Characteristics of selective chemical vapor deposition of tungsten on aluminum with a vapor phase precleaning technology

Abstract

A simple and efficient precleaning of an aluminum surface with hydrochloric acid vapor prior to selective chemical vapor deposition of tungsten was investigated. The vapor phase precleaning was shown to remove the aluminum native oxide as well as reduce the aluminum fluorides formed at the W/Al interface during initial reaction of WF6 with the aluminum underlayer. It was found that the precleaning process is spontaneous and the removal rate of aluminum is related to the concentration of reactants used. After precleaning, the aluminum surface was free of oxide and covered with a large amount of Cl species that were examined by x-ray photoelectron spectroscopy. These Cl species occupy active sites on the wafer surface and prevent further adsorption of WF6 on the aluminum during the initial stage in selective deposition of tungsten. Therefore, the probability of reaction between WF6 and the underlying aluminum is greatly suppressed. By using a hydrochloric acid vapor to pretreat the aluminum trench and via hole patterned substrates, a smooth and dense tungsten film and low selectivity loss (<50 pcs/cm(2)) were obtained. A low concentration of aluminum fluorides accumulated at the W/Al interface that were involved in low via resistance was also observed.