PREPARATION OF SUB 20 A THICK ULTRA-THIN STACK GATE DIELECTRICS BY IN-SITU RTCVD PROCESSES

摘要

The effects of surface preparation and gas purity on the properties of stack gate dielectric layers were investigated in the preparation of sub 20 A thick gate dielectrics using RTCVD techniques. Dielectric layers based on purified gas showed ～1 A thinner layer as compared to the layers based on regular gas. It may be due to the higher ratios of oxidizing species, N_2O and O_2, as impurities in the regular gas. Interfacial layers on surfaces prepared with HF-last cleaning were found to be ～0.5 A (regular gas) to ～ 1 A (purified gas) thinner as compared to those on RCA cleaned surfaces. Additional NH_3 annealing also affected the properties of stack layers. Post annealing with NH_3 did not affect the optical thickness of stack layers, while NH_3 pre-annealed stack layer was measured to be thicker layer. However, Tox values from non-contact and CV measurements for NH_3 pre-annealed stack layers were lower than that for NH_3-post annealed or no-annealed stack layer. This may be due to the increase of Si_3N_4 ratio in NH_3 pre-annealed stack layer as found by XPS measurements.