# Mathies:Glass Etching in BNC

## Glass Etching in BNC

Safety first

Any handling or use of hydrofluoric acid requires full safety gear. Wear a protective apron, chem-resistant gloves, and face shield. Be aware of the hazards related to HF and the proper response for any spills (especially on skin or clothing).

## Types of glass

Borofloat (Pyrex)

## Etching Protocol

1. Before etching any glass wafer, remove the back side silicon first. If you will have features on both sides of your wafer, then you should go to the microlab and follow the microlab etching protocol. Pinhole defects may appear even if the wafer is coated a-Si on the back side.

2. Etching with 49% HF: This should be done in the insert tank in sink 162. Make sure to fill the tank with enough acid to entirely cover your cassette and wafers, and gently agitate throughout the etch. Also fill up another tank with water for after etch rinsing.

3. Etching with 1:1:2 HF:HCl:H2O or 5:1 buffered HF: The 5:1 buffered HF etch can be done in the insert tank in sink 162. Please go to microlab if you want to set up an agitation tank using the a polypropylene tank, two polypropylene cassete-support blocks, and a teflon-coated stirbar. For the slower etches (which may run longer than 30 minutes or an hour), this is much simpler than agitating by hand. Note: If you use a thick photoresist (eg AZ4620), you may add 0.2% surfactant (3M Novec 4200 Electronic Surfactant) in the buffered HF.

## Etch Rate

Borofloat

   * 49% HF = 5-7 um/min
* 5:1 buffered HF = 2-3 um/hr
* 1:1:2 HF:HCl:H20 = too slow to measure


## Reuse HF

Please save HF by reusing the same etching. After rinsing the aspirator, put the empty HF bottle at the lower end and remove HF from the insert tank. Beware that HF might spill if the HF bottle were not secured. HF can be used for a few times until the etching rate goes below 5um/min.