A method for forming a bipolar junction transistor includes forming a collector intrinsic region, an emitter intrinsic region and an intrinsic base region between the collector intrinsic region and the emitter intrinsic region. A collector extrinsic contact region is formed in direct contact with the collector intrinsic region; an emitter extrinsic contact region is formed on the emitter intrinsic region and a base extrinsic contact region is formed in direct contact with the intrinsic base region. Carbon is introduced into at least one of the collector extrinsic contact region, the emitter extrinsic contact region and the base extrinsic contact region to suppress diffusion of dopants into the junction region.

An active region through which current flows in a semiconductor device includes an n.sup.-type silicon carbide epitaxial layer formed on a front surface of an n.sup.+-type silicon carbide semiconductor substrate; a p-type layer becoming a channel region; a trench formed so as to be in contact with a p-type layer and having an oxide film and a gate electrode embedded therein; a p.sup.+-type layer arranged beneath the trench and between trenches; an n.sup.-type layer in contact with the p-type layer, a p.sup.+-type layer, and the trench, and arranged in contact with a p.sup.+-type layer or on a surface side of the semiconductor substrate; an n-type layer in contact with the n.sup.-type silicon carbide epitaxial layer and the p.sup.+-type layer, and having an impurity concentration higher than that of the n.sup.-type layer and that of the n.sup.-type silicon carbide epitaxial layer.

A bipolar transistor comprises a semiconductor body including a collector region and a base region arranged on top of the collector region. The base region has a first crystalline structure and is at least partly doped with dopants of a first doping type. The collector region is laterally enclosed by a trench isolation and is doped with dopants of a second doping type. The transistor further comprises a conductive base contact layer laterally enclosing the base region which is doped with dopants of the first doping type. The base contact layer comprises a part with the first crystalline structure and a part with a second crystalline structure, wherein the part with the second crystalline structure laterally encloses the part with the first crystalline structure. The transistor further comprises an emitter region arranged on the base region.

A method includes providing a semiconductor structure having an active region and an isolation structure adjacent to the active region, the active region having source and drain regions sandwiching a channel region for a transistor, the semiconductor structure further having a gate structure over the channel region. The method further includes etching a trench in one of the source and drain regions, wherein the trench exposes a portion of a sidewall of the isolation structure, epitaxially growing a first semiconductor layer in the trench, epitaxially growing a second semiconductor layer over the first semiconductor layer, changing a crystalline facet orientation of a portion of a top surface of the second semiconductor layer by an etching process, and epitaxially growing a third semiconductor layer over the second semiconductor layer after the changing of the crystalline facet orientation.

Disclosed are embodiments of a transistor, which incorporates an airgap for low base-emitter capacitance (C.sub.be). Each embodiment of the transistor has a monocrystalline base and, within the monocrystalline base, an intrinsic base region and an extrinsic base region positioned laterally adjacent to the intrinsic base region, wherein the intrinsic and extrinsic base regions have co-planar top surfaces. An essentially T-shaped emitter in cross-section has a lower emitter region on the intrinsic base region and an upper emitter region above the lower emitter region. Each embodiment of the transistor further has an airgap, which is positioned laterally adjacent to the lower emitter region so as to be between the extrinsic base region and the upper emitter region. Thus, the entire airgap is above the co-planar top surfaces of the intrinsic base region and the extrinsic base region. Also disclosed herein are methods of forming the transistor embodiments.

Methods of forming integrated chips include forming a gate stack around a first semiconductor fin and a second semiconductor fin. The gate stack around the second semiconductor fin is etched away. An extrinsic base is formed around the second semiconductor fin in a region exposed by etching away the gate stack.

Integrated chips includes a first transistor and a second transistor. The first transistor includes a first semiconductor fin having a channel region and a gate stack formed around the first semiconductor fin that has upper and lower limits that are outside a respective upper and lower limit of the channel region. The second transistor includes a second semiconductor fin having a base region and an extrinsic base formed around the second semiconductor fin that has upper and lower limits that are within a respective upper and lower limit of the base region.

Integrated chips includes a first transistor and a second transistor. The first transistor includes a first semiconductor fin having a channel region and a gate stack formed around the first semiconductor fin that has upper and lower limits that are outside a respective upper and lower limit of the channel region. The second transistor includes a second semiconductor fin having a base region and an extrinsic base formed around the second semiconductor fin that has upper and lower limits that are within a respective upper and lower limit of the base region.

Various particular embodiments include an integrated circuit (IC) structure having: a stack region; and a silicon substrate underlying and contacting the stack region, the silicon substrate including: a silicon region including a doped subcollector region; a set of isolation regions overlying the silicon region; a base region between the set of isolation regions and below the stack region, the base region including an intrinsic base contacting the stack region, an extrinsic base contacting the intrinsic base and the stack region, and an amorphized extrinsic base contact region contacting the extrinsic base; a collector region between the set of isolation regions; an undercut collector-base region between the set of isolation regions and below the base region; and a collector contact region contacting the collector region under the intrinsic base and the collector-base region via the doped subcollector region.

Methods according to the present disclosure include: providing a substrate including: a first semiconductor region, a second semiconductor region, and a trench isolation (TI) laterally between the first and second semiconductor regions; forming an epitaxial layer on at least the first semiconductor region of the substrate, wherein the epitaxial layer includes a first semiconductor base material positioned above the first semiconductor region of the substrate; forming an insulator region on at least the first semiconductor base material, the trench isolation (TI), and the second semiconductor region; forming a first opening in the insulator over the second semiconductor region; and growing a second semiconductor base material in the first opening, wherein a height of the second semiconductor base material above the substrate is greater than a height of the first semiconductor base material above the substrate.