JP2000323741A - Fabrication of drift type silicon radiation detector having p-n junction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a detector having undeterirative characteristics and insusceptible to environment by forming a P-N junction without requiring any polishing after ending drift of impurities. SOLUTION: The method for fabricating a drift type silicon radiation detector comprises a step of forming an oxide film on the first and second planes of a semiconductor substrate by heating the semiconductor substrate in oxygen atmosphere after being cleaned, a photoprocess step for removing a diffused part, a first diffusion step of first impurities, and a second diffusion step of second impurities. A P-N junction is formed on the boundary of a first diffusion layer and a drift region extending from a second diffusion layer to the first diffusion layer. High resistance of the drift layer means a low carrier concentration and since the a depletion layer has a thickness equal to the effective thickness of the detector when the depletion layer is spread more under low voltage, a thicker detector can be formed as the carrier concentration decreases. Consequently, the detector has a sufficient resolution of 1.96%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a silicon radiation detector, and more particularly, to a method of manufacturing a drift type silicon radiation detector having a PN junction.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional method for manufacturing a silicon radiation detector has the following steps. (1) Cleaning of silicon wafer 1 (FIG. 2A) (2) Impurity diffusion (FIG. 2B) (3) Impurity drift (FIG. 2C) (4) Polishing finish (polishing finish on the surface opposite to the impurity diffusion layer) (FIG. 2D) (5) Metal deposition (forms a surface barrier) (FIG. 2E) (6) Adhesion (mount) (7) Electrode deposition In the impurity drift in the above step (3), the wafer is compared with the central part of the wafer. Due to the high drift speed at the periphery, when the impurity 4 (FIG. 2C) reaches the opposite surface of the wafer at the periphery, the impurity still does not reach the opposite surface of the wafer at the center.

[0003] Impurities (phosphorus, etc.) that hinder drift
And defects are more in the center than in the outer periphery of the wafer,
The drift speed is relatively high at the outer periphery of the wafer. The reason why there are many impurities and defects in the center of the wafer is that during crystal growth,
When a liquid is changed to a solid, impurities and defects are generally rejected to a portion that hardens later. Therefore, focusing on one cut wafer, impurities and defects increase in a central portion that is considered to be hardened later than the outer peripheral portion. It is.

[0004] In the drift method, holes due to P-type impurities B in Si are compensated by electrons due to N-type impurities Li to form a neutral region. Therefore, the speed at which Li advances is related to the B concentration. The Si substrate is a P type doped with a B impurity, but the B region diffused later is 3
It is a high concentration layer that is as many as an order of magnitude. Therefore, when the drifted Li reaches the B region diffused later, it takes a considerable time for Li compensation in that portion, and it appears that the Li has stopped.

[0005] For this reason, the surface of the opposite side of the wafer is polished (FIG. 2D) until the drift layer of the impurity in the center appears by performing the polishing in the above step (4), and the entire surface on the opposite side is drifted. Impurity 4 (FIG. 2D) must appear.

[0006] Such a conventional method has the following problems. (A) Polishing is required after the drift of impurities is completed. (A) After the impurity drift, a step (5) of depositing a metal to form a surface barrier is required. In the process of depositing the metal, the deposited metal is treated at a high temperature (500 ° C. or higher). On the other hand, the already formed impurity drift layer is formed by drifting the impurity diffusion layer at a temperature of about 150 ° C., and may be destroyed by such a high-temperature deposition process. . (C) In the drift type silicon detector manufactured by such a conventional method, since a surface barrier type diode is formed, the surrounding environment (pressure change, humidity, dust, etc.)
And the characteristics are easily degraded. The surface barrier type is vulnerable to the surrounding environment (pressure, humidity, dust, etc.) because the diode characteristics are determined between the electrode metal and Si. For example, if the electrode metal is damaged, the surface barrier type is completely deteriorated. (D) Due to the non-uniformity of the impurity distribution in the silicon base material forming the wafer, the drift speed of the impurity becomes non-uniform, and it is large in diameter (3 inches or more in diameter) and thick (5 mm or more).
Is difficult to fabricate. The reason why a thick detector is required is as follows. That is, the capacitance as a cause of noise can be reduced by the thickness of the detector, so that the performance as the detector is improved. The reason is that there is a relationship given by the following equation between the capacitance C and the thickness d of the detector.

C = ε _s ε ₀ S / d Here, ε _s represents the relative permittivity of silicon, ε ₀ represents the permittivity in a vacuum, and S represents the area of the detector. In particular, in a large area detector, this thickness is an important factor.

[0008]

SUMMARY OF THE INVENTION In order to solve the problems of the silicon radiation detector manufactured by the above-mentioned conventional manufacturing method and the difficulties of the manufacturing method, the present invention forms a PN junction type diode. Another object of the present invention is to manufacture a silicon radiation detector having a thickness that is strong even in a bad environment.

[0009]

To achieve the above object, the present invention provides a method for manufacturing a drift type silicon radiation detector having a PN junction, wherein a first conductivity type semiconductor substrate is cleaned. A cleaning process, heating the semiconductor substrate in an oxygen atmosphere to form an oxide film on a first main surface of the semiconductor substrate and a second main surface opposite to the first main surface; An oxidation process; removing a diffusion portion of the oxide film; a photo process process; and a portion of the first main surface of the semiconductor substrate exposed by removing the diffusion portion of the oxide film. Forming a first diffusion layer made of a first impurity of the first conductivity type, wherein the diffusion portion of the oxide film in the second main surface of the semiconductor substrate is removed. The first conductive material Forming a second diffusion layer made of a second impurity of a second conductivity type different from the second diffusion step, and drifting the second diffusion layer toward the first main surface; Forming a drift region of the second conductivity type extending from the second diffusion layer to the first diffusion layer, wherein a drift process is performed at a boundary between the drift region and the first diffusion layer; A method for manufacturing a drift-type silicon radiation detector, comprising: the drift process in which a PN junction is formed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIG. 3, the method for manufacturing a silicon radiation detector of the present application includes the following steps. (1) Cleaning of silicon wafer (2) Oxidation (3) Photo process (4) Diffusion of first impurity (FIG. 4B) (5) Diffusion of second impurity (FIG. 4C) (6) Second impurity Drift (FIG. 4D) (7) Polishing (8) Surface treatment (9) Adhesion (mount) (10) Electrode deposition Hereinafter, the manufacturing method of the present invention will be described with reference to specific examples.

The specifications of the specific example of the material silicon wafer used in the manufacturing method of the present invention are as follows. Crystal manufacturing method FZ method Crystal orientation <111> or <100> Doping agent B (boron) Resistivity 100 Ω · cm (to 3000 Ω · cm) Carrier lifetime 1 ms or more Dislocation density 1000 / cm ² or less P (adjacent) concentration 5 × 10 ¹² or less O (oxygen) concentration 1 × 10 ¹⁶ or less Surface finish Lapping or single-sided mirror finish In this specific example, boron (B) and second
(Li) was used as an impurity of the above. As the first impurity, boron (B), aluminum (Al), indium (In), which is a P-type impurity (acceptor),
Zinc (Zn), gallium (Ga), thallium (Ti)
However, lithium (Li), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi), which are N-type impurities (donors), may be used as the second impurities. good. (1) Cleaning Step First, an organic solvent cleaning is performed in which a wafer is ultrasonically cleaned or boiled with acetone and methanol. Next, the wafer is washed by boiling water. Next, the wafer is washed with running water with pure water or deionized water (15 MΩ · cm or more).
Finally, an etchant (eg, 1HF: 2HNO ₃ :
1CH ₃ COOH) to dissolve and remove the crushed layer on the surface of the wafer. (2) Oxidation process Wafer is heated at 850 ° C in pure oxygen (from 600 ° C to 900 ° C).
Heating for 7 hours to form a SiO ₂ film having a thickness of about 5000 Å. (3) Photo process (PEP) process S formed in the diffusion portion used in the subsequent diffusion process
The iO ₂ film is removed. Since the entire wafer is heated in the diffusion process, it is necessary to cover a portion not to be diffused with an oxide film. (4) B (boron) diffusion process PBF (Poly Boron Film) is applied to the diffusion part,
Heating at 0 ° C. (from 600 ° C. to 900 ° C.) for 24 hours, the diffusion depth is 0.4 μm (0.2 μm or more)
Is formed (FIG. 4B). (5) Li (lithium) diffusion process The surface of the wafer opposite to the surface on which the B diffusion layer is formed (hereinafter, referred to as “main surface of wafer”) (hereinafter, referred to as “opposite surface of wafer”) is placed in a vacuum. (1 × 10 ^-4 Torr or less)
And heated at 450 ° C. (from 400 ° C. to 500 ° C.) for 6 minutes (from 3 minutes to 15 minutes) to form a lithium diffusion layer 3 having a diffusion depth of from 0.3 mm to 0.7 mm. FIG. 4C) is formed. (6) Li (lithium) drift process First, the Li diffusion layer 3 (FIG. 4D) is formed so that the reverse characteristics of the PN junction diode formed in the wafer are improved, that is, the leakage current is reduced. The formed surface (Li side end face) is subjected to mesa etching or groove processing,
Voltage 1000V / cm (500V / cm to 2000V
/ Cm) at a temperature of 130 ± 20 ° C. for a time t defined by the following equation (FIG. 4).
D).

W = (2 × μVt) ^1/2 (Equation 1) where W is the width [cm] of the drift region, μ is the mobility [cm ² / V · sec] of lithium, and V is the reverse bias voltage. [V], t
Represents the drift time [sec], respectively.

As described above, when the drift process for the drift time t obtained from Equation 1 is completed, the drifted portion of Li (Li drift layer) is already formed in the entire cross section along the radial direction of the wafer. And a PN junction is formed between the Li drift layer 4 (FIG. 4D) and the B diffusion layer 2 (FIG. 4D). (7) Polishing process When a transmission type detector is manufactured, a polishing process is performed after a Li drift process to completely remove a Li diffusion layer. The transmission type is called a total depletion layer detector, and is used to detect the energy loss of radiation and the amount of charge generated at that time. Those that are not of the transmission type are used as partial depletion layer detectors. (8) Surface treatment process First, the wafer is treated with pure water or deionized water (15 MΩ · c).
In step m), pure water cleaning is performed. Next, an organic solvent cleaning is performed by ultrasonic cleaning or boiling cleaning of the wafer with acetone and methanol. Next, aqua regia cleaning is performed in which the wafer is boiled and washed with aqua regia. Next, the wafer is washed with running water with pure water or deionized water (15 MΩ · cm).
A second pure water cleaning is performed. Finally, the polished surface and the side surfaces (all surfaces other than the surface on which the B diffusion layer is formed) are etched using an etchant (for example, 1HF: 3HNO ₃ ). (9) Bonding (mounting) process The wafer 1 (FIGS. 5A and 5B) is bonded to an insulator 6 such as glass epoxy, acrylic, or ceramic (FIGS. 5A and 5B).
With an insulating adhesive. (10) Vapor deposition process By vacuum deposition, A is applied to both the main surface and the opposite surface of the wafer.
Metals such as u, Pt, Pd, Ni, and Al are deposited to form metal electrodes.

The specifications and characteristics evaluation results of the silicon radiation detector manufactured by the above-described manufacturing method of the present invention are shown below.

Specifications Shape Diameter 146 mm Thickness 10 mm Effective diameter 114 mm or more Effective thickness 6000 μm ± 200 μm Thickness uniformity in sensitive area Within ± 10 μm (95% of total area)
% Or more) Total depletion voltage 600 V Withstand voltage 800 V Leakage current 150 μA or less (600 V, 25 ° C.) Electrode side surface extraction Result of characteristic evaluation The voltage / current characteristics of the silicon radiation detector are shown in FIG. The current at the minimum voltage of 50 V in the characterization test was approximately 21 μA, and the current at the maximum voltage of 350 V was approximately 38 μA.

FIG. 7 shows the voltage-capacity characteristics of the silicon radiation detector. Regardless of the bias voltage,
The capacity is almost constant. This indicates that the depletion layer does not greatly expand due to the bias voltage because the resistivity of the drift layer is very high.

The high resistivity of the drift layer means that the drift layer has a high resistivity.
The low carrier concentration means that the depletion layer expands at a low voltage. Since the thickness of the depletion layer becomes the effective thickness of the detector (which is detected as a signal when radiation enters the portion), a thicker detector can be easily formed as the carrier concentration is lower. . The boron layer is about 0.5 μm, and the lithium drift layer is several meters.
m, and the boron layer serves as a radiation incident window, which is an insensitive layer. Therefore, the thickness is preferably as thin as possible. Since the lithium drift layer is a sensitive part, it is preferably as thick as possible. Also, if the depletion layer spreads to the boron side, a breakdown will occur.
The depletion layer is prevented from expanding into the boron layer.

FIG. 8 is a graph of a measured spectrum showing a result of the measurement performed for obtaining the α-ray resolution of the silicon radiation detector. The horizontal axis of the graph represents channels,
This channel corresponds to the energy of alpha rays, and the vertical axis is
Represents the count number, and the count number represents the count number detected by the detector for the α ray of each channel (energy).

The resolution is given by a value obtained by dividing the channel width at which the count number becomes 1/2 of the maximum value in the channel having the maximum count number. It is considered that the smaller the value of the resolution, the better the performance of the detector.

From the measurement results shown in FIG.
The maximum channel width is 8.7 channels (5.5 MeV), and the channel width at which the count number becomes 1/2 of the maximum value is 7.
It was measured to be 43 channels (108 keV). Therefore, the resolution of this detector is 108 keV /
5.5 MeV = 0.0196 = 1.96%.

One of the causes of increasing the value of the resolution is fluctuation of α-ray particles in the detector. And
A major factor of the fluctuation inside the detector is scattering of particles due to the presence of a surface insensitive layer on the surface of the detector. This surface insensitive layer is formed when the drift layer of the second impurity does not reach the diffusion layer of the first impurity. 5.
Since the α-ray of 5 MeV transmits only up to about 30 μm in silicon, the resolution value becomes large when such a dead layer is formed. In the detector manufactured according to the present invention, the resolution value is 1.96%,
Since it is a sufficiently good value, it is understood that the above-mentioned surface insensitive layer is not formed.

In the measured spectrum of FIG. 8, the pulsar is:
It represents the noise of the measurement system and represents the spectrum when a pseudo signal is directly input from a detector to a preamplifier that amplifies an output signal.

FIG. 9 shows the α-ray saturation characteristics of the silicon radiation detector. In this characteristic evaluation test, since the range of the α-ray in the silicon base material is about 30 μm, how much insensitive part (corresponding to the part where the drift layer has not reached) at the incident part
Made to find out if there is.

Next, a second embodiment of the present invention will be described with reference to FIG. 10, FIG. 11, and FIG.

FIG. 10 is a flowchart showing the steps of a manufacturing method according to the second embodiment of the present invention. The process of cleaning and oxidizing the silicon wafer is the same as the embodiment shown in FIG. In the photo process 1, the surface of the silicon substrate 1 on which the first impurity diffusion layer is formed, that is, the Si
A portion of the O ₂ film corresponding to the B diffusion layer formed is removed. Next, a diffusion process of the first impurity is performed to form the B diffusion layer of the circular central portion 2a and the diffusion layer of the annular portion 2b concentric with the central portion shown in FIGS. 11B and 12. You.

Next, in the process of forming the SiO ₂ film, the SiO ₂ film 7 is formed over the entire main surface of the wafer. Subsequently, in the second impurity diffusion process, a Li diffusion layer 3 is formed on the opposite surface of the wafer (FIG. 11C).

In the photo process 2, a portion of the SiO ₂ film 7 covering the main surface on which the B diffusion layers 2a and 2b are not formed is left, and another portion of the SiO ₂ film 7 is removed (FIG. 11D). ).

In the next drift process of the second impurity, drift processing is performed to form the Li drift layer shown in FIG. 11E. In the process of drifting the second impurity, the gold electrode 8 shown in FIG. 11E is used as a drift electrode. The gold electrode 8 is formed by vacuum evaporation after the photo process 2 is completed and before the drift process of the second impurity is started.

FIG. 12 is a plan view (FIG. 12A) and a side sectional view (FIG. 1) of a detector manufactured according to the second embodiment of the present invention.
2B). In FIG. 12A, the gold electrode 8 is omitted for clarity, but actually, the central portion 2 is not shown.
A circular gold electrode 8 is formed so as to cover a and the annular portion 2b. The annular portion 2b functions as a guard ring and has a function of preventing a leak current when the detector is used.

A polishing process, a surface treatment process, and a bonding (mounting) process performed thereafter are the same as those of the embodiment shown in FIG. In the electrode deposition process, an electrode is formed only on the opposite surface opposite to the main surface on which the gold electrode 8 is formed.

Next, a third embodiment of the present invention will be described with reference to FIG. 13, FIG. 14, and FIG.

FIG. 13 is a flowchart showing the steps of a manufacturing method according to the third embodiment of the present invention. The process of cleaning and oxidizing the silicon wafer is the same as the embodiment shown in FIG. In the photo process 1, the surface of the silicon substrate 1 on which the first impurity diffusion layer is formed, that is, the Si
A portion of the O ₂ film corresponding to the B diffusion layer formed is removed. Next, a first impurity diffusion process is performed, and the stripe-shaped B diffusion layer 2 shown in FIGS. 14B and 15 is formed.
c is formed.

Next, in the process of forming the SiO ₂ film, the SiO ₂ film 7 is formed over the entire main surface of the wafer. Subsequently, in the second impurity diffusion process, a Li diffusion layer 3 is formed on the opposite surface of the wafer (FIG. 14C).

In the photo process 2, the portion of the SiO ₂ film 7 covering the main surface where the stripe-shaped B diffusion layer 2c is not formed is left, and the other portion of the SiO ₂ film 7 is removed (FIG. 4). 14D).

In the next drift process of the second impurity, a drift process is performed to form the Li drift layer shown in FIG. 14E. In the drift process of the second impurity, the gold electrode 8 shown in FIG. 14E is used as a drift electrode. The gold electrode 8 is formed after the photo process 2 is completed and before the drift process of the second impurity is started.

FIG. 15 is a plan view (FIG. 15A) and a side sectional view (FIG. 1) of a detector manufactured according to the third embodiment of the present invention.
5B). In FIG. 15A, the gold electrode 8 is omitted for the sake of clarity, but a gold electrode having a shape corresponding to the stripe-shaped B diffusion layer 2c is actually formed.

The subsequent steps of polishing, surface treatment and bonding (mounting) are the same as those of the embodiment shown in FIG. In the electrode deposition process, when a one-dimensional position detector is manufactured, a process of forming a gold electrode formed on the main surface into a shape corresponding to the stripe-shaped B diffusion layer is performed, and the opposite surface is entirely formed. Electrodes are formed. When manufacturing a two-dimensional position detector, a stripe-shaped electrode orthogonal to the stripe-shaped electrode on the main surface is formed on the opposite surface.

The reason why the process of forming the SiO ₂ film is performed by the method according to the _second and third embodiments of the present invention will be described.

As in the third embodiment, the stripe-shaped B
When the diffusion layer is formed, in the portion of the silicon substrate between the stripe-shaped B diffusion layers, when the tip of the drift region reaches the gold electrode, the PN junction disappears at the position where the gold electrode has reached,
Drift stops before the entire portion of the silicon substrate between the B diffusion layers is converted into a neutral region by the drift layer. On the other hand, in the position detector, the region between the stripe-shaped diffusion layers must be a region having a high resistance value. When the region between the B diffusion layers is a region that remains the same conductivity type as the diffusion layer without being neutralized by the drift layer, each stripe-shaped diffusion layer is not electrically insulated, This is because the function as the position detector cannot be obtained. As described above, in order to prevent the drift from stopping before the neutralization by the drift layer is completed, before the drift process, the SiO 2 covering the main surface of the silicon substrate between the stripe-shaped diffusion layers is removed. _Two films were formed, and the drift region was kept out of contact with the gold electrode so that the drift was continued.

Further, when used as a radiation detector, including when used as a position detector, the shape of the diffusion layer on the main surface is set at the center in order to prevent leakage current flowing along the side surface of the silicon substrate. It is formed as an annular portion surrounding the portion and the central portion, and this annular portion is used as a guard ring for preventing leakage current.

In the case where the guard ring is formed in this manner, similarly to the case of the above-described position detector, the region between the central portion and the annular portion is completely made into a neutral region, and the region is made to have a high resistance value. It is necessary to

[0042]

According to the present invention, a PN junction can be formed without the need for polishing after completion of the impurity drift, which is required in the conventional method.
Since the PN junction is formed inside the Si substrate, it is possible to manufacture a detector that is not easily affected by the surrounding environment (pressure change, humidity, dust, etc.) and is not easily deteriorated. Further, according to the present invention, a detector having a large diameter (3 inches or more in diameter) and a large thickness (5 mm or more) can be manufactured, and a detector having a small electric capacity which causes noise is provided.

Further, according to the present invention, the portion of the silicon substrate between the diffusion layers is completely neutralized by the drift layer so as to electrically insulate each stripe-shaped diffusion layer of the manufactured position detector. Can be

[Brief description of the drawings]

FIG. 1 is a flowchart showing a process of a conventional method for manufacturing a silicon radiation detector.

FIGS. 2A to 2E are schematic views illustrating cross sections in steps of a silicon radiation detector made of A to E and manufactured by a conventional method of manufacturing a silicon radiation detector.

FIG. 3 is a flowchart showing the steps of a method for manufacturing a drift type silicon radiation detector according to the present invention.

FIGS. 4A to 4D are schematic views showing cross sections in each process of the silicon radiation detector which is composed of A to D and is manufactured by the method for manufacturing a drift type silicon radiation detector of the present invention.

FIG. 5 is a plan view of A and B, wherein A is a plan view of a silicon radiation detector manufactured by the method of the present invention, and B is a sectional side view of the silicon radiation detector manufactured by the method of the present invention.

FIG. 6 is a graph of voltage-current characteristics of a silicon radiation detector manufactured by the method of the present invention.

FIG. 7 is a graph of a voltage capacitance characteristic of a silicon radiation detector manufactured by the method of the present invention.

FIG. 8 is a graph of a measured spectrum for determining the α-ray resolution of a silicon radiation detector manufactured by the method of the present invention.

FIG. 9 is a graph of α-ray saturation characteristics of a silicon radiation detector manufactured by the method of the present invention.

FIG. 10 is a flowchart illustrating a process of a method for manufacturing a drift-type silicon radiation detector according to a second embodiment of the present invention.

FIGS. 11A to 11C are schematic views illustrating cross sections in steps of a silicon radiation detector made of A to E and manufactured by the method for manufacturing a drift type silicon radiation detector according to the second embodiment of the present invention.

FIG. 12 is a plan view of a silicon radiation detector manufactured by the method of the second embodiment of the present invention, comprising A and B, and B is manufactured by the method of the second embodiment of the present invention; FIG. 3 is a side sectional view of the silicon radiation detector.

FIG. 13 is a flowchart showing a process of a method for manufacturing a drift type silicon radiation detector according to the third embodiment of the present invention.

FIGS. 14A to 14C are schematic views illustrating cross sections in each step of a silicon radiation detector manufactured by the method for manufacturing a drift type silicon radiation detector according to the third embodiment of the present invention, which are composed of AE.

FIG. 15 is composed of A and B, where A is a plan view of a silicon radiation detector manufactured by the method of the third embodiment of the present invention, and B is manufactured by the method of the third embodiment of the present invention. FIG. 3 is a side sectional view of the silicon radiation detector.

[Explanation of symbols]

Reference Signs List 1 silicon base material 2 boron (B) diffusion layer 2a central circular portion of B diffusion layer 2b annular portion of B diffusion layer 2c striped B diffusion layer 3 lithium (Li) diffusion layer 4 lithium (Li) drift layer 5 metal layer 6 Insulator 7 SiO ₂ film 8 Gold electrode

Claims (7)

[Claims] 1. A method of manufacturing a drift-type silicon radiation detector having a PN junction, comprising: a cleaning step of cleaning a semiconductor substrate of a first conductivity type; and heating the semiconductor substrate in an oxygen atmosphere. A first main surface of a semiconductor substrate, and a second main surface opposite to the first main surface.
Forming an oxide film on a main surface of the semiconductor substrate; removing a diffusion portion of the oxide film; a photo process process; and forming a diffusion portion of the oxide film on the first main surface of the semiconductor substrate. In the part exposed by the removal of
A first diffusion step of forming a first diffusion layer made of the first impurity of the first conductivity type; and a step of removing the diffusion portion of the oxide film in the second main surface of the semiconductor substrate. Forming a second diffusion layer made of a second impurity of a second conductivity type different from the first conductivity type in a portion exposed by the second diffusion step; Forming a drift region of the second conductivity type extending from the second diffusion layer to the first diffusion layer by drifting toward a first main surface; A drift type silicon radiation detector, wherein a PN junction is formed at a boundary between the first diffusion layer and the first diffusion layer. 2. A method for manufacturing a drift-type silicon radiation detector having a PN junction, comprising: a cleaning step of cleaning a semiconductor substrate of a first conductivity type; and heating the semiconductor substrate in an oxygen atmosphere. A first main surface of a semiconductor substrate, and a second main surface opposite to the first main surface.
Forming an oxide film on the main surface of the semiconductor substrate, removing a diffusion portion of the oxide film, performing a first photoprocess, and forming an oxide film on the first main surface of the semiconductor substrate. In the part exposed by removing the diffusion part,
A first diffusion step of forming a first diffusion layer made of the first impurity of the first conductivity type; a second oxidation step of forming a second oxide film covering the first diffusion layer; A portion of the second main surface of the semiconductor substrate, which is exposed by removing the diffusion portion of the oxide film, includes a second impurity of a second conductivity type different from the first conductivity type. A second diffusion step of forming a second diffusion layer; a second photo process step of removing a portion of the second oxide film corresponding to the first diffusion layer; and a second diffusion step. Drifting a layer toward the first main surface to form a drift region of the second conductivity type extending from the second diffusion layer to the first diffusion layer, A PN junction is formed at a boundary between the drift region and the first diffusion layer; A method of manufacturing a drift-type silicon radiation detector, comprising: 3. The method of claim 2, wherein said first diffusion layer comprises a circular central portion and an annular portion formed concentric with said circular central portion. 4. The method of claim 2, wherein said first diffusion layer comprises a plurality of striped portions. 5. The method according to claim 1, wherein the first impurities are boron (B), aluminum (Al), indium (In), zinc (Zn),
Gallium (Ga) or thallium (Ti), wherein the second impurity is lithium (Li), phosphorus (P),
Arsenic (As), antimony (Sb), bismuth (Bi)
5. The method according to claim 1, wherein the method comprises: 6. The method according to claim 1, wherein the first impurity comprises boron (B), and the second impurity comprises lithium (Li). 7. The drift process is performed for a time t obtained by the following equation: W = (2 × μVt) ^1/2 where W is the width [cm] of the drift region, and μ is the width of the drift region. The mobility [cm ² ] of the second impurity, V is the reverse bias voltage [V], t
7. The method according to claim 1, wherein each represents a drift time [sec].