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High-aspect-ratio SiO 2 contact-hole etching is one of the key processes in the fabrication of ultralarge-scale integrated devices. However, there are many serious problems, such as charge-buildup damage, etching-stop, and microloading effects. Charge accumulation in high-aspect-ratio contact holes during etching is one of the main causes of these problems. In SiO 2 etching using fluorocarbon gases, it is well known that fluorocarbon film is deposited on the underlayer surface and sidewall of contact holes. It is expected that such deposited fluorocarbon polymer will exert a great influence on the etching characteristics and charge accumulation in SiO 2 contact holes. Therefore, it is necessary to measure the conductivity of the sidewall surfaces of contact holes with deposited fluorocarbon polymer. We made a monitoring device on a silicon wafer to evaluate the sidewall current of SiO 2 contact holes and determined the relationship between the chemical structure and electrical conductivity of the fluorocarbon films deposited in the contact holes as a function of fluorocarbon gases and incident ion flux. We found that the electrical conductivity of the sidewall surface in SiO 2 contact holes depends on the chemical structure of the deposited fluorocarbon polymer. It was also clear that the chemical structure of the deposited fluorocarbon polymer depended on nature of the radical species and ion flux incident on the etching surface. These results indicate that by controlling the chemical structure of the deposited fluorocarbon polymer one may be able to mitigate the influence of charge accumulation.

SiO 2 contact-hole etching with a high-aspect ratio is a key process in fabricating ultra-large scale integrated devices. However, charge accumulation in contact holes during plasma etching causes serious problems, such as charge-build-up damage, etching-stop, and microloading effects. Therefore, understanding the mechanism behind this electric charge accumulation and controlling the plasma etching processes would be very important to achieve the next-generation semiconductor devices. We found, through our previous research, that deposited fluorocarbon film in contact holes had high electric conductivity because of ion bombardment. In this experiment, we investigated the build up of charging potential during plasma processes by in situ on-wafer monitoring to control charge accumulation in the contact holes. We developed an on-wafer monitoring device to measure the charging potential in SiO2 contact holes (aspect ratio=5.7). The dc potential of the SiO2 contact hole top and bottom surfaces were measured during plasma exposure with/without deposited fluorocarbon film in the holes. The results revealed that the sidewall deposited fluorocarbon film has high electric conductivity that may mitigate electric charge accumulation at the bottom of contact holes during SiO2 etching processes.

In situ on-wafer monitoring of the electron and ion energies at the contact-hole bottom is primarily achieved in Ar ultrahigh-frequency plasma. The on-wafer probe reveals a lower electron density and higher electron temperature at the contact-hole bottom due to the electron-shading effect, as compared with that in the bulk plasma. The on-wafer probe also shows the ion energy distribution function (IEDF) at the contact-hole bottom. The peak energy of IEDF corresponded to the sheath potential. Accordingly, the authors found that the on-wafer probe is a very effective tool for investigating the electron and ion energies in real SiO2 contact structures.

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