Supercritical fluids for the fabrication of semiconductor devices: emerging or missed opportunities?

Next generation semiconductor devices and evolving opportunities in nanoelectronics present new challenges for fabrication technology. These include patterning and structure generation to define the smallest features, the deposition of metals, metal oxides, and other functional layers within challenging topographies, and development of the associated integration steps necessary to create working devices. Implementation of emergent technical solutions, however, is also subject to economic realities that require high volume process tools, reliability, and low cost per device layer. Changes in semiconductor process technology have to date largely been driven by the continued downscaling of device features to increase transistor density. Leading edge microprocessors are currently in production at the 45 nm device node. Device dimensions approaching 22 nm will be realized withinin the next several years. As manufacturing moves to smaller and smaller features, it is necessary to re-evaluate process technology and decide if evolutions in current methods are sufficient or if technical and/or economic considerations will mandate change. Semiconductor fabrication relies on a combination of gas (or vapor) based techniques and liquid phase processing. Each has its advantages. Gas phase techniques allow for dry processing, complete wetting of surfaces, and the absence of surface tension, which in turn allows facile transport of reagents into confined geometries. Vapor phase transport of reagents and processing aids, however, are subject to species volatility constraints. Liquid phase processes have the advantage of species transport in solution, but the presence of the liquid phase can give rise to contamination issues, sluggish mass transport, and difficulties such as pattern collapse for the smallest device features. The latter arises from surface tension and associated capillary forces. These limitations are especially relevant for processing and fabrication at the nanoscale.