Thin Film Deposition Process Research Articles

Temperature field analysis of TiO_2 films with high-absorptance inclusions

To deduce the location of absorptive inclusions in thin films, temperature distributions in pure TiO(2) films and TiO(2) films with high-absorptance inclusions are analyzed based on temperature field theory. According to our theoretic simulations, the surface temperature rise increases when absorptive inclusions are incorporated into thin films and shows different values for different inclusions. With the increase of inclusion thickness, the surface temperature rise varies and has a maximum value. A potential method is presented to deduce the location of absorptive inclusion through calculating the surface temperature rise at two modulated frequencies, if it is possible to know in advance the inclusion material or to prejudge this from a thin-film deposition process.

Lattice-size Dependence and Dynamics of Surface Mean Slope in a Thin Film Deposition Process

This work focuses on the study of the dynamic behavior and lattice size dependence of the surface root-mean-square slope in a porous thin film deposition process taking place on a triangular lattice. The simulation results indicate that the expected mean slope square reaches quickly a steady-state value and exhibits a very weak dependence with respect to lattice size variation. The simulation findings are corroborated by an analysis of appropriate finite-difference discretizations of surface height profiles computed by an Edwards-Wilkinson-type partial differential equation that can be used to describe the dynamics of surface height profile in the thin film deposition process under consideration.

Impact of Precursor Chemistry and Process Conditions on the Scalability of ALD HfO2 Gate Dielectrics

The downscaling of high-/metal gate transistor devices requires thin-film deposition processes that deliver not only an outstanding high- oxide quality, but also a strict interfacial oxide thickness control in the sub-1 nm thickness range. To study the impact of atomic layer deposition (ALD) process conditions and chemistry on the quality and interfacial oxide thickness, we have used tetrakis[ethylmethylamino]hafnium (TEMAH) as a metal precursor and and as oxidants. The deposition temperature ranged from 285 up to , where TEMAH decomposition plays a role in the growth mechanism. Physical characterization and Pt dot capacitor devices have been used to study the impact of the oxidant and process conditions on the equivalent oxide thickness and gate leakage current of 2–4 nm thin films. By combining X-ray reflectometry and ellipsometry, we evaluated the Si/high- interfacial oxide layer thickness. Time-of-flight secondary-ion mass spectroscopy was used to determine the C impurity levels. Both the interfacial oxide layer thickness and the C impurity level in the stacks are strongly dependent on the oxidant. The temperature dependence of the C impurity level is opposite for and . Furthermore, regrowth was found for the process.

Fabrication of Glass Fiber Reinforced Composite Films for Flexible Organic Light Emitting Diode Devices

We fabricated transparent composite films which have good thermal stability, low CTE (coefficient of thermal expansion) and high mechanical properties for flexible OLED substrate. Glass fiber reinforced composite films were made by UV light induced chemical crosslinking of composite materials consisted of glass fiber and UV curable resin in film state. It was noted that the pattern of the reinforce glass fiber had important effect on the optical and mechanical properties of the resulting composite film. The performance of the composite films in the ITO thin film deposition process and subsequent OLED device fabrication was better than those of the known polymer films such as PET, PC, and PES.

Investigation of film surface roughness and porosity dependence on lattice size in a porous thin film deposition process

The dependence of film surface roughness and porosity on lattice size in a porous thin film deposition process is studied via kinetic Monte Carlo simulations on a triangular lattice. For sufficiently large lattice size the steady-state value of the expected film porosity has a weak dependence on the lattice size and the steady-state value of the expected surface roughness square varies linearly with lattice size. An analysis of the film morphology based on a stochastic partial differential equation description of the film surface morphology supports and explains the findings of the numerical simulations.

Multi-scale Simulations for Plasma Processing of Thin Films

An inherent challenge to achieving improvements in thin film deposition processes is that requirements at the feature scale have to be somehow "tuned in" by modifying reactor scale geometry and process parameters. The simulation approach described allows for the solution of species fluxes and energies at the wafer surface as a function of process parameters. The reactor scale model addresses coupled flow, chemistry and plasma physics such as power deposition, volumetric reactions, species transport and deposition on chamber walls. The feature scale model computes growth of the film inside a trench. The objective of this work is to develop a comprehensive model for the high-density plasma chemical vapor deposition of silicon dioxide films in an inductively coupled plasma reactor. Using gas phase and surface reaction mechanisms from literature, trends in deposition characteristics with process variables such as inductive power are compared to experimental data in a commercial reactor.

Pulsed laser deposited Y-doped BaZrO 3 thin films for high temperature humidity sensors

Pulsed laser deposited (PLD) Y-doped BaZrO 3 thin films (BaZr 1- x Y x O 3- y/2 , x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures ( T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1,2]. indicate that bulk Y-doped BaZrO 3 could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO 3 thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films. X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar + etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO 3:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm −1 for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured.

Roll-to-Roll Deposition of a Semiconductor Film on a Flexible Substrate for Photovoltaics: Conception to Reality

T. W. Fraser Russell has made significant contributions to process engineering advances relating to the commercialization of photovoltaic technology. He recognized that its commercial viability would require the application of sound chemical engineering principles to solve a very nontraditional chemical engineering problem—in particular the engineering methodologies needed to transfer thin-film deposition processes from the laboratory scale into commercial production. In this paper, a historical narrative, spanning the late 1970s through the present day, is presented detailing Fraser’s contributions to the development of photovoltaic film deposition on a continuous moving web via thermal evaporation.

Residual stresses and mechanical properties of a ZnO pyroelectric sensor

The multilayer composite film stack is a common feature of the microsensors based on thin film technology. In this paper, we propose an analytical model to investigate the Young’s moduli, hardness, and residual stresses of the constitutive film layers of a multilayer film stack. A multilayer film stresses model is derived to evaluate the residual stress distributions in the constitutive film layers of a ZnO pyroelectric sensor. A good agreement among the multilayer film stresses model, the grain morphologies characterized by scanning electron microscopy, the mechanical properties testing by nanoindentation, and the voltage responsivity measurement of the ZnO pyroelectric sensor is found in this paper. The proposed multilayer film stresses model can therefore be used to quantitatively analyze the film stresses and proceed to the optimization of thin film deposition process.

Stochastic Modeling and Simultaneous Regulation of Surface Roughness and Porosity in Thin Film Deposition

This work focuses on stochastic modeling and simultaneous regulation of surface roughness and porosity for a porous thin film deposition process modeled via kinetic Monte Carlo (kMC) simulation on a triangular lattice. The microscopic model of the thin film growth process includes adsorption and migration processes. Vacancies and overhangs are allowed inside the film for the purpose of modeling thin film porosity. The definition of the surface height profile is first introduced for a porous thin film deposition taking place in a triangular lattice. The dynamics of surface height of the thin film are described by an Edwards-Wilkinson (EW) type equation, which is a second-order linear stochastic partial differential equation (PDE). The root-mean-square (RMS) surface roughness is chosen as one of the controlled variables. Subsequently, an appropriate definition of film site occupancy ratio (SOR) is introduced to represent the extent of porosity inside the film and is chosen as the second to-be-controlled variable. A deterministic ordinary differential equation (ODE) model is postulated to describe the time evolution of the film SOR. The coefficients of the EW equation of surface height and of the deterministic ODE model of the film SOR are estimated on the basis of data obtained from the kMC simulator of the deposition process using least-squares methods, and their dependence on substrate temperature is determined. The developed dynamic models are used as the basis for the design of a model predictive control algorithm that includes a penalty on the deviation of the surface roughness square and film SOR from their respective set-point values. Simulation results demonstrate the applicability and effectiveness of the proposed modeling and control approach in the context of the deposition process under consideration. When simultaneous control of surface roughness and porosity is carried out, a balanced trade-off is obtained in the closed-loop system between the two control objectives of surface roughness and porosity regulation.

Regulation of film thickness, surface roughness and porosity in thin film growth using deposition rate

This work focuses on distributed control of film thickness, surface roughness and porosity in a porous thin film deposition process using the deposition rate as the manipulated input. The deposition process includes adsorption and migration processes and it is modeled via kinetic Monte Carlo simulation on a triangular lattice with vacancies and overhangs allowed to develop inside the film. A distributed parameter (partial differential equation) dynamic model is derived to describe the evolution of the surface height profile of the thin film accounting for the effect of deposition rate. The dynamics of film porosity, evaluated as film site occupancy ratio, are described by an ordinary differential equation. The developed dynamic models are then used as the basis for the design of a model predictive control algorithm that includes penalty on the deviation of film thickness, surface roughness and film porosity from their respective set-point values. Simulation results demonstrate the applicability and effectiveness of the proposed modeling and control approach in the context of the deposition process under consideration.

A wafer-scale encapsulated RF MEMS switch with a stress-reduced corrugated diaphragm

A wafer-scale encapsulated DC-contact RF MEMS switch with a stress-reduced corrugated diaphragm is proposed and developed. The design, fabrication and characterization aspects of the MEMS switch are presented in this paper. The introduction of corrugation is proven to be an effective and easier way to reduce the residual stress in the diaphragm as compared to the approach by the stress control in the thin film deposition process. The measured pull-in voltage of the MEMS switch is significantly reduced from 105 V for a flat diaphragm to 51 V and 42 V for two-corrugation and four-corrugation diaphragms, respectively, which agree well with the calculation results by derived analytical equations. The estimated equivalent stresses in the two corresponding corrugated diaphragms are 11.9 MPa and 5.9 MPa, respectively, which are much lower than 56 MPa in the flat diaphragm. The fabricated MEMS switch can operate well, achieving more than 1 billion switching cycles for signal currents below 1 mA. The RF performance of fabricated switches was also characterized. The isolation is below −30 dB up to 5 GHz, and about −22 dB at 15 GHz. The insertion loss is about −0.8 dB up to 4 GHz, and −2.9 dB at 15 GHz.

Full-wafer mapping and response surface modeling techniques for thin film deposition processes

Computational techniques for representing and analyzing full-wafer metrology data are developed for chemical vapor deposition and other thin-film processing applications. Spatially resolved measurement data are used to produce “virtual wafers” that are subsequently used to create response surface models for predicting the full-wafer thickness, composition, or any other property profile as a function of processing parameters. Statistical analysis tools are developed to assess model prediction accuracy and to compare the relative accuracies of different models created from the same wafer data set. Examples illustrating the use of these techniques for film property uniformity optimization and for creating intentional film-property spatial gradients for combinatorial CVD applications are presented.

Simultaneous Regulation of Surface Roughness and Porosity in Thin Film Growth

Abstract Abstract This work focuses on simultaneous control of surface roughness and film porosity in a porous thin film deposition process modeled via kinetic Monte Carlo simulation on a triangular lattice. The microscopic model of the thin film growth process includes adsorption and migration processes. Vacancies and overhangs are allowed inside the film for the purpose of modeling thin film porosity. Appropriate closed-form dynamic models are first derived to describe the evolution of film surface roughness and porosity and used as the basis for the design of a model predictive control algorithm that includes penalty on the deviation of surface roughness and film porosity from their respective set-point values. Closed-loop simulations demonstrate that when simultaneous control of surface roughness and porosity is carried out, a balanced trade-off is obtained in the closed-loop system between the two control objectives of surface roughness and porosity regulation.

Long-lifetime thin-film encapsulated organic light-emitting diodes

Multiple fluorocarbon (CFx) and silicon nitride (Si3N4) bilayers were applied as encapsulation cap on glass-based organic light-emitting diodes (OLEDs). When CFx/Si3N4 bilayers were deposited onto the OLED structure, the devices showed performance worse than one without any encapsulation. The adverse effects were attributed to the damage caused by reaction species during the thin-film deposition processes. To solve this problem, a CuPc interlayer was found to provide effective protection to the OLED structure. With a structure of CuPc/(CFx/Si3N4)×5, the encapsulated device showed an operation lifetime over 8000 h (higher than 80% of that achieved with a conventional metal encapsulation).

The Nearest Uniformity Producing Profile (NUPP) optimization criterion for thin-film processing applications

A criterion for spatial uniformity control in thin-film deposition processes (e.g., chemical vapor deposition for semiconductor manufacturing) is presented, applicable to any measurable film quality (thickness, composition, microstructure, and electrical properties, among others) for all deposition systems where the substrate is rotated to improve uniformity. The approach is based on identifying the subspace of all deposition profiles on the stationary substrate that produce uniform films under rotation and then projecting a deposition profile to be controlled onto a sequence of uniformity producing basis functions spanning that subspace to determine the “Nearest Uniformity Producing Profile” (NUPP). This criterion depends only on the geometrical characteristics of the deposition system, and control and optimization methods can be developed to reduce the deviation from the NUPP giving a widely applicable film control methodology. An important contribution of the NUPP concept and underlying theory is that the latter reveals new structure in the uniformity and nonuniformity producing subspaces, providing insight into thin-film process design and control principles and an opportunity to unify these principles across a range of reactor designs. The implementation of this uniformity criterion is demonstrated using a numerical toolbox developed using the object-oriented features of MATLAB.

The thin-film deposition of conjugated molecules for organic electronics

Device-quality conjugated organic thin films are now routinely prepared in many different ways to fabricate light-emitting diodes, thin-film transistors, and photovoltaic devices. Understanding how to design molecules through versatile synthetic chemistry and the mechanisms of phase transformation and chemical reaction that occur during the thin-film deposition process becomes especially vital for the performance of the applications. This article reviews the current understanding of various thin-film deposition technologies for the conjugated organic molecules primarily used in optoelectronics, particularly in photovoltaic applications.

Optimization of Bi 2Te 3 and Sb 2Te 3 thin films deposited by co-evaporation on polyimide for thermoelectric applications

The optimization of the deposition process of n-type Bismuth Telluride and p-type Antimony Telluride thin films for thermoelectric applications is reported. The films were deposited on a 25 μm-thick flexible polyimide (kapton) substrate by co-evaporation of Bi and Te, for the n-type element, and Sb and Te, for the p-type element. The evaporation rate of each material was monitorized by an oscillating crystal sensor and the power supplied to each evaporation boat was controlled with a PID algorithm in order to achieve a precise user-defined constant evaporation rate. The influence of substrate temperature (in the range 240–300 °C) and evaporation rates of Bi, Te and Sb on the electronic properties of the films was studied and optimized to obtain the highest Seebeck coefficient. The best n-type Bi 2Te 3 films were deposited at 300 °C with a polycrystalline structure, a composition close to stoichiometry, electrical resistivity ∼20 μΩ m and Seebeck coefficient −195 μV/°C. The best p-type Sb 2Te 3 films were deposited at 240 °C, are slightly Te-rich, have electrical resistivity ∼20 μΩ m and Seebeck coefficient +153 μV/°C. These high Seebeck coefficients and low electrical resistivities make these materials suitable for fabrication of Peltier coolers and thermopile devices.

Optimization of a thin film deposition process using a dynamic model extracted from molecular simulations

This study presents and demonstrates an algorithm for computing a dynamic model for a thin film deposition process. The proposed algorithm is used on high dimensional Kinetic Monte Carlo (KMC) simulations and consists of applying principal component analysis (PCA) for reducing the state dimension, a self organizing map (SOM) for grouping similar surface configurations and simple cell mapping (SCM) for identifying the transitions between different surface configuration groups. The error associated with this model reduction approach is characterized by running more than 1000 test simulations with highly dynamic and random input profiles. The global error, which is the normalized Euclidean distance between the simulated and predicted states, is found to be less than 1% on average relative to the test simulation results. This indicates that our reduced order dynamic model, which was developed using a rather small simulation set, was able to accurately predict the evolution of the film microstructure for much larger simulation sets and a wide range of process conditions. Minimization of the deposition time to reach a desired film structure has also been achieved using this model. Hence, our study showed that the proposed algorithm is useful for extracting dynamic models from high dimensional and noisy molecular simulation data.

A Quasi-Planar Thin Film Field Emission Diode

A novel quasi-planar thin-film field emitter is fabricated by thin-film deposition and wet etching processes. The spacing between the emitters and collectors could be well controlled on the basis of the thicknesses of Cr thin films, which create submicron gaps. A forming process increases emitter surface roughness and results in a higher field enhancement factor, which shows better field emission characteristics. The turn-on voltage (at which the current level is 100 nA) of the device with a Cr thin film thickness of 300 nm is as low as 12 V, and the current fluctuation in 1 hour test at a driving voltage of 20 V represents a variation from -86 to +114%.