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 CHF/sub 3//C/sub 2/F/sub 6/ gas mixture with an O/sub 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 sccm (14%) O/sub 2/ into the 137 sccm CHF/sub 3/+18 sccm C/sub 2/F/sub 6/ 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.<
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