MgO is the oxide of magnesium. So you wouldn't get an native oxidation of MgO since it is fully oxidized already. Mg+2 O-2. However, MgO is hygroscopic. That is it will pull water out of the air. 2MgO and H2O --> 2MgOH. I suspect your wafers are pitted at the microscopic level and it looks like residue to the unaided eye. Being that you are living in Tampa, Florida, climatically a humidor, you probably need to keep your MgO wafers in a dry environment at all times. Of course it could also be that the plastic container is degassing or has contamination also. If the contamination is acidic it would pit your wafers. So would environmental contamination in your lab. Such as acidic materials left on benches or poor ventilation. Being that you are working in a university lab, it is a possibility. You could have one, two, or three of the above problems. I would contact your vendor and get advice, but I would start with this program of storage. 1. Dry box. (N2, or in a tightly fitting box with a pack of dessicant) 2. Polypropylene wafer carrier that hasn't been used in processing. Give it a mild dishwasher soap clean and thorough rinsing and rying. 3. Avoid temperature cycling. Edward H. Sebesta Independent MEMS and Semiconductor Process Engineer. -----Original Message----- From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On Behalf Of Evelyn B Sent: Saturday, February 07, 2009 9:53 AM To: General MEMS discussion; Evelyn Benabe Subject: [mems-talk] MgO Cleaning I have been using MgO wafers for some time and have noticed that if you leave them unused for a while they no longer look clean. I have tried cleaning them in an ultrasound bath using acetone and methanol but that does not remove whatever is on the surface. Since the wafers have not been processed I am assuming that what I see is oxidation on the surface and not resist. Does anyone know of a way of cleaning what seems to be a native oxide on MgO? I tried dipping the wafer on 10:1 BOE for ~ 2 minutes but that did not make a difference.