Grzegorz Jóźwiak

Tunneling/shear force microscopy using piezoelectric tuning forks for characterization of topography and local electric surface properties

Characterization of novel nanoelectronic structures and materials requires advanced and high-resolution diagnostic methods. In this article new approach for high sensitivity measurements of electric surface properties using scanning probe microscopy is presented. In this procedure topography and tunneling current flowing between the metallic tip and the surface are observed simultaneously. In our design piezoelectric tuning fork equipped with metallic tip in shear force microscope is used. In our experiments we also applied an additional feedback loop to maintain constant tunneling current while scanning over electrical inhomogeneous surfaces. In this way crosstalk between topography and tunneling current measurements is reduced. The described method was tested on nanocrystalline diamond and gold thin films deposited on silicon substrates.

Regularization mechanism in blind tip reconstruction procedure

In quantitative investigations of mechanical and chemical surface parameters using atomic force microscopy (AFM) techniques the determination of the probe radius and shape is required. To the most favorable methods of the microprobe characterization belongs the blind tip reconstruction method (BTR). The BTR similar to many other inverse problems is sensitive to noise and needs the so-called regularization mechanism. In this article we describe and investigate two the most popular regularization schemes, which were proposed in Villarubia et al. (1997) [30] and Tian et al. (2008) [31]. We have shown that the procedure described in Tian et al. (2008) [31] enables very effective probe shape reconstruction if we know the statistics of noise present in the AFM system. The increase of effectiveness with relation to the procedure described in Villarubia (1997) [30] is so significant that makes it possible to reconstruct probes with much larger resolution. We have also noticed the fact, that probes reconstructed by means of the procedure presented in Tian et al. (2008) [31] have flat apexes for AFM images with low signal to noise ratio (SNR). We propose procedure, which can improve the probe apex reconstruction. It uses the AFM image to estimate the initial shape of the reconstructed probe. This shape may be further improved by the BTR algorithm. We have shown that it is possible only for the procedure described in Tian et al. (2008) [31].

Investigation of thermal effects in through-silicon vias using scanning thermal microscopy.

Results of quantitative investigations of copper through-silicon vias (TSVs) are presented. The experiments were performed using scanning thermal microscopy (SThM), enabling highly localized imaging of thermal contrast between the copper TSVs and the surrounding material. Both dc and ac active-mode SThM was used and differences between these variants are shown. SThM investigations of TSVs may provide information on copper quality in TSV, as well as may lead to quantitative investigation of thermal boundaries in micro- and nanoelectronic structures. A proposal for heat flow analysis in a TSV, which includes the influence of the boundary region between the TSV and the silicon substrate, is presented; estimation of contact resistance and boundary thermal conductance is also given.

Thermal mapping of a scanning thermal microscopy tip.

Scanning thermal microscopy (SThM) is a very promising technique for local investigation of temperature and thermal properties of nanostructures with great application potential in contemporary nanoelectronics and nanotechnology. In order to increase the localization of SThM measurements, the size of probes has recently substantially decreased, which results in novel types of SThM probes manufactured with the use of modern silicon microfabrication technology. Quantitative SThM measurements with these probes need methods, which enable to assess the quality of thermal contact between the probe and the investigated surface. In this paper we propose a tip thermal mapping (TThM) procedure, which is used to estimate experimentally the distribution of power dissipated by the tip of an SThM probe. We also show that the proposed power dissipation model explains the results of active-mode SThM measurements and that the TThM procedure is reversible for a given probe and sample.

Atomic force microscopy of partially polished and epi-ready c-plane GaN substrates obtained by an ammonothermal method

In this paper, the propagation of scratches on the surfaces of c-plane GaN substrates due to slicing and polishing is studied through atomic force microscopy (AFM). For epi-ready substrates, the AFM images confirm a flat surface with atomic step roughness, while for partially polished GaN substrates, many scratches are visible in the AFM images. A Fourier analysis of the AFM images shows that the scratches propagate more easily along the {m-plane} and {a-plane} directions on a c-plane GaN surface. Most of these scratches are generated by the mechanical slicing of GaN crystals and/or non-optimal polishing conditions. A proper chemomechanical polishing process is able to remove the damaged material and obtain a flat surface with atomic step roughness. This observation is evidence for the anisotropy of mechanical properties of GaN crystals in the microscale range.

Characterization of fatigued Al lines by means of SThM and XRD: Analysis using fast Fourier transform

Abstract Longitudinal performance and reliability of microelectronic structures is strongly influenced by the condition of interconnects. Degradation processes invoke changes, progressive in time, on the surface, in the body of interconnect layer, in the boundary between interconnect and the Si/SiO 2 substrate, and in the area of substrate near Al line. Geometrical scale of these changes may vary in wide range, reaching nanometers. The authors investigate the condition of Al path of a fatigued commercial electronic circuit (memory), using in-house developed scanning thermal microscope (SThM) and commercial high resolution X-ray diffractometer (XRD). Series of SThM images were obtained for varying temperature of Wollaston probe working in active mode. The images, after processing by 2-dimensional spatial FFT, reveal various ingredients of the surface and internal structure of the Al line. FFT power spectrum dispersion is proposed as a measure of the amount of information available from the scan image. This measure may be used to determine the most efficient temperature of Wollaston probe. The result is a preliminary analysis of feasibility of the SThM approach for characterization of degradation process. In general SThM shall be perceived as a new technique for reliability analysis.

Standard and self-sustained magnetron sputtering deposited Cu films investigated by means of AFM and XRD

The goal of conducted investigations was to study microstructure and surface morphology of copper thin films deposited during standard (with argon) and self-sustained (without argon presence) magnetron sputtering deposition processes. Different types of magnetron source powering were used: direct current (DC), medium frequency (MF), pulsed-DC. The investigated copper films were deposited by means of balanced magnetron sputtering source on Si (1 1 1) substrates. The results of investigations showed that the average size of the copper crystallites of all samples were equal to dozens of nanometre. However, the self-sustained sputtering deposition processes, in comparison to the standard ones, resulted in smoother film surface.

Carrier density distribution in silicon nanowires investigated by scanning thermal microscopy and Kelvin probe force microscopy

The use of scanning thermal microscopy (SThM) and Kelvin probe force microscopy (KPFM) to investigate silicon nanowires (SiNWs) is presented. SThM allows imaging of temperature distribution at the nanoscale, while KPFM images the potential distribution with AFM-related ultra-high spatial resolution. Both techniques are therefore suitable for imaging the resistance distribution. We show results of experimental examination of dual channel n-type SiNWs with channel width of 100 nm, while the channel was open and current was flowing through the SiNW. To investigate the carrier distribution in the SiNWs we performed SThM and KPFM scans. The SThM results showed non-symmetrical temperature distribution along the SiNWs with temperature maximum shifted towards the contact of higher potential. These results corresponded to those expressed by the distribution of potential gradient along the SiNWs, obtained using the KPFM method. Consequently, non-uniform distribution of resistance was shown, being a result of non-uniform carrier density distribution in the structure and showing the pinch-off effect. Last but not least, the results were also compared with results of finite-element method modeling.

Application of FFT transformation for correlation analysis of near field microscopy measurements

The near field microscopy has been a dynamically developing diagnostic method for the last two decades. The number of measurement modes and data it delivers, sometimes make it difficult for interpreting. Thereby one needs sophisticated methods of extraction to get some specific information from the obtained results. Increasing complexity of the instruments as well as a software allows to acquire several signals simultaneously and to process them in a specific way in order to receive a particular result. Two dimensional Fast Fourier Transformation (2D FFT) is one of the most important tools in the picture analysis in near field microscopy. Such tools as finding specific spatial frequencies or noise filtering are very efficient. In the article we present some results of different modes of AFM measurements, where additional signals were acquired during measurements and by performing 2D FFT with the comparison approach, specific results and information were obtained.

DLTS and PR Studies of Partially Relaxed InGaAs/GaAs Heterostructures Grown by MOVPE

The studies of electrical activity of deep electron traps and the optical response of partially-strain relaxed InxGa1-xAs layers (x=5.5%, 7.7% and 8.6%) grown by metalorganic vapourphase epitaxy (MOVPE) have been performed by means of deep-level transient spectroscopy (DLTS) and photoreflectance (PR). DLTS measurements revealed two electron traps. One of the trap has been attributed to electron states at α-type misfit dislocations. The other trap has been ascribed to the EL2 point defect. The PR spectra at room temperature were measured and analysed. By applying the results of theoretical calculations which include excitonic and strain effects, we were able to estimate the extent of strain relaxation and the values of residual strain in the partially relaxed epitaxial layers.