Optimization of plasma density and radial uniformity of a point-cusp magnetic field applied capacitive plasma

• Published in: Journal of vacuum science & technology. A, Vacuum, surfaces, and films Vacuum, surfaces, and films, 2000-05, Vol.18 (3), p.823-829
• Main Authors: Wickramanayaka, Sunil, Nakagawa, Yukito, Sago, Yasumi, Numasawa, Yoichiro
• Format: Article
• Language: English
• Subjects: Electric currents; Electrodes; Magnetic field effects; Magnets; Plasma density
• ISSN: 0734-2101; 1520-8559
• DOI: 10.1116/1.582262

A feasibility study in the development of a large area high-density plasma source with a higher radial plasma uniformity for large area wafer processing was carried out. Experiments were performed for 200 mm diameter wafers using parallel plate capacitively coupled plasma excited by 60 MHz radio frequency current. Point-cusp magnetic fields that can be easily expanded for 300 mm diameter wafer processing reactors without any technical difficulties are applied to the upper electrode. The point-cusp magnetic fields are generated by arranging 115 permanent magnets on a 266 mm diameter upper electrode with alternate polarity and equal distance. This arrangement of magnets produces a strong magnetic field at the surface of upper electrode and almost a magnetic field-free environment at around 40 mm below the upper electrode. This magnetic field also causes no polarization of the plasma due to the E×B drift of electrons where E and B are the direct current electric and magnetic field strengths, respectively. Application of the point-cusp magnetic field increases the plasma density by a factor of 2 and decreases the radial nonuniformity by a factor >1.5. The radial nonuniformity of the plasma at 58 mm below the upper electrode is further reduced to ±3.5% across the central 200 mm region by the application of a bucket magnetic field to the reactor sidewall and removing 16 magnets from the central region of the upper electrode. This latter change, however, slightly reduces the earlier explained plasma density increment. The radial uniformity of large area plasmas can be controlled with considerable ease by removing selected magnets from the central region of the upper electrode or reducing the magnetic field strength at the central region.