TY - JOUR
T1 - Regression Methods for Virtual Metrology of Layer Thickness in Chemical Vapor Deposition
AU - Purwins, Hendrik
AU - Barak, Bernd
AU - Nagi, Ahmed
AU - Engel, Reiner
AU - Höckele, Uwe
AU - Kyek, Andreas
AU - Cherla, Srikanth
AU - Lenz, Benjamin
AU - Pfeifer, Günter
AU - Weinzierl, Kurt
PY - 2014/2
Y1 - 2014/2
N2 - The quality of wafer production in semiconductor manufacturing cannot always be monitored by a costly physical measurement. Instead of measuring a quantity directly, it can be predicted by a regression method (Virtual Metrology). In this paper, a survey on regression methods is given to predict average Silicon Nitride cap layer thickness for the Plasma Enhanced Chemical Vapor Deposition (PECVD) dual-layer metal passivation stack process. Process and production equipment Fault Detection and Classification (FDC) data are used as predictor variables. Various variable sets are compared: one most predictive variable alone, the 3 most predictive variables, an expert selection, and full set. The following regression methods are compared: Simple Linear Regression, Multiple Linear Regression, Partial Least Square Regression, and Ridge Linear Regression utilizing the Partial Least Square Estimate algorithm, and Support Vector Regression (SVR). On a test set, SVR outperforms the other methods by a large margin, being more robust towards changes in the production conditions. The method performs better on high-dimensional multivariate input data than on the most predictive variables alone. Process expert knowledge used for a priori variable selection further enhances the performance slightly. The results confirm earlier findings that Virtual Metrology can benefit from the robustness of SVR, an adaptive generic method that performs well even if no process knowledge is applied. However, the integration of process expertise into the method improves the performance once more.
AB - The quality of wafer production in semiconductor manufacturing cannot always be monitored by a costly physical measurement. Instead of measuring a quantity directly, it can be predicted by a regression method (Virtual Metrology). In this paper, a survey on regression methods is given to predict average Silicon Nitride cap layer thickness for the Plasma Enhanced Chemical Vapor Deposition (PECVD) dual-layer metal passivation stack process. Process and production equipment Fault Detection and Classification (FDC) data are used as predictor variables. Various variable sets are compared: one most predictive variable alone, the 3 most predictive variables, an expert selection, and full set. The following regression methods are compared: Simple Linear Regression, Multiple Linear Regression, Partial Least Square Regression, and Ridge Linear Regression utilizing the Partial Least Square Estimate algorithm, and Support Vector Regression (SVR). On a test set, SVR outperforms the other methods by a large margin, being more robust towards changes in the production conditions. The method performs better on high-dimensional multivariate input data than on the most predictive variables alone. Process expert knowledge used for a priori variable selection further enhances the performance slightly. The results confirm earlier findings that Virtual Metrology can benefit from the robustness of SVR, an adaptive generic method that performs well even if no process knowledge is applied. However, the integration of process expertise into the method improves the performance once more.
KW - Regression analysis
KW - semiconductor device measurement
KW - silicon semiconductors
U2 - 10.1109/TMECH.2013.2273435
DO - 10.1109/TMECH.2013.2273435
M3 - Journal article
SN - 1083-4435
VL - 19
SP - 1
EP - 8
JO - I E E E - A S M E Transactions on Mechatronics
JF - I E E E - A S M E Transactions on Mechatronics
IS - 1
ER -