Defect Engineering Using Boron and Germanium Doped Silicon Epitaxial Films for Electronic Applications

The diffusion of backside depositions of transition metals during rapid thermal annealing and the resulting frontside defect formation in silicon has been investigated. We have investigated the effect of nickel, copper, and gold on defect formation in silicon employing the rapid thermal processing (RTP) scheme. Treatment by RTP induces haze in the silicon wafer frontside when its backside is contaminated by either nickel, copper, or gold. Transmission electron microscopy studies showed that the haze consisted of metal silicide precipitates, which negates a previous suggestion that "oxidation-induced stacking faults" are the main defect forming the haze. The morphology and nature of these precipitates have been analyzed. The nickel silicide precipitates were found to be NiSi_2 and the copper silicide precipitates are most likely CuSi (zinc blende structure). Both kinds of precipitates exhibit an epitaxial relationship with the silicon substrate and adopted the shape of an inverted pyramid or section of a pyramid. Gold precipitates as rod shaped polycrystalline precipitates and small individual microcrystals. The control of dopants, impurities, and defects for ULSI of silicon integrated circuits requires a complex set of crystal and processing conditions to be satisfied simultaneously. In order to achieve the maximum yield and highest level of electrical performance for a given device design, we have manipulated the lattice constant and boron doping levels in CVD epitaxial silicon layers by alloying with a few percent of germanium during growth. By adjusting the ratios of germane and diborane in a dichlorosilane/hydrogen CVD reactor we can achieve either extrinsic gettering using the controlled introduction of interfacial misfit dislocations using Si(Ge), or buried, highly conducting layers which are strain-free and lattice matched to the silicon substrate. A variety of these epitaxial structures have been characterized using gated diode leakage, spreading resistance profiling, MOS lifetime, double crystal XRD, TEM, HRTEM, SEM/EBIC and SIMS depth profiling. Solid solubility and electrical activity limits of boron in strain compensated silicon epitaxial layers have been evaluated. We are now in a position to strategically locate co-doped Si(Ge,B) p ^{++} layers as recombination zones or buried field plates to suit the needs of MOS latch-up control, high speed devices, and radiation hard structures; as well as applications requiring defect free p ^{++} etch stops for thin membranes and three-dimensional silicon structures. In addition, Therma Wave imaging is used to nondestructively image the misfit dislocations and a semi-quantitative correlation between the Therma Wave signal and minority carrier lifetime on silicon substrates with a denuded zone and high quality epilayers grown with germanium induced misfit dislocations has been established. (Abstract shortened with permission of author.).