From mtang at stanford.edu Thu Nov 19 17:35:45 2009 From: mtang at stanford.edu (Mary Tang) Date: Thu, 19 Nov 2009 17:35:45 -0800 Subject: wbdiff update Message-ID: <4B05F271.4030709@stanford.edu> Dear wbdiff users: Thanks for your patience as we work to resolve resistivity and drying issues at this station. A rebuilt spin-rinse-dryer (SRD) was installed yesterday -- it's got completely new seals, hoses and valves and has been electropolished to a lovely finish. We soon found, however, that cleaned wafers still did not rinse to resistivity. Uli and Jim ran a number of experiments and found that the problem to be the teflon boats. The boats themselves are clean as ever -- when empty, they rinse to resistivity with a minute to spare after acid processing. But over time, grooves have formed in the wafers slots where trace amounts of acid get trapped by wafers. As acid is slowly released, the resistivity remains low... The solution is new teflon boats (you can see this easily -- the base of the wafer slots are shiny in new boats and dull and grooved in the old ones.) Nancy and Uli managed to find and decontaminate 5 unused/new teflon boats. All the old boats at wbdiff have been removed. Five boats may not be quite enough to keep everyone happy when the station is busy, so we ask all wbdiff users to remove your wafers and return the boats as soon as you are done processing. In the meantime, we have ordered more teflon cassettes. As for the drying problems, the rebuilt SRD has a newer controller which allows for a second, low speed dry cycle. The rationale is that slowing the spin allows better drying where the wafers contact the boats. This is recommended by the manufacturer and is standard industry practice. Several tests on this rebuilt SRD show that a full load of 25 wafers is consistently dry after processing. The SRD setup is now as follows: 1. Rinse runs for 180 seconds at 400 rpm. The resistivity setpoint is 16 MOhms. When both resistivity is met and time is out, the SRD will proceed to the first dry step. With the new boats, resistivity should be met well before 180 seconds is reached. 2. First dry runs for 240 seconds at 1600 rpm. The HEAT light should come on. This indicates that the N2 is being heated and the heating blankets around the drum are working. If the light is not on during the dry cycle, please report on Coral. 3. Second dry runs for 200 seconds at 400 rpm. The HEAT light should remain on in this cycle. This makes for a longer drying time, but will assure consistently dry wafers and cassettes. Thanks again for your patience and please do let us know how this works for you. Your SNF Staff -- Mary X. Tang, Ph.D. Stanford Nanofabrication Facility Allen Room 136, Mail Code 4070 Stanford, CA 94305 (650)723-9980 mtang at stanford.edu http://snf.stanford.edu