Multipolar Electron Cyclotron Resonance Research Articles

Low-Temperature SiO2 Layers Deposited by Combination of ECR Plasma and Supersonic Silane/Helium Jet

As the semiconductor industry strives toward wafer postprocessing and three-dimensional integration, a demand has arisen for high-quality thin films deposited at temperatures below . In this work, we present films deposited at near room temperature, using a multipolar electron cyclotron resonance (ECR) plasma source, introducing the gas by using a high-velocity jet of silane diluted in helium. The electrical properties were studied under varying deposition parameters, such as gas flow rate, deposition pressure, and postdeposition and postmetallization annealing processes. At a low pressure, low flow and high helium flow, device-quality layers were obtained after a deposition combined with a postmetallization annealing at . These layers exhibited a refractive index of 1.46, an ratio of 2, an interface trap density in the order of , an oxide charge density down to , and a breakdown field up to . They are thus suitable as a gate dielectric in a thin-film transistor.

Utilization of ECR mechanism of electrons heating in multipolar magnetic systems of low-pressure plasma Reactors

In this paper, the electron-cyclotron resonance (ECR) mechanism of electrons heating by electromagnetic wave in ECR microwave low-pressure plasma reactors is considered. In such reactors, ionization is mainly provided by fast electrons trapped by multipolar magnetic system. A particle simulation is carried out for statistical ensemble of electrons in magnetic systems of different configurations with taking into account previous experimental results. The escape of fast electrons from the magnetic traps to the walls is identified as the major factor behind the loss of electrons in the limit of a collisionless plasma. A comparative evaluation of different multipolar magnetic systems is made. Basic requirements are set out concerning the optimal design of multipolar ECR plasma reactors. Several approaches for providing the efficient ECR heating of electrons are proposed.

Low Hydrogen Content Silicon Nitride Films Deposited at Room Temperature with an ECR Plasma Source

Silicon nitride layers with very low hydrogen content (less than 1 atomic percent) were deposited at near room temperature, from and with a multipolar electron cyclotron resonance plasma. The influences of pressure and nitrogen flow rate on physical and electrical properties were studied in order to minimize the hydrogen and oxygen content in the layers. The optimized layers were characterized by a refractive index of 1.98, a dielectric constant of 7.2, and Si/N ratio values of 0.78. The layers exhibited very good dielectric strength, which was confirmed by large breakdown fields of 12 MV/cm, very high resistivities of Ω cm, and maximum charges to breakdown values of 90 C/cm2. Increasing the deposition pressure and decreasing the flow improved the SiN/Si interface, due to increased oxygen incorporation. The dominant conduction mechanism in the layers was the Poole-Frenkel effect. The critical field and the trap energy had similar dependencies on deposition pressure. Fowler-Nordheim tunneling occurred at high gate biases, for the layers deposited at the highest pressure of about 22 mTorr. © 2004 The Electrochemical Society. All rights reserved.

Conduction and trapping mechanisms in SiO2 films grown near room temperature by multipolar electron cyclotron resonance plasma enhanced chemical vapor deposition

Silicon dioxide layers with stoichiometric composition and excellent electrical properties were deposited at a substrate temperature of 60 °C with an electron cyclotron resonance plasma source. This work is focused on determining the electrical conduction and trapping mechanisms of the deposited films. From the temperature dependence of current density–electric field characteristics, Fowler–Nordheim tunneling was found to be the dominant conduction mechanism in SiO2 films obtained with low silane flow and at low pressure. For layers deposited with higher silane flows and higher pressures, the current at low biases is highly dependent on temperature. Positive charge was measured at the Si/SiO2 interface during low electric stress, while electrons were trapped at the interface for electric fields higher than 7 MV/cm. Constant current stress measurements confirmed that low silane flow and low total pressure are suitable deposition conditions for obtaining a film comparable to thermally grown oxide from the reliability point of view.

Room temperature SiO2 films deposited by multipolar ECR PECVD

The demand for high mobility TFTs realised on temperature unstable substrates is increasing. These devices require thin, low-temperature, high-quality gate dielectrics. It is known however, that a low deposition temperature degrades the films properties. In this work, we report that films comparable to thermally grown oxide can be deposited at room temperature, with a modified electron cyclotron resonance (ECR) plasma source, called multipolar ECR. SiO 2 films with interface charge in the order of 10 11 ions/cm 2 , critical field of 6 MV/cm and refractive index of 1.46 were obtained for optimal deposition conditions. The effects of total pressure and microwave power on material properties were studied. The electrical behaviour of the SiO 2 layers was explained in terms of film structure and deposition parameters.

Steady-state direct-current plasma immersion ion implantation using a multipolar magnetic field electron cyclotron resonance plasma source

In semiconductor plasma immersion ion implantation (PIII) applications such as the synthesis of silicon-on-insulator by hydrogen PIII and ion cut, only ions arriving at the top surface of the sample stage are important. The ions implanted into the other surfaces of the sample chuck actually not only decrease the efficiency of the power supply and plasma source but also give rise to metallic contamination. In addition, low energy ions introduced by the initial plasma sheath propagation, pulse rise time, and pulse fall time introduce a large surface hydrogen concentration that creates surface damage and affects the wafer bonding efficacy. We have theoretically demonstrated direct-current PIII (DC-PIII) which retains the x–y immersion characteristic while simultaneously reducing this low energy ion component, obviating the need for the expensive power modulator, and extending the voltage ceiling that is no longer limited by the vacuum chamber and power modulator. In this article, we describe our hydrogen DC-PIII experiments using a conducting grid placed between the wafer stage and a multipolar electron cyclotron resonance plasma source. The grounded grid stops the propagation of the plasma sheath, thereby removing the vacuum chamber size limitation. Ions are formed in the plasma sustained by an external plasma source above the grid and accelerated through the lower zone to be implanted into the wafer biased by only a dc power supply. Atomic force microscopy, hydrogen forward scattering, and secondary ion mass spectrometry analyses indicate uniform hydrogen PIII into a 100 mm silicon wafer and the surface hydrogen component is indeed reduced significantly compared to conventional pulsed PIII.

Experimental investigation of the matching and impressed electric field of a multipolar electron cyclotron resonance discharge

The experimental performance of an end excited, internally tuned, multipolar electron cyclotron resonance plasma source is investigated versus several independent input variables: (1) incident power (185–350 W), (2) discharge pressure (1–7 mTorr), and (3) microwave matching (applicator length, Ls, varies from 65–170 mm). Plasma source performance in argon gas is determined from measurements of (1) absorbed microwave power, (2) the magnitude, and (3) the spatial variation of the impressed electric field, and the output (4) plasma density and (5) electron temperature. The nonlinear experimental relationships between variations in the input variables and performance variables are established. Two well-matched stable discharge operational regions or modes are identified as Ls is varied. Using the measured impressed electric field patterns, these two modes are identified as TM, Φ symmetric, λg, and λg/2 standing wave modes. As Ls, pressure and power vary, considerable hysteresis in absorbed power and density is observed. However, it is shown that this complex input/output discharge behavior can be approximately explained using simple global plasma models. Despite the multiple steady states and hystereses, it is shown that the discharge can be easily maintained in well-matched, high density (ne>3×1011/cm3) stable operating conditions. The impressed electric field varies between 3 and 4.5 kV/m. An equivalent circuit of the plasma loaded cavity applicator is developed and provides important insights for the plasma matching process. The microwave coupling efficiencies are greater than 98% and the ion production costs vary between 300 and 450 eV/ion versus the experimental inputs. The data presented is useful for plasma source optimization and in developing intelligent plasma processing control strategies.

Investigation of multipolar electron cyclotron resonance plasma source sensors and models for plasma control

The sensors and models needed for the control of a high-density, multipolar, electron cyclotron resonance (ECR) plasma source have been studied for an argon soft-sputter clean process for semiconductor wafers. The ECR plasma source studied had a discharge diameter of 12.5 cm, a processing chamber diameter of 40 cm, and an excitation frequency of 2.45 GHz. The implementation of control on this plasma machine has been investigated by characterizing the machine using plasma diagnostic measurements, by implementing and testing sensors, and by developing both analytical and statistical models of the machine operation. The real-time usage of sensor data together with input parameter adjustments has been used to obtain predictable soft-sputter/etch rates in the process.

High-aspect-ratio Si etching for microsensor fabrication

Etching of high-aspect-ratio Si structures for microsensors was carried out in a Cl2 plasma generated by a multipolar electron cyclotron resonance (ECR) source. Si etch rate is found to increase with microwave and rf power, and it is the highest at 1 mTorr over the range of 0.5–50 mTorr. Optical emission spectroscopy (OES) and mass spectrometry (MS) were used to monitor the etch process to provide precise control for the sensor fabrication. The Si emission intensity at 288.1 nm and the mass spectrometric signal for 63SiCl+ follow the Si etch rate directly. The selectivity of etch masks decreases at higher rf power and Ni has higher selectivity than SiO2. Si etch rate is reduced for structures with smaller linewidth, but this microloading effect decreases at lower pressure. For the etch conditions used, the Si etch rate remains almost constant when flow rate is changed, but the optical emission and mass spectrometric signals of the etch products are found to decrease with increasing flow. Endpoint detection is applied to monitor etching of the resonators. Both OES and MS provide a clear indication when the polycrystalline Si is etched down to the oxide layer. With a Cl2 plasma at 3 mTorr, 100 W microwave power, 100 W rf power, and 8 cm below the ECR source, high-aspect-ratio microstructures in Si with vertical profile and smooth morphology were etched. These sensing elements are 28 μm deep with 1.5 μm gap, providing a high aspect ratio of 19 in Si. The width of the elements was reduced by oxidation followed by wet etching of the dry etched microstructures to provide better sensitivity for the microsensors.

Mass Spectrometry, Optical Emission Spectroscopy, and Atomic Force Microscopy Studies of Si Etch Characteristics in a Cl2 Plasma Generated by an Electron Cyclotron Resonance Source

Etching of Si with a Cl2 plasma generated by a multipolar electron cyclotron resonance source has been studied using mass spectrometry, optical emission spectroscopy (OES), and atomic force microscopy (AFM). It is found that the Si etch rate can be related to the SiCl63 intensity measured using mass spectrometry and the Si emission intensity at 634.6 nm using OES. At higher microwave or rf power, the Si etch rate, SiCl63 intensity, and Si emission intensity increase but the selectivity of Si over SiO2 decreases. Selectivity >80 is obtained with 30% O2 addition in Cl2. The induction time for Si etching is monitored by mass spectrometry and it decreases with microwave or rf power. Surface roughness is measured by AFM and it increases slightly with microwave or rf power. The optimized condition for Si etching was applied to the etching of polysilicon gate down to the thin gate oxide. A two-step etch process was developed for the etching of 0.35 µ m polysilicon gate with vertical profile, smooth morphology, and high selectivity to the underlying gate oxide. Only 0.5 nm of the gate oxide was removed with 100% overetch. End point for polysilicon gate etching was clearly monitored using mass spectrometry or OES.

Characterization of etch-induced damage for Si etched in Cl2 plasma generated by an electron cyclotron resonance source

A Cl2 plasma generated by a multipolar electron cyclotron resonance source is used for Si etching, and the effects of etch-induced damage are studied using Schottky diodes and metal–oxide–semiconductor (MOS) capacitors to investigate the effects of dry etching on device performance. The Schottky diode characteristics improved with increasing microwave power when the self-induced bias voltage was kept at −150 V, but degraded with increasing microwave power at −50 V. The diode characteristics were close to an ideal diode when low rf power, high Cl2 percentage, and close source distance were used. Varying the sample temperature during etching from −130 to 350 °C has no effect on the Schottky diode characteristics. The damaged layer was removed by reactive chlorine radicals and by wet etching. After removing 60 nm from the dry-etched surface, the Schottky diode performance was comparable to that of an ideal diode. Annealing at 800 °C in Ar for 5 min has similar effects. When the oxide was etched and MOS capacitors were fabricated on the etched oxide, no electrical degradation was observed. When Si was etched and the etched surface was oxidized to form MOS capacitors. The breakdown field was found to decrease with high microwave power, high rf power, and low Cl2 concentration. However, dry etching has no influence on fixed charge density, and the interface state density only increases slightly from 1.2 to 2.5×1010 cm−2.

Discharge characteristics of a 5 cm multipolar electron cyclotron resonance ion sourcea)

A compact 5-cm-diam multipolar electron cyclotron resonance (ECR) ion source is characterized. The source is experimentally studied with no grids using argon gas with 50–250 W of 2.45-GHz microwave input power. Using a microcoaxial probe it was confirmed that the exciting electromagnetic fields within the resonant cavity were indeed TE111, as expected from the critical cavity dimensions. Double Langmuir probe measurements indicate high densities of about (4–5)×1011/cm3 near the source, and 5 cm downstream from the source output the densities become very uniform with a value of about 5×1010/cm3 over a 10-cm diameter. Electron energy distribution functions (EEDF) were measured using a single Langmuir probe. Average electron energies were seen to be about 8–10 eV with an energy distribution function falling between a Maxwellian and a Druyvesteyn distribution. Ion energy distribution functions (IEDF) were measured with a multigrid energy analyzer. It was seen that the distribution functions were narrow and peaked [with a full width half maximum (FWHM) of about 5 eV] except under certain conditions. Above 200-W input power, and also below about 0.5 mTorr there is significant broadening of the ion distribution function. It is speculated that the former may be caused by gas heating, and the latter may be caused by the presence of Ar+2 ions. With its high current densities (≳10 mA/cm2) and low average ion energies (<40 eV), it is expected that this ion/plasma source will be very useful in many etching and deposition applications.

Discharge characteristics of a 5 cm multipolar electron cyclotron resonance ion source (abstract)a)

A compact 5-cm-diam multipolar electron cyclotron resonance (ECR) ion source is characterized. The source is experimentally studied with no grids using argon gas with 50–250 W of 2.45-GHz microwave input power. Using a microcoaxial probe it was confirmed that the exciting electromagnetic fields within the resonant cavity were indeed TE111, as expected from the critical cavity dimensions. Double Langmuir probe measurements indicate high densities of about (4–5)×1011/cm3 near the source, and 5 cm downstream from the source output the densities become very uniform with a value of about 5×1010/cm3 over a 10-cm diameter. Electron energy distribution functions (EEDFs) were measured using a single Langmuir probe. Average electron energies were seen to be about 8–10 eV with an energy distribution function falling between a Maxwellian and a Druyvesteyn distribution. Ion energy distribution functions (IEDF) were measured with a multigrid energy analyzer. It was seen that the distribution functions were narrow and peaked [with a full width half maximum (FWHM) of about 5 eV] except under certain conditions. Above 200-W input power, and also below about 0.5 mTorr there is significant broadening of the ion distribution function. It is speculated that the former may be caused by gas heating, and the latter may be caused by the presence of Ar+2 ions. With its high current densities (≳10 mA/cm2) and low average ion energies (<40 eV), it is expected that this ion/plasma source will be very useful in many etching and deposition applications.

Dependence of etch characteristics on charge particles as measured by Langmuir probe in a multipolar electron cyclotron resonance source

A multipolar electron cyclotron resonance (ECR) plasma source was characterized by Langmuir probe measurements and the charged particle energy and density are related to photoresist etch rate. Ion density was found to increase with microwave power but decrease with source distance, and is independent of rf power and flow rate. Among the different gases investigated, Ar plasma was found to have higher ion density compared to O2, N2, and Cl2 discharge. Ion density peaked at 5 mTorr for Ar and 2 mTorr for O2 plasma. For a N2 plasma, the maximum ion density was found to occur at 10 mTorr at 3 cm and 2 mTorr at 23 cm below the ECR source. Electron temperature is ∼3 eV for pressure ranging from 1 to 5 mTorr but decreases to 2 eV at 20 mTorr. Photoresist etch rate follows the same trend as ion density. It increases with microwave power and decreases with source distance. On the other hand, photoresist etch rate increases with rf power and flow rate, even though the ion density remains constant. This suggests that photoresist etching also depends on ion energy and concentrations of neutral species. Ion density uniformity of ±1% for a N2 plasma was measured across the central 24 cm along the stage at 23 cm below the source. For a source distance between 3 and 23 cm, uniformity of ±3% was obtained over a 12 cm diam region on the stage. In an O2 plasma, photoresist etch rate uniformity of ±2% was measured for a 10 cm diam wafer and the corresponding ion density uniformity was ±1%.

Surface Damage on GaAs Etched Using a Multipolar Electron Cyclotron Resonance Source

Surface damage on induced by etching using an electron cyclotron resonance (ECR) source has been studied as a function of pressure, microwave power, sample distance from the ECR source, RF power, and gas composition. Damage was evaluated by measuring the current‐voltage (I‐V) and capacitance‐voltage (C‐V) characteristics on Schottky diodes fabricated on the etched surface. Etch‐induced damage is found to depend mainly on the ion energy and the concentration of reactive species. The diode characteristics are improved when the samples are etched at lower pressure, higher microwave power, and closer distance to the ECR source. The diodes become more leaky and the intercept voltage extracted from the C‐V measurements increased at higher RF power, which suggests the formation of a heavily damaged layer at higher ion energy. It is also found that an Ar plasma introduces more damage than a plasma as observed by a higher ideality factor and a lower barrier height on the samples etched by Ar sputtering. Addition of , as little as 10%, results in diode characteristics close to that of the unetched sample. The damage observed can be classified into major and minor degrees of damage. In this study, most of the samples have only minor damage. Major damage was observed only on samples that were etched at high RF power or with a low concentration of reactive species.

Low Temperature Etching of Silylated Resist in an Oxygen Plasma Generated by an Electron Cyclotron Resonance Source

Dry development of silylated resist has been studied using an plasma generated by a multipolar electron cyclotron resonance source. Etch rate, uniformity, selectivity, and profile were investigated as a function of process parameters including microwave power, RF power, flow rate, sample area, pressure, temperature, and gas addition. It was found that etch rate increases as microwave and/or RF power increase. Vertical etch profile was obtained by using low pressure (3 mTorr) and 50 W RF power. As the area of the samples was increased from 1 to 81 cm2, the etch rate decreased from 0.85 to 0.6 μm/min at a flow of 10 sccm but remained constant at 0.9 μm/min with 100 sccm . Etch rate was independent of temperature and decreased with the addition of or . Etch uniformity was within ±3% across a 150 mm wafer for most etch conditions. The selectivity of the silylated layer over the photoresist degraded from 445 to 14 as RF power was increased from 25 to 100 W. Residue‐free surface and vertical profile have been obtained with features as small as 0.1 μm.

Etching of Si with Cl2 using an electron cyclotron resonance source

A Cl2 plasma generated by a multipolar electron cyclotron resonance (ECR) source was used to etch Si. Etch rate of Si was found to increase with microwave power and rf power, but decrease with source distance and Ar addition. Etch rate increases with pressure up to 1 mTorr, then decreases at higher pressure. Temperature ranging from − 130 to 100 °C has no significant influence on the etch rate, profile, and morphology. Vertical profile and smooth morphology in Si can be obtained by using low microwave power and low pressure. With a Cl2 plasma at 1 mTorr, 50 W microwave power, 70 W rf power, and 15 cm below the ECR source, 0.15-μm-wide features in Si were etched with 7:1 aspect ratio. Schottky diodes were fabricated on the etched surface to evaluate etch-induced damage. Breakdown voltage was found to increase with microwave power but decrease with rf power and source distance. Ideality factor and barrier height degrade at high rf power and long source distance. One of the most important factors to maintain high quality diode characteristics is by using low self-induced dc bias voltage. In a system with an ECR source and a rf-powered electrode, it has the advantage of generating high density ions at low ion energy, therefore providing high etch rate with minimal surface damage.

Experimental scaling laws for multipolar electron cyclotron resonance plasma sources

The performance of five different diameter multipolar electron cyclotron resonance (ECR) plasma sources is evaluated by comparing (1) ion production energy costs, (2) microwave coupling efficiency, (3) electron temperatures and ion energies, and (4) discharge absorbed power density versus input power and pressure. The experimental measurements demonstrate that ECR plasma source performance is a function of operating pressure, gas type, input power, discharge size, and applicator size. When using 2.45 GHz excitation the most efficient and optimum plasma source sizes have diffusion lengths of 1.5–2.5 cm and associated discharge diameters of 12.5–25 cm. Microwave coupling efficiencies are in excess of 90% and ion production energy costs are 600–700 eV/ion or less and absorbed power densities are less than 1 W/cm3. The 25 cm diam discharges are the most efficient with ion energy production costs of 400–200 eV/ion and absorbed power densities are less than 0.2 W/cm3. Small sources have lower microwave coupling efficiencies and much higher ion production energy costs and operate with very high absorbed power densities and electron temperatures. When the applicator size is increased to 30 cm or more, performance of a source excited with 2.45 GHz is limited by the ability to control the exciting electromagnetic modes.

Application of high-quality SiO2 grown by multipolar ECR source to Si/SiGe MISFET

A 5nm-thick SiO2 gate was grown on an Si (p+)/Si0.8Ge0.2 modulation-doped heterostructure at 26°C with an oxygen plasma generated by a multipolar electron cyclotron resonance source. The ultrathin oxide has breakdown field >12 MV/cm and fixed charge density ̃ × 1010cm-2. Leakage current as low as 1 μA was obtained with the gate biased at 4 V. The MISFET with 0.25 × 25 μm2 gate shows maximum drain current of 41.6mA/mm and peak transconductance of 21 mS/mm.

Relating Photoresist Etch Characteristics to Langmuir Probe Measurements in an Electron Cyclotron Resonance Source

AbstractIn this work, Langmuir probe measurements were used to characterize a multipolar electron cyclotron resonance (ECR) plasma source. This system has many controllable parameters including microwave power, rf power, gas, pressure, flow rate, and source distance. Both double and triple Langmuir probes were used for the plasma characterization. The results from the Langmuir probe measurements were correlated to the etch characteristics of photoresist. Ion density and photoresist etch rate were found to increase with microwave power but decrease with source distance. However, rf power does not have significant influence on ion density although the photoresist etch rate increases substantially with if power. Ion density first increases then decreases at higher pressure. Maximum ion density occurs at lower pressure for larger distance below the ECR source. Ion density uniformity for an O2 plasma is ±2% across a 16 cm diameter region at 23 cm below the source. For photoresist etched at 10 cm source distance, etch rate uniformity is ±2% for a 15 cm diameter wafer. The results from the Langmuir probe measurements indicate that photoresist etching is enhanced by ion density and ion energy.