US Patent 7700494 Low-pressure removal of photoresist and etch residue

A method is provided for low-pressure plasma ashing to remove photoresist remnants and etch residues that are formed during preceding plasma etching of dielectric layers. The ashing method uses a two-step plasma process involving an oxygen-containing gas, where low or zero bias is applied to the substrate in the first cleaning step to remove significant amount of photoresist remnants and etch residues from the substrate, in addition to etching and removing detrimental fluoro-carbon residues from the chamber surfaces. An increased bias is applied to the substrate in the second cleaning step to remove the remains of the photoresist and etch residues from the substrate. A chamber pressure less than 20 mTorr is utilized in the second cleaning step. The two-step process reduces the memory effect commonly observed in conventional one-step ashing processes. A method of endpoint detection can be used to monitor the ashing process.