Selective Etching of High-kDielectric HfO₂Films over Si in BCl₃-Containing Plasmas without rf Biasing

Abstract

High-k HfO2 films were etched in electron cyclotron resonance BCl3-containing plasmas without rf biasing. Addition of O2 and/or Cl2 to BCl3 was investigated for suppressing surface inhibitor deposition, to control the transition between deposition and etching regimes for HfO2 and Si. A high etch selectivity of >100 for HfO2/Si was achieved in BCl3/Cl2 with a HfO2 etch rate of ∼50 nm/min. The origin of the selectivity was confirmed by X-ray photoelectron spectroscopy to be surface chlorination on HfO2 and Si, where the deposition of BxCly layers still competed with etching on Si. The etched profile of HfO2 exhibited almost anisotropic sidewalls, which suggests a low-energy ion-assisted etching mechanism.

Mechanisms for plasma etching of HfO2 gate stacks with Si selectivity and photoresist trimming

“…The selectivity is as large as 12 at a bias of 32 V, decreasing monotonically to 2 for a bias of 200 V. The decrease in selectivity is largely a consequence of the removal of polymer on the Si by sputtering. 4,12,13 The increase in bias voltage also produces undercutting of the TiN. 4,13 The predicted decrease in selectivity as a function of increasing bias is also in general agreement with experiment, although our decrease in selectivity is more gradual.…”

Materials Informatics for Process and Material Co-Optimization

“…5 shows the discovered gas combination and the resultant etching rates of HfO 2 . As shown in the figure, the etching rates achieved by discovered gas combinations were 100 times higher than that of the traditional gas combination obtained from the literature [16]. We emphasize that only 55 experiments (equivalent to <0.00001% of all possible process/material candidates) were needed to discover the new conditions.…”

“…To evaluate the found materials and processes through our co-optimization procedure, we compared with the results obtained by a traditional gas combination and its process provided by Nakamura et al [16]. They etched a thin film of HfO 2 at 75 deg C using gasses of BCl 3 , Cl 2 , and O 2 (37.5:62.5:5) with a total flow rate of 40 sccm at 5 mTorr and achieved a relatively high etching rate of ∼150 nm/min.…”

“…To quantitatively compare with the conventional methodology, we estimated the necessary number of experiments, which ) is a traditional one obtained from literature [16], although the process is a little bit different, because high vacuum was not available.…”

“…5. Discovered gas combination and resultant etching rates of HfO 2 using discovered processes at 500 deg C. The condition on the left (BCl 3 + Cl 2 + O 2) is a traditional one obtained from literature[16], although the process is a little bit different, because high vacuum was not available.…”