IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Friday Sessions
       Session PS-FrM

Paper PS-FrM3
Measurements of the Spatiotemporal Variation of Ion Flux in Plasma Etching Reactors

Friday, November 2, 2001, 9:00 am, Room 104

Session: Diagnostics III
Presenter: T.-W. Kim, University of California, Santa Barbara
Authors: T.-W. Kim, University of California, Santa Barbara
S.J. Ullal, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
Variation of the ion flux and its spatial distribution across the wafer is critical in plasma etching: ion flux uniformity at the wafer determines the uniformity of etching. Most ion flux uniformity measurements to date have concentrated on studying the radial uniformity on a plane above the wafer. There are very few ion flux measurements on the plane of the wafer, especially in two dimensions. We have designed, built, and used planar Langmuir probes and probe arrays consisting of 10-30 probes on 75 mm and 200 mm diameter wafers to measure the variation of ion bombardment flux and its spatiotemporal distribution at the plane of the wafer in two different inductively coupled plasma reactors. Two-dimensional variation of the ion flux as a function of radial and angular positions on the plane of the wafer was mapped by interpolating between the probes. We demonstrate the uitility of these probes in studying factors that affect the ion flux and its uniformity including instabilities in an Ar discharge and effects of etching products in Cl@sub 2@ etching of Si. For example, in one of the reactors in Ar plasma at high pressure, a region of high ion flux ("hot spot") developes at the edge of the wafer at seemingly random positions and this "hot spot" rotates and moves around the edge on a time scale that depends on the plasma conditions. During etching of Si in a chlorine plasma, ion flux increases as a function of exposure time to the chlorine discharge and saturates on a time scale that is on the order of a few minutes. Through other diagnostic methods, this reproducible transient in the ion flux is related to the release of etching reaction products such as SiCl@sub x@ and subsequent deposition of a silicon oxychloride film on the reactor walls. Removal of this film from the wall with an SF@sub 6@ discharge resets the reactor walls back to a reproducible condition and returns the ion flux to the same level as at the beginning of the etching process.