Integrated chips and methods of forming the same 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.

Methods of according to the present disclosure can 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 a seed layer on the TI and the second semiconductor region of the substrate, leaving the first semiconductor region of the substrate exposed; forming an epitaxial layer on the substrate and the seed layer, wherein the epitaxial layer includes: a first semiconductor base material positioned above the first semiconductor region of the substrate, and an extrinsic base region positioned above the seed layer; forming an opening within the extrinsic base material and the seed layer to expose an upper surface of the second semiconductor region; and forming a second semiconductor base material in the opening.

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.

A method of making a bipolar transistor includes forming an extrinsic base layer over an oxide layer on a substrate. After an emitter window is opened in the extrinsic base layer, a sidewall spacer is formed on the sidewall of the emitter window. After forming the sidewall spacer, the oxide layer may be etched away to expose the substrate and to form a cavity extending beneath the extrinsic base layer. Subsequently, a monocrystalline emitter is formed in the emitter window whereby a peripheral part of the monocrystalline emitter fills the cavity. An anneal is then performed to form an emitter diffusion region and a base link region of the bipolar transistor.

According to various embodiments, a bipolar transistor structure may include: a substrate; a collector region in the substrate; a base region disposed over the collector region, an emitter region disposed over the base region; a base terminal laterally electrically contacting the base region, wherein the base terminal includes polysilicon.

The disclosure provides bipolar transistor structures with a cavity below an extrinsic base, and methods to form the same. A structure of the disclosure provides a bipolar transistor structure including an extrinsic base protruding from an intrinsic base of a bipolar transistor. The extrinsic base extends over a cavity. An insulator is horizontally adjacent the cavity and below a portion of the extrinsic base. A collector extension region of the bipolar transistor structure extends laterally below the insulator and the cavity.

The current disclosure describes techniques for forming gate-all-around (GAA) devices from stacks of separately formed nanowire semiconductor strips. The separately formed nanowire semiconductor strips are tailored for the respective GAA devices. A trench is formed in a first stack of epitaxy layers to define a space for forming a second stack of epitaxy layers. The trench bottom is modified to have determined or known parameters in the shapes or crystalline facet orientations. The known parameters of the trench bottom are used to select suitable processes to fill the trench bottom with a relatively flat base surface.

Methods, devices, and systems for using and forming vertically base-connected bipolar transistors have been shown. The vertically base-connected bipolar transistors in the embodiments of the present disclosure are formed with a CMOS fabrication technique that decreases the transistor size while maintaining the high performance characteristics of a bipolar transistor.

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.

The current disclosure describes techniques for forming gate-all-around (GAA) devices from stacks of separately formed nanowire semiconductor strips. The separately formed nanowire semiconductor strips are tailored for the respective GAA devices. A trench is formed in a first stack of epitaxy layers to define a space for forming a second stack of epitaxy layers. The trench bottom is modified to have determined or known parameters in the shapes or crystalline facet orientations. The known parameters of the trench bottom are used to select suitable processes to fill the trench bottom with a relatively flat base surface.