Harvest Imaging Blog

Please find below the agenda of the Harvest Imaging Forum 2019.  Do not pay too much attention on the timing, because the forum will run in 2 parallel sessions.  The (indicative) timing shown is valid for the first session, the second one will get another timing.

Albert, 14-11-2019.

My PhD project in the late ’70s involved the development of Indium-Tin-Oxide (ITO) CCD electrodes.  ITO is a transparent and conductive material, from the standpoint of view of those characteristics, ITO is ideally suited to be used as a CCD electrode.  In the first year of my research, I succeeded in the deposition of transparent ITO that was fully oxidized, and was actually non conductive.  By means of an appropriate anneal the ITO films could be made conductive as well.  Actually what was realized was a kind of conductive glass.

In the second year of my PhD project (= 40 years ago) I focused on using the ITO film as a gate electrode in a MOS structure.  And that turned out to be much more difficult than expected.  I still remember that I had to set up a measurement system to perform HF and LF capacitance measurements on the realized MOS capacitor with the ITO top gate.  A hard copy of the developed software code in Fortran is still present in my archives.  Unfortunately the RF sputtering technique applied to deposit the ITO films created too much radiation damage in the MOS structures.  As a result, the MOS capacitors showed a very high number of surface states.  A high number of surface or interface states would ultimately result in a very high dark current in the final CCDs.  Too bad !  I tried many annealing methods, various annealing atmospheres in combination with various temperatures, but none of them resulted in a low number of surface states.  I still remember that  I worked in close cooperation with the solar cell R&D team.  They offered me the opportunity to anneal my “dirty” structures in their furnaces at high temperatures, even in a reactor in which the structures could be annealed in hydrogen.  But no processing recipe could be found that resulted in a low number of surface states.  So the only solution was to give up the damaging RF sputter technique and to make use of magnetron sputtering for deposition of the ITO films.  Magnetron sputtering was known to result in a low level of radiation damage and seemed to be suited for deposition of gate material on MOS structures.

I remember that the university was willing to buy a new magnetron sputtering system from Balzers.  But Balzers was not really familiar with the sputtering of ITO, so I had to go to the company in Liechtenstein to perform ITO experiments.  This was my very first business trip ever, all the way flying to Zurich and then the train to Sargans if I recall well.  Once at Balzers’facility we succeeded immediately to deposit the right combination of Indium Oxide and Tin Oxide, so we gave a “go” to buy the machine.  It was Mr. Klinkemay of Balzers (probably misspelled ?!) who did the installation of the machine in our laboratory at the university.  Also with the final machine the first films of ITO were realized very quickly.  So ready to deposit ITO films with a low level of radiation damage !  My work with the magnetron sputter machine became so well accepted in the lab, that the machine was provided with a second aluminum target and the machine was going to be used in our lab as the “standard” deposition method for aluminum metallization of integrated circuits.  As a result, I almost had to beg on my bare knees to use my “own” machine for the ITO depositions.  After a while the management of the lab saw the problems, and decided to buy a second machine.  What a luxury, I got my own machine back for my own ITO depositions !  An incredible amount of test MOS capacitors were deposited, annealed and measured.  A Russian postdoc helped me out with the measurements (unfortunately I lost his name).  And yes, finally we succeeded in realizing MOS capacitors with an ITO gate material that showed a low number of surface states, not as low as a capacitor with a poly-silicon gate, but more than an order of magnitude less than the devices fabricated with the RF sputter machine.  A major step forward !

Albert, 14-11-2019.