Visual inspection results on ASI Timepix wafers 3 rd August, 2012 Hannele Heikkinen VTT Technical Research Centre of Finland

2 19/05/2015 Visual inspection summary 1/3  Visual inspection done for four ASI Timepix wafers arrived at VTT on 29 th June 2012:  # KUNXNXT  # KSNXTET  # KGNXY5T  # K4NXNMT  The wafers were not probed at ASI, but some chips on all wafers were probed at IBM.

3 19/05/2015 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.

4 19/05/2015 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.

5 19/05/2015 Damages from IBM processing 1/2

6 19/05/2015 Damages from IBM processing 2/2

7 19/05/2015 Dirt and residues 1/3

8 19/05/2015 Dirt and residues 2/3

9 19/05/2015 Dirt and residues 3/3