Buried interface characterization in optoelectronic materials by interference microscopy

Abstract

In optoelectronic materials development, the analysis of buried interfaces is sometimes necessary in order to achieve the best optical and electrical performance. Interference microscopy has been investigated as a means to characterize interfaces buried under transparent layers. This technique is typically used at the air/material surface but since it is a non-contacting optical far field technique, it can also be used to measure buried interfaces which are innaccessible by near field scanning probes. We have succeeded in measuring the nanometric roughness of interfaces of porous silicon layers on silicon and of up to three successive buried interfaces in rare earth doped fluoride glass planar waveguides having reflectivities as low as 10−4 using phase stepping microscopy. Errors in the measured roughness values were introduced with increased depth of the interface, due to the distortion of the wavefront passing through the overlying transparent layer. Scanning white light interferometry was also used to measure the depth of the different interfaces in cases where the refractive indices were known to be homogeneous. Further work is required to better understand the origin of errors in the measurements due to the presence of the overlying transparent layers in order to improve the accuracy of the technique.