Copper dry etching with precise wafer-temperature control using Cl-2 gas as a single reactant

Cu lines 0.25 mu m wide are successfully patterned by high-temperature dry etching without sidewall protection of the deposited films. Use of Cl-2 gas as a single reactant rather than a mixture of gaseous chlorine compounds is the key to this anisotropic etching. This reactant suppresses the side etching of Cu patterns without creating a residue when the wafer temperature is precisely controlled between 230 and 270 degrees C. In our fundamental examination by simulation, we found that the thermal reaction rate reaches a minimum at about 200 degrees C, and this minimum is much lower than the ion-assisted reaction rate in the actual patterning. This peculiar result is due to the transition of the rate-limiting steps which is caused by the depletion of the CuC1(x) layer on the Cu surface. That is, the formation of Cu3Cl3 appears to be a rate-limiting step at temperatures above 200 degrees C, while the dissociative adsorption of Cl-2 is a rate-limiting step at lower temperatures. The anisotropy in the actual patterning is attributed to the intrinsic suppression of Cu3Cl3 formation at temperatures ranging from 230 to 270 degrees C. (C) 1997 American Vacuum Society.