We are writing 1978, and I finished my first year of my PhD project.\u00a0 In the first months of my PhD I spent a lot of time on reading about transparent conductive gate electrodes.\u00a0 The intention of my research project was to replace the classical poly-silicon gate electrodes on top of a CCD by means of something that is more transparent as well as more conductive than the poly-silicon gates used on top of the CCDs.\u00a0 Poly-silicon gates do absorb the incoming light, and especially in the blue part of the visible spectrum.\u00a0 I found an incredible useful publication by J. Vossen of RCA about Indium-Tin-Oxide or ITO, published in Thin Solid Films.\u00a0 Vossen described the fundamental characteristics of ITO and explained how the characteristics of the film could be changed and optimized.\u00a0 I have been reading this paper over and over again, I think I knew the whole thing by heart.<\/p>\n
In the lab where I was working, I found an old RF-sputtering system that was no longer in use.\u00a0 So that piece of equipment could be used to deposit ITO layers, at least to show the feasibility of using ITO to replace poly-silicon.\u00a0 The RF-sputtering tool was refurbished where needed and a special indium-tin target was ordered.\u00a0 The size of the target was only 10 cm in diameter (cost !) and the substrates to be covered by the sputtered layer were just 2 cm in diameter (cost !).\u00a0 But it worked !!\u00a0 The sputtering of the pure metal In-Sn layer was done in 100 % oxygen and resulted in a pure In2O3-SnO2 layer on the substrates.\u00a0 The deposition rate was very low, but for the first experiments it was acceptable.\u00a0 Unfortunately the sputtering in pure oxygen resulted in a non-conducting, but a fully transparent film.\u00a0 The next step was the development of an annealing step at higher temperatures to make the films conductive.\u00a0 Several atmospheres and temperatures were tried out.\u00a0 To avoid any cross-contamination with other material in the clear room, a dedicated (pretty dirty) furnace was used outside the clean room to do the basic annealing experiments.\u00a0 Nitrogen, argon, hydrogen, they all had a positive effect on the conductivity of the ITO films.\u00a0 Finally we chose for forming gas (90 % N + 10 % H) at 425 deg.C, being also the very last temperature step in our CCD process at that time.\u00a0 So in this way we could deposit non-conducting ITO on the CCD and by the so-called sintering step needed for the aluminum interconnects, also the ITO became conductive.\u00a0 No extra processing was needed to get a conducting ITO film.<\/p>\n
It was really a lot of fun doing the research on ITO for CCD gate electrodes.\u00a0 No big obstacles were encountered (at least not in the first years of the research) and every experiment brought us a step forward.\u00a0 Amazing to see that with the old equipment, but for sure with the Vossen’s publication in my mind, thin films of transparent and conductive ITO could be realized.\u00a0 The next step forward was to deposit the ITO on top of MOS capacitors and to see whether the new structures (ITO-SiO2-Si) could be used in the MOS technology.<\/p>\n
Unfortunately in the early days of my experiments, also a bad accident happened.\u00a0 I was not carefull enough during the cleaning of the substrates and a few drops of diluted (luckely !!) sulferic acid landed in my eye.\u00a0 After an intense eye-shower a colleague (thansk Eddy !) brought me quickly to the hospital and I was lucky that all the\u00a0 initial damage to my eye could be healed and no permanent issues were left.\u00a0 So the lesson learned here : never forget the safely rules, for sure not if you become too much focussed on your research and\/or become too enthousiastic about the results obtained.<\/p>\n
Albert, 26-10-2018.<\/p>\n","protected":false},"excerpt":{"rendered":"
We are writing 1978, and I finished my first year of my PhD project.\u00a0 In the first months of my PhD I spent a lot of time on reading about transparent conductive gate electrodes.\u00a0 The intention of my research project was to replace the classical poly-silicon gate electrodes on top of a CCD by means […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-1736","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1736","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1736"}],"version-history":[{"count":1,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1736\/revisions"}],"predecessor-version":[{"id":1737,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1736\/revisions\/1737"}],"wp:attachment":[{"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1736"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1736"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/harvestimaging.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1736"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}