This work combines focused ion beam sputtering and ultra-precision machining for microfabrication of metal alloys and polymers. Specifically, micro-end mills are made by Ga ion beam sputtering of a cylindrical tool shank. Using an ion energy of 20keV, the focused beam defines the tool cutting edges that have submicrometer radii of curvature. We demonstrate 25µm diameter micromilling tools having 2, 4 and 5 cutting edges. These tools fabricate fine channels, 26–28 microns wide, in 6061 aluminum, brass, and polymethyl methacrylate. Micro-tools are structurally robust and operate for more than 5 hours without fracture.

We report a direct, ion drilling technique that enables the reproducible fabrication and placement of nanopores in membranes of different thickness. Using a 30 keV focused Ga ion beam column combined with an in situ, back face, multi-channelplate particle detector, nanopores are sputtered in Si(3)N(4) and W/Si(3)N(4) to have diameters as small as 12 nm. Transmission electron microscopy shows that focused ion beam-drilled holes are near-conical with the diameter decreasing from entry to exit side. By monitoring the detector signal during ion exposure, the drilled hole width can be minimized such that the exit-side diameter is smaller than the full width at half-maximum of the nominally Gaussian-shaped incident beam. Judicious choice of the beam defining aperture combined with back face particle detection allows for reproducible exit-side hole diameters between 18 and 100 nm. The nanopore direct drilling technique does not require potentially damaging broad area exposure to tailor hole sizes. Moreover, this technique successfully achieves breakthrough despite the effects of varying membrane thickness, redeposition, polycrystalline grain structure, and slight ion beam current fluctuations.

A diamond mill (a tiny end mill) can cut aspheric lenses and mirrors with diameters smaller than 0.5 mm. The cutting tool has a two-dimensional shape and is spun about the axis of the surface to be cut. As the spinning tool is plunged into the substrate, it cuts a radially symmetric surface to sub-micron accuracies. Commercially available circular diamond tools can be modified to aspheric shapes using a focused ion beam. Fabrication examples are presented and the optical performance of an array of micro-lenses are described

This work demonstrates accurate focused ion beam sculpting of micron-scale curved shapes into initially planar solids. Sculpting is accomplished by varying the dose per pixel within individual boustrophedonic scans and accounting for the material-specific angle-dependent sputter yield and the ion beam spatial distribution. We refine this technique by demonstrating how a range of preferred dwell times leads to improved sculpting. An optimized dwell time range is delineated by two effects. Excessively large dwell times lead to enhanced deposition of ejected species, asymmetric milled features (when symmetric features are intended), and depths greater than intended values. These effects occur for dwell times such that the depth removed per pixel in a given scan is on the order of the width of the focused ion beam. On the other end of the dwell time range, inordinately low times lead to undesired ion milling outside targeted areas. Milling outside targeted regions, such as a circle or an ellipse, can occur because the ion beam is retraced to a rectilinear frame bounding the area. When dwell times are chosen to be on the order of the time to transit from the rectilinear frame to an outlined area edge, this leads to a significant dose over unintended areas, thereby producing a feature with irregular boundaries. Despite these two effects, a large range of acceptable dwell times (approximately three to four decades) can be established for milling most curved shapes. Hemispherical, parabolic, and sinusoidal features are demonstrated in Si(100).

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

This work demonstrates accurate sculpting of predetermined micron-scale, curved shapes in initially planar solids. Using a 20keV focused Ga+ ion beam, various features are sputtered including hemispheres, parabolas, and sinusoidal wave forms having dimensions from 1to30μm. Ion sculpting is accomplished by varying the dose at different points within individual scans. The doses calculated per point account for the material-specific, angle-dependent sputter yield, Y(θ), the beam current, and the ion beam spatial distribution. Several target materials are sculpted using this technique. These include semiconductors that are made amorphous or disordered by the high-energy beam and metals that remain crystalline with ion exposure. For several target materials, curved feature shapes closely match desired geometries with milled depths within 5% of intended values. Deposition of sputtered material and reflection of ions from sloped surfaces are important factors in feature depth and profile evolution. Materials that are subject to severe effects of redeposition (e.g., C and Si) require additional dose in certain regions in order to achieve desired geometries. The angle-dependent sputter yields of Si, C, Au, Al, W, SiC, and Al2O3 are reported. This includes normal incidence values, Y(0°), and Yamamura parameters f and Σ.

We have conducted an extensive study of the evolution of surface morphology of single crystal diamond surfaces during sputtering by 20keV Ga+ and Ga++H2O. We observe the formation of well-ordered ripples on the surface for angles of incidence between 40 and 70°. We have also measured sputter yields as a function of angle of incidence, and ripple wavelength and amplitude dependence on angle of incidence and ion fluence. Smooth surface morphology is observed for <40°, and a transition to a step-and-terrace structure is observed for >70°. The formation and evolution of well-ordered surface ripples is well characterized by the model of Bradley and Harper, where sputter-induced roughening is balanced by surface transport smoothing. Smoothing is consistent with an ion-induced viscous relaxation mechanism. Ripple amplitude saturates at high ion fluence, confirming the effect of nonlinear processes. Differences between Ga+ and Ga++H2O in ripple wavelength, amplitude, and time to saturation of amplitude are consistent with the increased sputter yield observed for Ga++H2O. For angle of incidence <40°, an ion bombardment-induced “atomic drift” mechanism for surface smoothing may be responsible for suppression of ripple formation. For Ga++H2O, we observe anomalous formation of very large amplitude and wavelength, poorly ordered surface ridges for angle of incidence near 40°. Finally, we observe that ripple initiation on smooth surfaces can take place by initial stochastic roughening followed by evolution of increasingly well-ordered ripples.

We investigate evolving surface morphology during focused ion beam bombardment of C and determine its effects on sputter yield over a large range of ion dose (1017–1019ions/cm2) and incidence angles (Θ=0–80°). Carbon bombarded by 20keV Ga+ either retains a smooth sputtered surface or develops one of two rough surface morphologies (sinusoidal ripples or steps/terraces) depending on the angle of ion incidence. For conditions that lead to smooth sputter-eroded surfaces there is no change in yield with ion dose after erosion of the solid commences. However, for all conditions that lead to surface roughening we observe coarsening of morphology with increased ion dose and a concomitant decrease in yield. A decrease in yield occurs as surface ripples increase wavelength and, for large Θ, as step/terrace morphologies evolve. The yield also decreases with dose as rippled surfaces transition to have steps and terraces at Θ=75°. Similar trends of decreasing yield are found for H2O-assisted focused ion beam milling. The effects of changing surface morphology on yield are explained by the varying incidence angles exposed to the high-energy beam.

The effects of H2O vapor introduced during focused ion beam (FIB) milling of diamond(100) are examined. In particular, we determine the yield, surface morphology, and microstructural damage that results from FIB sputtering and H2O-assisted FIB milling processes. Experiments involving 20 keV Ga+ bombardment to doses ∼1018 ions/cm2 are conducted at a number of fixed ion incidence angles, θ. For each θ selected, H2O-assisted ion milling shows an increased material removal rate compared with FIB sputtering (no gas assist). The amount by which the yield is enhanced depends on the angle of incidence with the largest difference occurring at θ=75°. Experiments that vary pixel dwell time from 3 μs to 20 ms while maintaining a fixed H2O gas pressure demonstrate the additional effect of beam scan rate on yield for gas-assisted processes. Different surface morphologies develop during ion bombardment depending on the angle of ion incidence and the presence/absence of H2O. In general, a single mode of ripples having a wave vector aligned with the projection of the ion beam vector forms for θ as high as 70°. H2O affects this morphology by lowering the ripple onset angle and decreasing the ripple wavelength. At high angles of incidence (θ>70°) a step/terrace morphology is observed. H2O-assisted milling at θ>70° results in a smoother stepped surface compared with FIB sputtering. Transmission electron microscopy shows that the amorphized thickness is reduced by 20% when using H2O-assisted FIB milling.

In this paper, a process for 200 μm high-aspect-ratio micro-optical (HARM) structures fabricated by deep X-ray lithography (DXRL) of polymethylislesuioane-based spin-on glass (SOG) thick films is presented. The SOG material used in the whole procedures is polymethylsilsesquioxane (GR650), which is a kind of sol-gel derived material and can be cured at a reasonable low temperature (75 °C). A technique to cast thick GR650 films was established in the overall process. After consolidation, the GR650 thick films were machined to reach 200 μm uniformly. Then, as negative resists, the GR650 thick films were patterned directly by DXRL. X-ray irradiated regions can be selectively retained with high structural resolution by development in an organic solvent, such as methanol. Parameter screening was done to find minimum and maximum doses needed for patterning/cross-linking, to vary development time, and to explore different film thickness. The whole process is a novel of technique to create HARM structures based on SOG materials without using molds. This technique can be extended to considerably larger structural heights. Surface and bulk compositions of the irradiated films were measured by XPS and Fourier transform infrared spectroscopy. Surface quality by roughness testing system (WYKO RST) was investigated to fabricate the microstructure with a high-accuracy surface.

Focused ion beam (FIB) sputtering is used to shape a variety of cutting tools with dimensions in the 15–100 μm range and cutting edge radii of curvature of 40 nm. The shape of each microtool is controlled to a pre-specified geometry that includes rake and relief features. We demonstrate tools having rectangular, triangular, and other complex-shaped face designs. A double-triangle tip on one tool is unique and demonstrates the versatility of the fabrication process. The FIB technique allows observation of the tool during fabrication, and, thus, reproducible features are generated with sub-micron precision. Tools are made from tungsten carbide, high-speed tool steel, and single crystal diamond. Application of FIB-shaped tools in ultra-precision microgrooving tests shows that the cross-section of a machined groove is an excellent replication of the microtool face. Microgrooves on 40–150 μm pitch are cut into 3 mm diameter polymer rods, for groove arc lengths greater than 12 cm. The surface finish of machined features is also reported; groove roughness (Ra) is typically less than 0.2 μm. Ultra-precision machining of cylindrical substrates is extended to make bound metal microcoils having feature sizes of 20–40 μm.

In this paper, the applications of sol–gel materials and process to semiconductor industry are introduced. Based on the sol–gel technique, the spin-on glass (SOG) fabrication techniques to realize thin and thick films are presented hereby. The thin films were patterned by liquid embossing techniques. For thick films, the film thickness can reach more than 200μm. The whole process is a novel fabrication technique for thick SOG films, which can be performed at very low temperature without using molds. It is excluded from the original thermal deposition techniques required very high temperature or vacuum facilities. Furthermore, the requirement of the sol–gel process for equipments is simple and much less expensive. The desired microstructure can be obtained directly by organic solvent development after deep X-ray lithography (DXRL). Finally, the film structures were investigated by X-ray photoelectron spectroscopy (XPS), which shows that the films have the same characteristics of the thermal silicon dioxide after DXRL.

This work combines focused ion beam sputtering and ultra-precision machining as a first step in fabricating metal alloy microcomponents. Micro-end mills having ∼25 μm diameters are made by sputtering cobalt M42 high-speed steel and C2 micrograin tungsten carbide tool blanks. A 20 keV focused gallium ion beam is used to define a number of cutting edges and tool end clearance. Cutting edge radii of curvature are less than or equal to 0.1 μm. Micro-end mill tools having 2, 4 and 5 cutting edges successfully machine millimeter long trenches in 6061-T4 aluminum, brass, 4340 steel and polymethyl methacrylate. Machined trench widths are approximately equal to the tool diameters, and surface roughnesses (Ra) at the bottom of micromachined features are ∼200 nm. Microtools are robust and operate for more than 6 h without fracture. Results from ultra-precision machining aluminum alloy at feed rates as high as 50 mm/minute and an axial depth of 1.0 μm are included.

This paper presents techniques for fabricating microscopic, curvilinear features in a variety of workpiece materials. Microgrooving and microthreading tools with cutting widths as small as 13 μm are made by focused ion beam sputtering and used for ultraprecision machining. Tool fabrication involves directing a 20 keV gallium beam at polished cylindrical punches made of cobalt M42 high-speed steel or C2 tungsten carbide to create a number of critically aligned facets. Sputtering produces rake facets of desired angle and cutting edges having radii of curvature equal to 0.4 μm. Clearance for minimizing frictional drag of a tool results from a particular ion beam/target geometry that accounts for the sputter yield dependence on incidence angle. It is believed that geometrically specific cutting tools of this dimension have not been made previously. Numerically controlled, ultraprecision machining with microgrooving tools results in a close match between tool width and feature size. Microtools are used to machine 13-μm wide, 4-μm deep, helical grooves in polymethyl methacrylate and 6061 Al cylindrical workpieces. Microgrooving tools are also used to fabricate sinusoidal cross-sectional features in planar metal samples.

A process fabricate 100 m high aspect ratio micro-optical structures by direct X-ray exposure and development of polymethylsilsesquioxane spin-on glass (GR 650) is presented. This process is an advance over the previous process of fabricating micro-optical components by molding GR 650 using polymethylmethacrylate (PMMA) molds patterned by deep X-ray lithography (DXRL). The process presented in this article utilizes GR 650 as a DXRL resist. The polymethylsilsesquioxane is converted to silica on the surface exposed to air, and cross linked throughout the bulk. X-ray irradiated regions are then selectively retained by development in an organic solvent. A technique to cast 100 m thick GR 650 films was established. Although the height of the structures fabricated was 100 m, this technique can be extended to larger structural heights. An alternative positive tone process was also developed in which the irradiated regions of GR 650 films are etched in buffered HF. The structural height achieved by positive tone processing, however, was limited to 15 mum, which is the depth of conversion to silica. Surface and bulk compositions of the irradiated films were measured by XPS and Fourier Transform infrared spectroscopy.

This paper presents a new application of spin-on glass to fabricate nonplanar dielectric structures (channel plate microstructures) with aspect ratios (i.e., ratio of channel length to channel width) of 20:1. A variety of microchannel geometries have been fabricated. The LIGA process is used to make nickel molds up to 150 mu m in height with mechanically planarized surfaces. Spin-on glass (SOG) is applied to obtain glass structures in nickel molds. A multiple dispensing/drying/curing process was developed resulting in crack-free SOG structures. Reverse electroplating is used to remove the nickel mold and release the glass structures.' The resulting freestanding glass microchannel plates (>100 mu m in height) demonstrated good electrical properties (400-V/mu m breakdown voltage) and good spatial definition.

A mathematical model of focused ion-beam milling is used to generate dwell times for the vector scanned pixel address scheme of a focused ion-beam deflection system. The model incorporates the absolute sputter yield of the solid as a function of the angle of incidence, and the relationship between the ion-beam current distribution and the pixel size of the deflection pattern. The object of this work is to be able to call for an arbitrary geometric shape to be ion milled and then have the numerical model compute the pixel dwell times for the deflection system such that the final cavity is sputtered. Experimental verification of the procedure was accomplished with parabolic troughs, hemispherical troughs, and cosine troughs. The term “trough” means a plane of symmetry in the ion-milled cavity. These same geometric shapes were also ion milled using a rotational axis of symmetry, yielding sinusoidal ring patterns, parabolic dishes, and hemispherical dishes. The absolute maximum depth for each of the cavities is consistently between 0.8 and 0.9 of the programed (a priori) depth. The discrepancy between the programed depth and the observed depth is attributed to a slowly decreasing ion-beam current over the duration of the milling and to redeposition.