Controlled Ohmic Contact and Planarization for Very Shallow Junction Structures
Original Publication Date: 1978-Feb-01
Included in the Prior Art Database: 2005-Feb-20
Reproducible ohmic contact to shallow junction structures becomes increasingly important and more difficult to achieve as device contact holes grow smaller and junctions more shallow. Present schemes are satisfactory for relatively large contact windows and junctions of 0.5 mu m in depth. Such schemes use evaporated Pt sintered to PtSi and Al-Cu interconnective metal separated by a Cr diffusion barrier. This structure is shown in Fig. 1. When Pt is sintered to form PtSi, a volume of bulk Si from the substrate, approximately equal to the volume cf the Pt above the contact is consumed in the solid-solid Pt + Si - PtSi reaction. with 500 a of Pt, therefore, about 500 angstroms of Si is consumed, and the ohmic metal-semiconductor interface is now 500 angstroms below the surface of the original, opened contact hole.