Piezoresistive Properties of Boron-Doped PECVD Microcrystalline Silicon Films

  • PDF / 359,669 Bytes
  • 6 Pages / 420.48 x 639 pts Page_size
  • 51 Downloads / 290 Views

DOWNLOAD

REPORT


PIEZORESISTIVE PROPERTIES OF BORON-DOPED PECVD MICROCRYSTALLINE SILICON FILMS Shu Wen GUO, Song Sheng TAN and Wei Yuan WANG Laboratory of Transducer Technology Shanghai Institute of Metallurgy, Academia Sinica 865 Chang Ning Road, Shanghai 200050, China ABSTRACT The piezoresistive properties of boron-doped PECVD microcrystalline Si films (pc-Si) deposited on Si0 2 coated Si, The relations covar or quartz substrates have been investigated. between the gauge factor (G.F.) and doping concentrations as have been obtained experimentalwell as the film thickness etc. ly. The maximum longitudinal G.F. of 25 and 20 are measured for An expression for calcuSi and covar substrates respectively. lating G.F. of P-type pc-Si is derived theoretically by use of the splitting model of heavy and light hole band at k=0 and the The calculated dependences of G.F. thermionic emission theory. on the doping concentrations, grain size and trap state density agree well with the experimental results, which offer a better understanding of the piezoresistive characteristics of pc-Si or poly-Si, and enable optimized design and fabrication of pc-Si or poly-Si strain gauges. INTRODUCTION Strain gauges fabricated with pc-Si or poly-Si have an optimistic future because of their lower cost and wider selection of substrate materials in comparison with that of It is shown that the diffused single crystal Si [1-6j. piezoresistive effect of pc-Si films is more complicated than that of single crystal Si due to the effects of the grain boundaries. The G.F. of the piezoresistors has strong dependences on the doping concentrations, grain size, trap density and the film texture, as well as the film thickness and the surface smoothness of substrates. In this paper, the effects of the various factors mentioned above on the G.F. of boron-doped PECVD pc-Si film resistors and the theoretical description of piezoresistive properties of pc-Si films have been measured and derived respectively. EXPERIMENTAL PROCEDURES The growth of Vc-Si films was carried out in a PECVD Silane (SiH4 ) gas diluted to 10% with Ar was used process. as the source gas and diborane (B 2 H6 ) gas diluted to 1% with H2 The (100)-oriented Si, covar and quartz as the dopant gas. 2 substrates with thickness of 0.2-0.35mm and dimension of 40x9mm were used as substrates. The layers of 2-4pm CVD phosphosilicate glass (PSG) and 0.5pm CVD Si0 2 were used as electrical isolation for covar substrates and reflowed after deposition to For Si substrates, an provide a smooth, pin-hole free surface. In order isolated layer of lpm thermally grown Si0 2 was used. to obtain a high degree of crystallization, several methods such the substrate as enhancing the rf power [5,7j, increasing

Mot. Res. Soc. Symp. Proc. Vol. 106.

1988 Materials Research Society

232

temperature [8,91 and adding the impurity gases into the growth In this work, the substrate atmosphere [101 were adopted. temperature was controlled over a range of 400-450°C and the rf The doping ratio (B 2 H6 /SiH 4 ) DC power was maintained at 150W.

Data Loading...