Chemisorption and Etching on Silicon Surfaces

               

Principal Investigator

M. W. Radny

Physics Department,

University of Newcastle

The main aim of this project is to study theoretically the chemisorption of different adsorbates on semi conducting (silicon) and metallic (copper) surfaces and the associated desorption processses. Such studies are important because they help us to understand the growth of semiconducting thin films and the extent to which semiconductor surfaces can be modified for specific applications. Understanding the desorption processes on solid surfaces is also very important because of the direct application of these processes in the fabrication of semiconductor devices and the manufacture of substrates for the very-large-scale integrated (VLSI) circuits which underlie so much of modern day electronics.    

Co-Investigators

     

P. V. Smith

P. C. L. Stephenson

A . J. Dyson

Physics Department

University of Newcastle

     
             

Projects

g38 - VPP

           

     
             
               

What are the results to date and the future of the work?

Recent work has concentrated on studying the reconstructions of clean semiconductor surfaces and the chemisoprtion of a large number of different adsorbates onto such surfaces. Significant progress has been made on a number of projects:

· Ab initio Hartree-Fock/DFT calculations of the equilibrium structures and binding energies for various SiHx molecules (x=2,3) on the Si(111)7x7 surface have been completed.

· The equilibrium structures corresponding to the chemisorption of boron onto the Si(111)3x3 surface have been determined and the work extended to look at the Al/Si and Ga/Si systems.

· The extended Brenner Si-H empirical potential has been developed and applied to the study of Si:H chemisorbed systems including the chemisorption of H onto the Si(111)7x7 surface and the C2H2 and CH3 chemisorption on the Si(001)2x1 surface.

What computational techniques?

Experience has shown that in order to gain an adequate understanding of these semiconductor chemisorption/desorption systems it is necessary to employ a number of different and complementary techniques. Our general approach is thus to first employ a semiempirical technique, which is quite fast computationally, to delineate the various possible minimum energy chemisorption sites. More rigorous geometry optimisation calculations will then be

               

- Appendix B


 
               

     

conducted using the ab-initio GAUSSIAN'94 or CRYSTAL'92 Hartree-Fock (HF) programs or the local density functional (LDF) program from the Fritz-Haber Institute in Berlin. These programs allow for both cluster and periodic calculations as well as the incorporation of correlation effects. Electronic structure determinations are performed using either CRYSTAL'92 or the Berlin LDF code. At present, the bulk of these calculations are being conducted on our own workstation network which includes three IBM RISC6000 machines and two DEC-ALPHA's. To obtain sufficiently accurate results to discriminate between different possible structures or reaction pathways, however, it is often necessary to employ very sophisticated basis sets (HF) or very large numbers of plane waves (LDF). Such calculations are beyond the capacity of our workstations and demand the capabilities of a supercomputer. Our approach to date has thus been to obtain the best HF geometries possible on our own workstation network, and then use these structures as the starting point for more accurate calculations on the VPP300.

Publications

P.C.L. Stephenson, M.W. Radny and P.V. Smith, A modified Stillinger-Weber potential for modelling silicon surfaces, Surf. Sci. 366, 177(1996).

M.W. Radny, P.V. Smith, and P.L. Cao, Chemisorption of fluorine onto the cluster modelled Si(111)7x7 surface: an ab initio Hartree-Fock/DFT study, Surf. Sci 351, 75 (1996).

A.J. Dyson and P.V. Smith, Extension of the Brenner interatomic potential to Si-C-H systems, Surf. Sci. 355, 140 (1996).

M.W Radny P.V Smith and P.L. Cao, An ab initio Hartree-Fock/Density Functional Study of the cluster simulated Si(111)7x7:Cl adsorption system, Surf. Sci. 365, 15 (1996).

J-Z Que, M.W. Radny and P.V. Smith, High exposure hydrogen chemisorption on the Si(111)7x7 surface: a semiempirical cluster study, J. Phys.:Condensed Matter 8, 4205 (1996).