Development of radiation detectors based on hydrogenated amorphous silicon and its alloys Page: 100 of 182

                                
500
400
100  -
0
0     100    200     300    400    500    600
patterned width ( .m)
Figure 3.18. Comparison of calculated and experimental results for stress
reduction in the a-Si:H films grown on square islands as a function of the
lateral dimension of the squares. The dashed line and closed circles
represent calculated and experimental data, respectively.
However, since the thickness and the stress distribution for patterned substrates are
not uniform across the substrate, eqn. (2.3.6) in section 2.3.2 cannot be used to estimate
the stress in the patterned substrate. Also, since the films are amorphous, other stress
measurement techniques, such as photoluminescence or X-ray diffraction, cannot be
applied. Therefore, we used an equivalent thickness, ts, eqv, which is a thickness of an
imaginary, plain substrate having the same volume and area of the patterned substrate, in
place of the substrate thickness in eqn. (2.3.6). The resulting "apparent stress", is the
stress corresponding to a curvature of a plain substrate of thickness ts, eqv and can be
represented as follows:

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