AVS 47th International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1+MS-WeA

Paper PS1+MS-WeA6
Modeling and Real-time Control of RF Diode Sputtering for GMR Thin Film Deposition

Wednesday, October 4, 2000, 3:40 pm, Room 310

Session: Sensors and Control in Plasma Processing
Presenter: S. Ghosal, SC Solutions, Inc.
Authors: S. Ghosal, SC Solutions, Inc.
R.L. Kosut, SC Solutions, Inc.
J.L. Ebert, SC Solutions, Inc.
L. Porter, SC Solutions, Inc.
D.J. Brownell, Nonvolatile Electronics, Inc.
H.N.G. Wadley, University of Virginia
Correspondent: Click to Email
This presentation describes the development and implementation of real-time control of rf diode sputter deposition resulting in significantly reduced wafer-to-wafer variation in device properties. Giant magnetoresistive (GMR) materials have very important applications which include technologies such as hard disk read-heads, computer memory, and sensors. One common configuration for thin-film sensors made by NVE is the GMR multi-layer consisting of sixteen metallic layers with individual layer thickness ranging from 15 to 40 @Ao@. For maximum GMR, the acceptable variation in layer thickness from one deposition cycle to another is very small (0.5 @Ao@ for the critical CuAgAu conducting layer). Before this work, there was considerable variation in GMR properties from wafer to wafer, despite no change in the nominal values of layer thickness. Sensitivity studies using a steady-state physical model (integrating plasma, sputter and atom transport processes) showed deposition thickness falling out of acceptable range with relatively small changes in rf power, chamber temperature, pressure, and electrode spacing. Careful experiments showed that while three of the four variables were controlled relatively well, there was significant variation (>1%) in total rf power delivered due to transients at the onset of the plasma. A controller was designed to compensate for transient fluctuations by turning off the plasma based on the time-integrated DC bias voltage at the target. This approach keeps the total rf energy input into the plasma constant for individual layers deposited. As a result of implementing this controller, the standard deviation (wafer-to-wafer) in average GMR % and in sheet resistance were both reduced by more than half. Additionally, guided by the integrated physical model, within-wafer uniformity was considerably improved by optimal electrode spacing and target shaping.