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Glass Etch Wet ProcessINRF application note
Process name: GLASSETCH
Mark Bachman
Summer 2000
OverviewThis process describes a wet etch for glass with a
resulting smooth surface. HF-based etchesusually result in rough
surfaces, but this recipe provides a smooth surface. The etch
quality isalso a function of glass quality. This is a level-1
process and requires basic INRF safetycertification. The use of
dangerous chemicals requires that the user may not perform
theprocess alone.
Time neededApproximately 1 hour for 60 m etch.
Materials neededo Buffered HF (5 ml)o Hydrochloric acid (9.25
ml)o Water (85 ml)o Plastic beakero Neoprene gloveso Hot plate with
stirring rod, if buffered HF unavailableo Ammonium fluoride (NH 4
F) crystals (40 g), if buffered HF unavailableo Hydrogen fluoride,
49%, (10 ml), if buffered HD is unavailable
PreparationThe buffered HF mixture is a dangerous chemical and
protective gear must be worn whenusing it, in particular, neoprene
gloves and eye protection must be worn . Don protective gearand
work only in the fume hood devoted to acid work.
If a buffered HF mixture is not available, you can prepare a
fresh mixture in the followingmanner. Measure 40 g of NH 4F
crystals in a glass container. Add 60 ml DI water and stir. Youmay
need to heat the solution on a hotplate to get the ammonium
fluoride mixture to dissolve.The solution will appear clear when
ready. Transfer ammonium fluoride solution to apolypropylene or
Teflon container. Carefully add 10 ml of 49% hydrofluoric acid (HF)
to thesolution. Label the container Buffered HF etchantextremely
dangerous!, then add yourname, the date, and a target organs
sticker.
To create your glass etching solution, put 85 ml DI water in a
polypropylene or Tefloncontainer. Add 5 ml of buffered HF to the
water. Add 9-10 ml of HCl to the solution. Stir with aplastic
stirrer.
ProcedureMake sure the glass to etch has a hard resist mask
patterned on it such that desired etchregions are exposed, and that
the backside is protected. Many researchers pattern a metalmask on
the glass before etching, but an extra hard bake of resist can
sometimes be usedeffectively. For a photoresist mask, a hard bake
(130 C for 45 min) is recommended to makesure the resist firmly
adheres to the glass.
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Glass Etch ProcessChecklist
o Hard bake resist pattern on glass. 130 C for 45 minutes.
o Wear neoprene gloves. Do not breather HF vapors.
o If buffered HF unavailable, prepare buffered solution:60 ml DI
water40 g NH 4F crystals10 ml 49% HF
o Prepare glass etching solution:85 ml DI water in a
polypropylene or Teflon container.
5 ml of buffered HF9-10 ml of Stir with a plastic stirrer
o Etch glass in solution at room temperature. Approximately 1
m/min.
o Dispose etchant in labeled waste bottle.
o Rinse DI. Blow dry.
o Remove resist in warm acetone bath. Agitate or use ultrasound
if necessary.
o Rinse DI. Blow dry.
