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Technology scaling is a continuous challenge for scientific knowledge and money gain and the shrinking implicates structure's dimensions hugely small and open area even lower than 1%. Dry etching processes are controlled by end point (EP) detection technique, which stop the etching when an appropriate optical trace at fixed λ changes its intensity due to the consumption of the reactant's or by-products' concentration. The aim of the job is to qualify an optical emission spectroscopy tool on Lam dielectric etching reactor, working at high vacuum condition as few mTorr, for copper dual damascene applications. The HW consists of a spectrometer linked to the reactor by an optical fiber and a standalone computer connected to the main tool via Ethernet. The activity was carried on for Via application on Flash NOR devices for 0.090 μm technology node, which replaces anti reflecting coating layer, fluorine silicon glass and photo resist. According to the spectra emission 4 wavelengths were investigated on 2 different chemistries (C4F8 /C4F6); the significant presence of CO in the etch chemistry at low pressure, guaranteed by turbo molecular pump, dampen or obscure transitions in CO and CN coming from by-products when films are cleared. C4F6 increases under layer selectivity to SiNx allowing a formidable task in capturing an endpoint. Process shift induced by the Confinement Ring (CR) locking to reduce the EP fluctuation that will lead to erroneous EP was investigated: Critical dimensions and SEM cross section between CR lock delay and standard configuration are negligible. By means Principal Components Analysis (PCA), a proper algorithm was set and following cross sections on few wafers demonstrated the whole stack, till to Si3N4, was etched, so the called EP time by OES was appropriate. To guarantee high repeatability the EP algorithm was put in collective mode on production and on 974 processed wafers the simulation analysis showed only 7 wafers were rejected for EP not achieved. The best end point algorithm identified by trace analysis and PCA is the filtered slope of a linear combination of 3 integrated wavelength bands and the end point calling is the turning point of the slope signal. Further simulation ran on 1137 production wafers gave 0 failures. |