Selectively Electron-Transparent Microstamping 1093
and after stamping to determine the loss of resolution when calculating elastic lattice distortion, which is a combination of strain and local rotation. Epitaxial silicon is nearly strain and dislocation free, meaning that any measured distortion can be considered erroneous. Additionally, because it is a single crystal, any effect that orientation has on the noise level of HREBSD is mitigated. The scans were taken at 20 keV with a beam current of 13nA over a 60×60 μm area with a step size of 0.4 μm in a Helios™ SEM. The patterns were collected with no binning on a Hikari Super™camera with no gain and an exposure time of 200ms. The working distance was ~12 and 13mm, before and after stamping, respectively. The lattice distortion between neighboring patterns (β) was calculated [such as would be calculated to determine lattice distortion gradients (Ruggles et al., 2016a)] instead of the distortion relative to a single reference point. This was done to minimize the effect of pattern center error (Alkorta, 2013), but it also means that the interaction between the urethane stamp and HREBSD performed on patterns from very different pattern centers was not exam- ined. The relative elastic distortion is reported instead of the distortion gradient or dislocation density for easier com- parison with measurements from DIC. The HREBSD
a
calculations were performed with OpenXY (Brigham Young University, 2016). The measured distortion before stamping is shown in
Figure 2a, and the distortion after the stamp is shown in Figure 2b. This distortion is reported in the reference frame of the phosphor screen of the EBSD camera, i.e. the z- direction is normal to the phosphor screen. Presenting the data in this way allows for easy separation of the terms more sensitive to noise, β31 and β32 (Alkorta, 2013). The average Frobenius norm of the lattice distortion was 585 microstrain before the stamp and 751 microstrain after. Because this measured strain is entirely noise, these results suggest that the stamp increased the noise of HREBSD by 28%. If the problematic β31 and β32 terms are excluded, the error level drops to 271 and 308 microstrain before and after stamping, respectively, for an increase of only 13%. This small increase in error demonstrates the compatibility of HREBSD with urethane microstamped patterns. It is also relevant that there is no apparent correlation between the noise and the SEM micrograph of the stamp shown in Figure 2c. This suggests that the decrease in pattern quality associated with the beam passing through a speckle is negligible compared with the total error.
b
β11
β12
β13
β11
β12
β13
β21
β22
β23
β21
β22
β23
β31
β32
β33
β31
β32 c 60 m -600 -300 0 microstrain
Figure 2. Lattice distortion measured over a 60 μm2 area of an epitaxial Si single crystal at a 400nm step size before (a) and after (b) microstamping. The distortion at each point is calculated relative to its neighbor to the right. The distortion components are given in the reference frame of the phosphor screen, where the three-direction is normal to the surface. An scanning electron microscope micrograph of the area after stamping is shown in (c).
300 600
β33
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