Diffuse x-ray scattering from p+ porous silicon by triple axis diffractometry

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Abstract
Strain and microstructure of porous silicon on (001) wafers with different porosity were investigated by triple axis x-ray diffractometry using an instrumental resolution of 12 arcsec. The Bragg diffraction peaks arising from the porous Si contain information both on the mean strain (1.29–2.95×10−3) and on strain gradients (0.70–1.42×10−3) in these samples. In specimens with a porosity of 60% the pores are shown to be elongated over about 200 nm along the [001] direction, and over 50 nm in directions parallel to the growth plane. It is demonstrated 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 diffuse x-ray scattering a crystallographical damage in the silicon skeleton 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.