| AVS 54th International Symposium | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS2-TuA |
| Session: | Plasma Sources |
| Presenter: | M. Bhargava, University of Houston |
| Authors: | M. Bhargava, University of Houston B. Craver, University of Houston H. Guo, University of Houston A.K. Srivastava, Axcelis Technologies J.C. Wolfe, University of Houston |
| Correspondent: | Click to Email |
We describe a plasma system for removing photoresist from silicon wafers where reactant gas flowing in a quartz tube is activated by a high power, 2.45 GHz surface wave discharge at pressures near 80 Torr.The plasma applicator is based on Moisan’s ‘surfaguide’ design1 where the discharge tube passes through a thin-walled coupling aperture in a reduced-height wave-guide section. Microwave electric fields loop out of the aperture and launch surface waves in both directions along the interface between the discharge tube and the plasma. The directional flow (3slm) of process gas in the tube (6 mm inside diameter) effectively suppresses the discharge on the upstream side of the waveguide. This same flow, in conjunction with the downstream surface wave, produces a plasma jet that emerges from the end of the discharge tube and carries hot, activated gases to a scanning wafer below.The discharge tube is cooled by a counter-flow of clean, dry air confined in a coaxial outer tube; this enables extended operation at 2.5 kW for O2/N2 discharges. The wafer is clamped to a heated, 200 mm chuck with a backside pressure of about 35 Torr. An x-y stage, actuated by in-vacuum linear motors, translates the wafer with speed and acceleration up to 1.1 m/s and 2 g, respectively. The efficiency of converting microwave power to thermal jet power is 21% and 19% for respective substrate-to-source distances of 0.9 cm and 2.9 cm, independent of oxygen concentration. For an O2:N2= 9:1 plasma jet operating at 2.5 kW, 80 Torr pressure, and a flow of 3slm, the etched track profile is Gaussian in shape with a full-width-at-half-maximum of 1.5 cm. A serpentine raster pattern with 7 mm pitch is used to cover an entire 200 mm wafer. The time to clear 1.2 µm thick, unimplanted photoresist is about 10 seconds for a 70 cm/s scan speed and 200 °C chuck temperature. This corresponds to an instantaneous etch rate of about 4000 µm/min. A detailed analysis of the transient heating process will be presented at the conference. Acknowledgements: Partially supported by the Texas Center for Superconductivity at the University of Houston. The authors are grateful to Ivan Berry for insightful discussions. The opinions expressed are solely the responsibility of the authors.
1 M. Moisan et al., IEEE Trans. Plasma Sci. PS-12, 203-214 (1984).