双面三维多孔硅中子探测器的结构制备、电学和探测性能的研究

An unique structure of three dimentional (3D) silicon radiation detectors, where columnar electrodes penetrate through the silicon, enables reducing active thickness and electrodes distances. 3D silicon radiation detectors with low operation voltages, fast time responses and high charge collection efficiencies and strong radiation hardnesses are being studied for neutron detection and pixel readout. The fabrication of 3D neutron detector is facing the challenge of fabrication process in dual-type dopings and ohmic contacts in deep pores on a silicon surface. So a double-side 3D (DS-3D) detector is proposed for simplifing the fabrication process. The DS-3D structure is designed for doping silicon surfaces and depositing ohmic contacts from two side of silicon without fabricating very thick layers of polysilicon, and wafer bonding.. RIE for fabricating DS-3D silicon structure faces the limitations of introducing surface defect, high cost and depth-diameter ratio. So electrochemical etching, which could overcome these limatations, is expected to further simplify process of 3D detector fabrication. The detection efficency, spatial and temporal resolution of this new DS-3D silicon detector have not been clearly confirmed.. This project focuses on relation between the detection properties of this new DS-3D silicon detector and the structural parameters of the pores. The double-side electrochemical etching of silicon to form DS-3D silicon pore arrays and the electrical property of the doped DS-3D arrays for neutron detector will be studied. The DS-3D silicon pore arrays will be prepared by the electrochemical etching by optimizing etching solution, current, illumination, back side contact and prefabricated pits. The uniformity of doping and electrical property of doped DS-3D silicon pore arrays will be investigated. A prototype of neutron detector based on DS-3D silicon pore arrays will be fabricated via available technologies in fabricating semiconductor devices and filling a neutron converter material. The detection properties will be measured on a 2.5 MV proton electrostatic accelerator and a neutron radiation field equiped with necessary electronic devices. The secondary ion range produced by neutron in the DS-3D detector will be simulated for optimizing the sizes and distances of pores in the DS-3D detector. The ralation between detection properties and pore structures will be confirmed for the DS-3D neutron detector. The mechanism of detection will be studied in experiment and theory.

三维探测器被认为是新一代的高效率中子探测器和高像素分辨系统。基于单面多孔硅的三维探测器面临如相邻孔间的不同类型掺杂、孔内材料和涂层的填充等问题。双面三维硅结构是从硅片两面刻蚀形成的穿插结构，只需要考虑硅片每一面的同类型掺杂，可简化中子探测器制作的工艺。本申请拟研究电化学刻蚀制备双面三维多孔硅阵列的方法，以进一步简化三维探测器的制作工艺。研究双面三维硅结构的电学性能随多孔硅结构参数的变化规律。通过掺杂、电极制备和填充的工艺，制作双面三维硅探测器的原型器件，研究多孔硅结构参数对电学性能的影响。通过中子辐照测试和理论计算，研究双面三维探测器探测效率、时间和空间分辨率与多孔硅结构参数的变化关系，找到影响探测器性能的因素和规律。

三维硅探测器是提高探测效率、空间和时间分辨率的最具前景的新型器件。国际上大型设备更新换代的需求加速了研究者对三维探测器的关注和研究。本工作，实验上研究了电化学刻蚀三维硅结构的技术路线，理论上通过COMSOL软件计算和分析了刻蚀结构参数的变化规律和限制。通过构建模型和基于蒙特卡罗的Geant4 程序的计算，获得了三维结构的不同孔径、孔深、间距等参数下的探测效率。分别采用外协加工和自制两种方式，在半导体公司进行流片，对制备的三维多孔结构进行掺杂、沉积电极、填充转换材料，并研究了其电学性能，对实验和理论过程进行评价。结果表明：在三维硅结构的制备上，5.1% HF 和3.9% HF 刻蚀的孔有一定的变化规律，可实现规整多孔硅阵列的刻蚀，电流对孔有重构的作用，孔底的形状可从所建立的方程估算；探测效率随孔径尺寸或孔间距的增大先增大后减小，随孔深度的增大而增大，直到一个极限值，三维方孔硅探测器的最佳尺寸为孔间距6 μm、孔径尺寸30 μm、孔深度1 mm，其探测效率可达59.5%，若将该三维结构再推广到多层的全三维化，探测效率可达68.7%；由三维结构制备的器件在暗室和室光下的10 V和20 V漏电流曲线显示，漏电流的大小在微安级，在室光条件下电流有较大的增加，增加幅度近达4倍以上，并且该器件还可加更高的电压，孔内也填充了中子转换材料，该器件在探测热中子上可能有更好的探测效果。本工作探讨了三维中子探测器的工艺过程中遇到的问题，明确了多孔硅形成机制、计算了探测效率与孔参数的关系、探讨了工艺过程。意义在于指明了面向应用还存在工艺和技术问题，为进一步研究提供了研究基础。