A Process Control Methodology Applied to Manufacturing GaAs MMIC ’ s

A methodology for guiding process-driven manufacturing organizations in instituting process control on a facility-wide basis is proposed. The methodology begins with a definition of the customer’s expectations and of the manufacturing process used to meet these expectations. The output, of a given process or subprocess must reach four progressive levels of control. When the output can be reliably measured, it is considered measureable. The second level is reached when this output, viewed in aggregate and over time, is found to be predictable. When the distribution of outputs is centered within the spec limits and a “sufficient” fraction of the output lies within the spec limits, the process is considered acceptable. Finally, when the process, as it is currently operated, is fully documented and operator technique is passed on through training, the process reaches the fourth and final level of control, recoverable. An application of this methodology to the control of submicron gate lithography on a GaAs monolithic microwave integrated circuits (MMIC) process at Hewlett-Packard’s Microwave Technology Division is discussed.