Process Chamber Research Articles

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

In this study, plasma density measurements were performed near the plume region of the remote plasma source (RPS) in Ar/ gas mixtures using a microwave cutoff probe. The measured plasma density is in the range of 1010–1011 cm−3 in the discharge conditions with RPS powers of 2–4 kW and gas pressures of 0.87–4 Torr. The plasma density decreased with increasing gas pressures and RPS powers under various Ar/ mixing ratios. This decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of We also performed downstream etching of silicon and silicon oxide films in this system. The etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and powers. It was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode, and that the etch selectivity reached 96–131 in the discharge conditions of RF powers (3730–4180 W) and gas pressures (3.6–4 Torr).

An in situ monitoring method for PECVD process equipment condition

A key to successful consistent plasma processing is maintaining a consistent process chamber condition over a certain production period. To alleviate the concern, in situ process monitoring sensors are employed to investigate the plasma chamber conditions of both the deposition step with direct plasma and the cleaning step with a remote plasma system. In situ sensors are optical emission spectroscopy (OES), optical plasma monitoring sensors (OPMS), voltage current probes (VI-probes), and self-plasma OES (SP-OES). During the deposition, we perform the monitoring of a plasma condition associated with the applied RF power via OES, OPMS, and a VI-probe. In the chamber cleaning step using a remote plasma system does not allow plasma monitoring through the sidewall because the plasma is not formed in the process chamber, thus we employed SP-OES to monitor the by-product gas chemistry during the chamber cleaning process step. Successful monitoring results with some useful applications, such as arc detection, part failure detection, and cleaning process chemistry analysis, are presented in this paper. The use of in situ sensors with proper combination can help to understand the plasma process better, to achieve more precise control of plasma processing.

Wafer delay analysis and control of dual-armed cluster tools with chamber cleaning operations

As the design of integrated circuits has become increasingly complicated and dense, serious wafer quality problems are observed in modern wafer fabrication facilities. Therefore, in cluster tools of leading fabs process chambers are periodically cleaned in order to eliminate residual chemicals and impurities that can damage the wafer quality. A chamber cleaning operation is mainly applied to tools in which a wafer delay has a crucial impact on the wafer quality, and hence the need of wafer delay control becomes more significant when chamber cleaning is considered. Thus, we first examine how wafer delays can be specified for cluster tools with chamber cleaning operations. We confirm that wafer delays are substantially increased when chambers are periodically cleaned, and we show that such increased wafer delays cannot be eliminated or reduced using the existing scheduling methods. In such a case, we prove that a partial loading strategy can minimise both the tool cycle time and the wafer delays by controlling the number of wafers being loaded into parallel chambers. We also present how wafer delays under the partial loading strategy can be further reduced by introducing a timing control method that regulates the start times of robot tasks.

Real-Time Plasma Uniformity Measurement Technique Using Optical Emission Spectroscopy With Revolving Module

A measurement technique for analyzing real-time plasma abnormality using optical emission spectroscopy (OES) is proposed to detect process uniformity during semiconductor processing. Among many measurement techniques, OES is a non-contact plasma measurement system for detecting process end points and plasma abnormality without influencing the process. Thus, this system can be widely used and utilized essentially in almost all tools for plasma processing. Despite easy installation and high utilization in plasma manufacturing tools, most OES systems are not able to detect real-time plasma uniformity. Therefore, the improved OES systems are required to overcome the limitations. In this paper, the measurement technique of the plasma light intensity in the left and right sides of a process chamber by a revolving module adapted to conventional OES in real time is investigated. This technique can be used to measure the plasma light in specific regions in the process chamber and detect real-time plasma process abnormalities by comparing light intensities from different regions.

Influence of process atmosphere circulation on the distribution of nitriding conditions in unconventional active screen plasma nitriding (ASPN) systems

The aim of this work is to verify the possibility of designing an active screen plasma nitriding (ASPN) process with a controlled gas flow direction in order to implement multifunctional hybrid devices. The specimens have been subjected to nitriding processes under the established process conditions in which two different gas flow directions have been used. In the first configuration, the gas has been supplied at the top part of the chamber and pumped out from the bottom part of the chamber. In the second configuration, the gas has been supplied at the bottom part of the chamber and evacuated from its top part. The distribution of hardness and thick-ness of the nitrided layers has been evaluated on the prepared metallographic cross-sections. The results of material tests have been compared with the results of simulation tests showing the circulation of the atmosphere inside the process chamber. The presented research results show that using both gas flow directions and the unconventional shape of the process chamber it is possible to carry out efficient nitriding processes. However, further research is necessary to obtain a homogenous layer in the entire chamber space.

Surface coupling of plasma optical emission spectra with bent metal-clad waveguide

We present the design of compact bent metal-clad waveguides to collect the vertically emitted light and to transmit to the horizontal direction. The intention of the design is to collect the plasma optical emission spectra inside the semiconductor etch process chamber to monitor plasma gas phase chemistry resides in the process chamber. Coupler A has been designed for visible spectra range from 748 to 753 nm at which the maximum coupling efficiency is over 52%, while Coupler B operates at the wavelength range from 775 to 780 nm with coupling strength of 62% and Coupler C covers the visible spectrum from 808 to 813 nm with its maximum efficiency of 60%. The surface couplers reveal good spectral characteristics, considerable alignment tolerance and minimal size of 9 × 5 × 1.6 µm3 each. Relatively simple geometrical structure over conventional grating coupler is advantageous to lower the fabrication cost as well.

Monitoring of a dielectric barrier discharge-based process using the gas gap voltage

A method to monitor a temperature-sensitive process based on a sine-driven dielectric barrier discharge (DBD) has been developed and investigated. It uses the gas gap voltage in the active phases during the self-pulsing operation to obtain a value representing the gas temperature in the process chamber. The influence of pressure to the gas gap voltage is taken into account. By comparing the results to measurements by a thermistor and numerical simulations, it was found that the method in the considered application can deliver reasonable results that are robust against variations in the gas flow rates. Therefore, the generated data are potentially suitable as an input parameter to control processes such as the production of specific reactive species in flow-driven DBD-based devices. In particular, the method allows controlling a heat-up phase without gas flow prior to the actual usage of the device.

Open-source automated chemical vapor deposition system for the production of two- dimensional nanomaterials.

The study of two- dimensional (2D) materials is a rapidly growing area within nanomaterials research. However, the high equipment costs, which include the processing systems necessary for creating these materials, can be a barrier to entry for some researchers interested in studying these novel materials. Such process systems include those used for chemical vapor deposition, a preferred method for making these materials. To address this challenge, this article presents the first open-source design for an automated chemical vapor deposition system that can be built for less than a third of the cost for a comparable commercial system. The materials and directions for the system are divided by subsystems, which allows the system to be easily built, customized and upgraded, depending upon the needs of the user. We include the details for the specific hardware that will be needed, instructions for completing the build, and the software needed to automate the system. With a chemical vapor deposition system built as described, a variety of 2D nanomaterials and their heterostructures can be grown. Specifically, the experimental results clearly demonstrate the capability of this open-source design in producing high quality, 2D nanomaterials such as graphene and tungsten disulfide, which are at the forefront of research in emerging semiconductor devices, sensors, and energy storage applications.

Scheduling and Control of a Wafer Transfer Robot for Foundry Equipment Innovation Competition

This paper presents a design and implementation of a wafer transfer robotic system for a Foundry Equipment Innovation Competition. In this system, a 4-DOF robotic arm was designed and constructed for wafer transfer between a cassette and processing chambers. The purpose of this competition was to promote intelligent automation for wafer fabrication, in which multiple wafers and chambers need to be handled simultaneously. A scheduling algorithm is proposed for efficient task execution of wafer to process recipes assigned during the competition. The task also features to integrate defect detection and endpoint determination of wafer processing. The robot was required to receive the processing data from the mission platform to determine the endpoint of wafer processing in a chamber and complete the recipe automatically. The online inspection algorithm detects wafer defects during the task execution and report to the task planner. The state of each wafer and chamber are taken into consideration for scheduling in order to complete the wafer fabrication in an efficient and flexible manner. The developed robotic system spent 9 minutes to complete the assigned mission of transferring 6 wafers among multiple chambers and 2 cassettes and achieved 93.4% defect-detection rate in the competition.

A New Class of Sequences Without Interferences for Cluster Tools With Tight Wafer Delay Constraints

Robotized cluster tools for semiconductor wafer fabrication may have a wafer wait within a processing chamber after processing there until the wafer is unloaded from the chamber by a robot. Such wafer delays cause wafer quality degradation or variability due to residual gases and heats within the chamber. There have been numerous works on characterizing wafer delays and scheduling under upper limits on wafer delays while presuming that the tools are operated by well-known simple robot task sequences such as swap or backward sequences. However, when the wafer delay constraints are tight, there may not be feasible schedules for such sequences. We wish to know whether there can be alternative robot task sequences which can satisfy such tight wafer delay constraints. In this paper, we identify a new class of robot task sequences that can better satisfy tight wafer delay constraints than the conventional swap or backward sequences while keeping the same minimum tool cycle time. By examining the circuits of timed event graph (TEG) models for the tool operation behaviors in many different robot task sequences, we identify that such robot task sequences do not make interferences between the work cycles of the resources such as the robot and chambers. The resource interference can cause delays in the work cycles, and hence increase the wafer delays or the tool cycle time. To prove this, we examine circuits in an extended TEG model, a negative event graph, which incorporates time constraints as negative places and tokens. From this, we derive closed-form conditions for which such sequences are feasible against given wafer delay constraints. By experiments, we show that the proposed new sequences have shorter wafer delays, and hence better satisfy tight wafer delay constraints than conventional sequences. Note to Practitioners —As circuit widths shrink down to several nanometers, cluster tools for semiconductor fabrication require extreme process quality control. Even wafer delays within processing chambers of cluster tools can cause wafer quality degradation and variability. Therefore, it is desirable for cluster tools to have much shorter wafer delays. However, conventional sequences such as the swap and backward sequences, which are being prevalently used in practice, may not satisfy tight wafer delay constraints. Our proposed sequences, which are as simple as the conventional sequences, have much shorter wafer delays while keeping the same minimum tool cycle time.

Processes in the area of laser beam exposure to metal research during laser welding in vacuum

Research results are presented of secondary emission signals in the zone of interaction of a laser beam with metal in order to study the possibility of monitoring the process of formation of laser weld in vacuum. Experimental studies of the parameters of the secondary emission electron and ion currents during pulsed laser welding in vacuum have been carried out. The dependences of the parameters of the secondary emission signals from the laser welding zone in vacuum on the distance between the collector of charged particles registering these signals and the product being welded, as well as the effect of the degree of vacuuming of the process chamber on the parameters of the secondary emission signals, are investigated. The results of the research will make up the basis for the development of methods of secondary emission control of the process of weld formation during laser welding in vacuum; its implementation into industrial production will ensure high reproducibility of the quality of welded joints produced by laser welding in vacuum and the absence of defects in welds.

Scheduling Dual-Armed Cluster Tools With Chamber Cleaning Operations

Circuit widths and nodes of semiconductor wafers have been continually shrinking down to less than 20 nm. Therefore, modern wafer fabs enforce extremely strict process control to prevent wafer quality failures. A wafer processing chamber is now frequently cleaned to remove residual chemicals and impurities. Yu et al. show that such cleaning operations significantly change the tool operation of single-armed cluster tools, and they suggest an idea of partial wafer loading to improve the tool throughput under cleaning requirements. However, little is known about how a dual-armed tool could be effectively scheduled when chamber cleaning exists. A dual-armed robot allows more flexible tool operational sequences, and hence, the scheduling problem becomes further complicated and challenging. In this paper, we propose a scheduling method by which the dual arms can be properly exploited for better tool productivity. We show that the suggested hybrid sequence significantly reduces the tool cycle time as compared to previously developed scheduling methods. Through this research, we conclude that the productivity gain of the dual arms against single arm is more significant when chambers are cleaned. Note to Practitioners —This paper is motivated by the scheduling issues of cluster tools with chamber cleaning requirements. Though an efficient scheduling method for single-armed cluster tools is presented by Yu et al. , its performance is not sufficiently close to the optimal when a dual-armed robot is considered. More specifically, we cannot expect any productivity improvement from adopting a dual-armed robot, although it allows more flexible tool operations and is known to have higher throughput than a single-armed robot. Thus, we propose a novel scheduling method for dual-armed cluster tools that require chamber cleaning operations. The experimental results show that the suggested method achieves optimal tool throughput in most of the practical tool conditions.

Ground level ice nucleating particles measurements at Capo Granitola, a Mediterranean coastal site

This study presents near-surface measurements of ice nucleating particle (INP) concentrations at a ground level Mediterranean site (Capo Granitola, CGR), located in southern Sicily. A coastal area like CGR can be influenced by marine and anthropogenic aerosols, and even by Saharan dust. To obtain the INP concentration in the PM1 and PM10 fractions, an experimental campaign was carried out in April 2016 at the WMO/GAW “I-AMICA” Observatory. Aerosol was sampled on nitrocellulose membranes twice a day. INP concentrations were detected by a dynamic filter processing chamber (DFPC), a replica of the Langer dynamic chamber, at −18 °C and − 22 °C activation temperatures, at different conditions of supersaturation with respect to ice and water.The sampling period was characterized by three main wind directions, along the coast (from North-West and from South-East), during daytime, and mainly from the land side during the night. INP concentration, in the PM10 size fraction, ranged 0.5–27, 3.3–65 and 13–115 m−3, at −18 °C below water saturation, at −18 °C at water supersaturation and at −22 °C at water supersaturation, respectively.Two weak dust transport events occurred during the experimental campaign, both characterized by an increase in coarse particle number and PM10 concentration, not associated with fine particles or other pollutants. Air mass back-trajectories, during the events, were observed to originate from the North African region.Results of the experimental campaign were compared with INP concentrations previously measured at San Pietro Capofiume, a rural site in the Po Valley, and at Mt. Cimone (“O. Vittori” Italian Climate Observatory, 2165 m a.s.l) in the northern Apennines. Both INP concentrations, in the PM1 and PM10 fractions, and activated fractions, at CGR, were prevalently lower than the concentrations obtained at the other two sites. This may be, likely, related to the lower nucleation efficiency of soluble marine aerosols and aged dust particles, partly coated and mixed with hygroscopic material, at CGR.

Continuous monitoring of temperature of electron beam heated metal evaporation surface using controlled gas purge at viewing port in a vacuum chamber

In Electron beam gun (EB-gun) assisted metal evaporator, monitoring of surface temperature is essential for characterisation. Pyrometers having the advantage of non-contact measurement are used for monitoring the temperature of EB heated surface. The opacity introduced by the deposition of metal vapour on the viewing port during evaporation process hinders the monitoring. Indirect viewing using methods like periscope viewing has been reported to have poor accuracy of measurement due to uncertain value of reflectivity of in-situ coated metal mirrors. Multiple collisions of approaching atomic vapour with purge gas molecules and scattering the atoms is an attractive technique for long duration monitoring of surface temperature. In this method a controlled leak of inert gas is introduced to locally increase the pressure, without significantly increasing the pressure of process chamber. This approach increases the collision probability of the approaching atoms with gas molecules due to higher molecular number density, and scatters the atoms away from optics window.In the current study this technique has been successfully tested for monitoring of temperature of electron beam heated surface, using direct viewing optics port, with high evaporation rate. Successful monitoring of the surface temperature had been demonstrated for more than an hour.

Design and Applications of Soft Sensors in Polymer Processing: A Review

In manufacturing industry, process monitoring is a key to observe the product quality, operational health, safety, and also for achieving good/satisfactory process control performance. In polymer processing, the level of control of the process operational quality is vastly dependent upon the performance of the process monitoring techniques as it is quite difficult to observe the inside of an extruder barrel (or processing chamber) during the process operation. Currently, a number of physical sensing devices/techniques are widely available for industrial applications for monitoring of parameters, such as melt temperature, melt pressure, screw/processing speed, product dimensions, and so on, in real-time. However, there may be some limitations in using physical sensors in practical process measurements (such as melt viscosity and melt temperature profile) due to several constraints such as their access requirements, disruptive effects to the melt flow, fragility, complexity, and so on. Therefore, soft sensing techniques should be highly useful for improved process monitoring and modeling, and hence for advanced process control. In this paper, a general description is presented on the state of the art of soft sensor design. Then, a comprehensive review is made on the use of soft sensing techniques in polymer processing applications while identifying their capabilities and limitations. Eventually, the importance of developing of such soft sensing techniques (together with some sort of built-on intelligence) for the advancement of process monitoring is discussed while indicating some of the possible directions for future industry.

Refining the Microstructure of Fe‐Nd‐B by Selective Laser Melting

Lab scale additive manufacturing of Fe‐Nd‐B based permanent magnet material (Fe75‐Nd18‐B7) has been performed. For fabrication a special inert gas process chamber for laser powder bed fusion has been used. This is required because Fe‐Nd‐B powders are extremely sensitive to oxidation. Selective laser melting (SLM) of the powders allows to realize very fine microstructures with a directed crystal growth and finely dispersed Nd‐rich phase. It is shown, that this fine and textured microstructure leads to large coercivity in sintered Fe‐Nd‐B magnets. A prototype has been realized by milling the SLM alloy and sintering.

Application of PI-VM for management of the metal target plasma etching processes in OLED display manufacturing

Generation of the defect particles during the plasma-assisted metal dry etching process is induced by the various mechanisms. Most of these mechanisms are caused by the non-volatility of metal-halide compounds generated during the etching process. Degeneration of the metal etching process chamber condition is observed as the frequent process fault caused by the defects, but the worse condition is not recovered by itself. Because of this property of the metal etching process, proper work of the preventive maintenance (PM) to restore the process chamber or the addition of a discharge cleaning step is required periodically. However, inadequate PM or discharge cleaning by the uncertain cause analysis of the defect generation should be a just temporary remedy, and might lead the repetition of similar problems. To solve this problem, the virtual metrology (VM) model based on the plasma information (PI) parameters, known as PI-VM, was developed and applied for the defect control of the metal layer dry etching processes in organic light emitting diode (OLED) display manufacturing. To obtain the information about the generation rates of non-volatile compounds and their removal rates by the exhaustion system, PI parameters are designed with the consideration of the reaction kinetics in the metal etching plasma volume, sheath, and reacting surface using the big data of equipment engineering system (EES) and optical emission spectroscopy (OES) accumulated during the mass production process. The developed PI-VM index could be applied to a 2–3 h earlier alarm system for the defect occurrence, and had succeeded over 90% of alarm rate. This PI-VM alarm was applied to predictive control of the process by the early substitution of the discharge cleaning step or by the repair of the proper parts in the process chamber. By the control of processes based on the predicted results of the PI-VM, management of the mass production line with about 30% decreased defect was possible in OLED display manufacturing.

Preparation and Characterization of Sprayed-Yttrium Oxyfluoride Corrosion Protective Coating for Plasma Process Chambers

This study investigates the microstructure, mechanical and electrical properties of dense yttrium oxyfluoride (YOF) coatings fabricated by the atmospheric plasma spraying technique. Transmission electron microscopy and X-ray diffraction analysis revealed a well crystallized YOF coating with preferred orientations. The YOF coatings were more porous (approximate porosity 0.5%), with higher hardness (290 ± 30 HV), lower electrical resistivity (1016 Ω⋅cm), and breakdown voltage (5.57 kV), than conventional yttrium-fluoride plasma-protective coating. These results indicate the potential of the YOF coating as a novel antiplasma and corrosion-resistant ceramic.

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.

On morphological surface features of the parts printed by selective laser melting (SLM)

Among the most popular additive manufacturing processes for metals, Powder bed fusion technology involves a layer by layer manufacturing approach utilizing a high power source, such as a laser or an electron beam, interacting with the metal powder on selected surfaces. Beam-powder interaction brings up a handful of phenomena affecting the quality of the final part in its volume and surface. In this study, different surface features generated by Selective Laser Melting of an Al-Si7-Mg alloy are investigated and interpreted based on their morphology, microstructure and hardness to improve the general understanding of defect genesis. Ballings, spatter particles and partially melted metal powders are distinguished by their morphology, size and microstructure. It is shown that these differences arise from different cooling rates during their generation. Ballings share the same microstructure with the bulk material both experiencing cooling in conduction mode. Spatters and partially melted powders show coarser microstructure driven by solidification mainly ruled by convection and radiation during their flight in the inert atmosphere of the process chamber.