Study on metrology of ERU tuning in TCP reactor, using PVx2 sensor wafer

The effect of the transformer-coupled capacitive tuning (TCCT) parameter on the etch rate uniformity (ERU) in a high density plasma etch chamber was studied by the following means: blanket wafer experiments; tests on patterned wafers with 20-nm half-pitch BEOL interconnect trenches, created by spacer defined double patterning; and PlasmaVolt™ X2 (PVx2) sensor wafer experiments. Besides pure Ar and pure SF₆ chemistries, several typical process chemistries of poly-Si and SiO₂ etching were selected for study. It was shown that the ERU data (expressed as 3σ) were in good agreement for all the chemistries applied to both PVx2 and blanket SiO₂ with different TCCTs. The ERU of blanket poly-Si, however, did not generally correlate well with the PVx2 data. Only Ar sputtering and Cl₂/HBr-based processes showed a similar 3σ trend for both PVx2 and poly-Si. For the 20-nm half-pitch wafers, a study was performed on three separate etch steps with different chemistries, used for SiOC, BARC, and SiN etching. The critical dimension (CD) uniformity data was compared to the PVx2 results and demonstrated a good correlation in the first two cases. Based on these results, it was concluded that PVx2 is able to predict the behavior of the ion-assisted etch component in terms of uniformity, while spontaneous chemical reactions and/or ion-assisted polymer deposition could result in a substantial discrepancy between the actual ERU data and the PVx2 results. Finally, for materials that are typically etched using a dominant ion-assisted etch component, it was estimated that use of this PVx2-based method of ERU tuning may result in lot turn time savings of 80% when compared to single-use blanket wafer ERU tests.