Effects of Surface Pre-Cleaning and High Temperature Deposition on the Formation of Cobalt Silicides and Growth Kinetics of SiO2 on (001) Si Catalyzed by Cu3Si at Elevated Temperatures

• Main Authors: Hisn-Yuan Huang, 黃新員
• Other Authors: Lih-Juann Chen
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/92696302339979403435

博士 === 國立清華大學 === 材料科學工程學系 === 88 === CoSi2 has been a promising candidate material to replace TiSi2. However, the major issues on Co salicide processes are its sensitivity to surface contamination and oxidation during ex-situ rapid thermal annealing (RTA), which cause poor reproducibility. In the present study, the effects of precleaning treatments on the formation of Co silicide have been investigated. Several wet and dry cleaning Si surfaces were prepared before metal deposition. The formation of CoSi2 tends to be inhibited by n-type dopants. Thick oxide interlayer between Co and Si would retard the silicidation reaction and lead to the formation of rough CoSi2/Si interface. Nitride interlayer is a good diffusion barrier in the Co/Si reaction. A thin nitride layer (2 nm) could inhibit the reaction to a temperature as high as 800 oC on n-type single crystalline Si. In addition, dewetting between Co and nitride was found after high temperature annealing. Thin oxide layers were formed after wet etching in sulfuric peroxide mixture (SPM) or hydrogenchloride peroxide mixture (HPM) solution. The thin oxide interlayer was also found to inhibit the silicidation. It was found that the first RTA temperature should be higher to grow the same thickness of silicide as in the samples with the absence of oxide interlayer. For the poly-Si substrates, the thermal stability of CoSi2 films deteriorates with thick oxide interlayers. Formation of Co silicide on polycrystalline silicon with or without pre-amorphization has also been studied. The sheet resistance of the pre-amorphization implantation (PAI) sample is lower than that of the non-PAI samples which is likely due to the presence of more uniform silicide thickness on the PAI samples after annealing. On the other hand, the thermal stability of CoSi2 film on PAI samples is worse than that on non-PAI sample due to the presence of the arsenic atoms from the PAI. Effects of high temperature sputtering deposition (HTSD) on the properties of Co thin films on Si have been investigated. In as-deposited samples, there is no clear intermixing between Co and (001) Si in samples deposited at room temperature or 300 oC. On the other hand, polycrystalline CoSi phase and a high density of pinholes were found in samples deposited at 450 oC. After the two-step annealing, small and polycrystalline CoSi2 grains were formed in HTSD samples. Pinholes were still found to form at the CoSi2 surface. The size and density of pinholes were largely reduced by further annealing treatments. The thermal stability of CoSi2 thin film was improved by HTSD. The alleviation of agglomeration of CoSi2 is attributed to the higher nucleation density of CoSi2 and the presence of pinholes at the surface, which led to the retardation of grain growth in high temperature sputtering deposition samples. As the device size steadily scales down, the packing density is increasing. Concurrently, interconnection lines increase in length and reduce in feature size. Reduction in interconnects pitch increases wiring resistance and parasitic capacitance. These conditions result in an increase in resistance-capacitance (RC) delay time and crosstalk noise. To satisfy the demands for ULSI circuit fabrication, it is necessary to look for a new material to replace Al and its alloys. Cu is an attractive material for interconnects due to its low bulk resistivity and high resistance to electromigration. Cu3Si was found to be the first phase to form in the reaction of a copper film with a silicon substrate. Very peculiar oxidation behaviors on both (001) Si and (111) Si catalyzed by Cu3Si were found. Mechanisms of fast oxidation of silicon substrate in the presence of Cu3Si at room temperature (RT) are now largely understood. The data on oxidation kinetics at elevated temperatures are scarce, compared with that at room temperature, owing to the difficulty to conduct the experiments in a timely manner so that the RT oxidation would not interfere with the interpretation of high temperature oxidation behaviors. In the present study, the oxidation of Si catalyzed by 170-nm-thick Cu3Si at elevated temperatures has been investigated by transmission electron microscopy, glancing angle X-ray diffraction and Auger electron spectroscopy. For wet oxidation at 140-180 oC, the thickness of the oxide was found to increase parabolically with time with an activation energy of 0.4 ± 0.2 eV. The activation energy is close to that of the diffusivity of Cu in Si. At 180-200 oC, the growth rate became slower with increasing temperature. The growth of oxide tended to be discontinuous at the surface as the oxidation temperature was increased to a temperature at or higher than 300 oC. The anomalously fast growth of oxide at low temperatures is attributed to the presence of filamentary structures of Cu clusters in the oxide to expedite the diffusion of the oxidants through oxide. At 200-250 oC, more Cu atoms diffuse to the Cu3Si/Si interface and less Cu atoms stay in the oxide, which slows down the oxide growth. The lack of filamentary structures of Cu as diffusion paths retards the growth of SiO2. At 300 oC or higher temperatures, the lack of filamentary structures of Cu clusters stops the growth of continuous oxide layer altogether.