Visual inspection results on ASI Timepix wafers

3rd August, 2012Hannele Heikkinen

VTT Technical Research Centre of Finland

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Visual inspection summary 1/3

Visual inspection done for four ASI Timepix wafers arrived at VTT on 29th June 2012:

# KUNXNXT # KSNXTET # KGNXY5T # K4NXNMT

The wafers were not probed at ASI, but some chips on all wafers were probed at IBM.

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Visual inspection summary 2/3

Results: A lot of residues and dirt. The wafers have always particles,

resist residues etc. but this time the wafers were particularly dirty.

Most of the residues have a size of one or few pixels, but also larger residues.

Number of dirty and/or damaged areas per chip: 0…4. Number of dirty and/or damaged areas per wafer: 27…98. # KUNXNXT worst with 98 reported dirty and/or damaged

points. The origin of the impurities and damages unknown. Also the

composition of the impurities unknown.

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Visual inspection summary 3/3

At least some damages originate from the IBM processing (see slides 5 and 6)

Possible sources for the dirt and residues: handling of the wafers at any stage and the shipping packages.

Dirt may also originate from the probing at IBM. The visual inspection is the first step at VTT; most probably the

dirt has already been on the wafers when arriving to VTT. The wafers have been cleaned by oxygen plasma and solvents

after the visual inspection at VTT. The cleaning didn’t help much. Either extra cleaning with plasma didn’t help the situation.

Pictures on the dirt and damages on following slides.

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Damages from IBM processing 1/2

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Damages from IBM processing 2/2

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Dirt and residues 1/3

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Dirt and residues 2/3

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Dirt and residues 3/3