Wet Etching Behavior of Poly-Si in TMAH Solution

Abstract

Since Tetramethylammonium Hydroxide (TMAH) became widely used as a silicon etchant, e.g. the dummy gate removal for gate-last approach (RMG) [1, or Si fin formation on FinFET [, some careful preparations and optimizations have required implementation. These adaptations have involved not only chemical-related issues, but also hardware-related in order to satisfy the necessary process performance.

State of the Art and Future Perspectives in Advanced CMOS Technology

“…In the nano-scale transistors, the replacement metal gate (RMG) was introduced by using dummy gate (poly silicon) and dummy gate oxide (silicon dioxide) to go through all the high-temperature annealing processes [ 228 ]. This gate oxide is eventually removed in a wet-etch process by using quaternary ammonium hydroxide (QAH) and hydrogen fluoride acid-based solutions [ 229 , 230 , 231 ], respectively. There are many merits for RMG.…”

The Challenges of Advanced CMOS Process from 2D to 3D

“…The replacement metal gate (RMG) was introduced by using poly-Si as dummy gate and SiO 2 as dummy gate oxide [131] where eventually these layers are removed with wet process by means of none metal alkaine solutions, as shown in Figure 19 [132][133][134]. One of benefits of RMG is to avoid crystallization of the high-k dielectric during the rapid thermal annealing (RTA) process for dopants activation [135].…”

“…Compared to the 2D devices, the RMG for 3D structures are even more complicated as shown for vertically stacked nanowire process in Figure 20. Firstly, poly-Si dummy gate has to be completely removed without any residues in narrow and steep trenches [132][133][134], otherwise, due to chemical nature of the HF-based wet etchant for the dummy gate oxide etching could not remove the poly-Si without any oxidizer [137][138][139]. Therefore, the residues occupy the space where the high-k and metal gates should be filled in, which might cause device failure.…”

“…The commonly used GPE is a HF vapor process. Recently, GAA transistors have been manufactured by using HCl vapor process as well [130][131][132][133][134][135][136][137][138][139][140][141][142].…”