I don't think there is a wafer that is that thin out in the market. However, you can try to detach a thin silicon layer from a SOI wafer simply by etching out the buried oxide layer. Refer to Khang et al. Science v311 p208 (2006).

I know that Si-Mat is selling such thin wafers. Here is the link: http://si-mat.com/silicon-wafers.html

At Universitywafer you can even buy 5µm thin wafers: http://www.universitywafer.com/Wafers_Services/Super-Thin_Silicon_Wafers/super-thin_silicon_wafers.html

We are working with such thin wafers and normally they have a thick surrounding and are thin in the middle. This makes the handling much easier.

thanks guys. I'm more interested in fabrication technology.