SELECTIVE EPITAXIAL-GROWTH OF SILICON BY THE AC TECHNIQUE .1. NONIMPLANTED SUBSTRATE OXIDE SURFACES/

Alternating cyclic, A.C., selective area epitaxial growth of silicon i n the Si-H-Cl and Si-H-Cl-Ar systems was carried out in a hot wall, lo w pressure epitaxial reactor, using patterned thermal oxide masks. The A.C. process is based on the existence of an embedded disproportionat ion reaction within the overall deposition chemistry, which provides a n effective mechanism for preventing the formation of nuclei in the ar eas where deposition is not desired. This disproportionation chemistry is made dominant cyclically, by pulsing the hydrogen off and on perio dically, in order to eliminate incipient nucleation. Experiments were conducted over a portion of the available parameter space, as determin ed by extensive thermodynamic analyses, using a reference non-A.C. dep osition process as a control, and comparing it with different A.C. fre quencies. Thus, the temperature was varied from 750 to 1000 degrees C, the pressure from 1.5 to 10 Torr, the H-2/SiCl4 ratio from 12.5/1 to 100/1, the Ar/H-2 ratio from 0 to 11. Total system now rate was varied from 2.04 slpm to 24.04 slpm, with the argon flow rate accounting for 0 to 22 slpm of these total values. Oxide coverage was varied from 10 0% (worst case situation) to 0% (best case situation). Epitaxial thick ness varied between 0.1 and 3.5 mu m. It was found that the substrate topology, and various experimental conditions influenced, to varying d egrees, the tendency for spurious nucleation in the masked areas. Howe ver, under all conditions, the A.C. technique prevented formation of s purious nuclei, guaranteeing essentially 100% selectivity control.