# Experiment Research on Micro-/Nano Processing Technology of Graphite as Basic MEMS Material
## 3 Results and Discussion  
Photoresist patterns were directly processed on the graphite surface based on the aforementioned micro-/nanotechnology, shown in Figure 1a-d. In addition, Figure 2b,c and Figure S1b show the photoresist patterns observed under an optical microscope. Figure 2d-h show the photoresist pattern observed under atomic-force microscopy (NTEGRA Solaris, T-MDT Company, Russia). As can be seen from the above Figures, lithography could be directly applied to the micrograph of the graphite surface, and photoresist patterns of different shapes and sizes can be stably and controllably processed in large quantities. Moreover, the microstructure of the photoresist processed on the graphite surface was neatly arranged. Figure 2b-e shows that the height of the photoresist ranges from 565 nm-579 nm, which means the photoresist has good height uniformity. Additionally, the photoresist pattern shown in Figure 2b was processed from the mask pattern in the mask template shown in Figure 2a. The pattern comparison in Figure 2a,b shows that the photoresist pattern obtained by lithography on the graphite surface is substantially identical to the pattern on the designed mask template. This finding indicates that the graphite surface can be directly processed by lithography. Therefore, different the photoresist patterns can be designed according to requirements, and various photoresist patterns and photoresist microstructures can be accurately and controllably processed on graphite surface by optical lithography. By using the etching process shown in Figure 1e-g, the designed microstructure pattern was machined on the graphite. Furthermore, the graphite micro-/nanostructures was characterized by atomic-force and scanning-electron microscopy. The result shows that the photoresist could still resist plasma etching before it was completely etched. As we can see from the Figure 3, part of photoresist is etched by the oxygen plasma, but most of photoresist still covered on the graphite surface with about 45\({}^{\circ}\) sidewall. Although the oxygen plasma is also a photoresist etching, the 600 nm thickness photoresist still can resist the O\({}_{2}\) etching while process tens of nanometers height of graphite structures. Moreover, we studied the amount of photoresist etched during process graphite micro-/nanostructures. The result shows that about 100 nm amount of photoresist etched during process about 30 nm amount  
Figure 2: (**a**) Mask template observed under optical microscope; (**b,c**) photoresist patterns observed under optical microscope; (**d,e**) photoresist pattern observed under atomic-force microscopy; (**f–h**) the results of the step height characterization. of graphite. For example, a 1.06 um thickness of photoresist would have resulted in 957 nm thickness of photoresist left behind after etching, and a thicker thickness of photoresist would have resulted in more photoresist left behind. In addition, we design experiments vary the oxygen flow rate (20 sccm; 30 sccm), power (100 W; 150 W) and pressure (7 Pa; 8 Pa; 10 Pa) to find optimum RIE conditions to fabricate graphite micro-/nano structures with larger degree sidewall. The result shows that the etch rate of the graphite changed with the different etch conditions, e.g., we could get the etch rate of 0.93 nm/s and the 3.1 nm/s with the parameter of 10 Pa chamber pressure, 100 W power, 20 sccm oxygen flow rate; the etch rate of 1.2 nm/s with the parameter of 8 Pa chamber pressure, 100 W power, 20 sccm oxygen flow rate; the etch rate of 1.53 nm/s with the parameter of 7 Pa chamber pressure, 100 W power, 20 sccm oxygen flow rate. Therefore, the smaller the cavity pressure, the greater the etch rate of graphite. Besides, Figure 4 is the graphite nanostructures with about 23\({}^{\circ}\) sidewall (Sentech's Etchlab 200 reactive ion etching machine; chamber pressure, 10 Pa; power, 100 W; oxygen flow rate, 20 sccm; etching rate 0.93 nm/s).