TRIPLE AXIS X-RAY DIFFRACTION STUDY OF POLISHING DAMAGE IN III-V SEMICONDUCTORS. C.D.Moore, I.Pape and B.K.Tanner Physics Department, Durham University, Durham. DHI 3LF, UK

High resolution x-ray diffraction has been performed on single crystals of GaAs and InP which have been polished by various techniques. Chemical techniques include polishing with bromine methanol, hydrogen peroxide/ammonia, and sodium hydrochloride solution with alumina powder. The GaAs samples used the same substrate, whereas the InP crystals were produced by various companies, to show the applicability of this method as a means of substrate screening. A BEDE D³ diffractometer was used to record triple axis reciprocal space maps, to allow tilt and strain contributions to be resolved. Use of symmetric and asymmetric reflections enabled the depth penetration to be varied and the in-plane and out-of-plane components of strain to be separated.

The FWHM and EWl/50M have been extracted from the maps, and compared, in both the q_y direction (corresponding to lattice tilts) and in the q_z direction (corresponding to changes in lattice parameter). We find that for 004 symmetric reflections the lattice strain normal to the surface does not vary with sample preparation, but the tilt component to the rocking curve varies greatly. In the 224 asymmetric scans, where only approximately the top 1um contributes to the rocking curve, the strain present in the GaAs is again virtually independent of the polishing technique. The tilt contribution is seen to vary, but less substantially than in the 004 scans. This implies that polishing results in significant damage in the region of crystal below the very top surface, and that refinement of polishing technique serves to remove tilts from the crystal, but does not affect the crystal strains. Triple axis diffraction has thus been shown to provide a quantitative comparison of polishing standards in III-V semiconductor wafers.