SiO2 Etch Rate Research Articles

Study of radiation damage and contamination by magnetized inductively coupled plasma etching

Radiation damage and contamination on the silicon surfaces etched by magnetized inductively coupled C4F8 plasmas were investigated. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, spectroscopic ellipsometry, and transmission electron microscopy were used to characterize contamination and high resolution transmission electron microscopy, and I–V characteristics of Schottky diodes fabricated on the etched and/or annealed silicon surface were used to evaluate radiation damage. As the magnetic field applied to the inductively coupled plasmas increased from 0 to 12 G, the thickness of the residue layer formed on the silicon surface increased with the increase of SiO2 etch rate and selectivity. XPS analysis showed that the composition of the residue layer changed from fluorine rich to carbon rich film by changing the carbon binding state from C–CFx to C–C. Dense defects distributed about 40 Å deep from the etched silicon surface were found for the 0 G condition and thicker but less dense defects were observed for higher magnetic field conditions. The electrical damage estimated from the I–V characteristics of Schottky diodes was reduced with increasing applied magnetic field strength.

The role of diluents in electronegative fluorinated gas discharges

To study the role of diluents in NF3 plasma processing we have correlated SiO2 and plasma chemical vapor deposition silicon nitride (SiN) etch rate measurements with rf electrical impedance analysis. A series of rare gas (He, Ar) and molecular (N2, O2, N2O) mixing gases were added to NF3 plasmas at different pressures to understand the effect of diluents on the chemical and physical properties of NF3 discharges. The etch rate experiments show that for NF3 plasmas the choice of mixing gas can have a profound effect on the etch rates of SiO2 and SiN with 25 mol % NF3 in Ar yielding the highest rates and 25 mol % NF3 in N2O the lowest. The electrical measurements revealed that the diluents have a profound effect on the plasma impedance and actual power dissipated in the discharge. NF3 plasmas diluted with Ar exhibited the lowest impedances and highest real power dissipation at higher pressures while N2O diluted plasmas had the highest impedances and lowest power dissipation levels. These results indicate that the diluents which result in the highest power dissipation in the discharge, at high pressures, result in the highest etch rates. We propose that the dominant role of the diluent in NF3 plasmas is to control the electronegativity of the discharge, and thus to control real power dissipation. This function is in contrast to the role of diluents in plasmas based on other fluorinated gases, where the diluents are seen as primarily affecting the concentrations of reactive species which deposit or remove materials from the surface of the thin film being processed.

Characterization of Highly Selective SiO2/Si3N4 Etching of High-Aspect-Ratio Holes

The pattern size dependence of SiO2 and Si3N4 etch rates of contact holes (RIE-lag) in C4F8+CO plasma was studied. It was found that these etch rates can be characterized by the aspect ratio, regardless of the pattern size. SiO2 etch rate decreased with increasing aspect ratio and became 0 at an aspect ratio of 6. Si3N4 etch rate also decreased; however, etching still occurred at an aspect ratio of 30. From ion current measurements through capillary plates (CPs), it was deduced that etch rates decreased because of decreasing ion current. XPS analyses revealed that fluorocarbon film deposited on the Si3N4 surface at the bottom of a hole was more F-rich than that deposited on a flat Si3N4 surface. This explained why Si3N4 is etched even in high-aspect-ratio holes. A small amount of O2 addition to the C4F8+CO plasma resolved the RIE-lag. It was found that the ion current density at high aspect ratio increased with O2 addition, which would enhance SiO2 etching and contribute to suppressing RIE-lag.

SiO2 Etching Employing Inductively Coupled Plasma with Hot Inner Wall

The selective etching of SiO2 on Si employing C4F8/H2 inductively coupled plasma (ICP) was studied based on measurements of radical and ion densities, flow rate and wall temperature. Since polymer films were not deposited when the reacter wall was heated to temperatures above 200° C, CF1 radical density at 200° C was one order higher than that at the wall temperature of 30° C. Thus both Si and SiO2 etch rates decreased rapidly with increasing H2 concentration in C4F8, and Si etching stopped at 15% H2. The etch stop was attributed to insufficient removal of polymer with a reduced amount of ions and was suppressed considerably by increasing the RF power to generate a large amount of ions. The use of poly-Si masks reduced the microloading effect in comparison to resist masks and a contact hole feature with 0.2 µ m size and aspect ratio of 6 was successfully obtained.

Symmetric rate model for fluorocarbon plasma etching of SiO2

A symmetric rate model for plasma etching and plasma deposition in fluorocarbon plasmas is proposed. When there is no deposition, the symmetric rate model gives a plasma etch rate. When there is no etching, the model gives a plasma deposition rate. Electron cyclotron resonance and reactive ion etcher etch rates of SiO2 in CF4 plasma are found to be consistent with the model.

Enhanced dry etching of silicon with deuterium plasma

The etching of Si and SiO2 for H2 and D2 plasma exposure has been investigated. The Si is etched rapidly by a factor of 34 for D2 plasma exposure compared with H2 plasma exposure. On the other hand, the etching rate of SiO2 does not change. This suggests a possibility of dry etching of Si with D2 gas.

Neutral-Beam-Assisted Etching System for Low-Damage SiO2 Etching of 8-Inch Wafers

A novel neutral-beam-assisted etching apparatus has been developed for large-diameter etching. Neutral radicals from halide molecules and energetic neutral beams are irradiated on the specimen surface. The etching reaction of these neutral radicals is enhanced by neutral-beam bombardment. The neutral-beam source and the neutral-radical source are produced from a magneto-microwave plasma source. These plasmas are arranged in tandem in front of the specimen. This arrangement enables highly uniform supply of neutral radicals over a large area. This etching system was applied to SiO2 etching using Ar and CHF3 mixed gas. The SiO2 etch rate was 76 nm/min, and the etch rate uniformity was within ±7.4% for an 8-inch-diameter specimen and ±3.4% for a 6-inch-diameter specimen. In addition, highly anisotropic etching shapes of submicron patterns were obtained.

Fabrication of Si field emitters by dry etching and mask erosion

A Cl2 plasma generated by an electron cyclotron resonance source was used to etch field emitter arrays in Si. Compared to wet etching, emitter arrays with sharper emitter tips and higher packing density can be formed by dry etching. Mask erosion was used to control the etch profile in Si. SiO2 masks with different profiles were patterned by wet and dry etching, and the effects of the initial SiO2 masks slope and etch conditions on the resultant Si profile were investigated. The lateral etch rate of SiO2 decreased from 363 to 150 nm/min as the SiO2 slope increased from 17° to 45°. As a result, the slope of the Si etch profile increased from 52° to 78° after dry etching to a depth of 1.8 μm. The ion flux and energy, controlled through coupled microwave and rf power, were used to obtain the desired etch rate and basewidth of the emitters. By increasing the pressure during etching, the lateral etch rate of SiO2 was reduced and more vertical Si profiles were developed. As pressure was increased from 0.5 to 10 mTorr, the lateral etch rate of SiO2 reduced from 414 to 144 nm/min while the vertical Si etch rate did not change significantly. This caused the slope of the Si etch profile to increase from 42° to 69°. Using the above technique, arrays of sharp emitter tips in Si with 2.2 μm basewidth and 11 μm height were fabricated and packing densities up to 1×107 tip/cm2 were achieved.

Effects of Vacuum-Ultraviolet-Light-Induced Surface Reaction on Selective and Anisotropic Etching of Silicon Dioxide Using Anhydrous Hydrogen Fluoride Gas

Vacuum-ultraviolet (VUV) light induced etching of thermally grown silicon dioxide films was investigated near room temperature. We used synchrotron radiation as a VUV light source and anhydrous-hydrogen-fluoride as an etching gas. The silicon dioxide is etched only in the VUV light irradiated area, and etched selectively with respect to (100) oriented singlecrystalline silicon, which is not etched even under the irradiation. Moreover, we have found anisotropic etching with the patterned polycrystalline silicon etching mask. The ratio of the etch rate of SiO2 in the vertical direction compared to the horizontal direction of the substrate surface is about 30. From these results, the etching process is due to the photo-induced surface reaction. The excitation of the adsorbed AHF molecules or SiO2 surface would be a dominant process.

Temperature dependence of the etch rate and selectivity of silicon nitride over silicon dioxide in remote plasma NF3/Cl2

The etch rates and selectivity of Si3N4 over SiO2 have been investigated by microwave discharging a mixture of NF3 and Cl2 and flowing the resultant fluorine and chlorine atoms and interhalogenous molecules simultaneously over a silicon wafer covered with low pressure chemical vapor deposition (LPCVD) Si3N4, and a wafer covered with thermally grown SiO2. The temperature dependence of the etch rates of Si3N4 and SiO2 in the NF3/Cl2 mixture was examined in the range from 25 to 500 °C, and the selectivity of the nitride etch over the oxide etch as well as nitride etch rate was found to increase with increasing temperature. It was also found that both etch rates and selectivities increase with NF3 flow rates within the range used in this study.

Electron cyclotron resonance plasma reactor for SiO2 etching: Process diagnostics, end-point detection, and surface characterization

An electron cyclotron resonance plasma reactor for low-pressure etching of SiO2 layers on Si is described. Under typical operating conditions of 1.1 mTorr neutral pressure, 5 sccm CF4/46 sccm He, and 400 W net microwave power, an average etch rate of 35–40 nm/min is obtained. Ion densities were measured by using a quadrupole mass analyzer (QMA) immersed in the downstream plasma; an optical multichannel analyzer was used for actinometric measurements of atomic F and O concentrations. The results are correlated with process variables and SiO2 etch rates. Real-time end-point detection was effected by actinometry and by monitoring the concentrations of etch products using a differentially pumped QMA. H2 addition inhibits SiO2 etching but improves SiO2/Si etch selectivity. For selective etching, in situ, off-line surface analysis by Auger electron spectroscopy demonstrated an increase in the surface C concentration during SiO2 etching and deposition of a fluorocarbon layer at the end point which strongly inhibits Si etching.

Development of neutral-beam-assisted etcher

Advanced neutral-beam-assisted etching machines have been developed for very low-damage SiO2 etching. The etching reactions are enhanced by a neutral beam and neutral radicals. This enhancement effect was first demonstrated by a prototype etcher equipped with independent sources for the neutral beam and neutral radicals. Next, a simple co-axial type etcher was developed. Only one co-axial discharge tube generates two cylindrical plasmas: the inner one is a neutral beam source; the outer one is a neutral radical source. The typical SiO2 etch rate was 60 nm/min. To further increase the etch rate, the beam and etching characteristics were studied in detail. We found that the neutral radical density had to be increased. To achieve a high etch rate, a tandem type etcher was designed and developed. It generates two plasmas side by side in only one discharge tube. This etcher can supply high-density uniform neutral radicals from one of the tandem plasmas very close to the specimen. This new etcher is expected to be a significant advance toward the development of a practical, low-damage, high rate etcher.

Dose–time relation in BF3 plasma immersion ion implantation

Etching and deposition rates of silicon and SiO2 during BF3 plasma immersion ion implantation are measured. The relation between total dose and plasma immersion ion implantation processing time is developed through computer modeling. The results are in very good agreement with the experimental data. Comparison with a previously published model is also given.

Effects of SC-1 Dilution and Temperature Variations on Etch Rate and Surface Haze

ABSTRACTThe slight etch and accompanying roughening of the silicon by the APM solution are of great concern as device geometrys and gate oxide thicknesses decrease. This report covers the variations in the SiO2 etch rate and surface roughening of an APM solution as a function of NH4OH and H2O2 concentration and temperature. In general, the etch rate and roughening increased with increasing temperature and NH4OH concentration but was unaffected by H2O2 concentration. Other portions of the larger APM study covering the addition and removal of metals and the removal of particles by APM are published elsewhere. Together, these studies provide a complete set of process response surfaces for the SC-1 chemistry. These surfaces can be used to select the most promising regime of parameter space for any particular process.

Pulse-time modulated electron cyclotron resonance plasma etching for highly selective, highly anisotropic, and less-charging polycrystalline silicon patterning

Highly selective, highly anisotropic, notch-free and charge build-up damage-free polycrystalline silicon etching is achieved using an electron cyclotron resonance plasma modulated at a pulse time in the range of 10–20 μs. In this plasma, the selectivity ratio of the polycrystalline silicon etching rate to the SiO2 etching rate is increased significantly by the same etching rate as that attained using a continuous discharge. Additionally, vertical and notch-free phosphorus-doped polycrystalline silicon etching profiles and suppressing charge build-up damage can be achieved. These results are attained by controlling the ion energy distribution through the duty ratio, maintaining a high ion current density, generating a collimated ion flux, and eliminating surface charge with the pulsed discharge.

Influence of Reaction Products and Oxygen on Highly Selective Electron Cyclotron Resonance Ion Stream Etching of Si

The behavior of reaction products during Si etching by electron cyclotron resonance (ECR) ion stream etching with Cl2 is investigated using the emission of SiCl as a monitor of the reaction products. A strong correlation is found between the emission intensity of SiCl and the SiO2 etch rate, and it is confirmed that an increase in the reaction products promotes SiO2 etching. As the SiO2 etching mechanism, we propose the occurrrence of a reaction with a volatile compound, (SiCl3)2O, on the SiO2 surface. When O2 is added to Cl2, the concentration of reaction products in the plasma decreases. This is shown to occur because the redesorption of the reaction products from the chamber wall is hindered by O2. The suppression of SiO2 etching upon O2 addition is related not only to the oxidation of the SiO2 surface but also to the decrease in reaction product concentration in the plasma.

Etching Characteristics by M= 0 Helicon Wave Plasma

The each characteristics of SiO2 and Al–Si–0.5%Cu were studied using the M=0 helicon wave plasma etching apparatus. A high concentration of F radicals was observed during SiO2 etching using fluorocarbon gases. The etch rate of SiO2 was strongly dependent on the concentration of F radicals in the plasma. A method of increasing the selectivity of SiO2 to poly-Si was discussed. The Al–Si–0.5%Cu film deposited on the wafer of 200 mm diameter was anisotropically etched with high selectivity to photoresist using Cl2 and BCl3 gases. The etch rate uniformity across a wafer was also discussed.

Fluorocarbon high density plasmas. VIII. Study of the ion flux composition at the substrate in electron cyclotron resonance etching processes using fluorocarbon gases

An important component in the basic chemical and physical mechanisms which govern etching and deposition processes in high density plasmas is the chemical identity and relative fluxes of ionic species at the substrate surface. Here we report line of sight measurements of relative ion fluxes made with a quadrupole mass spectrometer through an orifice in the substrate holder of an electron cyclotron resonance reactor configured for fluorine-based etching. The relative ion fluxes versus microwave power and pressure for CF4 and CHF3plasmas have been studied. These data have been compared with Si and SiO2 etch rates to determine the effect of ion flux composition changes on etching processes. It was observed that the F+ ion flux increases relative to the fluorocarbon ion fluxes as the microwave power is increased or the chamber pressure is decreased. This relative increase in the F+ ion flux may be caused by the increased dissociation of the source gas. Changes in the ion flux composition seem to have little effect on the Si and SiO2 etch rates. It was also observed that the F+ ion flux increases as the percentage of hydrogen in a CHF3/H2plasma is increased while the neutral fluorine optical emission intensity decreases for the same conditions. The data suggest that for these conditions dissociative ionization reactions involving fluorine containing molecules make a significant contribution to the production of F+, in addition to the ionization of neutral fluorine.

Etching of Thermally Grown SiO2 by NH4OH in Mixture of NH4OH and H2O2 Cleaning Solution

We have investigated the etching behavior of thermally grown SiO2 by ammonium hydroxide ( NH4OH) in NH4OH–H2O2–H2O cleaning solution (SC-1). The SiO2 etching rate increases with increasing impurity (boron or phosphorus) concentration in the SiO2 as well as concentration of NH4OH and temperature of SC-1 solution. Moreover, postoxidation SC-1 treatment with a low concentration of NH4OH (less than 3.15 wt% of NH4OH) does not degrade or improve oxide reliability. These indicate that if SC-1 treatment, which is performed after post-thin-oxide ( ∼20 nm) or high-impurity-doped Si oxide formation, is carried out in ULSI device fabrication processes, SC-1 with low temperature and low NH4OH concentration must be applied after those processes to minimize SiO2 thickness reduction and preserve oxide reliability.

Pulse-time-modulated electron cyclotron resonance plasma etching for highly selective, highly anisotropic, and notch-free polycrystalline silicon patterning

Highly selective, highly anisotropic, and notch-free etching for polycrystalline silicon is achieved in a few tens of μs pulse-time-modulated electron cyclotron resonance plasma. In the pulsed plasma, the selectivity ratio of polycrystalline silicon etching rate to the SiO2 etching rate is drastically improved with high etching rate, as compared with the ratio with a continuous discharge. Furthermore, vertical and notch-free phosphorus-doped polycrystalline silicon etching profiles can be achieved even with 100% over etching. These etching characteristics are achieved by controlling ion energy distributions through the duty ratio, maintaining a high ion current density, generating a collimated ion flux and eliminating surface charging with a pulsed discharge of a few tens of μs.