No abstract

No abstract

The mechanism of highly selective etching of Si3N4 by a pulsed-microwave electron-cyclotron-resonance plasma was investigated by analyzing surface-reaction layers formed by etching using a CH3F/O2/Ar gas chemistry. A hydrofluorocarbon (HFC) layer formed not only on nonpatterned materials (Si3N4 and others) but also at the bottoms of line-and-space patterns were analyzed by X-ray photoelectron spectroscopy. Thermal reactivity between the HFC layer and the Si3N4 layer was also investigated by thermal-desorption spectroscopy. The investigation results show that nitrogen contained in the Si3N4 layer thermally reacted with the HFC layer to form NH3 or HCN, and silicon contained in Si3N4 had high reactivity with fluorine contained in the HFC layer. Owing to the high reactivity between the fluorine-rich HFC layer and the Si3N4 layer in the pulsed-microwave plasma, the HFC layer became thin, even at a low wafer bias, and thus promoted ion-assisted etching. A wide process window was provided by the formation of the fluorine-rich thin HFC layer using the pulsed-microwave plasma.

The mechanism of highly selective etching by a pulsed-microwave electron-cyclotron-resonance plasma was investigated by analyzing surface-reaction layers formed on nonpatterned poly-Si and SiO2 samples and gate-patterned samples with a gate width of 32 nm. The samples were etched by using an HBr/O2/Ar/CH4 gas chemistry and varying the duty cycle of the pulsed microwave. The reaction layers, which were revealed as a hydrocarbon layer on a SiBr x O y layer, were analyzed by X-ray photoelectron spectroscopy. The upper layer was a hydrocarbon layer, which protected SiO2 from ion bombardment and also prevented Br flux from being supplied to the SiO2. The lower layer was a SiBr x O y layer, which suppressed the etching of the underlying Si substrate. The formation of the hydrocarbon layer was controlled by the duty cycle of the microwave plasma. Etch stop, which occurred at a low peak-to-peak voltage (wafer bias) of the continuous microwave plasma, was prevented by controlling the thickness of the hydrocarbon layer in the pulsed-microwave plasma. Gate-oxide punch-through, which occurred at a high peak-to-peak voltage of wafer bias in the case of the continuous microwave plasma, was also prevented in the case of the pulsed microwave plasma by forming reaction layers with high C/Br ratio.

No abstract