Cristian Abraham - Academia.edu (original) (raw)
Papers by Cristian Abraham
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1996
This study examines the influence of plasma chemistry on SiO2 to Si etch selectivity in high dens... more This study examines the influence of plasma chemistry on SiO2 to Si etch selectivity in high density C2H2F4(1,1,1,2-tetrafluoroethane)/O 2 and CHF3/H2 discharges. Etch rate measurements of Si and SiO2 have been combined with chemical characterizations of the discharge using optical diagnostics and an in-line quadrupole mass spectrometer. The gas phase concentrations of CF2 and F as well as the mass spectrum of ions incident at the substrate have been measured for conditions producing SiO2/Si selectivities from 1 to over 30. For low density sources with high neutral to ion fluxes, the conventional theory is that selectivity is governed by the relative content of fluorine versus carbon in the fluorine and fluorocarbon radicals incident on the substrate. However, for the high density plasma discharges studied, the conventional theory may apply only when the contributions of both neutral radicals and fluorocarbon ions, CF+x, are considered. For the case of oxygen addition to C2H2F4 disc...
Aps Annual Gaseous Electronics Meeting Abstracts, Oct 1, 1998
Aps Annual Gaseous Electronics Meeting Abstracts, 1997
Aps Meeting Abstracts, Oct 1, 1997
International Conference on Plasma Science (papers in summary form only received), 1995
ABSTRACT Summary form only given. Spectroscopic measurements using Fourier transform infra-red (F... more ABSTRACT Summary form only given. Spectroscopic measurements using Fourier transform infra-red (FTIR) were made between 700 cm-1 and 4000 cm-1 in a magnetically confined inductively coupled plasma (MCICP) etching tool. The operating pressure range was 2-9 mTorr. The peak plasma density was of the order of 5×1011 cm -3 (at 750 W), and extended over the inner 30 cm diameter of the 40 cm diameter vacuum system. The axial length of the source is 50 cm. The electron temperature is 2-3 eV. Two fluorocarbon gases have been studied so far. The breakup of the tetrafluoromethane (CF4) parent gas was measured vs. power and pressure. The vibrational temperature of the parent gas was measured vs. Power between 500-1000 W and ranged between 315-350 K. The temperatures were slightly lower (10% lower at 1000 W) than previous results in an electron cyclotron resonance (ECR) etching tool. These results show that the rotational temperatures are close to the temperature of the vacuum walls. The MCICP has water cooled walls (~25°C). The ECR source chamber typically operates at 50-70°C. Products of the CF4 plasma discharge identified were SiF4, CO, CO2, and a fluorocarbon film that deposited on the windows. No substantial signal in the CF3 absorption region was observed. The rotational temperature of CO was measured at 500 W and 1000 W (370 K and 383 K, respectively). Preliminary results were obtained using trifluoromethane (CHF3) as the parent gas, where much more breakup of the parent gas was observed
This report documents measurements in inductively driven plasmas containing SF 6 / Argon gas mixt... more This report documents measurements in inductively driven plasmas containing SF 6 / Argon gas mixtures. The data in this report is presented in a series of appendices with a minimum of interpretation. During the course of this work we investigated: the electron and negative ion density using microwave interferometry and laser photodetachment; the optical emission; plasma species using mass spectrometry, and the ion energy distributions at the surface of the rf biased electrode in several configurations. The goal of this work was to assemble a consistent set of data to understand the important chemical mechanisms in SF 6 based processing of materials and to validate models of the gas and surface processes. Project Overview The purpose of this report is to document measurements in inductively driven plasmas containing SF 6 / Argon gas mixtures. During the course of this work a number of measurements were performed to begin to assemble a consistent set of data to 1) understand the important physical and chemical mechanisms active in SF 6 based processing of microelectronic materials and 2) to generate a data set to validate models of the gas and surface processes, including feature evolution. While SF 6 has been used for many years in plasma processes, there is a significant lack of fundamental data of the type required to validate models. Results from the various measurements are presented in a series of appendices. The appendices include a brief description of the measurement technique and then the data. In many cases, there is a minimum of interpretation. Appendix 1 includes the results of optical emission measurements of SF 6 gas mixtures over a range of powers and pressures. Appendix 2 reviews data obtained using a mass spectrometer. A mass spectrometer was used to survey the ion and neutral species present in the plasma and in the case of ion species, measure the scaling with plasma condition. Appendix 3 is a preprint of a paper submitted to the Journal of Applied Physics on measurements of the electron and negative ion density in SF 6 / Ar gas mixtures. Appendix 4 is a preprint of a paper submitted to the Journal of Vacuum Science and Technology A on measurements of the ion energy at the surface of a rf biased electrode with surface features.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2003
We measured electrical and plasma properties of a deep reactive ion etching Bosch process (Ar/SF6... more We measured electrical and plasma properties of a deep reactive ion etching Bosch process (Ar/SF6/C4F8) used for micromachining bulk silicon. The plasma-potential oscillations were measured by a glass-enclosed capacitive probe immersed in the plasma. We used rf-potential and current sensors installed at the output of the chuck’s matching network and a calibrated equivalent circuit model to compute the chuck potential wave form. The plasma density and electron temperature were measured using a floating Langmuir double probe. Time-resolved measurements were made throughout the etch and deposition cycles of the Bosch process. Plasma densities in the reactor were quite nonuniform, with plasma densities close to the wafer chuck being more than a factor of 4 lower than densities in the center of the “bulk plasma” formed by the induction coil. Estimates of the ion energy distribution were obtained from a validated numerical model that employed the experimental data. For standard process co...
We demonstrate the effect of varying the bias frequency on the energy distributions of ions strik... more We demonstrate the effect of varying the bias frequency on the energy distributions of ions striking an rf-biased electrode in discharges in an inductively-driven Gaseous Electronics Conference Reference cell. The discharge in this cell was formed by an inductive drive operating at 13.56 MHz. Using a mass-and-energy sensitive ion analyzer we examined the ion energy spectra for ions of several
We report the energy distributions of ions striking an rf-biased electrode in discharges in an in... more We report the energy distributions of ions striking an rf-biased electrode in discharges in an inductively-driven Gaseous Electronics Conference Reference cell. Using a mass-and-energy sensitive ion analyzer we examined the ion energy spectra for ions of several masses in discharges containing mixtures of the noble gases Ar, Ne, and Xe. The ions were sampled thru a pinhole in the rf-biased
Absolute densities of CF4 discharge products were measured in a magnetically confined inductively... more Absolute densities of CF4 discharge products were measured in a magnetically confined inductively coupled plasma (MCICP) etching tool. Input power levels of 800, 1000, and1200 W were used at 4 mTorr and 25 sccm of CF4 flow rate, and also at 10 mTorr and 3 sccm. The observed products are present in the discharge under steady state conditions, resulting from etching of the quartz window in the ICP source. The only detectable species in the plasma were CF4 and the stable neutral etch products CO, CO_2, COF_2, and SiF_4. About one third of the total neutral pressure was accounted for by the identified species. The largest product fractions were SiF_4and COF_2. The rotational temperature of CO was 350-450 K, slightly increasing with power. The CO vibrational temperature was estimated to be close to the rotational temperature, after careful exclusion of the infrared emission from the plasma, as confirmed by the complete removal of the intense atomic emission lines observed in the spectrum...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2003
We present an experimental and theoretical study of ion fluxes, energy distributions, and angular... more We present an experimental and theoretical study of ion fluxes, energy distributions, and angular distributions close to 300 μm tall “steps” on rf-biased wafers in high-density argon plasmas. This feature size is important in the etching of microelectromechanical systems. The theory and data show good agreement in most of the trends in the ion distributions as our sampling point approaches the foot of the step: (1) the ion flux decreases, (2) the ions move away from vertical, turning towards the step, and (3) the widths of the double-peaked ion energy distributions become narrower. The theory predicts that the hot neutral flux near the foot of the step is comparable to the ion flux. These hot neutrals may have important effects on the etching process.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002
We report the measurement of ion energy distributions at a radio frequency (rf)-biased electrode ... more We report the measurement of ion energy distributions at a radio frequency (rf)-biased electrode in inductively driven discharges in argon. We compare measurements made with a gridded energy analyzer and a commercial analyzer that contains a mass spectrometer and energy analyzer in tandem. The inductive drive and the rf bias in our Gaseous Electronics Conference reference cell were both at 13.56 MHz. By varying the plasma density, we were able to examine the transition region between the “low frequency limit” for rf bias and the intermediate frequency region where, at fixed bias frequency, the ion energy distribution width varies with the plasma density. We find that the experimental ion energy distributions become narrower as the time for ion transit through the sheath approaches the rf period, but that the ion distributions still have widths which are ∼90% of their low frequency limit when the ion transit time is 40% of the rf period. Space-charge-induced beam broadening inside ou...
Journal of Applied Physics, 2002
The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a... more The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a combination of computational modeling and experimental diagnostics has been utilized to understand charged species dynamics in an inductively coupled Ar/SF6 plasma discharge. The model is based on the two-dimensional Hybrid Plasma Equipment Model with a detailed plasma chemical mechanism for Ar/SF6. In the experiments, absolute electron density and total negative ion density have been measured using microwave interferometry and laser photodetachment, respectively. In addition, we have also utilized prior measurements of mass and energy resolved ion fluxes by Goyette et al. [J. Vac. Sci. Technol. A 19, 1294 (2001)]. Computational results show that all SFx+(x=0–5) ions are present in the plasma discharge. Important negative ions include SF6−, SF5−, and F−. Electron and positive ion densities increase with coil power due to enhanced ionization. However, negative ion densities decrease with...
Journal of Applied Physics, 2002
We present an experimental study of ion fluxes, energy distributions, and angular distributions i... more We present an experimental study of ion fluxes, energy distributions, and angular distributions inside surface features on radio frequency-biased wafers in high-density, inductively driven discharges in argon. Specifically, we present data on ion distributions at the bottom of 100-μm-square, 400-μm-deep “holes” in the wafer. Transmission of ions to the bottom of the holes increases with increasing ion energy and decreases as the sheath size becomes comparable to the hole size. Ion energy distributions at the bottom of the holes are narrower than distributions on the flat wafer surface. The flux of ions remains normal to the wafer surface over most of the hole area but the flux of ions within 6 μm of the wall is angled towards the wall. The observed trends are consistent with effects expected due to bowing of the plasma sheath around the surface features on the wafer. Scattering of ions off sidewalls contributes at most, only a small part of the ion flux reaching the bottom of the hole.
Journal of Applied Physics, 2002
Electron and negative ion densities were measured in an inductively driven plasma containing mixt... more Electron and negative ion densities were measured in an inductively driven plasma containing mixtures of SF6 and Argon. The electron and negative ion density were measured as functions of the induction coil power, pressure, bias power, and SF6/argon ratio. To investigate the influence of surface material, the rf biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf biased electrode were also measured for both surfaces as functions of induction coil power, pressure, rf bias, and SF6/argon ratio. For the range of induction powers, pressures, and bias powers investigated, the electron density had a maximum of 5×1012 cm−2 (line-integrated) or approximately 5×1011 cm−3. Over this same range the negative ion density ha...
Journal of Applied Physics, 2000
Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of... more Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of neutral copper, ground and metastable states, and neutral argon, metastable and resonance states, in an ionized physical vapor deposition plasma. Spectroscopic measurements were carried with a xenon arc lamp as a high intensity, continuum light source, and an optical multichannel detector. Copper radiative transitions in the wavelength range of 324.8–510.6 nm and argon radiative transitions in the 706.7–811.5 nm range were employed. The curve of growth method has been used to calculate the absolute line average densities from fractional absorption data. For a copper–argon plasma of neutral pressure 30 and 10 mTorr copper metastable state densities were found to lie in the range of 1010–1012 cm−3. Comparison of these densities with neutral copper densities derived from independent measurements of neutral copper flux at the substrate indicate gas phase temperatures greater than 1500 K und...
Journal of Applied Physics, 2001
Electron and negative ion densities were measured in inductively coupled discharges containing C4... more Electron and negative ion densities were measured in inductively coupled discharges containing C4F8. In addition, the identity of the negative ions in C2F6, CHF3, and C4F8 containing discharges was investigated with a photodetachment experiment utilizing a microwave resonant cavity structure. To investigate the influence of surface material, the rf-biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line-integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of the plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf-biased electrode were also measured for both surfaces as functions of induction coil power, pressure, and rf bias. For the range of induction powers, pressures, and bias power investigated, the electron density peaked at 6×1012 cm−2 (line integrated), or approximately 6×1011 cm−3. The negative ion density peaked...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002
In this article, we present ion energy distributions (IEDs) at a rf-biased surface as a function ... more In this article, we present ion energy distributions (IEDs) at a rf-biased surface as a function of driving frequency and ion mass. The experiments were carried out in high-density inductively coupled rare-gas (Ne,Ar,Xe) plasmas. Our quadrupole mass and cylindrical-mirror energy analyzer sampled ions incident on a rf-biased pinhole located in the center of the wafer chuck. The electron density, electron temperature, and plasma and chuck potential oscillations were measured, and they provided inputs to numerical models used to predict IEDs, which were shown to closely match our experimental results under certain conditions. For a given driving frequency, heavier ions showed narrower IEDs and, for a given ion mass, the IED became narrower and shifted to a higher mean energy with increased driving frequency, in agreement with calculations.
SPIE Proceedings, 2005
Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-t... more Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-term component reliability because it is within this environment that all internal materials age. As MEMS package sizes decrease with miniaturization, characterization of the internal atmosphere becomes increasingly difficult. Typical transistor metal cans (e.g., TO-5 type) and large MEMS devices have internal volumes of tenths of
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1996
This study examines the influence of plasma chemistry on SiO2 to Si etch selectivity in high dens... more This study examines the influence of plasma chemistry on SiO2 to Si etch selectivity in high density C2H2F4(1,1,1,2-tetrafluoroethane)/O 2 and CHF3/H2 discharges. Etch rate measurements of Si and SiO2 have been combined with chemical characterizations of the discharge using optical diagnostics and an in-line quadrupole mass spectrometer. The gas phase concentrations of CF2 and F as well as the mass spectrum of ions incident at the substrate have been measured for conditions producing SiO2/Si selectivities from 1 to over 30. For low density sources with high neutral to ion fluxes, the conventional theory is that selectivity is governed by the relative content of fluorine versus carbon in the fluorine and fluorocarbon radicals incident on the substrate. However, for the high density plasma discharges studied, the conventional theory may apply only when the contributions of both neutral radicals and fluorocarbon ions, CF+x, are considered. For the case of oxygen addition to C2H2F4 disc...
Aps Annual Gaseous Electronics Meeting Abstracts, Oct 1, 1998
Aps Annual Gaseous Electronics Meeting Abstracts, 1997
Aps Meeting Abstracts, Oct 1, 1997
International Conference on Plasma Science (papers in summary form only received), 1995
ABSTRACT Summary form only given. Spectroscopic measurements using Fourier transform infra-red (F... more ABSTRACT Summary form only given. Spectroscopic measurements using Fourier transform infra-red (FTIR) were made between 700 cm-1 and 4000 cm-1 in a magnetically confined inductively coupled plasma (MCICP) etching tool. The operating pressure range was 2-9 mTorr. The peak plasma density was of the order of 5×1011 cm -3 (at 750 W), and extended over the inner 30 cm diameter of the 40 cm diameter vacuum system. The axial length of the source is 50 cm. The electron temperature is 2-3 eV. Two fluorocarbon gases have been studied so far. The breakup of the tetrafluoromethane (CF4) parent gas was measured vs. power and pressure. The vibrational temperature of the parent gas was measured vs. Power between 500-1000 W and ranged between 315-350 K. The temperatures were slightly lower (10% lower at 1000 W) than previous results in an electron cyclotron resonance (ECR) etching tool. These results show that the rotational temperatures are close to the temperature of the vacuum walls. The MCICP has water cooled walls (~25°C). The ECR source chamber typically operates at 50-70°C. Products of the CF4 plasma discharge identified were SiF4, CO, CO2, and a fluorocarbon film that deposited on the windows. No substantial signal in the CF3 absorption region was observed. The rotational temperature of CO was measured at 500 W and 1000 W (370 K and 383 K, respectively). Preliminary results were obtained using trifluoromethane (CHF3) as the parent gas, where much more breakup of the parent gas was observed
This report documents measurements in inductively driven plasmas containing SF 6 / Argon gas mixt... more This report documents measurements in inductively driven plasmas containing SF 6 / Argon gas mixtures. The data in this report is presented in a series of appendices with a minimum of interpretation. During the course of this work we investigated: the electron and negative ion density using microwave interferometry and laser photodetachment; the optical emission; plasma species using mass spectrometry, and the ion energy distributions at the surface of the rf biased electrode in several configurations. The goal of this work was to assemble a consistent set of data to understand the important chemical mechanisms in SF 6 based processing of materials and to validate models of the gas and surface processes. Project Overview The purpose of this report is to document measurements in inductively driven plasmas containing SF 6 / Argon gas mixtures. During the course of this work a number of measurements were performed to begin to assemble a consistent set of data to 1) understand the important physical and chemical mechanisms active in SF 6 based processing of microelectronic materials and 2) to generate a data set to validate models of the gas and surface processes, including feature evolution. While SF 6 has been used for many years in plasma processes, there is a significant lack of fundamental data of the type required to validate models. Results from the various measurements are presented in a series of appendices. The appendices include a brief description of the measurement technique and then the data. In many cases, there is a minimum of interpretation. Appendix 1 includes the results of optical emission measurements of SF 6 gas mixtures over a range of powers and pressures. Appendix 2 reviews data obtained using a mass spectrometer. A mass spectrometer was used to survey the ion and neutral species present in the plasma and in the case of ion species, measure the scaling with plasma condition. Appendix 3 is a preprint of a paper submitted to the Journal of Applied Physics on measurements of the electron and negative ion density in SF 6 / Ar gas mixtures. Appendix 4 is a preprint of a paper submitted to the Journal of Vacuum Science and Technology A on measurements of the ion energy at the surface of a rf biased electrode with surface features.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2003
We measured electrical and plasma properties of a deep reactive ion etching Bosch process (Ar/SF6... more We measured electrical and plasma properties of a deep reactive ion etching Bosch process (Ar/SF6/C4F8) used for micromachining bulk silicon. The plasma-potential oscillations were measured by a glass-enclosed capacitive probe immersed in the plasma. We used rf-potential and current sensors installed at the output of the chuck’s matching network and a calibrated equivalent circuit model to compute the chuck potential wave form. The plasma density and electron temperature were measured using a floating Langmuir double probe. Time-resolved measurements were made throughout the etch and deposition cycles of the Bosch process. Plasma densities in the reactor were quite nonuniform, with plasma densities close to the wafer chuck being more than a factor of 4 lower than densities in the center of the “bulk plasma” formed by the induction coil. Estimates of the ion energy distribution were obtained from a validated numerical model that employed the experimental data. For standard process co...
We demonstrate the effect of varying the bias frequency on the energy distributions of ions strik... more We demonstrate the effect of varying the bias frequency on the energy distributions of ions striking an rf-biased electrode in discharges in an inductively-driven Gaseous Electronics Conference Reference cell. The discharge in this cell was formed by an inductive drive operating at 13.56 MHz. Using a mass-and-energy sensitive ion analyzer we examined the ion energy spectra for ions of several
We report the energy distributions of ions striking an rf-biased electrode in discharges in an in... more We report the energy distributions of ions striking an rf-biased electrode in discharges in an inductively-driven Gaseous Electronics Conference Reference cell. Using a mass-and-energy sensitive ion analyzer we examined the ion energy spectra for ions of several masses in discharges containing mixtures of the noble gases Ar, Ne, and Xe. The ions were sampled thru a pinhole in the rf-biased
Absolute densities of CF4 discharge products were measured in a magnetically confined inductively... more Absolute densities of CF4 discharge products were measured in a magnetically confined inductively coupled plasma (MCICP) etching tool. Input power levels of 800, 1000, and1200 W were used at 4 mTorr and 25 sccm of CF4 flow rate, and also at 10 mTorr and 3 sccm. The observed products are present in the discharge under steady state conditions, resulting from etching of the quartz window in the ICP source. The only detectable species in the plasma were CF4 and the stable neutral etch products CO, CO_2, COF_2, and SiF_4. About one third of the total neutral pressure was accounted for by the identified species. The largest product fractions were SiF_4and COF_2. The rotational temperature of CO was 350-450 K, slightly increasing with power. The CO vibrational temperature was estimated to be close to the rotational temperature, after careful exclusion of the infrared emission from the plasma, as confirmed by the complete removal of the intense atomic emission lines observed in the spectrum...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2003
We present an experimental and theoretical study of ion fluxes, energy distributions, and angular... more We present an experimental and theoretical study of ion fluxes, energy distributions, and angular distributions close to 300 μm tall “steps” on rf-biased wafers in high-density argon plasmas. This feature size is important in the etching of microelectromechanical systems. The theory and data show good agreement in most of the trends in the ion distributions as our sampling point approaches the foot of the step: (1) the ion flux decreases, (2) the ions move away from vertical, turning towards the step, and (3) the widths of the double-peaked ion energy distributions become narrower. The theory predicts that the hot neutral flux near the foot of the step is comparable to the ion flux. These hot neutrals may have important effects on the etching process.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002
We report the measurement of ion energy distributions at a radio frequency (rf)-biased electrode ... more We report the measurement of ion energy distributions at a radio frequency (rf)-biased electrode in inductively driven discharges in argon. We compare measurements made with a gridded energy analyzer and a commercial analyzer that contains a mass spectrometer and energy analyzer in tandem. The inductive drive and the rf bias in our Gaseous Electronics Conference reference cell were both at 13.56 MHz. By varying the plasma density, we were able to examine the transition region between the “low frequency limit” for rf bias and the intermediate frequency region where, at fixed bias frequency, the ion energy distribution width varies with the plasma density. We find that the experimental ion energy distributions become narrower as the time for ion transit through the sheath approaches the rf period, but that the ion distributions still have widths which are ∼90% of their low frequency limit when the ion transit time is 40% of the rf period. Space-charge-induced beam broadening inside ou...
Journal of Applied Physics, 2002
The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a... more The chemistry of high-density SF6 plasma discharges is not well characterized. In this article, a combination of computational modeling and experimental diagnostics has been utilized to understand charged species dynamics in an inductively coupled Ar/SF6 plasma discharge. The model is based on the two-dimensional Hybrid Plasma Equipment Model with a detailed plasma chemical mechanism for Ar/SF6. In the experiments, absolute electron density and total negative ion density have been measured using microwave interferometry and laser photodetachment, respectively. In addition, we have also utilized prior measurements of mass and energy resolved ion fluxes by Goyette et al. [J. Vac. Sci. Technol. A 19, 1294 (2001)]. Computational results show that all SFx+(x=0–5) ions are present in the plasma discharge. Important negative ions include SF6−, SF5−, and F−. Electron and positive ion densities increase with coil power due to enhanced ionization. However, negative ion densities decrease with...
Journal of Applied Physics, 2002
We present an experimental study of ion fluxes, energy distributions, and angular distributions i... more We present an experimental study of ion fluxes, energy distributions, and angular distributions inside surface features on radio frequency-biased wafers in high-density, inductively driven discharges in argon. Specifically, we present data on ion distributions at the bottom of 100-μm-square, 400-μm-deep “holes” in the wafer. Transmission of ions to the bottom of the holes increases with increasing ion energy and decreases as the sheath size becomes comparable to the hole size. Ion energy distributions at the bottom of the holes are narrower than distributions on the flat wafer surface. The flux of ions remains normal to the wafer surface over most of the hole area but the flux of ions within 6 μm of the wall is angled towards the wall. The observed trends are consistent with effects expected due to bowing of the plasma sheath around the surface features on the wafer. Scattering of ions off sidewalls contributes at most, only a small part of the ion flux reaching the bottom of the hole.
Journal of Applied Physics, 2002
Electron and negative ion densities were measured in an inductively driven plasma containing mixt... more Electron and negative ion densities were measured in an inductively driven plasma containing mixtures of SF6 and Argon. The electron and negative ion density were measured as functions of the induction coil power, pressure, bias power, and SF6/argon ratio. To investigate the influence of surface material, the rf biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf biased electrode were also measured for both surfaces as functions of induction coil power, pressure, rf bias, and SF6/argon ratio. For the range of induction powers, pressures, and bias powers investigated, the electron density had a maximum of 5×1012 cm−2 (line-integrated) or approximately 5×1011 cm−3. Over this same range the negative ion density ha...
Journal of Applied Physics, 2000
Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of... more Optical absorption spectroscopy has been used to measure absolute, average gas phase densities of neutral copper, ground and metastable states, and neutral argon, metastable and resonance states, in an ionized physical vapor deposition plasma. Spectroscopic measurements were carried with a xenon arc lamp as a high intensity, continuum light source, and an optical multichannel detector. Copper radiative transitions in the wavelength range of 324.8–510.6 nm and argon radiative transitions in the 706.7–811.5 nm range were employed. The curve of growth method has been used to calculate the absolute line average densities from fractional absorption data. For a copper–argon plasma of neutral pressure 30 and 10 mTorr copper metastable state densities were found to lie in the range of 1010–1012 cm−3. Comparison of these densities with neutral copper densities derived from independent measurements of neutral copper flux at the substrate indicate gas phase temperatures greater than 1500 K und...
Journal of Applied Physics, 2001
Electron and negative ion densities were measured in inductively coupled discharges containing C4... more Electron and negative ion densities were measured in inductively coupled discharges containing C4F8. In addition, the identity of the negative ions in C2F6, CHF3, and C4F8 containing discharges was investigated with a photodetachment experiment utilizing a microwave resonant cavity structure. To investigate the influence of surface material, the rf-biased electrode was covered with a silicon wafer or a fused silica (SiO2) wafer. Line-integrated electron density was determined using a microwave interferometer, and absolute negative ion densities in the center of the plasma were inferred using laser photodetachment spectroscopy. Voltage and current at the induction coil and rf-biased electrode were also measured for both surfaces as functions of induction coil power, pressure, and rf bias. For the range of induction powers, pressures, and bias power investigated, the electron density peaked at 6×1012 cm−2 (line integrated), or approximately 6×1011 cm−3. The negative ion density peaked...
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2002
In this article, we present ion energy distributions (IEDs) at a rf-biased surface as a function ... more In this article, we present ion energy distributions (IEDs) at a rf-biased surface as a function of driving frequency and ion mass. The experiments were carried out in high-density inductively coupled rare-gas (Ne,Ar,Xe) plasmas. Our quadrupole mass and cylindrical-mirror energy analyzer sampled ions incident on a rf-biased pinhole located in the center of the wafer chuck. The electron density, electron temperature, and plasma and chuck potential oscillations were measured, and they provided inputs to numerical models used to predict IEDs, which were shown to closely match our experimental results under certain conditions. For a given driving frequency, heavier ions showed narrower IEDs and, for a given ion mass, the IED became narrower and shifted to a higher mean energy with increased driving frequency, in agreement with calculations.
SPIE Proceedings, 2005
Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-t... more Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-term component reliability because it is within this environment that all internal materials age. As MEMS package sizes decrease with miniaturization, characterization of the internal atmosphere becomes increasingly difficult. Typical transistor metal cans (e.g., TO-5 type) and large MEMS devices have internal volumes of tenths of