Spectroscopic ellipsometry (SE) characterization of several complex Si xGe1-x/Si heterostructures prepared for device fabrication, including structures for heterojunction bipolar transistors (HBT), p- and n-type heterostructure modulation-doped field-effect transistors, has been performed. It is shown that SE can simultaneously determine all active layer thicknesses, SixGe1-x compositions, and the oxide overlayer thickness, with only a general knowledge of the structure topology needed a priori. The characterization of HBT material includes the SE analysis of a SixGe1-x layer deeply buried (600 nm) under the silicon emitter and cap layers. In the SE analysis of n-type heterostructures, a silicon layer under tensile strain was examined. It was found that an excellent fit can be obtained using optical constants of unstrained silicon to represent the strained silicon conduction layer. SE was also used to measure lateral sample homogeneity, providing quantitative identification of the inhomogeneous layer. Surface overlayers resulting from prior sample processing were also detected and measured quantitatively. These results should allow SE to be used extensively as a nondestructive means of characterizing SixGe 1-x/Si heterostructures prior to device fabrication and testing.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)