Texture and stress profile in thick polysilicon films suitable for fabrication of microstructures

Abstract

In this paper we report on results concerning the texture and mechanical stress of thick polycrystalline silicon films, grown in an epitaxial reactor. These phosphorus doped films were subjected to different annealing treatments at temperatures at or above 1100 °C in nitrogen and oxygen ambients, respectively. The morphology and texture of the films, respectively, were obtained using TEM and X-ray diffraction analysis. The samples texture does not present any significant changes related to the used annealing treatment. The stress gradient of released micromachined test structures was determined with optical interference measurements and compared with -Raman spectroscopy stress profiles and X-ray diffraction stress data using the sin 2÷-method obtained at different depths. We show that annealing in oxygen changes the stress state in the top regions of the polycrystalline films to a more compressive value, thus causing released beams to bend downwards. On the contrary, annealing in nitrogen atmosphere shifts the stress towards tensile values and released beams bend upwards.