IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Manufacturing Science and Technology Tuesday Sessions
       Session MS-TuA

Paper MS-TuA7
Real-Time CVD Wafer State Metrology using a Downstream Acoustic Sensor

Tuesday, October 30, 2001, 4:00 pm, Room 131

Session: In Line and In Situ Process Control
Presenter: L. Henn-Lecordier, University of Maryland
Authors: L. Henn-Lecordier, University of Maryland
J.N. Kidder, University of Maryland
G.W. Rubloff, University of Maryland
A. Wajid, Inficon, Inc.
C.A. Gogol, Inficon, Inc.
Correspondent: Click to Email
An acoustic gas sensor, the Inficon Composer@super TM@, was implemented downstream in a production-scale tungsten chemical vapor deposition (CVD) cluster tool for process sensing to achieve real-time, in-situ film thickness measurements. Process gases were sampled at the reactor outlet and compressed with a diaphragm pump from the 10 Torr process pressure regime to above 50 Torr as required for gas sound velocity measurements in the acoustic cavity. Processes were carried out for various deposition times at 10 Torr, with a H@sub 2@ / WF@sub 6@ flow ratio of 6 to 1 and at wafer temperatures ranging from 300 to 450 °C. The sensor measures the average molecular weight of the gas mixture and is normally employed for control of inlet (upstream) gas flows into the reactor. For downstream applications, depletion of the H@sub 2@ and WF@sub 6@ reactants, as well as generation of the HF product, shift the gas composition with changes in reaction rate in the process. The high depletion rate of the WF@sub 6@ precursor (i.e. 30% or more) during blanket W deposition induced a substantial variation of the average molecular weight of the exhaust gas mixture. By integrating the resonant frequency over the deposition time, real-time in-situ metrology signals were obtained which correlated to post-process thickness measurements within 1%. This makes the acoustic sensor attractive for advanced process control, either in run-to-run control or through real-time end point control.