Low open-area endpoint detection using a PCA-based T-2 statistic and Q statistic on optical emission spectroscopy measurements

This paper will examine an approach for automatically identifying endpoint (the completion in etch of a thin film) during plasma etching of low open a rea wafers. Because many end-pointing techniques use a few manually selecte d wavelengths or simply time the etch, the resulting endpoint detection det ermination may only be valid for a very short number of runs before process drift and noise render them ineffective. Only recently have researchers be gun to examine methods to automatically select and weight spectral channels for estimation and diagnosis of process behavior. This paper mill explore the use of principal component analysis (PCA)-based T-2 formulation to filt er out noisy spectral channels and characterize spectral variation of optic al emission spectroscopy (OES) correlated with endpoint. This approach is a pplied and demonstrated for patterned contact and via etching using Digital Semiconductor's CMOS6 (0.35-mu m) production process.