CMOS with dual raised source and drain for NMOS and PMOS
An apparatus and a method for creating a CMOS with a dual raised source and drain for NMOS and PMOS. The spacers on both stack gates are of equal thickness. In this method, a first insulating layer is formed on the surface. The first region is then masked while the other region has the first layer etched away and has an epitaxial source and drain grown on the region. A second layer is formed to all exposed surfaces. The second region is then masked while the first region is etched away. The epitaxial source and drain is formed on the first region. The second region can also be masked by adding a thin layer of undoped silicon and then oxidize it. Another way to mask the second region is to use a hard mask. Another way to form the second source and drain is to use amorphous material.
1. A method of forming a CMOS structure, the method comprising:
providing a silicon-on-insulator substrate having a first substrate surface in a first region and a second substrate surface in a second region, wherein the first substrate surface and the second substrate surface are isolated by a shallow trench isolation;
forming a first gate stack on the first substrate surface and a second gate stack on the second substrate surface;
forming a first insulating layer on all exposed surfaces in the first and second regions;
etching the first insulating layer in the second region to form insulating spacers on sidewalls of the second gate stack;
forming raised epitaxial source and drain layers on the second substrate surface;
forming a second insulating layer on all exposed surfaces in the first and second regions;
removing the second insulating layer in the first region to expose the first insulating layer;
etching the first insulting layer in order to form insulating spacers on sidewalls of the first gate stack and expose the first substrate surface;
forming undoped raised epitaxial source and drain layers on the first substrate surface;
implanting a dopant into the raised source and drain layers on the first substrate surface;
removing the second insulating layer in the second region, leaving the insulating spacers on the sidewalls of the first and second gate stacks;
if the raised source and drain layers on the second substrate surface are undoped, implanting a dopant into the raised source and drain layers on the second substrate surface; and
forming a second set of spacers between the raised source and drain layers and the insulating spacers on the sidewalls of the first and second gate stacks; and
with the insulating spacers still remaining on the sidewalls of the first and second gate stacks, forming silicide contacts on the source and drain layers in both the first and second regions and on the first and second gate stacks.
2. The method of claim 1 , wherein the step of removing the second insulating layer from the first region is carried out by using photolithography to expose the second insulating layer in the first region and using a wet etch to remove the second insulating layer.