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Ohmic Contacts to Lightly Doped Silicon Using Rare Earth Metals

IP.com Disclosure Number: IPCOM000050124D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Howard, JK: AUTHOR

Abstract

A new class of ohmic contacts to silicon is described. Rare earth metals and yttrium are shown to have barrier heights which are low with respect to Si; the low barrier height also implies a low contact resistance structure. The lowest barrier observed on p-type Si is that formed by PtSi with Phi Beta(-4)=0.25 eV.(2) At room temperature, the contact resistance is about 10 ohm-cm/2/, which is low enough to be considered ohmic unless the contact area is very small. Very large scale integration requirements make the ohmic contact for small (micron or sub micron) devices very important.

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Ohmic Contacts to Lightly Doped Silicon Using Rare Earth Metals

A new class of ohmic contacts to silicon is described. Rare earth metals and yttrium are shown to have barrier heights which are low with respect to Si; the low barrier height also implies a low contact resistance structure. The lowest barrier observed on p-type Si is that formed by PtSi with Phi Beta(-4)=0.25 eV.(2) At room temperature, the contact resistance is about 10 ohm-cm/2/, which is low enough to be considered ohmic unless the contact area is very small. Very large scale integration requirements make the ohmic contact for small (micron or sub micron) devices very important.

To demonstrate the ohmic contact properties of rare earth metal, yttrium was selected because it is chemically stable and can be easily evaporated using electron gun deposition. Other rare earth structures comprehended are Gd, Nd, Er, Yb, Dy (samples that do not oxidize at room temperature). See Original (Table I). the barrier height, and thus ohmic properties, should be nearly identical because the metal work functions of these materials are very close (electronegativity also) Phi Beta approximately equal to X(m) (electronegativity

parameter).

X(m) approximately 1.1 - 1.2 (rare earth metals)

A Schottky barrier diode test structure was used to determine the properties of Y-P Si. The samples were prepared by the deposition of 1000 Angstroms Y onto P Si, the Y was capped by TiW film (1500 Angstroms), and finally by Al (5000...