**3. Repair of UV nanoimprint mold by using FIB etching and CVD**

#### **3.1 Characteristics of SiOx material deposited by FIB-CVD using tetraethoxysilane as source gas**

In photomask repair and thermal NIL mold repair, the material deposited by FIB-CVD is DLC, which is not clear. In UV-NIL, UV-curable resin is irradiated by UV through the UV-NIL mold. Therefore, the material deposited by FIB-CVD must be transparent, meaning we cannot use DLC as the deposited material. However, we are able to deposit a SiOx material, which is transparent, by FIB-CVD using tetraethoxysilane [Si(OC2H5)4] as a source gas. To examine whether the SiOx-deposited material has sufficient transmittance and hardness to withstand UV-NIL, we measured the atomic composition, transmittance, and hardness of SiOx film fabricated by FIB-CVD using tetraethoxysilane.

(a) (b)

(a) (b)

**3.1 Characteristics of SiOx material deposited by FIB-CVD using tetraethoxysilane as** 

In photomask repair and thermal NIL mold repair, the material deposited by FIB-CVD is DLC, which is not clear. In UV-NIL, UV-curable resin is irradiated by UV through the UV-NIL mold. Therefore, the material deposited by FIB-CVD must be transparent, meaning we cannot use DLC as the deposited material. However, we are able to deposit a SiOx material, which is transparent, by FIB-CVD using tetraethoxysilane [Si(OC2H5)4] as a source gas. To examine whether the SiOx-deposited material has sufficient transmittance and hardness to withstand UV-NIL, we measured the atomic composition, transmittance, and hardness of

Fig. 5. SEM images of lines imprinted by T-NIL using repaired (a) protrusion- and (b)

**3. Repair of UV nanoimprint mold by using FIB etching and CVD** 

SiOx film fabricated by FIB-CVD using tetraethoxysilane.

hollow-defective SiO2/Si mold.

**source gas** 

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

500 nm 500 nm

500 nm 500 nm

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

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 as the repair material for a UV-NIL mold.

#### **3.2 Necessity of antistatic treatment**

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.

Repairing Nanoimprint Mold Defects by Focused-Ion-Beam Etching and Deposition 163

(a) (b)

(a) (b) Fig. 9. (a) 3D structure fabricated by FIB-CVD with ESPACER300Z at 1 pA. (b) Thorns were

To determine why the thorns were fabricated on the edges, we observed them by scanning transmission electron microscopy (STEM) and measured their atomic composition by SEM-EDX. Figure 10 shows the STEM images of the Au-coated thorns. Although the pillar fabricated by FIB-CVD has a gallium core due to Ga ion implantation, no such gallium core was observed in the thorns. According to the SEM-EDX results, the atomic composition of the thorns was 16% Si, 68% O, 13% C, and 3% Ga. In contrast, the atomic composition of the

formed on the corners of the 3D structure with ESPACER300Z at 7 pA.

Fig. 8. SIM images of 200-nm wide patterns fabricated by FIB-CVD at 1 pA on quartz

substrates without and with antistatic agent.

3μm 1μm

1μm 1μm

We evaluated the antistatic effect of ESPACER300Z on a quartz substrate. We performed FIB-CVD using tetraethoxysilane on quartz substrates both with and without an antistatic agent. Figure 8 (a) and (b) shows the scanning ion microscopy (SIM) images of the 200-nm wide patterns fabricated by FIB-CVD at 1 pA on the two substrates. The line pattern was not formed on the substrate with no antistatic agent because of substrate drift caused by electrical charge. In contrast, the line pattern was clearly formed on the substrate that did use the antistatic agent, as shown in Fig. 8(b). Next, we fabricated 3D structures by FIB-CVD on ESPACER300Z-coated quartz substrates at 1 pA and 7 pA to examine the beam current dependency. When the beam current was 1 pA, the 3D structure was successfully fabricated on the quartz substrate, as shown in Fig. 9(a). However, as shown in Fig. 9(b), thorns were formed on the edges of the 3D structure fabricated by FIB-CVD at 7 pA.

Fig. 7. Schematic of methods to control static: (a) FIB-CVD performed with an electron shower and (b) using an antistatic agent (ESPACER 300Z: Showa Denko Co.) spin-coated on the UV-NIL mold.

We evaluated the antistatic effect of ESPACER300Z on a quartz substrate. We performed FIB-CVD using tetraethoxysilane on quartz substrates both with and without an antistatic agent. Figure 8 (a) and (b) shows the scanning ion microscopy (SIM) images of the 200-nm wide patterns fabricated by FIB-CVD at 1 pA on the two substrates. The line pattern was not formed on the substrate with no antistatic agent because of substrate drift caused by electrical charge. In contrast, the line pattern was clearly formed on the substrate that did use the antistatic agent, as shown in Fig. 8(b). Next, we fabricated 3D structures by FIB-CVD on ESPACER300Z-coated quartz substrates at 1 pA and 7 pA to examine the beam current dependency. When the beam current was 1 pA, the 3D structure was successfully fabricated on the quartz substrate, as shown in Fig. 9(a). However, as shown in Fig. 9(b), thorns were

(1)

(2)

(3)

(a) (b)

Fig. 7. Schematic of methods to control static: (a) FIB-CVD performed with an electron shower and (b) using an antistatic agent (ESPACER 300Z: Showa Denko Co.) spin-coated on

(4) Water wash

Spin-coated ESPACER300Z

Quartz substrate

FIB

**20 nm**

film thickness

formed on the edges of the 3D structure fabricated by FIB-CVD at 7 pA.

Electron shower FIB

(1)

(2)

(3)

the UV-NIL mold.

Quartz substrate

Fig. 8. SIM images of 200-nm wide patterns fabricated by FIB-CVD at 1 pA on quartz substrates without and with antistatic agent.

Fig. 9. (a) 3D structure fabricated by FIB-CVD with ESPACER300Z at 1 pA. (b) Thorns were formed on the corners of the 3D structure with ESPACER300Z at 7 pA.

To determine why the thorns were fabricated on the edges, we observed them by scanning transmission electron microscopy (STEM) and measured their atomic composition by SEM-EDX. Figure 10 shows the STEM images of the Au-coated thorns. Although the pillar fabricated by FIB-CVD has a gallium core due to Ga ion implantation, no such gallium core was observed in the thorns. According to the SEM-EDX results, the atomic composition of the thorns was 16% Si, 68% O, 13% C, and 3% Ga. In contrast, the atomic composition of the

Repairing Nanoimprint Mold Defects by Focused-Ion-Beam Etching and Deposition 165

**36 nm**

**29 nm**

(a) (b)

hollow-line fabricated by FIB etching and (b) repaired mold.

FIB and the repaired line pattern was clearly imprinted (Fig. 13(b)).

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

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

pattern was clearly imprinted (Fig. 15(b)).

Fig. 11. SEM images of lines imprinted by UV-NIL using (a) quartz mold with narrow

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

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

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 defect repair by FIB-CVD.

Fig. 10. STEM image of Au-coated thorns on 3D structure. The atomic content inside the circle was measured by SEM–EDX.
