Hi Kevin, Thanks for your comments. For my case, a little lateral nitride etch is acceptable. If I can have a rough idea about PAN etch rate for Al and nitride, then I won't worry about the lateral etch. Regards Lawrence K.P.Nichols@utwente.nl »¡¡G If the etch rate is really that important for you, you should really think about calibrating it yourself. Any numbers you're likely to have quoted to you can vary wildly depending on the exact conditions that these two layers were deposited under, and the total surface area being etched. - Kevin Nichols