Semiconductor micromachining

Nanotechnology involves the manipulation of matter on atomic and molecular scales. This technology combines nanosized materials in order to create entirely new products ranging from computers to micromachines and includes even the quantum level operation of materials. The structural control of materials on the nanometer scale can lead to the realization of new material characteristics that are totally different from those realized by conventional methods, and it is expected to result in technological innovations in a variety of materials including metals, semiconductors, ceramics, and organic materials. 

Mahajan, Deformation Behavior of Compound Semiconductors J. P. Hirth, Injection of Dislocations into Strained Multilayer Structures D. Kendall, C. B. Fleddermann, and K. J. Malloy, Critical Technologies for the Micromachining of Silicon... 

A micromachined CE device featuring a truly monolithically integrated detector has been recently reported by Webster et al. [79]. A semiconductor radiation detector was fabricated together with a separation channel on a silicon substrate in a 10-mask process. The preliminary results achieved with the detection of beta decay events of 32P-labeled DNA at 27 V/cm demonstrate the feasibility of the concept. 

Substrates The substrates in microelectronics are mainly Si wafers. For mobile applications, silicon-on-insulator (SOI) wafers increasingly replace bulk Si wafers and for very specific high-frequency applications, III-V compound semiconductors (e.g., GaAs) are used. The majority of substrates in microfabrication are Si wafers, but metal, glass, and ceramic substrates are also common. Particularly when using glass, quartz, and ceramic wafers in CMP processes, it has to be taken into account that they are brittle and easy to break. The situation is worse when the material is also under stress induced by deposited layers. For applications where the backside of the wafer has to be structured (e.g., in bulk micromachining), double-side polished substrates are employed. 

Zinc oxide (ZnO, wurtzite structure) eliminates oxygen on heating to form nonstoichio-metric colored phases, Zni+xO with x < 70 ppm. ZnO is almost transparent and is used as white pigment, polymer stabilizer, emollient in zinc ointments, creams and lotions, as well as in the production of Zu2Si04 for TV screens. A major application is in the rubber industry to lower the temperatures and to raise the rate of vulcanization. Furthermore, it is an n-type semiconductor (band gap 3.37 eV) and shows piezoelectric properties, making zinc oxide useful for microsensor devices and micromachined actuators. Other applications include gas sensors , solar cell windows and surface acoustic devices. ZnO has also been considered for spintronic application because of theoretical predictions of room-temperature ferromagnetism . 

G. Lorenz, R. Neul, Network-type modeling of micromachined sensor systems, Proc. Int. Conf. Modeling and Simulation of Microsystems, Semiconductors, Sensors and Actuators, MSM98, Computational Publications, Cambridge MA, USA, April 1998, 233-238. 

Electrical evaluation. Electrical process-control monitors that are included at critical steps in the manufacturing as a means of evaluating the process steps are an important component of surface micromachining. The diffusion profiles and semiconductor junctions, as well as the quality of the oxides and contacts, can all be... 

The convincing advantage of surface micromachining is its similarity to classical IC fabrication, which is limited to the wafer surface as well. Both fabrication techniques and structures are therefore similar and well understood. Only a few specific processes had to be developed to supplement the established standard semiconductor processing steps. 

The CVD method is very versatile and can work at low or atmospheric pressure and at relatively low temperatures. Amorphous, polycrystalline, epitaxial, and uniaxially oriented polycrystalline layers can be deposited with a high degree of purity, control, and economy. CVD is used extensively in the semiconductor industry and has played an important role in past transistor miniaturization by making it possible to deposit very thin films of silicon. CVD also constitutes the principal building technique in surface micromachining (see below). 

Szot J, Hornsey R, Ohnishi T, Minagawa S (1992) Focused ion beam micromachining for transmission electron microscopy specimen preparation of semiconductor laser diodes. J Vac Sci Technol B 10 575-... 

Zinc oxide, ZnO, is a p-type semiconductor and shows piezoelectric properties which make this material useful for microsensor devices and micromachined actuators [69, 70]. The Al-doped material is used as a transparent electrode [71]. Other applications of ZnO include gas sensors [72], solar cell windows [73] and surface acoustic devices [74]. The organometallic compounds diethylzinc, ZnEt2 [75-77], and dimethylzinc, ZnMe2 [78], are frequently used as precursors for the deposition of zinc oxide. However, these reagents are highly pyrophoric and tend to react prematurely in the presence of water or oxygen. If ZnEt2 is combined with an alcohol in the reaction chamber, stable intermediates, presumably zinc alkoxides and/or alcohol adducts, are formed in the vapor-phase [79]. These compounds are more stable than dialkyl zinc rea-... 

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