Semiconductor structures and methods for crystalline junctionless transistors used in nonvolatile memory arrays are introduced. Various embodiments in accordance with this disclosure provide a method of fabricating a monolithic 3D cross-bar nonvolatile memory array with low thermal budget. The method incorporates crystalline junctionless transistors into nonvolatile memory structures by transferring a layer of doped crystalline semiconductor material from a seed wafer to form the source, drain, and connecting channel of the junctionless transistor.

A method for producing a 3D semiconductor device including: providing a first level, the first level including a first single crystal layer; forming first alignment marks and control circuits in and/or on the first level, where the control circuits include first single crystal transistors and at least two interconnection metal layers; forming at least one second level disposed above the control circuits; performing a first etch step into the second level; forming at least one third level disposed on top of the second level; performing additional processing steps to form first memory cells within the second level and second memory cells within the third level, where each of the first memory cells include at least one second transistor, where each of the second memory cells include at least one third transistor, performing bonding of the first level to the second level, where the bonding includes oxide to oxide bonding.

A method for producing a 3D semiconductor device including: providing a first level, the first level including a first single crystal layer; forming first alignment marks and control circuits in and/or on the first level, where the control circuits include first single crystal transistors and at least two interconnection metal layers; forming at least one second level disposed above the control circuits; performing a first etch step into the second level; forming at least one third level disposed on top of the second level; performing additional processing steps to form first memory cells within the second level and second memory cells within the third level, where each of the first memory cells include at least one second transistor, where each of the second memory cells include at least one third transistor, performing bonding of the first level to the second level, where the bonding includes oxide to oxide bonding.

A semiconductor device, the device comprising: a plurality of transistors, wherein at least one of said plurality of transistors comprises a first single crystal source, channel, and drain, wherein at least one of said plurality of transistors comprises a second single crystal source, channel, and drain, wherein said second single crystal source, channel, and drain is disposed above said first single crystal source, channel, and drain, wherein at least one of said plurality of transistors comprises a third single crystal source, channel, and drain, wherein said third single crystal source, channel, and drain is disposed above said second single crystal source, channel, and drain, wherein at least one of said plurality of transistors comprises a fourth single crystal source, channel, and drain, and wherein said third single crystal channel is self-aligned to said fourth single crystal channel being processed following the same lithography step.

A semiconductor device is provided and includes a semiconductor fin protruding from a semiconductor substrate. The semiconductor fin includes plural pairs of semiconductor layers on the semiconductor substrate, each pair of semiconductor layers consists of a first semiconductor layer of a first conductivity type, and a second semiconductor layer of a second conductivity type. The second semiconductor layer is stacked on and contacts the first semiconductor layer.

A field effect transistor (FET) structure includes a substrate, an internal gate, an insulation layer, a semiconductor strip, a gate dielectric insulator, and a gate conductor. The internal gate includes a floor portion located on the substrate and a wall portion extending from the floor portion. The insulation layer is located on the floor portion of the internal gate. The semiconductor strip is located on the wall portion and a portion of the insulation layer, and the semiconductor strip includes source/drain regions and a channel region adjacent to the source/drain regions. The gate dielectric insulator is located on the channel region. The gate conductor is located on the gate dielectric insulator.

A semiconductor device may include a gate electrode, an insulating layer, a first channel member, and a second channel member. The insulating layer may overlap the gate electrode. The first channel member may be positioned between the gate electrode and the insulating layer. The second channel member may be positioned between the gate electrode and the first channel member. A semiconductor material of the second channel member may be different from a semiconductor material of the first channel member.

A semiconductor device, the device including: a plurality of transistors, where at least one of the plurality of transistors includes a first single crystal channel, where at least one of the plurality of transistors includes a second single crystal channel, where the second single crystal channel is disposed above the first single crystal channel, where at least one of the plurality of transistors includes a third single crystal channel, where the third single crystal channel is disposed above the second single crystal channel, where at least one of the plurality of transistors includes a fourth single crystal channel, and where the fourth single crystal channel is disposed above the third single crystal channel; and at least one region of oxide to oxide bonds.

A device, including: a first layer including first transistors and a second layer including second transistors, where at least one of the first transistors is self-aligned to one of the second transistors, where the second transistors are horizontally oriented transistors, and where the second layer includes a plurality of resistive-random-access memory (RRAM) cells, the memory cells including the second transistors.

Methods for tuning effective work functions of gate electrodes in semiconductor devices and semiconductor devices formed by the same are disclosed. In an embodiment, a semiconductor device includes a channel region over a semiconductor substrate; a gate dielectric layer over the channel region; and a gate electrode over the gate dielectric layer, the gate electrode including a first work function metal layer over the gate dielectric layer, the first work function metal layer including aluminum (Al); a first work function tuning layer over the first work function metal layer, the first work function tuning layer including aluminum tungsten (AlW); and a fill material over the first work function tuning layer.