Investigation on capacitively coupled He discharges with a structured electrode and effective design of a high-density and uniform plasma

Abstract In this paper, a fluid model is performed to investigate the effect of a structured electrode on capacitively coupled helium discharges operated at 13.56 MHz with 100 V peak-to-peak voltage, and 200 Pa. Compared to discharges with conventional planar electrodes, it is found that the plasma density produced by the structured electrode is raised by 28.5%–161.2% from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>1.86</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> as the trench size (i.e. width and depth) in structured electrode varies. The results also indicate that the trench dimensions have a great effect on the plasma characteristics under the operating conditions in this study. With the increase of trench width, the plasma density below the trench region increases at trench widths lower than 22 mm, after which the opposite trend is observed. As the trench depth varies from 5 mm to 25 mm, the plasma density increases monotonously from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>2.46</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>4.86</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> . Based on the results above, a modified ring-shaped structured electrode (MRSE) is proposed to successfully generate a large-area uniform and high-density plasma by adjusting the trench dimensions, position and number according to the discharge conditions. Compared to the flat electrode case, the plasma density and radial uniformity rise to 94.2% and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>3.25</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> from 92.2% and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mn>2.49</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> <mml:mstyle scriptlevel="0"/> <mml:msup> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> , respectively, with the adoption of MRSE. The simulation results also validate potential of the structured electrode as an effective tool in improvement of plasma processing.