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.
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.
Poly-Si etching under Hg-Xe lamp irradiation in a Cl2 atmosphere was investigated. It was found that n+ poly-Si is etched by chemical reaction with Cl radicals photodissociated in the gas phase, while undoped and p+ poly-Si cannot be etched without irradiation by UV light. The primary effect of the photoirradiation is to produce electrons arising from electron-hole pair generation. The etch rates, etched features and etching products depend strongly on the electron concentration in the conduction band. The experimental results are explained by assuming that electron-attached Cl- ions penetrate into the Si lattice.
Complementary metal-oxide-semiconductor-compatible and self-aligned catalyst formation for carbon nanotube synthesis and interconnect fabrication Low resistance polysilicon interconnects with selfaligned metal
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