This dissertation presents performance improvement of a wet etching system by the megasonic agitation. For the fabrication of MEMS devices, it is essential that the etched surface of silicon or glass is smooth and defect-free with high dimensional uniformity. In this dissertation, we have proposed, designed and developed the wet etching system with the megasonic agitation for improving the characteristics of wet etching. The proposed wet etching system consists of etch bath module, circulation bath module, transfer module and control module. To adopt the megasonic energy into the wet etching, we have proposed the megasonic agitated module and accomplished the performance tests. To transfer the megasonic energy into the wafer without distortion effectively, the thickness of alumina for the megasonic agitated module (MAM) has been selected. The characteristics of the megasonic agiated module have been performed by measuring the impedance and the acoustic power. The proposed wet etching system has been designed and fabricated for improving the etching characteristics, namely, the etch uniformity, the etch rate, the surface roughness, and defect-free surface, by the megasonic agitation.
At first, the characteristics of the wet etching system were evaluated by the anisotropic wet etching of (100) Si in KOH solution under various process conditions, namely the etching time, the megasonic power, and the temperature of the solution. In addition, the performance tests have been performed with the glass wafer and the (110) Si.
Eventually, the megasonic energy from MAM improved the roughness and uniformity of the etched surface remarkably. Here, we suggests the best way to maintain the original surface roughness with MAM during the etching process. The results confirmed that the megasonic agitation is an effective way to improve the etching characteristics, such as the etch rate, etch uniformity and surface roughness, and that the wet etching system is suitable for the fabrication of devices with complex structures.
