Harold M. Anderson

Fluorocarbon-based plasma etching of SiO2: Comparison of C4F6/Ar and C4F8/Ar discharges

A gas phase and surface chemistry study of inductively coupled plasmas fed with C4F6/Ar and C4F8/Ar intended for SiO2 etching processes was performed. Adding Ar to those fluorocarbon gases results in a strong increase of the ion current, by up to a factor of 5 at 90% Ar relative to the pure fluorocarbon gases. The fluorocarbon deposition rate is higher for C4F6/Ar than for C4F8/Ar, whereas the fluorocarbon etching rate is lower, and both quantities decrease as the amount of Ar is increased. For both C4F6/Ar and C4F8/Ar, the CF2 density is more than an order of magnitude greater than the CF density. The CF2 partial pressure decreases as more Ar is added to the C4F6/Ar plasmas. A comparison of these data with corresponding results obtained with C4F8/Ar shows that the CF2 partial pressure in C4F6 is higher for Ar-lean gas mixture than for C4F8/Ar. This remains true up to 40% Ar. Above 40% Ar the CF2 partial pressure in C4F8 is higher than for C4F6. The CF and COF2 partial pressures in C4F8 are higher than fo...

Effects of Ar and O2 additives on SiO2 etching in C4F8-based plasmas

Gas mixtures based on C4F8 are promising for the development of high-performance SiO2 plasma etching processes. Measurements of important gas phase species, thin film etching rates and surface chemistry changes were performed for inductively coupled plasmas fed with C4F8/Ar and C4F8/O2 gas mixtures. The addition of Ar to C4F8 causes a strong increase of the plasma density relative to that of pure C4F8 (by up to a factor of 4× at 90% Ar). For O2 addition the changes in plasma density are small up to 90% O2 relative to pure C4F8. Infrared laser absorption spectroscopy was used to determine the absolute densities of neutral CF, CF2 and COF2 radical species as a function of the gas composition. The densities of CF and CF2 were enhanced for certain operating conditions when Ar was added to C4F8 as long as the amount of Ar remained below 20%. For instance, the partial pressure of CF was 0.1 mTorr for a 20 mTorr 1400 W source power discharge for pure C4F8, and increased to 0.13 mTorr at 20% Ar. Above 20% Ar it d...

Role of C2F4, CF2, and ions in C4F8∕Ar plasma discharges under active oxide etch conditions in an inductively coupled GEC cell reactor

Utilizing infrared diode-laser absorption spectroscopy (IRDLAS) and UV-Visible absorption spectroscopy (UV-Vis), we show that it is possible to make a near complete mass balance of etch reactants and products in a GEC inductively coupled fluorocarbon discharge while actively etching SiO2 substrates. Langmuir probe measurements were performed to measure the total ion current density. C2F4 and CF2 are shown to be the main dissociation products in a C4F8 plasma discharge. The C2F4 concentration decreases as the SiO2 etching rate increases, along with CF2 and CF radicals, suggesting a role in the SiO2 etching process. The addition of Ar to the C4F8 discharge increased the ion flux at the wafer surface, and the consumption rate of C2F4 relative to CF2. The increased ion flux enhanced the SiO2 etching rate, until at a very high degree of Ar dilution of C4F8∕Ar the etching rate became neutral limited. We also monitored SiF2 using UV-Vis absorption and CO by IRDLAS. In our work we found SiF2 and CO to be the prevalent Si and C gas phase etch products for the SiO2 etching process.Utilizing infrared diode-laser absorption spectroscopy (IRDLAS) and UV-Visible absorption spectroscopy (UV-Vis), we show that it is possible to make a near complete mass balance of etch reactants and products in a GEC inductively coupled fluorocarbon discharge while actively etching SiO2 substrates. Langmuir probe measurements were performed to measure the total ion current density. C2F4 and CF2 are shown to be the main dissociation products in a C4F8 plasma discharge. The C2F4 concentration decreases as the SiO2 etching rate increases, along with CF2 and CF radicals, suggesting a role in the SiO2 etching process. The addition of Ar to the C4F8 discharge increased the ion flux at the wafer surface, and the consumption rate of C2F4 relative to CF2. The increased ion flux enhanced the SiO2 etching rate, until at a very high degree of Ar dilution of C4F8∕Ar the etching rate became neutral limited. We also monitored SiF2 using UV-Vis absorption and CO by IRDLAS. In our work we found SiF2 and CO to be the prev...

Oxide etch behavior in a high-density, low-pressure, inductively coupled C2F6 plasma: Etch rates, selectivity to photoresist, plasma parameters, and CFx radical densities

Silicon dioxide and photoresist substrates were etched in a gaseous electronics conference inductively coupled plasma reference cell using C2F6 feed gas. The power/pressure/bias parameter space of the study generated a plasma which has plasma and ion current densities, plasma potential, ion energy, and etch rate characteristics typical of commercial high density plasma (HDP) etch tools. Absolute number density trends of CF and CF2 were measured using wavelength-modulated infrared spectroscopy in situ with etch rate experiments. For nonreactive surfaces such as Si and photoresist, typical CF and CF2 number densities varied around 4.9×1012 and 4.8×1013 cm−3, respectively. Over an SiO2 surface, these values decreased and evidence of the reaction of CFx radicals with an oxide surface to form COF2 was observed. Source and bias powers were mapped into ion current densities and ion energies, and correlations were made with etch rate, which was in the 0–150 A/s range. Selectivity ranged from 1 to 6. Typical plasm...

Characteristics of C4F8 plasmas with Ar, Ne, and He additives for SiO2 etching in an inductively coupled plasma (ICP) reactor

We have characterized the effect of adding Ar, Ne, and He noble gases to C4F8 inductively coupled plasmas for SiO2 etching. The systematic variation of their ionization potentials, metastable energy levels, and mass of the dominant ion in C4F8/X% discharges (X=He, Ne, or Ar) containing a high percentage of the noble gas provides a means to evaluate the relative importance of gas phase and surface processes in the etching of SiO2. The total ion flux, ion composition, FC deposition and etching rates, and composition of the surface reaction layer formed on Si or SiO2 in these discharges show systematic differences as a function of process parameters because of the different electron impact ionization thresholds for Ar, Ne, and He gases, and differences in the mass of the dominant ion for discharges containing a large proportion of the noble gas. For given experimental conditions (600 W and 20 mTorr for most of this work), Ar addition gives rise to the largest ion current density, and He to the smallest ion c...

Study of C4F8/CO and C4F8/Ar/CO plasmas for highly selective etching of organosilicate glass over Si3N4 and SiC

We have examined the effect of CO addition to C4F8 or C4F8/Ar plasmas for selective etching of organosilicate glass (OSG) over SiC etch stop layers. The variation of important gas phase species, thin film etching rates and surface chemistry with feedgas composition was determined. CO addition exhibits dramatically different consequences on OSG/SiC etching selectivity when added to C4F8 or C4F8/Ar plasmas containing a high proportion of Ar. An improvement of the OSG/SiC etching selectivity results from CO addition to C4F8. We observe little CO dissociation in this case, which is plausible considering the lower dissociation energy threshold of C4F8 relative to CO. X-ray photoelectron spectroscopy (XPS) analysis of OSG and SiC surfaces shows that the etching selectivity improvement for C4F8/CO may be explained not only by an increase of the thickness and a reduction of the F/C ratio of the steady-state fluorocarbon surface layer on the SiC surface during etching, but little incorporation of CO into deposited fluorocarbon films. Adding CO to C4F8/Ar discharges with a high proportion of Ar leads to a reduction of the OSG/SiC etching selectivity. Significant dissociation of CO in Ar-rich C4F8/Ar/CO discharges is observed, consistent with the fact that the dissociation energy threshold of CO is lower than the Ar ionization and metastable energies. Oxygen incorporation in deposited fluorocarbon films and a reduction of the steady-state fluorocarbon surface layer thickness on SiC are observed by XPS in this case, explaining the loss of OSG/SiC etching selectivity for C4F8/Ar/CO discharges.We have examined the effect of CO addition to C4F8 or C4F8/Ar plasmas for selective etching of organosilicate glass (OSG) over SiC etch stop layers. The variation of important gas phase species, thin film etching rates and surface chemistry with feedgas composition was determined. CO addition exhibits dramatically different consequences on OSG/SiC etching selectivity when added to C4F8 or C4F8/Ar plasmas containing a high proportion of Ar. An improvement of the OSG/SiC etching selectivity results from CO addition to C4F8. We observe little CO dissociation in this case, which is plausible considering the lower dissociation energy threshold of C4F8 relative to CO. X-ray photoelectron spectroscopy (XPS) analysis of OSG and SiC surfaces shows that the etching selectivity improvement for C4F8/CO may be explained not only by an increase of the thickness and a reduction of the F/C ratio of the steady-state fluorocarbon surface layer on the SiC surface during etching, but little incorporation of CO into deposited...