Articles you may be interested inPlasma etching of Hf-based high-k thin films. Part II. Ion-enhanced surface reaction mechanismsThe relation between SiO 2 etch rates and incident fluxes of reactive species in a dual-frequency ͑27 MHz and 800 kHz͒ parallel-plate system was evaluated by using various in situ measurements tools. C 4 F 8 /Ar/O 2 was used for etching gases. The steady-state thickness T C-F of a fluorocarbon polymer layer on the etched SiO 2 surface was also measured. The SiO 2 etch rate could be related to total F atom flux ⌫ F-total , which depends on both the incident fluxes of C-F reactive species and the surface reaction probability s. The s is a function of the net energy on the reactive layer (V net ). This energy is determined by the incident ion energy and the energy loss at the C-F polymer on the etched surface. A change in V net from 500 to 1450 V was estimated to correspond to a change in s from 0.01 to 0.1. The steady-state thickness of the C-F polymer T C-F increased when excess C-F species were supplied to the etched surface. A thick polymer (T C-F Ͼ1 nm) decreases the ion energy and slows or stops the etching in fine holes. A polymer 5 nm thick can decrease the ion energy by about 750 V. The T C-F must therefore be controlled when high-aspect contact holes are etched.
Plasma enhanced chemical vapor deposition Si-rich silicon oxynitride films for advanced self-aligned contact oxide etching in sub-0.25 μm ultralarge scale integration technology and beyond Fully large-scale integration-process-compatible Si field emitter technology with high controllability of emitter height and sharpness J. Vac. Sci. Technol. B 15, 488 (1997); 10.1116/1.589605 Pattern profile control of polysilicon in magnetron reactive ion etching J. Vac. Sci. Technol. B 15, 221 (1997); 10.1116/1.589268 Effect of plasma polymerization film on reducing damage of reactive ion etched silicon substrates with CHF3+O2 plasmas J.The etch rates of SiO 2 , photoresist, Si, and SiN in a 27 MHz reactive ion etching system at constant ion flux of 6ϫ10 16 cm Ϫ2 s Ϫ1 and ion energy of 1450 V were studied. Typical incident flux densities of CF 2 and CF ϩ were on the order of 10 17 and 10 16 cm Ϫ2 s Ϫ1 , respectively. The SiO 2 etch rate was determined by the balance of the energy supplied by the total ion flux and the amount of the C-F reactive species supplied by radicals and ions. When we roughly assumed the surface reaction probabilities of F, CF, CF 2 and CF 3 to be 0.1, 0.1, 0.1, and 0.5, the SiO 2 etch rate could be expressed well as a function of the total number of F in the net radical fluxes. To clarify the dominant flux including radicals and ions, however, further research on surface reaction probabilities on the actual etched surface must be conducted because the incident fluxes strongly depend on these constants of the surface reaction probability. Lowering the total ion flux or ion energy decreased the etch rate of SiO 2 . A higher ion flux or higher ion energy is required to obtain higher etch yields. When excess C-F reactive species exist on the etched surface, they disturb the etching reaction by wasting the energy of incident ions. Under these conditions, a reactive species is no longer an ''etchant,'' but an ''inhibitor.'' Therefore, it is important to control the amount of total reactive species according to the ion conditions. Oxygen contributed to the removal of these excess C-F species, resulting in a higher etch yield. In contrast, the etch rates of a photoresist, Si, and SiN did not depend on flux of the C-F reactive species, but on the oxygen concentration. It is concluded that a process with high selectivity requires low oxygen concentration, high ion flux, and optimized flux of C-F reactive species.
Articles you may be interested inNanostructured silicon formations as a result of ionized N 2 gas reactions on silicon with native oxide layers Appl. Phys. Lett. 82, 3653 (2003); 10.1063/1.1579124 Subsurface reactions of silicon nitride in a highly selective etching process of silicon oxide over silicon nitrideKinetics and crystal orientation dependence in high aspect ratio silicon dry etching
The mechanism of highly selective etching of SiO2 using pulsed-microwave electron-cyclotron-resonance plasma was investigated by analyzing the relationship between plasma dissociations and fluorocarbon layers formed on surfaces during etching with a cyclo-C4F8/Ar gas mixture. Dissociated molecules of CxFy and CFx species were measured without fragmentations using ion attachment mass spectrometry, and both thicknesses and atomic concentrations of reaction layers formed on etched surfaces were analyzed using x-ray photoelectron spectroscopy. Thus, the impact of CxFy molecules on the formation of fluorocarbon layers were analyzed using this measurement system. The authors found that the process window of highly selective etching of SiO2 over Si was enlarged by using pulsed-microwave plasma because a thinner fluorocarbon layer was formed by controlling C4F8 dissociation by changing the duty cycle of the pulsed-microwaves. With conventional continuous plasma, an etch stop occurred at low wafer bias conditions because a thicker fluorocarbon layer, which protects the SiO2 surface from the ion bombardment, was formed on the SiO2 surface. The thicker fluorocarbon layer was formed from a large amount of CxFy species, such as C2F2, which were generated in the highly dissociated continuous plasma. On the contrary, with pulsed plasma, a thinner fluorocarbon layer was formed due to the lower flux of CxFy species because the dissociation of C4F8 was controlled by reducing the duty cycle of the pulsed-microwave plasma. As a result, the process window was enlarged to the low wafer bias conditions using the pulsed-microwave plasma.
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