Focused ion beam (FIB) systems using gallium liquid metal ion sources can remove material with a lateral resolution below 50 nm and can produce metal deposition at a similar resolution with ion beam-enhanced chemical vapour deposition. These capabilities have resulted in many valuable applications for the microelectronics industry. Circuit modifications are possible because existing connections can be severed and reconnected to different locations. Testing of circuitry can be enhanced by isolation of specific circuits, removal of overlayers and by creation of probe pads where desired. Grain sizes can be determined from secondary electron images by the delineation of individual grains due to orientation-dependent channeling of the ion beam. Secondary ion mass spectrometry analyses of small areas can provide ion images, elemental identification of small areas and endpoint detection with depth profiles. Scanning electron microscopy and transmission electron microscopy sections are prepared routinely using the FIB. These FIB-prepared sections are notable because specific features, such as defects, can be exposed and a range of materials including silicon, indium phosphide, gallium arsenide and even metal layers can be cut without distortion. Transmission electron micrographs of superior quality have been obtained with a large area of very uniform thickness that permits identification of features such as areas under stress.

Changes in secondary ion yields of matrix and dopant species have been correlated with changes in surface topography during O+2 bombardment of Si and GaAs. In Si, profiles were measured in (100) wafers at 6- and 8-keV impact energy. At 6 keV, a yield increase of about 70% occurred for Si+ over a depth range of 2.5 to 3.5 μm, with changes in other species ranging from a decrease of ∼20% for Si+3 to an increase of more than 25% for O+. The development of a rippled surface topography was observed in scanning electron micrographs over the same depth range. Similar effects occurred over a 3–5 μm depth range for 8-keV ions, and in (111) silicon at a depth of 3 to 4 μm for 6-keV ions. No differences were noted between p- and n-type silicon, or implanted and unimplanted silicon. In GaAs, profiles were measured in (100) wafers at 2.5-, 5.5-, and 8-keV impact energies. At 8 keV, a yield increase of about 70% was found for GaO+ in the range 0.6–1.0 μm, with smaller changes for other matrix species. At 5.5 keV, similar effects were observed, but over a depth interval of 0.3 to 0.7 μm. No yield changes were detected at 2.5-keV impact energy. The yield changes at the higher energies were again correlated with the onset of changes in topography. No change in ion yield or surface topography was noted for Cs+ bombardment of Si or GaAs. The topography and ion yield changes are affected by the angle of incidence and, for Si, the oxygen coverage. The results show that the practice of normalizing secondary ion mass spectrometry dopant profiles to a matrix signal must be modified for situations where matrix yield changes occur.

Experiments were carried out to study the effects of fluorine additions to a dry oxidation ambient. Two distinct classes of fluorine sources, liquid dichlorofluoroethane (C2H3C12F), and gaseous nitrogen trifluoride (NF3), were investigated. We experimentally found that small fluorine additions (up to 0.11% by volume) caused large enhancements in oxidation kinetics. The oxidation kinetics data were analyzed by both the power of time and linear-parabolic models as a function of fluorine addition, temperature, and the type of fluorine additive. Thermodynamic calculations for these classes of fluorine sources were extensively carried out to determine the active oxidizing species that cause the significant enhancement of the oxidation. According to these calculations, the enhancement of oxidation could be explained by the presence of hydrogen fluoride (HF) and atomic fluorine (F). Secondary ion mass spectrometry (SIMS) was performed to study the incorporation behavior of fluorine into the oxide layer. C2H3C12F oxides displayed peaks at the silicon-oxide interface, while NF3 oxides exhibited flat fluorine profiles.

Boron contamination has been detected by secondary ion mass spectrometry at almost every surface and interface in silicon microelectronics structures. Areal densities for boron are typically 102–1013 atoms/cm2 and can cause counterdoping if the boron is distributed by an anneal into a lightly doped n-type region. Boron was quantified by encapsulating the surface of the layer of interest with an identical layer and thereby retaining matrix homogeneity across the interface where the original surface is located. The origin of boron was shown to be airborne contamination. Boron in the atmosphere and the borosilicate glass in the high efficiency particulate air filters used in clean room construction have been identified as contamination sources. Accumulation of boron on a polysilicon surface follows a relationship similar to that for oxide growth. Processing with hydrogen, buffered HF cleaning of the surface, or growth of a removable SiO2 layer will reduce or eliminate boron from the silicon surface.