Broad Beam Ion Milling for Microstructure Characterization

Two techniques for dry etching of sol-gel lead zirconate titanate (PZT 52/48) thin films were investigated: reactive ion etching and argon ion milling. Etched profiles were characterized by scanning electron microscopy. For reactive ion etching, a parallel plate etcher was used with HC2ClF4, an environmentally safe etch gas, in a process described by other researchers. Etch rates were measured and compared as a function of electrode shield material (ardel, graphite, alumina) and RF input power (100 to 500 W). These etch rates varied from 10 to 100 nm/min. Reactive ion etched sidewall angles 12° off normal were consistently produced over a wide range of RF powers and etch times, but overetching was required to produce a clean sidewall. For argon ion milling, a 300 mA/500 V beam 40° off normal to the substrate operating in a 72 mPa argon pressure was used. These ion milling conditions produced an etch rate of 250 nm/min with a sidewall slope angle of about 70°. The ion milling etch rate for sol-gel PZT was significantly faster than rates reported for bulk PZT. The 500 nm thick PZT films used in this study were prepared by the sol-gel process that used methoxyethanol solvent, spin coating on t/Ti/SiO2 silicon substrates, and rapid thermal annealing for 30 s at 650 °C for crystallization of the perovskite phase.

A method for directly observing the ferroelectric domain structure by scanning electron microscopy after argon ion milling has been established. Its advantages are exemplified by exposing the domain structure in three widely used ferroelectric ceramics, BaTiO3, (Na,K)NbO3, and Pb(Ti,Zr)O3. Stable high‐resolution images revealing domains with widths <30 nm have been obtained. The domain contrast is caused by electron channeling and is strongly dependent on the sample tilt angle. Owing to a strain‐ and defect‐free surface generated by gentle ion milling, pronounced orientation contrast is observed.

Polishing and cross-sectioning of integrated circuits is standard practice in failure analysis. With most integrated circuit defects, all that is usually needed is mechanical polishing to the cross-sectioned plane of interest. The sample is then ready for examination in the scanning electron microscope (SEM). However, some defects are too small or too subtle to be seen without delineating them in some way. Chemical etching is useful in many situations but sometimes does not highlight the defect and may introduce artifacts. In this experiment, cross-sectioned chips were ion milled for a short period to highlight or uncover defects.After locating failing transistors, samples were cross-sectioned on diamond paper using the open block method (i.e., not encapsulated in epoxy). A special ion mill sample holder was designed to accommodate the polishing fixture. This holder is inserted into the ion mill. (This eliminates the need to transfer the chip from one fixture to another, avoiding damage or contamination.) Samples were milled in a Gatan ion mill for an initial period of two minutes at a 20 degree tilt. A current of ˙5 mA and voltage of 5 kV were used. Samples were positioned so that maximum milling occurred in the area of the failing transistors.

Conventional mechanical sample preparation is a difficult and uncontrolled process that does not allow targeting of a specific depth or layer. Because of the difficulties presented by mechanical sample preparation, there has been an emergence of beam-based techniques for device delayering applications. Cross-sectioning is another commonly used technique used in microelectronics industry investigations; when combined with delayering, one can gain complete knowledge about a device's faults. This paper presents a development in semiconductor device investigation using low energy, broad-beam argon ion milling. The results highlight that broad-beam Ar ion milling produces excellent surface quality, which allows high resolution scanning electron microscope observation and energy dispersive spectrometry analyses, even at low energy.

ABSTRACTThe nature of disorder produced by low energy Ar+ and I+ ions (and atoms) in the III–V compound semiconductors InP and InSb, and in the II–VI semiconductors CdTe, ZnS and ZnSe has been studied in detail by conventional and high resolution transmission electron microscopy. It is demonstrated that for Ar+ ion bombardment the disorder in the III–V compounds comprises segregated indium islands which accumulate on the machined surfaces, while for the II–VI compounds the disorder consists of dense arrays (∼1011 cm−2) of small dislocation loops near to each bombarded surface. When Ar+ ions or Ar atoms are used for thin specimen preparation by milling prior to electron microscopy, the disorder produced gives contrast which seriously obscures images and so complicates their interpretation. This problem concerning the presence of artifactual defects can be greatly reduced or even eliminated by the use of reactive I+ ion milling for the final thinning of specimens.

In this study, we present the detailed investigation of the influence of the etching medium (acidic or basic Piranha solutions) and the etching time on the morphology and surface relief of ultrafine grained (UFG) and coarse grained (CG) titanium. The surface relief and morphology have been studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and the spectral ellipsometry. The composition of the samples has been determined by X-ray fluorescence analysis (XRF) and X-ray Photoelectron Spectroscopy (XPS). Significant difference in the etching behavior of UFG and CG titanium has been found. UFG titanium exhibits higher etching activity independently of the etching medium. Formed structures possess higher homogeneity. The variation of the etching medium and time leads to micro-, nano-, or hierarchical micro/nanostructures on the surface. Significant difference has been found between surface composition for UFG titanium etched in basic and acidic Piranha solution. Based on the experimental data, the possible reasons and mechanisms are considered for the formation of nano- and microstructures. The prospects of etched UFG titanium as the material for implants are discussed.

Effect of surface treatment on photo-electric properties of CZT thick film for radiation detector

A method for preparing needle-shaped and platelike crystals for electron microscopical investigation was elaborated. Crystals of H-Nb2O5 were embedded in a synthetic resin and disks were cut off perpendicular to the desired direction of observation. The thickness of the sample was reduced by planar grinding and then by using a dimple grinder and furthermore by ion milling with argon ions. With the precision ion milling system small crystal areas were selected and subsequently irradiated. The TEM investigations showed that the desired crystallographic orientation was reached and that the crystal structure has been preserved. The contrast of highly resolved images was reduced by an amorphous surface layer which was not removable.

Redeposition-free patterns have been etched in 3000Å thick permalloy films using the technique of chemically assisted sputter-etching. This technique involves the simultaneous adsorption of a reactant gas from a molecular beam source and normally incident argon ion bombardment. Experimental conditions with Cl2 adsorption can be maintained to etch the permalloy at 80Å/min and to etch positive photoresist at 110Å/min. These etch rates are not significantly different from rates obtained with argon ion milling, even though the permalloy surface is known to incorporate Cl2. Re-deposited material observed with Cl2 chemically assisted sputtering has been shown to be water soluble, and can be completely removed from feature side-walls prior to stripping the resist. Linewidth measurements show that no feature broadening occurs on 2 micron line and space patterns, within the precision of the measurement (±0.2 micron).

Redeposition-free patterns have been etched in 3000 Å thick permalloy films using the technique of chemically assisted sputter etching. This technique involves the simultaneous adsorption of a reactant gas from a molecular beam source and normally incident argon ion bombardment. Experimental conditions with Cl2 adsorption can be maintained to etch the permalloy at 80 Å/min and to etch positive photoresist at 110 Å/min. These etch rates are not significantly different from rates obtained with argon ion milling, even though the permalloy surface is known to incorporate Cl2. Redeposited material observed with Cl2 chemically assisted sputtering has been shown to be water soluble, and can be completely removed from feature sidewalls prior to stripping the resist. Linewidth measurements show that no feature broadening occurs on 2 μ line and space patterns, within the precision of the measurement (±0.2 μ). Chemically assisted sputter etching with the adsorption of CO resulted in reduced etch rates and increased redeposition. Both of these effects are attributed to the formation of carbides on the alloy surface during the process.

The most common conventional preparation techniques for cross-sectional transmission electron microscope (TEM) samples are a combination of mechanical grinding, polishing, and ion milling. These techniques suffer from the fact that they are very time consuming and that it is extremely difficult to do site-specific cross-sections. Conventional ion-milling techniques for TEM specimen preparation are essentially site blind, even with the so-called precision ion polishing systems (PIPS). Thus, it is left to chance whether the specimen detail of interest is thin enough for TEM-imaging. Even if subsequent ion milling of TEM specimens is possible in extending the thin areas, it is a tedious and mostly uncontrolled procedure. Because continuous high-resolution control of the ion milling process is not possible, the specimen areas of interest may easily be destroyed.

Formation and occurrence of organic matter-hosted porosity in shales

An ultrafine grained (UFG) ferrite/cementite microstructure was produced by use of large strain warm deformation in two plain C-Mn steels. In order to overcome the characteristic restricted tensile ductility of this steel, an intercritical annealing was applied to obtain an UFG ferrite/martensite dual phase (DP) steel. Suitable intercritical annealing parameters have been worked out using dilatometry. Microstructure evolution during intercritical annealing has been investigated by means of scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The study revealed that increasing the Mn content from 0.87 to 1.63 mass% was highly beneficial for the formation of martensite. This effect is explained by the enrichment of Mn in cementite which is partly inherited by austenite. The final microstructure consists of martensite islands embedded in an ultrafine grained polygonal ferrite matrix. The average grain size is 1-2 μm. Small amounts of retained austenite (<1 μm) are finely dispersed. The grain size is hardly affected by the intercritical annealing, whereas the fraction of high-angle grain boundaries in the ferrite matrix is reduced. Tensile tests revealed that strain hardenability is drastically improved by the introduction of martensite as a second phase. The UFG-DP steel exhibits a good combination of high strength and uniform elongation and considerable strain hardenability.

Mass-separated broad beam ion implantation of 25keV N+ in titanium

A new dry etching technique called magnetron-plasma ion beam etching (MIBE) is described which allows for decoupling of the chemical etch component from the ionic (physical) component which cannot be achieved in other conventional plasma processing methods. In MIBE, a rf discharge at 10−4 Torr is sustained and confined by a magnetic field. Concurrently, a broad beam ion source is used to independently deliver an energetic physical flux of Ar+ ions with energies ranging from 400 to 1500 eV which passes through the confined plasma to the substrate with little interaction or deflection. It was observed that the MIBE etch rates of Si using SF6 as the etch gas were greater than the independent magnetically enhanced reactive ion etching (MIE) and the Ar+ ion milling rates combined. However, the structure profiles were observed to be directly related to the separately controllable etch components. Isotropic etching of silicon was obtained from the chemical MIE plasma but as the energy of the ionic flux was increased, physical ion milling characteristics were observed to dominate the etch profile.