Intelligent quality controllers for on-line parameter design

Parameter design methods, in general, do not take into account the common occurrence that some of the uncontrollable factors are observable for products and processes, during operation and production, respectively. This paper introduces a methodology that facilitates on-line parameter design for products and processes utilizing the extra information available about observable uncontrollable factors. Implementation of the proposed methodology leads to a quality controller that operates in two distinct modes: identification mode and on-line parameter design mode, identification mode involves establishing a model that relates quality response characteristics with significant controllable and uncontrollable variables. On-line parameter design mode involves optimization of the controllable variables with respect to desired levels of output quality parameters, with consideration to levels of the observable uncontrollable variables. A plasma etching semiconductor manufacturing process is used as a testbed for the proposed intelligent quality controllers. Results reveal that the proposed quality controllers can be used for on-line parameter design of manufacturing processes. Results also reveal that significant improvements in quality (measured in terms of average deviation of process outputs from target) over off-line parameter design approaches are to be expected in production processes with some level of control on uncontrollable variables. Even in the absence of any control on uncontrollable variables, the proposed controllers always perform better than traditional off-line robust parameter design techniques; however, the improvements may not be significant.