High-speed polysilicon emitter—base bipolar transistor

Abstract

High-speed polysilicon emitter and base electrode Si n-p-n bipolar devices were fabricated showing performances of 55-ps ECL gate delay (FI = FO = 1) and cutoff frequency of 15.6 GHz (at VcE = 3 V, L VcEo = 6.8 V). These devices were built on an oxide-isolated substrate produced by planarizing oxide which is deposited after device Si island etching. The final emitter width is 0.5 pm, and a 1.3-pm-thick arsenicdoped LPCVD epitaxial layer of 0.25 Q.cm is utilized. Emitter-base (E-B) junctions formed by direct implantations of arsenic and boron ions into a substrate were compared with junctions induced by diffusing dopants from implanted polysilicon. Indhe case of diffused junctions, an emitter junction depth of less than 500 A along with a 1000-A base width can be obtained.T HE USE OF polysilicon for base and emitter electrodes enables higher performance in Si bipolar transistors. This is due to minimized collector-base parasitic capacitance when the extrinsic base contact is opened in the portion of the polysilicon base electrode that is over field oxide, and to narrow spacing between the self-aligned emitter and base electrodes [1]-[6]. Compared to a conventional device structure where the extrinsic base contact is placed on top of the active device area, the polysilicon base electrode structure will typically reduce the collector-base overlap area up to 60 percent. In addition, the use of a polysilicon emitter yields forward current gain three to ten times higher than a direct metal emitter contact [7], This enables increased doping of the base to prevent premature punchthrough when using the shallow base widths required for high speed. With this process technology, n-p-n silicon bipolar transistors have been reported to achieve fT of 9-17 GHz and sub-100-ps ECL gate delays by numerous investigators [ 2 ] -[ 5 ] . With minimized collector-base parasitic capacitance, the effect of shallow emitter and base junctions is even more important in realizing high-speed devices. One process technique for achieving shallower emitter-base (E-B) junctions is to form junctions by diffusion from an implanted polysilicon overlayer [6] which we refer to as the diffused E-B process. We compared devices fabricated by this process to devices having E-B junctions implanted directly into single crystal silicon (implanted junction devices). Devices made with the diffused E-B process resulted in very shallow junctions, superior E-B breakdown characteristics, and higher speed.In this process, devices are built on an oxide-

High-Energy Radiation Effects on Silicon NPN Bipolar Transistor Electrical Performance: A Study with 1 MeV Proton Irradiation

“…Silicon-based bipolar junction transistors (BJTs) have emerged as prominent candidates for such applications, primarily due to their versatile functionality in various electronic circuits [1][2][3]. A particular emphasis is placed on scrutinizing the emitter-base junction of silicon NPN transistors, as these transistors constitute integral components of modern electronics [4,5].…”

Comparison of Effects of Ionizing Radiation and High-Current Stress on Characteristics of Self-Aligned Bipolar Transistors

“…Recent progress in advanced self-aligned bipolar technology has resulted in high-perfonnance ECL circuits with sub-75ps gate delays (1)(2)(3)(4)(5). To achieve such high performance, advanced bipolar devices generally have thin bases, shallow emitters, and, in particular, reduced parasitics.…”

Deposition of Doped Polysilicon Films by Plasma‐Enhanced Chemical Vapor Deposition from AsH3 / SiH4 or B 2 H 6 / SiH4 Mixtures

“…Doped polysilicon also has potential applications in bipolar integrated technology, as a diffusion source for dopants and/or as the emitter material of the bipolar transistor (1). However, most applications, such as gate electrodes of MOS integrated circuits, require the polysilicon film to be highly conductive.…”

“…This is typically achieved by doping the polysilicon by either ion implantation or diffusion from a dopant-rich source. Doped polysilicon also has potential applications in bipolar integrated technology, as a diffusion source for dopants and/or as the emitter material of the bipolar transistor (1). Polysilicon is also a crucial material for the fabrication of electronic devices over large surface areas, such as active matrix fiat panel displays (2,3).…”