Hi Polly,
The REAL answer could be almost anything.  It really depends IF the
wafers have a correct secondary flat location.

Even though someone mentioned that after 1990 to protocol on 150mm N
type 1-0-0 wafers is the secondary at 135 degree, it has rarely been
used as most 150 mm wafers have only a single flat or a notch. I have
also seen 150mm with a secondary flat in the normal locations for
smaller diameters, even after 1990.
If the wafers are a smaller diameter, the only way to tell is to have
them tested for TYPE and Orientation.
If they are single side polished and Caustic etched on the back, the
orientation check is quite simple. Use a single bulb LED ( white, blue
or green see to work best). Point it to the center of the backside and
see what pattern you get. If it has 4  lines 90 degrees apart it is
1-0-0.    If it has 3 or 6 lines it is 1-1-1.
Type testing would need an electronic tester.
If you are planning to spend money on processing these wafers, it would
be prudent to test them.
I say this since it is NOT uncommon for Silicon Suppliers to offer
wafers out with secondary flats in the wrong location with customer
knowledge of same.  Any of this type of material that we would supply is
always clearly identified.
But it is possible that the wafers were on someone's shelf and they were
not aware of the non compliant secondary flat.

Good luck

Cheers
Ken

polly wrote:

>
>Dear Sir
>I have a query regarding the WAFER FLATS. I HAVE A WAFER WHOSE PRIMARY FLAT IS
AT AN ANGLE OF 135 DEGREE WITH SECONDARY FLAT I DONT KNOW ITS TYPE OR
ORIENTATION