**3.2 PCT technique**

Figure 16 shows the PCT technique. The energy distribution is deposited in the resist by scanning, as shown in the figure. Three-dimensional structures were fabricated by

Fabrication of 3-D Structures Utilizing Synchrotron Radiation Lithography 329

With the pixels exposure technique, it is possible to fabricate arbitrary 3-D microstructures using a mask with an appropriate pattern. In this technique, SR light is shaped by the aperture, and the amount of exposure energy is controlled by opening and closing the aperture with an actuator (Figure 18A). This technique applies the energy distribution in a mosaicked shape, as shown in the figure. Because the array was difficult to fabricate, we fabricated a 20-m-thick, 75- 80-m single aperture made of Ni to distribute an ideal mosaicked exposure energy by two-axis scanning of the PMMA resist (Figure 18B). Because fabrication masks were not needed and it is suitable for rapid prototyping, fabrication time and cost were reduced. When the PMMA resist is exposed to a mosaicked energy distribution with the same aperture size, a smooth free-form surface cannot be fabricated. Thus, because the resolution of PMMA is very high, if even a few adjoining pixels overlap or there is a gap between pixels, channels or pillars appear on the boundary surface. Based on these basic studies, fabrication of structures with smooth free-form surfaces was achieved using an exposure method in which the pixels were overlapped beforehand. Moreover, an algorithm to determine the amount of exposure energy while taking overlap into consideration was written for the target form to fabricate a 3-D structure that had an

arbitrary shape. The target forms and fabrication structures are shown in Figure 19.

ablation technology and the mechanism of fabrication are described.

This section describes 3-D PTFE microstructures fabricated by SR ablation. Advantages of

PTFE is a fluoroplastic material known for its excellent material characteristics, including insulation against high voltages, resistance to chemicals and creep, and high thermal stability. PTFE was discovered in 1938 by Dr. Roy J. Plunkett, who was a researcher of E.I. du Pont de Nemours and Company, a commercial reality in 1946. PTFE is best known by the DuPont brand name Teflon®. In addition to its primary use in non-stick frying pans and filters, PTFE is also used in a broad range of fields, such as those involving household articles, OA equipment, semiconductors, and cars. Despite its long (> 60-year) history, new uses for PTFE are developed continuously because of its outstanding characteristics. Because PTFE has excellent material characteristics, it is expected to be applicable to MEMS.

Fig. 19. The target forms and fabrication structures

**3.3 Pixels exposure technique** 

**4. PTFE fabrication by SR ablation** 

**4.1 PTFE** 

subsequent development. Additionally, a more complex energy distribution can be given by rotating the mask 90. For example, a needle shape can be fabricated using the PCT method. When the PCT technique is used, a shape similar to that of the mask absorber pattern is expected to be fabricated. Therefore, if the exposure distribution onto the resist is expected to form a curved shape or sloped-sidewall structure whose cross-section is similar to the mask absorber pattern as the target shape. As shown in Figure 16, when the PCT technique is used, it is possible to fabricate a microneedle array structure, as indicated by the diagram below. If this method is used, it is possible to fabricate both a microneedle and microlens array. Fabrication results of 3-D structures are shown in Figure 17.

Fig. 17. Fabrication results of 3-D structures

Fig. 18. Pixels exposure technique; (A) SR light is shaped by the aperture, and the amount of exposure energy is controlled by opening and closing the aperture with an actuator; and (B) an ideal mosaicked exposure energy by two-axis scanning of the PMMA resist

Fig. 19. The target forms and fabrication structures

### **3.3 Pixels exposure technique**

328 Recent Advances in Nanofabrication Techniques and Applications

subsequent development. Additionally, a more complex energy distribution can be given by rotating the mask 90. For example, a needle shape can be fabricated using the PCT method. When the PCT technique is used, a shape similar to that of the mask absorber pattern is expected to be fabricated. Therefore, if the exposure distribution onto the resist is expected to form a curved shape or sloped-sidewall structure whose cross-section is similar to the mask absorber pattern as the target shape. As shown in Figure 16, when the PCT technique is used, it is possible to fabricate a microneedle array structure, as indicated by the diagram below. If this method is used, it is possible to fabricate both a microneedle and microlens

array. Fabrication results of 3-D structures are shown in Figure 17.

Fig. 17. Fabrication results of 3-D structures

(A) (B) (C)

Fig. 18. Pixels exposure technique; (A) SR light is shaped by the aperture, and the amount of exposure energy is controlled by opening and closing the aperture with an actuator; and (B)

an ideal mosaicked exposure energy by two-axis scanning of the PMMA resist

With the pixels exposure technique, it is possible to fabricate arbitrary 3-D microstructures using a mask with an appropriate pattern. In this technique, SR light is shaped by the aperture, and the amount of exposure energy is controlled by opening and closing the aperture with an actuator (Figure 18A). This technique applies the energy distribution in a mosaicked shape, as shown in the figure. Because the array was difficult to fabricate, we fabricated a 20-m-thick, 75- 80-m single aperture made of Ni to distribute an ideal mosaicked exposure energy by two-axis scanning of the PMMA resist (Figure 18B). Because fabrication masks were not needed and it is suitable for rapid prototyping, fabrication time and cost were reduced. When the PMMA resist is exposed to a mosaicked energy distribution with the same aperture size, a smooth free-form surface cannot be fabricated. Thus, because the resolution of PMMA is very high, if even a few adjoining pixels overlap or there is a gap between pixels, channels or pillars appear on the boundary surface. Based on these basic studies, fabrication of structures with smooth free-form surfaces was achieved using an exposure method in which the pixels were overlapped beforehand. Moreover, an algorithm to determine the amount of exposure energy while taking overlap into consideration was written for the target form to fabricate a 3-D structure that had an arbitrary shape. The target forms and fabrication structures are shown in Figure 19.
