DESIGN OF A NEW SENSOR FOR MASS-FLOW CONTROLLER USING THIN-FILM TECHNOLOGY-BASED ON AN ANALYTICAL THERMAL-MODEL

Thermal mass flow controllers are widely used in the semiconductor ind ustry to deliver accurate process gas compositions and concentrations to the processing chamber. The sensor, a stainless-steel capillary tub e, is the most critical part of the mass flow controller. We have desi gned a new sensor using thin-him technology in order to improve its re liability and to decrease its response time. The two temperature senso rs are deposited platinum on an electrical insulating layer directly u pon the capillary tube (without exposure to the gas stream) whereas th e sensor is constantly heated by a resistive wire. The so-obtained sen sors are very promising and the new design and technology could give u s improvements which the old design and technology (two resistive coil s) would not have been able to give us. The physical mechanisms of thi s new sensor are described by a third-order steady-state analytical th ermal model which gives good results when compared with experiments. T his fundamental study also includes the evolution of the correction fa ctors as a function of the flow. We present here the thermal model, th e new structure of the sensor, and its advantages. (C) 1998 American V acuum Society. [S0734-2101(98)02306-9].