阅读说明：本技术 硅漂移探测器的制备方法 (Preparation method of silicon drift detector ) 是由 陶科 贾锐 姜帅 刘新宇 金智 张立军 王冠鹰 欧阳晓平 于 2020-06-15 设计创作，主要内容包括：本说明书提供一种硅漂移探测器的制备方法,包括沉积步骤；所述沉积步骤包括：以四氟化锗、高阶硅烷和掺杂剂硅烷作为反应气体,采用化学气相沉积工艺在具有钝化膜的硅衬底上沉积重掺杂锗薄膜,使重掺杂锗薄膜在硅衬底的对应区域形成功能区。因为高阶硅烷能够在较低温情况下被激活而与四氟化锗反应,所以在锗薄膜形成过程中可以采用低温工艺,而低温工艺可以避免扩散工艺和离散注入工艺中的高温对硅衬底的损伤,有利于获得较高的体寿命,提高硅漂移探测器的能量分辨率。(The specification provides a preparation method of a silicon drift detector, which comprises a deposition step; the depositing step comprises: and (3) taking germanium tetrafluoride, high-order silane and dopant silane as reaction gases, and depositing a heavily doped germanium film on the silicon substrate with the passivation film by adopting a chemical vapor deposition process, so that the heavily doped germanium film forms a functional region in a corresponding region of the silicon substrate. Because the high-order silane can be activated at a lower temperature to react with the germanium tetrafluoride, a low-temperature process can be adopted in the formation process of the germanium film, and the low-temperature process can avoid the damage of the high temperature in a diffusion process and a discrete injection process to the silicon substrate, thereby being beneficial to obtaining a longer body life and improving the energy resolution of the silicon drift detector.)

1. A preparation method of a silicon drift detector is characterized by comprising a deposition step;

the depositing step comprises: and (3) taking germanium tetrafluoride, high-order silane and a dopant compound as reaction gases, and depositing a heavily doped germanium film on the silicon substrate with the passivation film by adopting a chemical vapor deposition process, so that the heavily doped germanium film forms a functional region in a corresponding region of the silicon substrate.

2. The manufacturing method according to claim 1, wherein the corresponding region includes a collector electrode and a ground ring on the front surface of the silicon substrate;

the preparation method comprises the following steps: adopting a patterning process and an etching process to open a current collecting electrode window and a grounding ring window on the front passivation film of the silicon substrate:

the depositing step comprises: depositing and forming an N heavily doped germanium film on the surface of the silicon substrate by adopting germanium tetrafluoride, higher-order silane and phosphine as reaction gases;

the preparation method further comprises the following steps: and removing the N heavily doped germanium film except the collector electrode window and the grounding ring window region.

3. The method of claim 2, wherein:

after removing the N heavily doped germanium film except the collector electrode window and the grounding ring window region, the preparation method further comprises the following steps: adopting a patterning process and an etching process to open a drift ring window and a guard ring window on the front passivation film of the silicon substrate, and opening an incident window and a guard ring window on the incident surface passivation film of the silicon substrate;

the depositing step comprises: and (3) adopting germanium tetrafluoride, higher-order silane and diborane as reaction gases to deposit and form a P heavily doped germanium film on the surface of the silicon substrate.

4. The production method according to claim 3, characterized in that: after depositing and forming the P heavily doped germanium film, the method further comprises the following steps:

forming an etching window corresponding to a passivation film between the collector electrode window and the innermost drift ring window and an etching window corresponding to a passivation film in the region where the protection ring is located by adopting a patterning process;

and removing the P heavily doped germanium film on the passivation film between the collector electrode window and the innermost drift ring window and the P heavily doped germanium film on the passivation film in the region where the protection ring is positioned by adopting an etching process.

5. The production method according to claim 3, characterized in that: after the P heavily doped germanium film is formed by deposition, the method further comprises the following steps:

removing the P heavily doped germanium film except the collector electrode window, the grounding ring window, the drift ring window, the protection ring window and the incident window region;

and preparing a voltage divider on the passivation film between the windows of the drift rings.

6. The production method according to claim 3, characterized in that:

the thickness of the N heavily doped germanium film is 10-30 nm, and the doping concentration is 1 × 10¹⁹cm^-3～1×10²¹cm^-3The thickness of the P heavily doped germanium film is 10-50 nm, and the doping concentration is 1 × 10¹⁹cm^-3～1×10²¹cm^-3。

7. The production method according to any one of claims 1 to 5,

the higher-order silane is Si_nH_2n+2，2<n<6。

8. The production method according to any one of claims 1 to 6, wherein the passivation film is formed by:

soaking the silicon substrate in HF, and oxidizing with nitric acid to form a tunneling silicon oxide film;

growing an aluminum oxide film on the tunneling silicon oxide film by adopting an atomic layer deposition process;

growing a silicon oxide film on the surface of the aluminum oxide film by adopting a CVD (chemical vapor deposition) process;

the tunneling silicon oxide film, the aluminum oxide film and the silicon oxide film form the passivation film.

9. The method of claim 8, wherein:

the thickness of the tunneling oxide thin layer is less than 1.5nm, and the thickness of the aluminum oxide thin layer is 2.0-8.0 nm; the thickness of the silicon oxide film is 400-600 nm.

10. The production method according to any one of claims 1 to 6, wherein the passivation film is formed by the following steps:

growing an intrinsic amorphous silicon film on the surface of the silicon substrate by adopting a CVD (chemical vapor deposition) process;

growing an alumina film on the intrinsic amorphous silicon film by adopting an atomic layer deposition process;

growing a silicon oxide film on the surface of the aluminum oxide film by adopting a CVD (chemical vapor deposition) process;

the intrinsic amorphous silicon thin film, the aluminum oxide thin film and the silicon oxide thin film form the passivation film.

Technical Field

The specification relates to the technical field of semiconductor devices, in particular to a preparation method of a silicon drift detector.

Background

Drift detectors are semiconductor detectors (typically silicon-based detectors) for detecting high-energy radiation. When the drift detector works, the drift ring in the drift detector enables the substrate to be in a fully depleted state, and the majority carriers formed on the substrate through the incidence window drift to the collecting electrode along the direction of the surface of the device and are collected.

In the current manufacturing process of the silicon drift detector, the doping of the corresponding functional region is realized by adopting an ion implantation mode. Although the ion implantation method can control the concentration of the dopant and the doping depth of the formed dopant more precisely, it has the corresponding disadvantages: (1) in the ion implantation process, high-energy ions can cause damage to the surface of the silicon substrate; in order to repair the damage, a high-temperature annealing process is needed for repairing, but the damage cannot be completely repaired; (2) activating at a high temperature of about 1000 ℃ after boron ion implantation; but the high temperature activation process can cause the quality of the silicon substrate to be degraded; (3) the minimum junction depth formed by ion implantation is 40nm, which is larger than the depth process requirement of the ultra-shallow junction required at present, and the preparation process difficulty of the ultra-shallow junction is larger due to the depth; drift detectors formed by ion implantation processes are not conducive to the detection of low energy X-rays: (4) in the activation process after ion implantation, the doped atoms have the phenomenon of lateral expansion, so that the imaging size of the drift ring of the silicon drift detector is increased.

Disclosure of Invention

The specification provides a preparation method of a silicon drift detector, which comprises a deposition step;

the depositing step comprises: and (3) taking germanium tetrafluoride, high-order silane and a dopant compound as reaction gases, and depositing a heavily doped germanium film on the silicon substrate with the passivation film by adopting a chemical vapor deposition process, so that the heavily doped germanium film forms a functional region in a corresponding region of the silicon substrate.

Optionally, the corresponding region comprises a collector electrode and a ground ring on the front surface of the silicon substrate;

the preparation method comprises the following steps: adopting a patterning process and an etching process to open a current collecting electrode window and a grounding ring window on the front passivation film of the silicon substrate:

the depositing step comprises: depositing and forming an N heavily doped germanium film on the surface of the silicon substrate by adopting germanium tetrafluoride, higher-order silane and phosphine as reaction gases;

the preparation method further comprises the following steps: and removing the N heavily doped germanium film except the collector electrode window and the grounding ring window region.

Optionally, after removing the heavily N-doped germanium film except for the collector electrode window and the ground ring window region, the preparation method further includes: adopting a patterning process and an etching process to open a drift ring window and a guard ring window on the front passivation film of the silicon substrate, and opening an incident window and a guard ring window on the incident surface passivation film of the silicon substrate;

the depositing step comprises: and (3) adopting germanium tetrafluoride, higher-order silane and diborane as reaction gases to deposit and form a P heavily doped germanium film on the surface of the silicon substrate.

Optionally, after depositing and forming the P heavily doped germanium film, the method further includes:

forming an etching window corresponding to a passivation film between the collector electrode window and the innermost drift ring window and an etching window corresponding to a passivation film in the region where the protection ring is located by adopting a patterning process;

and removing the P heavily doped germanium film on the passivation film between the collector electrode window and the innermost drift ring window and the P heavily doped germanium film on the passivation film in the region where the protection ring is positioned by adopting an etching process.

Optionally, after depositing and forming the P heavily doped germanium film, the method further includes:

removing the P heavily doped germanium film except the collector electrode window, the grounding ring window, the drift ring window, the protection ring window and the incident window region;

and preparing a voltage divider on the passivation film between the windows of the drift rings.

Optionally, the thickness of the N heavily doped germanium film is 10-30 nm, and the doping concentration is 1 × 10¹⁹cm^-3～1×10²¹cm^-3The thickness of the P heavily doped germanium film is 10-50 nm, and the doping concentration is 1 × 10¹⁹cm^-3～1×10²¹cm^-3。

Optionally, the higher order silane is Si_nH_2n+2，2<n<6。

Optionally, the passivation film is formed by the following steps:

soaking the silicon substrate in HF, and oxidizing with nitric acid to form a tunneling silicon oxide film;

growing an aluminum oxide film on the tunneling silicon oxide film by adopting an atomic layer deposition process;

growing a silicon oxide film on the surface of the aluminum oxide film by adopting a CVD (chemical vapor deposition) process;

the tunneling silicon oxide film, the aluminum oxide film and the silicon oxide film form the passivation film.

Optionally, the thickness of the tunneling oxide thin layer is less than 1.5nm, and the thickness of the aluminum oxide thin layer is 2.0-8.0 nm; the thickness of the silicon oxide film is 400-600 nm.

Optionally, the passivation film is formed by the following steps:

growing an intrinsic amorphous silicon film on the surface of the silicon substrate by adopting a CVD (chemical vapor deposition) process;

growing an alumina film on the intrinsic amorphous silicon film by adopting an atomic layer deposition process;

growing a silicon oxide film on the surface of the aluminum oxide film by adopting a CVD (chemical vapor deposition) process;

the intrinsic amorphous silicon thin film, the aluminum oxide thin film and the silicon oxide thin film form the passivation film.

Because the high-order silane can be activated at a lower temperature to react with the germanium tetrafluoride, a low-temperature process can be adopted in the formation process of the re-germanium film, and the low-temperature process can avoid the damage of the high temperature in a diffusion process and a discrete injection process to the silicon substrate, thereby being beneficial to obtaining a longer body life and improving the energy resolution of the silicon drift detector.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention.

FIG. 1 is a schematic cross-sectional view of a silicon drift detector fabricated by the method of the present embodiment;

FIG. 2 is a flow chart of a method for fabricating a silicon drift detector according to an embodiment;

wherein: 11-silicon substrate, 12-passivation film, 13-collector electrode, 14-drift ring, 15-guard ring, 16-ground ring, 17-incident window electrode.

Detailed Description

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.

Fig. 1 is a schematic junction cross-sectional view of a silicon drift detector provided by an embodiment. As shown in fig. 1, the silicon drift detector provided in the present embodiment includes an N-type doped silicon substrate 11, passivation films 12 provided on both surfaces of the silicon substrate 11, and functional regions.

The functional region comprises an N-type heavily doped collector electrode 13, a P-type heavily doped drift ring 14, a P-type heavily doped guard ring 15, an N-type heavily doped ground ring 16 and a voltage divider arranged between adjacent drift rings 14, which are arranged on one surface of the silicon drift detector, and also comprises a P-type heavily doped incident window electrode 17 and a P-type heavily doped guard ring 15, which are arranged on the other surface of the silicon drift detector.

When the silicon drift detector is used, the voltage of each drift ring 14 is gradually reduced from the drift ring 14 close to the anode to the drift ring 14 far away from the anode, and the incidence window is also communicated with positive voltage, so that the drift region of the silicon drift detector forms a drift electric field. The silicon substrate 11 is formed into electron-hole pairs by X-ray irradiation of electrons into the substrate through the entrance window, the holes in the electron-hole pairs are rapidly consumed by the electrons transferred through the drift ring 14, and the electrons move toward the collector region under the action of the electric field and are collected by the collector electrode 13.

In order to avoid the problems of performance deterioration of the silicon substrate 11 caused by the ion implantation process mentioned in the background art, the embodiments of the present disclosure provide a method for manufacturing a silicon drift detector, in which the heavily doped portions of various functional regions are all implemented by a deposition step.

The deposition step comprises: and (3) taking germanium tetrafluoride, higher-order silane and a dopant compound as reaction gases, and depositing a heavily doped germanium film on the substrate with the passivation film 12 by adopting a chemical vapor deposition process, so that the heavily doped germanium film forms a functional region in a corresponding region of the silicon substrate 11.

Specifically, the foregoing deposition step is carried out in a low temperature region (at a temperature of 300 ℃ C. and 400 ℃ C.). Because higher order silanes have a stronger reducibility than silanes and disilanes, their reaction with germanium tetrafluoride requires lower reactant temperatures than other gases; during the deposition process, the epitaxial growth of the germanium film can be realized only by providing the temperature for maintaining the normal progress of the oxidation-reduction reaction.

As described above, since the temperature for forming the germanium film is low compared to the annealing temperature after ion implantation, the silicon substrate 11 is not exposed to a high temperature environment (such as 1000 ℃) during the formation of the germanium film using this process, and thus the problem of severe degradation of the performance of the silicon substrate 11 does not occur. In addition, the thickness of the germanium film in the implementation can be controlled by the reaction time and the reaction rate, so that an ultra-shallow junction can be formed, and the detection of low-energy X-rays is facilitated.

Fig. 2 is a flowchart of a method for manufacturing a silicon drift detector according to an embodiment. How to fabricate the silicon drift detector in combination with other processes and the deposition process described above is described below in conjunction with fig. 2. As shown in fig. 2, the preparation method provided in this embodiment includes steps S101 to S109.

S101: a passivation film 12 is formed on the silicon substrate 11.

In this embodiment, the process of forming the passivation film 12 may adopt a conventional thermal oxidation process, or may adopt other various processes; the present embodiment provides the following two processes for forming the passivation film 12 in consideration of reducing the temperature applied to the substrate as much as possible during the process.

First Process for Forming passivation film

The first process of forming the passivation film 12 includes steps S1011 to S1013.

S1011: after the silicon substrate 11 is soaked in HF, a tunneling silicon oxide film is formed by nitric acid oxidation.