Wafer Handling Procedures

Wafer Handling Procedures

Manual wafer transfer using tweezers:

1. Obtain tweezers.

Make sure they are made of the appropriate material for your process.
Make sure they are decontaminated to the appropriate level of cleanliness for your process (see tweezer clean procedures on the SNF website.

2. Obtain an empty receiver cassette.

Receiver cassette is the one which you are going to transfer wafers into.
The donor cassette contains the wafers to be transferred.

3. Place the cassettes next to each other, with their H-bars facing the same direction.

By convention, the backside of the wafers (the dull, unpatterned side) should face the H-bar.
If you are right-handed, it is recommended to orient the cassettes so the H-bar is to the right (the wafers face left, making them easier to see while transferring.)

4. Using your tweezers:

From the donor cassette, grab a wafer at its edge. Ensure the tweezer grips do not touch any device areas, but place them far enough in to get a good handle on the wafer. This is typically about 3-4 mm from the edge. If you are using metal (or teflon-coated metal) tweezers, they will usually have convenient metal prongs, or "stops" which help guide placement of the grips.
Lift the wafer straight up and out of the cassette. Movement should be smooth and silent; avoid scraping your wafer along the sides of the cassette slot, as this generates particles.
Place the wafer into the receiver cassette. Movement should be smooth and scraping should be avoided. Ensure the wafer is not "cross-slotted." (Improperly slotted wafers cannot be picked up by automated equipment and can lead to breakage.)
Where possible, start the transfer of the donor cassette from BACK to FRONT. Where possible, place the wafers into the receiver cassette from FRONT to BACK. Working the donor and receiver cassettes in this way helps avoid scratching the front side of a wafer by the wafer being moved.
It is good practice (and helps to minimize contamination) if you place the cassettes in such a way that you can avoid working over the wafers.

"Flip Transfer" of wafers:

1. Obtain an empty receiver cassette.

Make sure it is the appropriate kind and level of cleanliness for your process.
Make sure you are wearing clean vinyl gloves.

2. Place the receiver cassette upside down over the donor cassette.

The protruding pins should mate with the alignment holes on both sides of the cassettes.

3. Grasp both cassettes in both hands and "flip" the donor cassette upside down onto the receiver cassette. Make sure you have a firm grip on both cassettes and that they are properly aligned and mated; otherwise, you risk dropping (and thus damaging) all your wafers.

4. Your wafers have now been transferred.

_______________________________________________________________
Stanford Nanofabrication Facility
Last Modified 08/29/2003