Ion Cristian Abraham

Charged species dynamics in an inductively coupled Ar/SF6 plasma discharge

The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a combination of computational modeling and experimental diagnostics has been utilized to understand charged species dynamics in an inductively coupled Ar/SF6 plasma discharge. The model is based on the two-dimensional Hybrid Plasma Equipment Model with a detailed plasma chemical mechanism for Ar/SF6. In the experiments, absolute electron density and total negative ion density have been measured using microwave interferometry and laser photodetachment, respectively. In addition, we have also utilized prior measurements of mass and energy resolved ion fluxes by Goyette et al. [J. Vac. Sci. Technol. A 19, 1294 (2001)]. Computational results show that all SFx+(x=0–5) ions are present in the plasma discharge. Important negative ions include SF6−, SF5−, and F−. Electron and positive ion densities increase with coil power due to enhanced ionization. However, negative ion densities decrease with coil power as the main...

Characterization of electron and negative ion densities in fluorocarbon containing inductively driven plasmas

Electron and negative ion densities were measured in inductively coupled discharges containing C4F8. In addition, the identity of the negative ions in C2F6, CHF3, and C4F8 containing discharges was investigated with a photodetachment experiment utilizing a microwave resonant cavity structure. To investigate the influence of surface material, the rf-biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line-integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of the plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf-biased electrode were also measured for both surfaces as functions of induction coil power, pressure, and rf bias. For the range of induction powers, pressures, and bias power investigated, the electron density peaked at 6×1012 cm−2 (line integrated), or approximately 6×1011 cm−3. The negative ion density peaked at approximately 2.2×1...

Characterization of SF6 / Argon Plasmas for Microelectronics Applications

This report documents measurements in inductively driven plasmas containing SF{sub 6}/Argon gas mixtures. The data in this report is presented in a series of appendices with a minimum of interpretation. During the course of this work we investigated: the electron and negative ion density using microwave interferometry and laser photodetachment; the optical emission; plasma species using mass spectrometry, and the ion energy distributions at the surface of the rf biased electrode in several configurations. The goal of this work was to assemble a consistent set of data to understand the important chemical mechanisms in SF{sub 6} based processing of materials and to validate models of the gas and surface processes.

Surface dependent electron and negative ion density in SF6/argon gas mixtures

Electron and negative ion densities were measured in an inductively driven plasma containing mixtures of SF6 and Argon. The electron and negative ion density were measured as functions of the induction coil power, pressure, bias power, and SF6/argon ratio. To investigate the influence of surface material, the rf biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf biased electrode were also measured for both surfaces as functions of induction coil power, pressure, rf bias, and SF6/argon ratio. For the range of induction powers, pressures, and bias powers investigated, the electron density had a maximum of 5×1012 cm−2 (line-integrated) or approximately 5×1011 cm−3. Over this same range the negative ion density had a maximum of 2×1011 c...

Ions in holes: An experimental study of ion distributions inside surface features on radio-frequency-biased wafers in plasma etching discharges

We present an experimental study of ion fluxes, energy distributions, and angular distributions inside surface features on radio frequency-biased wafers in high-density, inductively driven discharges in argon. Specifically, we present data on ion distributions at the bottom of 100-μm-square, 400-μm-deep “holes” in the wafer. Transmission of ions to the bottom of the holes increases with increasing ion energy and decreases as the sheath size becomes comparable to the hole size. Ion energy distributions at the bottom of the holes are narrower than distributions on the flat wafer surface. The flux of ions remains normal to the wafer surface over most of the hole area but the flux of ions within 6 μm of the wall is angled towards the wall. The observed trends are consistent with effects expected due to bowing of the plasma sheath around the surface features on the wafer. Scattering of ions off sidewalls contributes at most, only a small part of the ion flux reaching the bottom of the hole.

Unified characterization of surfaces and gases in MEMS devices

Chemical and physical materials-aging processes can significantly degrade the long-term performance reliability of dormant microsystems. This degradation results from materials interactions with the evolving microenvironment by changing both bulk and interfacial properties (e.g., mechanical and fatigue strength, interfacial friction and stiction, electrical resistance). Eventually, device function is clearly threatened and as such, these aging processes are considered to have the potential for high (negative) consequences. Sandia National Laboratories is developing analytical characterization methodologies for identifying the chemical constituents of packaged microsystem environments, and test structures for proving these analytical techniques. To accomplish this, we are developing a MEMS test device containing structures expected to exhibit dormancy/analytical challenges, extending the range of detection for a series of analytical techniques, merging data from these separate techniques for greater information return, and developing methods for characterizing the internal atmosphere/gases. Surface analyses and data extraction have been demonstrated on surfaces of various geometries with different SAMS coatings, and gas analyses on devices with internal free volumes of 3 microliters have also been demonstrated.