Cleaning and Baking of Si Sensors

Objectives: Remove organic contaminants

Clean off dirt such as Si chips

Remove water (including water from cleaning)

Important General Comments

 

Make sure that at ALL times you are absolutely certain which sensor is which! There are NO identifying marks on them.

Make sure that everything is clean.

Always store used sieves in the clean acetone box

Make sure never to touch anything (sensors (especially!), outside of gloves, sieves, inside of clean acetone container, etc) with bare hands.

Before using gloves to touch sensors and/or sieves, clean them in dirty acetone container.

Make sure that sensors are lint and dirt free before baking them, otherwise things can be baked into the surface.

Sensors should be stored immediately in dessicator after baking

Try to work on clean surfaces, ideally covered with clean tissue, especially the place you put down the clean sieves.

Make sure you have everything in place before starting the cleaning procedure,

Tool List

Two baths of acetone, one of which is kept clean (used only for sieves with sensors).

One cleaned sieve for each sensor.

Vacuum jig for gelpacks and vacuum pen with pumps.

One glove.

Plastic tool to lift sensors.

Full bottle of deionized water.

One cleaned glass disk for each sensor.

Rubber air bulb.

Cleaning Procedure

 

  1. Have sensors ready, removed in their gelpacks from clean room.
  2. Put on one glove and keep the other hand uncovered. Use the uncovered hand for uncleaned items (vacuum pen, gelpacks, etc).
  3. The fume hood should be on with the clean acetone bath open. Have sieves arranged on the clean surface.
  4. Have a clear diagram showing which sensor will go in which sieve and in what order the sieves will go into the acetone bath.
  5. Put gelpack on vacuum jig and use vacuum pen to place sensor in a sieve. Repeat for all sensors. Pay close attention that you are putting sensors in correct sieves.
  6. Stack sieves on top of each other in the correct order. Make sure they fit together securely.
  7. Immerse stacked sieves slowly into clean acetone bath. The sensors tend to float and may hit the bottom of the sieves above if you dunk them too quickly. Cover the bath to limit acetone evaporation.
  8. Leave sieves in the bath for about 15 minutes, carefully moving them a bit every 5 minutes or so to circulate the acetone around the sensors.
  9. Now, the hard part, removing the sensors, rinsing with deionized water and placing in glass trays in the oven.
  10. The tool used to help lift the sensors is a plastic rod with a small plastic brush at the end, normally stored in the small plastic container marked "acetone". Use this tool to raise the edge of the sensor and grab it firmly with your gloved hand. The sensor surface can be scratched if it slides between your fingers. Avoid touching the surface of the sensor with the tool. Work the tool under the sensor using the holes in the bottom of the sieve.
  11. Quickly start spraying the sensor with deionized water. You will use 1/3 to ¼ of the bottle per sensor. The acetone may leave residue as it evaporates so it’s important to start spraying quickly. Make sure you hit the whole surface, front and back.
  12. To rinse the part of the sensor, you are holding, you need to move your hand. Either put the edge of the sensor on a clean surface or transfer it by grabbing with the vacuum pen.
  13. After thorough rinsing, blow off as much water as possible (front and back surfaces) using the rubber airbulb.
  14. Attach the vacuum pen to the sensor, release it from your hand, and gently lower it into the glass dish. This must be done carefully because it is a close fit. You can blow off additional water from the top surface of the sensor. Be careful because the sensor is light and can fly.
  15. Stop and make sure you know for certain which sensor is in which dish!
  16. Move glass dishes to oven. Again, have a clear drawing and work slowly so you keep track of which dish is which.
  17. Bake sensors for 1 hour at 125° C. Minimum ramping up and down time should be 15 minutes. Read the manual for instructions on programming the oven if it has lost the standard sensor schedule. When the oven is cooling, it helps to open the air vents on top of the oven but be careful because they get very hot.
  18. Make sure the glass dishes are at most slightly lukewarm before placing the sensors back in their gelpacks. As always, work carefully to keep track of which sensor is which.
  19. Put everything away so that it all stays clean.