Silicon germanium (SiGe) has moved from being a research material to accounting for a small but significant percentage of manufactured semiconductor devices. This percentage is predicted to increase substantially as SiGe begins to be used in complementary metal oxide semiconductor (CMOS) technology in the future to substantially improve performance. It is the development of Si/SiGe heterostructures which has enabled band structure and strain engineering allowing Si/SiGe to be used in many different ways to improve conventional microelectronic device performance along with allowing new concepts to be explored. This paper presents a review of the material properties, growth techniques, band structure and the main electronic devices of the Si/SiGe heterostructure system. In particular, the important device technologies in mainstream microelectronics of the SiGe heterostructure bipolar transistor (HBT) and strained-Si CMOS will be reviewed before future device and optoelectronics concepts are explored.

https://iopscience.iop.org/article/10.1088/0268-1242/19/10/R02/pdf

Si/SiGe heterostructures: from material and physics to devices and circuits

Lithographic Imaging Techniques for the Formation of Nanoscopic Features

Latent nuclear tracks are damaged zones, created along the paths of rapidly moving ions in solids. They are stored indefinitely in many insulators and can be used to initiate a phase separation process by one of several procedures that remove, collect, or transform material along the latent track. The resulting two-step technique is based on separate inscription and development stages, similar to the lithographic techniques using visible light, uv, x rays, or electrons. In contrast to these other techniques, however, it is applicable even to mechanically very stable, chemically inert, radiation-resistant dielectric materials. The most common development procedure is track etching, which acts as a chemical "amplifier" that dissolves the damaged zone of the latent track preferentially, creating etch pits or channels that can be extremely fine. Etched track diameters start around 10 nm and increase linearly with the etching time. The most outstanding feature of the technique is that one single particle is sufficient to create a developable damage. This unique combination of recording and revealing properties makes possible a single-particle structuring tool with a very wide array of applications. With the advent of high-energy, heavy-ion accelerators, with ion ranges between micrometers and centimeters, large-scale application of the technique to the imprinting of structure onto solids has become possible. At present, most frequently random track arrays are employed to induce global property changes of the solid volume or surface. In the future, scanning ion microbeam technology will make possible local generation of oriented track structures with high precision. This "ultimate" microtool should provide the versatility of a computer-controlled mechanical lathe. This review describes the processes involved in track generation. It outlines applications that are on the verge of being commercialized at present and considers future possibilities.

Production and use of nuclear tracks: imprinting structure on solids

Silver has useful surface-plasmon-resonance properties for many potential applications. However, chemical activity in silver nanoparticles exposed to laboratory air can make interpretation of optical scattering and extinction spectra problematic. We have measured the shift of the plasmon polariton wavelength of arrays of silver nanoparticles with increasing exposure to ambient laboratory air. The resonance peak wavelength shifts 65 nm in 36 h (1.8 nm/h). We show by scanning Auger spectroscopy that the shift is due to contamination from sulfur, most likely chemisorbed on the surface. The rate of corrosion product growth on the nanoparticles is estimated to be 3 nm per day, 7.5 times higher than that of bulk Ag under the same conditions.

Rapid tarnishing of silver nanoparticles in ambient laboratory air

Publisher Summary This chapter provides an overview of the new techniques for fabrication at a size scale below 100 nm. A number of nanometer-scale devices and scientific studies have become possible with these techniques, and research in this field has seen a number of recent successes. The chapter focuses on the limits and applications of the nanometer-scale fabrication techniques, not their practicality for current device production. The chapter presents the three-dimensional techniques that seem to permit fabrication of structures smaller than 10 nm. However, there are a variety of effects that limit their resolution. The most obvious is penumbra because of limited collimation of the ion beam or evaporant flux. This effect can be eliminated at the cost of reduced flux by simply using apertures or moving the source further from the sample. The chapter also describes the utilization of the third dimension and new three-dimensional lithographic approaches. Such approaches are of clear advantage for achieving high-aspect-ratio patterns, high resolution, and good line width control over a large field of view. When three-dimensional approaches are combined with other self-aligning or self-limiting processes, very powerful device micro-fabrication approaches can be developed.

Chapter 4 - Nanometer-Scale Fabrication Techniques

Ion beams have increased usefulness for high‐resolution microstructure fabrication if they are patterned to small dimensions before they strike a target. First, results are presented of maskless micromachining, doping, and resist exposure with a scanning focused gallium ion beam of sub‐1000‐A diameter. Secondly, an ion‐beam‐transmission mask is described, and results are presented showing 1X replicated mask patterns with 0.6‐μm features that were exposed in PMMA resist by irradiating the mask with a conventional size 150‐kV proton beam. The potentials of ion‐beam lithography using masks and focused ion beams are discussed.

R. D. Olney

Papers

High-resolution, ion-beam processes for microstructure fabrication