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====== Best practices for handling chips ======

Silicon wafers and quartz wafers are cut into square pieces called "chips" or "dies" or "coupons". Each chip is used as a table top for an experiment. All experimental physicists working in this field need to learn best practices for handling chips.

First, you should have your own pair of tweezers. Aven Tools sells a great pair of stainless steel, anti-acid, anti-magnetic, [[https://www.aventools.com/technik-tweezers-2a-sa|high-precision tweezers]] for about $5. They become an extension of your body. If they are dropped on the delicate end, they are ruined. Look after your tweezers well - they should last for years.

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{{::rounded_tweezers.jpg?150|}} Rounded-tip tweezers work well for handling chips.

|{{::wash_tweezers.jpg?300|}}|Like your hands, your tweezers should always be clean. Typically, a researcher will wash their tweezers at the start of each day by sonicating in acetone for 60 seconds, then spraying with IPA and DI water and then blow drying with the N2 gun.|

{{:hold_chip_on_edge.jpg?200|}} When you pick up a chip, don't let the tweezers go more than 2 mm past the edge

|{{::washing_chips.jpg?350|}}|When you wash a chip, the spray from the bottle should be hit the chip and flow towards your tweezers. Don't put the tweezers upstream of the chip. This is easier said than done because liquid will tend to flow down the tweezers onto your gloves. Experiment with a dummy chip. Transition between acetone and IPA quickly, never let the acetone evaporate before you have a chance to rinse it off with IPA. Similarly, transition between IPA and DI water quickly.|

|{{::blowing_dry.jpg?400|}}|Blow drying a chip can be tricky. Too much power and the chip flies out of your tweezers. Too little drying time and liquid remains under the tweezers. I like to support the chip on a cleanroom wipe while I blow off most of the liquid (be careful, the cleanroom wipe will flap around if you are not careful). Then I put down the chip and blow off the tweezers. Then I pick up the chip in a different spot and get any remaining liquid.|

===== Dicing wafers into pieces =====

**Danger:** Wear safety glasses when breaking silicon into pieces.

Sometimes you have to break (cleave) a whole wafer into smaller pieces. The small pieces are called dies or chips. It's helpful to have two pairs of wafer-handling tweezers for this process:

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The process works best with a silicon (1,0,0) wafer. The wafer has a flat edge to show you which way it will naturally break (along the crystal axis). Use a diamond scribe to scratch a notch on the flat edge. The depth of the notch should be about 10% of the wafer thickness. Use wafer-handling tweezers to grab the wafer on either side of the notch, then gently twist.

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After the wafer is broken down into smaller pieces you can use a different technique. Notch the silicon piece where you want the crack to start. Place the silicon piece on a glass slide (or two glass slides) so the notch lines up with the edge of the glass. Use the back end of tweezers to apply gentle pressure to either end of the silicon piece. 

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