No abstract

The development of stabilized multifrequency lasers makes fractional fringes an increasingly attractive technique for length measurement. Determination of an unknown length from the measured fractional fringes is aided by the development of analytical equations for the length and its uncertainty, and criteria are given for selecting the wavelengths.

Vacuum pressure standards of the orifice-flow type require known gas flows of 10−6 mol/s (10−2 atm cm3/s at 0 °C) and less. Known gas flows can also be used to calibrate ‘‘standard’’ leaks by comparing the pressures generated when flows from the leak and the flowmeter are alternately passed through a constant conductance. Two constant-pressure, piston displacement flowmeters developed at the National Bureau of Standards are described that can generate flows between 10−6 and 10−10 mol/s with an estimated uncertainty of 0.8% to 2%. Comparisons of the flowmeters with alternate calibration techniques, and repeated low-range leak and vacuum gauge calibrations, have been used to confirm the estimated uncertainty and random errors of the flowmeter.

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.