Preparations
- Remove any obstacles that might come in your way
- Prepare the tools
- Prepare space on a table for tools and wafer case
- Take a picture of the guard ring (before the measurement) using the microscope in the bonding lab and the IC captures program
Prepare probe station
- Check that the vibration isolation table is at ~4bar
- Switch on probe station
- Switch on vacuum
- Check that the vacuum pins are suitable for the sensor size
- Set rotation of the chuck to 10° to provide the full range of rotation when aligning the chuck
Loading a new sensor
Preparation
- Lift the platen to a reasonable distance (at least 5 mm) from the lifted chuck
- Lower the chuck
- Set chuck to the front most position
- Wipe vacuum tweezers and clean chuck cand pogo pins
- Move the golden add-on chuck to the center of the silver chuck
- Get the wafer in its paper envelope
Loading procedure
- Place the envelope on the table and carefully extract the wafer on the cardboard support
- Turn the cardboard support until the wafer has its final orientation
- Pick up the sensor using the vacuum tweezer with your right hand
- Hold the cardboard support with the wafer on your left hand (or put it on the table next to the setup)
- Never take your eyes off the sensor!
- Approach the chuck, hold the cardboard support next to and slightly higher than it
- Place the sensor on the chuck
- Keep the vacuum tweezer in place until the vacuum is on to prevent sliding on air cushion
- Turn on the vacuum and let the tweezer go
- Remove dust particles with the duster (practice using duster first),
- Attention: if you hold the air can in a tilted position, it might release liquid
Alignment procedure
- Move the chuck below the probe card, the two pogo pins in the front should be approximately above their contact pads
- Move the chuck up using the coarse handle (Attention: the pogo pins should be at least 5mm above the sensor now)
- Look through the central hole in the probe card with the microscope
- You should be able to see now the central Mercedes cross like intersection of three hexagons now
- Position the center of the cross centrally using the x and y micrometer screws
- You can use the mouse cursor of the computer to remember the position of the intersection
- Picture of the central cell:
- Now move the chuck in y-direction in your direction until you see the last contact pad at the boarder of the sensor
- If the sensor was rotated slightly w.r.t the probe card, this Mercedes cross is not perfectly centered
- Before alignment:
- Move the mercedes cross again to the center by a rotation of the chuck
- After alignment:
- Move the chuck again inwards (along the y-axis only) until you see the last contact pad that you can reach
- Correct the Mercedes cross position again by rotation (and x-movements)
- Iterate the last two steps until all Mercedes stars in the central row in y-direction are in the center (where you mouse cursor is)
Contacting procedure
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Move the chuck now again such that the two pogo pins in the front are approximately above their contact pads
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Correct the y-position such that the central Mercedes star, which is visible now in the microscope, is exactly in the center of the probe card opening
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Lower the platen using the z micrometer screws and carefully touch down on the sensor
- Be careful since moving these moves the whole structure, therefore make sure the needle is not in place yet
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The pogo pins should be half way in, maybe a bit more
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Take a picture of the guard ring before contacting it
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Position the needle on the guard ring using the other microscope (use the mirror image to see the bisection and understand the final position)
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Once the needle touches the sensor, it does not move anymore and you are done
- There are two guard rings. The outer one is thinner and not contacted (floating), the inner one is thicker and is grounded. Thats the one you want to contact.
- Contacting the grounded guard ring to close to the floating guard ring can create sparks at HV and permanently damage the sensor. So be careful to contact the inner guard ring not too close to its outer edge!
- Correct position of guard ring needle:
- Switch off the light in the dark box, unplug the microscopes (this switches off their lights, too)
- Close the dark box gently (to avoid strong movements, the door does not need to be inserted in the bottom slit of the box)
Take the measurements
- Run "test_contact" measurement ( = IV @ 1V forward bias) to test if all pins have contact * Cells showing 0 nA have probably grease on the pogo pins which creates a high contact resistance
- Run "IV" scan (5s voltage delay, 0.1s switch delay)
- Monitor if the total current reaches the compliance
- Run "CV" scan (20s voltage delay, 0.1s switch delay)
- Check if some cells behave strangely in CV, try to retake these cells again in single channel scans (or find a solution to fix this :) )
- After the measurement, check contact marks (position and size) on guard ring and some example contact pads (there are usually already some probe marks from the manufacturer)
Unloading a sensor
Preparation
- Prepare wafer cardboard support and the envelope
- Wipe the vacuum tweezers clean
Unloading procedure:
- First remove the needle attached to the guard ring (it is important that this is done before the pogo pins are lifted to avoid scratches on the guard ring!)
- Move the platen such that the pogo pins are at least 5mm above the sensor using the micrometer screw
- Use separation up
- Use the coarse handle to lower the chuck
- Extract the chuck to the front as far as possible
- Put the tweezers in place and hold the wafer off-center towards you (off-center: easier to lift one side)
- Turn off the vacuum
- Take the cardboard support in the left hand close to the chuck and slightly lower than it
- Two options:
- Pick up the wafer and place it on the support (attention, despite may create air cushion below and wafer hovers! Risk of falling!)
- Lift one side of the wafer and slide it on to the cardboard
- Put the support and the wafer on the table
- Release the tweezers
- Add the top cover
- Insert the support with the wafer in the envelope and bring it back to its compartment