Formation of Raised Source/Drain Junctions by Rapid Thermal Chemical Vapor Deposition

Abstract

AbstractIn this paper, we present alternative uses of rapid thermal chemical vapor deposition (RTCVD) in forming junctions for the raised source/drain MOSFET. The results will include applications of epitaxial silicon, SixGe1−x and TiSi2 all selectively deposited in dedicated coldwalled, lamp heated high or ultra high vacuum RTCVD reactors. Two general approaches will be considered : 1) ultra shallow junction formation in silicon followed by a selective deposition process to form a raised contact, 2) selective deposition to obtain a layer that can be used as a solid diffusion source and as a sacrificial layer for self-aligned silicide formation. In the first approach, junctions are formed typically by low energy ion-implantation. In this paper, we present rapid thermal vapor phase doping (RTVPD) as an alternative to ion-implantation to form defect free ultra-shallow junctions in Si. The method involves exposing a silicon wafer to a dopant gas (such as B2H6) at a moderate temperature (∼600°C) for a short time and subsequent annealing for drive-in. This is followed by either selective epitaxy and conventional self-aligned TiSi2 formation or selective deposition of a low-resistivity C54 TiSi2 from TiCl4 and SiH4. In the second approach, first, a semiconductor (Si, polysilicon or SixGe1−x) is deposited selectively. If the material is undoped, doping can be achieved by ion-implantation. In-situ doping is also possible as will be shown with p- and n-type SixGe1−x at temperatures as low as 625°C using B2H6 or PH3. The doped layer is then used as a solid diffusion source to form the junctions by out-diffusion. Using these different approaches, we present examples of high quality junctions in Si as shallow as a few hundred angstroms. The techniques are compared based upon their robustness, complexity, equipment and thermal budget requirements.