Fredric Ericson

Micromechanical fracture strength of silicon

In order to test the statistical influence of some process and micromachining parameters on the fracture strength of silicon microelements, arrays of identical microsized cantilever beams were bulk micromachined in single‐crystalline silicon wafers. The beams were exposed to various surface treatments (diamond polishing with different grades, oxidization, stripping of oxide) in different combinations. The influence on fracture strength was investigated by bending the beams to fracture in a micromanipulator mounted in situ in a scanning electron microscope while registering force‐versus‐deflection curves. Average fracture strengths, standard deviations, Weibull moduli, crack‐initiating flaw sizes, and in some cases elastic moduli were evaluated. Diamond polishing was found to decrease the fracture strength drastically, but polishing followed by oxidization not only restored the original strength, but actually increased it, due to crack healing. Polishing, oxidization, and subsequent stripping of oxide resu...

Mechanical characterization of thick polysilicon films: Young's modulus and fracture strength evaluated with microstructures

Youngs modulus and the fracture strength of thick polysilicon films were evaluated with surface micromachined test structures. The polysilicon films were deposited in an epitaxial reactor and were ...

In situ tensile strength measurement and Weibull analysis of thick film and thin film micromachined polysilicon structures

Abstract A method is introduced in which tensile tests can be performed in situ on micromachined structures. The testing equipment consists of a testing unit mounted on a micromanipulator in a scanning electron microscope. The fracture loads of micromachined beam structures made from thick and thin film polysilicon were measured, and the fracture strengths were then calculated via measurements of the fracture surface areas. Characterization of the film materials was also performed with transmission electron microscopy, atomic force microscopy and scanning electron microscopy to locate the critical defects in the materials. The statistical scatter of the fracture strength values was evaluated using Weibull statistics, which yielded the mean fracture strength and the Weibull modulus—a measure of the amount of scattering. In this study, for the first time, Weibull theory was also applied to a real micromechanical structure, i.e. standard test results were transformed into expected strength limits of a more complex structure.

Influence of surface coatings on elasticity, residual stresses, and fracture properties of silicon microelements

Microscale silicon cantilever beams of (100)〈100〉 and (100)〈110〉 orientations were magnetron sputtered with submicron layers of Al, Ti, or TiN, or thermally coated with SiO2. Theoretical expressions for the elastic deflection induced by residual stresses were derived, and utilized to deduce such stresses from observed deflections. A theory for the elastic stress distribution in coated beams exposed to external bending moments was utilized to deduce maximum stress levels at fracture in the coatings and in the substrates. The fracture tests were performed in situ in a scanning electron microscope by means of specially designed equipment. For uncoated beams, the average fracture stress was 6 GPa (maximum 13 GPa) for 〈100〉 beams, and 4 GPa (maximum 6 GPa) for 〈110〉 beams. Most coatings proved to have a strength‐reducing effect, particularly the brittle, thin coatings of TiN, but also the Ti coatings (which displayed brittle fracture behavior). Ductile, thin coatings of Al were either neutral, or induced a sma...

Morphological and phase stability of nickel–germanosilicide on Si1−xGex under thermal stress

Continuous and uniform Ni(Si,Ge) layers are formed on polycrystalline Si and Si0.42Ge0.58 substrate films at 500 degreesC by rapid thermal processing. The germanosilicide is identified as NiSi0.42G ...

Hardness and fracture toughness of semiconducting materials studied by indentation and erosion techniques

Abstract In recent years, the growing field of semiconductor micromechanics has created an increasing demand for strength data on semiconductors and for adequate tests and evaluations of their mechanical properties. In a recently published paper, the present authors have demonstrated that the solid particle erosion rate can be taken as a simple and highly reproducible statistical measure of the susceptibility of silicon and GaAs to contact damage in the micron range. In the present work the scope is broadened to include several new crystal orientations (and one new doping level), as well as three other materials: germanium, InP and InAs, for which the hardness and fracture toughness K Ic values are determined by means of the indentation technique. K Ic values are also derived from erosion data by means of a recently reported brittle fracture model, based on non-lateral spalling in single-crystal semiconductors. These values are compared with results obtained by the indentation technique and conventional test methods reported in the literature. Fracture surface energies are deduced from the experimental K Ic results. The materials tested are ranked with respect to elastic properties, microhardnesses, fracture toughnesses, and sensitivities to contact damages in general. The influence of crystallographic orientation on room temperature microfracture properties is clearly established, but the corresponding influence on microhardness is found to be rather limited. The influence of doping on the room temperature mechanical properties is noticeable but small.

A transmission electron microscopy study of hillocks in thin aluminum films

Hillocks, small outgrowths on a film surface, form when compressional stresses in an aluminum film are relaxed at elevated temperature (≥90 °C), for instance during the phase of rising temperature in an annealing cycle. This paper reports a study of hillock formation in Al films of thicknesses in the interval 0.25–2.2 μm and which have been deposited by electron beam evaporation. Hillock sizes, shapes, number and formation temperatures were determined, the latter on a heating stage in situ in a scanning electron microscope. The internal structure of the hillocks was studied by cross‐sectional transmission electron microscopy technique. These studies provided strong support for the idea that hillocks are formed by migration of material along grain boundaries, presumably at triple junctions, up to the surface where it is deposited in a growing hillock. Initially, the hillocks are separated from the original film surface by a grain boundary‐like interface, but prolonged annealing will cause underlaying grain...

High-sensitivity surface micromachined structures for internal stress and stress gradient evaluation

The internal stress and stress gradient of thick () and thin () polysilicon films were evaluated with surface micromachined test structures. The structure that measured internal stress consisted of actuator beams rotating an indicator through an angle corresponding to the stress. The indicator deflection was measured in an SEM. Finite element analysis (FEA) was used both to optimize the design and to calibrate the structure. A folded beam design was used to minimize the total area the structure occupied so that it could be incorporated in the wafer layout of other surface micromachined details, and used for online process diagnostics. The indicator was provided with a Vernier scale to facilitate quick evaluation in an optimal microscope. The stress gradient was measured from the deflection of long () cantilever beams. The deflection was measured in an optical microscope and the output was calibrated with FEA calculations.

Evaluation of mechanical materials properties by means of surface micromachined structures

For all micromechanical devices, mechanical properties such as elasticity constants, internal stresses, fracture limits and, for ductile materials, yield limits and strain-hardening behaviour, are ...

Hydroxylapatite growth on single-crystal rutile substrates.

Titanium is widely used as an implant material. In addition to the bulk properties of titanium, the biological response is to a large degree controlled via the surface. The native amorphous titanium oxide that forms spontaneously on the surface gives a very good biological response. Lately it has been shown that crystalline titanium oxides (rutile and anatase) have in vitro bioactive properties. In addition to its potential for new materials development, this finding also opens up for the possibility of studying the mechanisms of bioactivity on materials with strictly controlled surfaces. In this paper the mechanisms behind the in vitro bioactivity are studied, using rutile single crystals. Three single-crystal rutile substrates: (100), (110), and (001), and a polycrystalline rutile substrate obtained by physical vapour deposition were soaked in a phosphate buffered saline solution for up to 4 weeks. The hydroxylapatite films that formed were analysed by X-ray diffraction, scanning electron microscopy, focused ion beam, and transmission electron microscopy. The hydroxylapatite grew faster on the (001) surface than on the other two. It was also found that on the (001) surface the direction of fast growth in hydroxylapatite was aligned parallel to the surface. This is in contrast to the (110) rutile surface where the fast growth of the hydroxylapatite crystal was directed outwards from the surface. The (100) face had poor adhesion at the interface. The orientations of the precipitated crystallites play a significant role in the faster coverage of the (001) rutile face. Based on the experimental results, a model for the hydroxylapatite growth process is given.