The 193nm photoresist (ArF resist) degradation mechanism in dielectric etching was investigated by using an ultra-high-frequency electron-cyclotron-resonance plasma. This investigation focused on via-hole etching. It was found that the bottom-antireflection coating (BARC) etching condition is a critical factor in the reduction of striation and pitting after via-hole etching. X-ray photoelectron spectroscopy and scanning electron spectroscopy studies revealed that argon-less and low-incident-ion-energy conditions in BARC etching can keep the resist surface smooth and maintain a carbon-rich micromask-less state because decomposition of the C–H or OC–O bonds is suppressed. As a result, resist damage after via-hole etching is reduced remarkably. Furthermore, in the via-hole etching, it was also found that the characteristics of the fluorocarbon polymer, i.e., deposition rate and flourine-to-carbon ratio of the fluorocarbon polymer, stacked on the resist surface during etching strongly affect the ArF resist degradation. Low-sticking-coefficient radicals such as CF2 and a low amount of deposition thickness are suitable for damage-less etching. In regard to the formation of striations at the pattern corner, the sputtering effect was taken into consideration. As a result, in the case of via-hole etching, line-edge-roughness in the trench pattern was improved by about 50%, and a striation-less and pitting-less hole etched profile was obtained by using either an argon-and-xenon (20%) mixture as a dilution gas or a fluorocarbon gas at low flow rate under low gas pressure.
The bowing mechanism in high-aspect-ratio contact hole (HARC) etching was investigated by taking into account reactive sticking on the sidewall of the hole. Sticking coefficients of radicals on the sidewall have been estimated by comparing the observed deposition profile with the calculated one. It was found that the coefficients of C rich radicals and CF x radicals were 0.5 and 0.004, respectively, and that F radical reaction probability to the fluorocarbon polymer is 0.07. These coefficient values were deduced that the excessive flux of O and F onto the sidewall of a hole causes bowing during HARC etching. It was also indicated that the bowing can be suppressed by reducing of the flux of oxygen. These findings were confirmed by the results of experiments using an ultra-high frequency-electron cyclotron resonance (UHF-ECR) plasma.
An atomic layer etching process for silicon nitride (Si 3 N 4 ) has been developed in which ammonium fluorosilicate [(NH 4 ) 2 SiF 6 ] is formed and desorbed using infrared annealing. The cycle of forming and removing ammonium fluorosilicate was repeated, demonstrating that the Si 3 N 4 etching depth was accurately controlled with high selectivity to SiO 2 by changing the number of cycle. An X-ray photoelectron spectroscopy peak, which had been previously assigned as N-H bond of an ammonium salt, was observed after radical exposure, indicating that the ammonium fluorosilicate-based modified layer had formed. This peak disappeared after infrared annealing for 10 s, demonstrating desorption of the modified layer. In thermal desorption spectroscopy, NH 3 , HF, and SiF x were detected, providing further evidence for the formation of the ammonium fluorosilicate-based modified layer. In addition, this layer has a multilayer structure, protecting the Si 3 N 4 from exposure to reactive radicals.
Transition state structures for the reaction of allyltetrafluorosilicate with formaldehyde as well as structures of the silicate and related compounds were located with ab initio MO calculations. The origin of the unique reactivity of pentacoordinate allylsilicates observed experimentally is discussed on this basis.
Novel selective cyclic etching of SiN over SiO2 via the formation and desorption of ammonium fluorosilicate was developed. The formation of ammonium fluorosilicate was observed using X-ray photoelectron spectroscopy after hydrofluorocarbon-based radical exposure. Etching of SiN was observed after ammonium fluorosilicate was removed by thermal annealing. Cyclic etching tests were carried out by repeated radical exposure and thermal annealing. The etching depth increased on increasing the number of cycles. It was found that the cyclic etching is self-limiting because the etching depth does not depend on the radical exposure time but on the number of cycles.
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