Plasma Process Monitoring Research Articles

Quantitative analysis of optical emission spectroscopy for plasma process monitoring

In the field of plasma materials processing, various plasma parameters should be evaluated quantitatively and precisely to control the plasma process adequately, particularly with non-invasive methods, one of which is optical emission spectroscopy (OES) measurement. It has sufficient scientific feasibility to derive the electron density N e, electron temperature T e, and the electron energy distribution function (EEDF) even for various processing plasmas in a state of non-equilibrium. In this review, previous studies are reviewed to measure the N e, T e, and EEDF values of argon plasma with low-electron temperature (T e ≃ 1–10 eV) under not only low-pressure conditions but also atmospheric-pressure discharge using the OES measurement. First, to diagnose low-pressure discharge argon plasmas, we explain the basics and applications of the “collisional radiative model”, which models the population kinetics of the excited states in plasma at the elementary process level in non-equilibrium plasma. Methods for analyzing the plasma parameters are shown from the actual measurement results of emission spectra, including machine learning analysis of the excited-state populations. Next, the research results of the method to measure N e, T e, and EEDF are introduced for the measurement of atmospheric-pressure non-equilibrium plasmas using OES measurement of continuum emission, which also includes methods based on machine learning and data-scientific methods for the analysis of the OES data observed as bremsstrahlung of free electrons scattered against neutral molecules.

Operando XPS for Plasma Process Monitoring: A Case Study on the Hydrogenation of Copper Oxide Confined under h-BN

Operando XPS for Plasma Process Monitoring: A Case Study on the Hydrogenation of Copper Oxide Confined under h-BN

In Situ Plasma Impedance Monitoring of the Oxide Layer PECVD Process

The use of plasma in semiconductor fabrication processes has been continuously increasing because of the miniaturization of semiconductor device structure, and plasma enhanced chemical vapor deposition (PECVD) has become a major process in thin film deposition. As a consequence, plasma diagnosis has become crucial during the deposition process, but the lack of in situ plasma monitoring sensors requires further development of existing in situ sensors, such as the Langmuir probe and optical emission spectroscopy (OES), for in situ plasma process monitoring. In this study, electrically equivalent circuit models of the PECVD chamber functioned as a plasma impedance model with respect to the deposited thin film thickness while plasma impedance was measured using a radio frequency voltage–current (VI) probe. We observed a significant correlation between the deposited film thickness of the chamber wall and the measured impedance of the PECVD chamber cleaning application in the semiconductor industry.

The multipole resonance probe: simultaneous determination of electron density and electron temperature using spectral kinetic simulation

The multipole resonance probe (MRP) is an innovative sensor suitable for monitoring and control of industrial plasma processes. It is a realization of ‘active plasma resonance spectroscopy’, a class of electromagnetic diagnostic methods which employ the ability of plasmas to resonate on or near the plasma frequency. A signal in the GHz range is fed to the plasma via an electrical probe; the spectral response S(ω) is recorded, and then evaluated with a mathematical model to obtain information on the internal plasma parameters. In this study, a spectral kinetic model of the MRP is discussed. It is superior to previous analyses based on the Drude model, as it allows to determine not only the electron density n e but also the electron temperature T e from S(ω). Good agreement with independent measurements shows the suitability of the model.

Electric signals measured during plasma thin-film etching and their connection to the electron concentration and the properties of the treated surface

The electric characteristics of a discharge are usually changed when a thin film is deposited on or etched from a discharge electrode or a substrate. The electric characteristics include the plasma potential, discharge voltage and discharge current, including higher harmonic frequencies of these quantities. This fact can be used for the monitoring of various plasma processes, but the mechanism by which the thin film influences the electric characteristics of the discharge has not been fully clarified. Our study of diamond-like carbon (DLC) film etching verified that variations of electric discharge parameters are caused by variations of electron concentration, which is caused by a difference in the electron emission yield between the DLC film and its substrate.

On the Multipole Resonance Probe: Current Status of Research and Development

During the last decade a new probe design for active plasma resonance spectroscopy, the multipole resonance probe (MRP), was proposed, analyzed, developed, and characterized in two different designs: the spherical MRP (sMRP) and the planar MRP (pMRP). The advantage of the latter is that it can be integrated into the chamber wall and can minimize the perturbation of the plasma. Both designs can be applied for monitoring and control purposes of plasma processes for industrial applications. As usual for this measurement technique, a mathematical model is required to determine plasma parameter (electron density, electron temperature, and collision frequency of electrons with neutral atoms) from the measured resonances. Based on the cold plasma model a simple relationship between the resonance frequency and the electron density can be derived and leads to excellent measurement results. However, a simultaneous measurement of the electron temperature in low-pressure plasmas requires a kinetic model, because the half-width of the resonance peak is broadened by kinetic effects. Such a model has been derived and first results show the broadening of the spectra as expected. Deriving a relation between the half-width and the electron temperature will allow the simultaneous measurement and an improvement of monitoring and control concepts.

Anti-contamination SMART (Spectrum Monitoring Apparatus with Roll-to-roll Transparent film) window for optical diagnostics of plasma systems.

Optical emission spectroscopy is widely used in semiconductor and display manufacturing for plasma process monitoring. However, because of the contamination of the viewport, quantitative analysis is extremely difficult; therefore, qualitative analysis is used to detect species in the process. To extend plasma monitoring in advanced precise processes, the contamination problem of the viewport must be solved. We propose a new spectrum monitoring apparatus with a roll-to-roll transparent film window for optical diagnostics of a plasma system. By moving a transparent film in front of the viewport, contamination in the emission light path becomes negligible. However, the speed of the film should be optimized to reduce the maintenance period and to minimize measurement errors. We calculated the maximum thickness of SiO2, Si3N4, ITO, and the Ar/CHF3 plasma contaminant to suppress the electron temperature error measured by the line-intensity-ratio within 2% at 2eV. The thickness of the Si3N4, ITO, and Ar/CHF3 plasma contaminant should be thinner than 12.5nm, 7.5nm, and 100nm, respectively.

Analytical investigation into the resonance frequencies of a curling probe

The term ‘active plasma resonance spectroscopy’ (APRS) denotes a class of closely related plasma diagnostic methods which utilize the natural ability of plasmas to resonate on or near the electron plasma frequency ; an electrical radio frequency signal (in the GHz range) is coupled into the plasma via an antenna or a probe, the spectral response is recorded and a mathematical model is employed to determine plasma parameters such as the plasma density and the electron temperature. The curling probe, recently invented by Liang et al (2011 Appl. Phys. Express 4 066101), is a novel realization of the APRS concept which has many practical advantages. In particular, it can be miniaturized and flatly embedded into the chamber wall, thus allowing the monitoring of plasma processes without contamination nor disturbance. Physically, the curling probe can be understood as a ‘coiled’ form of the hairpin probe (Stenzel 1976 Rev. Sci. Instrum. 47 603). Assuming that the spiralization of the probe has little electrical effect, this paper investigates the characteristcs of a ‘straightened’ curling probe by modeling it as an infinite slot-type resonator that is in direct contact with the plasma. The diffraction of an incident plane wave at the slot is calculated by solving the cold plasma model and Maxwell’s equations simultaneously. The resonance frequencies of the probe are derived and are found to be in good agreement with the numerical results of the probe inventors.

Analytical calculation of the light-collection efficiency of an optical emission spectrometer with the effective solid-angle method.

A method is proposed for calculating the optical emission spectrometer (OES) light-collection efficiency using the effective solid angle from an arbitrary point source. Based on the point source-OES relative positioning, the effective solid angle is derived for four cases: (1)on axis and on the object plane; (2)on axis and outside the object plane; (3)off axis and on the object plane; and (4)off axis and outside the object plane. The results were in good agreement with those obtained through Monte Carlo ray tracing. After calculating the OES geometrical collection efficiency with respect to the object plane distance in three different-sized cylindrical volume sources, we suggest a simple strategy to increase this efficiency in plasma process monitoring.

다변량 분석기법을 통한 플라즈마 공정 모니터링 기술

Plasma diagnosis and multivariate analysis techniques for plasma processes are reviewed. The principles and applications of optical emission spectroscopy (OES) and VI probe are discussed briefly. The research results of principal component analysis (PCA), one of the widely used multivariate analysis techniques for plasma process monitoring is discussed in this article.

In Situ Monitoring Capabiities of Quantum Cascade Laser Absorption Spectroscopy in Industrial Plasma Processes

AbstractPlasmas in interaction with surfaces are of key importance in a wide range of applications, which include materials technology, microelectronics, environmental issues, and biomedicine. The intense use of plasma technological processes demands proper plasma diagnostic techniques for monitoring, controlling and optimization purposes in industrial environments. In particular, for the improvement of the efficiency of a production process, in situ diagnostic techniques with online capabilities are favorable. From the middle of the last decade a variety of phenomena in molecular non‐equilibrium plasmas in which many short‐lived and stable species are produced have been successfully studied with quantum cascade laser absorption spectroscopy (QCLAS) in the mid‐infrared spectral range. It has been possible to determine absolute concentrations of species, temperatures, degrees of dissociation, dynamics of reaction processes and phenomena involving plasma‐surface interactions using spectroscopy, thereby providing a link with chemical and kinetic modelling of the plasma. Since quantum cascade lasers (QCLs) emit near room temperature, i.e., without the need of cryogenic cooling, very compact and robust spectroscopic instruments can be designed. This has stimulated the adaptation of infrared spectroscopic techniques to industrial requirements. Recent applications of infrared absorption spectroscopy using QCLs for in situ monitoring of plasma processes in industrial environments are reviewed. Examples which emphasize the capabilities of QCLAS as plasma diagnostic technique in industrial plasma processes will be given. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Failure Analysis of Filaments of Quadrupole Mass Spectrometer for Plasma Process Monitoring

A failure analysis of tungsten filaments used in quadrupole mass spectrometer for plasma process monitoring was carried by using SEM and EDS. Failed at high temperature, filaments showed two kinds of failure modes. The one is that diameter of filament became thinner gradually and finally snapped. The other is that filament abruptly snapped almost at a right angle. The EDS analysis showed Fe and C, including W and Fe, on the surface of failed filament. when failed filaments were treated with plasma in mixture of Ar and <TEX>$CF_4$</TEX>, the amount of Fe and C decreased. The failure analysis of filament showed that the cause of filament failure is thermal evaporation and grain growth of tungsten at high temperature.

Optical In-Situ Plasma Process Monitoring Technique for Detection of Abnormal Plasma Discharge

Advanced semiconductor manufacturing technology requires methods to maximize tool efficiency and improve product quality by reducing process variability. Real-time plasma process monitoring and diagnosis have become crucial for fault detection and classification (FDC) and advanced process control (APC). Additional sensors may increase the accuracy of detection of process anomalies, and optical monitoring methods are non-invasive. In this paper, we propose the use of a chromatic data acquisition system for real-time in-situ plasma process monitoring called the Plasma Eyes Chromatic System (PECS). The proposed system was initially tested in a six-inch research tool, and it was then further evaluated for its potential to detect process anomalies in an eight-inch production tool for etching blanket oxide films. Chromatic representation of the PECS output shows a clear correlation with small changes in process parameters, such as RF power, pressure, and gas flow. We also present how the PECS may be adapted as an in-situ plasma arc detector. The proposed system can provide useful indications of a faulty process in a timely and non-invasive manner for successful run-to-run (R2R) control and FDC.

A dc-pulsed capacitively coupled planar Langmuir probe for plasma process diagnostics and monitoring

An improvement to the RF-biased planar Langmuir probe technique proposed by Braithwaite et al (1996 Plasma Sources Sci. Technol. 5 67) is demonstrated, and applied to the case of an industrial CCP reactor. Compared with the RF-biased probe, the new technique uses dc pulses instead of RF bursts, which provides similar results but with simpler electronics. The ion fluxes determined by both techniques are compared under the same O2/Ar plasma conditions using available literature data for the RF-biased case. The data show not only the same trends but very close absolute values of ion fluxes for all studied plasma conditions after correcting for the chamber-area difference. Furthermore, the new technique has the additional benefit of providing information on the ‘electron transition region’ of the I–V curve, as well as allowing the resistance and capacitance of films deposited on the probe to be determined. Finally, both experimental data and numerical simulations of the I–V characteristics and the film parameters are presented for different oxidizing plasmas.

Real-time In-situ Plasma Etch Process Monitoring for Sensor Based-Advanced Process Control

To enter next process control, numerous approaches, including run-to-run (R2R) process control and fault detection and classification (FDC) have been suggested in semiconductor manufacturing industry as a facilitation of advanced process control. This paper introduces a novel type of optical plasma process monitoring system, called plasma eyes chromatic system (PECSTM) and presents its potential for the purpose of fault detection. Qualitatively comparison of optically acquired signal levels vs. process parameter modifications are successfully demonstrated, and we expect that PECSTM signal can be a useful indication of onset of process change in real-time for advanced process control (APC).

Plasma process monitoring of BCl3 using high-resolution infrared laser absorption spectroscopy

Boron trichloride (BCl3) is used as a source gas in various industrial plasma applications. The online monitoring of its ground state concentration in the plasma process reactor is vital for improved insight into the plasma chemistry and to increase productivity, reliability and reproducibility of the process. Infrared absorption spectroscopy was applied for in situ measurements of absolute densities of BCl3 and HCl in planar microwave plasma sources as well as in an industrial pulsed dc discharge reactor. In this paper procedures for the determination of HITRAN format line strength data files for BCl3 are described together with results of concentration measurements. The results show the influence of the discharge parameters on the dissociation of BCl3 and its conversion to HCl. Observations using tuneable diode lasers are compared with measurements using quantum cascade lasers and the applicability of this diagnostic technique for industrial plasma process monitoring is shown.

Quantum cascade laser absorption spectroscopy – A new method to study molecular plasma components

The recent development of quantum cascade lasers (QCLs) offers an attractive new option for the monitoring and control of industrial plasma processes and for trace-gas analysis as well as for highly time-resolved studies on the kinetics of plasma processes. The contribution reviews selected examples of the application of QCLs for infrared absorption studies in basic research and for plasma monitoring and control in industry.

In situ diagnostic of etch plasmas for process control using quantum cascade laser absorption spectroscopy

The combination of quantum cascade lasers and infra red absorption spectroscopy (QCLAS) opens up new possibilities for plasma process monitoring and control. First measurements are reported with an especially designed quantum cascade laser arrangement for application in semiconductor industrial environments to track the approach for in situ process control in silicon etch plasmas. In gas mixtures with N2 and in microwave (MW) plasmas at pressures below 30 Pa concentrations of C4F6 and of SiF4 were measured simultaneously online for the first time. It could be demonstrated, that using quantum cascade lasers (QCL) it is possible to control ex situ mass flow controllers (MFC) based on in situ measured species concentrations in the gas phase and in the MW plasma bulk.

Wafer2Wafer Etch Monitor via In Situ QCLAS

In this paper, first measurements with a particularly designed quantum-cascade-laser (QCL) arrangement for application in semiconductor industrial environments for in situ wafer-to-wafer etch monitoring are reported. The combination of QCLs and infrared absorption spectroscopy (QCLAS) opens up new possibilities for plasma process monitoring and control. In silicon etch plasmas, concentrations of the etch product SiF4 were measured real time in an industrial-production environment. The comparison of the results with inline data of the processed wafers shows a correlation between the amount of produced SiF4 and the measures of the trench depth and the bottom void. Furthermore, it is shown that the characteristics of the refractive index of Si and SiO2 in the mid-infrared can be used to determine etch rates of SiO2 and Si wafers during the processing.

In-Line Monitoring of Atmospheric Pressure Plasma Processes by Fourier Transform Infrared Spectroscopy

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