Design of Experiments for (100) Si Vertical Wall Wet Etching Using Sonicated NaOH Solution

Silicon-based thermoelectric device fabricated using standard semiconductor manufacturing technique is a promising technology that could lead to a mass production of clean energy. The vertical wall fabrication on Si substrates is typically achieved by high cost plasma etching and involved hazardous gases. The proper wet etching condition offers an economically alternative method in obtaining vertical wall on the Si substrate. Experimental trials were conducted by design of experiments (DOE) technique to find an anisotropic wet etching condition that achieves vertical etched wall on (100) Si wafer. Three considered factors assigned to the DOE were NaOH concentration, solution temperature, and IPA addition. The response aimed for this study was not only targeting at 90° wall but also providing highest etch rate. The experimental results showed that in order to get the 90° wall, the best etching condition achieved was using 45% wt of NaOH concentration, 40°C solution temperature, and without IPA added. This condition gave an etch rate of 97.11 nm/min with surface roughness (Ra) of 10.58 nm.

Fabrication of 90° Wall of {100} Plane on (100) Si by NaOH Solution via Design of Experiments

The experimental trials were conducted by design of experiments (DOE) technique to find an anisotropic wet etching condition that achieves 90° wall angle on silicon (100) orientation wafer. Three considered factors assigned to the DOE were NaOH concentration, solution temperature, and stirring speed. The response aimed for this study was not only targeting at 90° wall but also providing highest etch rate. The experimental results showed that in order to fabricate the 90° wall angle, the best etching condition using was 30% wt NaOH concentration, 80°C solution temperature, and 300 rpm stirring speed. This condition gave an etch rate of 1245 nm/min with surface roughness (Ra) of 701.48 nm.

Terrace Formation of SrTiO3 (111) Substrates for Epitaxial Thin Film Growth with Various Etching Conditions

The optimized terrace formation of SrTiO3 (111) substrates was investigated in various etching conditions. HCl-HNO3 solution was unstable for etching the SrTiO3 (111) substrates with different surface states. It was found that etching in buffered HF (BOE) solution for 2min provides a stable etching condition for SrTiO3 (111) substrates with various surface states and etching process is an important factor for the formation of step-terrace structures. The surface degradation of SrTiO3 (111) in normal atmosphere was also observed and it is considered that the humidity is a important factor for the surface degradation.