Strain measurements in silicon using X-ray interferometry

• Main Author: Walmsley, C. F.
• Published: University of Edinburgh 1979
• Subjects: 620.110287
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663424

The aim of this work was to investigate by X-ray interferometer techniques the strain induced in silicon after thermal oxidation and boron diffusion processing. An elasticity model was developed by which the resulting strain and interferometer moire fringe pattern could be predicted when the oxidation or diffusion took the form of a circular disc. By this means, the stress in oxide thermally grown at 950 °C was measured to be 1.65 x 10' dynes/cm2. Double crystal techniques were used to measure the wafer bowing after oxidation, giving good agreement with the interferometer measurements. The solute lattice contraction coefficient for boron was measured by interferometry and found to be 6.0 x 10-2'tm'/atom. Combining this result with four point probe measurements, the mobility of holes in degenerate silicon was found to be 122 cm2/volt sec. By keeping the total dose of boron below the critical value of 3 x 10 5 atoms/cm2 in order to avoid lattice dislocation, it was found by double crystal measurements that this was insufficient to produce a significant diffraction peak from the diffused region under conditions of total Bragg reflection. The possibility of using oxidation or diffusion processing to alter the lattice parameter of silicon or germanium suitably in order to construct an X-ray monochromator or resonator capable of performing at room temperature was shown to be impracticable. Finally, the Burger's vectors of dislocations appearing in an interferometer after oxidation were successfully determined.