Requirements

There are several different requirements for a practical ashing process.

• The cost of the stripping process needs to be low cost per wafer, calling for cheap and simple equipments as well as high throughput. To achieve resonable wafers per hour the ashing rate should be higher than $\rm 1-2\mu m/min$ for single wafer tools, barrel (batch) type equipments can be slower, depending on the batch size.
• To remove the resist without leaving residues or contamination is the key requirement for the ashing process. Residue free stripping of an untreated resist is usually no problem, much more difficult are the polymers (see page ) or crust (see page ) formed by etching or high dose/energy implantation.
• The ashing process must be gate oxide damage free (see section ). Also other potential damages like low-k dielectric degradation need to be considered when relevant.