Abstract Tetramethylammonium hydroxide (TMAH) is the widely used CMOS compatible anisotropic etchant in silicon wet bulk micromachining to fabricate MEMS structures. 25 wt% TMAH is commonly used because it provides the best etch selectivity between silicon and silicon dioxide with smooth etched surface morphology. If Triton X-100 is used as an additive, it results in significant decrease in the corner undercut while maintaining the good etch rate which is very useful to create mesa structures. This paper mainly focuses on the changes in etching characteristics of 0.1% Triton added 25 wt% TMAH solution when used to fabricate 380 μm deep cavities involving mesa structures in SOI wafer. We observed that the changes in etching characteristics are due to change in the concentration of etching solution which primarily arises because of loss of water content. By replenishing the etching solution with lost water content of same temperature, etching characteristics comparable to that of fresh solution have been obtained. The change in the etchant concentration during the course of etching has been studied. Further, corner undercut and etch rate of silicon have been investigated in both fresh etching solution and the solution replenished with lost water content. This study is especially useful for the control of etching characteristics like the etch rate and undercut during the fabrication of bulk-micromachined structures involving long duration of etching by replenishing the etching solution with the lost water content of same temperature at prefixed intervals of time during the course of etching to regain the etching properties of fresh solution.

中文翻译：

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在 SOI 晶片中制造具有台面结构的深腔期间，0.1% 氚添加 25 wt% TMAH 的浓度变化的影响

摘要 四甲基氢氧化铵 (TMAH) 是广泛用于硅湿体微加工制造 MEMS 结构的 CMOS 兼容各向异性蚀刻剂。通常使用 25 wt% TMAH，因为它提供了硅和二氧化硅之间的最佳蚀刻选择性，具有光滑的蚀刻表面形态。如果使用 Triton X-100 作为添加剂，它会显着减少角部底切，同时保持良好的蚀刻速率，这对于创建台面结构非常有用。本文主要研究了在 SOI 晶片中用于制造 380 μm 深的涉及台面结构的腔时，添加 0.1% Triton 的 25 wt% TMAH 溶液的蚀刻特性变化。我们观察到蚀刻特性的变化是由于蚀刻溶液浓度的变化，这主要是由于水分的损失而引起的。通过用相同温度损失的水分补充蚀刻溶液，获得了可与新鲜溶液相媲美的蚀刻特性。已经研究了蚀刻过程中蚀刻剂浓度的变化。此外，已经研究了在新鲜蚀刻溶液和补充有损失的水分的溶液中硅的角底切和蚀刻速率。