**2. Thermal nanoimprint mold repair using FIB technique**

Watanabe et al. previously reported on SiO2/Si mold repair for thermal NIL using FIB etching and CVD. We first fabricated an SiO2/Si mold with protrusion and hollow defects by EB lithography and reactive ion etching (RIE). The scanning electron microscopy (SEM) images of the fabricated SiO2/Si mold shown in Fig. 1 depict both the (a) protrusion and (b) hollow defects. The width and length of the protrusion defect were 210 and 130 nm, respectively, and the width of the hollow defect was 250 nm.

Fig. 1. SEM images of fabricated SiO2/Si mold with (a) protrusion and (b) hollow defects.

Fig. 2. SEM images of imprinted (a) protrusion- and (b) hollow-defective lines on NEB-22.

must perform FIB etching and CVD directly on the substrate material to repair protrusion and hollow defects, respectively. From an economic viewpoint it is best to use existing technology, so we applied FIB etching and CVD to repair the NIL molds and then examined

Watanabe et al. previously reported on SiO2/Si mold repair for thermal NIL using FIB etching and CVD. We first fabricated an SiO2/Si mold with protrusion and hollow defects by EB lithography and reactive ion etching (RIE). The scanning electron microscopy (SEM) images of the fabricated SiO2/Si mold shown in Fig. 1 depict both the (a) protrusion and (b) hollow defects. The width and length of the protrusion defect were 210 and 130 nm,

(a) (b)

(a) (b)

Fig. 2. SEM images of imprinted (a) protrusion- and (b) hollow-defective lines on NEB-22.

Fig. 1. SEM images of fabricated SiO2/Si mold with (a) protrusion and (b) hollow defects.

500 nm 500 nm

500 nm 500 nm

**2. Thermal nanoimprint mold repair using FIB technique** 

respectively, and the width of the hollow defect was 250 nm.

the resulting repair resolution.

We performed thermal nanoimprinting on NEB-22 (Sumitomo Chemical Co.) using this mold. The mold and resin were heated at 150 C. Imprinting pressure and time were 10 MPa and 1min, respectively. The protrusion and hollow defects were clearly imprinted on the resin. We repaired these defects by FIB etching and CVD.

Figure 3(a) and (b) shows the schematic of the repair process for the protrusion and hollow defects, respectively, on the mold. We used SMI2050MS2 (SII NanoTechnology Inc.) as a FIB system. The ion source, acceleration voltage, and beam current were gallium, 30 kV, and 1 pA, respectively. The protrusion defect was removed by FIB etching. When we repaired the hollow defect, we performed FIB-CVD using phenanthrene (C14H10) as a source gas to fill in the hollow defect. Using the phenanthrene caused a diamond-like carbon (DLC) to be deposited, which upon examination we found to contain gallium. Gallium contained in DLC deposited by FIB-CVD can be evaporated by annealing at over 500 C, but this evaporation does not occur in general thermal nanoimprinting because in such processes the temperature is usually from 100 to 200 C. Figure 4(a) and (b) shows the SEM images of the repaired SiO2/Si mold with protrusion and hollow defects, respectively. The protrusion defect was removed by FIB etching and the hollow defect was filled in by FIB-CVD. The etching and deposition times in this case were about 1 min and 30 sec, respectively. We then performed thermal nanoimprinting using the repaired mold on NEB-22, as shown in Fig. 5(a) and (b). The repaired lines were clearly imprinted on NEB-22. These results indicate that we can repair the protrusion and hollow defects on the thermal nanoimprint mold by FIB etching and CVD.

Fig. 3. Schematic of repair process of (a) protrusion and (b) hollow defects on mold.

Repairing Nanoimprint Mold Defects by Focused-Ion-Beam Etching and Deposition 161

365 nm

Fig. 6. Transmittance of SiOx film fabricated by FIB-CVD using tetraethoxysilane.

330 350 370 390 410 430 Wavelength (nm)

The atomic composition of the SiOx film measured by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) was 13% Si, 58% O, 9% C, and 20% Ga. A small amount of carbon is included in the SiOx film because tetraethoxysilane is composed of Si, O, H, and C. Ga is incorporated into SiOx film because Ga ion implantation is induced by the Ga ion beam used in FIB-CVD. We measured the transmittance of the 720 720μm2, 1μm thick SiOx film using a monochromator (Hamamatsu Photonics: PMA-11) with a Xenon lamp. Figure 6 shows the results of measuring the SiOx film's transmittance. 365-nm UV is typically used in UV-NIL. The transmittance of the SiOx film was 83 % at 365 nm. This result demonstrated that the SiOx material deposited by FIB-CVD has a sufficient transmittance to carry out UV-NIL. Next, we measured the hardness of the SiOx film with a nanoindenter (Elionix: ENT-1100a). The hardness of the 150 150μm2, 1μm thick SiOx film was 5 GPa. This result shows that the deposited SiOx material has a sufficient hardness because UV-NIL is usually performed at pressures below 1 MPa. These results clearly demonstrate that SiOx material deposited by FIB-CVD using tetraethoxysilane can be used

When FIB is used to repair defective photomasks, the photomasks do not develop a charge because Cr metal patterns are formed on the quartz substrate. On the other hand, UV-NIL molds do develop a charge because the patterns are formed on the surface of the quartz substrate. It is therefore necessary to prevent electrical charge during the repair of a UV-NIL mold. There are two methods for controlling static. One is electron shower irradiation during FIB (Fig. 7(a)). In this method, however, the region of electron irradiation is also deposited, as in FIB-CVD. This makes it very difficult to apply an electron shower as an antistatic method. The other method is using an antistatic agent spin-coated on the UV-NIL mold (Fig. 7(b)). In this case, the deposition by FIB irradiation is possible. We used a 20-nm thick ESPACER300Z (Showa Denko) as an antistatic agent to prevent electrical charge. The FIB-irradiated part on ESPACER300Z was first etched away and then the SiOx was deposited, as shown in Fig. 7(b).

ESPACER300Z can easily be washed away with water after the repair.

0

as the repair material for a UV-NIL mold.

**3.2 Necessity of antistatic treatment** 

50

Transmittance (%)

100

Fig. 4. SEM images of repaired SiO2/Si mold with (a) protrusion and (b) hollow defect.

Fig. 5. SEM images of lines imprinted by T-NIL using repaired (a) protrusion- and (b) hollow-defective SiO2/Si mold.
