Effects of Indium Preamorphization on Boron Implanted Silicon Annealed by RTA
- PDF / 1,006,174 Bytes
- 7 Pages / 417.6 x 639 pts Page_size
- 44 Downloads / 196 Views
EFFECTS OF INDIUM PREAMORPHIZATION ON BORON IMPLANTED SILICON ANNEALED BY RTA E. Ganin, G. Scilla, T.O. Sedgwick and G. A. Sai-Halasz IBM T.J. Watson Research Center Yorktown Heights, NY 10598
Abstract Preamorphization by indium of boron implanted silicon layers has been studied as a means of reducing defects in the annealed and activated shallow junctions. The In preamorphized samples after RTP annealing at 950 to 11500C show an absence of 0 spanning dislocations. A 5 sec. anneal at 1 100 C results in the complete annihilation of residual dislocation loops at the original crystalline/amorphous (c/a) interface. The minimum dose to preamorphize Si with 200keV In was 5x10 13 /cm? During annealing the In was found to localize at two peaks, one at the original c/a interface and the other closer to the surface, where In precipitation was observed.
Introduction Formation of shallow p+/n junctions by boron ion implantation doping of Si has been studied extensively and reviewed in [1]. To avoid deep penetration of B due to channeling into the crystalline substrate, prior amorphization of the Si is required. Ion implantation of Si, Ge, As, Ar and Sn have been used to amorphize a thin layer of the substrate prior to the B implantation [2-6]. However, in most cases the subsequent annealing treatment resulted in either a high density of residual defects or a significant amount of B diffusion, which made the junctions too deep for shallow junction applications. The most serious problem, commonly observed in the self-amorphization by Si, is the formation of "spanning" dislocations. These dislocations emerge from the original crystalline/amorphous (c/a) interface [2,7]. and extend to the surface. They may form pipes for diffusion of dopants or act as gettering sites for heavy metals which may be recombination-generation centers in the space charge region. The density of "spanning" or hairpin dislocations is reduced by using Ge preamorphization [7]. Sands et al.[7] proposed a model where the spanning dislocation density is a function of the width of the c/a transition region. The narrower c/a transition regions produced by heavy ions, such as Ge or As, contain a lower density of potential nucleation sites for hairpin dislocations. However, formation of "spanning" dislocations can not be completely eliminated by usThere is also lack of a clear picture whether Ge ing Ge for amorphization. preamorphization enhances the B diffusion [3] or not [1]. Another factor, relevant to the formation of shallow B doped junctions, is the large misfit of substitutional B in the Si crystal lattice. Since the covalent radius of B is much smaller than that of Si, 0.82 as compared to 1.11, the misfit results in a significant defect (dislocation) density. To reduce the misfit, some compensation for the size factor can be introduced by implanting species with relatively large covalent radii. Indium is a good candidate for the aforementioned purpose. It is the same conductivity type as B and it is heavy enough to create a narrow c/a transition region. S
Data Loading...
