PLASMA PLANARIZATION FOR SENSOR APPLICATIONS

Filling trenches in silicon using phosphosilicate glass (PSG) provides many possibilities for novel device structures for sensors and actuators, This paper describes a plasma planarization technique that provides fully planarized PSG filled silicon trenches for sensor applications. The technique consists of planarizing the substrate using two photoresist layers and plasma etching-back, The lower resist layer is the AZ5214 image reversal resist, which is patterned and then thermally cured, The upper resist layer is a global HPR204 coating, The plasma etching-back is carried out using CHF3/C2F6 gas mixture with an O-2 addition. It is shown that by using the image reversal photoresist approach, fully planarized surface coating can be obtained without resorting to an additional mask, By adding 25 seem (14%) O-2 into the 137 seem CHF3 +18 seem C2F6 gas mixture, the etch rates for the photoresist and PSG can be matched, Process optimization for the two layer resist coating and plasma etching is discussed.