GMR Thin Films Manufacturing
Physical Vapor Deposition (PVD)
SC Solutions has developed techniques and tools for physical modeling and model-based control for advanced materials processing. This technology has been successfully applied to the manufacturing of Giant MagnetoResistive (GMR) thin films. The results of the physical model provided guidelines for selecting process parameters, and identifying causes for wafer-to-wafer variability in film properties. This variability was reduced by more than 50% using SC’s controller.
GMR Production Using RF Diode Sputtering
The cornerstone of SC Solutions’ technology is Model-Based Control Design. With this approach a physical model of the GMR chamber and the sputter process is used directly in the control design. This "virtual" integrated prototyping environment can also be used to evaluate or optimize performance for either existing equipment or for the next generation equipment. GMR materials have tremendous potential for application to technologies such as hard disk read heads for computer data storage, computer memory, and sensors. A common method of producing thin-film GMR material is by RF diode sputtering.
SC Solutions has developed, in collaboration with Nonvolatile Electronics (NVE) of Eden Prairie, MN and the University of Virginia, Charlottesville, VA, a set of computer models for the physical processes that occur in radio-frequency (RF) diode sputtering for thin film deposition. The resulting RF integrated-voltage controller implemented at NVE reduced wafer-to-wafer variability in film properties by more than 50%. In addition, within-wafer thickness uniformity was substantially improved by adopting equipment modifications suggested by the simulations. This work was funded by DARPA, Applied & Computational Mathematics Program.
Model of the RF Sputtering Chamber
An integrated model of the GMR RF sputtering chamber was developed that consists of the following modules which simulate the various physical phenomena occurring during thin film deposition:
- fluid flow model,
- RF plasma & sputter models,
- direct simulation Monte Carlo (DSMC) model,
- thermal model of the chamber.
Integrated Voltage Controller
Guided by the results of the integrated model, careful measurements were made to detect correlations between the process parameters (performance variables) and the critical device properties, viz, the GMR ratio, saturation magnetic field strength (hsat), and the sheet resistance (rhos). The data showed that three of the four variables were relatively well-controlled, with the integrated target bias voltage correlating with variations in wafer hsat. An integrated voltage controller was developed that compensates for the RF bias voltage fluctuations by adjusting the plasma on-time so as to regulate the time-integrated voltage (for all layers of the same material deposited). This approach keeps the total RF energy input into the plasma constant.
Within-Wafer Uniformity
The integrated model indicated that reduced electrode spacing would significantly improve deposition uniformity. Experiments were conducted and the results show that this closer spacing produced wafers with excellent GMR. Calculations using the model also showed that a concave shaped target would reduce deposition non-uniformity across the wafer, since the reduced spacing at the edges would compensate for the flux of atoms escaping from the plasma boundary. Deposition (and hence film property) uniformity within a wafer has shown significant improvement following recommendations obtained from simulations with the model.
Related Publications
| Multi-Scale Model of the RF Diode Sputter Deposition of GMR Thin Films | |
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S. Ghosal, R. L. Kosut, J. L. Ebert, A. Kozak, T. E. Abrahamson, W. Zou, X. W. Zhou, J. F. Groves, Y. G. Yang, H. N. G. Wadley, D. Brownell, and D. Wang, Multi-Scale Model of the RF Diode Sputter Deposition of GMR Thin Films, Application notes, 2000. |