To echo and add to David's comments - first, if you go to the site and look at their FZ Silicon Offerings, all they can do is offer >200 ohm-cm material as one would expect in this business, knowing who can produce this type of product. Currently none of the Russian nor Chinese Float Zone producers can produce >5000 ohm-cm ( most are FAR lower) and none of these to date that I am aware can produce 1-0-0 orientation growth as it is much more difficult than 1-1-1. The 250 K ohm-cm may be able to be achieved in a very specialize super clean lap under optimum condition and multiple refining of the FZ, but it would be of a fluke than some that can be produced with any repeatability. When running the UniSil Float Zone division we did achieve some product > 20-30 K ohm-cm but never repeatable. > 10,000 ohm-cm is produced repeatibly and some of this product can exceed >15,000 but this is the upper limit of commercially defined Float Zone Silicon and even this is a very limited supply and quite expensive. The major problem with growing this higher res material is that the smallest levels of any contamination in or on the raw material, handling and transport mediums and the grower itself have a huge effect on the level of resistivity- While a theoretical resistivity is there- the reality of the final product is often far less than that- Given this reason- the Russian and Chinese systems, including their water and Gas systems , let alone their precleaning and handling- prevent them in the short term from achieving much over 1500 ohm-cm at the best case and since the 1-0-0 orientation is so much more difficult to get the initial structure and keep it, the combination makes it very unlikely that they can produce any higher resistivity FZ products that would be usable in MEMS applications. I cant talk to the suggestion that using thermal ox will limit the base resistivity, but I have supplied > 10,000 ohm-cm wafers with Thermal Oxide with good end results- The wafers are more susceptible to contamination selective doping in the Wafer Fab side, but just thermal treatments do not create a large change in the resistivity as long as they are clean- Just a few additional thoughts on the subject. Good luck Ken David Nemeth wrote: > First, 250 K-Ohm cm seems like an unrealistically high value. I've seen > silicon up to 12 KOhm-cm, and have used material up to 6KOhm-cm. Looking at > the web site, they don't actually seem to produce this value - it might just > be the theoretical resistivity of pure silicon with no dopants that they are > quoting. > > There are other suppliers of high-resistivity silicon, for example wacker > and topsil. > > Next, I've heard (but can't say for sure) that if you grow a thermal oxide, > the resistivity will never be higher than a few thousand ohm-cm when your > done, no matter how good it was to start. Any thermal treatment will > diffuse some impurities into the wafer, depending on the time and > temperature of the treatment. > > If you need to end up with 2000 ohm-cm, your probably fine. If you need to > end up with 6000 ohm-cm, you will need to be careful about your thermal > processing and may have problems. If you need 250000 ohm-cm, your probably > out of luck. > > > David Nemeth > Senior Process Engineer > Sophia Wireless, Inc. > 14225-C Sullyfield Circle > Chantilly, VA > Ph: (703) 961-9573 x206 > Fax:(703) 961-9576 > > -----Original Message----- > From: mems-talk-admin@memsnet.org [mailto:mems-talk-admin@memsnet.org]On > Behalf Of Fred Hussain > Sent: Monday, May 20, 2002 6:47 AM > To: mems-talk@memsnet.org > Subject: [mems-talk] Highest resistivity silicon? > > > Dear all, > > I am looking for silicon substrates which can be machined using conventional > MEMS type processes, but at the same time are highly insulating. I've found > a web page with silicon of 250Kohm-cm resistivity - > http://www.tydex.ru/materials/materials2/Si.html. > > Does anybody: > have any experience of working with such materials? > know of any issues, for example the stability of the resistivity with > temperature? > micromachined it without any major issues? > know of any suppliers? > > Thanking you in advance. > > Regards, > > Fred. > > -------------------------------------------- > Dr Fred Hussain > The Technology Partnership plc > Melbourn Science Park > Cambridge Road > Melbourn > Royston > Hertfordshire > SG8 6EE > > Tel: 01763 262626 > Fax: 01763 261582 > www.ttpgroup.com > --------------------------------------------- > _______________________________________________ > 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.mems-exchange.org/ > _______________________________________________ > 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.mems-exchange.org/ > > -- Kmbh Associates 47 Rocket Circle Rancho Cordova, CA 95742 U S A 510-714-5055 Efax- 510 217 4421 or 561 658 6136 High Purity Float Zone and Specialty CZ Silicon for Power, IR and Mirror Optics, Optoelectronics, MEMS, SOI, and other Semiconductor applications. 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