Eero Haimi

Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties

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 (Al 2O3) 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%). Al 2O3 was grown from Me3 Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al 2O3/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.

On the reliability of nanoindentation hardness of Al2O3 films grown on Si-wafer by atomic layer deposition

The interest in applying thin films on Si-wafer substrate for microelectromechanical systems devices by using atomic layer deposition (ALD) has raised the demand on reliable mechanical property data of the films. This study aims to find a quick method for obtaining nanoindentation hardness of thin films on silicon with improved reliability. This is achieved by ensuring that the film hardness is determined under the condition that no plastic deformation occurs in the substrate. In the study, ALD Al2O3 films having thickness varying from 10 to 600 nm were deposited on a single-side polished silicon wafer at 300 °C. A sharp cube-corner indenter was used for the nanoindentation measurements. A thorough study on the Si-wafer reference revealed that at a specific contact depth of about 8 nm the wafer deformation in loading transferred from elastic to elastic–plastic state. Furthermore, the occurrence of this transition was associated with a sharp increase of the power-law exponent, m, when the unloading data we...

Oxygen in Silicon

Oxygen and oxygen related phenomenon affects Silicon in many ways, which can be either beneficial or harmful. Oxygen is incorporated to silicon, because molten silicon dissolves oxygen from silica crucibles used in the growth process. The basic aspects of oxygen-related phenomenon in silicon such as oxygen in silicon solid solution, formation of small oxygen aggregates, oxygen precipitation, precipitation induced defects as well as behavior of oxygen in basic heat treatment procedures are briefly explained. Diffusivity of oxygen is dominated by the process of jumping from one interstitial site to another. The stage of oxygen aggregation including the formation of small oxygen aggregates are viewed successfully in this lesson. Precipitation of oxygen in silicon which is a diffusion control in solid state phase transformation is described effectively. Interaction of oxygen with the other constituents in association with oxygen has also been observed experimentally. Oxide precipitates in silicon are strongly strained as the volume expansion connected with oxide formation. Precipitate-induced defects are attempted effectively in this chapter. The effects of low and high temperature and heat treatment procedures that silicon wafers experience during MEMS device manufacturing is also explained.

Processing and Characterization of Porous Silica-Ag-Nanoparticle Composites Produced by Pulsed Electric Current Sintering

This paper studies influence of the process temperature and time on the properties of the compacts made of Ag-SiO2 powder by the pulsed electric current sintering (PECS). Silica particles doped with Ag nanoparticles were prepared by modified Stöber method, and calcinated at 573 K in air resulting in average silica particle size of ~1.1 µm and agglomerate size up to 32 µm. There was about 7 wt.% of silver in the structure and the diameter of the silver particles on the silica carriers was 30 ±7 nm on average. The composite powder was sintered into porous compacts by PECS at 873, 973, 1073, or 1173 K for 10, 20, or 30 min under pressure of 50 MPa. Samples were characterized by SEM, XRD, UV-vis-spectrometer, and laser diffraction. During PECS compaction grain growth of silver particles was observed and the measured average size of Ag in 873 K and in 1173 K samples were 65 nm and 170 nm, respectively. The porosity of the materials did not show remarkable change, as the relative density ranged from 76 to 79 %. Thus, it is possible to produce porous silica based materials with controlled Ag-nanoparticle size by PECS. These materials may be optimized for, e.g., different kinds of antibacterial filters.

Tribological properties of thin films made by atomic layer deposition sliding against silicon

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...