Low-bandgap source and drain formation for short-channel MOS transistors

Abstract

Abstract A transistor having source and drain regions which include lower-bandgap portions and a method for making the same are provided. A gate conductor is formed over a gate dielectric on a semiconductor substrate. The gate conductor is covered on all sides with oxide or another dielectric for protection during subsequent processing. Anisotropic etching is used to form shallow trenches in the substrate on either side of the gate conductor. The trenches are bounded by the dielectric-coated gate conductor and by dielectric isolation regions, or by an adjacent gate conductor in the case of non-isolated transistors. A selective epitaxy technique may then be used to grow a layer within each trench of a material having a bandgap lower than that of the semiconductor substrate. The lower-bandgap material is preferably grown only on the exposed semiconductor surfaces in the trenches, and not on the surrounding dielectric regions. The lower-bandgap material may be an undoped layer used as a buffer for interdiffusion of dopants between the channel and source/drain regions of the transistor. The lower-bandgap material may also be a heavily doped layer with the same carrier type as the semiconductor substrate, used as a halo region to reduce punchthrough and threshold voltage lowering effects. The buffer and halo functions may also be combined using multilayer source/drain structures. The portion of the trench above such buffer and/or halo layers is filled with a semiconductor material doped with the opposite carrier type than that of the substrate to form lightly-doped-drain portions of the transistor source and drain.

Inventors

• 👤 Karsten Wieczorek
• 👤 Manfred Horstmann
• 👤 Frederick N. Hause

Bibliographic Details