The ultimate shallow source drain junction depth for a transistor is achieved by removing or detaching a source from the semiconductor substrate and forming an electron source on the surface of the semiconductor substrate adjacent to the transistor gate. The removal or detachment of an electron source from the semiconductor substrate eliminates the heavily-doped source drain diffusion or implant into a source region of the substrate, thereby avoiding non-uniform doping profiles that degrade long-channel subthreshold characteristics of a device as well as the punchthrough behavior of short-channel devices. A metal plug is used as an electron source which is removed or detached from the from the semiconductor substrate. The metal plug is vastly superior to doped semiconductor materials as an electron source. A method of fabricating an integrated circuit includes forming a lightly-doped drain (LDD) MOSFET structure prior to source/drain doping. The MOSFET structure includes a gate formed on a substrate over a gate oxide layer, spacers formed on sides of the gate, LDD doping of the substrate in a source region and a drain region self-aligned with the gate, and drain doping in the drain region self-aligned with the gate and spacers. The method further includes forming an oxide layer over the substrate and LDD MOSFET structure, forming a polysilicon layer over the oxide layer, cutting a via through the polysilicon layer and source layer to the substrate surface adjacent to the gate and spacer and abutting the source region of the substrate, and forming a metal plug in the via, the metal plug electrically coupling to the LDD doping in the source region of the substrate and electrically coupling to the polysilicon layer, the metal plug serving as a source for the MOSFET.

A method for manufacturing a multi-level transistor on a substrate. The method includes forming a first transistor on a first active region, forming a first selective epitaxial growth (SEG) layer on the substrate, and forming a preliminary second SEG layer and a dummy layer, wherein the preliminary second SEG layer is formed directly on only the first SEG layer and a portion of the first insulating layer formed on the cell region of the substrate, and wherein the dummy layer is formed on the peripheral region of the substrate. The method further includes planarizing the preliminary second SEG layer using the dummy layer as a stop layer to form a second SEG layer, forming a second active region from the second SEG layer formed on a first insulating layer, and forming a second transistor on the second active region.

A process is provided for producing active and passive devices on various levels of a semiconductor topography. As such, the present process can achieve device formation in three dimensions to enhance the overall density at which an integrated circuit is formed. The multi-level fabrication process not only adds to the overall circuit density but does so with emphasis placed on interconnection between devices on separate levels. Thus, high performance interconnect is introduced whereby the interconnect is made as short as possible between features within one transistor level to features within another transistor level. The interconnect achieves lower resistivity and capacitance by forming a single gate conductor which is shared by an upper level transistor and a lower level transistor. The shared gate conductor is interposed between a pair of gate dielectrics and each gate dielectric is configured between the single gate conductor and a respective substrate. Thus, the upper level transistor is inverted relative to the lower level transistor. The upper level transistor includes a substrate and junction region formed within and opening of an interlevel dielectric. The opening serves to receive the substrate material, but also to demarcate the formation of a pre-existing gate dielectric prior to substrate deposition. Sharing a single gate conductor among two transistors not only minimizes the overall routing between transistor inputs, but also is particularly attuned to inverter formation.

An elevated transistor formation includes a plurality of planes upon which transistors are formed. The plurality of transistor planes are formed at multiple relative elevations overlying a substrate wafer using deposited polysilicon to form a substrate between the layers. The polysilicon is deposited in a multiple-grain form to achieve an advantageous balance between deposition rate and substrate quality. In particular, columnar polysilicon is deposited at a temperature of approximately 620.degree. C. and above to achieve a high deposition rate directly overlying a lower-elevation transistor plane. High quality polysilicon is then deposited overlying the columnar polysilicon layer at a temperature of approximately 580.degree. C. or below. The deposition rate for high quality polysilicon is substantially lower than the deposition rate for columnar polysilicon. The highest quality substrate, upon which transistors in an elevated transistor plane are formed, is amorphous polysilicon.

A process is provided for producing active and passive devices on various levels of a semiconductor topography. As such, the present process can achieve device formation in three dimensions to enhance the overall density at which an integrated circuit is formed. The multi-level fabrication process not only adds to the overall circuit density but does so with emphasis placed on interconnection between devices on separate levels. Thus, high performance interconnect is introduced whereby the interconnect is made as short as possible between features within one transistor level to features within another transistor level. The interconnect achieves lower resistivity and capacitance by forming a single gate conductor which is shared by an upper level transistor and a lower level transistor. The shared gate conductor is interposed between a pair of gate dielectrics and each gate dielectric is configured between the single gate conductor and a respective substrate. Thus, the upper level transistor is inverted relative to the lower level transistor. The upper level transistor includes a substrate and junction region formed within and opening of an interlevel dielectric. The opening serves to receive the substrate material, but also to demarcate the formation of a pre-existing gate dielectric prior to substrate deposition. Sharing a single gate conductor among two transistors not only minimizes the overall routing between transistor inputs, but also is particularly attuned to inverter formation.