Microelectronic applications of the conductor-thin insulator-semiconductor (CIS) structure

摘要

In this thesis selected applications of both minority and majority carrier conductor- thin insulator - semiconductor (CIS) tunnel structures to microelectronic devices such asbipolar and field-effect transistors are studied. Minority carrier CIS structures have propertieswhich approach those of an ideal p-n junction diode when the insulator issufficiently thin to allow a large current to flow through it. The effective junction depth ofsuch a CIS diode is of the order of the thickness of the electrostatically induced inversionlayer at the semiconductor-insulator interface. On the other hand, majority carrier CIStunnel diodes have shown interesting properties such as an internal current gain.First, by replacing the normally diffused emitters of silicon bipolar transistors withmetallic conductor CIS heterojunction tunneling emitters, significant improvements in thecurrent gain and in the breakdown voltage of super gain silicon bipolar transistors havebeen obtained. Current gains above 3xl04 have been achieved for devices with a breakdownvoltage in excess of 30V. Lateral bipolar transistors having such CIS emitters andcollectors have been fabricated. These are shown to possess lower leakage and highercurrent gains than those previously reported.Then, the emitter of a newly proposed transistor structure, the bipolar inversionchannelfield-effect transistor (BICFET), is replaced by a majority carrier CIS tunnelemitter. Experimental BICFETs of this type are fabricated more simply than originallyproposed and are shown to possess characteristics of the general form predicted. Both Aland n + poly have been used as the conductor overlying the tunnel insulator. In the lattercase, where a self-aligned scheme is implemented, a good quality interfacial oxide isshown to have an essential role in device operation.The shallow junction depth of the minority carrier CIS structures has been used toadvantage by replacing the normally diffused source and drain regions of a MOSFET withsuch structures. This has enabled a novel metal gate NMOS transistor with near-zerodepth source and drain junctions to be fabricated.Finally, a novel self-alignment scheme which is particularly suitable for very shortchannel MOSFETs with CIS source and drain junctions is incorporated by interposing apoly silicon gate between these regions. The characteristics of polysilicon source and drainMOSFETs with and without a deliberately grown oxide under the polysilicon regions arecompared. The deliberately grown interfacial oxide is shown to suppress short-channeleffects in the shortest channel devices studied.