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Optimal parameter estimation for the online control of ion milling etch depth
Author(s) -
Klein Eric J.,
Ramirez W. Fred
Publication year - 2002
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690480215
Subject(s) - photoresist , materials science , kalman filter , etch pit density , etching (microfabrication) , process (computing) , layer (electronics) , control theory (sociology) , optics , computer science , composite material , physics , control (management) , artificial intelligence , operating system
The use of optimal parameter estimation for the online regulation of final etch depth in an ion milling process is described. A model‐based control system utilizes a 3‐D surface evolution model to predict dynamic surface profiles and etch depth. A heterodyne laser interferometer is used to measure trench height in situ for calculation of the difference in etch rates between the photoresist layer and the exposed portion of the underlying substrate layer. Adaptive material‐specific etch rate parameters and operating parameters such as ion beam strength and angle of incidence are estimated optimally with an extended Kalman filter. Optimal estimates of the in situ etch depth are calculated from the adaptive model, allowing the stopping time of the milling process to be varied from run to run to regulate final etch depth in the presence of disturbances. The system installed on an ion milling machine shows that the controller is capable of accurately regulating final etch depth in the presence of large process faults.