Aluminum—Silicon Schottky barriers and ohmic contacts in integrated circuits

Experimental observations (electrical characteristics and in depth Auger analysis) have been made of the interface behavior in aluminum-silicon contacts. The barrier heights of these contacts (φ
bn
for n-type, φ
bp
for p-type silicon) are sensitive to heat treatments (HT) that are a part of normal integrated circuit processing. If oxide layers (≃20 Å) are present in the Al-Si interface, φ
bn
can be as low as 0.45 eV and φ
bp
as high as 0.75 eV. One can obtain reproducible barrier heights φ
bp
≃ 0.7 eV and φ
bp
≃ 0.5 eV by HT at T ≤ 300deg;C. As the temperature of HT is increased (up to ≃ 550deg;C) φ
bn
can reach ≃ 0.9 eV and φ
bp
drop to < 0.35 eV. The HT at higher temperatures are accompanied by changes in the Al and Si profiles across the interface region. Two mechanisms have been found to be responsible for the changes in barrier height: 1) the removal of positive charges from the oxide, and 2) metallurgical reactions between the Al and Si. These two mechanisms have been separated and their individual behaviors qualified.