Focused ion beam sculpting curved shape cavities in crystalline and amorphous targets
Schematic in (a) depicts the FIB sculpting technique. Details of serpentine scanning are described in (b) whereby a beam of width is moved through a Cartesian coordinate system in steps of S. The dimension represents the beam overlap in one direction.
Two procedures that define features for determining the angular dependence of yield. (a) shows a target tilted prior to ion bombardment–a procedure appropriate for amorphizable or amorphous materials. The fixed crystal technique (b) is used for metals that remain crystalline. For (b) the substrate normal is parallel to the ion beam vector.
Plots of for Si(100) (●), SiC(100) (◇), and (▾). The lines represent fits to the formulation of Yamamura et al. A pixel dwell time is used for each experiment.
Plots of for Ga ion bombardment of Au(100). (a) displays the yield determined using the “fixed crystal” technique. The line in this plot indicates a fit using the formulation of Yamamura et al. (b) shows the yield determined using the “tilted specimen” method. Several low Miller index orientations are indicated to highlight the effects of ion channeling. The solid line in this plot is a guide to the eye. A pixel dwell time is used for each experiment.
Plot of Au(100) yield determined when using different pixel dwell times. For these experiments, the angle of ion incidence with respect to the initial (unmilled) surface is fixed at . Results are shown for milling with a focused ion beam of width (×) and (▴). Each datum represents a single milled feature.
Results from ion sculpting (a) parabolas and (b) sinusoids in C(100) as determined from scanning electron micrographs. Measured depths depicted by unfilled symbols (◻ and 엯) are taken from features sculpted using a technique that accounts for the yield dependence on angle and the ion beam spatial distribution. Depths represented by filled symbols (∎ and ●) describe features sculpted using a method that accounts for the angular dependence, the ion distribution, and the effects of redeposition.
Scanning electron micrographs of ion-sculpted parabola and sinusoid in diamond C(100). Features are created with a technique that empirically accounts for redeposition. “Bright” layer is Pt deposited after ion sculpting so as to preserve milled shape through FIB cross sectioning. These features are depicted in Fig. 6 with filled symbols.
Cross-sectional scanning electron micrographs of an ion-sculpted hemisphere, parabola, and sinusoid in Au(100). Images are tilted slightly to show off shape. Also displayed are measured depths taken from edge-on micrographs compared with targeted profiles (indicated by solid lines).
Calculated reflection coefficient for Ga ions incident on Au and C targets, from TRIM.
Calculated angular distributions of (a) backscattered Ga ions and (b) sputtered atoms from gold and carbon substrates for Ga ions incident at 70° using TRIM. Arrow indicates the direction of the incident ion. Radial dimension is proportional to the number of particles.
Sputter yields at 0° determined from experiments (denoted with subscript “expt”) and calculated using the formula of Matsunami et al., Eq. (3) , (denoted with subscript ). Also included are experimentally determined values and . Values and are determined using the theory of Yamamura et al. n/c indicates values not calculated.
Results from sculpting various target materials. Depths are measured using white light interferometry and atomic force microscopy.
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