Microwave ECR plasma electron flood for low pressure wafer charge neutralization

Abstract

Modern ion implanters typically use dc arc discharge Plasma Electron Floods (PEFs) to neutralize wafer charge. The arc discharge requires using at least some refractory metal hardware, e.g. a thermionically emitting filament, which can be undesirable in applications where no metallic contamination is critical. rf discharge PEFs have been proposed to mitigate contamination risks but the gas flows required can result in high process chamber pressures. Axcelis has developed a microwave electron cyclotron resonance (ECR) PEF to provide refractory metals contamination-free wafer neutralization with low gas flow requirement. Our PEF uses a custom, reentrant cusp magnet field providing ECR and superior electron confinement. Stable PEF operation with extraction slits sized for 300 mm wafers can be attained at Xe gas flows lower than 0.2 sccm. Electron extraction currents can be as high as 20 mA at absorbed microwave powers < 70 W. On Axcelis' new medium current implanter, plasma generation has proven robust against pressure transients caused by, for example, photoresist outgassing by high power ion beams. Charge monitor and floating potential measurements along the wafer surface corroborate adequate wafer charge neutralization for low energy, high current ion beams.

Design and Experiment of a Slotted Antenna Surface Wave Plasma Flood Gun

“…To avoid the breakdown of floating wafers, plasma flood gun (PFG) is employed to produce electrons for charge neutralization during ion doping process [2]. At present, there are multiple PFGs used in ion implantation machines, including hot filament PFG [3], radio frequency (RF) PFG [4], and electron cyclotron resonance (ECR) PFG [5][6][7]. However, each of these PFGs has some disadvantages.…”

Improvement of miniaturized 2.45 GHz ECR plasma flood gun at PKU

“…Besides, with permanent magnet configuration and ceramic microwave RF matching, the structure of the ECR ion source is more compact and the maintenance is more simple [9]. Based on these facts, 2.45 GHz ECR ion sources, especially compact PMECR ion sources, have shown great potential to become excellent PFGs [10][11][12]. Recently, a more compact PMECR 2.45 GHz ion source that named as miniaturized PMECR ion source has been developed as a PFG at PKU [13,14].…”