IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Electronics Wednesday Sessions
       Session EL-WeM

Paper EL-WeM10
Kinetics of the Selective Oxidation of Si(100) versus W by H@sub 2@O Steam in Hydrogen

Wednesday, October 31, 2001, 11:20 am, Room 124

Session: Si Surface Dynamics and Reactions
Presenter: Y. Liu, Axcelis Technologies, Inc.
Authors: Y. Liu, Axcelis Technologies, Inc.
J. Hebb, Axcelis Technologies, Inc.
Correspondent: Click to Email
The selective oxidation (SELOX) of Si versus tungsten (W) is an important process to form W gate electrodes on SiO@sub 2@ dielectric in the advanced CMOS devices. The SELOX was studied using a small quartz reactor, a catalytic water vapor generator (WVG), a quadrupole mass spectrometer (QMS), an ellipsometer and a 4-point probe. New kinetics data were obtained for the wet SiO@sub 2@ growth on Si(100) at 1 atmosphere and 900-1150°C, with the steam (H@sub 2@O) in H@sub 2@ percentage being 0 to 80%. A Si(100) or a W-covered Si(100) wafer was rapidly heated to a desired temperature in an inert gas. Fast gas sequencing was carried out to expose the wafer to (1) H@sub 2@ for W passivation, (2) steam+H@sub 2@ for Si oxidation and (3) H@sub 2@ for WO@sub x@ reduction. Gases in the reactor were analyzed with the QMS. The SiO@sub 2@ thickness was measured with the ellipsometer while the W film was characterized by its sheet resistance change. Preliminary results showed that the SiO@sub 2@ thickness is proportional to the steam percentage at a given set of oxidation temperature and time, suggesting that the SiO@sub 2@ growth follows the first-order kinetics. At a 20% steam percentage and during the first 60 sec, the SiO@sub 2@ growth rates at 955°C and 1047°C have been determined to be 0.96 Å/sec and 2.89 Å/sec, respectively. This yields an activation energy of 1.67 eV in agreement with the published values using O@sub 2@ or steam+O@sub 2@. Between 60 and 180 sec, the growth rates decreased to 0.73 Å/sec and 1.81 Å/sec, respectively. Hence, the earlier oxidation stage is kinetically controlled by an interface reaction step while the later stage is limited by a different slow step. Besides the detailed kinetic studies for the wet Si oxidation in the H@sub 2@ reducing ambient, systematic data will be presented for the W oxidation and WO@sub x@ reduction to explore the selectivity window for Si SELOX.