My background is in Materials.... If your problem is related to erosion (mechanical) and less on corrosion (electrochemical) then one of principal means to combat erosion is to focus on the strength or hardness (nearly the same). Ok, now one of most obvious parameters is the temperature. The tensile strength of aluminum will change 100 times between 350C and RT and the cryogenic properties of aluminum are very good..... So the rule would be to consider your process and try to do everything you can do to keep the temperature down, chill plate, pulse the ion gun, or stage the process with intermediate cool down steps. Maintain good thermal control to maintain high hardness and erosion resistance for long life. The second consideration for a strength increase is to alloy it (metallurgists just love this stuff). The tensile strength of high purity fully annealed aluminum is about 1.5 ksi...where as commercial high strength aluminum can exceed 80-100 ksi. Alloying additions of one to several percent can produce significant effects to the mechanical strength. Realizing we are talking about a sputter deposit material, common sputter materials like Cr and Cu have limited solubility in aluminum but can change the strength to an "engineering" value. One to two weight percent could make a major difference. Other "contaminants" like Si, Zn, Mn and Mg also can be used. The difference in the atomic radii D=(rx -ral)% can be used to judge the effect of solid solution strengthening of high purity aluminum. The D for Si -3.8; Zn -6.0; Cu -10.7; Mn -11.3 and Mg is +11.8. These produce a relative increase in tensile strength per wt% of alloy addition of 5.7, 2.2, 6.3, 7.8 and 7.3 respectively. Therefore a process that adds 2 wt% Cu will change the strength nearly 15%. Less practical approaches to aluminum strengthening are grain refinement, precipitation hardening and cold work....like I said less practicable. I have sputtered using contaminated targets and ended up with several % contaminant levels in the deposit. Good luck and let us know how your experiments turn out...MEMS tribology is an interest to me. Rob -----Original Message----- From: mems-talk-admin@memsnet.org [mailto:mems-talk-admin@memsnet.org]On Behalf Of Nicholas Jankowski Sent: Monday, June 17, 2002 9:09 PM To: mems-talk@memsnet.org Subject: [mems-talk] Thermal growth rates of Aluminum Oxide New to the list. I searched through the archives and didn't find this question, but if its there and anyone can point me to the thread I'd be obliged. Anyway, here we go: Performing some relatively deep RIE of SiO2 using an aluminum mask. Problem is that mask is eroding more than we'd like (it's not sacrificial), even after trying to tweak the recipe. What we are looking at now are ways to 'harden' this aluminum mask such that the unwanted milling will be reduced. The mask is only 15m thick (not negotiable), and we need the majority of the mask to remain aluminum for functionality after processing. What we had in mind was enhancing the oxidation of the aluminum, making for a thicker Al2O3 layer at the top of the metal than the normal native oxide. Even though it is likely to still be milled away, the thicker oxide should last longer and result in less overall aluminum milling. Not sure on thickness requirements, as I don't quite know the etch selectivity between Al2O3 and Al, but the normal process is currently milling away about 30-40% of the thickness, so we'd probably want to find the optimum somewhere between the native 2.5nm and 250nm. Here's the problem: I've been hunting through the literature trying to find something for Aluminum like the SiO2 oxidation curves that I could find in 5 minutes if I needed to. Basically, I need to know aluminum oxide thickness as a function of time _at elevated temperatures_, and so far I've been coming up short. Would anyone out there be able to point me to the appropriate reference, or at least in the right direction? Also, I've seen that plasma oxidation could be another option instead of thermal oxidation, and possibly a better one since it wouldn't require temperatures as high, and we could keep the wafer in the closed system for both processes. Any advice on this would be greatly appreciated as well. If providing more info would be helpful, I'd be happy to do so. Thanks. _______________________________________________ MEMS-talk@memsnet.org mailing list: to unsubscribe or change your list options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk Hosted by the MEMS Exchange, providers of MEMS processing services. Visit us at http://www.memsnet.org/