . As a result, as shown in FIG. 3, the surface 13 </ b> A of the thin portion 13 obtained by the progress of etching becomes rough and uneven film thickness is likely to occur. If unevenness occurs in the film thickness of the thin portion 13 where the detection portion 15 is formed, the detection accuracy when detecting the energy rays is reduced.
[0031]
On the other hand, the semiconductor substrate 10 according to the present embodiment is a directly bonded wafer formed by adhering two silicon wafers having different plane orientations. For this reason, the surface of the second layer 12 located at the boundary between the two silicon wafers serves as a stopper surface, and the first layer 11 is completely thinned by forming a through-hole 11A by etching. When it is removed, the stopper surface is reached, and the etching process is finished as it is. For this reason, it is not necessary to precisely control the etching time, and the film thickness can be reliably controlled. Further, the etching process is finished when the through-hole 11A is formed in the first layer 11, and the second layer 12 remains without being etched. For this reason, the position corresponding to 11 A of penetration parts of the 1st layer 11 in the 2nd layer 12 is maintained as a smooth surface, and does not become a rough surface. Therefore, when manufactured as the energy ray discriminator 1, the β ray and the γ ray can be reliably transmitted without deteriorating the detection accuracy of the α ray when detecting the energy ray.
[0032]
After the thin portion 13 is formed, the SiN film 23 is removed, and then, as shown in FIG. 2C, the N + layer 17 is formed on the entire surface (exposed portion surface) of the first layer silicon including the through portion 11A. Form.
[0033]
Thereafter, as shown in FIG. 1, a part of the SiO ₂ film 19 formed on the surface of the second layer 12 is removed, and an anode electrode 20 is provided on the thick portion on the SiO ₂ film 19 and connected to the P + layer 16. Is done. Further, an aluminum layer 21 is laminated on the back surface side of the first layer 11, and Ni / Au plating is applied to the position to attach the cathode electrode 22. Thus, the energy beam discriminator 1 is manufactured.
[0034]
In the energy ray discriminator 1 thus manufactured, the thickness of the thin portion 13 where the detection portion 15 is formed is thin, the thickness is appropriately controlled, and the surface is not roughened. For this reason, it is possible to reliably detect α rays and to transmit β rays and γ rays having higher energy than α rays. Further, the semiconductor substrate 10 includes a thick portion 14 in addition to the thin portion 13. The thick portion 14 can sufficiently develop the strength of the semiconductor substrate 10 as a whole.
[0035]
Next, a second embodiment of the present invention will be described.
[0036]
FIG. 4 is a side sectional view of the energy beam discriminator according to the present embodiment.
[0037]
As shown in FIG. 4, the energy beam discriminator 3 according to the present embodiment has a semiconductor substrate 30. The semiconductor substrate 30 is configured using a so-called SOI (Silicon On Insulator) wafer. For example, the first layer 31 using a silicon wafer having a plane orientation (100) and a silicon wafer having a plane orientation (111) are used. A second layer 32 is provided. An SiO ₂ film 33 having a thickness of 1 μm, for example, is interposed between the first layer 31 and the second layer 32. Further, a through portion 31 </ b> A is formed in a part of the first layer 31, and a position where the through portion 31 </ b> A is formed is a thin portion 34 in the semiconductor substrate 30. In addition, a thick portion 35 is formed around the thin portion 34, and the thin portion 34 includes the second layer 32, and the thick portion 35 includes the first layer 31 and the second layer 32. It has become. A detection portion 36 is formed in the thin portion 34.
[0038]
Furthermore, the position corresponding to the penetration part 31A in the SiO ₂ film 33 is removed, and the back side of the second layer 32 is exposed through the penetration part 31A. An N + layer 37 is formed on the back surface of the first layer 31, the penetrating portion 31 A, and the exposed portion on the back surface side of the second layer 32. Other configurations are substantially the same as those of the first embodiment.
[0039]
In the present embodiment, as in the first embodiment, since the film thickness of the thin portion 34 can be accurately controlled to a desired thickness, the detection unit 36 in the thin portion 34 detects α rays, It is possible to increase the accuracy when transmitting β rays and γ rays having higher energy than α rays. Further, since the thick portion 35 is formed around the thin portion 34, the strength of the entire semiconductor substrate can be increased.
[0040]
Next, the manufacturing method of the energy beam discriminator 3 which concerns on this embodiment is demonstrated.
[0041]
FIG. 5 is a process diagram showing a procedure for manufacturing the energy beam discriminator according to the present embodiment.
[0042]
In this embodiment, an SOI wafer in which a SiO ₂ film 33 is formed between the first layer 31 and the second layer 32 is used as the semiconductor substrate 30. With respect to this SOI wafer, as shown in FIG. 5A, P + impurities are diffused on the surface of the second layer 32 to form a P + layer 16. A channel stopper 18 is formed around the P + layer 16 by diffusing N + impurities. Further, an SiO ₂ film 19 is formed on the surface side of the second layer 12.
[0043]
Next, the first layer 31 is etched. For this etching process, the front and back surfaces of the semiconductor substrate 30 are covered with the SiN film 23, and the portions of the first layer 31 where the through portions 31A are formed are removed. Next, etching processing by Si wet etching using KOH is performed to form a through portion 31A in the first layer 31 as shown in FIG. By forming the through portion 31A, the thin portion 34 in the semiconductor substrate 10 is formed.
[0044]
In forming the penetrating portion 31A, in this embodiment, one surface of the SiO ₂ film 33 functions as a stopper surface. The SiO ₂ film 33 functions as a stopper having better etching selectivity than the Si / Si stopper using the difference in plane orientation in the first embodiment. Therefore, the film thickness can be more reliably controlled more easily than in the first embodiment, and the surface of the thin portion 34 does not become rough, and the film thickness can be prevented from becoming uneven. . Thereafter, as shown in FIG. 5C, a portion of the SiO ₂ film 33 exposed by forming the through portion 31A is removed.
[0045]
Thereafter, in the same manner as the manufacturing procedure shown in the first embodiment, the SiN film 23 is removed, and an N + layer 37 is formed on the entire surface (exposed portion surface) of the first layer silicon including the through portion 31A. To do. Then, as in the first embodiment, the anode electrode 20 is provided, the aluminum layer 21 is formed, the Ni / Au plating is performed, and the cathode electrode 22 is provided, whereby the energy beam discriminator 3 can be manufactured. it can.
[0046]
The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. The wafer used when directly bonding the semiconductor substrates is not limited to the silicon wafer, and other wafers can be used. Even at this time, similarly to the above-described embodiment, it is preferable to use silicon wafers having different plane orientations.
[0047]
As described above, according to the present invention, in the radiation detector for detecting α-rays, the α-rays are detected, and the semiconductor substrate is thinned with high precision so that the radiation having higher energy than the α-rays can pass through Further, even when the film is thinned, high strength can be achieved.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing an energy beam discriminator according to a first embodiment of the present invention.
FIG. 2 is a process diagram showing a procedure for manufacturing the energy beam discriminator according to the first embodiment.
FIG. 3 is a side sectional view showing a state in which film thickness unevenness has occurred in a thin film portion of a semiconductor substrate.
FIG. 4 is a side sectional view showing an energy ray discriminator according to a second embodiment of the present invention.
FIG. 5 is a process diagram showing a procedure for manufacturing the energy beam discriminator according to the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,3 ... Energy ray discriminator 10,30 ... Semiconductor substrate 11,31 ... 1st layer, 11A, 31A ... Penetration part, 12,32 ... 2nd layer, 13,34 ... Thin part, 14,35 ... thick portions, 15 and 36 ... detection unit, 16 ... P + layer, 17 and 37 ... N + layer, 18 ... channel stopper, 19 ... SiO ₂ film, 20 ... anode electrode, 21 ... aluminum layer, 22 ... cathode electrode , 23... SiN film, 33... SiO ₂ film.

Claims (5)

A first layer through portions by an etching process is formed, and a second layer which is laminated on the surface side of definitive to the first layer, the part where the through portion is formed in said first layer is a thin portion The portion where the first layer and the second layer are laminated is a thick portion , a P-type semiconductor layer is formed on the surface side of the thin portion in the second layer, A semiconductor substrate on which an N-type semiconductor layer is formed over a portion exposed from the penetrating portion formed in the first layer and a back surface side of the first layer ;
The thin-walled portion of the semiconductor substrate is formed with an α-ray detector that detects β-rays and transmits β-rays or γ-rays ,
An energy ray discriminator characterized in that a stopper surface is formed as a stopper when performing an etching process for forming a penetrating portion in the first layer. The semiconductor substrate is configured using a directly bonded wafer in which two wafers having different plane orientations are laminated and adhered,
2. The energy ray discriminator according to claim 1, wherein the stopper surface is formed by a surface facing the first layer of a wafer forming the second layer. The first layer is configured using a silicon wafer having a plane orientation (100),
The energy ray discriminator according to claim 2, wherein the second layer is configured using a silicon wafer having a plane orientation (111). The semiconductor substrate is configured using an SOI wafer in which a SiO ₂ film is formed between the first layer and the second layer;
The energy ray discriminator according to claim 1, wherein one surface of the SiO ₂ film in the SOI wafer is the stopper surface.   2. The energy ray discrimination according to claim 1, wherein an electrode connected to a bonding wire is disposed on the second layer of the thick portion of the semiconductor substrate in which the first layer and the second layer are stacked. vessel.

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