Tetramethylammonium hydroxide (TMAH) provides a highly controllable anisotropic silicon etch with smooth etched surfaces and predictable etch rates. Engineers use TMAH to form cavities, trenches, and membranes in crystalline silicon while preserving critical device layers and surrounding structures. Thermal silicon dioxide is an effective TMAH etch mask. Thick thermal oxide grown on the wafer resists TMAH chemistry, so patterned oxide masks define cavities, diaphragms, and suspended device structures with precision. TMAH etches the cavity and preserves the device. A patterned thermal oxide mask defines the backside opening; anisotropic TMAH forms smooth 54.74° sidewalls and thins the wafer to a diaphragm while critical device layers and surrounding structures stay intact.
