Browsing by Subject "UV"
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Item Mechanistic study of plasma damage to porous low-k : process development and dielectric recovery(2010-05) Shi, Hualiang; Ho, Paul S.; Niu, Qian; Shi, Li; Swift, Jack B.; Yao, ZhenLow-k dielectrics with porosity are being introduced to reduce the RC delay of Cu/low-k interconnect. However, during the O2 plasma ashing process, the porous low-k dielectrics tend to degrade due to methyl depletion, moisture uptake, and densification, increasing the dielectric constant and leakage current. This dissertation presents a study of the mechanisms of plasma damage and dielectric recovery. The kinetics of plasma interaction with low-k dielectrics was investigated both experimentally and theoretically. By using a gap structure, the roles of ion, photon, and radical in producing damage on low-k dielectrics were differentiated. Oxidative plasma induced damage was proportional to the oxygen radical density, enhanced by VUV photon, and increased with substrate temperature. Ion bombardment induced surface densification, blocking radical diffusion. Two analytical models were derived to quantify the plasma damage. Based on the radical diffusion, reaction, and recombination inside porous low-k dielectrics, a plasma altered layer model was derived to interpret the chemical effect in the low ion energy region. It predicted that oxidative plasma induced damage can be reduced by decreasing pore radius, substrate temperature, and oxygen radical density and increasing carbon concentration and surface recombination rate inside low-k dielectrics. The model validity was verified by experiments and Monte-Carlo simulations. This model was also extended to the patterned low-k structure. Based on the ion collision cascade process, a sputtering yield model was introduced to interpret the physical effect in the high ion energy region. The model validity was verified by checking the ion angular and energy dependences of sputtering yield using O2/He/Ar plasma, low-k dielectrics with different k values, and a Faraday cage. Low-k dielectrics and plasma process were optimized to reduce plasma damage, including increasing carbon concentration in low-k dielectrics, switching plasma generator from ICP to RIE, increasing hard mask thickness, replacing O2 by CO2 plasma, increasing CO addition in CO/O2 plasma, and increasing N2 addition in CO2/N2 plasma. By combining analytical techniques with the Kramers-Kronig dispersion relation and quantum chemistry calculation, the origin of dielectric loss was ascribed to the physisorbed water molecules. Post-ash CH4 plasma treatment, vapor silylation process, and UV radiation were developed to repair plasma damage.Item Tetrachloroethylene Degradation by Dithionite with Ultraviolet Activation(2013-07-30) Zhang, JingyuanTetrachloroethylene (PCE) is a contaminant that has been frequently detected in ground water, surface water, air and soil. Advanced reduction processes (ARP) make up a set of wastewater treatment technologies that have been proposed recently. This project has conducted research on degrading PCE with an ARP that combines dithionite and ultraviolet activation. The purpose of the project is to provide knowledge for the development of potential wastewater treatment technologies. Several control experiments (blank control, reagent control and UV control) were conducted to prove the feasibility of applying the dithionite/UV ARP to degrade PCE. ARP degradation of PCE was studied under different pH (5, 7, 8, 9) and light intensities (2, 4, 7.3 mW/cm2). The results showed that the fastest degradation was observed at pH 7 and that degradation becomes faster at higher light intensities. Combining dithionite and UV light resulted in a faster degradation of PCE than only using UV light to photolyze PCE.