Browsing by Author "Broas, Mikael"

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Atomic layer deposition of AlN from AlCl3 using NH3 and Ar/NH3 plasma
(2018-01) Rontu, Ville; Sippola, Perttu; Broas, Mikael; Ross, Glenn; Lipsanen, Harri; Paulasto-Kröckel, Mervi; Franssila, Sami
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The atomic layer deposition (ALD) of AlN from AlCl3 was investigated using a thermal process with NH3 and a plasma-enhanced (PE)ALD process with Ar/NH3 plasma. The growth was limited in the thermal process by the low reactivity of NH3, and impractically long pulses were required to reach saturation. Despite the plasma activation, the growth per cycle in the PEALD process was lower than that in the thermal process (0.4A ° vs 0.7A ° ). However, the plasma process resulted in a lower concentration of impurities in the films compared to the thermal process. Both the thermal and plasma processes yielded crystalline films; however, the degree of crystallinity was higher in the plasma process. The films had a preferential orientation of the hexagonal AlN [002] direction normal to the silicon (100) wafer surface. With the plasma process, film stress control was possible and tensile, compressive, or zero stress films were obtained by simply adjusting the plasma time.
Blistering mechanisms of atomic-layer-deposited AlN and Al2O3 films
(2017-10-02) Broas, Mikael; Jiang, Hua; Graff, Andreas; Sajavaara, Timo; Vuorinen, Vesa; Paulasto-Kröckel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Blistering of protective, structural, and functional coatings is a reliability risk pestering films ranging from elemental to ceramic ones. The driving force behind blistering comes from either excess hydrogen at the film-substrate interface or stress-driven buckling. Contrary to the stress-driven mechanism, the hydrogen-initiated one is poorly understood. Recently, it was shown that in the bulk Al-Al2O3 system, the blistering is preceded by the formation of nano-sized cavities on the substrate. The stress-and hydrogen-driven mechanisms in atomic-layer-deposited (ALD) films are explored here. We clarify issues in the hydrogen-related mechanism via high-resolution microscopy and show that at least two distinct mechanisms can cause blistering in ALD films. Published by AIP Publishing.
Chemical stability of alumina fabricated by atomic layer deposition
(2017-01-31) Kanninen, Olli
Kemian tekniikan korkeakoulu | Master's thesis
Alumina films formed with atomic layer deposition (ALD) can be utilized in silicon on insulator (SOI) wafers exploited as substrates for advanced microelectromechanical systems (MEMS) applications. Both SOI wafer manufacturing processes and the actual operational environment of MEMS, such as those of medical micro device applications, can expose the ALD alumina coatings to a variety of wet chemistries. As these solutions may deteriorate the coatings and hence either contaminate processing tools in manufacturing or decrease the biocompatibility, it is necessary to prevent dissolution of the films in wet chemistries. The goal of this thesis was to study the effect of microstructural characteristics of ALD alumina contributing to a low solubility in neutral, basic, and acidic wet chemistries, and to further understand the etching mechanisms. ALD alumina films were formed with four different precursor combinations and the stability of the films was enhanced by annealing. Various etching experiments were performed on as-deposited and annealed ALD alumina films. The films were characterized and chemical analysis was carried out for the basic and acidic etchants used in the etching experiments. Crystallization of as-deposited amorphous alumina into gamma-Al2O3 transition phase during annealing significantly increased the chemical stability of ALD alumina. Annealing at the temperature of 1000 C for 1 hour resulted in an improved crystallinity of gamma-Al2O3 and in an excellent chemical stability. According to the characterizations and chemical analysis such high stability ALD alumina films could potentially be used in SOI manufacturing as the amount of contamination would be diminishing in wafer cleaning solutions.
Chemically Stable Atomic-Layer-Deposited Al2O3 Films for Processability
(2017-07-31) Broas, Mikael; Kanninen, Olli; Vuorinen, Vesa; Tilli, Markku; Paulasto-Kröckel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Atomic-layer-deposited alumina (ALD Al2O3) can be utilized for passivation, structural, and functional purposes in electronics. In all cases, the deposited film is usually expected to maintain chemical stability over the lifetime of the device or during processing. However, as-deposited ALD Al2O3 is typically amorphous with poor resistance to chemical attack by aggressive solutions employed in electronics manufacturing. Therefore, such films may not be suitable for further processing as solvent treatments could weaken the protective barrier properties of the film or dissolved material could contaminate the solvent baths, which can cause cross-contamination of a production line used to manufacture different products. On the contrary, heat-treated, crystalline ALD Al2O3 has shown resistance to deterioration in solutions, such as standard clean (SC) 1 and 2. In this study, ALD Al2O3 was deposited from four different precursor combinations and subsequently annealed either at 600, 800, or 1000 °C for 1 h. Crystalline Al2O3 was achieved after the 800 and 1000 °C heat treatments. The crystalline films showed apparent stability in SC-1 and HF solutions. However, ellipsometry and electron microscopy showed that a prolonged exposure (60 min) to SC-1 and HF had induced a decrease in the refractive index and nanocracks in the films annealed at 800 °C. The degradation mechanism of the unstable crystalline film and the microstructure of the film, fully stable in SC-1 and with minor reaction with HF, were studied with transmission electron microscopy. Although both crystallized films had the same alumina transition phase, the film annealed at 800 °C in N2, with a less developed microstructure such as embedded amorphous regions and an uneven interfacial reaction layer, deteriorates at the amorphous regions and at the substrate-film interface. On the contrary, the stable film annealed at 1000 °C in N2 had considerably less embedded amorphous regions and a uniform Al-O-Si interfacial layer.
Corrosion protection of steel with multilayer coatings: Improving the sealing properties of physical vapor deposition CrN coatings with Al2O3/ TiO2 atomic layer deposition nanolaminates
(2017-04) Leppäniemi, Jarmo; Sippola, Perttu; Broas, Mikael; Aromaa, Jari; Lipsanen, Harri; Koskinen, Jari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Atomic Layer Deposition (ALD) of Al2O3/TiO2 nanolaminatewas applied to improve the sealing properties of CrN coating deposited with Physical Vapor Deposition (PVD) on high speed steel (HSS). The corrosion protection propertieswere explored with Linear Sweep Voltammetry and visual estimation. Nearly two orders of magnitude decrease in corrosion current density was obtained by applying plasma pre-treatment prior to ALD coating. Sealing of CrN pinholes was shown with Focused Ion Beam/Scanning Electron Microscope technique. The effect of the ALD deposition parameters to adhesion of the ALD coatings was investigated with Rockwell indentation and microscope analysis. Thickness and refractive index of the ALD coatings were measured with ellipsometry, and density and roughness of the ALD coatingswere investigatedwith X-Ray Reflectivity measurements. Neutral Salt Spray testing was used to investigate the corrosion resistance of PVD/ALD nanolaminates on HSS dental curettes.
Evaluation of Characterization Methods for Cu-Sn Micro-Connects
(2016-02-15) Mäntyoja, Nikolai
Sähkötekniikan korkeakoulu | Master's thesis
The microelectronics industry constantly aspires to shrink the device features. At the package level, this implies a decrease in the interconnect size leading to small volume interconnections that are commonly called micro-connects. Smaller material volumes may give rise to new reliability challenges, such as open circuits, due to Kirkendall voiding. The root cause(s) for Kirkendall voiding is not yet clear and the methods for characterization are still varied. This thesis reviews techniques to characterize the microstructure and impurities in Cu-Sn micro-connects. The evaluated techniques are Auger Electron Spectroscopy (AES), Electron Energy Loss Spectroscopy (EELS), Energy-Dispersive X-Ray Spectroscopy (EDX), X-Ray Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS), Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (EELS), Transmission Electron Microscopy (TEM), Focused Ion Beam (FIB), and Scanning Acoustic Microscopy (SAM). From the reviewed techniques, EDX, FIB, SAM, and TEM are used in the experimental section. For the first time, impurities are measured directly inside Kirkendall voids. It was discovered that the Kirkendall voids in annealed Cu-Sn samples contained a significant amount of chlorine and oxygen. The ASTM grain size counting method was applied to FIB-polished samples. It was observed that the grain size did not increase by annealing at 150 ◦C. Furthermore, for the first time, GHz-SAM was used to characterize Kirkendall voids. The technique is promising but it is still affected by the low lateral resolution.
Galvanic corrosion of structural non-stoichiometric silicon nitride thin films and its implications on reliability of microelectromechanical devices
(2015) Broas, Mikael; Liu, Xuwen; Ge, Yanling; Mattila, Toni Tuomas; Paulasto-Kröckel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
In-situ annealing characterization of atomic-layer-deposited Al2O3 in N2 , H2 and vacuum atmospheres
(2019-07-31) Broas, Mikael; Lemettinen, Jori; Sajavaara, Timo; Tilli, Markku; Vuorinen, Vesa; Suihkonen, Sami; Paulasto-Kröckel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Atomic-layer-deposited Al 2 O 3 films can be used for passivation, protective, and functional purposes in electronic devices. However, as-deposited, amorphous alumina is susceptible to chemical attack and corrosion during manufacturing and field-use. On the contrary, crystalline Al 2 O 3 is resistant against aggressive chemical treatments and corrosion. Here, high-temperature treatments in N 2 , H 2 , and vacuum were used to crystallize alumina which exhibited different crystalline phases. The annealing process was monitored continuously in situ by measuring the film temperature and surface reflectance to understand the crystallization kinetics. Ex-situ x-ray diffraction, electron microscopy, and composition analysis were used to probe the structure of the crystallized films and explain the formation of different alumina phases. This study provides a set of boundary conditions, in terms of temperature and atmosphere, for crystallizing chemically stable atomic-layer-deposited alumina for applications requiring a film thickness in the range of tens of nanometers without defects such as cracks.
MOCVD Al(Ga)N Insulator for Alternative Silicon-On-Insulator Structure
(2020-09-15) Ross, Glenn; Luntinen, Ville; Broas, Mikael; Suihkonen, Sami; Tuomi, Turkka; Lankinen, Aapo; Danilewsky, Andreas; Tilli, Markku; Paulasto-Kröckel, Mervi
A4 Artikkeli konferenssijulkaisussa
Due to the functional limitations of SiO2 for SOI applications, alternative dielectric materials have been investigated. Alternative SOI materials in this work include, AlN and AlGaN. The dielectrics were deposited using MOCVD, and with the aid of PECVD deposited SiO2, and the SiO2 was directly bonded to a handle Si wafer. Tensile tests were performed on the samples to examine the fracture behavior and maximum tensile stresses, with results being comparable to a traditional SOI. Characterization was undertaken using TEM to understand the microstructural and interfacial properties of alternative SOI. High crystal quality Al(Ga)N was achieved on a Si(111) substrate that generally contained well defined chemical interfaces. Finally, synchrotron X-ray diffraction topography was used to understand the topographical strain profile of the device and handle wafers. Topography results showed different strain network properties between the device and handle wafer. This work has demonstrated preliminary feasibility of using alternative dielectrics for SOI applications.
Embrittlement of Polysilicon Thin Films Under a Corrosive Atmosphere
(2013-11-18) Broas, Mikael
Sähkötekniikan korkeakoulu | Master's thesis
Piipohjaisten MEMS-komponenttien vauriomekanismien tutkimusmenetelmiä
(2011) Broas, Mikael
Sähkötekniikan korkeakoulu | Bachelor's thesis
Quality, Microstructural Refinement and Stability of Atomic-layer-deposited Aluminum Nitride and Aluminum Oxide Films
(2018) Broas, Mikael
School of Electrical Engineering | Doctoral dissertation (article-based)
High-quality, stable ALD films are required in microelectronics when the films are exposed to further processing during device manufacturing, or if the films are exposed to a demanding environment. For example, front-end-of-line processing exposes the deposited materials to high temperatures and aggressive chemicals during process steps such as dopant activation and wafer cleaning. Furthermore, a protective film against humidity and corrosion may need to maintain its structural integrity for the lifetime of the device which can be several years. Therefore, engineering the film quality and understanding the effects of high-temperature processing on thin films are required for the successful integration of the films to a semiconductor device. The goal of this thesis was to study the quality, microstructural refinement, and the stability of ALD AlN and Al2O3 films. The results were divided to the process development of ALD AlN and Al2O3 films, the examination of their microstructural development due to high-temperature thermal treatments, and the resulting stability of the ALD films. Film stability was understood to encompass thermal stability (e.g. oxidation) and chemical stability (ability to resist dissolution and corrosion). Film quality comprised of attributes such as the amount of impurities, stoichiometry, and crystallinity which were characterized for the as-deposited films and after the high-temperature treatments. The emphasis on ALD AlN was in process development. Trimethylaluminum (TMA) -based AlN was amorphous and contained a high amount of hydrogen when deposited at 200 °C. The hydrogen outgassed during high-temperature treatments and the AlN films began to oxidize at and above 800 °C. AlCl3-based AlN films, processed closer to 500 °C, had less impurities and a polycrystalline microstructure as opposed to the TMA-based films deposited at 200 °C. The AlN film residual stress was also tunable in the plasma-enhanced AlCl3 process by adjusting the plasma time of the nitrogen precursor. ALD AlN studied in this thesis and the literature review show promise of the film quality continuously improving. The main challenges are in improving the crystalline quality and minimizing the amount of impurities, such as hydrogen, in the AlN films. The focus on ALD Al2O3 was in understanding the effects of the high-temperature treatments. As-deposited ALD Al2O3 was amorphous and dissolved into wet chemical cleaning solutions. Heat treatments at and above 800 °C crystallized the films. However, high vacuum annealing caused blistering of the alumina films, whereas atmospheres with hydrogen and nitrogen produced crystalline films without blisters. The fully-crystallized alumina films were stable in SC-1 and HF cleaning solutions. The crystallized alumina films are demonstrated to be suitable for technologies such as silicon on insulator. Furthermore, crystallized ALD alumina could be utilized as a protective layer in a variety of applications that withstand the crystallization temperature.
Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films
(2016-07-01) Broas, Mikael; Sippola, Perttu; Sajavaara, Timo; Vuorinen, Vesa; Pyymaki Perros, Alexander; Lipsanen, Harri; Paulasto-Kröckel, Mervi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Plasma-enhanced atomic layer deposition was utilized to grow aluminum nitride (AlN) films on Si from trimethylaluminum and N2:H2 plasma at 200 °C. Thermal treatments were then applied on the films which caused changes in their chemical composition and nanostructure. These changes were observed to manifest in the refractive indices and densities of the films. The AlN films were identified to contain light element impurities, namely, H, C, and excess N due to nonideal precursor reactions. Oxygen contamination was also identified in the films. Many of the embedded impurities became volatile in the elevated annealing temperatures. Most notably, high amounts of H were observed to desorb from the AlN films. Furthermore, dinitrogen triple bonds were identified with infrared spectroscopy in the films. The triple bonds broke after annealing at 1000 °C for 1 h which likely caused enhanced hydrolysis of the films. The nanostructure of the films was identified to be amorphous in the as-deposited state and to become nanocrystalline after 1 h of annealing at 1000 °C.