Anisotropic Etch Stop Layers - 1
• Controlling the absolute depth of an etch is often difficult,
particularly if the etch is going most of the way through a
wafer.
• Etch stop layers can be used to drastically slow the etch
rate, providing a stopping point of high absolute accuracy.
• Boron doping is most commonly used for silicon etching.
• Requirements for specific etches:
– HNA etch actually speeds up for heavier doping
– KOH etch rate reduces by 20´ for boron doping > 1020 cm-3
– NaOH etch rate reduces by 10´ for boron doping > 3 ´ 1020 cm-3
– EDP etch rate reduces by 50´ for boron doping > 7 ´ 1019 cm-3
– TMAH etch rate reduces by 10´ for boron doping > 1020 cm-3