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Understanding the dynamics of ions in the magnetron sputtering process of transparent conductive oxide (TCO) films is essential for clarifying the mechanisms of sputtering-induced damage and developing effective suppression strategies. In this work, indium tin oxide (ITO) is used as a cathode target in an RF magnetron sputtering system operating under pure argon atmosphere, and a positively biased auxiliary anode is introduced to modulate the plasma potential and investigate its effect on the ion energy distribution functions (IEDFs) at the substrate position. The ion energy spectra are measured using a commercial energy–mass spectrometer (EQP 1000, Hiden), and the plasma parameters such as potential and electron density are characterized using a radio-frequency compensated Langmuir probe. The results show that the incident positive ions consist mainly of O+, Ar+, In+, Sn+, as well as multiple metal oxide molecular and doubly charged ions. Their energies are determined by the combined effects of the initial ejection or backscattering energy of sputtered particles and the plasma potential. Increasing the auxiliary anode bias leads to an elevation of the plasma potential, thereby enhancing both the kinetic energy and flux of positive ions. In contrast, negative ions such as O– and O2– originate predominantly from cathode sputtering, exhibiting broad, multi-peaked energy distributions that are strongly influenced by RF oscillations of the cathode voltage and plasma potential, as well as relaxation effects during ion transport. Heavier metal oxide negative ions (InO–, InO2–, SnO–, SnO2–) respond more slowly to RF sheath modulation, with their high-energy peaks converging toward the cathode bias potential. Applying a positive auxiliary anode bias effectively reduces the cathode bias voltage, thereby suppressing the high-energy tail of negative ions without significantly affecting their total energy-integrated intensity. This demonstrates that auxiliary anode biasing provides an effective means for adjusting the ion energy distributions in magnetron sputtering discharges. The proposed approach provides a potential pathway for mitigating sputtering-induced damage and improving the structural and electronic quality of ITO films. Future work will focus on correlating the measured ion energy modulation with comprehensive film characterizations—including optical, electrical, and interfacial analyses—to further verify the physical mechanisms and evaluate the practical effectiveness of damage suppression during TCO deposition.
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Keywords:
- radio frequency magnetron sputtering /
- indium tin oxide (ITO) /
- ion energy distribution /
- auxiliary anode
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图 1 基于辅助阳极的ITO射频磁控溅射装置及等离子体诊断系统
Figure 1. RF magnetron sputtering system for ITO film deposition with auxiliary anode and integrated plasma diagnostics.
图 2 ITO射频磁控放电中, 阴极偏置电压$ {V}_{\mathrm{C}0} $、附加阳极电流$ {I}_{\mathrm{A}\mathrm{A}} $及等离子体电势$ {V}_{\mathrm{P}} $随辅助阳极偏压$ {V}_{\mathrm{A}\mathrm{A}} $的变化关系
Figure 2. Cathode bias voltage $ {V}_{\mathrm{C}0} $, auxiliary anode current $ {I}_{\mathrm{A}\mathrm{A}} $, and plasma potential $ {V}_{\mathrm{P}} $ as functions of the auxiliary anode bias $ {V}_{\mathrm{A}\mathrm{A}} $ during an ITO RFMS discharge.
图 3 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)对氩同位素离子36Ar+ (m/z = 36)和40Ar+ (m/z = 40)能量分布的影响(气压: 0.6 Pa, 放电功率: 100 W)
Figure 3. Effect of different auxiliary anode voltages (0 to +50 V) on the energy distributions of argon isotope ions 36Ar+ (m/z = 36) and 40Ar+ (m/z = 40) in an ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 4 ITO射频磁控放电中, 不同辅助阳极偏压(0—+50 V)对36Ar+(m/z = 36), 40Ar2+(m/z = 20), O+(m/z = 16)和O2+(m/z = 32)离子能量分布的影响(气压: 0.6 Pa, 放电功率: 100 W)
Figure 4. Energy distributions of positive charged 36Ar+ (m/z = 36), 40Ar+ (m/z = 20), O+ (m/z = 16), and O2+ (m/z = 32) ions in an ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W). Measurements have been carried out for different auxiliary anode voltages ranging from 0 to +50 V.
图 5 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)对In+(m/z = 115), In2+(m/z = 57.5), 118Sn+(m/z = 118), 118Sn2+(m/z = 59)和InSn+(m/z = 233)等金属离子能量分布的影响(气压: 0.6 Pa, 放电功率: 100 W)
Figure 5. Effect of different auxiliary anode voltages (0 to +50 V) on the energy distributions of metal ions In+ (m/z = 115), In2+ (m/z = 57.5), 118Sn+ (m/z = 118), 118Sn2+ (m/z = 59), and InSn+ (m/z = 233) in an ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 6 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)对InO+(m/z = 131), InO2+(m/z = 147), InO3+(m/z = 163), SnO+(m/z = 134), SnO2+(m/z = 150), InSnO+(m/z = 249)和InSnO2+(m/z = 265)等金属氧化物离子能量分布的影响(气压: 0.6 Pa, 放电功率: 100 W)
Figure 6. Effect of different auxiliary anode voltages (0 to +50 V) on the energy distributions of metal oxide ions InO+ (m/z = 131), InO2+ (m/z = 147), InO3+ (m/z = 163), SnO+ (m/z = 134), SnO2+ (m/z = 150), InSnO+ (m/z = 249), and InSnO2+ (m/z = 265) in an ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 7 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)下单电荷离子(Ar+, O+, O2+, In+, Sn+和InSn+)及双电荷离子(Ar2+, In2+和Sn2+)的能量积分强度(气压: 0.6 Pa, 放电功率: 100 W)
Figure 7. Energy-integrated count rates of singly charged ions (Ar+, O+, O2+, In+, Sn+ and InSn+) and doubly charged ions (Ar2+, In2+, and Sn2+) in an ITO RFMS discharge at different auxiliary anode voltages from 0 to +50 V (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 8 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)下金属氧化物离子(InO+, InO2+, InO3+, SnO+, SnO2+, InSnO+和InSnO2+)的能量积分强度(气压: 0.6 Pa, 放电功率: 100 W)
Figure 8. Energy-integrated count rates of metal oxide ions (InO+, InO2+, InO3+, SnO+, SnO2+, InSnO+, and InSnO2+) in an ITO RFMS discharge at different auxiliary anode voltages from 0 to +50 V (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 9 ITO射频磁控放电中, 不同辅助阳极偏压(0—+50 V)对O–(m/z = 16)和O2–(m/z = 32)负离子能量分布的影响(气压: 0.6 Pa, 放电功率: 100 W)
Figure 9. Effect of different auxiliary anode voltages (0 to +50 V) on the energy distributions of O– (m/z = 16) and O2– (m/z = 32) negative ions in an ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 10 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)对InO–(m/z = 131), InO2–(m/z = 147), SnO–(m/z = 134)和InO2–(m/z = 150)负离子能量分布的影响(气压: 0.6 Pa, 放电功率: 100 W)
Figure 10. Effect of different auxiliary anode voltages (0 to +50 V) on the energy distributions of negative ions InO– (m/z = 131), InO2– (m/z = 147), SnO– (m/z = 134), and SnO2– (m/z = 150) in an ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 11 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)下负离子(O–, O2–, InO–, InO2–, SnO–和SnO2–)的能量积分强度(气压: 0.6 Pa, 放电功率: 100 W)
Figure 11. Energy-integrated intensities of negative ions (O–, O2–, InO–, InO2–, SnO–, and SnO2–) in an ITO RFMS discharge at different auxiliary anode voltages from 0 to +50 V (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 12 ITO射频磁控放电中, 不同辅助阳极电压(0—+50 V)下基片台表面IEDFs的径向分布情况(气压: 0.6 Pa, 放电功率: 100 W)
Figure 12. Radial distributions of IEDFs on the substrate surface under different auxiliary anode voltages from 0 to +50 V during ITO RFMS discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
图 13 ITO射频磁控放电中, 辅助阳极电压$ {V}_{\mathrm{A}\mathrm{A}}=0\;\mathrm{V} $条件下近基片台表面等离子体电势Vp及电子密度ne的径向分布情况(气压: 0.6 Pa, 放电功率: 100 W)
Figure 13. Radial distributions of plasma potential Vp and electron density ne near the substrate surface under auxiliary anode voltage $ {V}_{\mathrm{A}\mathrm{A}}=0\;\mathrm{V} $ during ITO RF magnetron discharge (Gas pressure: 0.6 Pa, discharge power: 100 W).
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