Monitoring Of Thin Film Growth Research Articles

Numerical ellipsometry: Artificial intelligence for real-time, in situ absorbing film process control

Ellipsometry is a material analytical method in which the desired parameters, for example, film thickness and index of refraction, are related to the instrument measurements through Maxwell’s equations, light wavelength, and measurement geometry. Consequently, obtaining the desired parameters has required solving the model equations using a wide variety of methods. A commonly used method is least squares curve fitting, frequently the Levenberg–Marquardt method. This numerical method depends upon not only the model but also the initial estimates of solution, the possible interference of local minima, and the algorithm stopping conditions. Being iterative, it also takes nonzero time. The work here demonstrates the use of artificial intelligence in the form of a multilayer perceptron artificial neural network to avoid these problems and find solutions in the millisecond time scale. This noniterative, stable, and fast performance lends itself to real-time, in situ monitoring of thin film growth. Examples for thin (up to 30 nm) films will be given using a multilayer perceptron configuration consisting of four input and four output neurons with two hidden layers of 40 neurons each. Solutions are predicted by the artificial neural network at each wavelength independently and do not rely on fitting functions which express a relationship between optical properties and wavelength.

Grazing incidence fast atom diffraction in high-pressure conditions

Grazing Incidence Fast Atom Diffraction (GIFAD) is a recent technique for characterizing surface structures and real-time monitoring of thin film growth. Up to now, GIFAD has only been used in Ultra-High-Vacuum conditions, typically in the range of 10−10 to 10−8 mbar, and has therefore only been considered for high vacuum deposition methods like Molecular Beam Epitaxy or very low-pressure Chemical Vapor Deposition (CVD). At pressures exceeding 10−6 mbar, gas phase collisions along the atom beam trajectory not only reduce the mean free path but also degrade the beam coherence length and thus potentially suppress the diffraction signal. In addition, pressures lower than 10−5 mbar are required to maintain a low noise level on the scattered particle detector. In a new configuration, we demonstrate that GIFAD can operate at pressure as high as 10−2 mbar of argon with well-contrasted diffraction patterns. This opens wide avenues for the study of surface reactivity, thin film growth in Magnetron Sputtering Deposition, where electron diffraction is inevitably perturbed by the electromagnetic fields. This High-Pressure version of GIFAD could also be extended to Reactive Pulsed Laser Deposition and many CVD variants.

Development of a scanning probe microscopy integrated atomic layer deposition system for in situ successive monitoring of thin film growth

A dual chamber system integrated with atomic layer deposition (ALD) and atomic force microscopy (AFM) was developed for the successive monitoring of nanoparticles to thin film growth process. The samples were fabricated in the ALD chamber. A magnetic transmission rod enabled sample transferring between the ALD and the AFM test chambers without breaking the vacuum, avoiding possible surface morphology change when frequently varying the growth condition and oxidation under ambient condition. The sample transmission also avoids deposition and contamination on the AFM tip during the successive testing. The sample stage has machined a group of accurate location pinholes, ensuring the 10 μm2 measurement consistency. As a demonstration, the platinum thin films with different thickness were fabricated by varying ALD cycles. The surface morphology was monitored successively during the deposition. Under vacuum with controlled oxygen partial pressure, the aging and sintering phenomenon of particles has been studied in the AFM testing chamber after high temperature treatment. The integrated AFM/ALD instrument is potentially a powerful system for monitoring the thin film preparation and characterization.

In situ conductance monitoring of Pt thin film growth by area-selective atomic layer deposition

In situ monitoring of thin film growth on the lateral nanoscale provides insight into different growth stages and establishes a basis for feedback-controlled optimization of the growth process. Here we present a novel approach towards in situ monitoring of area-selective atomic layer deposition of metals, in particular platinum, using the electrical conductance of the growing layer as probed quantity. Area-selectivity is reached by thin platinum seed layers fabricated by focused electron beam induced deposition (FEBID). Different growth stages are identified by their respective impact on the conductance. The growth rate is optimized in a feedback-loop that controls the cycling periods of the atomic layer deposition process employing a genetic algorithm. Our approach is sufficiently general to be applicable to a large variety of other deposition setups that do not use FEBID for seeding.

301 アンテナ発振超音波共鳴法による薄膜成長モニタリング(GS-3 薄膜・細線(1))

301 アンテナ発振超音波共鳴法による薄膜成長モニタリング(GS-3 薄膜・細線(1))

Design and simulation of excitation laser system for in-situ Raman monitoring

A system for in-situ Raman monitoring of thin film growth during Microwave Plasma Assisted Chemical Vapour Deposition (μPACVD) process was developed. Dedicated Raman probe system was designed for precise focusing of an excitation laser beam into the growing film. The probes have to be placed outside the reaction chamber (working distance about 20 cm) in order to avoid interference of the process by work of measurement devices (non-invasive measurements). Analysis and calculation supported by simulations based on Monte-Carlo ray-tracing method and Beam Propagation Method showed that glancing-incidence optical configuration is of the Raman system is the most sufficient one. Range of the most effective incidence angles of the excitation beam was determined. Shape and size of laser spot at the sample was determined. Correction of spherical aberrations by use of doublets was proposed to ensure efficient focusing of the excitation beam into the investigated film.

Real-time optical monitoring of thin film growth by in situ pyrometry through multiple layers and effective media approximation modeling

A model combining multiple layer description and effective media approximation is developed for pyrometry in the case of thin film synthesis, in order to estimate the film property evolution along its thickness during the growth process in real time. The model is used to investigate optical properties of polycrystalline diamond film prepared by H2∕CH4∕N2 microwave plasma. It is shown that in the presence of nitrogen, the growth is strongly nonhomogeneous. The deposit, initially composed of large amounts of void and nondiamond phases, evolves rapidly towards highest quality dense film where the diamond phase is predominant.

In-situ monitoring of the growth of oxide thin films in PLD using high-pressure reflection high energy electron diffraction

Reflection high-energy electron diffraction (RHEED) is very surface sensitive and often used for the analysis and monitoring of thin film growth in ultrahigh vacuum deposition system (for instance, Molecular Beam Epitasis). In order to in-situ monitor the growth of oxide thin films at high oxygen pressure up to 50Pa, a high-pressure RHEED designed and fabricated by our group was used for first time in our pulsed laser deposition system (PLD). Using the PLD system the Nb-doped SrTiO3 (STNO) and Y1Ba2Cu3O7 (YBCO) thin films have been epitaxially grown on SrTiO3 (001) substrates. T he RHEED patterns of the STNO and YBCO films and the oscillation of the intensity of the pattern have been measured by the high-pressure RHEED during deposition. In addition,the surface morpholoyg of the films and the dynamic analysis of film growth process were discussed.

紫外・可視反射分光法による表面薄膜解析

This review gives an overview of the principles and experimental methods of UV-visible reflectance spectroscopy including potential-modulated reflectance spectroscopy (PMRS) and real-time spectroscopic ellipsometry (RTSE). The capabilities of in-situ, non-invasive, surface-sensitive analysis are demonstrated for the composition determination of passive films using PMRS and for the real-time monitoring of thin film growth and dissolution processes using RTSE.

In-situ monitoring during pulsed laser deposition using RHEED at high pressure

Reflection high energy electron diffraction (RHEED) is, due to its surface sensitivity, often used for the analysis and monitoring of thin film growth in ultra-high vacuum deposition systems. RHEED is usually applied in combination with pulsed laser deposition (PLD) by adjusting the background pressure. However, the pressure during PLD is an important parameter because it influences the shape and size of the plasma. Low deposition pressures during PLD can lead to stress, usually compressive, in the film. Moreover, the oxidation power is much higher at higher pressures, which enables growth at higher temperatures, leading to better crystallinity of the as-deposited films. Therefore, relative high pressures are favourable in PLD. Unfortunately, these high pressures hamper the diagnostics of the growing film surfaces by in-situ RHEED. Here, a RHEED system designed for growth monitoring at high deposition pressures is presented. The main problem that has been solved is the increased scattering loss. The losses are minimised by keeping the travelling path of the electrons in the high-pressure region as short as possible. Using a two-stage differential pumping system, we are able to increase the deposition pressure up to 50 Pa. With this system, we have monitored the growth of SrTiO 3, YBa 2Cu 3O 7− δ and SrCuO x , in a background pressure of 15 Pa of oxygen. The first two systems show clear oscillations of the diffracted intensity, indicating two-dimensional growth, with the possibility to control the thin film growth on an atomic level at standard PLD pressures. Furthermore, the mobility of material deposited with one single laser pulse is represented by an additional modulation of the intensity of the RHEED pattern. This gives excess information about the diffusion and nucleation of the deposited material.

Monitoring of Thin Film Growth by an Ultrasonic Interference Method

A better correlation between thickness values of a thin film grown on a substrate and on an auxiliary monitor is obtained by using the same substrate material in both cases. The velocity change of ultrasonic surface waves in the film and substrate is measured as a function of the film thickness by interference of the surface wave with a bulk (volume) wave in the substrate. Interference periods of 50–500 Å are measured and computed for Au, Ag, and Cu at 30 and 50 MHz; the values of the interference period could be decreased to a few tens of angstroms for frequencies above 100 MHz.