A MISFET having a graded semiconductor alloy channel layer of silicon germanium in which the germanium is graded to a single peak percentage level. The single peak percentage level defines the location of the charge carriers within the layer. The transconductance of the device can be optimized by controlling the location of the carriers within the channel.
This is a continuation of application Ser. No. 07/785,547 filed on Oct. 31, 1991, now abandoned, which is a divisional of application Ser. No. 07/639,625, filed on Jan. 10, 1991 now abandoned.
The present invention relates generally to a semiconductor device having a channel region comprising a semiconductor alloy of a first semiconductor material and a second, different material, and wherein atomic distribution of the second material in the channel region is graded along a direction that is substantially parallel to a substrate surface in which the semiconductor device is located. Specifically, the semiconductor device comprises a field effect transistor (FET) that has a SiGe channel with a laterally graded germanium content.
A transistor structure comprises a channel region overlying a substrate region. The substrate region comprises a first semiconductor material with a first lattice constant. The channel region comprises a second semiconductor material with a second lattice constant. The source and drain regions are oppositely adjacent the channel region and the top portion of the source and drain regions comprise the first semiconductor material. A gate dielectric layer overlies the channel region and a gate electrode overlies the gate dielectric layer.
A process for fabricating CMOS devices, featuring a channel region comprised with a strained SiGe layer, has been developed. The process features the selective growth of a composite silicon layer on the top surface of N well and P well regions. The composite silicon layer is comprised of a thin, strained SiGe layer sandwiched between selectively grown, undoped silicon layers. The content of Ge in the SiGe layer, between about 20 to 40 weight percent, allows enhanced carrier mobility to exist without creation of silicon defects. A thin silicon dioxide gate insulator is thermally grown from a top portion of the selectively grown silicon layer, located overlying the selectively grown SiGe layer.
A process for fabricating CMOS devices, featuring a channel region comprised with a strained SiGe layer, has been developed. The process features the selective growth of a composite silicon layer on the top surface of N well and P well regions. The composite silicon layer is comprised of a thin, strained SiGe layer sandwiched between selectively grown, undoped silicon layers. The content of Ge in the SiGe layer, between about 20 to 40 weight percent, allows enhanced carrier mobility to exist without creation of silicon defects. A thin silicon dioxide gate insulator is thermally grown from a top portion of the selectively grown silicon layer, located overlying the selectively grown SiGe layer.
A CMOS integrated circuit includes a substrate having an NMOS region with a P-well and a PMOS region with an N-well. A shallow trench isolation (STI) region is formed between the NMOS and PMOS regions and a composite silicon layer comprising a strained SiGe layer is formed over said P well region and over said N well region. The composite silicon layer is disconnected at the STI region. Gate electrodes are then formed on the composite layer in the NMOS and PMOS regions.
