• A 20:1 BHF (Buffered HF) or BOE (Buffered Oxide Etch)A 20:1 BHF (Buffered HF) or BOE (Buffered Oxide Etch) etches thermal oxide at ~ 300Å /min but the etch rate for silicon nitride is only ~10Å/min! • PtilthtfSiPractical etch rates for Si 3 N 4 are achi d i h h ihieved using phosphoric acid (H 3 PO 4) @ 140-200°C.

HF with or without the addition of ammonium flouride (NH 4F). The addition of ammonium flouride creates a buffered HF solution (BHF) also called buffered oxide etch (BOE). The addition of NH 4F to HF controls the pH value and replenishes the depletion of the fluoride ions, thus maintaining stable etch rate. SiO 2 + 6HF = H 2SiF 6 + 2H 2O HF Etching The buffering agent is added to maintain a constant pH as the HF is consumed in its reaction with SiO 2: 4HF + SiO 2 => SiF 4 ([arrowdblup]) + H 2 O Since the etch rate is a function of the solution pH, BHF has a much more controlled etch rate (about 1000Å/min at room temperature) over the life of the etchant. Buffered Oxide Etch 6:1 IEN - Micro/Nano Fabrication Facility. IEN Calendar. Become a User

Wet Etching - an overview | ScienceDirect Topics

mask sufficiently against buffered HF at the excessively long etching times necessary (2 hours for a film 1200Å thick). Silicon nitride films have a reasonably fast etch rate (200-300 Å/min) in concentrated HF (48%), but it was found that the ordinary photoresist materials, as used for SiO 2, do not mask sufficiently against the concentrated HF. 'HSHQGHQFHRIZHWHWFKUDWHRQGHSRVLWLRQ annealing temperature were varied to decrease the etch rate of SiNx:H by HF solution. A low etch rate was achieved A low etch rate was achieved by increasing the SiH 4 gas flow rate or annealing temperature, or decreasing the NH 3 and N 2 gas flow rate.

Buffered Oxide Etch 6:1

+ HF The actual etch rate of the oxide is dependent on a range of factors. For example, deposited SiO 2 is etched at a much higher rate than thermally grown oxide. 4 The concentration of HF and NH F in the solution coupled with temperature also effects the etch rate as seen in the following figures. Etch rate of SiO 2