Damage-free selective etching of Si native oxides against Si has been achieved by NH3/NF3 and SF6/H2O down-flow etching. In the NH3/NF3 etching, the wafer was covered with a film, and after its removal by heating above 100 °C, only SiO2 was found to be etched with an extremely high selectivity with respect to Si. Selective etching of Si oxides has also been obtained for SF6/H2O microwave discharge. In this case, a film of liquid solution containing HF and H2SOx is considered to form on the wafer surface. The selective etching of SiO2 takes place by the dissolved HF just as in the wet etching by an HF solution. The mechanisms of these selective reactions are discussed in detail based on the covalency of Si and SiO2 bondings.

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The water absorption properties of a PE-CVD (plasma-enhanced chemical vapor deposition) fluorine-doped SiO2 film with a low dielectric constant were studied. It was concluded that highly stable F-doped SiO2 film was obtained at F contents from 2.0% to 4.2% (3.2≤k≤3.6) using high-density plasma CVD. However, at F contents higher than 4.2% (k<3.2), the amount of water absorption was markedly increased due to the presence of Si–F bonds, such as Si(–F)2 bonds, which are highly reactive with water. On the other hand, water absorption was observed at every F content for conventional plasma CVD films. Through gas phase component analysis and investigation of the incident ion energy distribution using a quadrupole mass spectrometer, it was confirmed that a high efficiency of gas dissociation and high-energy ion bombardment are the keys to obtaining high-quality films with a high resistance to water absorption.

In this paper, we describe the effect of electron-beam (EB) curing on ultra-low-k dielectric porous SiOC material (k ¼ 2:2) and the application of this technology to the 90-nm-node Cu/low-k multilevel damascene process. A significant improvement of dielectric porous SiOC films with EB curing has been demonstrated. The mechanical and adhesion strength of these films were increased by a factor of 1.5-1.6 without degrading the film's k. This result can be explained by the reconstruction of a Si-O random network structure from cage Si-O bonds and Si-CH 3 bonds through EB curing. Additionally, the EB curing of spin-on dielectric (SOD) porous low-k films contributes to a decrease in their curing temperature and a decrease in their curing time. Under optimum EB curing conditions, no degradation of transistor performance was revealed. The excellent adhesion strength obtained by EB curing, has contributed to the success of multilevel damascene integration. On the basis of our findings, this EB curing technology can be applied in devices of 65-nm-node and higher.

With the use of a newly developed electron beam (EB) curing process, an advanced methylsilsesquioxane (MSQ) low-k dielectric (LKD) film of k=2.9 was developed. It is noteworthy that the EB curing process can drastically improve the mechanical strength of LKD film and reduces the thermal budget without increasing the k value. The X-ray absorption fine structure (XAFS) study on the LKD was conducted to clarify the structural change upon EB curing. The structure of the film was compared with those of two different types of other MSQ films, the ladder-network structure and the random-network structure, and a chemical vapor deposition (CVD) film. The Si–O–Si bond angle and Si–O (Si–C) bond length were determined by fitting the Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra. Si–O–Si bond angle of LKD film was found to be between those of the ladder and the random structure, which are 135° and 147°, respectively. The X-ray absorption near-edge structure (XANES) spectra of LKD film revealed two broad features corresponding to a mixture of the two structures. In contrast, Si–O–Si angles of the EB-cured LKD film and the CVD film were similar, and the XANES features of both films were almost identical with those of the random structure. The electronic structure as determined from XANES spectra was also discussed by comparing three-dimensional-linkage models obtained by ab initio calculations. We confirmed that the EB curing process of LKD film causes a drastic structural change. The change from the mixture of ladder and random structures to the completely random structure was caused by C–H bond breaking followed by the formation of new polymer-like clusters with C–C bonds.