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RAPID THERMAL ANNEALING OF ION-IMPLANTED SILICON AND GALLIUM ARSENIDE*

J. NARAYAN Solid State Division, Oak Ridge National Laboratory, Oak Ridge,

TN

37831

ABSTRACT We have investigated the annealing of ion implantation damage (in the form of amorphous layers and/or the layers containing only dislocation loops) in silicon and gallium arsenide. The annealing of amorphous layers occurs by solidphase-epitaxial growth and that of dislocation loops involves primarily loop-coalescence as a result of conservative climb and glide processes. The annealing of isolated loops occurs primarily by a bulk diffusion process. Almost a "complete" annealing of displacement damage is possible for shallow implants provided loop-coalescence does not lead to the formation of cross-grid of dislocations. For deep implants, the free surface cannot provide an effective sink for defects as in the case of shallow implants. Dopant profiles can be controlled to less than 1000 A in layers having good electrical properties. The enhanced diffusion of dopants is observed probably due to entrapment of point defects in the annealed regions.

INTRODUCTION Ion implantation is now well established for a controlled introduction of dopants in semiconductors. It is an essential feature of all integrated circuit (IC) fabrication because of dopant profile control, reproducibility, and high throughput. However, the concomitant lattice damage produced by the energetic ions must be minimized or preferably removed to achieve electrical activation of dopants and recover carrier mobility.[1,2] For conventional devices, which can tolerate dopant redistributions up to one micron, furnace processing in the temperature range 950 to 10000C for times 20 to 40 minutes has been quite successful. However, for advanced IC technology requiring less than 0.1 Jim dopant redistribution, new methods of removing displacement damage are needed. In the last few years, various new methods of removing displacement damage have been attempted, which provide bright prospects for advanced IC technologies. These new methods can be broadly classified into three categories: (1) adiabatic annealing, (2) thermal flux annealing, and (3) rapid thermal annealing (RTA).[3-7] In this paper, we summarize fundamental aspects of annealing of ion implantation damage, and then cover in detail the results of RTA. The emphasis will be placed on mechanisms of annealing of displacement damage and dopant redistribution in ion implanted silicon and gallium arsenide. The paper is organized in the following sections: (1) nature of ion implantation damage, (2) fundamentals of annealing, (3) TEM (transmission electron microscopy) studies of displacement damage, (4) Rutherford backscattering (RBS) and Secondary Ion Mass Spectroscopy (SIMS) studies of dopant profiles after rapid thermal annealing, and (5) discussion and concluding remarks. (1)

Nature of Ion Implantation Damage

When an energetic ion penetrates a solid, it makes collisions with the electrons and the nuclei of the target material. The energy lost