Heemyong Park

Effects of hydrostatic pressure on dopant diffusion in silicon

A point‐defect‐based model for the stress effects on dopant diffusion in silicon is presented. Variations in binding energies and diffusivities of dopant‐defect pairs under hydrostatic pressure are modeled, and a pressure‐dependent dopant diffusion equation is derived. New experimental work was performed on boron pileup near dislocation loops, and compared to the model. Qualitative agreement is possible, which suggests that stress might be a significant effect in scaled modern device structures.

High-resolution x-ray diffraction for characterization and monitoring of silicon-on-insulator fabrication processes

High-resolution x-ray diffraction (HRXRD) was used to monitor silicon-on-insulator (SOI) device fabrication processes. The use of HRXRD is attractive since it is nondestructive and can be applied directly to product wafers. We show the usefulness of this technique for the characterization of amorphizing implants for shallow junctions, solid phase recrystallization of implanted junctions, cobalt-silicide formation, and oxidation; all are critical processes for complementary metal oxide semiconductor device fabrication on SOI. We also found the technique applicable to multilayered SOI structures fabricated by wafer bonding, where the tilt and rotation of each SOI layer with respect to the handle substrate, allowed us to obtain independent measurements of each SOI film.

Point defect based modeling of low dose silicon implant damage and oxidation effects on phosphorus and boron diffusion in silicon

Point defect kinetics are important for understanding and modeling dopant diffusion in silicon. This article describes point defect models and compares them with experimental results for intrinsically doped material. Transient dopant diffusion due to low dose silicon implant damage can be modeled with the same parameters as oxidation enhanced diffusion, and therefore provides an additional technique to probe point defect behavior. Parameters are extracted consistently for both experimental conditions and fit to Arrhenius relationships. The theory of dopant‐defect pairing is found to be crucial in modeling the implantation damage effects, and the effective binding energies for boron‐defect and phosphorus‐defect pairs are experimentally determined.

Effects of low-dose Si implantation damage on diffusion of phosphorus and arsenic in Si

The effects of low‐dose Si implantation damage on diffusion of low‐concentration P and As in Si wafers are investigated. Dopants are implanted at a low dose and subsequently preannealed to remove any self‐damage. An enhanced diffusion of P is observed by directly comparing dopant profiles in damaged and undamaged regions. Monitoring effective diffusivity of P at various annealing temperatures and times reveals that the enhanced diffusion is a transient process with a time constant which is larger at lower temperature. This enhancement is larger and of longer duration the lower the annealing temperature is. In contrast to P, As diffusion in the damaged region does not show any enhancement. This implies that the defects induced by the Si implants have separate mechanisms for interaction with each type of dopant.

The effects of strain on dopant diffusion in silicon

A point defect based model for the stress effects on dopant diffusion is presented. Binding energies and diffusivities of dopant-defect pairs under pressure are modeled and encapsulated into diffusion equations. Boron segregation around dislocation loops in silicon is explained by the pressure effects, and the simulation agrees with the measured data. Two-dimensional simulation of diffusion in the pressure field leads to better prediction of threshold voltage shift in short channel LDD MOS transistors. The model also shows that retarded diffusion of phosphorus under oxide-padded nitride film of various widths is caused by the stress at the film edge.<<ETX>>

A Point Defect Based Two‐Dimensional Model of the Evolution of Dislocation Loops in Silicon during Oxidation

A point defect based model is developed in two dimensions for the evolution of a group of dislocation loops induced by high dose ion implantation in silicon. Assuming an asymmetric triangular density distribution of periodically oriented circular dislocation loops provides an efficient model reflecting the nonuniform morphology of the loops as observed in transmission electron microscopy (TEM) experiments. The effective pressure from the ensemble of dislocation loops is numerically calculated on the basis of the established formulation of pressure from a single circular loop. The pressure field from the layer of dislocation loops is fundamental to the modeling, as it largely affects equilibrium point defect concentrations and boundary conditions governing emission and absorption of the point defects

Theory of dopant diffusion assuming nondilute concentrations of dopant‐defect pairs

Current dopant diffusion theory is based on dopant‐point‐defect interaction, and assumes that the number of dopant‐defect pairs is much smaller than the unpaired dopant concentration. In cases where a large number of excess defects are created from implantation damage, this may no longer be a valid assumption. A new derivation of the dopant and defect equations is presented which is valid for any concentration of dopant‐defect pairs.

Diffusion‐limited interaction of dislocation loops and interstitials during dry oxidation in silicon

The interaction of implantation‐induced dislocation loops and interstitials in silicon is studied. Experiments under dry oxidation conditions consistently show a significant reduction of OED (oxidation enhanced diffusion) of boron in a buried layer due to very efficient interstitial capturing action of dislocation loops, suggesting diffusion‐limited dislocation loop growth. Simple analytic solution of interstitial supersaturation and analysis of the data in terms of time dependence of the OED suppression demonstrate that the interaction of dislocation loops and interstitials is not a reaction‐limited but a diffusion‐limited process. Simulations incorporating the model for the interaction mechanism agree with both secondary ion mass spectroscopy and transmission electron spectroscopy data.

Strain induced changes in gate leakage current and dielectric constant of nitrided Hf-silicate metal oxide semiconductor capacitors

Uniaxial-mechanical-stress altered gate leakage current and dielectric constant of silicon metal-oxide-semiconductor (MOS) devices with nitrided Hf-silicate (HfSiON) dielectric are measured as a function of uniaxial stress applied using four-point wafer bending along the [110] direction. The gate leakage current and dielectric constant are found to increase by ∼2% per 100MPa of tensile and compressive stresses. A decrease in hole trap activation energy in hafnium oxide-based dielectric is used to explain the mechanical stress altered gate leakage. It is proposed that the HfSiON dielectric constant increase results from band gap narrowing caused by strain induced N p band splitting.

Dopant redistribution in SOI during RTA: a study on doping in scaled-down Si layers

We present a systematic study on redistribution of B, P, and As in silicon-on-insulator (SOI) during RTA as the top silicon layer is scaled down to /spl sim/0.05 um. New observations are reported on dopant diffusion in the thin SOI layers compared with bulk Si and its dependence on silicon thickness, initial doping distribution, and anneal conditions. It is shown, for the first time, that pile-up of boron occurs in the thinner SOI near the buried oxide (BOX) interface during inert RTA, while phosphorus is depleted. We show that the amount of each dopant inside the SOI layers changes due to interface transport as Si layer thickness is reduced. Theoretical models of the BOX effects are tested experimentally by using high resolution X-ray diffraction and direct-contact rapid thermal heating.