REAL-TIME MULTIVARIABLE CONTROL OF PECVD SILICON-NITRIDE FILM PROPERTIES

This paper reports on the application of quadrupole mass spectrometry (QMS) sensing to real-time multivariable control of film properties in a plasma-enhanced CVD silicon nitride process. Process variables beli eved to be most important to film deposition are defined (i.e., disila ne pressure, triaminosilane pressure, and de bias voltage) and their r esponses to system inputs are modeled experimentally. Then, a real-tim e controller uses this information to manipulate the process variables and hence film performance in real time during film deposition, The r elationships between gas concentrations and film performance are shown explicitly where the controller was used to drive the concentrations to constant setpoints. Also, an experiment investigating the effects o f an out-of-calibration mass flow controller demonstrates the compensa ting ability of the real-time controller, The results indicate that ii i situ sensor-based control using quadrupole mass spectrometry can sig nificantly assist in optimizing film properties, reducing drift during a run, reducing run-to-run drift, creating a better understanding of the process, and making the system tolerant to disturbances.