Try this
1       Put the wafer on a piece of paper
2       Scratch the edge where you want the break with a diamond scriber
3       Lift one end of the paper and the slight curvature will cause the crack
to propagate along a nearby plane.
Not the most accurate of ways, mainly because of hand-eye coordination but...
The advantage of this is that you don't have to align the blade with the plane.
As Michael says - it gets easier with practice.  When I started working with
thin wafers, all I had to do was look at them and they would shatter ;-)

        -----Original Message-----
        From:   Michael Barger [SMTP:[email protected]]
        Sent:   Monday, April 21, 2003 11:17 AM
        To:     General MEMS discussion
        Subject:        RE: [mems-talk] cleaving of ultra-thin Si wafers

        Dr. Broitman,

        I don't know if you have been helped, yet, but I used a fairly crude
method
        on thicker silicon wafers. I used an Exacto knife blade that had a
curved
        tip. I placed the wafer on a very flat surface. I then placed the knife
        blade next to the edge of the wafer, aligned with the (100) cleavage
plane.
        I then rocked the blade onto the edge of the wafer. A crack would start
at
        the edge and progress across the wafer, producing a very clean break.
This
        process did not work every time, but seemed to improve with practice.

        I did not have any success with scribing or dicing. Scribing generated a
        multitude of defects that caused cracks to radiate in all directions.
Dicing
        tore the wafer creating a lot of damage.

        I hope this helps.

        Regards,

        Mike Barger


        -----Original Message-----
        From: [email protected]
        [mailto:[email protected]]On Behalf Of Mario Robles
        Sent: Thursday, April 17, 2003 3:51 PM
        To: 'General MEMS discussion'
        Subject: RE: [mems-talk] cleaving of ultra-thin Si wafers


        Hello,

        It sounds like you have tried a "scribe and break" process. This is when
        you use a diamond tip to scribe the top surface of the silicon then
        apply pressure on the backside to break the cleave mark. It could be
        that the wafer is too stressed and not able to break properly.

        How is the wafer thinned to the 30µm thickness? The thinning process is
        critical to reduce the stress of the wafer. I would guess it was ground
        then lapped or polished.

        You can also use a dicing saw to cut he wafer to final substrate or die
        size. This uses a diamond blade to cut through the wafer, which is
        mounted on an adhesive tape or could be waxed onto another silicon wafer
        for better support.  You can choose the blades specification to achieve
        the best cut quality.

        If you like I can supply you with the names of companies that perform
        dicing, grinding and scribing services.  They could perform some test
        cuts to show you the results. Or if you are looking to cut your wafers
        in house I can also point you in the right direction. You can then
        decide what your best option is.

        Thank you,

        Mario Robles

        Tanaka Systems, Inc.
        2577 Leghorn Street
        Mountain View, CA 94043

        650-966-8001 ofc
        650-966-1881 fax
        www.dicingblades.com



        -----Original Message-----
        From: [email protected]
        [mailto:[email protected]] On Behalf Of Esteban Broitman
        Sent: Tuesday, April 15, 2003 8:57 AM
        To: [email protected]
        Subject: [mems-talk] cleaving of ultra-thin Si wafers

        Does anybody know how to "cleave" ultra thin Si wafers?
        I need to cut, from ultra-thin (30 microns) Si wafers, substrates of ~
        10 x 20 mm. I tried to use different kind of diamonds, but I always have
        the same problem: the substrate is not more "flexible", if I try to bent
        it, it cracks in many parts. I suspect that I am generating defects
        during the cutting of the substrates that propagate during the bending.
        Any suggestion?.
        Thanks for the reply to my e-mail: [email protected]
        E. Broitman
        ----------------------------------
        Dr. Esteban Broitman
        Senior Research Associate
        Department of Chemical Engineering
        Carnegie Mellon University
        Pittsburgh,  PA 15213
        Phone: (412) 268-9537
        FAX: (412) 268-7139
        ----------------------------------


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