Charge generation, transport, and recombination processes in UNIBOND® silicon-on-insulator wafers are studied via an optical second-harmonic generation (SHG) technique. The electric fields at the interfaces vary with time due to charge trapping. The presence of a thin native oxide layer on the top Si film contributes significantly to the SH intensity due to the strong time-dependent electric field generated by electrons transported to the surface. For the thick buried oxide, the electric field is primarily due to carrier trapping at the interface, and it varies with time weakly. The SHG signals depend strongly on the externally applied electric field, which can differentiate the contribution of each interface to the total SH signal.

In order to continue improving strained silicon-on-insulator ͑sSOI͒ crystal quality, high-resolution defect monitoring needs to be developed and implemented for further defects reduction. The study presented in this paper evaluates and compares two techniques for revealing crystal defects in sSOI wafers produced by the Smart-Cut Technology. Two different etching techniques, based on the use of gaseous HCl in an epitaxy reactor or of a diluted Secco wet etching solution, were compared on their ability to delineate various defects. Both techniques should provide the required defects density resolution for analysis of thin and thick strained silicon layers. For the sake of analysis and discussion, samples with a high defects density were chosen in order to simplify the quantitative comparison ͑within the resolution of optical microscopy͒. We have observed a difference in etching selectivity between the two techniques. After a statistical comparison of defects delineated by the two techniques ͑in terms of threading dislocations, areal densities, and planar defect linear densities͒, we have demonstrated complementarities rather than a direct correlation between the HCl and Secco etch. The HCl etch seems quite suitable for revealing threading dislocations through etch pits and shows a higher sensitivity for pit delineation compared to Secco ͑difference corresponding to a factor of 10 in defects density͒. Meanwhile, the Secco chemical etching appears more appropriate to highlight the planar defects ͑linear density between 600 and 1000 cm −1 ͒. Moreover, a minimum etched thickness for sSOI defect revelation has been determined for both techniques ͑between 26 and 36 nm for HCl and between 20 and 30 nm for Secco for a 600 Å thick starting layer͒. Because the Secco etch is particularly sensitive for the delineation of various types of defects ͑isolated etch pits and planar defects͒, it is now used by us as a quality control method for SOI and sSOI. Thanks to it sSOI process improvements are tracked and current and next generations of this product evaluated.

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A review of defect selective etchings used for process monitoring of Si, SiGe and Ge is presented. Cr-based and Cr-free solutions as well a gaseous HCl etch technique are described. Some applications of these techniques on Si and SiGe relaxed substrates as well their etching mechanisms are highlighted and discussed.

For the first time, we have evidenced a real correlation between 3 techniques used for defect delineation on Ge layers. Possible and different mechanisms of preferential etching will be also discussed. In the present paper we studied, namely, Cr- free wet-etching solution, gas phase HCl etching and Secco solution. Using optical microscope in the Nomarski contrast and AFM, we have studied the dislocations density and etch pits shape as a function of the etched thicknesses. Datas were compared with plan view TEM. Values close to 1E07cm-2 have been obtained in both cases, confirming the ability of the Cr-free solution to reveal dislocations. Similar values have been obtained on such thick Leti Ge layers after some Secco etch. The EPD values found using Secco are in good agreement with the ones found after HCl and Cr-free etches.