Two-dimensional modeling of solid phase epitaxial regrowth using level set methods

Solid Phase Epitxial Regrowth (SPER) has a huge technological relevance in the formation of source/drain regions of MOS devices. Source/drain regions are patterned amorphous regions that need to be modeled in 2D/3D. The macroscopic velocity, v, of an interface between amorphous (alpha) and crystalline (c) phases (also referred to as the SPER or regrowth front/interface) is known to be a thermally-activated process with an activation energy of ∼2.7 eV. Additionally, SPER is affected by the crystal orientation of alpha-Si/c-Si interface, impurities, and applied mechanical stress.;In this work, level set model was set up to model SPER. The alpha-c Si interface propagation velocity was computed using a substrate orientation dependent velocity term along with a local interface curvature term. This velocity was fed to the advection equation of level set formulation for simulating SPER. Simulations were checked against observed TEM images of SPER of ∼120 nm deep, patterned amorphous trench at T = 500°C and at t = 1 h, 2 h and a good matching was observed for all times.;More experiments were done to confirm the presence of interface curvature term on SPER using structures containing both convex and concave interfaces. During SPER at T = 500°C, the concave interface sharpened while the convex interface flattened out. The simulations were successfully able to predict the shapes of alpha-c Si interface during SPER at all times. The experiment when repeated at a higher temperature of 575°C resulted in similar regrowth shapes implying a negligible effect of temperature on the curvature factor.;Effect of n and p dopants on patterned SPER was studied in an experiment with very low resistivity (∼0.003 ohm-cm) wafers. The results showed the isotropic nature of dopant enhancement (both p and n type) on SPER, something that extends the generalized Fermi level shifting theory (for dopant enhancement of SPER) for all substrate orientations. The results also helped de-link the curvature effect from the electronic effect of dopants on SPER. Models for dopant diffusion in amorphous Si were linked to the SPER model to get accurate dopant profile after regrowth.;Finally, the effect of uniaxial stress on patterned SPER was studied in an experiment where stresses (both tensile and compressive) upto ∼1.3 GPa were applied. The experiments showed the strong effect of in-plane uniaxial compression on regrowth shapes that resulted in the formation of mask-edge defects. The results for the tensile case were found to be exactly the same as nostress case, something that was observed previously for planar regrowth of (001) Si. The curvature factor was able to encapsulate the effect of external in-plane uniaxial stress and simulations matched up to the observed results. A more physical understanding of the curvature factor was explored using simulations with rough alpha-c Si interfaces. Ultimately, a complete 2-D model for patterned SPER was developed using level set methods for interface propagation.