# What's the simplest way to etch Nickel and Chromium sputtered layers?

I have to etch a very thin film (50 nm) of Nickel ($\ce{Ni}$) on a 100 nm $\ce{SiO2}$/$\ce{Si}$ substrate. Additionally, there is a ~5 nm adhesion layer of $\ce{Cr}$ under the $\ce{Ni}$ that I'd also like to etch.

So I found this page which has a fairly long list of etches for $\ce{Ni}$ and $\ce{Cr}$.

Ni:

1 : 1 : 1 - HNO3 : HAc : Acetone
1 : 1 - HF : HNO3
30% FeCl3
3 : 1 : 5 : 1 - HNO3 : H2SO4 : HAc : H2O 85 C 10 microns/min
3 : 7 - HNO3 : H2O
1 : 1 - HNO3 : HAc
10% g/ml Ce(NH4)2(NO3)6 : H2O
HF, concentrated – slow etchant
H3PO4 – slow etchants
HNO3 – rapid etchant
HF : HNO3 – etch rate determined by ratio, the greater the amount of HF the slower the reaction
4 : 1 - HCl : HNO3 – increase HNO3 concentration increases etch rate
30% FeCl3
5g : 1ml : 150ml - 2NH4NO3.Ce(NO3)3.4(H2O) : HNO3 : H2O – decreasing HNO3 amount increases the etch rate
3 : 3 : 1 : 1 - H3PO4 : HNO3 : CH3COOH : H2O ~15min/micron @ RT with air exposure every 15 seconds


Cr:

2 : 3 : 12 KMnO4 : NaOH : H2O
3 : 1 H2O : H2O2
concentrated and dilute HCl
3 : 1 HCl : H2O2
2 : 1 FeCl : HCl
Cyantek CR-7s (Perchloric based) 7 min/micron (24A/s new)
1 : 1 HCl : glycerine 12min/micron after depassivation
1 : 3 [50gNaOH+100mlH2O] : [30g K3Fe(CN)6+100mlH2O] 1hr/micron

I'd really like to avoid HF if I can (it terrifies me!), but I have pretty much everything else at my disposal.

So far, everything I've done has been at room temperature.

First I tried concentrated $\ce{FeCl3}$. No bubbling or signs of anything after ~20min.

Then I tried weak $\ce{H3PO4}$. Nothing.

Today I tried strong (98%) $\ce{H3PO4}$, nothing.

Then I tried concentrated fuming $\ce{HNO3}$. Nothing after ~1hr.

Then I tried about 1:1 $\ce{HNO3}$:$\ce{HCl}$, nothing.

Am I missing something here? Do the solutions need to be heated up or something?

• I don't know the exact chemistry, but nickel actually etches better in dilute nitric acid than concentrated. Many commercial etchants are just ~15% nitric acid in water with a bit of surfactant added. Heating typically increases the etch rate, but dilute nitric acid should still give you 3 or 4 nm/s at room temperature. – Michael DM Dryden May 27 '15 at 18:26
• @MichaelD.M.Dryden, huh, strange. Very counterintuitive to my 8th grade level knowledge of chemistry. I'll try that. Now that you mention it, several of those recipes above call for DI H2O in addition to the acids. I kind of assumed they were actually slowing down the rate, but maybe they're necessary. – YungHummmma May 27 '15 at 19:40

Nickel can be etched using diluted (1:1 V) $HCl$. 50 nm will be dissolved within seconds.
The etching solution for the chromium layer contains $\ce{Ce(NH4)2(NO3)6}$+$\ce{CH3COOH}$+$\ce{H2O}$ in ratio 165g : 45 ml (con.) :100 ml DI water. The chromium layer is dissolved within 5 minutes of etching.