**3.3 UV nanoimprint mold repair by FIB etching and CVD**

To examine the repair resolution of the FIB etching, we fabricated a narrow line by FIB etching on a quartz mold and performed UV-NIL using this mold. The mold was pressed onto UV-curable resin (Toyo Gosei: PAK-01). The UV-NIL pressure and UV wavelength were 0.9 MPa and 365 nm, respectively. The mold was held for 90 sec during imprinting. The release agent (Daikin Industries; OPTOOL DSX: demnamsolvent = 1 : 1000 by weight) was precoated on the mold to avoid the adhesion of resin and to enable a smooth separation of the mold and the substrate. Figure 11(a) shows the imprinted line pattern using the mold on the PAK-01. The linewidth was 29 nm. Results demonstrated that FIB can etch a narrow line on the quartz substrate.

We also examined the repair resolution of FIB-CVD. First, we fabricated a narrow line by FIB etching, and then deposited it on the quartz mold by FIB-CVD. The pattern imprinted by UV-NIL using this mold is shown in Fig. 11(b). The fabricated narrow linewidth was 36 nm. These results indicate that a 30-nm defect can be repaired by FIB etching and CVD.

3D structure was 21% Si, 51% O, 9% C, and 19% Ga. Ga content in the thorns was much less than that in the deposited SiOx. These results indicate that the thorn structure was caused by electric charge accumulation on the FIB-deposited region due to the increasing beam current. This makes it clear that we must use an optimum beam current to achieve hollow

Fig. 10. STEM image of Au-coated thorns on 3D structure. The atomic content inside the

To examine the repair resolution of the FIB etching, we fabricated a narrow line by FIB etching on a quartz mold and performed UV-NIL using this mold. The mold was pressed onto UV-curable resin (Toyo Gosei: PAK-01). The UV-NIL pressure and UV wavelength were 0.9 MPa and 365 nm, respectively. The mold was held for 90 sec during imprinting. The release agent (Daikin Industries; OPTOOL DSX: demnamsolvent = 1 : 1000 by weight) was precoated on the mold to avoid the adhesion of resin and to enable a smooth separation of the mold and the substrate. Figure 11(a) shows the imprinted line pattern using the mold on the PAK-01. The linewidth was 29 nm. Results demonstrated that FIB can etch a narrow

We also examined the repair resolution of FIB-CVD. First, we fabricated a narrow line by FIB etching, and then deposited it on the quartz mold by FIB-CVD. The pattern imprinted by UV-NIL using this mold is shown in Fig. 11(b). The fabricated narrow linewidth was 36 nm. These results indicate that a 30-nm defect can be repaired by FIB etching and CVD.

100 nm

defect repair by FIB-CVD.

circle was measured by SEM–EDX.

line on the quartz substrate.

**3.3 UV nanoimprint mold repair by FIB etching and CVD** 

Fig. 11. SEM images of lines imprinted by UV-NIL using (a) quartz mold with narrow hollow-line fabricated by FIB etching and (b) repaired mold.

## **3.3.1 Repair of protrusion defects on UV-NIL mold**

To repair a UV-NIL mold by 30-kV FIB etching at 1 pA, we fabricated program protrusion defects on it using a quartz substrate by EB lithography and RIE. Figure 12(a) shows the program protrusion-defective template. The protrusion width and length were 40 nm and 150 nm, respectively. Figure 12(b) shows the defective line pattern transferred by UV-NIL on the PAK-01 and as we can see, the defective line pattern was clearly imprinted on the substrate. We repaired the protrusion defects on the UV-NIL mold by FIB etching. Figure 13(a) shows the line pattern repaired by FIB etching on the mold. The repair time for one protrusion defect was about 10 sec. The protrusion defect was successfully etched away by FIB and the repaired line pattern was clearly imprinted (Fig. 13(b)).

#### **3.3.2 Repair of hollow defects on UV-NIL mold**

Figure 14(a) shows the program hollow-defective mold. The hollow-width was 60 nm. Figure 14(b) shows the imprinted line pattern using the defective mold on the substrate. The defective line pattern was clearly imprinted on the substrate. We repaired the hollow defect on the UV-NIL mold by FIB-CVD. Figure 15(a) shows the line pattern on the mold repaired by FIB-CVD using tetraethoxysilane. The repair time for one hollow defect was about 20 sec. Figure 15(b) shows the line pattern transferred using the repaired mold on the substrate. The hollow defect region was successfully deposited by FIB-CVD, and the repaired line pattern was clearly imprinted (Fig. 15(b)).

Repairing Nanoimprint Mold Defects by Focused-Ion-Beam Etching and Deposition 167

(a) (b)

Fig. 14. SEM images of (a) program hollow defective quartz mold and (b) PAK-01 defective

(a) (b)

Fig. 15. SEM images of (a) line pattern repaired by FIB-CVD on quartz mold and (b) PAK-01

line pattern imprinted by UV-NIL using the repaired quartz mold.

line pattern imprinted by UV-NIL using the hollow defective quartz mold.

500nm 500 nm

500 nm 500 nm

220 nm

60 nm

Fig. 12. SEM images of (a) program protrusion-defective quartz mold and (b) PAK-01 defective line pattern imprinted by UV-NIL using the protrusion-defective quartz mold.

Fig. 13. SEM images of (a) line pattern in Fig. 12(a) repaired by FIB etching and (b) PAK-01 line pattern imprinted by UV-NIL using the repaired quartz mold.

(a) (b)

(a) (b)

Fig. 13. SEM images of (a) line pattern in Fig. 12(a) repaired by FIB etching and (b) PAK-01

line pattern imprinted by UV-NIL using the repaired quartz mold.

Fig. 12. SEM images of (a) program protrusion-defective quartz mold and (b) PAK-01 defective line pattern imprinted by UV-NIL using the protrusion-defective quartz mold.

500nm 500 nm

500 nm 500 nm

210 nm 40 nm

150 nm

Fig. 14. SEM images of (a) program hollow defective quartz mold and (b) PAK-01 defective line pattern imprinted by UV-NIL using the hollow defective quartz mold.

Fig. 15. SEM images of (a) line pattern repaired by FIB-CVD on quartz mold and (b) PAK-01 line pattern imprinted by UV-NIL using the repaired quartz mold.

Repairing Nanoimprint Mold Defects by Focused-Ion-Beam Etching and Deposition 169

In this work, we used gallium-FIB to repair the NIL molds. Recently, helium ion microscopy (HIM) with a subnanometer probe size has become commercially available. Apart from the obvious advantage of small probe sizes, HIM also boasts a narrow interaction volume in the substrate and the predominance of secondary electron emission. A helium ion microscope can also be used for nanofabrication. We expect the mold repair resolution to dramatically

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**5. References** 

The durability of a repaired mold is crucial for applying UV-NIL to mass production. Therefore, we tested the durability of the SiOx material deposited by FIB-CVD by observing over 200 repeated uses of the mold repaired by FIB-CVD. Figure 16(a) and (b) shows the SEM images of the 100th and 200th imprinted pattern. After nanoimprintings, the pattern was still clearly imprinted on the resin. This result indicates that the deposited SiOx material has sufficient durability for repeated UV-NIL.

Fig. 16. SEM images of (a) 100th and (b) 200th imprinted patterns on PAK-01 formed by UV-NIL using quartz mold repaired by FIB-CVD.
