bromine-based etch

Bromine-based etching utilizes hydrogen bromide (HBr) and other bromine-containing gases as the primary etch chemistry for silicon and polysilicon patterning in semiconductor manufacturing. HBr is the dominant bromine source gas, often mixed with chlorine (Cl2), oxygen (O2), or fluorocarbon gases to optimize etch performance. In plasma, HBr dissociates to produce Br* radicals and H* atoms, which react with silicon to form volatile SiBr4 and other silicon bromide species. Bromine chemistry offers several critical advantages over fluorine and chlorine for silicon gate etching. First, Br radicals have very low spontaneous etch rate on silicon at typical wafer temperatures — etching requires ion bombardment, providing inherently anisotropic profiles with vertical sidewalls essential for gate patterning. Second, the SiBrx etch byproducts and oxidized silicon bromide species deposit on feature sidewalls, forming a protective passivation layer that further enhances anisotropy. Third, HBr provides excellent selectivity to SiO2 (>100:1) because bromine radicals cannot efficiently attack the Si-O bond network, making it ideal for gate etch where the underlying gate oxide is only 1-2 nm thick and must not be breached. The addition of small amounts of O2 to HBr plasmas enhances sidewall passivation through SiBrxOy formation and improves selectivity. Cl2 is often added to increase etch rate, as chlorine provides faster silicon etching than bromine, while the HBr component maintains profile control and selectivity. Modern gate etch processes for FinFET and gate-all-around (GAA) transistors use carefully optimized HBr/Cl2/O2 mixtures with multiple etch steps — a breakthrough etch to clear native oxide, a main etch for bulk silicon removal, and an overetch with high selectivity to stop on the gate dielectric. The precise control afforded by bromine chemistry makes it indispensable for critical dimension control at advanced nodes.