Measurement Of Substrate Temperature Research Articles

Опыт выращивания посадочного материала Thuja occidentalis ᾽Smaragd᾽ с ЗКС по технологии «Контейнер в контейнере»

In the Russian nursery industry, there are certain standards for planting material developed for all types of plants that dictating clear requirements for nursery products, in case of deviation from which, the competitive-ness of the nursery in the plant market decreases. In order to grow healthy planting material that meets all the required standards, it is necessary to apply modern cultivation technologies that provide all the conditions for the uniform development of the aboveground and underground parts of the plant, without any disease. This article discusses the experience of growing Thuja occidentalis ‘Smaragd’ planting material with a closed root system in containers. Observations on the condition of 180 containerized seedlings on three experimental sites in the nursery - an open area, a shaded area and a "Pot-in-pot" technology area were made. Measurements of substrate temperature in containers throughout the day, biometric indicators of seedlings – plant height, root neck diame-ter, root length and density were analyzed. All the advantages and disadvantages of the "Pot-in-pot" system, dif-ferences from the classical cultivation are shown, and the influence of this method on the physiology and productivity of plants is determined.

Fiber Bragg grating sensor for in situ substrate temperature measurement in a magnetron sputtering system

Fiber Bragg grating sensors are used to monitor physical parameters like temperature even in inaccessible, unconventional environments. One such application is monitoring the temperature of a substrate from the back surface like any conventional thermocouple sensor and simultaneously monitoring the temperature on the front surface, which is in contact with ion plasma in a magnetron sputtering system. Since thin film parameters depend on substrate temperature, precise measurement plays an important role and thermocouple-like sensors are erroneous when placed on the front side of a substrate exposed to ion plasma. The lateral variation of temperature on the front side for larger substrates also has been established at four different locations, exploiting the multiplexing capability of FBGs. In this report, we demonstrate and utilise the versatility and capability of fiber Bragg grating sensors for online monitoring of substrate temperatures during thin film deposition, for the first time to the best of our knowledge, on different types of substrates. FBG based approach is expected to significantly aid in better control of thin film devices.

Hot filament chemical vapor deposition temperature field optimization for diamond films deposited on silicon nitride substrates

The influence of some key parameters of hot filament chemical vapor deposition (HFCVD) on the temperature distribution during the deposition of diamond coatings on silicon nitride (Si3N4) substrates was assessed with the help of the finite element method. Solid heat transfer, fluid heat transfer and surface radiation heat transfer mechanisms were used to calculate the substrate temperature in the steady state during the deposition process. The accuracy of the model was verified by comparing the simulation model with experimental measurements. The comparison shows that the deviation between the model and the actual substrate temperature measurements is within 3%. Furthermore, a Taguchi orthogonal experiment was designed (3 factors, 3 levels, L9). By changing the number of hot filaments, the distance between the filaments and the substrate, and the separation between two adjacent hot filaments, the influence trend of these parameters on the substrate temperature was assessed, leading to an optimal hot filament arrangement. A deposition experiment was carried out using the optimized parameters, and the results showed that the substrate surface temperature obtained by numerical simulation is highly consistent with the temperature measured by the infrared thermometer. The optimized deposition parameters contributed to a more suitable temperature range and more uniform temperature distribution on the Si3N4 ceramic substrate. The deposited diamond film exhibited uniform crystal quality and grain morphology, thus verifying the validity of the simulation results.

Optical in-situ temperature management for high-quality ZnO molecular beam epitaxy

Temperature management of the substrate is of great importance for molecular beam epitaxy as well as for other thin film deposition techniques. In this work, we compare different in-situ methods for simultaneous measurement of substrate temperature and growth rate for wide band semiconductors such as ZnO and GaN. The different analysis techniques investigated are emissivity-corrected pyrometry as well as band gap thermometry and reflectivity-based growth-rate determination. Combining in-situ and ex-situ measurements with simulation data, we demonstrate characteristic behaviors of common substrate mounting techniques for Al2O3 and ZnO substrates. Moreover, we investigate the performance of reflectometry-based growth rate determination during ZnO homoepitaxy.

An experimental-numerical study of active cooling in wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is a metal additive manufacturing process based on gas metal arc welding and it is known to be economically convenient for large metal parts with low complexity. The main issue WAAM is the sensibility to heat accumulation, i.e., a progressive increase in the internal energy of the workpiece due to the high heat input of the deposition process, that is responsible of excessive remelting of the lower layers and the related change in bead geometry. A promising technique to mitigate such issue is to use an air jet impinging on the deposited material to increase the rate of convective heat transfer. This paper presents an analysis of air jet impingement performances by means of a hybrid numerical-experimental approach. Different samples are manufactured using AWS ER70S-6 as filler material, using as cooling approaches free convection and air jet impingement, with different interlayer idle times. The measurement of substrate temperatures has been used to validate the process simulation, used for obtaining the temperature field of the whole part. The results indicate that air jet impingement has a significant impact on the process, limiting the progressive increase in the interlayer temperature as compared to free convection cooling. From the results arise that the optimal idle time is 30 s, as a compromise between productivity and reduction of heat accumulation, independently from the cooling strategy.

Spatial thermal dose delivery in atmospheric pressure plasma jets

Atmospheric pressure plasma jets (APPJs) are increasingly used in plasma medicine and materials processing applications. Reproducible and effective operation of APPJs requires regulating the cumulative effects of plasma on a target substrate in the face of variabilities and exogenous disturbances. This article investigates spatial delivery of thermal effects—thermal dose—of plasma using a kHz-excited APPJ in helium translated over a dielectric substrate. A dose metric is presented for quantifying the cumulative, nonlinear thermal effects of plasma along the translation trajectory of the APPJ. An optimization-based feedback control strategy is proposed for real-time regulation of thermal dose delivery using spatial measurements of substrate temperature. Experimental investigation reveals that feedback control is crucial for achieving spatially uniform dose delivery.

Studying heating of magnetron target based on measurement of substrate temperature

The present work aims to develop the method for indirect determination of the magnetron target temperature. This method is based on the measurements of heating kinetic curves of the thermocouple sensor's sensing element. The measurements were performed during operation of the magnetrons with cold and hot titanium targets. In order to calculate the hot target temperature, a transcendental equation was derived using the Stefan-Boltzmann law and the Hertz-Knudsen equation. In the general case, the equation uses the difference of the fluxes transferred to the sensing element. The study revealed that in the target temperature range of 1000–1500 °C, the influence of the heat flux transferred by the evaporated atoms of the titanium target on the substrate temperature can be neglected. And the heat fluxes caused by the gas discharge with a current density in the range of 50–100 mA/cm2 have a significant influence on the substrate temperature.

Ellipsometric Method of Substrate Temperature Measurement in Low-Temperature Processes of Epitaxy of InSb Layers

The present study is aimed at solving the problem of in situ thermometry of lowtemperature processes of molecular beam epitaxy of indium antimonide. A spectral ellipsometric method for measuring the temperature of InSb epitaxial layers is proposed. The method is based on the temperature dependence of the energy positions of the critical points. The spectra of ellipsometric parameters of the material in the temperature range from 25 to 270 °C are measured. The analysis of these spectra shows that the most temperature-sensitive parameters are the spectral positions of the peaks of the ellipsometric parameter, which are manifested near the critical points E1 and E1 + Δ1. It is found that the dependences of the peak positions on temperature in the above-mentioned temperature range are linear functions with the slope factors of 0.21 and 0.10 nm/°C, respectively. These factors determine the sensitivity of the method and ensure the temperature measurement accuracy within 2–3 °C.

Enhanced PVD process control by online substrate temperature measurement

In physical vapor deposition (PVD) processes pressure and temperature are of outstanding importance for process control and coating performance. The pressure measurement and its integration into the process control are state of the art in industrial coating units. In contrast, the precise determination of the substrate temperature Tsub presents an unequally greater challenge. In PVD processes the temperature control has a great importance in two respects. On the one hand, the morphology of the coating as well as the adhesion between the coating and substrate directly depend on Tsub. On the other hand, the process temperature is limited by the maximum permissible temperature Tmax as for example of heat-treated steel. Exceeding can easily lead to a critical loss of hardness and size accuracy of the substrate and production reject. The online measurement of Tsub using currently applicable systems such as drag pointer or pyrometer is either extremely complicated or simply not possible. This is particularly the case for large-volume industrial coating units with a rotating substrate table. Therefore, in coating processes, the influence of the different process parameters on Tsub is usually not quantified. Hence, Tsub is often several tens centigrades below Tmax. Within the scope of this paper, a temperature measuring system developed at the Surface Engineering Institute (IOT) of the RWTH Aachen University is used in an industrial coating unit with rotating substrate table. With this, the online temperature measurement of rotating substrates is possible throughout the entire coating process, from the heating to the etching over the coating to the cooling process phase. In the heating, etching and coating process phases, the influence of the heating power on Tsub was analyzed and described by characteristic trend lines. The results were used to improve the substrate temperature profile of an industrial-like coating process with regard to Tmax. Here the temperature difference between Tmax of the heat-treated steel and the realized Tsub was reduced to a feasible minimum over the entire process time. Investigations on the compound properties show an improved adhesion between coating and substrate.

Development of a Long-Wave Infrared Band-Edge (LWIR BE) thermometry instrument.

Accurate measurement of substrate temperature is one of the most critical process control parameters for molecular beam epitaxy (MBE) growth. Band-edge thermometry instruments have proven to be a valuable tool for process control during MBE growth of semiconductor films, providing as high as ±1 °C temperature resolution. The increasing use of InAs, GaSb, and AlSb iii-v materials necessitates a method for accurately measuring the temperature of their closely lattice-matched GaSb substrates. Current-technology instruments typically rely on InGaAs detector materials which have a maximum wavelength λ detection of ∼1.7 μm, but GaSb substrates have a band gap energy corresponding to λ > 2 μm. A band-edge thermometry instrument capable of λ > 2 μm has been developed using an InAs/InGaSb strained-layer superlattice detector sensitive to 2-9.5 μm long-wave IR wavelengths.

Noncontact measurement of substrate temperature by optical low-coherence interferometry in high-power pulsed magnetron sputtering

Substrate temperature is one of the important parameters that affect the quality of deposited films. The monitoring of the substrate temperature is an important technique of controlling the deposition process precisely. In this study, the Si substrate temperature in high-power pulse magnetron sputtering (HPPMS) was measured by a noncontact method based on optical low-coherence interferometry (LCI). The measurement was simultaneously performed using an LCI system and a thermocouple (TC) as a contact measurement method. The difference in measured value between the LCI system and the TC was about 7.4 °C. The reproducibilities of measurement for the LCI system and TC were ±0.7 and ±2.0 °C, respectively. The heat influx from the plasma to the substrate was estimated using the temporal variation of substrate temperature and increased from 19.7 to 160.0 mW/cm2 with increasing target applied voltage. The major factor for the enhancement of the heat influx would be charged species such as ions and electrons owing to the high ionization degree of sputtered metal particles in HPPMS.

Model and experiments of the transient evolution of a thin, evaporating liquid film

Experimental thickness profiles of evaporating thin films of n-octane and n-heptane on silicon were recorded using reflectometry. These films ranged from approximately ten nanometers thick in the adsorbed region to several micrometers thick in the meniscus region. For steady-state measurements, the reflectometer was traversed along the film to give thickness versus horizontal distance. For transient measurements, the reflectometer was fixed at several points as thickness was measured over time. While film thickness and substrate temperature measurements are practical, those of the evaporative flux profile and total heat transfer are not. Hence, a numerical model was formulated based on transient lubrication theory and modified to include kinetic evaporation and disjoining pressure. The model uses an ordinary differential equation solver to advance the governing equations in time with staggered finite differences for the spatial derivatives. Good correlation of the transient film thickness was achieved between the simulations and experiments. Thus, we have confidence in the inferred evaporative flux profiles and liquid–vapor interface temperatures. With this information, instantaneous heat transfer coefficients were derived for the entirety of the thin film region.

Thermocapillary convection inside a stationary sessile water droplet on a horizontal surface with an imposed temperature gradient

The present study reports the fluid flow inside a stationary water droplet placed on a hydrophobic surface subjected to a temperature gradient. The development of temperature gradient substrate surface is accomplished using two thermoelectric coolers. Confocal microscale PIV and IRT measurements have been carried out for measurement of internal convection flow field and substrate temperature, respectively. The substrate temperature gradient is set equal to 1.8 °C/mm, and droplet diameter is varied between 1.20 and 1.94 mm. The convection pattern inside the droplets changes with droplet size. For small droplets, the fluid flows from hot side to cold side along the contact line leading to formation of two recirculation bubbles. In contrast, the flow direction near the substrate surface becomes unidirectional from cold side to hot side of the droplet for large droplet. The buoyancy effect becomes predominant for large droplets, and the fluid flows from hot side to cold side along the apex of the droplet. The present experimental results demonstrate the presence of complex three-dimensional flow structures, indicating the importance of three dimensionality in droplet fluid dynamics on a temperature gradient surface contrary to various simulation results reported in the literature based on lower-dimensional lubrication and two-dimensional models.

Langmuir probe and optical emission spectroscopy studies in magnetron sputtering plasmas for Al-doped ZnO film deposition

This work reports investigation of the Al-doped ZnO (AZO) film deposition process, at different working pressures, in a conventional magnetron sputtering system. The primary goal of this study is to investigate the plasma formation and deposition process using various diagnostic tools, by utilizing low-temperature deposition process. In addition, this paper also presents a systematic Langmuir probe (LP) analysis procedure to determine the maximum information about plasma parameters. For the present study, we have extensively used LP method to characterize the deposition process for the control of plasma parameters. Along with the LP method, we have also used optical emission spectroscopy diagnostic to examine the favorable deposition condition for the fabrication of conductive AZO film. Utilizing diagnostics, this also reports measurements of ion current density, substrate temperature, and deposition rates to fabricate low resistivity films of ∼3 mΩ cm.

Raman measurements of substrate temperature in a molecular beam epitaxy growth chamber.

A method is described for directly measuring the temperature of a substrate in a molecular-beam epitaxy (MBE) growth system. The approach relies on the establishment of the temperature dependence of Raman-active phonons of the substrate material using independently known calibration points across the range of interest. An unknown temperature in this range is then determined based on the Raman peak position with the substrate in situ the MBE chamber. The apparatus relies on conventional optics and Raman components. Shifting and broadening of the Raman spectrum are described based on the effects of thermal expansion and anharmonic decay. The choice of reference temperature is discussed. The method is qualified by examining the substrate temperature dependence, relative to that of a standard thermocouple, during a commonly used ramp procedure. Both temperature difference and time lag are obtained.

Real-time measurement of substrate temperature in molecular beam epitaxy using low-coherence tandem interferometry

It was demonstrated that the low-coherence interferometry technique can be successfully applied to real-time substrate temperature evaluation during molecular beam epitaxy in a wide range down to room temperature. The proposed technique was used for formation of silicon layers delta-doped by antimony. Due to shortening of the growth interruptions needed for temperature switching the low-coherence interferometry technique allows improving the crystal quality of the grown samples and reducing the material and time consumption. These advantages become extremely beneficial with lowering of the growth temperatures.

Rapid measurement of substrate temperatures by frequency-domain low-coherence interferometry

Rapid high-precision temperature monitoring systems for silicon wafers applicable even during plasma processing have been developed using frequency-domain low-coherence interferometry without a reference mirror. It was found to have a precision of 0.04 °C, a response time of 1 ms, and a large tolerance to mechanical vibrations and fiber vending when monitoring the temperature of commercial Si wafers. The performance is a substantial improvement over the previous precision of 0.11 °C measured in a few seconds using a time-domain method. It is, therefore, a powerful real-time technique to monitor rapidly varying wafer temperatures with high precision.

HgCdTe Molecular Beam Epitaxy Growth Temperature Calibration Using Spectroscopic Ellipsometry

In this work, spectroscopic ellipsometry (SE) is demonstrated as a technique to calibrate growth temperature measurement devices (thermocouples and pyrometers) prior to real mercury cadmium telluride (HgCdTe) growth. A pyrometer is used to control the substrate temperature in molecular beam epitaxy (MBE) for the growth of HgCdTe-based material. It is known that a very narrow optimal growth temperature range exists for HgCdTe, typically ±5°C. A nonoptimal growth temperature will negatively impact on material quality by inducing growth defects, reducing composition uniformity, causing difficulty in controlling doping incorporation, promoting poor electronic properties, and having other adverse effects. Herein, we present a method for measuring and calibrating substrate temperature measurement equipment by using spectroscopic ellipsometry (SE) prior to real HgCdTe growth. This method is easy to implement, nondestructive, and reliable. The proposed method requires one substrate with a surface material with optical properties well known in the temperature range of interest, but not necessarily the same base material as the material to be grown. In the specific case of this work, we use epitaxial CdTe material on top of a Si substrate. This wafer was used to create a database of its optical properties as a function of temperature by using SE. From the collected optical parameters, a model is built and a fit is generated from the SE data collected. The temperature can then be determined by fitting the temperature-dependent SE measurements from this specific CdTe material. The angle offset and surface roughness parameters are also included in the model to account for changes in the average run-to-run angle variations and surface conditions over time. This work does not attempt to obtain an absolute temperature, but rather a reliable and repeatable relative temperature measurement.

Feature Profiles on Plasma Etch of Organic Films by a Temporal Control of Radical Densities and Real-Time Monitoring of Substrate Temperature

The precise etching of organic films with a low dielectric constant (low-k) in a dual-frequency capacitively coupled plasma etching reactor with a plasma generation of 100 MHz and an applied bias of 2 MHz employing a gas mixture of hydrogen and nitrogen was performed by real-time control of the densities of hydrogen (H) and nitrogen (N) radicals based on real-time measurement of the Si substrate temperature. H and N radical densities were monitored near the sidewall of the reactor by vacuum ultraviolet absorption spectroscopy, and temperature was monitored by an optical fiber-type low-coherence interferometer. On the basis of the results of surface analysis by X-ray photoelectron spectroscopy, etched profiles were effectively determined from the chemical component of protection layers on the sidewall of the etched pattern affected by the ratio of H/(H+N) and substrate temperature. As the etching feature evolves, the ratio of radical density should be controlled temporally to maintain vertical profiles according to the change in substrate temperature. As a result, we have successfully realized an organic film with a vertical feature. These results indicate the need for autonomous control of the etch process based on real-time information on the plasma process for the next-generation ultrafine etching.

Feature Profiles on Plasma Etch of Organic Films by a Temporal Control of Radical Densities and Real-Time Monitoring of Substrate Temperature

The precise etching of organic films with a low dielectric constant (low-k) in a dual-frequency capacitively coupled plasma etching reactor with a plasma generation of 100 MHz and an applied bias of 2 MHz employing a gas mixture of hydrogen and nitrogen was performed by real-time control of the densities of hydrogen (H) and nitrogen (N) radicals based on real-time measurement of the Si substrate temperature. H and N radical densities were monitored near the sidewall of the reactor by vacuum ultraviolet absorption spectroscopy, and temperature was monitored by an optical fiber-type low-coherence interferometer. On the basis of the results of surface analysis by X-ray photoelectron spectroscopy, etched profiles were effectively determined from the chemical component of protection layers on the sidewall of the etched pattern affected by the ratio of H/(H+N) and substrate temperature. As the etching feature evolves, the ratio of radical density should be controlled temporally to maintain vertical profiles according to the change in substrate temperature. As a result, we have successfully realized an organic film with a vertical feature. These results indicate the need for autonomous control of the etch process based on real-time information on the plasma process for the next-generation ultrafine etching.