Process control microelectronics manufacturing

The fabrication of microelectronic and photonic components involves long sequences of batch chemical processes. The manufacture of advanced microstructures can involve more than 200 process steps and take from 2 to 6 weeks for completion. The ultimate measure of success is the performance of the final circuits. The devices are highly sensitive to process variations and are difficult, if not impossible, to repair if a particular chemical process step should fail. Furthermore, because of intense competition and rapidly evolving technology, the development time from layout to final product must be short. Therefore, process control of electronic materials processing holds considerable interest [30, 31]. The process control issues involve three levels ... 

The design and fabrication of some gas-phase micro reactors are oriented on those developed for chip manufacture in the framework of microelectronics, relying deeply on silicon micromachining. There are obvious arguments in favor the infrastructure exists at many sites world-wide, the processes are reliable, have excellent standards (e.g. regarding precision) and have proven mass-manufacturing capability. In addition, sensing and control elements as well as the connections for the whole data transfer (e.g. electric buses) can be made in this way. 

Chemical vapor deposition is a key process for thin film formation in the development and manufacture of microelectronic devices. It shares many kinetic and transport phenomena with heterogeneous catalysis, but CVD reactor design has not yet reached the level of sophistication used in analyzing heterogeneous catalytic reactors. With the exception of the tubular LPCVD reactor, conventional CVD reactors may be viewed as variations on the original horizontal reactor. These reactors have complex flow fields and it is consequently difficult to control and predict the effect of operating conditions on the film thickness and composition. 

The chemical, electrochemical, and photoelectrochemical etching processes by which microelectronic components are made are controlled by electrochemical potentials of surfaces in contact with electrolytes. They are therefore dependent on the specific crystal face exposed to the solution, on the doping levels, on the solution s redox potential, on the specific interfacial chemistry, on ion adsorption, and on transport to and from the interface. Better understanding of these processes will make it possible to manufacture more precisely defined microelectronic devices. It is important to realize that in dry (plasma) processes many of the controlling elements are identical to those in wet processes. 

The problem of impurity trapping in growing nanoparticles during their formation in a deposition from the gas phase is of interest for both different kinds of atmospheric processes and processes of modem technology (e.g., manufacture of nanoparticles). 11 i s well known that e ven a very small concentration of impurity molecules in a condensed phase can substantially change certain physicochemical properties of the product. The control of the concentration of impmity molecules in the substance is of paramount significance in the production of microelectronics elements. 

Chemical reactions initiated in gas discharges and plasmas, in particular in low-temperature, nonequilibrium plasmas, have become indispensable for the advancement of many key technologies in the past 10-15 years (see, e.g Becker et al., 1992 Garscadden, 1992). The plasma-assisted etching of microstructures and the deposition of high-quality thin films with well-defined properties have become crucial steps in the fabrication of microelectronic devices with typical feature sizes of less than 0.5 /rm. The manufacture of state-of-the-art microchips now involves hundreds of process steps, most of them serial, to yield circuits with millions of discrete elements and interconnections in an area of a single square centimeter (Garscadden, 1992). Each step is a physical-chemical interaction that must be controlled. More than one-third of the process steps rely on plasma... 

It is the manufacturing technology - exemplified by the micro-turbines discussed above - that is important to both microelectronics and micro-intensified processes, and those involved in the latter can learn much from the former. See, for example, Helvajian, 1999. The links between refrigeration cycles and electronics thermal control has also spawned some micro-refrigerators that can incorporate PI technology (see Section 11.2). 

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