We have identified the monohydride Si(001)-(2X 1):H surface and the dihydride Si(001)-(1X1)::2H surface by angle-resolved electron-energy-loss spectroscopy and elastic lowenergy electron diffraction. On the monohydride (2X1):H surface the S3 transition from the back-bond surface state was distinctly observed although the Sl transition from the dangling-bond surface state disappeared, while on the dihydride (1X1)::2Hsurface both the S3 and the Sl transitions completely disappeared. These facts show that on the monohydride surface the subsurface strain due to dimerization remains; on the other hand, on the dihydride surface the strain is healed out. The hydrogen-induced transitions for the two surfaces were clearly distinguished; the transition energy for the (2X 1):H surface (SHl) was 8.0 eV and that for the (1 X 1)::2H surface (SHq) increased from 7.0 to 7.5 eV with increas-ing~k~~~due to dispersion. The present results support and develop the models for the monohydride and the dihydride surfaces proposed by Sakurai and Hagstrum.

Single Si etching profile by Cl2 and a mixture of Cl2 and CHF3 are discussed in terms of experimentation and simulation. A microprobe Auger analysis of a trench side wall has proven that the bombardment of obliquely impinging ions to a side wall leads to both concave and tailed features. In the case of a mixture of Cl2 and CHF3, the polymer film produced by CHF3 protects the side wall from species impinging from an inclined direction. Furthermore, the difference in the polymer sputtering rate, resulting from subsequently impinging ions between the tailed part and the flat bottom regions improves the tailed part to the rectangular bottom. A profile simulation supports the idea that obliquely impinging species, polymer deposition and sputtering of a polymer are important factors in determining the single Si etching profile.

Measurements of the ion species generated in the planar type neutral loop discharge of tetrafluoroethyl trifluoromethyl ether (CF3–O–CHF–CF3;HFE 227) demonstrate the presence of CFx+ species and CFx radicals, in a comparable manner to plasmas of more established gases such as C4F8, C2F6 or CHF3. However, as the etch selectivity of boron phosphorus silica glass (BPSG) to resist is quite poor in HFE 227 plasmas, organosilane Si(CH3)xH4−x additive gases are investigated as a source of Si to improve the BPSG/resist selectivity. The addition of 10% trimethylsilane to HFE 227 is capable of providing selectivity close to 5, which is desirable for the fabrication of deep holes. It is shown that the HFE 227/trimethylsilane plasma chemistry also preserves the resist hole pattern and does not cause hole expansion during the etching process. These latter observations are attributed to the deposition of polymer precursors induced by the trimethylsilane addition which reduces the top resist surface etch rate and balances the removal rate of the resist sidewalls. As a result, 0.15 μm diam holes with an aspect ratio of 15 are successfully fabricated. Mass spectrometry measurements of fluorocarbon radicals and ionic species imply that the high aspect ratio feature can be fabricated by having mostly CF3+ ions and lower density of fluorocarbon radicals. Furthermore, the microloading-free etching of contact holes is achieved at a bias voltage of −500 V for diameters down to 0.15 μm holes. The limit of the etching performance of the HFE 227/10% trimethylsilane plasma etch chemistry is investigated using very fine patterns defined by electron beam lithography. Trenches of 20 nm in width and mesh holes of 70 nm can be fabricated.

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