A process control methodology applied to sub-micron gate lithography in manufacturing GaAs MMICs

A methodology for guiding the pursuit of process control at Hewlett-Packard´s Microwave Technology Division is presented. 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 measurable. 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 in a GaAs MMIC process is discussed. The unexpectedly broad organizational implications of developing and instituting this methodology are briefly described