Plasma Process Chamber Research Articles

Plasma-chamber wall interaction and its impact on polymer deposition in inductively-coupled C4F8/Ar plasmas

Plasma processing chambers, key tools in semiconductor device fabrication, must be meticulously maintained to ensure tool-to-tool matching. Processing chamber walls are liable to contamination with fluorocarbon (CxFy) film, which acts as a source and/or sink for active species during plasma processes. This contamination potentially affects processing quality and alters the plasma properties, increasing deviations between processing chambers. However, quantitative studies on the impact of wall contamination on the substrate deposition outcomes have been limited. Additionally, spatially resolved investigations are crucial for understanding the plasma-wall interaction. Therefore, this study evaluated the influence of polymer (CxFy) film wall contamination on plasma deposition via various plasma diagnostics and surface analyses. When the chamber inner wall was coated with polymer film, the thickness, surface roughness, and chemical composition of the deposited film on the bottom substrate were more uniform. These results were linked to alterations in the uniformity of active species in the plasma, such as CF2 and F, resulting from interaction with the polymer film on the wall's surface. The C–Fx and C–CFx composition ratios in the wall-coated films dramatically reduced, indicating that this film supplied the depositing precursors to the plasma. These results suggest that controlling the chamber wall conditions is important to maintain tool-to-tool matching and modulate the processing performance.

Unintended gas breakdowns in narrow gaps of advanced plasma sources for semiconductor fabrication industry

Occurrence of unintended gas breakdown in the narrow gaps of plasma processing chambers is one of the critical challenges in developing advanced plasma sources. We present a combined experimental and theoretical study of unintended discharges in the narrow gaps of plasma processing chambers and report significant drop of the gas breakdown voltage in the presence of a background plasma facing the gap. Experimentally measured breakdown voltages decrease in subsequent breakdown events due to wall erosion caused by the discharge. Therefore, preventing and mitigating the first discharge is of paramount importance. An analysis of kinetic simulation results indicates that the charged particle influx from the background plasma in the processing chamber into the gap is responsible for the onset of early breakdown: higher charged particle density within the gap modifies the electric field profile, allowing unintended breakdowns to occur at a significantly reduced threshold voltage.

Plasma sheath with multi‐species of positive ions and surface produced negative ions

AbstractThe structure of a plasma sheath has been investigated in front of a caesium‐coated metallic plate, using a simple theoretical model. Along with the electrons, the plasma is composed of multi‐species of positive ions, and surface and volume produced negative ions. While the volume produced negative ions are common in many plasma processing chambers, the surface produced negative ions are of critical importance, especially to the Neutral Beam Injection (NBI) systems. The surface negative ions are produced via the coated metallic plate. With a single species of positive ion, the Bohm criterion, which determines the sheath edge potential, is multi‐valued for a specific range of electronegativity (). The width of the multi‐valued region has been reported to increase with the surface production yield (). Calculations are done for hydrogen plasma with a slight admixture of a second gas such as argon. Besides discussing the differences brought in by the mere presence of a second ion, the paper highlights the importance of the positive ion current density in determining the Bohm criterion. In addition, the effect of three species of positive ions in the surface production process has been discussed.

Effect of charge-up of surfaces of sintered Y2O3 and yttrium oxyfluoride on their erosion rates due to ion bombardment

The erosion rate of sintered Y2O3 and yttrium oxyfluoride (Y-O-F) due to Ar ion bombardment was investigated for use in the plasma process chamber. The Ar ion bombardment was performed by irradiations of Ar plasma and Ar ion beam. In addition, charge-up behavior of these ceramics was investigated by two methods. One was the measurement of the surface voltage during the plasma irradiation (the so-called self-bias voltage), and the other was the measurement of the surface voltage generated due to the accumulation of static electricity in the clean room air. It was found that the negative self-bias voltage of the Y2O3 surface was smaller than that of Y-O-F. It was also found that Y2O3 was easily positively charged by the accumulation of the static electricity compared to Y-O-F, which was consistent with the observed relationship of the self-bias voltages between Y2O3 and Y-O-F. For the evaluation of the erosion rate due to Ar ion bombardment, it was found that the material and setting of masks to make the erosion step for evaluating the rate greatly affected the results. When electrically conductive masks with electrically connecting to a substrate were used, the erosion rate of Y-O-F was smaller than that of Y2O3. The results suggested that the intrinsic ion-bombardment-induced erosion rate of Y-O-F was smaller than that of Y2O3, because the ion bombardment energy was expected to be almost the same due to the existence of the conductive masks. On the other hand, when insulating masks were used, the rates of Y2O3 and Y-O-F were almost the same level. Considering the aforementioned charge-up behavior, the results suggested that a relatively larger positive charge-up of the Y2O3 surface during the ion bombardment decelerated injecting ions, resulting in the decrease in ion bombardment energy and, thus, the erosion rate.

Plasma resistance of sintered and ion-plated yttrium oxyfluorides with various Y, O, and F composition ratios for use in plasma process chamber

Yttrium oxyfluoride was developed for use in the plasma process chamber using various corrosive gases. In this paper, sintered yttrium oxyfluorides with various Y, O, and F composition ratios (YxOyFz) and ion-plated YOF and Y5O4F7 films were prepared, and the physical etching behavior due to Ar ion bombardment and NF3/Ar plasma resistance was investigated. It was found that the etching rate of the sintered yttrium oxyfluoride due to the bombardment of Ar ions with an energy of 500 eV decreased as the oxygen composition ratio in the samples decreased, i.e., F-rich yttrium oxyfluoride had better resistance against energetic-ion bombardment. It was also found that the surface roughness of sintered YOF and Y5O4F7, both of which had the stable phases, was much smoother after Ar ion bombardment than that of yttrium oxyfluorides without the stable phase. NF3/Ar plasma resistance was also investigated. For the sintered yttrium oxyfluoride, both YOF and Y5O4F7 showed good resistance against the NF3/Ar plasma, where the ideal stoichiometric atomic composition ratio could be kept even after plasma irradiation. For both as-deposited ion-plated YOF and Y5O4F7 films, the F composition ratio was slightly smaller than the ideal stoichiometric ratios, suggesting that some amount of fluorine was escaped from the starting materials of YOF and/or Y5O4F7 during the ion-plated film deposition processes. After NF3/Ar plasma irradiation, F composition ratios were increased for both ion-plated YOF and Y5O4F7 films, and the atomic composition ratio becomes closer to the ideal stoichiometric ratios for both films.

Three-dimensional measurements of plasma parameters in an inductively coupled plasma processing chamber

Inductively coupled plasmas (ICPs) are extensively used for materials processing and microelectronics fabrication. However, their electromagnetic properties have not been fully characterized. In this regard, we have performed fully three dimensional (3D), time dependent measurements of the magnetic field, electron density, and electron temperature for an ICP sustained in argon in an industrial reactor designed for plasma etching in microelectronics fabrication. These measurements were compared to modeling results. The plasma was generated using pulsed power delivered at 2 MHz by a planar coil. The magnetic field was measured using a three axis magnetic probe at 15 366 locations throughout the plasma volume during the H-mode portion of the pulse at temporal intervals of 2 ns. A swept Langmuir probe was used to measure plasma parameters at the same locations. The plasma density measurement was calibrated with line-integrated densities obtained using a 96 GHz interferometer. During a single radio frequency (RF) cycle, the 3D current density [derived from B(r→,t)]is initially maximum just below the coil and moves downward toward the center of the chamber. Isosurfaces of current are nearly symmetric toroids. The total electric field, space charge field, and inductive electric field were derived and used to calculate the dissipated power, plasma current, and Poynting flux. Computer modeling of the experiment reproduces the phase dependent behavior. Animations showing the time dependent 3D measurements are presented in the supplementary material.

Corrosion resistance of sintered SiC against fluorinated plasmas

α-SiC fabricated by the sintering method was developed as an alternative to the widely used β-SiC made by chemical vapor deposition for various functional components used in the plasma process chamber. By adapting the sintering method, larger and thicker SiC components can be fabricated practically compared with the chemical vapor deposition. Two sintering additives, Y2O3-Al2O3 and B4C, were used in the sintering processes, and the etching stability of sintered SiC against fluorinated plasmas, including SF6/Ar plasma and CF4/O2/Ar plasma, was investigated. For sintered SiC with Y2O3-Al2O3 additives, the etching rate was smaller than that of the chemical-vapor-deposited SiC, mainly because nonvolatile fluoride and/or oxides of Y and Al remained on the surface and served as a protective layer. For sintered SiC, the B4C additives, the etching rate, and the surface structure after plasma irradiation were similar to the case of the chemical-vapor-deposited SiC. The results suggest that the B4C additive has little effect on the etching stability, because fluorides of B and C are volatile, and no residue is formed, contrary to the case of the Y2O3-Al2O3 additives.

In-Situ Detection Method of Abnormal Plasma Discharge in Plasma-Assisted Deposition Processes

Arc is an abnormal discharge in a plasma-processing chamber that results in high current discharge marks and particles on wafers. However, it is difficult to identify or observe it during an ongoing process. In this study, we report on the observations of plasma arcs during various plasma processes through a non-invasive optical plasma monitoring system devised for the in situ detection of abnormal discharge. The employed optical monitoring based arc detection system provides valuable indications of particle generation resulting from a charge imbalance in the chamber. The devised non-invasive and real-time method can detect such disturbances down to the order of tens of microseconds. Successful monitoring of arcs that appear in various types of plasma-assisted deposition processes are presented in this paper. We also present examples of detected arcs in various plasma processes, such as plasma-enhanced chemical vapor deposition, high density plasma-chemical vapor deposition, amorphous carbon layer deposition, and plasma-enhanced atomic layer deposition. The suggested method plays an important role for the next level of arc-detection research and plasma diagnostics applications.

Real-time dielectric-film thickness measurement system for plasma processing chamber wall monitoring

An in-situ real-time processing chamber wall monitoring system was developed. In order to measure the thickness of the dielectric film, two frequencies of small sinusoidal voltage (∼1 V) signals were applied to an electrically floated planar type probe, which is positioned at chamber wall surface, and the amplitudes of the currents and the phase differences between the voltage and current were measured. By using an equivalent sheath circuit model including a sheath capacitance, the dielectric thickness can be obtained. Experiments were performed in various plasma condition, and reliable dielectric film thickness was obtained regardless of the plasma properties. In addition, availability in commercial chamber for plasma enhanced chemical vapor deposition was verified. This study is expected to contribute to the control of etching and deposition processes and optimization of periodic maintenance in semiconductor manufacturing process.

Investigation of Plasma Enhanced Chemical Vapor Deposition Chamber Mismatching by Photoluminescence and Raman Spectroscopy

Slight differences between supposedly identical process chambers are a well known problem in semiconductor manufacturing. In particular, individual plasma-aided process chambers are difficult to characterize and tune to match each other because plasma is a non-equilibrium state and can leave its “footprint” in subtle ways on a wafer. This process chamber mismatching phenomena was investigated in a dual chamber, commercial, high density plasma chemical vapor deposition system by monitoring SiO2/Si interface quality using multiwavelength room temperature photoluminescence and Raman spectroscopy. Effects on the SiO2/Si interface quality, from altering the gas flow pattern in the plasma process chamber, are also studied.

Effect of rare-earth elements on the plasma etching behavior of the RE–Si–Al–O glasses

The effect of rare-earth elements on the plasma etching behavior of oxide glasses were investigated to develop the window glass for a plasma processing chamber in the semiconductor industry. Aluminosilicate glasses with various rare-earth elements (Y, Gd and La) were prepared and their optical transmittance and plasma etching depth were evaluated. The plasma etching behavior of the glasses was estimated by X-ray photoelectron spectroscopy analysis at the fluorine plasma exposure surface of the glasses. The rare-earth element in the glass was highly related to various properties such as density, molar volume, mechanical properties and plasma etching depth. The cationic field strength of the rare-earth element more strongly affected the plasma etching depth of the glasses than the sublimation point of the fluorine compounds and this may be related to the plasma etching condition.

Gas Flow Characteristics in a Plasma Process Chamber and Proposal of New Pulse-Controlled Gas Injection Method Using Interference Matrix Operation for Rapid Stabilization of Gas Pressure

Gas Flow Characteristics in a Plasma Process Chamber and Proposal of New Pulse-Controlled Gas Injection Method Using Interference Matrix Operation for Rapid Stabilization of Gas Pressure

Gas Flow Characteristics in a Plasma Process Chamber and Proposal of New Pulse-Controlled Gas Injection Method Using Interference Matrix Operation for Rapid Stabilization of Gas Pressure

To realize precise and high-throughput multiprocesses in a single plasma process chamber with a rapid alternative of multiple gases, gas flow characteristics in a plasma process chamber are investigated and a pulse-controlled gas injection method is developed. It is found that gas replacement characteristics greatly depend on the gas supply method used. An upper shower plate has a great advantage in realizing a rapid gas replacement over the case without using the upper shower plate, resulting from the realization of the down flow pattern of feed gas in the chamber. The pulse-controlled gas injection method employs the intentional overshoot pulse at the beginning of gas supply to rapidly stabilize gas pressure. Interference matrix operation is newly introduced to determine the pulse size for the arbitrary gas flow pattern in the chamber. The optimum pulse size can be successfully obtained in the case of HBr addition to a pure Ar plasma.

In-Situ Leak Detection of Plasma Processing Chamber Using Neural Network and Optical Emission Spectroscopy

Monitoring a leak of plasma processing chamber is crucial to maintaining process quality and improving device yield and equipment throughput. A new technique to detect chamber leak is presented. This is accomplished by constructing a neural network model of optical emission spectroscopy (OES). Using OES, a total of 47 patterns were collected. A neural network model developed with OES pattern yielded accuracies of 1.08% and 1.58% for training and testing data, respectively. The appropriateness of neural network model was tested with the remaining OES patterns. The errors for leaky data were considerably larger, enough to be detectable. The performance of leak detection was evaluated more by applying cumulative sum (CUSUM) control chart to statistical mean, model prediction, and major radical intensity. The neural network model-based CUSUM was found the most effective to monitoring chamber leak.

Monitoring of plasma processing chamber using ion energy analyser and time series neural network

A new technique to monitor plasma processes is presented. An autocorrelated neural time series (A-NTS) network was used to model ion energy distribution (IED). The ion energy data were collected during a deposition of silicon nitride films in a SiH4–NH3 inductively coupled plasma. A backpropagation neural network was used to build IED model. Prediction performance of A-NTS model was evaluated as a function of training tolerance as well as a detection sensitivity. The A-NTS models demonstrated detection sensitivities high enough to detect plasma faults. Maximum sensitivity of A-NTS models obtained was more than 55% for all fault cases. Optimised A-NTS models yielded the prediction errors of 1·41 and 2·18% for 80 and 60% IED respectively. The presented technique can be applied to monitor any kinds of plasma faults and is expected effective particularly to those faults sensitive to ion bombardment variations.

Effect of the resonant growth of harmonics on the electron density in capacitively coupled plasma

The growth of harmonics is known to occur under the condition of plasma series resonance (PSR). In an actual plasma process chamber, the external circuit also affects the PSR. We experimentally demonstrated the resonant growth of the third and fourth harmonics by tuning a variable capacitor attached to the electrode, and investigated the influence of the growth on the electron density. We observed significant increases in electron density as the amplitude of harmonics grows. The result clearly shows that nonlinear electron resonance heating actually takes place.

Electrode assembly and plasma processing chamber utilizing thermally conductive gasket and O-rings

Electrode assembly and plasma processing chamber utilizing thermally conductive gasket and O-rings

Precise and high-speed control of partial pressures of multiple gas species in plasma process chamber using pulse-controlled gas injection

Multiprocesses in a single plasma process chamber with high throughput require precise, sequential, high-speed alteration of partial pressures of multiple gas species. A conventional gas-distribution system cannot realize this because the system seriously overshoots gas pressure immediately following valve operation. Furthermore, chamber volume and conductance of gas piping between the system and chamber should both be considered because they delay the stabilizing time of gas pressure. Therefore, the authors proposed a new gas-distribution system without overshoot by controlling gas flow rate based on pressure measurement, as well as a method of pulse-controlled gas injection immediately following valve operation. Time variation of measured partial pressure agrees well with a calculation based on an equivalent-circuit model that represents the chamber and gas piping between the system and chamber. Using pulse-controlled gas injection, the stabilizing time can be reduced drastically to 0.6s for HBr added to pure Ar plasma, and 0.7s for O2 added to Ar∕HBr plasma; without the pulse control, the stabilizing times are 3 and 7s, respectively. In the O2 addition case, rapid stabilization can be achieved during the period of line/space pattern etching of poly-Si on a thin SiO2 film. This occurs without anomalous etching of the underlying SiO2 film or the Si substrate near the sidewall, thus obtaining a wide process margin with high throughput.

Fast Gas Replacement in Plasma Process Chamber by Improving Gas Flow Pattern

The precise and high-speed alteration of various gas species is important for realizing precise and well-controlled multiprocesses in a single plasma process chamber with high throughput. The gas replacement times in the replacement of N2 by Ar and that of H2 by Ar are measured in a microwave excited high-density and low electron-temperature plasma process chamber at various working pressures and gas flow rates, incorporating a new gas flow control system, which can avoid overshoot of the gas pressure in the chamber immediately after the valve operation, and a gradational lead screw booster pump, which can maintain excellent pumping capability for various gas species including lightweight gases such as H2 in a wide pressure region from 10-1 to 104 Pa. Furthermore, to control the gas flow pattern in the chamber, upper ceramic shower plates, which have thousands of very fine gas injection holes (numbers of 1200 and 2400) formed with optimized allocation on the plates, are adopted, while the conventional gas supply method in the microwave-excited plasma chamber uses many holes only opened at the sidewall of the chamber (gas ring). It has been confirmed that, in the replacement of N2 by Ar, a short replacement time of approximately 1 s in the cases of 133 and 13.3 Pa and approximately 3 s in the case of 4 Pa can be achieved when the upper shower plate has 2400 holes, while a replacement time longer than approximately 10 s is required for all pressure cases where the gas ring is used. In addition, thanks to the excellent pumping capability of the gradational lead screw booster pump for lightweight gases, it has also been confirmed that the replacement time of H2 by Ar is almost the same as that of N2 by Ar.

Control of Plasma Uniformity Using Phase Difference in a VHF Plasma Process Chamber

Very high frequency (VHF) capacitively coupled plasma sources are widely used for semiconductor manufacturing processes. Uniform plasma can be difficult to achieve at VHF for different load conditions (pressure, power, gas mixture electronegativity, etc.). This paper discusses how voltage phase difference between top and bottom electrodes can be used to control plasma uniformity above the wafer.