Thickness metrology and end point control in W chemical vapor deposition process from SiH 4 / WF 6 using in situ mass spectrometry Process sensing and metrology in gate oxide growth by rapid thermal chemical vapor deposition from SiH 4 and N 2 O Quadrupole mass spectrometry has been used to monitor reactant and product partial pressures in a selective W chemical vapor deposition process. A 4/1H 2 /WF 6 molar reactant ratio was used to produce W films on Si wafers, at 67 Pa ͑0.5 Torr͒ total pressure, and for wafer temperatures around 400°C. A relatively fast response time ͑ϳ4 s͒ sensor system sampled gas directly from a commercial Ulvac ERA-1000 reactor in order to minimize the effect of wall reactions. The signal from the volatile HF product, integrated over the deposition cycle, and corrected for contributions from reactions in the ion-source region of the quadrupole and for sensor drifts, was found to vary linearly with the weight of the W film deposited, to within an uncertainty of ϳ7%. This provides the basis for real-time, noninvasive thickness metrology to drive process control. Depletion of both H 2 and WF 6 reactants was observed. The time integral of the H 2 reactant depletion was also linearly related to the film weight, though the data exhibited a somewhat larger scatter due to the low conversion efficiency of the process. In addition, volatile SiF 4 and SiHF 3 products of the initial rapid W nucleation reaction on the Si surface were clearly observed, indicating that initial surface conditions may be monitored in real time under selective growth conditions.
Articles you may be interested inReal-time acoustic sensing and control of metalorganic chemical vapor deposition precursor concentrations delivered from solid phase sources In situ mass spectrometry in a 10 Torr W chemical vapor deposition process for film thickness metrology and real-time advanced process control Thickness metrology and end point control in W chemical vapor deposition process from SiH 4 / WF 6 using in situ mass spectrometry Process diagnostics and thickness metrology using in situ mass spectrometry for the chemical vapor deposition of W from H 2 / WF 6 Process gases were sampled from the outlet of a tungsten chemical vapor deposition ͑CVD͒ reactor into an Inficon Composer™ acoustic sensor for in situ chemical gas sensing and real-time film thickness metrology. Processes were carried out on an Ulvac W CVD cluster tool at 10 Torr from 340 to 400°C using a H 2 /WF 6 gas mixture. Sampled gases were compressed through a diaphragm pump up to 100 Torr as required for accurate measurements in the acoustic cell. The high depletion of the heavy WF 6 precursor ͑up to 30%͒ generated a significant variation of the average gas molecular weight and consequently of the mass-dependent resonant frequency measured by the acoustic sensor. The monitored signal was integrated over the process time, and the integrated area was correlated to the deposited W film thickness determined by ex situ measurements. The average error on this in-tool and real-time metrology was less than 1% over 30 wafers processed, either under fixed process conditions or while varying key process variables such as deposition time or temperature. A dynamic physically based simulator was also developed to validate the system response under different process conditions and demonstrate the fundamental understanding of this method. The metrology achieved represents a significant improvement over previously published data ͓L. Henn-Lecordier et al., J. Vac. Sci. Technol. A 19, 621 ͑2001͔͒ obtained on the same system but in the sub-Torr process pressure regime, where low depletion rates ͑around 3%͒ had limited the metrology to 7% error. With an error less than 1%, this in situ chemical sensing approach could be efficiently exploited for real-time course correction, e.g., using end-point film thickness control.
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