Scott Edward Beck

THE ROLE OF DILUENTS IN ELECTRONEGATIVE FLUORINATED GAS DISCHARGES

To study the role of diluents in NF3plasma processing we have correlated SiO2 and plasma chemical vapor depositionsilicon nitride (SiN) etch rate measurements with rf electrical impedanceanalysis. A series of rare gas (He, Ar) and molecular (N2, O2, N2O) mixing gases were added to NF3plasmas at different pressures to understand the effect of diluents on the chemical and physical properties of NF3discharges. The etch rate experiments show that for NF3plasmas 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. NF3plasmas 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 NF3plasmas 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.

Degradation of rapid thermal oxides due to the presence of nitrogen in the oxidation ambient

Ultrathin rapid thermal oxides have been formed in oxygen with varying levels of nitrogen incorporated into the oxidation ambient. Metal‐oxide‐semiconductor capacitors were subsequently fabricated and tested. It was observed that the interface trap density and the frequency of low field breakdowns increased with increasing nitrogen concentration in the oxidation ambient. No improvement in the interface state generation rate due to nitrogen incorporation in the oxidation ambient was observed in this study.

A VAPOR PHASE CLEAN TO REMOVE SODIUM USING 1,1,1,5,5,5-HEXAFLUORO-2,4-PENTANEDIONE

Sodium is removed from silicon wafer surfaces by a vapor phase method utilizing the chelation compound 1,1,1,5,5,5-hexafluoro2,4-pentanedione (H+ hfac). At a total pressure of 7.6 Torr, sodium is removed from the wafer surface at temperatures above 190°C. Several mechanisms may play a role in the reaction of H+ hfac with surface sodium species.

Chemical vapor cleaning of Si and SiO/sub 2/ surfaces

A novel vapor phase clean is shown to be a viable method for removing copper and iron from wafer surfaces. Utilizing thin films and sub-monolayer samples of copper and iron on Si or SiO/sub 2/ substrates the reaction of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (CF/sub 3/COCH/sub 2/COCF/sub 3/ or H/sup +/hfac) with these metals has been explored as a potential vapor phase clean. It is shown that the chemical state of the surface metal is an important factor in the removal of these metals. The reaction of CuO and Cu/sub 2/O with H/sup +/hfac results in volatile reaction by-products of Cu/sup 11/(hfac)/sub 2/ and H/sub 2/O. Additionally, the reaction with Cu/sub 2/O yields Cu/sup (0/). Reaction of H/sup +/hfac with iron contamination is more complex and leads to at least two different types of reactions. These reactions include a nucleophilic substitution reaction and a reaction leading to a mixed ligand system. The final surface metal concentration is dependent upon the processing conditions and can result in concentrations similar to those achieved with standard wet cleans.

Avoiding the pitfalls in the use of surface analysis in the IC industry

A variety of surface analytical tools are currently available. With each of these tools come hidden pitfalls that one map encounter in the process of doing surface analysis. Examples of the use of X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), total reflection X-ray fluorescence (TXRF), and atomic force microscopy (AFM) in the development of a novel vapor phase cleaning methodology are used to illustrate many of these pitfalls. Suggestions are made to assist users of these techniques in avoiding these pitfalls.

Effects of nitrogen incorporation during growth on thin oxide wearout and breakdown

Abstract Thin oxides, 6.4–7.6 nm thick, have been formed in oxygen with varying levels of nitrogen incorporated into the oxidation ambient. In addition to films with no nitrogen, the nitrogen concentration was varied from 0.00001 to 10% in decade increments. The wearout and breakdown characteristics of these oxides were measured. Wearout was quantified by measuring the changes in the low-level leakage currents, the changes in the mid-gap interface trap densities, the shifts in the flat-band voltages, and the number of traps generated inside of the oxides, all by high voltage stresses. Breakdown was characterized by measuring the time-zero-breakdown voltage distributions. It was found that the wearout was independent of the nitrogen concentration but the breakdown voltages decreased as the nitrogen concentration increased. The average breakdown voltage dropped by |1 V| for oxides with 0.1% N 2 and by |3 V| for oxides with 10% N 2 , with the number of low-voltage breakdowns also increasing as the nitrogen concentration increased. It was felt that the nitrogen was incorporated into the oxide both relatively uniformly throughout the oxide and in local non-uniform regions. The uniform distribution inside of the oxide did not affect the wearout properties of the oxide, which were determined by high-field, bond breaking of silicon-oxygen bonds. The regions with non-uniform concentrations of nitrogen introduced local asperities that affected the breakdown voltage distributions by generating local high field regions and locally high trap concentrations.

Effects of microcontaminants in oxygen during gate oxide growth: interfacial effects and device reliability

The effects of different levels of water, nitrogen, and methane contamination in an oxidation ambient during the production of ultra-thin rapid thermal oxides have been investigated. Careful characterization of the oxidation and argon anneal steps have been performed. High levels of water and hydrogen in these ambients were shown to be generated during the process. Nuclear reaction analysis indicates that the final water level in the oxide depends on the water level in both the oxidation ambient and post-oxidation ambient. Increasing nitrogen concentrations in the oxidation ambient resulted in increased interface trap densities and the frequency of low field breakdown. Initial studies of methane in the oxidation ambient show that it also plays a similar role in oxide degradation.

The Effects of Chemical Vapor Cleaning Chemistries on Silicon Surfaces

This study explores the effects of two chemical vapor cleaning chemistries on silicon surfaces. The silicon surfaces are not significantly roughened by exposure to either process. Trace amounts of fluorine are found on the surfaces exposed to 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (HFAC). A thin silicon nitride film forms on the silicon surface as a result of exposure to the HMDS process and is attributed to the H 2 /N 2 plasma treatment used in the first step of the process.