Browsing by Author "Sintonen, Sakari"

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Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties
(2017-01-01) Ylivaara, Oili M E; Kilpi, Lauri; Liu, Xuwen; Sintonen, Sakari; Ali, Saima; Laitinen, Mikko; Julin, Jaakko; Haimi, Eero; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo-Pekka; Ronkainen, Helena; Puurunen, Riikka
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Atomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on silicon were explored as a function of growth temperature (110-300 °C), film thickness (20-300 nm), bilayer thickness (0.1-100 nm), and TiO2 content (0%-100%). Al2O3 was grown from Me3Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al2O3/TiO2 nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO2 fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon.
Characterization of atomic layer deposition films by x-ray scattering and atomic force microscopy
(2012) Ali, Saima
School of Electrical Engineering | Master's thesis
Atomic Layer Deposition (ALD) is a thin film deposition technique that has received a lot of attention in many fields of science and industry due to its sequential, self-limiting reactions. Although it is slow method, it allows uniform, high density films with conformal depositions on 3D high aspect ratio structures. ALD allows thickness control of the film down to sub nanometre range. For more understanding and future applications, certain properties like accurate thickness, density and roughness of film is needed to get characterized. In this work ALD deposited aluminium oxide, titanium dioxide, aluminium nitride and a nanolaminate sample are characterized by X-ray Diffraction (XRD), X-ray Reflectivity (XRR) and Atomic Force Microscopy (AFM) methods. The density, thickness and roughness of films are measured by XRR method. Grazing Incidence X-ray Diffraction (GIXRD) is used to examine the crystal nature of the deposited films. There were no peaks found for the amorphous films. The crystallite size and phases of crystalline films are determined by this method. AFM technique was used to see the morphology of the films. AFM gives the roughness of the films as well which was giving quiet similar results to that of roughness values found by XRR. These results give a better understanding of ALD films deposited at different temperature conditions and with different thickness values.
Incorporation and effects of impurities in different growth zones within basic ammonothermal GaN
(2016-12-15) Sintonen, Sakari; Kivisaari, Pyry; Pimputkar, Siddha; Suihkonen, Sami; Schulz, Tobias; Speck, James S.; Nakamura, Shuji
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The ammonothermal method is one of the most promising candidates for large-scale bulk GaN growth due to its scalability and high crystalline quality. However, emphasis needs to be put on understanding the incorporation and effects of impurities during growth. This article discusses how impurities are incorporated in different growth zones in basic ammonothermal GaN, and how they affect the structural, electrical and optical properties of the grown crystal. The influence of growth time on the impurity incorporation is also studied. We measure the oxygen, silicon, and carbon impurity concentrations using secondary ion mass spectrometry, and measure their effect on the lattice constant by high resolution x-ray diffraction (HR-XRD). We determine the resulting free carrier concentration by spatially resolved Fourier transform infrared spectroscopy and study the optical properties by spatially resolved low-temperature photoluminescence. We find that oxygen is incorporated preferentially in different growth regions and its incorporation efficiency depends on the growth direction. The oxygen concentration varies from 6.3×1020 cm-3 for growth on the 112-2 planes to 2.2×1019 cm-3 for growth on the (0001) planes, while silicon and carbon concentration variation is negligible. This results in a large variation in impurity concentration over a small length scale, which causes significant differences in the strain within the boule, as determined by HR-XRD on selected areas. The impurity concentration variation induces large differences in the free carrier concentration, and directly affects the photoluminescence intensity.
Mechanical and optical properties of as-grown and thermally annealed titanium dioxide from titanium tetrachloride and water by atomic layer deposition
(2021-08-31) Ylivaara, Oili M.E.; Langner, Andreas; Liu, Xuwen; Schneider, Dieter; Julin, Jaakko; Arstila, Kai; Sintonen, Sakari; Ali, Saima; Lipsanen, Harri; Sajavaara, Timo; Hannula, Simo-Pekka; Puurunen, Riikka L.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The use of thin-films made by atomic layer deposition (ALD) is increasing in the field of optical sensing. ALD TiO2 has been widely characterized for its physical and optical properties, but systematic information about the influence of thermal history to optical and mechanical properties of the film is lacking. Optical applications require planar surface and tunability of the refractive index and residual stress. In addition, mechanical properties such as elastic modulus and film hardness influence the performance of the layer, especially, when optics is integrated with microelectromechanical systems. In this work, optical properties, density, elemental analysis, residual stress, elastic modulus and hardness of as-grown ALD TiO2 thin films on silicon were studied at temperature range from 80 to 350 °C and influence of post-ALD thermal annealing was studied on films annealed up to 900 °C. ALD TiO2 films were under tensile stress in the scale of hundreds of MPa. The stress depended both on the ALD temperature and film thickness in a complex way, and onset of crystallization increased the residual stress. Films grown at 110 and 300 °C were able to withstand post-ALD annealing at 420 °C without major change in residual stress, refractive index or extinction coefficient. Elastic modulus and hardness increased upon crystallization with increasing ALD temperature. The results presented here help to improve the design of the optical devices by choosing films with desired optical properties, and further help to design the post-ALD thermal budget so that films maintain their desired features.
Microscratch testing method for systematic evaluation of the adhesion of atomic layer deposited thin films on silicon
(2016-01-01) Kilpi, Lauri; Ylivaara, Oili M. E.; Vaajoki, Antti; Malm, Jari; Sintonen, Sakari; Tuominen, Marko; Puurunen, Riikka L.; Ronkainen, Helena
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The scratch test method is widely used for adhesion evaluation of thin films and coatings. Usual critical load criteria designed for scratch testing of coatings were not applicable to thin atomic layer deposition (ALD) films on silicon wafers. Thus, the bases for critical load evaluation were established and the critical loads suitable for ALD coating adhesion evaluation on silicon wafers were determined in this paper as LCSi1, LCSi2, LCALD1, and LCALD2, representing the failure points of the silicon substrate and the coating delamination points of the ALD coating. The adhesion performance of the ALD Al2O3, TiO2, TiN, and TaCN+Ru coatings with a thickness range between 20 and 600 nm and deposition temperature between 30 and 410°C on silicon wafers was investigated. In addition, the impact of the annealing process after deposition on adhesion was evaluated for selected cases. The tests carried out using scratch and Scotch tape test showed that the coating deposition and annealing temperature, thickness of the coating, and surface pretreatments of the Si wafer had an impact on the adhesion performance of the ALD coatings on the silicon wafer. There was also an improved load carrying capacity due to Al2O3, the magnitude of which depended on the coating thickness and the deposition temperature. The tape tests were carried out for selected coatings as a comparison. The results show that the scratch test is a useful and applicable tool for adhesion evaluation of ALD coatings, even when carried out for thin (20 nm thick) coatings.
Superhilarakenteiden karakterisointi röntgendiffraktio- ja röntgenheijastusmenetelmillä
(2009) Sintonen, Sakari
Elektroniikan, tietoliikenteen ja automaation tiedekunta | Master's thesis
Tässä diplomityössä esiteltiin menetelmä superhilarakenteiden karakterisoimiseksi. Superhilarakenteiden karakterisointi kattaa sen eri osien hilavakioiden, paksuuksien ja moniyhdisteiden kompositioiden määrittämisen. Lisäksi on selvitettävä rakenteen jännitystilat. Superhilojen karakterisointi suoritettiin röntgenheijastus- ja röntgendiffraktiomittausten avulla. Röntgenheijastusmittaukset mahdollistavat nanometrin luokkaa olevien paksuuksien mittaamisen. Tässä työssä esitellyssä menetelmässä superhilarakenteiden kerrosten paksuudet mitattiin röntgenheijastusmittausten avulla, jonka jälkeen loput tuntemattomista parametreista määritettiin röntgendiffraktiomittausten perusteella. Menetelmää sovellettiin näytteisiin joiden kompositiot ja paksuudet määritettiin myös röntgendiffraktiomittauksia simuloimalla. Menetelmän antamat tulokset vastasivat simuloituja tuloksia erittäin hyvin. Menetelmä soveltuu kaikkien superhilarakenteiden karakterisointiin, lukuun ottamatta rakenteita joiden pinnat ovat liian karheita ja/tai aaltoilevia sekä rakenteita joiden periodisuus on heikko. Superhila voidaan myös karakterisoida simuloimalla röntgendiffraktiota. Simuloinnista saatavien tuloksien ongelmana on, että ne eivät ole yksikäsitteisiä. Työssä esitellyn menetelmän etuna on, että tulokset ovat yksikäsitteisiä, jolloin simulointia voidaan hyödyntää pelkästään tulosten oikeellisuuden tarkistamiseen.
Synchrotron radiation x-ray topography and defect selective etching analysis of threading dislocations in GaN
(2014) Sintonen, Sakari; Rudzinski, Mariusz; Suihkonen, Sami; Jussila, Henri; Knetzger, Michael; Meissner, Elke; Danilewsky, Andreas; Tuomi, Turkka O.; Lipsanen, Harri
School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid and non-destructive technique for dislocation analysis on a large scale. In this study, the defect structure of an ammonothermal c-plane GaN substrate was recorded using SR-XRT and the image contrast caused by the dislocation induced microstrain was simulated. The simulations and experimental observations agree excellently and the SR-XRT image contrasts of mixed and screw dislocations were determined. Apart from a few exceptions, defect selective etching measurements were shown to correspond one to one with the SR-XRT results.
Synchrotron radiation x-ray topography of crystallographic defects in GaN
(2014) Sintonen, Sakari
School of Electrical Engineering | Doctoral dissertation (article-based)
In this thesis, the crystal structures of bulk, homoepitaxial and heteroepitaxial GaN were characterized by synchrotron radiation x-ray topography (SR-XRT), x-ray diffraction (XRD) and defect selective etching (DSE). The SR-XRT image contrast of threading screw dislocations and threading mixed dislocations in GaN were determined. The images caused by the strain fields of threading screw dislocations and threading screw dislocation clusters were simulated, and the simulated and experimental topograph images of low defect density ammonothermal GaN were in excellent agreement. Topograph images corresponding to strain fields of large dislocations with Burgers vector magnitudes equal to multiples of the elemental screw dislocation Burgers vector were observed. DSE experiments were performed to determine whether these large defect images originate from single dislocation strain fields, i.e. super screw dislocations or micropipes, or from combined strain fields of several elemental dislocations in close proximity. DSE images revealed that all observations but one were caused by groups of adjacent elemental threading dislocations. The determined topograph image contrasts of threading mixed and threading screw dislocations were utilized in large area studies of bulk GaN grown by the ammonothermal method. In one of the studies, threading mixed dislocations were observed to form arrays consisting of mixed dislocations with identical Burgers vectors. The minute lattice tilt and twist caused by the dislocation arrays were calculated based on dislocation spacing and confirmed with high resolution XRD measurements. SR-XRT analysis of grain boundaries and basal plane dislocations in ammonothermal GaN were also discussed. The structural quality of homoepitaxial GaN and heteroepitaxial GaN on patterned substrates was characterized by SR-XRT and XRD. The GaN layers were grown by metallo-organic vapour phase epitaxy (MOVPE) on ammonothermal GaN substrates, patterned sapphire substrates and substrates consisting of patterned MOVPE grown GaN layers on sapphire. SR-XRT is a technique especially suited for imaging the defect structure of materials with low crystalline defect density, whereas XRD is applicable to characterization of materials with higher defect density as well. SR-XRT measurements enabled imaging of individual dislocations and identification of different dislocation types.
Thermomechanical properties of aluminum oxide thin films made by atomic layer deposition
(2022-12-01) Ylivaara, Oili M.E.; Langner, Andreas; Ek, Satu; Malm, Jari; Julin, Jaakko; Laitinen, Mikko; Ali, Saima; Sintonen, Sakari; Lipsanen, Harri; Sajavaara, Timo; Puurunen, Riikka L.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In microelectromechanical system devices, thin films experience thermal processing at temperatures some cases exceeding the growth or deposition temperature of the film. In the case of the thin film grown by atomic layer deposition (ALD) at relatively low temperatures, post-ALD thermal processing or high device operation temperature might cause performance issues at device level or even device failure. In this work, residual stress and the role of intrinsic stress in ALD Al2O3 films grown from Me3Al and H2O, O3, or O2 (plasma ALD) were studied via post-ALD thermal processing. Thermal expansion coefficient was determined using thermal cycling and the double substrate method. For some samples, post-ALD thermal annealing was done in nitrogen at 300, 450, 700, or 900 °C. Selected samples were also studied for crystallinity, composition, and optical properties. Samples that were thermally annealed at 900 °C had increased residual stress value (1400-1600 MPa) upon formation of denser Al2O3 phase. The thermal expansion coefficient varied somewhat between Al2O3 made using different oxygen precursors. For thermal-Al2O3, intrinsic stress decreased with increasing growth temperature. ALD Al2O3 grown with plasma process had the lowest intrinsic stress. The results show that ALD Al2O3 grown at 200 and 300 °C is suitable for applications, where films are exposed to post-ALD thermal processing even at temperature of 700 °C without a major change in optical properties or residual stress.
Tribological properties of thin films made by atomic layer deposition sliding against silicon
(2018-01-01) Kilpi, Lauri; Ylivaara, Oili M.E.; Vaajoki, Antti; Liu, Xuwen; Rontu, Ville; Sintonen, Sakari; Haimi, Eero; Malm, Jari; Bosund, Markus; Tuominen, Marko; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo Pekka; Puurunen, Riikka L.; Ronkainen, Helena
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Interfacial phenomena, such as adhesion, friction, and wear, can dominate the performance and reliability of microelectromechanical (MEMS) devices. Here, thin films made by atomic layer deposition (ALD) were tested for their tribological properties. Tribological tests were carried out with silicon counterpart sliding against ALD thin films in order to simulate the contacts occurring in the MEMS devices. The counterpart was sliding in a linear reciprocating motion against the ALD films with the total sliding distances of 5 and 20 m. Al2O3 and TiO2 coatings with different deposition temperatures were investigated in addition to Al2O3-TiO2-nanolaminate, TiN, NbN, TiAlCN, a-C:H [diamondlike carbon (DLC)] coatings, and uncoated Si. The formation of the tribolayer in the contact area was the dominating phenomenon for friction and wear performance. Hardness, elastic modulus, and crystallinity of the materials were also investigated. The nitride coatings had the most favorable friction and wear performance of the ALD coatings, yet lower friction coefficient was measured with DLC a-C:H coating. These results help us to take steps toward improved coating solutions in, e.g., MEMS applications.
X-ray reflectivity characterization of atomic layer deposition Al2O3/TiO2 nanolaminates with ultrathin bilayers
(2014) Sintonen, Sakari; Ali, Saima; Ylivaara, Oili M. E.; Puurunen, Riikka L.; Lipsanen, Harri
School of Electrical Engineering | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Nanolaminate structures have many prospective uses in mechanical, electrical, and optical applications due to the wide selection of materials and precise control over layer thicknesses. In this work, ultrathin Al2O3/TiO2 nanolaminate structures deposited by atomic layer deposition from Me3Al, TiCl4, and H2O precursors with intended bilayer thicknesses ranging from 0.1 to 50 nm were characterized by x-ray reflectivity (XRR) measurements. The measurements were simulated to obtain values for thickness, density, and roughness of constituting layers. XRR analysis shows that the individual layers within the nanolaminate remain discrete for bilayers as thin as 0.8 nm. Further reduction in bilayer thickness produces a composite of the two materials.