sacvd (sub-atmospheric cvd)

Sub-Atmospheric Chemical Vapor Deposition (SACVD) is a CVD process variant that operates at pressures between atmospheric pressure (760 Torr) and typical low-pressure CVD conditions (0.1-1 Torr), generally in the range of 100-600 Torr. SACVD combines advantages of both atmospheric and low-pressure processes: the higher pressure compared to LPCVD provides faster deposition rates and improved gap-fill through enhanced surface mobility of adsorbed species, while the sub-atmospheric pressure avoids the gas-phase nucleation and particle generation problems associated with full atmospheric pressure operation. The most common SACVD process deposits silicon dioxide using ozone (O3) and tetraethylorthosilicate (TEOS) as precursors at temperatures of 350-480°C. The O3/TEOS chemistry is particularly effective for conformal gap fill because ozone's high reactivity promotes a surface-reaction-limited deposition regime where the film growth rate is relatively independent of local geometry, enabling uniform coating of high-aspect-ratio trenches and steps. The conformality of O3/TEOS SACVD is superior to conventional silane-based PECVD, making it a critical process for pre-metal dielectric (PMD) and inter-metal dielectric (IMD) planarization layers. The film quality of SACVD O3/TEOS oxide depends strongly on the ozone concentration, substrate surface condition, and deposition temperature. Films deposited at lower temperatures or on certain surfaces (particularly those with different hydrophilicity) can exhibit surface sensitivity — a phenomenon where the deposition rate and film properties vary depending on the underlying material. This surface sensitivity must be carefully managed through process optimization and surface preparation. SACVD oxide films typically have higher moisture content and lower density compared to LPCVD or HDP-CVD oxides, requiring post-deposition annealing or densification at 700-800°C or UV cure to improve film stability and reduce wet etch rate. Modern SACVD tools use single-wafer processing chambers with precise temperature control, ozone generation systems capable of producing 12-16 wt% O3 concentration, and multi-zone gas injection for uniformity optimization.