## 3 Results and Discussion  
### Effects of the Shape of the Microstructure  
Figure 7 presents the images obtained by observing the three shapes of the machined microstructures by SEM. In order to observe each machined result more clearly, the cross-section of the microstructures was formed by the FIB (focused ion beam) milling process, and then observed with SEM. In order to minimize the shape changes of a cross-section during the FIB milling process, Pt (platinum) was deposited on the microstructure before the FIB milling process commenced.  
The microstructures with a trapezoidal cross-sectional shape did not show any burrs or deformation when the depth of cut was 1 \(\upmu\)m or 0.1 \(\upmu\)m. As a result of the square-shaped microstructures, burrs of about 0.18 \(\upmu\)m that formed at the upper edge were observed under the machining conditions of a 1-\(\upmu\)m depth of cut. Burrs were not observed under the condition where the depth of cut was reduced to 0.1 \(\upmu\)m. In microstructures with a triangular cross-section, a deformation of about 0.39 \(\upmu\)m occurred  
Figure 6: Machining with different tool paths: (**a**) changed tool path 1 (continuous contact area ‘P1’), (**b**) changed tool path 2 (continuous contact area ‘P2’).  
Figure 7: SEM photos for the three shapes of the machined microstructures: depth of cut of 1.0 \(\upmu\)m (**a–c**) and 0.1 \(\upmu\)m (**d–f**).  
under a machining condition with a depth of cut of 1 \(\upmu\)m. This shape error did not occur under the machining conditions with a depth of cut of 0.1 \(\upmu\)m.  
[PERSON] et al. reported that deformation of the microstructure of the material surface increased when the depth of cut was increased in precision machining. Studies by [PERSON] et al. and [PERSON] et al. showed that the shape accuracy improved when the depth of cut was reduced [9; 10; 11]. In this experiment, the relationship between the depth of cut and shape error was similar to the results obtained by other researchers.  
The experiments showed that the different results depended on the shape of the microstructure in the experiments when using similar machining conditions. For the case of a cutting depth of 1 \(\upmu\)m, the shape error types according to the shape of the microstructure are obtained from Figure 6 by using the diagrams. Burrs or deformation did not occur in the case where the angle between the surface contacting the tool and the adjacent surface was 120\({}^{\circ}\) (a microstructure with a trapezoidal cross-section). In the case of 90\({}^{\circ}\) (a microstructure with a rectangular cross-section), a burr formed at the upper edge of the microstructure. When the angle was 60\({}^{\circ}\) (microstructure where the shape of the cross-section is triangular), local deformation occurred at the upper edge of the microstructure. The experimental results showed that the shape error tended to be larger when the angle between the surface in contact with the tool and the adjacent surface at the time of machining the microstructure was smaller. These shape errors did not appear when the depth of cut had been reduced to 0.1 \(\upmu\)m.  
The shape errors of the microstructures of several microns in size occurred intensively at the upper edge of the microstructure. It was found that the form accuracy of the microstructure changed depending on the angle between the surface that comes into contact with the tool and the adjacent surface in the experimental results of the fabrication of the three kinds of microstructures. Figure 8 summarizes these phenomena. It should also be noted that if the form accuracy of the microstructure is improved due to the reduction of the depth of cut, the productivity will decrease because the machining time is increased.