Plasma chemistry of fluorocarbon RF discharges used for dry etching

ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr. J.H. van Lint, voor een commissie aangewezen door het College van Dekanen in het openbaar te verdedigen op dinsdag 10 september 1991 te 16.00 uur doo

Measurement of the gas temperature in fluorocarbon radio frequency discharges using infrared absorption spectroscopy

The translational gas temperature was measured in 13.56 MHz radio-frequency (rf) discharges in CF4 and CHF3. Infrared absorption spectra of CF4 and CF2 were recorded using a tunable diode laser and the gas temperature was deduced from the linewidths of the absorption lines of these molecules. It is shown that linewidth measurements yield a simple and direct method to determine the gas temperature, with an accuracy up to ~ 10 K. The results obtained in CF4 and CHF3 plasmas indicate that the translational temperatures of all particles investigated in these plasmas are, at most, 50 K above the room temperature. The temperature increases with increasing gas pressure and rf power, but it is independent of the flow rate. This is attributed to an increased heating rate of the gas. Moreover, it was found that the temperature rise is significantly smaller in CHF3 than in CF4, under the same plasma conditions. This can be attributed to a higher power dissipation by chemical conversion of the parent gas in a CHF3 discharge, as compared with a CF4 plasm

Production and destruction of CFx radicals in radio-frequency fluorocarbon plasmas

Spacially resolved densities of CF, CF2, and CF3¿ radicals in capacitively coupled 13.56 MHz radio-frequency (rf) discharges in CF4¿and CHF3 were determined by means of infrared absorption spectroscopy employing a tunable diode laser spectrometer. It was established that the stationary CF2 density and density profile in a CF4 plasma depend strongly on the electrode material. This is attributed to different sticking coefficients of CF2 on different surfaces. Furthermore, it was found that the densities of all CFx radicals increase near the electrodes at high gas pressures and rf powers in a CHF3 plasma. This leads to the conclusion that production of CFx radicals takes place in the sheath region close to the electrodes. It is proposed that collisions between ions and source gas molecules are responsible for this production of CFx radicals. In the presence of a destruction process in the plasma glow (e.g., by three-body recombination with other radicals) and the absence of a fast surface loss process this results in the observed increase of CFx densities near the electrodes. In order to study the radical kinetics time dependent measurements were performed during power modulation of the plasma. It was found that the decay time of the CF2 density in the afterglow of a CF4 plasma is much shorter than the corresponding decay time in a CHF3¿discharge. This suggests that the surface loss is relatively less important in the latter case, in agreement with measurements of spatial density distributions. This is explained by the presence of a (CFx)n layer, which is readily deposited on the electrodes in a CHF3 discharge, and by low sticking probabilities of CF and CF2 radicals on such a layer. © 1996 American Vacuum Societ

The chemistry of a CCl2F2 radio frequency discharge

A systematic study of the chemistry of stable molecules and radicals in a low pressure CCl2F2 radio frequency discharge for dry Si etching has been performed. Various particle densities have been measured and modeled. The electron density, needed as an input parameter to model the CCl2F2 dissociation, is measured by a microwave cavity method. The densities of stable molecules, like CClF3, CF4, 1,2-C2Cl2F4 and the etch product SiF4, are measured by Fourier transform absorption spectroscopy. The density of the CF2 radical is measured by means of absorption spectroscopy with a tunable diode laser. Its density is in the order of 1019 m-3. All density measurements are presented as a function of various plasma parameters. Moreover, optical emission intensities of Cl and F have been recorded as a function of plasma parameters. It appears that the feed gas (CCl2F2) is substantially dissociated (about 70%–90%) in the discharge. Based on the obtained data the dissociation rates of several molecules have been estimated. The measured total dissociation rate of CCl2F2 is 8×10-15 m3¿s-1. For this molecule the dissociation rate is substantially higher than the dissociative attachment rate (10-15 m3¿s-1). The dissociation rate for CClF3 is 2×10-15 m3¿s-1 and for CF4 about 3×10-16 m3¿s-1. The total dissociation rate of C2Cl2F4 is higher than 5 ×10-15 m3¿s-1, of which 2.5±0.5 × 10-15 m3¿s-1 is due to dissociative attachment. Furthermore it has been found that the presence of a silicon wafer strongly affects the plasma chemistry. Optical emission measurements show that the densities of halogen radicals are significantly depleted in presence of Si. Moreover, the densities of several halocarbon molecules display a negative correlation with the density of the etch product SiF4. © 1995 American Vacuum Societ

Breakdown in mm-sized discharges : modifying the electric field

Due to the small size of the gas gap in micro- and millimeter sized discharges, the presence of a metallic structure in its vicinity profoundly influences the breakdown process. This is a drawback because it makes electrical probing impossible, but can also be an advantage because it allows control over the electric field in the discharge reactor. Optical and electrical measurements were performed in an argon atmosphere at 0.3 or 0.7 bar. A pin-pin geometry was used, with 4 or 7mm between the electrode tips. We found that both active and passive structures influence breakdown, and we demonstrated the differences between the two types and their effects on the breakdown process

In situ ellipsometry during plasma etching of silica films on Si

The etching of SiO2 films on a Si substrate in an rf plasma in CF4 has been studied with i n s i t uellipsometry. The etch rate was measured as a function of flow, rf power and pressure. An accurate analysis of the experimental data using numerical simulations based on multilayermodels has yielded information both on the refractive index of the etched SiO2 film and on the existence of a top layer. It could be established that a layer is present on top of the SiO2 during etching, which is probably caused by roughening of the SiO2 layer. Furthermore at high pressures (>8 Pa) it was demonstrated that after the complete removal of the SiO2 film a polymer layer starts growing on the Si substrate

The energy balance of Hg-free HID lamps and the influence of electrode distance

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High-frequency AC breakdown in near-atmospheric pressure noble gasses

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