Xue-Yu Qian

Characteristics and mechanism of etch process sensitivity to chamber surface condition

Process variation with chamber surface condition in high density plasma reactors can seriously affect the process performance and productivity of device manufacturing. In this work, the impact of chamber surface coating on polycrystalline-silicon (polysilicon) gate etching with Cl2- and HBr-based plasma has been studied. The dependence of process sensitivity to surface coating on various processing conditions has been characterized and the mechanism of process shift has been analyzed. Based on the experimental results, the root cause of process sensitivity has been attributed to the change of surface recombination rate of free radicals on different chamber surfaces which leads to a variation in reactive neutral density. Under a certain discharge condition, the Cl and Br densities in a clean chamber with anodized aluminum and alumina surfaces are >60% lower than those in a seasoned chamber with silicon oxide deposition, resulting in lower polysilicon and oxide etch rate in the former case. In general, the ...

Fluorocarbon polymer formation, characterization, and reduction in polycrystalline–silicon etching with CF4-added plasma

Addition of CF4 into HBr-based plasma for polycrystalline–silicon gate etching reduces the deposition of an etch byproduct, silicon oxide, onto the chamber wall but tends to generate organic polymer. In this work, a detailed study has been carried out to analyze the mechanism of polymerization and to characterize the polymer composition and quantity. The study has shown that the polymer formation is due to the F-radical depletion by H atoms dissociated from HBr. The composition of the polymer changes significantly with CF4 concentration in the gas feed, and the polymer deposition rate depends on CF4% and other process conditions such as source power, bias power, and pressure. Surface temperature also affects the polymer deposition rate. Adding O2 into the plasma can clean the organic polymer, but the O2 amount has to be well controlled in order to prevent the formation of silicon oxide. Based on a series of tests to evaluate polymer deposition and oxide cleaning with O2 addition, an optimized process regi...

Pulse-time-modulated inductively coupled plasma etching for high-performance polysilicon patterning on thin gate oxides

Pulse-time-modulated inductively coupled plasma with HBr gas can provide highly selective, high etching rate, charge-free poly-Si metal–oxide–semiconductor field effect transistor etching. We observed that, when the HBr plasma is cycled ON and OFF at a rate of a few tens of microseconds, the etching and deposition on the substrate surface can be controlled precisely. The use of pulsed plasma can also reduce charge buildup because the electron temperature decreases significantly during the pulse-OFF time. As a result, poly-Si can be etched with extremely high selectivity (relative to the resist and gate oxide), and neither trenching of the gate oxide nor topography-dependent charging occurs.