Thanks dude. The JMEMSetchrates i tried, it did not work. I am thinking of using Nh4oh:H202:H20. Btw, does pyrex or glass be handled @ 80C which they have specified

As I know, pyrophosphoric acid react to sapphire at elevated temperatures (about 100C). So, I think, you may use it to etch your samples. Although, in this case the surface possibly will be contaminated by phosphorus compounds

How much you actually want to remove?

I want to remove the whole 500 microns, because i want to create a free hanging film!

I tried etching with Nh4Oh: H202: DI water @ 80 C. this also does not work. To add bromine with any Metal oxide such as KoH also is difficult, as i don't have access to Bromine solution in singapore. Is there any other way to get rid of the sapphire. I don't want to use acids because i am trying to make a free hanging film of Metals.

i don't think you can etch 500 microns of a single crystal of sapphire and be selective with respect to your free hanging film. what material is your free hanging film? Perhaps you can look for epitaxial thin films of sapphire on other substrates, and etch the supporting substrate. You might be able to obtain something like that using a collaboration with an institution that has made that before.

Alternatively, you can bond it to some other substrate and use polishing to reduce the Al2O3 thickness to perhaps 10 microns.

Dear Douwe Monsma: Thanks for your response. I tried the etchants specified in some university Micromachining center webpage. It did not work. Right now i am trying to drill the sapphire using Laser processing leaving few microns of sapphire (around 5), then etch the same. I am achieveing a surface roughness of ~ 1 Um. still working on it to improve the process. I have Cu/Nb films on the sapphire substrate, which i want to make it free hanging! So using acids is nearly impossible!!

why do you use sapphire substrate, are you trying to get epitaxial Cu/Nb? If not, then there are many much easier free standing film methods

I already have grown epitaxial Cu/Nb single crystal thin films on the sapphire. So i want to use those samples.

what are the thicknesses of the cu and nb? and which layer is first on the al2o3?

you should definitely read this book, it tells you everything about etching

Thin Film Processes by John L. Vossen, Werner Kern

and look at the company Transene.com, and perhaps email them

perhaps it is better that you peel the film. if you have deposited copper first, then the adhesion to the al2o3 should be pretty poor. What you can do is epitaxial lift off. look it up in the literature. In the simplest case you could put scotch tape on the metal film, and remove the metal film, then place it onto something else with a hole (etched silicon for example), and you have a free standing film. If scotch tape doesnt stick enough, you can use some mylar or so, and epoxy it to the metal top surface. the epoxy is easy to remove with etchants that don't attack the metals.

Thanks Douwe for your great ideas, really appreciate that. I have never thought in your lines. Ya, i will give it a thought of peeling the films and placing it. I succeeded in making a thru hole in sapphire using laser drilling. Even did a blind hole with 10 microns left. the average surfcae roughness arnd 1u but Rz is arnd 3u. But i will try to work on your lines. The overall thickness of my film arnd 3u with Cu/nb of 20 nm each.

The first layer is actually Nb which is sitting on the sapphire.

ah, the niobium adhesion may be too good for easy lifting off the whole film. Have you tested to scrape off a little of the film to see how well it sticks? e.g. removal test with scotch tape, nail scratch, metal tweezer scratch, does it survive all?

I have not tried any of these lift off techniques which you have suggested. I will do it the following week and update, how it goes.

oh i guess niobium adheres too good to al2o3 to do lift off, check http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.79.5062

Extraordinary Adhesion of Niobium on Sapphire Substrates

Phys. Rev. Lett. 79, 5062 – Published 22 December 1997

G. Song, A. Remhof, K. Theis-Bröhl, and H. Zabel

Hi Karthic,

The standard etchant for sapphire is the mixture of H2SO4 and H3PO4. The temperature can be set between 200-270C so that the etching rate can be well controlled. But be careful: the hot mixture is very corrosive. Handle with care. For details, check my RG page for several publications on this topic.

Best,

Yang

What is the best gas mixture to etch sapphire using ICP?