Substrate containing aperture and methods of forming the same

A method of forming an aperture within a substrate, the method comprising:

• providing the substrate;
• irradiating the substrate with a laser beam to form a laser-machined feature within the substrate, the laser-machined feature having a sidewall;
• etching the sidewall to change at least one characteristic of the laser-machined feature, wherein the etching includes:
• etching the sidewall with a first etchant solution containing a first reactant at a first concentration;
• and
• after etching the sidewall with the first etchant solution, etching the sidewall with a second etchant solution containing the first reactant at a second concentration less than the first concentration, wherein the second etchant solution is treated to reduce an etch initiation period of the second etchant solution before etching the sidewall with the second etchant solution.