Semiconductor structure with improved channel stack and method for fabrication thereof
A method for fabricating a semiconductor structure with a channel stack includes forming a screening layer under a gate of a PMOS transistor element and a NMOS transistor element, forming a threshold voltage control layer on the screening layer, and forming an epitaxial channel layer on the threshold control layer. At least a portion of the epitaxial channel layers for the PMOS transistor element and the NMOS transistor element are formed as a common blanket layer. The screening layer for the PMOS transistor element may include antimony as a dopant material that may be inserted into the structure prior to or after formation of the epitaxial channel layer.
1. A method for fabricating a transistor structure with a channel stack, the transistor structure having a semiconductor substrate with a plurality of pre-formed doped wells formed therein, comprising:
in a first region having a first doped well providing a foundation for a PMOS transistor element:
ion implanting in the semiconductor substrate a first doped screening layer in contact with the first doped well, the first doped screening layer including antimony;
ion implanting in the semiconductor substrate a first doped threshold voltage control layer in contact with the first doped screening layer;
in a second region having a second doped well providing a foundation for an NMOS transistor element:
ion implanting in the semiconductor substrate a second doped screening layer in contact with the second well;
ion implanting in the semiconductor substrate a second doped threshold voltage control layer in contact with the second doped screening layer;
forming a third layer on the semiconductor substrate, separate from and on top of the first and second doped threshold voltage control layers, by way of multiple blanket undoped epitaxial growth to establish an intrinsic channel for each of the PMOS and NMOS transistor elements;
wherein the third layer of the PMOS transistor element is formed with a different channel thickness than the third layer of the NMOS transistor element.
2. The method of claim 1 , wherein ion implanting the first doped threshold voltage control layer includes implanting arsenic.
3. The method of claim 1 , wherein the first doped screening layer is doped with antimony and arsenic.
4. The method of claim 1 , further comprising:
forming an isolation region separating the PMOS transistor element and the NMOS transistor element after forming the third layer.
5. The method of claim 1 , further comprising:
forming a fourth layer by way of a blanket undoped epitaxial growth on the third layer for only one of the PMOS and NMOS transistor elements so that one of the PMOS and NMOS transistor elements has an overall channel thickness greater than the other one of the PMOS and NMOS transistor elements.
6. The method of claim 1 , further comprising:
forming one or more additional PMOS transistor elements in a same manner as the PMOS transistor element;
forming a fourth layer by way of a blanket undoped epitaxial growth on the third layer for only the one or more additional PMOS transistor elements so that the one or more additional PMOS transistor elements has an overall channel thickness greater than that of the PMOS transistor element.
7. The method of claim 1 , further comprising:
forming one or more additional NMOS transistor elements in a same manner as the NMOS transistor element;
forming a fourth layer by way of a blanket undoped epitaxial growth on the third layer for only the one or more additional NMOS transistor elements so that the one or more additional NMOS transistor elements has an overall channel thickness greater than that of the NMOS transistor element.
8. The method of claim 1 , wherein the first doped screening layer is doped with one or more of antimony, phosphorous, and arsenic.