Characterization of Si, SiGe and SOI Structures Using Photoluminescence
- PDF / 5,183,012 Bytes
- 12 Pages / 417.6 x 639 pts Page_size
- 16 Downloads / 225 Views
V. HIGGS Bio-Rad Micromeasurements, Hemel Hempstead, HP2 7TD UK
ABSTRACT A new Photoluminescence (PL) method has been developed to detect defects in the near surface region of Si wafers and Si-on-insulator (SOI) structures. Wafer maps (up to 300 min diameter) can be readily acquired and areas of interest can be scanned at high resolution (ad1 gim). The excitation laser beam is modulated to confine the photogenerated carriers; defects are observed due to the localised reduction of the carrier lifetime. Si p-type (10 Ohm.cm) wafers were intentionally contaminated with various levels of Ni and Fe (lxi 95x10 10 atoms/cm 2) and annealed. The PL intensity was observed to decrease due to the metal related non-radiative defects. Whereas in contrast, for Cu, (lx10 9-5x10' 0 atoms/cm 2 ) the PL intensity actually increased initially and reached a maximum value at 5x10 9 atoms/cm 2 . It is suggested that during contamination the Cu related defects have complexed with existing defects (that have stronger recombination properties) and increased the PL. Further Cu contamination (lxl01°-5x10' 0 atoms/cm 2) produced a reduction in the PL intensity. PL mapping of strained SiGe epilayers showed that misfit dislocations can be detected and PL can be used to evaluate material quality. PL maps of SOI bonded wafers revealed that the non-bonded areas, voids or gas bubbles could be detected. This was confirmed using defect etching and polishing, voids as small as a30 [im in diameter could be detected. SOI wafers fabricated using the separation by implanted oxygen (SIMOX) technique were also analysed, variations in the recombination properties of the layer could be observed. Further inspection using transmission electron
microscopy (TEM) revealed that the defects were non-uniformities of the buried oxide covering several microns and containing tetrahedral stacking faults. Focused ion beam (FIB) milling and secondary ion mass spectrometry (SIMS) showed that these defects were at the Si/Si0 2 interface and were chemically different to the surrounding area. INTRODUCTION Photoluminescence (PL) spectroscopy is an extremely sensitive technique to investigate the intrinsic and extrinsic electronic transitions associated with defects and impurities in semiconductors. PL can also be used to measure the energy gap of a semiconductor, and for ternary alloys this is an extremely rapid practical method to measure their composition. PL is also a valuable characterization tool for low dimensional semiconductor structures such as quantum wells and quantum dots. At low temperatures, each impurity produces characteristic spectral features, therefore by recording a PL spectrum a specific impurity type can be detected and also the existence of other impurities readily evaluated [1]. Cryogenic PL spectroscopy is routinely used in Si to detect defects and impurities [2]. In addition, PI. is used to probe the processes occurring during device manufacture such as 129 Mat. Res. Soc. Symp. Proc. Vol. 588 ©2000 Materials Research Society
thermal diffusion and im
Data Loading...
