A radio-frequency(RF) inductively coupled negative hydrogen ion source(NHIS) has been adopted in the China Fusion Engineering Test Reactor(CFETR) to generate negative hydrogen ions.By incorporating the level-lumping m...A radio-frequency(RF) inductively coupled negative hydrogen ion source(NHIS) has been adopted in the China Fusion Engineering Test Reactor(CFETR) to generate negative hydrogen ions.By incorporating the level-lumping method into a three-dimensional fluid model,the volume production and transportation of H^(-) in the NHIS,which consists of a cylindrical driver region and a rectangular expansion chamber,are investigated self-consistently at a large input power(40 k W) and different pressures(0.3–2.0 Pa).The results indicate that with the increase of pressure,the H^(-) density at the bottom of the expansion region first increases and then decreases.In addition,the effect of the magnetic filter is examined.It is noteworthy that a significant increase in the H^(-) density is observed when the magnetic filter is introduced.As the permanent magnets move towards the driver region,the H^(-) density decreases monotonically and the asymmetry is enhanced.This study contributes to the understanding of H-distribution under various conditions and facilitates the optimization of volume production of negative hydrogen ions in the NHIS.展开更多
In this work,a two-dimensional hybrid model,which consists of a bulk fluid module,a sheath module and an ion Monte-Carlo module,is developed to investigate the modulation of ion energy and angular distributions at dif...In this work,a two-dimensional hybrid model,which consists of a bulk fluid module,a sheath module and an ion Monte-Carlo module,is developed to investigate the modulation of ion energy and angular distributions at different radial positions in a biased argon inductively coupled plasma.The results indicate that when the bias voltage amplitude increases or the bias frequency decreases,the ion energy peak separation width becomes wider.Besides,the widths of the ion energy peaks at the edge of the substrate are smaller than those at the center due to the lower plasma density there,indicating the nonuniformity of the ion energy distribution function(IEDF)along the radial direction.As the pressure increases from 1 to 10 Pa,the discrepancy of the IEDFs at different radial positions becomes more obvious,i.e.the IEDF at the radial edge is characterized by multiple low energy peaks.When a dual frequency bias source is applied,the IEDF exhibits three or four peaks,and it could be modulated efficiently by the relative phase between the two bias frequencies.The results obtained in this work could help to improve the radial uniformity of the IEDF and thus the etching process.展开更多
The effects of coil and dielectric window structures on the plasma distribution are examined in a cylindrically symmetric planar inductively coupled plasma(ICP).A two-dimensional(2 D)fluid model is employed to investi...The effects of coil and dielectric window structures on the plasma distribution are examined in a cylindrically symmetric planar inductively coupled plasma(ICP).A two-dimensional(2 D)fluid model is employed to investigate the design issues of ICP source for etching.When the gradient coil structure is applied at 400 W and 20 mTorr,the ionization rate caused by the power deposition decreases at the reactor center as compared to that in a reactor with a planar coil above the planar dielectric window,and a rather uniform plasma is obtained.However,for the vertical coil geometry,all the coils move to the position of the outermost coil,and the peaks of the power deposition and ionization rate appear at the radial edge of the substrate.In this case,the plasma density is characterized by an edge-high profile.Further,it is observed that the plasma uniformity is improved by increasing the source power under a gas pressure of 20 mTorr and becomes better when the gas pressure increases to 30 mTorr with the source power being fixed at400 W in the gradient coil configuration,but the uniformity of plasma worsens with the rising source power or pressure due to the strong localization in the vertical coil geometry.Moreover,when the discharge is sustained in a reactor with a stepped dielectric window at r=0.135 m,the best plasma uniformity is obtained at 400 W and 20 m Torr because the ionization rate is enhanced at the outermost coil,and the dielectric window at r=0.135 m blocks the diffusion of plasma towards the axis.In addition,higher source power and lower gas pressure produce more uniform plasma for the designs with a stepped window near the symmetry axis.When the dielectric window is stepped at r=0.135 m,the non-uniformity of plasma initially decreases and then increases with the increase in source power or gas pressure.When the dielectric window is stepped at the radial edge of the chamber,the plasma uniformity is improved by increasing the source power and gas pressure due to the enhanced ionization at the larger radius caused by the severe localization.展开更多
Changes of the electron dynamics in hydrogen （H2） radio-frequency （RF） inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device （ICCD）. The electron density, p...Changes of the electron dynamics in hydrogen （H2） radio-frequency （RF） inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device （ICCD）. The electron density, plasma emission intensity, and input current （voltage） are measured during the E to H mode transitions at different pressures. It is found that the electron density, plasma emission intensity, and input current jump up discontinuously, and the input voltage jumps down at the E to H mode transition points. And the threshold power of the E to H mode transition decreases with the increase of the pressure. Moreover, space and phase resolved optical emission spectroscopic measurements reveal that, in the E mode, the RF dynamics is characterized by one dominant excitation per RF cycle, while in the H mode, there are two excitation maxima within one cycle.展开更多
In this work, a two-dimensional fluid model has been employed to study the characteristics of Ar/O2 radio frequency（RF） inductively coupled plasma discharges. The emphasis of this work has been put on the influence ...In this work, a two-dimensional fluid model has been employed to study the characteristics of Ar/O2 radio frequency（RF） inductively coupled plasma discharges. The emphasis of this work has been put on the influence of the external parameters（i.e., the RF power, the pressure, and the Ar/O2 gas ratio） on the plasma properties. The numerical results show that the RF power has a significant influence on the amplitude of the plasma density rather than on the spatial distribution.However, the pressure and the Ar/O2 gas ratio affect not only the amplitude of the plasma density, but also the spatial uniformity. Finally, the comparison between the simulation results and the experimental data has been made at different gas pressures and oxygen contents, and a good agreement has been achieved.展开更多
In the design of negative hydrogen ion sources,a magnetic filter field of tens of Gauss at the expansion region is essential to reduce the electron temperature,which usually results in a magnetic field of around 10 Ga...In the design of negative hydrogen ion sources,a magnetic filter field of tens of Gauss at the expansion region is essential to reduce the electron temperature,which usually results in a magnetic field of around 10 Gauss in the driver region,destabilizing the discharge.The magnetic shield technique is proposed in this work to reduce the magnetic field in the driver region and improve the discharge characteristics.In this paper,a three-dimensional fluid model is developed within COMSOL to study the influence of the magnetic shield on the generation and transport of plasmas in the negative hydrogen ion source.It is found that when the magnetic shield material is applied at the interface of the expansion region and the driver region,the electron density can be effectively increased.For instance,the maximum of the electron density is 6.7×10^(17)m^(-3)in the case without the magnetic shield,and the value increases to 9.4×10^(17)m^(-3)when the magnetic shield is introduced.展开更多
In this paper,Maxwell equations are coupled with a radially localized global model and an analytical sheath model to investigate the electromagnetic effects under various frequencies and electron powers in large-area ...In this paper,Maxwell equations are coupled with a radially localized global model and an analytical sheath model to investigate the electromagnetic effects under various frequencies and electron powers in large-area very high frequency symmetric capacitive argon discharges.Simulation results indicate that both the vacuum wavelength and the sheath width decrease with frequency,leading to the reduced surface wavelength.As a result,the standing wave effect becomes pronounced,causing the fact that the radial profiles of the electron density,radio frequency voltage,and sheath width shift from uniform over center-high to multiple-node.When the frequency is close to or higher than the series resonance frequency,the surface waves cannot propagate to the radial center because of the significant radial damping.Due to the lack of power deposition near the radial center,the electron density is nearly zero there,i.e.the stop band effect.As power increases,the higher electron density leads to the decrease of the skin depth.Therefore,the importance of the skin effect gradually exceeds that of the standing wave effect,giving rise to the transition from the center-high to edge-high electron density profiles.The method proposed in this work could help to predict the plasma distribution under different discharge conditions in a few minutes,which is of significant importance in optimizing the plasma processing.展开更多
Two classic radio-frequency(RF) plasmas, i.e., the capacitively and the inductively coupled plasmas(CCP and ICP),are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasma...Two classic radio-frequency(RF) plasmas, i.e., the capacitively and the inductively coupled plasmas(CCP and ICP),are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures(m Torr-Torr), high-frequency electric field(13.56 MHz-200 MHz),reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas,and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.展开更多
The effect of the dielectric ring on the plasma radial uniformity is numerically investigated in the practical 450-mm capacitively coupled plasma reactor by a two-dimensional self-consistent fluid model. The simulatio...The effect of the dielectric ring on the plasma radial uniformity is numerically investigated in the practical 450-mm capacitively coupled plasma reactor by a two-dimensional self-consistent fluid model. The simulations were performed for N2/Ar discharges at the pressure of 300 Pa, and the frequency of 13.56 MHz. In the practical plasma treatment process,the wafer is always surrounded by a dielectric ring, which is less studied. In this paper, the plasma characteristics are systematically investigated by changing the properties of the dielectric ring, i.e., the relative permittivity, the thickness and the length. The results indicate that the plasma parameters strongly depend on the properties of the dielectric ring. As the ratio of the thickness to the relative permittivity of the dielectric ring increases, the electric field at the wafer edge becomes weaker due to the stronger surface charging effect. This gives rise to the lower N~+ ion density, flux and N atom density at the wafer edge. Thus the homogeneous plasma density is obtained by selecting optimal dielectric ring relative permittivity and thickness. In addition, we also find that the length of the dielectric ring should be as short as possible to avoid the discontinuity of the dielectric materials, and thus obtain the large area uniform plasma.展开更多
A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas a...A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determi- native role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase （decrease） at the E to H （H to E） mode transition, indicating an improved （worsened） inductive power coupling efficiency.展开更多
The inflexion point of electron density and effective electron temperature curves versus radio-frequency （RF） bias voltage is observed in the H mode of inductively coupled plasmas （ICPs）. The electron energy proba...The inflexion point of electron density and effective electron temperature curves versus radio-frequency （RF） bias voltage is observed in the H mode of inductively coupled plasmas （ICPs）. The electron energy probability function （EEPF） evolves first from a Maxwellian to a Druyvesteyn-like distribution, and then to a Maxwellian distribution again as the RF bias voltage increases. This can be explained by the interaction of two distinct bias-induced mechanisms, that is： bias- induced electron heating and bias-induced ion acceleration loss and the decrease of the effective discharge volume due to the sheath expansion. Furthermore, the trend of electron density is verified by a fluid model combined with a sheath module.展开更多
基金supported by the National Key R&D Program of China (No. 2017YFE0300106)National Natural Science Foundation of China (Nos. 11935005 and 12075049)the Fundamental Research Funds for the Central Universities(Nos. DUT21TD104 and DUT21LAB110)。
文摘A radio-frequency(RF) inductively coupled negative hydrogen ion source(NHIS) has been adopted in the China Fusion Engineering Test Reactor(CFETR) to generate negative hydrogen ions.By incorporating the level-lumping method into a three-dimensional fluid model,the volume production and transportation of H^(-) in the NHIS,which consists of a cylindrical driver region and a rectangular expansion chamber,are investigated self-consistently at a large input power(40 k W) and different pressures(0.3–2.0 Pa).The results indicate that with the increase of pressure,the H^(-) density at the bottom of the expansion region first increases and then decreases.In addition,the effect of the magnetic filter is examined.It is noteworthy that a significant increase in the H^(-) density is observed when the magnetic filter is introduced.As the permanent magnets move towards the driver region,the H^(-) density decreases monotonically and the asymmetry is enhanced.This study contributes to the understanding of H-distribution under various conditions and facilitates the optimization of volume production of negative hydrogen ions in the NHIS.
基金financially supported by National Natural Science Foundation of China(Nos.11935005 and 11875101)the Fundamental Research Funds for the Central Universities(No.DUT21LAB110)。
文摘In this work,a two-dimensional hybrid model,which consists of a bulk fluid module,a sheath module and an ion Monte-Carlo module,is developed to investigate the modulation of ion energy and angular distributions at different radial positions in a biased argon inductively coupled plasma.The results indicate that when the bias voltage amplitude increases or the bias frequency decreases,the ion energy peak separation width becomes wider.Besides,the widths of the ion energy peaks at the edge of the substrate are smaller than those at the center due to the lower plasma density there,indicating the nonuniformity of the ion energy distribution function(IEDF)along the radial direction.As the pressure increases from 1 to 10 Pa,the discrepancy of the IEDFs at different radial positions becomes more obvious,i.e.the IEDF at the radial edge is characterized by multiple low energy peaks.When a dual frequency bias source is applied,the IEDF exhibits three or four peaks,and it could be modulated efficiently by the relative phase between the two bias frequencies.The results obtained in this work could help to improve the radial uniformity of the IEDF and thus the etching process.
基金supported by National Natural Science Foundation of China(Nos.11905307 and 11875101)the Fundamental Research Funds for the Central Universities(No.DUT21LAB110)the China Scholarship Council。
文摘The effects of coil and dielectric window structures on the plasma distribution are examined in a cylindrically symmetric planar inductively coupled plasma(ICP).A two-dimensional(2 D)fluid model is employed to investigate the design issues of ICP source for etching.When the gradient coil structure is applied at 400 W and 20 mTorr,the ionization rate caused by the power deposition decreases at the reactor center as compared to that in a reactor with a planar coil above the planar dielectric window,and a rather uniform plasma is obtained.However,for the vertical coil geometry,all the coils move to the position of the outermost coil,and the peaks of the power deposition and ionization rate appear at the radial edge of the substrate.In this case,the plasma density is characterized by an edge-high profile.Further,it is observed that the plasma uniformity is improved by increasing the source power under a gas pressure of 20 mTorr and becomes better when the gas pressure increases to 30 mTorr with the source power being fixed at400 W in the gradient coil configuration,but the uniformity of plasma worsens with the rising source power or pressure due to the strong localization in the vertical coil geometry.Moreover,when the discharge is sustained in a reactor with a stepped dielectric window at r=0.135 m,the best plasma uniformity is obtained at 400 W and 20 m Torr because the ionization rate is enhanced at the outermost coil,and the dielectric window at r=0.135 m blocks the diffusion of plasma towards the axis.In addition,higher source power and lower gas pressure produce more uniform plasma for the designs with a stepped window near the symmetry axis.When the dielectric window is stepped at r=0.135 m,the non-uniformity of plasma initially decreases and then increases with the increase in source power or gas pressure.When the dielectric window is stepped at the radial edge of the chamber,the plasma uniformity is improved by increasing the source power and gas pressure due to the enhanced ionization at the larger radius caused by the severe localization.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11075029,11175034,and 11205025)the Fundamental Research Funds for Central Universities,China(Grant No.DUT12RC(3)14)
文摘Changes of the electron dynamics in hydrogen （H2） radio-frequency （RF） inductively coupled plasmas are investigated using a hairpin probe and an intensified charged coupled device （ICCD）. The electron density, plasma emission intensity, and input current （voltage） are measured during the E to H mode transitions at different pressures. It is found that the electron density, plasma emission intensity, and input current jump up discontinuously, and the input voltage jumps down at the E to H mode transition points. And the threshold power of the E to H mode transition decreases with the increase of the pressure. Moreover, space and phase resolved optical emission spectroscopic measurements reveal that, in the E mode, the RF dynamics is characterized by one dominant excitation per RF cycle, while in the H mode, there are two excitation maxima within one cycle.
基金Project supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant No.2011ZX02403-001)the National Natural Science Foundation of China(Grant No.11205025)
文摘In this work, a two-dimensional fluid model has been employed to study the characteristics of Ar/O2 radio frequency（RF） inductively coupled plasma discharges. The emphasis of this work has been put on the influence of the external parameters（i.e., the RF power, the pressure, and the Ar/O2 gas ratio） on the plasma properties. The numerical results show that the RF power has a significant influence on the amplitude of the plasma density rather than on the spatial distribution.However, the pressure and the Ar/O2 gas ratio affect not only the amplitude of the plasma density, but also the spatial uniformity. Finally, the comparison between the simulation results and the experimental data has been made at different gas pressures and oxygen contents, and a good agreement has been achieved.
基金supported by the National Key R&D Program of China(No.2017YFE0300106)National Natural Science Foundation of China(No.12075049)the Fundamental Research Funds for the Central Universities(Nos.DUT20LAB201 and DUT21LAB110)。
文摘In the design of negative hydrogen ion sources,a magnetic filter field of tens of Gauss at the expansion region is essential to reduce the electron temperature,which usually results in a magnetic field of around 10 Gauss in the driver region,destabilizing the discharge.The magnetic shield technique is proposed in this work to reduce the magnetic field in the driver region and improve the discharge characteristics.In this paper,a three-dimensional fluid model is developed within COMSOL to study the influence of the magnetic shield on the generation and transport of plasmas in the negative hydrogen ion source.It is found that when the magnetic shield material is applied at the interface of the expansion region and the driver region,the electron density can be effectively increased.For instance,the maximum of the electron density is 6.7×10^(17)m^(-3)in the case without the magnetic shield,and the value increases to 9.4×10^(17)m^(-3)when the magnetic shield is introduced.
基金supported by National Natural Science Foundation of China(NSFC)(Nos.11935005,11875101,12020101005,12005035)the Natural Science Foundation of Liaoning Province(No.2020-MS-114)+2 种基金the China Postdoctoral Science Foundation(No.2020M670741)the Fundamental Research Funds for the Central Universities(No.DUT20LAB201)financial support from the China Scholarship Council。
文摘In this paper,Maxwell equations are coupled with a radially localized global model and an analytical sheath model to investigate the electromagnetic effects under various frequencies and electron powers in large-area very high frequency symmetric capacitive argon discharges.Simulation results indicate that both the vacuum wavelength and the sheath width decrease with frequency,leading to the reduced surface wavelength.As a result,the standing wave effect becomes pronounced,causing the fact that the radial profiles of the electron density,radio frequency voltage,and sheath width shift from uniform over center-high to multiple-node.When the frequency is close to or higher than the series resonance frequency,the surface waves cannot propagate to the radial center because of the significant radial damping.Due to the lack of power deposition near the radial center,the electron density is nearly zero there,i.e.the stop band effect.As power increases,the higher electron density leads to the decrease of the skin depth.Therefore,the importance of the skin effect gradually exceeds that of the standing wave effect,giving rise to the transition from the center-high to edge-high electron density profiles.The method proposed in this work could help to predict the plasma distribution under different discharge conditions in a few minutes,which is of significant importance in optimizing the plasma processing.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 11935005 and 11875100)。
文摘Two classic radio-frequency(RF) plasmas, i.e., the capacitively and the inductively coupled plasmas(CCP and ICP),are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures(m Torr-Torr), high-frequency electric field(13.56 MHz-200 MHz),reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas,and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.
基金supported by the National Natural Science Foundation of China(Grant Nos.11335004 and 11405019)the Important National Science and Technology Specific Project of China(Grant No.2011ZX02403-001)
文摘The effect of the dielectric ring on the plasma radial uniformity is numerically investigated in the practical 450-mm capacitively coupled plasma reactor by a two-dimensional self-consistent fluid model. The simulations were performed for N2/Ar discharges at the pressure of 300 Pa, and the frequency of 13.56 MHz. In the practical plasma treatment process,the wafer is always surrounded by a dielectric ring, which is less studied. In this paper, the plasma characteristics are systematically investigated by changing the properties of the dielectric ring, i.e., the relative permittivity, the thickness and the length. The results indicate that the plasma parameters strongly depend on the properties of the dielectric ring. As the ratio of the thickness to the relative permittivity of the dielectric ring increases, the electric field at the wafer edge becomes weaker due to the stronger surface charging effect. This gives rise to the lower N~+ ion density, flux and N atom density at the wafer edge. Thus the homogeneous plasma density is obtained by selecting optimal dielectric ring relative permittivity and thickness. In addition, we also find that the length of the dielectric ring should be as short as possible to avoid the discontinuity of the dielectric materials, and thus obtain the large area uniform plasma.
基金supported by the National Natural Science Foundation of China(Grant Nos.11175034,11205025,11305023,and 11075029)
文摘A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to in- vestigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures, by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determi- native role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase （decrease） at the E to H （H to E） mode transition, indicating an improved （worsened） inductive power coupling efficiency.
基金supported by the National Natural Science Foundation of China(Grant Nos.11075029,11175034,and 11205025)the Fundamental Research Funds for Central Universities,China(Grant No.DUT12RC(3)14)
文摘The inflexion point of electron density and effective electron temperature curves versus radio-frequency （RF） bias voltage is observed in the H mode of inductively coupled plasmas （ICPs）. The electron energy probability function （EEPF） evolves first from a Maxwellian to a Druyvesteyn-like distribution, and then to a Maxwellian distribution again as the RF bias voltage increases. This can be explained by the interaction of two distinct bias-induced mechanisms, that is： bias- induced electron heating and bias-induced ion acceleration loss and the decrease of the effective discharge volume due to the sheath expansion. Furthermore, the trend of electron density is verified by a fluid model combined with a sheath module.
