## 4 Results
The CT unstable DTRA, one of the causes, has been clustered after the target equipment and data collection period was extended because the occurrence rate was only 0.09%. Since it belongs to the wafer loading time, it was required to be normalized. Nevertheless, clustering was completed without normalizing. We have been able to find the solution in the definition of the wafer loading time (Equation (7)). To analyze all the time of the equipment, the system defined the time between the wafer exposure as the wafer loading time. Contrarily, there are other detailed processes between wafer loading and exposure start. The detailed processes after the actual wafer loading are not affected by the waiting time and do not require normalizing. Hence, the normalizing method has been modified. Figure 4b,c are examples of a cause that required normalizing and could classify clusters only after normalizing was completed. Three layers have similar max \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Equipment. 1** & **Equipment. 2** & **Equipment. 3** & **Equipment. 4** & **Equipment. 5** & **Equipment. 6** \\ \hline Cause 1 & 3738 & 445 & 0 & 0 & 1 & 68 \\ \hline Cause 2 & 42 & 21 & 307 & 67 & 95 & 113 \\ \hline Cause 3 & 2029 & 1475 & 652 & 435 & 1113 & 824 \\ \hline Cause 4 & 53 & 20 & 87 & 477 & 18 & 20 \\ \hline Cause 5 & 771 & 1354 & 817 & 2744 & 785 & 756 \\ \hline Cause 6 & 7853 & 1697 & 150 & 3433 & 2 & 0 \\ \hline Cause 7 & 4989 & 6925 & 6507 & 6238 & 7856 & 7891 \\ \hline Cause 8 & 94 & 384 & 9 & 13 & 2546 & 2 \\ \hline Cause 9 & 116 & 117 & 123 & 633 & 77 & 35 \\ \hline Cause 10 & 245 & 79 & 2297 & 3878 & 43 & 231 \\ \hline Cause 11 & 184 & 743 & 24 & 3902 & 6 & 2175 \\ \hline Cause 12 & 0 & 13 & 1 & 0 & 0 & 1 \\ \hline Unclassified & 276 & 286 & 206 & 282 & 86 & 114 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Cause classification result shows the frequency of occurrence by each cause. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Equipment. 1** & **Equipment. 2** & **Equipment. 3** & **Equipment. 4** & **Equipment. 5** & **Equipment. 6** \\ \hline Time-increased wafer (\%) & 23.50 & 9.94 & 8.30 & 17.45 & 7.85 & 7.39 \\ \hline Cause classification & 98.65 & 97.89 & 98.16 & 98.72 & 99.32 & 99.07 \\ ratio (\%) & 1.35 & 2.11 & 1.84 & 1.28 & 0.68 & 0.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ratio of time-increased wafers in total wafers and ratio of cause and time classification. increased time of the detailed process (Xi) and a different increased time of total process (Yi). The normalizing process of correcting the waiting time (Ti) for each layer is essential in mass production. In the case of SOSI_fallback, the probability of occurrence is only 0.9%. In addition, approximately thirty process layers have different waiting times (Ti) in mass production. Hence, the system recognizes the probability of occurrence of the cause as 0.03% and cannot complete clustering. We have been able to generalize more data by correcting the waiting time (Ti), which is characteristic of the equipment and process layer. In the future, the classification ratio of time-increased wafers is expected to be higher than the current 98.6%. \[ \begin{array}{ll}\textit{Wafer loading}&\textit{time}\\ &=\textit{previous wafer exposure end}\\ &-\textit{next wafer exposure start}\\ \end{array}  \tag{7}\]