From dcaudillo at worldnet.att.net Sat Dec 1 01:37:01 2001 From: dcaudillo at worldnet.att.net (David Caudillo) Date: Sat, 1 Dec 2001 01:37:01 -0800 Subject: tyan nitride cancellation 0830-1730 Message-ID: <000901c17a4b$c22ab840$171c510c@pavilion> Better late than never....Sorry for the late notice. David Caudillo From balaji at sunray.snffab.stanford.edu Mon Dec 3 11:12:19 2001 From: balaji at sunray.snffab.stanford.edu (Balaji Venkateshwaran) Date: Mon, 3 Dec 2001 11:12:19 -0800 (PST) Subject: tube out for 1 hour Message-ID: <200112031912.LAA24351@sunray.snffab.stanford.edu> It is 11:15am right now and whoever is running Tylan Nitride, your tube has been out for a long time. Balaji From dlaser at stanford.edu Mon Dec 3 18:29:51 2001 From: dlaser at stanford.edu (Daniel James Laser) Date: Mon, 3 Dec 2001 18:29:51 -0800 (PST) Subject: canc. res. Wed 1830-2400 Message-ID: Tube is free until 8am tomorrow. Sorry for the late notice. From mcvittie at stanford.edu Thu Dec 6 13:51:20 2001 From: mcvittie at stanford.edu (Jim McVittie) Date: Thu, 06 Dec 2001 13:51:20 -0800 Subject: Results of LPCVD Nitride Flow Calibrations Message-ID: <3C0FE858.9E71C237@stanford.edu> Nitride Users, Here are the results of the calibrations done on Monday. Actual NH3 flow = 0.5+1.04*setting in sccm. Actual DCS flow = 0.6+0.91*setting in sccm. Basicly, these results say that the NH3 flow is running 4% above the setting and the DCS flow is running 9% below the setting. These flow errors are small than I had expected. They do not explain any of the problems we have seen with films out of the nitride tube. We are running more tests looking at wet etch rates and bubble formation. On the bubble problem, our present thinking is that they may have been there all along for our low stress films and they got worst when we upped the DCS/NH3 flow rate a few years back to lower the stress. Jim McVittie From goksenin at stanford.edu Fri Dec 14 11:13:37 2001 From: goksenin at stanford.edu (Goksenin Yaralioglu) Date: Fri, 14 Dec 2001 11:13:37 -0800 Subject: reservation cancelation Message-ID: <5.1.0.14.2.20011214111219.00a76d80@goksenin.pobox.stanford.edu> Hello all, I had to cancel my reservation today (13:30-24:00). Goksen --------------------------------------------------- Goksenin Yaralioglu, PhD Stanford University Ginzton Lab. Stanford CA, 94305 e-mail: goksenin at stanford.edu off tel.: (650) 725 49 42 home tel.: (650) 857 18 22 --------------------------------------------------- From mcvittie at stanford.edu Mon Dec 17 14:46:33 2001 From: mcvittie at stanford.edu (Jim McVittie) Date: Mon, 17 Dec 2001 14:46:33 -0800 Subject: LPCVD Nitride Update Message-ID: <3C1E75C9.D1D1CF39@stanford.edu> Tylan Nitride Users, I want to update you on what is being done to address some of the reported problems with our low stress LPCVD nitride films. There are three problems that we are looking at: 1. Bubbles (1 um range) in nitride films, 2. Increased nitride etch in hot KOH, and 3. Higher stress (> 150 MPa in our low stress process). History: Our low stress nitride process was developed in the mid 80?s by Sung-Tae Ahn, who was a grad student in material science. He found that the nitride stress decreases as the SiH2Cl2 / NH3 ratio (R )increases. His results were summarized in a short paper published by the Pattie Beck, who was an Applied Physics grad student, in a MRS conference proceedings in 1990. Sung-Tae Ahn and I were co-authors of this paper. The original low stress process was run at 785C with an R of 6:1 at a pressure of 300 mT. At this flow ratio, the film had a reflactive index of 2.55 and a stress of around 50 MPa on oxide and around 150MPa on bare silicon. No bubbles were seen in the film and the etch rate in 33% KOH was 8A/hr at R= 6.0 and 16 A/hr at R=6.5. Increasing R above 6 increases the KOH etch rate significantly. By 1996 our low stress process (SIN5.5 with NH3 = 30 and DCS = 165) was running at a DCS/NH3 ratio of 5.5 with the stress still around 150 MPa on bare silicon. In 1998 the flowmeters for the nitride tube were changed from the Mono-block construction as used in all the other Tylan tubes (except in the Tystar) to individual flowmeters. I have no record of stress problems being reported at that time. During the summer of 1999, several users reported stress levels between 600 and 700 MPa for films deposited with R at 5.5. At that time a series of nitride runs were done by the staff and several users with R increased up to 15. In October of 1999, we settled on LONH78 (NH3 = 13.5 and DCS = 189) which had R at 14.0. The rational for allowing the process to be change was that we thought that the flowmeters had most likely gone out of calibration. At the time we did not a means of doing in-situ flow calibrations like what is done on most of the plasma etch equipment. Current Issures: ---Bubbles in films: About a month ago a remote user sent us an SEM showing 1um sized bubbles in a low stress film deposited for him by us. Upon checking, we found out that bubbles have been seen in our films for sometime. Checking low stress films from 1996 with R = 5.5 showed no sign of bubbles. In addition, recent tests using R= 11, 8 and 5.5 showed that the bubbles disappear as R is reduced to 5.5. The bubble problem indicates that the 1999 increase in R was likely a mistake. ---Flowmeter Calibration: During the summer we together a measurements system for in-situ calibrating flowmeters in LPCVD systems. The method uses rate of pressure increase with the gate valve closed and N2 feed into the flowmeter under test. This system was recently used to calibrate all the flowmeters on the nitride tube. The flowmeter error was found to be < 10% for all the flowmeters. For LONH378 the actual R value was found to 11.7 instead of the set value of 14. While there is an error in R, the error is not large enough to explain the need for the large change made is 1999. Our actual R value of 11.7 is consistent with our current bubble problem. For SIN5.5, which was the pre-1999 process, the actual R value is 4.6 instead of the set value of 5.5. This explains, why an increase in R of around 20% was needed. ---High etch rate in KOH: At least one user has found that the current (deposited during summer) low stress nitride does not hold up in KOH as well as films deposited in 2000. XPS measurements showed that the 2000 film had slightly less oxygen, perhaps due to a lower leak rate during deposition. From the data in the 1990 paper, it is likely the etch rate would be greatly reduced by reducing R back to 6. --- High process pressure: Currently, the process pressure is running over 500 mT. We suspect that the pump is the problem since it may have been damaged last month when a user let the system pump on air for sometime before the burn box failed. The pump will be replaced during the shut down. --- High Stress: We still have not answered why the stress went up so high in 1999 and why we are still seeing higher stress than expected when we lower R back to around 6. Note that both Berkeley and Cornell run their low stress processes with R near 6. Some the issues that we are looking into are: 1. Calibration of our stress measurement tool: Our FSM system is old and a number of users have noted that it gives inconsistent measurements. We are going to do a low stress run and measure the stress on at least 2 other systems to verify that our FSM system is not a source of our problem. 2. Deposition temperature: While we have always run our nitride depositions around 780C, Both Berkeley and Cornell around 880C. We will do a 880C run to see its affect. If you have any comments and ideas on the nitride problems, please send them to me. Thanks, Jim McVittie