A two-step wet etching process of PZT thin film with ultra-low undercut for MEMS applications

Abstract

Wet etching methods of lead zirconate titanate (PZT) film suffer from high residual risk and severe undercut erosion. In this study, a two-step etching approach replace with the traditional concept of multi-acid mixing etchant, which increases the precision of PZT film and fixes the residual issues that were difficult to avoid in the conventional scheme. The two-step etching of the PZT film's mechanism is investigated using XRD and TEM. The impact of the etchant's composition ratio on the etching effect is demonstrated, and the ideal process range and debugging direction can be accurately identified. The undercut ratio (0.62) of the etching method proposed in this study is substantially lower than that in prior studies. In addition, the etching rate and selectivity between photoresists are 60 nm/s and 1.14, respectively. The sidewall forms an inclined plane of around 30 degrees due to the crystal orientation dependent etch rates. The results of the polarization hysteresis loop demonstrate that there is no significant performance loss before and after the wet etching process. A two-step wet etching process of PZT thin film with ultra-low undercut ratio (0.62) is developed. The baseline recipe with a high etch rate, and the selectivity with photoresist is 1.14, and the sidewalls etch into an inclined plane of about 30 degrees. • A new two-step wet etching recipe for PZT film, which use different etchant to etch different phases in PZT film, obtains ultra-low undercut ratio (0.62) and does not generate residual risk, has been developed. • Experimental results have demonstrated that ultra-low undercut, high etch rate, no residual and high selectivity can be simultaneously achieved without using any special processing condition. • Etch results with different acid concentrations in different etchant, processing phenomenon analysis with XRD and TEM, and Interpretation of the etching process and comparison of ferroelectric parameters for the results before and after etching, which can be proven suitability for various etching purposes.