ORCID Profile
0000-0003-3625-2632
Current Organisation
University of Tasmania
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Publisher: American Physical Society (APS)
Date: 03-1995
Publisher: American Physical Society (APS)
Date: 03-1995
Publisher: American Vacuum Society
Date: 03-1994
DOI: 10.1116/1.578876
Abstract: Fluorocarbon film deposition in discharges used for oxide etching plays a key role in determining the profile shape of contact holes and the etch selectivity with respect to the mask and the underlayer. For low-density capacitatively coupled rf discharges this deposition is due to neutral radicals. We report a study of fluorocarbon film deposition and etching phenomena in electron cyclotron resonance (ECR) discharges of CF4 and CHF3. Plasma operation without rf s le bias in the pressure range below 10 mTorr results in the deposition of fluorocarbon films for both gases, with the highest deposition rate in each case at 2 mTorr (≂120 nm/min for a 1000 W CF4 plasma and ≂180 nm/min for CHF3 using the same conditions). For CF4 this behavior differs dramatically from that seen for conventional rf diode plasmas where no deposition occurs. The deposition is due to the more efficient breakdown and ionization of CF4 and CHF3 in the ECR discharge and the lack of energetic ion bombardment of the substrate as compared to capacitatively coupled rf diode plasmas. We have used a double grid ion energy analyzer in front of a silicon wafer being ellipsometrically s led to unambiguously demonstrate that in these high-density discharges, fluorocarbon deposition is primarily due to bombardment with low energy ions. The fluorocarbon growth rate dropped by a factor of 5 if positive biasing of the grid prevented ions from reaching the fluorocarbon film surface in a CHF3 plasma at 2 mTorr. The energy distribution of the ions which may be obtained from these data is in good agreement with measurements of the plasma potential. The ion fluxes for CF4 are ≂4–5 times greater than the fluorine and carbon atom fluxes required to explain the deposition rates (assuming a sticking coefficient of 1). Film-growth due to direct ion incorporation rather than ion enhancement can explain the experimental results. For CHF3 plasmas the deposition rates are ≂100 nm/min greater than for CF4 for all conditions. This suggests that neutrals contribute strongly to fluorocarbon film growth for CHF3 since the ion currents are nearly the same as for CF4. The ion enhancement effect of film growth rate decreases at higher pressure and lower microwave powers and mirrors the behavior of the ion current. This finding has important implications for etch selectivity, etching profiles, and the slow-down of the SiO2 etch rates in high-aspect ratio contact holes. Biasing the substrate reduces the net fluorocarbon deposition rate for low rf bias values. At higher rf bias values, etching of the initially deposited film takes place. These threshold voltages for etching are higher for CHF3 than CF4, e.g., 55 versus 35 V for 1 mTorr operation. Oxide etching can only take place for rf bias values equal or greater than these threshold voltages.
Publisher: American Vacuum Society
Date: 07-1992
DOI: 10.1116/1.578248
Abstract: Recent experimental and theoretical work on the interaction of electrons with a moving radio-frequency (rf) sheath has shown that this interaction is an important electron heating mechanism in capacitive rf plasmas. It is usually assumed in the theoretical treatment of rf sheaths that electron inertia can be neglected and the velocity distribution in the sheath vicinity remains close to Maxwellian. This assumption is examined critically and limits to its applicability are derived from a model of the sheath structure. The litude of the oscillating sheath voltage Vrf must satisfy eVrf/kBTe ≲ (1/√8π)√mi/me if electron loss is to remain thermal. Two mechanisms enhance electron loss: field reversal at the electrode and distortion of the velocity distribution near the moving sheath edge. The latter is important if the maximum sheath velocity in an rf cycle approaches a critical value υsm = ῡe/2 where ῡe is the thermal velocity. Particle simulations of the electron–sheath interaction are used to study the distortion of the electron velocity distribution in the sheath vicinity and the details of the electron loss to the wall. Plasma oscillations can be excited near the expanding sheath edge when the sheath modulation litude is large, and this may have an important influence on the electron velocity distribution in the plasma.
Publisher: American Vacuum Society
Date: 03-1991
DOI: 10.1116/1.585611
Abstract: The results of a study of the mode transitions in the helicon source when used in the geometry required for plasma processing are presented. We find that the basic characteristics of high density (& ×1011 cm−3 in the processing chamber at 500 W) and low plasma potential (∼15 V) are observed in this configuration. The mode transitions can be interpreted in terms of the dispersion relation for the helicon wave. A study of the initial plasma breakdown has also been made and the results have aided in the understanding of the operation of the helicon source during pulsed plasma etching.
Publisher: American Vacuum Society
Date: 03-1994
DOI: 10.1116/1.578877
Abstract: We report a study of the application of CF4 and CHF3 electron cyclotron resonance (ECR) discharges to selective etching of SiO2 over Si. Due to significant fluorocarbon film deposition for plasma operation without rf s le bias in the pressure range below 10 mTorr, rf biasing is required for etching of SiO2 and Si. The rf threshold voltage for etching is 55 V for CHF3 and 35 V for CF4 at a pressure of 1 mTorr. At 100 V rf bias, silicon dioxide etch rates were greater than ≂600 nm/min in CF4 and 450 nm/min for 1000 W plasmas at 1 mTorr pressure. A plot of the oxide etch rate vs rf bias exhibits a fluorocarbon film suppression regime at low rf voltages and an oxide sputtering regime at higher rf voltages. In the fluorocarbon suppression regime, the etch rate is primarily determined by fluorocarbon deposition which results in a thin fluorocarbon film being present on the SiO2 surface during steady-state etching. In the oxide sputtering regime, the oxide etch rate increases linearly with the ion current to the wafer and the square root of the ion energy. The etch yields decrease with increasing microwave power and decreasing pressure and are in the range 0.5–2 atoms per incoming ion. The silicon etch rate is much lower in CHF3 than in CF4, which translates into better SiO2-to-Si etch selectivity in CHF3 (≂15) than in CF4 (≂5). The lower Si etch rate in CHF3 is due to a greater thickness of the fluorocarbon film present on the silicon surface during steady-state etching. The fluorocarbon film thickness is ≂5.5 nm in CHF3 as compared to ≂2.5 nm in a CF4 discharge (at a rf bias of 100 V). The oxide surface is free of fluorocarbon film for the same conditions. The etch depth of ≂2.5 μm deep contact holes etched using 1 mTorr CHF3 plasmas into photoresist patterned SiO2 was measured by scanning electron microscopy as a function of the feature width. The etch depth decreased by ≂10% as the feature size was reduced from 1.3 to 0.6 μm.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-1990
DOI: 10.1109/27.57527
Publisher: IOP Publishing
Date: 22-10-1999
Publisher: American Physical Society (APS)
Date: 07-09-2001
No related grants have been discovered for David Vender.