Sk. Lee et al., REACTIVE ION ETCHING MECHANISM OF COPPER FILM IN CHLORINE-BASED ELECTRON-CYCLOTRON-RESONANCE PLASMA, JPN J A P 1, 36(1A), 1997, pp. 50-55
In order to investigate the reactive ion etching mechanism of the copp
er films in CCl4/N-2 electron cyclotron resonance (ECR) plasma, the de
pendences of the copper etch rate on various etching parameters, the e
tch products as well as their depth distributions and the concentratio
n of chlorine radicals in the plasma were examined. It was found that
the etching species in CCl4 plasma is not CClx but atomic chlorine (Cl
) and the etch product formed at the surface of the copper film is not
CuCl but CuCl2. In order to carry out reactive ion etching of copper
film in chlorine-based plasma the substrate temperature should be abov
e 210 degrees C, below which the etch product has too low vapor pressu
re to be volatile. At the substrate temperature above 210 degrees C, t
he copper etch rate is not limited by the removal rate of the etch pro
duct but limited by its formation rate which depends on the concentrat
ion of chlorine radicals and the reaction rate between the etching spe
cies and the copper film. The etch rate is also increased by applying
a negative bias to the substrate, the role of which is the enhancement
of the formation rate of the etch product by activating chemical reac
tions due to energetic ion bombardment. Adding small amounts of CF4 to
CCl4 plasma increases the etch rate dependence on ion bombardment ene
rgy by forming involatile copper fluoride on the etched surface.