Dear Scott,

It's quite unusual for the sapphire wafer to crack at 350C. Single crystal
sapphire should be able to withstand high temperatures such as 1500C. The
surface will form atomic steps and terraces but it won't crack. If you are
interested you can read my papers in Surface Science 565 (2004) 251 - 258,
Journal of Materials Science 39 (2004) 2911 - 2914, Diamond and Related
Materials 12 (2003) 1663 - 1669. In one case I even abrade the sapphire
substrate with diamond powder and it was still intact after reaching 850C.

My guess is that if the temperature of the sapphire wafer is raised very fast,
it may crack. Or there is uneven heating on the wafer.

If you would like to have a copy of the papers please let me know.

Kind regards,

Dr. Kim Guan Saw
School of Distance Education,
Universiti Sains Malaysia,
Minden,
11800 Penang,
Malaysia.

Fax:++604 6576000
Tel:++ 604 6534570

-----Original message-----
From: "Goodwin, Scott" [email protected]
Date: Fri, 09 Feb 2007 22:26:21 +0000
To: [email protected]
Subject: [mems-talk] thermal shock of sapphire wafers

> Hi,
>
> I recently had a 100mm sapphire wafer crack shortly after it was placed
> on a 350C PECVD platen.  From google it appears there is some increased
> risk with sapphire compared to silicon wafers.   Does anyone have some
> direct experience with handling sapphire wafers who could give me some
> pointers, or was I just unlucky?  (Is scribing a bigger problem than for
> silicon, can they handle hot plate dehydration bakes, etc)  Thanks