Study of electrochemical etch-stop for high-precision thickness control of single-crystal Si in aqueous TMAH : IPA : pyrazine solutions

In this paper, we describe a method of controlling the thickness of single-crystal Si membranes, fabricated by wet anisotropic etching in aqueous tetramethyl ammonium hydroxide (TMAH) : isopropyl alcohol (IPA) : pyrazine solutions. The Si surface of the etch-stopped microdiaphragm is extremely flat with no noticeable taper or nonuniformity. The benefits of the electrochemical etch-stop method for the etching of n epilayer-embedded p-type single-crystal Si(0 0 1) wafers in aqueous TMAH became apparent when the reproducibility of the microdiaphragm’s thickness in mass production was realized. The results indicated that the use of the electrochemical etch-stop method for the etching of Si in aqueous TMAH provided a powerful and versatile alternative process for the fabrication of high-yield Si microdiaphragms (20 ± 0.26 μm s.d). With etch-stop, the pressure sensitivity of devices fabricated on the same wafer can be controlled to within ±2.3% s.d.