Meso-epitaxy: Epitaxial Growth of Silicon Over Buried Single Crystal CoSi 2 Layers
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Meso-epitaxy: Epitaxial Growth of Silicon Over Buried Single Crystal CoSi 2 Layers.
J. W. Osenbach*, A. E. White**, K. T. Short** H. C. Praefcke* and V. C. Kannon*** *AT&T Bell Laboratories, 2525 North 12th Street, Reading, Pennsylvania 19612-3566 **AT&T Bell Laboratories, 600 Mountain Avenue, Murray Hill, NJ 07960-4499 ***AT&T Bell Laboratories, 555 Union Boulevard, Allentown, Pennsylvania 18103
ABSTRACT Buried single-crystal layers of CoSi 2 were formed in 150n-cm, p-type (100) silicon by high dose implantation of Co followed by furnace annealing. Subsequently, epitaxial silicon layers were grown over these buried CoSi 2 layers using SiCl 2H2 /HCI/H 2 . The RBS channel yield of the buried CoSi 2 and the epitaxial Si layer is less than 4% indicating good crystallinity of the layer. The defect density in the epitaxial silicon 2 layer as revealed by a dilute Schimmel etch, was in excess of 108 dislocations/cm which appear to originate from CoSi 2 facets. However, both the substrate/CoSi 2 and the CoSi 2 /epi interface are single crystal as revealed by lattice fringes in TEM. To our knowledge, this is the first report of such a structure.
I. INTRODUCTION The cut-off frequency (fT) and maximum frequency (fm,,) that a bipolar transistor can achieve is in part determined by the collector series resistance. In addition, the rate at which the high current frequency rolls off is dependent to a large extent on the collector series resistance.(') For high speed transistors, the collector series resistance is minimized by ion implantation of a heavily-doped n÷ or p+ buried layer above which an epitaxial silicon layer is grown. Although the buried layer yields a relatively low resistivity collector contact, it also leads to increased transistor size and ultimately poor transistor performance due to lateral diffusion of the buried layer.(2) Furthermore, autodoping from the buried layer can limit the minimum epitaxial thickness required 3 for a transistor to sustain a given applied voltage.( )
Mat. Res. Soc. Symp. Proc. Vol. 198. @1990 Materials Research Society
568
We have produced buried collector contacts by growing 1000A buried layers of CoSi 2 using mesotaxy (4) followed by CVD deposition of an epitaxial silicon overlayer. Not only do these buried layers have much lower resistivity than the buried n+ or p+ layers (-20x10- 6 f-cm versus 10-3f-cm), but also autodoping and lateral diffusion are virtually eliminated. We call this new buried layer epitaxial process meso-epitaxy (Mepi) and our results on the growth and structural characteristics of this heterostructure are reported.
A. Experimental: To form the buried silicide layer, 2.7x1017 59 Co+/cm 2 was implanted into (100), 150 0-cm, p-type 75 mm float zone silicon wafers at 200 keV. The beam current density was 20 l±A/cm 2 and the silicon substrates were clamped to a stainless steel block which was held at 350'C during the implant to promote dynamic annealing. Postimplant annealing was done in two steps: 600 *C for 100 min. to partially regrow the Si and 1000*C for
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