Eric S. Windsor

Application of Inkjet Printing Technology to Produce Test Materials of 1,3,5-Trinitro-1,3,5 Triazcyclohexane for Trace Explosive Analysis

The feasibility of the use of piezoelectric drop-on-demand inkjet printing to prepare test materials for trace explosive analysis is demonstrated. RDX (1,3,5-trinitro-1,3,5 triazcyclohexane) was formulated into inkjet printable solutions and jetted onto substrates suitable for calibration of the ion mobility spectrometry (IMS) instruments currently deployed worldwide for contraband screening. Gravimetric analysis, gas chromatography/mass spectrometry (GC/MS), and ultraviolet-visible (UV-vis) absorption spectroscopy were used to verify inkjet printer solution concentrations and the quantity of explosive dispensed onto test materials. Reproducibility of the inkjet printing process for mass deposition of the explosive RDX (1,3,5-trinitro-1,3,5 triazcyclohexane) was determined to be better than 2% for a single day of printing and better than 3% day-to-day.

Bevel Depth Profiling SIMS for Analysis of Layer Structures

We are evaluating the use of bevel depth profiling Secondary Ion Mass Spectrometry (SIMS) for the characterization of layered semiconductor materials. In this procedure, a sub‐degree angle bevel is cut into the analytical sample with an oxygen or cesium primary ion beam in a commercial SIMS instrument. The elemental distribution of the resulting bevel surface is then imaged with a focused ion beam in the same instrument. This approach offers maximum flexibility for depth profiling analysis. The primary beam energy, incident angle and species used to cut the bevel can be optimized to minimize ion beam mixing and surface topography independent of the conditions used for secondary ion analysis. In some cases, depth resolution can be greater than available from conventional depth profiling. Removal of residual surface damage/topography created during beveling has also been investigated by the cleaning of the bevel surfaces using gas‐cluster ion beam sputtering before imaging analysis.

Accuracy of the double variation technique of refractive index measurement

Errors in the double variation teclinique of refractive index measurement are analyzed using a new approach. The ability to measure matching wavelength is characterized, along with the effect on the calculated refractive index. Refractive index accuracy and precision are very dependent on the specifics of each calibration set, particularly the difference in dispersion between the liquid and solid. Our best precision (±1 or 2×10−4) is attained only when the difference in dispersion between liquid and solid is small, and is dependent on an individual operator’s ability to perceive changes in relief. This precision is impossible to achieve for the other glass/liquid combinations, where we are limited by a precision of approximately 1 nm in the selection of matching wavelength. A bias in the measurement of matching wavelength exists that affects the accuracy of the calculated refractive indices. The magnitude of the bias appears to be controlled by the bandpass of the graded interference filter. The errors in refractive index using a graded interference filter with a bandpass of 30 nm FWHM (full width at half maximum intensity) are an order of magnitude larger than the errors using a filter with a bandpass of 15 nm FWHM.

Particle Fabrication Using Inkjet Printing onto Hydrophobic Surfaces for Optimization and Calibration of Trace Contraband Detection Sensors.

A method has been developed to fabricate patterned arrays of micrometer-sized monodisperse solid particles of ammonium nitrate on hydrophobic silicon surfaces using inkjet printing. The method relies on dispensing one or more microdrops of a concentrated aqueous ammonium nitrate solution from a drop-on-demand (DOD) inkjet printer at specific locations on a silicon substrate rendered hydrophobic by a perfluorodecytrichlorosilane monolayer coating. The deposited liquid droplets form into the shape of a spherical shaped cap; during the evaporation process, a deposited liquid droplet maintains this geometry until it forms a solid micrometer sized particle. Arrays of solid particles are obtained by sequential translation of the printer stage. The use of DOD inkjet printing for fabrication of discrete particle arrays allows for precise control of particle characteristics (mass, diameter and height), as well as the particle number and spatial distribution on the substrate. The final mass of an individual particle is precisely determined by using gravimetric measurement of the average mass of solution ejected per microdrop. The primary application of this method is fabrication of test materials for the evaluation of spatially-resolved optical and mass spectrometry based sensors used for detecting particle residues of contraband materials, such as explosives or narcotics.

Copper Oxide Precipitates in NBS Standard Reference Material 482.

Copper oxide has been detected in the copper containing alloys of NBS Standard Reference Material (SRM) 482. This occurrence is significant because it represents heterogeneity within a standard reference material that was certified to be homogeneous on a micrometer scale. Oxide occurs as elliptically to spherically shaped precipitates whose size differs with alloy composition. The largest precipitates occur in the Au20-Cu80 alloy and range in size from submicrometer up to 2 μm in diameter. Precipitates are observed using light microscopy, electron microscopy, and secondary ion mass spectrometry (SIMS). SIMS has demonstrated that the precipitates are present within all the SRM 482 wires that contain copper. Only the pure gold wire is precipitate free. Initial results from the analysis of the Au20-Cu80 alloy indicate that the percentage of precipitates is less than 1 % by area. Electron probe microanalysis (EPMA) of large (2 μm) precipitates in this same alloy indicates that precipitates are detectable by EPMA and that their composition differs significantly from the certified alloy composition. The small size and low percentage of these oxide precipitates minimizes the impact that they have upon the intended use of this standard for electron probe microanalysis. Heterogeneity caused by these oxide precipitates may however preclude the use of this standard for automated EPMA analyses and other microanalysis techniques.

Gate dielectric thickness metrology using transmission electron microscopy

Silicon oxynitride blanket films approximately 2 nm in thickness were characterized in cross section using a 300 keV TEM/STEM. High resolution imaging was used to investigate the accuracy and precision of TEM film thickness measurements and their comparability to other techniques such as spectroscopic ellipsometry, secondary ion mass spectrometry, x-ray reflectivity, x-ray photoelectron spectroscopy, and medium energy ion scattering. Silicon oxynitride films were grown by SEMATECH and were characterized by several techniques in a SEMATECH-sponsored round robin. Cross sectional TEM samples were prepared by dimpling/ion milling and HRTEM micrographs were acquired at 297 keV using an imaging energy filter and a multiscan CCD camera. Thickness measurements were performed after calibrating the magnification using a phase contrast image of the silicon substrate. Approximately 10 measurements were performed for each film, including measurements on both sides of the cross section glue line and both sides of the d...

Use of Drop‐on‐Demand Inkjet Printing Technology to Produce Trace Metal Contamination Standards For the Semiconductor Industry

The feasibility of using piezoelectric drop‐on‐demand inkjet printing technology to produce trace metal contamination standards on silicon wafers has been demonstrated. Prototype standards of Fe and Cu contamination with surface concentrations between 1013 atoms/cm2 and 1015 atoms/cm2 have been produced using a piezoelectric inkjet printer. Preliminary secondary ion mass spectrometry (SIMS) measurements show that secondary ion intensities are linear with respect to concentration. The success of these preliminary experiments has prompted further work that is currently underway to prepare additional elements at concentrations ranging from 107 atoms/cm2 to 1015 atoms/cm2 for characterization by both SIMS and total reflection x‐ray fluorescence (TXRF).

Techniques for Improving SIMS Depth Resolution: C60+ Primary Ions and Backside Depth Profile Analysis

We are evaluating methods to improve depth resolution for SIMS analyses of semiconductors. Two methods that show promise are: (1) backside depth profile analysis and (2) the use of cluster primary ion beams. Backside analysis improves depth resolution by eliminating sample‐induced artifacts caused by sputtering through processing layers on the front side of the wafer. Mechanical backside sample preparation however, also introduces artifacts. The most troublesome artifact is inclined (non‐planar) polishing. Using a combination of both secondary ion image depth profiling and image analysis techniques, the effects of inclined polishing are minimized. A Buckminsterfullerene C60+ primary ion source has been interfaced to a magnetic sector SIMS instrument for the purpose of depth profile analysis. Application of this source to NIST SRM 2135a (nickel/ chromium multilayer depth profile standard) demonstrated that all layers of this standard were completely resolved. Initial applications of C60+ to silicon have pr...