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Residual strain in annealed GaAs single crystal wafers measured by scanning infrared polariscopy and x-ray diffraction

: Herms, M.; Fukuzawa, M.; Melov, V.G.; Schreiber, J.; Yamada, M.

Ogawa, T.:
Defects - recognition, imaging and physics in semiconductors 1999. Proceedings : September 15 - 18, 1999
Amsterdam: North-Holland, 2000 (Journal of crystal growth 210,1/3)
International Conference on Defects in Semiconductors <8, 1999, Narita>
Fraunhofer IZFP ()
residual strain; x-ray diffraction; GaAs

The fabrication of most of micro and optoelectronic devices is based on substrates cut as wafers from melt-grown single crystals. The growth of crystals, the subsequent annealing steps and the fabrication of devices itself are a run of numerous different thermal procedures which induce residual strains due to a spatially inhomogeneous cooling of the material. These thermally induced strains both intensify the problems of breakage and warpage of wafer, influence the properties of surface with respect to subsequent steps of epitaxy and deposition, and change the electrical and optical parameters of crystal because of piezoelectric and photoelastic effects. As rule of thumb, temperature gradients of an order of magnitude between 1 and 100 K cm-1 cause a stress in a range of 1 and 100 MPa (10-6 and 10-3 on the scale of strain). As already discussed elsewhere [1,2], thermal gradients around 10 K cm-1 are typical of wafer annealing procedures.
Consequently, there is a strong demand for techniques which are able for the nondestructive quantitative characterization of strain in large diameter semiconductor wafers. As demonstrated in numerous papers, the polariscopy based on the strain-induced birefringence has proved as the technique both of the highest sensitivity (10-7) and of an adequate high spatial resolution (<100 µm), in particular achieved by means of the Scanning Infrared Polariscope (SIRP).
Nevertheless, until now there has been a lack to compare the results obtained by the polariscopy with those of other suitable techniques on the same scale. The limit of sensitivity in strain of the Raman spectroscopy amounts to about 10-4 only. In this paper we present X-ray diffraction data of strain resolved down to 10-6. For the comparison we have particularly to take into account that the SIRP provides combinations of the strain tensor components whereas the X-ray diffraction technique yields the separate ones.
The targets of comparison here presented are GaAs wafers multi-step annealed in arrangements of different geometry. Both the level and the spatial distribution of strain have significantly changed in dependence of this geometry. The maximum strain determined both by SIRP and by x-ray diffraction amounts to several 10-5. The points of x-ray measurement were chosen from characteristic areas in the highly resolved SIRP map. The strain data were converted into terms of separate stress components.