Insights into the copper HiPIMS discharge: deposition rate and ionised flux fraction
Joel Fischer, Max Renner, Jón Tómas Guðmundsson, Martin Rudolph, Hamidreza Hajihoseini, N. Brenning, Daniel Lundin
Abstract
Abstract The influence of pulse length, working gas pressure, and peak discharge current density on the deposition rate and ionised flux fraction in high power impulse magnetron sputtering discharges of copper is investigated experimentally using a charge-selective (electrically biasable) magnetically shielded quartz crystal microbalance (or ionmeter). The large explored parameter space covers both common process conditions and extreme cases. The measured ionised flux fraction for copper is found to be in the range from ≈10% to 80%, and to increase with increasing peak discharge current density up to a maximum at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>1.25</mml:mn> </mml:mrow> <mml:mrow> <mml:mtext>A</mml:mtext> </mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>cm</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> , before abruptly falling off at even higher current density values. Low working gas pressure is shown to be beneficial in terms of both ionised flux fraction and deposition rate fraction. For example, decreasing the working gas pressure from 1.0 Pa to 0.5 Pa leads on average to an increase of the ionised flux fraction by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>14</mml:mn> </mml:mrow> </mml:math> percentage points (pp) and of the deposition rate fraction by <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mtext>pp</mml:mtext> </mml:mrow> </mml:math> taking into account all the investigated pulse lengths.