STRUCTURE AND NONUNIFORM STRAIN ANALYSIS ON P-TYPE POROUS SILICON BY X-RAY REFLECTOMETRY AND X-RAY-DIFFRACTION

Structural properties of porous silicon layers performed on p-type (10 0) silicon wafers have been studied by X-ray reflectometry and X-ray d iffraction techniques. The mean surface porosity of the layers has bee n obtained by comparing the critical reflection angles of the porous l ayer and the silicon substrate. The obtained values are in agreement w ith microgravimetry measurements. The strain of the porous layer as a function of the technological parameters has been analyzed by X-ray di ffraction. The origin of the strain in the porous silicon is discussed according to the presence of stress and changes in the porosity acros s the layer. Finally, a minimum strain condition has been found, allow ing the optimization of the fabrication process.