Highly Selective Etching of Silicon Dioxide Over Aluminum Using Mixtures of Sulfuric Acid and Hydrofluoric Acid

This paper introduces a novel and simple etching technique that utilizes a mixture of sulfuric acid (H
$_{\mathbf{2}}$
SO
$_{\mathbf{4}}$
) and hydrofluoric acid (HF). This method selectively etches silicon dioxide (SiO
$_{\mathbf{2}}$
) over aluminum (Al) in Micro-Electro-Mechanical Systems (MEMS) fabrication, offering an alternative to traditional methods that often damage Al or require expensive setups. Here, we employ H
$_{\mathbf{2}}$
SO
$_{\mathbf{4}}$
’s hygroscopic properties to effectively dehydrate HF, reducing water content and limiting fluoride ion generation, which is the cause for Al etching during SiO
$_{\mathbf{2}}$
etching. Experimental results demonstrate an exceptional selectivity ratio exceeding 130,000:1 for SiO
$_{\mathbf{2}}$
over Al, confirming the method’s precision and the preservation of Al’s integrity. The etching technique preserves the electrical and mechanical properties of Al films, even after extended exposure to the etchant, and demonstrates its effectiveness in the practical fabrication of back-end-of-line (BEOL) micro-electromechanical switches. By utilizing readily available chemicals, the proposed etching method enhances economic feasibility and accessibility, demonstrating significant advancements in MEMS fabrication. The reliability and cost-effectiveness offer a promising solution for integrating microscale structures composed of Al without compromising device performance. 2024-0115