## 3 Result and Discussion
### Optical Constant and Thickness Analysis of Ta\({}_{2}\)O\({}_{5}\) Thin Film  
We use an optical spectrophotometer to measure the transmission spectrum of the Ta\({}_{2}\)O\({}_{5}\) thin film. It can be found that the curves of the transmission spectra almost overlap, as shown in Figure 8. There is no obvious waveform drift, which means that the thickness of the film deposited at different positions is uniform. The average transmittance in the wavelength of 400 to 800 nm is higher than 85%, which has a good optical transmittance. But it was found that the transmittance is different, which means that the refractive index or extinction coefficient of different segments will be different. The transmission spectra were measured from different positions of the samples. The transmittance difference is about 1%. The optical constants are determined by an ellipsometer. The refractive indices of the five segments are 2.023, 2.039, 2.045, 2.026, and 2.031, as shown in Table 2. The highest refractive index is 2.045 for the segment three. The lowest refractive index is 2.023 for the segment one. The extinction coefficients of the Ta\({}_{2}\)O\({}_{5}\) thin films for different segments are also analyzed. The analyzed extinction coefficients are 0.004, 0.007, 0.007, 0.004, and 0.003, respectively. The maximum extinction coefficient is 0.007 for the segments two and three.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Segment** & **Refractive Index** & **Extinction Coefficient** & **Film Thickness (nm)** \\ \hline One & 1.429 & 0.0007 & 566.76 nm \\ Two & 1.437 & 0.0007 & 567.58 nm \\ Three & 1.443 & 0.0004 & 566.17 nm \\ Four & 1.438 & 0.0005 & 567.76 nm \\ Five & 1.449 & 0.0006 & 570.47 nm \\ \hline \end{tabular}
\end{table}
Table 1: Optical constants of SiO\({}_{2}\) thin films with different segments.  
Figure 7: Relative thickness of SiO\({}_{2}\) thin film deposited on a large substrate with a radius of 275 mm.  
The minimum extinction coefficient is 0.003 for the segment five. The analysis results show that the extinction coefficients are very small, the absorption of the Ta\({}_{2}\)O\({}_{5}\) thin films at longer wavelengths is less than \(1\times 10^{-3}\).  
The surface profiler was used to measure and analyze the film thickness of different segments. The film thicknesses of the five segments are 480.38 nm, 480.82 nm, 482.23 nm, 483.86 nm, and 483.53 nm, respectively. The results show that the film thickness of the segment five is the thickest. The film thickness of the segment one is the thinnest. The average thickness of the Ta\({}_{2}\)O\({}_{5}\) thin film at different positions is 483.86 nm. The thickness difference between the thickest and thinnest films was 3.48 nm, so the uniformity of the film thickness distribution was good. If the film thicknesses of the five segments are normalized, the thickness uniformity of the Ta\({}_{2}\)O\({}_{5}\) film can be calculated to be 0.36%, and the relative thicknesses of segments 1 to 5 are close, as shown in Figure 9.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Segment** & **Refractive Index** & **Extinction Coefficient** & **Film Thickness (nm)** \\ \hline One & 2.023 & 0.004 & 480.38 nm \\ Two & 2.039 & 0.007 & 480.82 nm \\ Three & 2.045 & 0.007 & 482.23 nm \\ Four & 2.026 & 0.004 & 483.86 nm \\ Five & 2.031 & 0.003 & 483.53 nm \\ \hline \end{tabular}
\end{table}
Table 2: Optical constants of Ta\({}_{2}\)O\({}_{5}\) thin film for different segments.  
Figure 8: Transmission spectra of Ta\({}_{2}\)O\({}_{5}\) thin film deposited on different segments.  
Figure 9: Relative thickness of Ta\({}_{2}\)O\({}_{5}\) thin film deposited on a large substrate with a radius of 275 mm.