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.

Comprehensive measurements of charged particles and neutral radicals in an inductively coupled plasma (ICP) are performed to understand and control the etching process using a CF4/H2 gas. The electron density in the ICP reactor decreases exponentially in a downstream region while the most abundant ionic species CF+ increases in proportion to the rf power with the CF+3 density almost constant. The neutral radical diagnostics by appearance mass spectrometry indicate 10 times more F atoms and somewhat fewer CFx radicals (x=1–3) in ICP, compared with a high-pressure capacitively coupled plasma diode. Such a small ratio of the CFx density to the F density is possibly a cause of the low etch selectivity of SiO2 to Si in ICP etching. Two innovative methods to achieve the high selectivity in ICPs are demonstrated. One is wall heating (100–200 °C), which leads to a drastic increase in CFx densities with the F density almost constant. The other is a pulse modulation of rf power at 30–50 μs durations where the time-resolved measurement of electron temperatures indicates a 6 μs rise time and a 70 μs decay time. The density ratio CFx/F (x=2,3) increases with decreasing rf-on time. The mechanisms of the radical composition change and the resultant high selectivity in pulsed plasmas are discussed.

Real-time control of deuterium or helium gas injection by feedback on Langmuir probe signals is implemented in Tore Supra ergodic divertor discharges. The feedback schemes are based on the robust experimental observation that the density limit coincides with the edge temperature T e ∼ 10 eV. Three control algorithms are used: (1) proportional feedback on the central line-averaged density with real-time attenuation of the system gain and security cut-off of the gas injection if the edge temperature becomes too low; (2) proportional feedback on the central line-averaged density with security cut-off controlled by the degree of detachment (DoD);(3) proportional feedback on edge temperature with security cut-off on the DoD.The DoD is defined for deuterium discharges, but not for helium since those do not detach. All three feedback modes permit operation close to the density limit and have been successfully applied for plasma currents 0.4 < I p < 1.8 MA, and at I p = 1.4 MA with up to 4 MW of ICRH power.

The radicals of capacitive plasmas actually used in mass production were analyzed using various measurement systems. The composition of radicals in bulk plasma depends on the gas chemistry, the dissociation process, and interaction with the wall. It is revealed that parent gas (C4F8) is dissociated by multiple collision with electrons according to τ·n e<σv>, where τ is the residence time, n e is the electron density, σ is the dissociation collision cross section and v is the electron velocity. A high-performance etching process, which can realize 0.09 µmφ contact holes with aspect ratio of 11, was achieved using a short residence time to suppress the excess dissociation and the control of deposition species through the addition of O2 to C4F8/Ar plasma as well as the reduction of the density of F radicals through the reaction with the Si wall.