Multiple transistor types formed in a common epitaxial layer by differential out-diffusion from a doped underlayer

摘要

Multiple transistor types are formed in a common epitaxial layer by differential out-diffusion from a doped underlayer. Differential out-diffusion affects the thickness of a FET channel, the doping concentration in the FET channel, and distance between the gate dielectric layer and the doped underlayer. Differential out-diffusion may be achieved by differentially applying a dopant migration suppressor such as carbon; differentially doping the underlayer with two or more dopants having the same conductivity type but different diffusivities; and/or differentially applying thermal energy.

主权项

1. A method of forming a first plurality of transistors of a first device type, and a second plurality of transistors of a second device type on a substrate, comprising:
forming a first plurality of wells of a first conductivity type in the substrate; forming a second plurality of wells of a first conductivity type in the substrate; doping each of the first plurality of wells to form a corresponding first plurality of screen layers of the first conductivity type, each screen layer of the first plurality of screen layers being disposed closer to a surface of the substrate than the well in which it is formed; doping each of the second plurality of wells to form a corresponding second plurality of screen layers of the first conductivity type, each screen layer of the second plurality of screen layers being disposed closer to a surface of the substrate than the well in which it is formed; doping the first plurality of screen layers to introduce a first diffusion-inhibiting dopant species, the first diffusion-inhibiting dopant species being effective to inhibit, but not stop, out-diffusion of dopants from each of the first plurality of screen layers by a first amount; growing substantially undoped epitaxial layers over the first plurality of screen layers, and over the second plurality of screen layers; and thermal cycling the substrate; wherein energy from the thermal cycling drives out-diffusion from each screen layer of the first plurality of screen layers into the corresponding overlying epitaxial layer such that a first range of threshold voltages is obtained in the transistors of the first device type, and drives out-diffusion from each screen layer of the second plurality of screen layers into the corresponding overlying epitaxial layer such that a second range of threshold voltages is obtained in the transistors of the second device type; wherein doping the first plurality of wells to form the first plurality of screen layers comprises: implanting at least a first dopant species having a first diffusivity in the first plurality of screen layers, and implanting a second dopant species having a second diffusivity in the second plurality of screen layers; wherein the first diffusivity is greater than the second diffusivity.