Semi E135
SEMI E135 defines a test method for characterizing an RF generator's transient response — how quickly and cleanly its output power settles to a commanded setpoint after a step change, rather than its behavior once it has already reached steady state. E113, E114, and E115 together establish how a fab specifies, tests, and matches an RF power-delivery system once it is running at a fixed setpoint; none of them address what happens during the brief window right after a recipe step changes the commanded power — a window a plasma process depends on just as much as steady-state delivery, because a slow or oscillatory transient can let the plasma momentarily extinguish, overshoot into a damaging power spike, or drift off the process window before the control loop catches up.
The reason transient response needed its own dedicated test method rather than being folded into E113's general power-delivery specification is that steady-state accuracy and transient behavior are genuinely independent properties of an RF generator's control loop — a generator can hold a rock-steady setpoint once settled while still overshooting by a damaging margin or oscillating for several milliseconds every time a recipe step commands a change, and a spec sheet built entirely around steady-state numbers would never catch that. Plasma processes with frequent step changes — multi-step etch or deposition recipes, pulsed-RF schemes — spend a non-trivial fraction of their total process time in transition, not steady state, which is exactly why E135 treats the step-response window as its own measurable, standardized quantity rather than an unspecified implementation detail left to each generator vendor's control-loop design.
E135 is what gives a fab a standardized way to catch a failure mode steady-state specifications were never designed to detect — by measuring settling time, overshoot, and oscillation after a commanded step change rather than only the final accuracy once a generator has settled, it closes the gap between "this generator holds setpoint correctly" and "this generator gets to setpoint correctly," two claims E113's steady-state power-delivery specification alone cannot distinguish.