Mechanical and piezoresistive properties of thin silicon films deposited by plasma-enhanced chemical vapor deposition and hot-wire chemical vapor deposition at low substrate temperatures

Abstract

This paper reports on the mechanical and piezoresistance characterization of hydrogenated amorphous and nanocrystalline silicon thin films deposited by hot-wire chemical vapor deposition (HWCVD) and radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using substrate temperatures between 100 and 250 °C. The microtensile technique is used to determine film properties such as Young’s modulus, fracture strength and Weibull parameters, and linear and quadratic piezoresistance coefficients obtained at large applied stresses. The 95%-confidence interval for the elastic constant of the films characterized, 85.9 ± 0.3 GPa, does not depend significantly on the deposition method or on film structure. In contrast, mean fracture strength values range between 256 ± 8 MPa and 600 ± 32 MPa: nanocrystalline layers are slightly stronger than their amorphous counterparts and a pronounced increase in strength is observed for films deposited using HWCVD when compared to those grown by PECVD. Extracted Weibull moduli are below 10. In terms of piezoresistance, n-doped radio-frequency nanocrystalline silicon films deposited at 250 °C present longitudinal piezoresistive coefficients as large as −(2.57 ± 0.03) × 10−10 Pa−1 with marginally nonlinear response. Such values approach those of crystalline silicon and of polysilicon layers deposited at much higher temperatures.

Piezoresistivity of thin film semiconductors with application to thin film silicon solar cells

“…0.06% [39] p-type a-Si:H Glow discharge 21 n.s. 0.06% [43] n-type a-Si:H RF-PECVD À 18 n.s. 1% -18 for intrinsic, n-type and p-type m-Si:H whereas it amounts to -51, -51 and 0 for intrinsic, n-type and p-type a-Si:H. M β takes a value of 10, -4 and 21.5 for intrinsic, n-type and p-type m-Si:H whereas it takes a value of À 1.5, 0 and 4.5 for intrinsic, n-type and p-type a-Si:H.…”

“…Material type Fabrication Gl Gt Maximal strain [41] n-type μ-Si:H RF-PECVD À 25 À 6 0.04% [41] p-type μ-Si:H RF-PECVD 25 7 0.04% [42] p-type μ-Si:H CMOS-MEMS 35 À 10 0.01% [43] n-type μ-Si:H HW-CVD À 14 n.s. 1% [44] n-type μ-Si:H RF-PECVD À 39 À 7.6 0.01% [44] p-type μ-Si:H RF-PECVD 20.8 À 7.8 0.01% [39] n-type a-Si:H Glow discharge À 18 À 7 0.06% [39] intrinsic a-Si:H Glow discharge À 8 n.s.…”

Influence of annealing on microstructure and piezoresistive properties of boron-doped hydrogenated nanocrystalline silicon thin films prepared by PECVD

“…Nc-Si:H thin films have also attracted growing interest due to their remarkable piezoresistive properties, and they are even identified as a promising material for potential application in piezoresistive sensors [13,14]. However, like other semiconductor materials, nc-Si:H thin films' piezoresistive properties are effected by many factors, such as deposition process parameters and doping type.…”

Size Effects of Hardness and Strain Rate Sensitivity in Amorphous Silicon Measured by Nanoindentation

“…Amorphous silicon (a-Si) is one of the most common materials used for manufacturing of MEMS. [1,2] In the literature, one can find evidence that processing conditions like deposition temperature, pressure, and flow rate of gases and processes like etching, chemical treatments, or ion implantation are known to affect the microstructural features as well as the distribution of volume and surface defects in this material. [3][4][5] To gain a deeper understanding between processing-structure-property-performance relationship for a-Si, much recent research interest has focused on characterizing hardness, Young's modulus, and pressure-induced phase transformations measured, i.e., by nanoindentation.…”