INTERNAL-STRESS, THERMAL-EXPANSION COEFFICIENT AND BI-ELASTIC MODULUS OF PHOTOCHEMICALLY VAPOR-DEPOSITED HYDROGENATED AMORPHOUS-SILICON FILMS

The internal stress in photochemically vapour deposited hydrogenated amorphous silicon films decomposed from disilane (Si2H6) was studied by (n, -n) X-ray double-crystal spectrometry. It is tensile with magnitudes of 10(7) - 10(8) N m-2 and becomes more tensile with increasing growth rate, boron doping ratio and deposition temperature. Analyses of the stress-temperature curves of identical films deposited on two different substrates yield a thermal expansion coefficient of 2.2 x 10(-6) K-1 and bi-elastic modulus E/(1 - nu) of 3.2 x 10(11) N m-2 for the films over the temperature range 20-150-degrees-C in the atmosphere. The mechanical stress properties of the films are found to depend on the conditions of preparation through some features of the film structure such as hydrogen bonding modes, doping concentrations and grain boundaries.