D. P. Griffis

H2O enhanced focused ion beam micromachining

The use of H2O vapor as a chemical adjunct for focused ion beam micromachining has been investigated. The presence of H2O vapor during micromachining with a 25 keV Ga+ beam increases the removal rate of carbon‐containing materials such as polyimide, PMMA, and other resists by a factor of 20 (relative to physical sputtering), and that of diamond by a factor of 10. In addition, H2O causes a decrease in the removal rate of some other materials (e.g., Si and Al) by as much as a factor of 10, effectively increasing the selectivity of polymers over these other materials by as much as a factor of 200. The dependence of the removal rate on H2O pressure at the sample, pixel dwell time, pixel size, pattern frame time (corresponding to pattern size), and current density has been investigated utilizing PMMA. PMMA removal rates were calculated by measuring the depth of rectangular pits micromachined into PMMA films under the various experimental conditions. In addition to investigating the effect of H2O on material re...

Chemically and geometrically enhanced focused ion beam micromachining

Improvements in focused ion beam (FIB) material removal rates utilizing geometric and chemical enhancement were investigated. Geometrical optimization of FIB micromachining of Permalloy and diamond was investigated to determine the magnitude of material removal rate gains that could be attained by increasing the angle of the ion beam with respect to the sample surface normal. The combination of geometrical optimization with chemical enhancement (C2Cl4 for Permalloy and H2O and XeF2 for diamond) was then investigated to determine whether additional gains in material removal rate could be attained. FIB sharpening of a diamond nanoindenter tip is also presented as a practical example of diamond micromachining with H2O as the removal rate enhancing species.Improvements in focused ion beam (FIB) material removal rates utilizing geometric and chemical enhancement were investigated. Geometrical optimization of FIB micromachining of Permalloy and diamond was investigated to determine the magnitude of material removal rate gains that could be attained by increasing the angle of the ion beam with respect to the sample surface normal. The combination of geometrical optimization with chemical enhancement (C2Cl4 for Permalloy and H2O and XeF2 for diamond) was then investigated to determine whether additional gains in material removal rate could be attained. FIB sharpening of a diamond nanoindenter tip is also presented as a practical example of diamond micromachining with H2O as the removal rate enhancing species.

Chemical and spatial differentiation of syringyl and guaiacyl lignins in poplar wood via time-of-flight secondary ion mass spectrometry.

As a major component in plant cell walls, lignin is an important factor in numerous industrial processes, especially in wood saccharification and fermentation to biofuels. The ability to chemically differentiate and spatially locate lignins in wood cell structures provides an important contribution to the effort to improve these processes. The spatial distribution of the syringyl (S) and guaiacyl (G) lignins, both over larger regions and within a single cell wall, on poplar ( Populus trichocarpa ) wood cross-sections was determined via time-of-flight secondary ion mass spectrometry (ToF-SIMS). This is the first time that direct chemically specific mass spectrometric mapping has been employed to elucidate the spatial distribution of S and G lignins. In agreement with results obtained by UV microscopy, ToF-SIMS images clearly show that the guaiacyl lignin is predominantly located in the vessel cell walls of poplar wood while syringyl lignin is mainly located in the fiber cell walls. The G/S ratio in vessel cell walls was determined to be approximately twice that found in fiber cell walls. A combination of Bi ToF-SIMS spectral image acquisition and C(60) sputtering provided the ability to attain the combination of spatial resolution and signal-to-noise necessary to determine the distribution of S and G lignins in a single cell wall. By this technique, it was possible to demonstrate that more guaiacyl lignin is located in the middle lamella layer and more syringyl lignin is located in the inner cell wall area.

Focused ion beam machining of Si, GaAs, and InP

The focused ion beam (FIB) has been demonstrated as a precision fabrication tool for a wide variety of applications, primarily for semiconductor related processing. In order to facilitate the practical utilization of this tool, the Ga+ FIB micromachining characteristics of Si (100), Si(111), GaAs (100), and InP (100) were investigated. Rectangular wells having dimensions of 4×10×1 μm were sputtered into the above materials at 15 and 25 keV and dwell times ranging from 25 μs to 100 ms per point for a fixed total machining time. Planview and cross section scanning electron microscope examination was used to quantify sputter yield and characterize feature shapes. Sputter yield and material redeposition variations dependent on beam dwell times were observed as evidenced by changes in side wall slope, crater bottom flatness, and material redeposition.

Electron beam induced metalization of palladium acetate

Films of palladium acetate Pd(OOCH3)2 0.1 and 0.3 μm thick have been stoichiometrically altered through exposure to electron beams of 1–30 keV. The lowest required doses for alteration, 1000 and 2500 μC/cm2, were obtained using beam energies of 4 and 5 keV, respectively. These results have been related to Monte Carlo simulations of energy absorbed within a thin surface film. The minimum line widths of features produced was less than 100 nanometers with estimated Pd/C ratio of 1 and measured resistivities as low as 100 μΩ cm.

Characterization and removal of ion yield transients in the near surface region of secondary ion mass spectrometry depth profiles

A method for removing ion yield transients from the beginning of secondary ion mass spectrometry (SIMS) depth profiles is evaluated. Ion yield transients, which result from the concentration buildup of yield enhancing primary ion species, may be characterized by depth profiling standards which are bulk doped with the element of interest. The transients of B+ and B− in Si were characterized using an O+2 and Cs+ primary ion beam, respectively. The resulting transient correction functions were used to correct depth profiles of 10 and 4 keV B implants in Si.

Channeling effects during focused-ion-beam micromachining of copper

The rapid introduction of copper metallization for semiconductor devices has prompted increased research into focused-ion-beam micromachining of copper. Studies with the aim of increasing the material removal rate of Cu by focused-ion-beam micromachining have been complicated by variable micromachining behavior apparently resulting from differing Cu film morphologies produced by the various Cu deposition procedures. This work examined the micromachining behavior of thin copper films produced by physical-vapor deposition (PVD) and electroplating, as well as single-crystal copper samples. PVD copper films were found to be preferentially textured along 〈111〉, with a columnar grain structure. Channeling effects within this type of grain structure provide a geometric enhancement of the material removal rate of 30% when the sample normal is tilted 12° from the incident ion beam, regardless of sample rotation. Single-crystal (111) copper was found to exhibit similar material removal rate enhancement (averaged ov...

Characterization of focused ion beam micromachined features

The use of the liquid metal ion source focused ion beam (FIB) as a microfabrication tool depends, to a large extent, on the understanding of ion beam/substrate interactions. In addition to material removal and redeposition, the alteration of the underlying substrate by the ion beam can affect the performance and characteristics of semiconductor microelectronic and optoelectronic devices, and the physical properties of micromechanical components. Chemical modification to FIB machined substrates has been investigated by energy dispersive x‐ray spectroscopy (EDS) and Auger electron spectroscopy (AES). EDS has proven useful for determining the residual implanted ion dose in micromachined features with good correlation to theoretical values. AES has been used to observe the lateral and depth distribution of the implanted ion species in the machined features and surrounding areas.

Secondary ion mass spectrometry/digital imaging for the three‐dimensional chemical characterization of solid state devices

The use of a microcomputer based digital imaging system for automated acquisition of secondary ion image depth profiles is demonstrated. By combining the ion microscope’s capabilities of elemental imaging and depth profiling, image depth profiling provides information on the three‐dimensional distribution of elements within microvolumes of the near surface region of solids. The technique is used for the three‐dimensional multielement characterization of a solid state device (a npn bipolar transistor). Several methods for processing and displaying the multidimensional data are presented.

Secondary ion mass spectrometry backside analysis of barrier layers for copper diffusion

Secondary ion mass spectrometry (SIMS) backside analyses have been performed on a Cu/TaN/Ta/SiO2/Si structure to determine barrier effectiveness for Cu diffusion. Sample backside access to the barrier layers was obtained by removal of the Si substrate using a polishing method that maintains parallelism between the sample surface and the polished back side by monitoring changes in facets at the four corners of the specimen. Determination of the Si thickness remaining during the polishing process was improved through the use of optical interference measurements using a narrow band pass optical filter. Samples having slopes with respect to the original surface less than 6 nm over 60 μm have been obtained. A difference in polishing rate between SiO2 and Si was exploited to obtain this parallelism. For SIMS analyses, the presence of a SiO2 layer required electron gun charge neutralization for the O2+ 0.5 keV impact energy analysis. SIMS analyses show the ability to distinguish all layers and to monitor copper ...