Impact of HF-based cleaning solutions on via resistance for sub-10 nm BEOL structures

BEOL Post-Etch Clean Robustness Improvement with Ultra-Diluted Hf for 28nm Node

“…Tungsten layer consumption was almost zero. For copper layers, thickness variation was only 10 Å, which corresponds to copper oxide removal only, in agreement with previous studies [3][4][5]. Glycolic acid was confirmed to be a good copper corrosion inhibitor in diluted HF solution, but it was not mandatory as soon as the oxygen content in the solution and in the process chamber is controlled with shield plate low position and N2 flows.…”

“…In the past 10 years, post-etch cleaning with diluted HF and diluted organic acid for Copper interconnections was successfully implemented in the technology node from 120 nm down to 45 nm [1,3]. These solutions allowed efficient, flexible and cheap processes.…”

“…Indeed, as the global "HF budget" drastically decreases with interconnections dimensions [1][2][3], HF solution dilution, and process time both decreased stepwise. However, very short recipes with process time shorter than 15s start to suffer from lack of robustness, in particular for the monitoring of inline parameters such as flow-rates and temperature.…”

Optimization of wet clean and its impact on sub-50 nm pitch BEOL yield

“…Furthermore, the narrow spaces are more susceptible to pattern displacement during the clean process, as seen in Figure 2 (b) and (c). To reduce the damage and improve the electrical yield, the clean chemistry was tuned to suit the material stack by lowering the concentration to 10000:1 dHF [1]. Although this chemistry reduced the etch damage, the process window was marginal with pattern displacement, as shown in Figure 3.…”

“…The effect is assessed by monitoring the yield of M1 metal line and V0 via opens. Reduction of dHF concentration [1] and addition of IPA [2] to the dHF clean chemistry improved the line and via open yield by more than 10X.…”