摘要：
多晶硅薄膜具有良好的压阻特性,晶粒结构和掺杂浓度决定其压阻特性.一般通过调节掺杂浓度改变压阻参数,但现有的多晶硅薄膜压阻系数与掺杂浓度的理论关系和适用范围不够全面.为了完善多晶硅薄膜压阻理论,基于多晶硅纳米薄膜隧道压阻模型,以及硅价带和空穴电导质量随应力改变的机理,提出了一种p型多晶硅薄膜压阻系数算法.该算法分别求取了晶粒中性区和复合晶界区的压阻系数π11,π12和π44的理论公式,据此可以计算任意择优晶向排列多晶硅的纵向和横向压阻系数.根据材料的结构特性,求取了p型多晶硅纳米薄膜和普通多晶硅薄膜应变因子,绘制了应变因子与掺杂浓度的关系曲线,与测试结果比较,具有较好的一致性.因此,该算法全面和准确,对多晶硅薄膜的压阻特性的改进和应用具有重要意义.%The polysilicon thin film piezoresistors are widely used in semiconductor pressure sensors. The polysilicon thin film has good piezoresistance properties, which are determined by the grain structure and doping concentration. The gauge factor of the polysilicon thin film is usually modified according to the relationship between gauge factor and doping concentration. The polysilicon thin films are classified into common polysilicon thin films and polysilicon nanofilms ac-cording to their thickness. The common polysilicon thin film thickness is more than 0.3 μm, which has good temperature characteristic, but its piezoresistance coefficient is small. However, the polysilicon nanofilm thickness is less than 0.1 μm, which has good temperature characteristic and high piezoresistance coefficient. The existing piezoresistance theory of the common polysilicon thin film cannot explain reasonably the experimental result of polysilicon nanofilm piezoresistance. Therefore, the tunneling piezoresistance model and an algorithm for the p-type polysilicon nanofilm piezoresistance coef-ficient were established in 2006. However, this algorithm presents an incomplete fundamental piezoresistance coefficient. In order to improve the polysilicon thin film piezoresistance theory, based on the tunneling piezoresistance model and the mechanism of silicon and the valence band hole conductivity mass with the change of stress, a novel algorithm for the piezoresistance coefficient of the p-type polysilicon thin film is presented. The theoretical formulas for three fundamental piezoresistance coefficientsπ11,π12 andπ44 of the grain neutral and grain boundary regions, are presented respectively. With these formulas for the coefficients, the longitudinal and transverse piezoresistance coefficients for arbitrary crystal direction texture polysilicon can be obtained. According to the structure characteristics, the gauge factors of the p-type polysilicon nanofilm and the common polysilicon thin film are calculated, and then the longitudinal and transverse gauge factors are plotted each as a function of doping concentration, which are compared with the experimental results. Ac-cording to the experimental results of the polysilicon nanofilm, the grain size is L=30 nm, the grain crystal directions are randomly distributed. The trap density in grain boundary region is Nt=1013 cm-2, the Young's modulus of elastic diaphragm is Y = 1.69 × 1011 Pa, the Poisson ratio of elastic diaphragm is ν = 0.062, the grain boundary width isδ=1 nm, and the thickness is 80 nm. The comparison indicates that the gauge factor average error between calculation and experiment is 0.5 times less than the average experimental difference between the maximum and the minimum for each doping concentration. For the common polysilicon thin film, according to the experimental results, its grain size L is 135 nm, thickness is 400 nm, the orientations of crystal grain neutral region are [311], [111] and [110] in the ratio of 49:31:20, i.e., 〈311〉:〈111〉:〈110〉=49:31:20, and the gauge factor calculated result is also good agreement with the experimental result. Therefore, the proposed algorithm is comprehensive and accurate, which is applicable to the p-type common polysilicon film and the polysilicon nanofilm.
