Microstructure of thick polycrystalline silicon films for MEMS application

Influences of deposition and crystallization kinetics on the properties of silicon films deposited by low-pressure chemical vapour deposition from silane and disilane

“…Since sigmoid variations were evidenced in figures 4 and 8, the residual stress  of silicon films annealed at 600°C was studied versus the polysilicon volume fraction fp-Si (figure 9). A linear relation was thus evidenced for both samples: (16) In the case of the silane SiH4 gaseous source, the a-Si and rp-Si values are constant whatever the deposition conditions and the residual stress  of silicon films depends finally only on the polysilicon volume fraction fp-Si: (12), (13) and (16), the residual stress of silicon films deposited from disilane Si2H6 is finally given by: Concerning the final stress value rp-Si, the discontinuity between silane SiH4 and disilane Si2H6 is obvious. Since the rp-Si values obtained for each gaseous source are constant whatever the deposition conditions, their difference should be related to LPCVD fundamentals, and therefore to the main chemical species responsible for the silicon films deposition in gaseous phase (see section 3.1).…”

“…Typically, the SEM pictures evidenced the growth of polysilicon grains, starting from an amorphous silicon (a-Si) microstructure and leading to a volume randomly polycrystalline silicon (rp-Si) one [8,16,21,24,28]. Nevertheless, by estimating the volume fraction of the polysilicon phase fp-Si, a good fit was obtained with equation 9 (figure 5), demonstrating the impact of the crystallization phenomena on the silicon films refractive index.…”

“…for the highest Vd/Vc ratios (Vd/Vc > 50), the silylene SiH2 pyrolysis is responsible for high hydrogen contents into the deposited amorphous silicon films [14][15][16]. Thus, as-deposited, dehydrogenated (thanks to a 15-minutes anneal at 600°C), and annealed (thanks to a 15-hours crystallization anneal at 600°C) samples were studied (figure 7).…”

“…The investigations have mainly concerned the silane SiH4 gaseous source [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. They evidenced that the deposition temperature T, the SiH4 partial pressure P and/or the deposition rate Vd were the main parameters for understanding the silicon films properties: cristallinity, microstructure, roughness, residual stress,… In parallel, the disilane Si2H6 gaseous source was also studied [18][19][20][21].…”

Roughness characteristic length scales of micro-machined surfaces: A multi-scale modelling

“…A serious difficulty is that all the micro machined surface topography cannot be recorded because the limits of the maximal scanning length: AFM areas rarely exceed 100 m × 100 m, and confocal or interferometric microscopy scanning is imposed by lens magnitude and camera resolution often limited to 1024 × 1024 pixels that does not allow to both having high definition and high scanning area. To characterise roughness surfaces, the Peak to Valley parameter [17,18] that represents the range of the roughness amplitude (called R t or PV) is of major interest in the case of dimensional tolerance characterisation for MEMS. However, this parameter depends on the evaluation length [19,20] and as the scanning area is often lower than the part area, the R t parameter of the part cannot be evaluated on the whole surface.…”