Single crystal emitter gap for epitaxial Si- and SiGe-base transistors

Abstract

An epitaxial base bipolar technology has been used for fabrication of graded SiGe-base HBT's or Si-base pseudo-HBT's with a self-aligned, in-situ doped n-type low temperature epitaxial (LTE) emitter. The thin LTE emitter provides an EB junction with low tunnelling current and low capacitance in a n + poly/n/p + /n thin base HBT design with very high base doping. We report here on Si and SiGe devices utilizing a 40 nm P doped LTE emitter with an nf poly contact and silicided p + poly extrinsic base contact. Nearly ideal DC characteristics were obtained for a device with a peak base doping concentration of over 1 x 1019crn-3. 44 G H z~T devices with an AC base resistance of only 150 ohms were used to fabricate 24 ps ECL and 19 ps NTL ring oscillators to demonstrate the performance potential of the structure. BackgroundIn principle, the availability of high-quality Si-based low temperature epitaxy processes allows definition of arbitrarily thin basewidth transistors in a manner analogous to GaAs-based epitaxial technologies. Scaling to 30-40 nm basewidths in an n/p+ /n Si-based HBT technology, however, requires precise control of the emitter formation process with base doping (boron) concentrations in the 1 x 10'9 to 1 x 1OZ0crn-range. The emitter thermal cycle must be minimlzed to maintain a very narrow basewidth and the emitter doping concentration must be low enough to prevent excessive tunnelling while still being high enough to provide a low emitter resistance, minimize emitter charge storage, and prevent junction non-idealities associated with shallow polysilicon contacts. In a polysilicon emitter technology, however, formation of an n/p+ junction (as opposed to n+ /p) through reduction of the diffusion source concentration does not satisfy these criteria.GaAs-based epitaxial technologies typically employ an insitu doped single crystal emitter layer deposited immediately after base deposition to address the emitter doping problem and rely on the heterojunction effects to maintain adequate current gain. Direct extension of mesa type GaAs epitaxial structures for Si-based devices is not desirable, however, due to perimeter passivation, current gain, parasitic resistance, and narasitic capacitance concerns, and thus poor performance rel-..:ive to aggressive ion-implanted double-poly device structures. Over the last few years epitaxial base transistor structures have been proposed which address the isolation, resistance and capacitance related concerns noted above for an epitaxial technology and allow fabrication of high performance Si and SiGe base transistors in a double-poly process [1,2]. This work

SiGe HBT for application in BiCMOS technology: II. Design, technology and performance

“…The formation of the parasitic barriers due to outdiffusion of boron is illustrated in figure 14. Note that the B profile width has become larger than the Ge profile width due to R75 King [41] 1989 0.31 400 Kamins [42] 1989 0.31 32-48 29 Patton [43] 1990 a 75 Comfort [44] 1990 a 50 24.6 (ECL) Comfort [45] 1991 a 44 24 (ECL) Comfort [45] 1991 a 44 19 (NTL) Sturm [46] b 1991 a 11 000 Crabbé [47] 1992 a 73 34 (ECL) Crabbé [47] 1992 a 73 28 (NTL) Gruhle [48] 1992 0.21-0.28 42 40 Sato [49] 1992 a 120 51 50 19 (ECL) Harame [50] 1992 a 50 59 18.9 (ECL) Cressler [51] c 1992 a 500 61 21.9 (ECL) Namba [52] 1991 0 64 Meister [31] 1992 0 44 18 (CML) Takemura [53] outdiffusion of B. At small CB bias calculated conduction band edges for these profiles show large parasitic barriers to the flow of minority electrons into the collector.…”