The Study of F Doped SiO2 Films Grown by PECVD
We can divide the thesis into two parts. One part of the thesis studies the un-doped oxide. Another studies the F-doped oxide. We grew the thin films by the PD-240 PECVD from SAMCO International Inc and found the optimum conditions of the oxide films. First, we deposit the un-doped oxide films by PECVD process using TEOS/O2 gases. There are five controlled conditions, which are O2 flow rate, RF power, pressure, temperature, and TEOS flow rate, to deposited the un-doped oxide films. We found that optimum TEOS flow rate was 7sccm for the PD-240 PECVD. Also, with increasing RF power, pressure, and temperature, we can get better quality of the un-doped oxide films. In order to improve the quality of the un-doped oxide films, the as-deposited oxide films were annealed by furnace or RTA process. FSG films were deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) process using TEOS/O2/CF4 gases. The dielectric constants of the as-deposited films decreased from 4.08 to 3.37 with the increase CF4 flow rate from 0sccm to 40sccm. We also tried to use furnace annealing at 8500C for 30 mins and Rapid Thermal Anneal (RTA) at 10000C for 30sec after the as-deposited FSG films. The relative dielectric constant of as-deposited films with thermal annealing was higher than the SiOF films without thermal annealing. The result of higher dielectric constant was induced by fluorine desorption from the SiOF films. At the high F concentration of the SiOF films, the SiOF films become more unstable to moisture absorption. The moisture absorption of SiOF with high fluorine concentration are caused by the porosity and the formation of Si-F2 in the films. The absorbed water causes increase of dielectric constant and reliability problems in ULSIs. In order to improve the moisture resistance of the SiOF films, we would use N2 plasma annealing as the post treatment to stabilize the films. With increasing the plasma post treatment time above 20min, it is effective to stabilize the SiOF films.
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