DIFFUSE-X-RAY SCATTERING FROM P(+) POROUS SILICON BY TRIPLE AXIS DIFFRACTOMETRY

Strain and microstructure of porous silicon on (001) wafers with diffe rent porosity were investigated by triple axis x-ray diffractometry us ing an instrumental resolution of 12 arcsec. The Bragg diffraction pea ks arising from the porous Si contain information both on the mean str ain (1.29-2.95 X 10(-3)) and on strain gradients (0.70-1.42 X 10(-3)) in these samples. In specimens with a porosity of 60% the pores are sh own to be elongated over about 200 nm along the [001] direction, and o ver 50 nm in directions parallel to the growth plane. It is demonstrat ed that the correlation function for the pores has an extension along the [001] direction which is about a factor of 4 larger than along the [010] direction. From measurements of the intensity distribution of d iffuse x-ray scattering a crystallographical damage in the silicon ske leton can be excluded. Regions of the porous layer near the interface to air are shown to be tensilely strained both along and perpendicular to the substrate normal.