Development of manufacturable technologies for nanoelectronics and MEMS devices for advanced computing and sensing applications presents significant challenges. Modeling and simulation of the fabrication processes, extensively used by the microelectronics industry, offer significant advantage in meeting these challenges.
Existing technologies, while mature for microelectronics fabrication, need further development in order to meet reliability, repeatability and yield requirements. Mature fabrication technologies of nanoelectronic, photonic, and MEMS devices will be at the heart of the advanced computing and sensing needs of exploration systems. Assembly of novel nanomaterials based composites, critical to advanced systems, will also rely on such technologies for high yield production and processing of nanomaterials.
NASA Ames has an active modeling and simulation group with several years of experience in microelectronics and nanomaterials fabrication processes. The group has developed a suite of tools to simulate plasma and thermal CVD reactors spanning a range of length scales, from the reactor scale down to the feature scale. At the reactor scale, the models use continuum transport equations for plasma, gas flow, finite rate gas-phase chemistry and heat transfer. Figure 1. Evolution of a microscopic trench in silicon during a chlorine plasma etch.
Gas-surface chemistry is also modeled self-consistently at the reactor scale in order to simulate molecular adsorption chemistry resulting in surface modification due to growth or etching of micro and nano structures. A separate set of tools is also available to simulate the profile evolution of these nanostructures based on the molecular fluxes from the gas phase. The profile evolution codes currently use level set and phase field methods to track the motion of the interfaces between multiple phases due to catalyzed or uncatalyzed growth, and isotropic or anisotropic etching of the micro and nanostructures. These tools have been used extensively in a variety of applications, chief among them are plasma and thermal CVD for carbon nanotube growth, and fluorocarbon and chlorine etching of silicon based materials for microelectronics applications.
Scalable production and assembly of the building blocks of nanotechnology ( e.g. carbon nanotubes, semiconductor nanowires, nano-particles, etc.) present some of the biggest challenges in the development of nanoelectronic devices and nanomaterial based composites. The technologies traditionally employed in the manufacturing of integrated circuits at the micron to sub-micron scales are currently being extended to the nano scale.Figure 2. Reactor scale simulation of an inductively coupled etch tool. Plasma density is shown.
Some of these technologies such as chemical vapor deposition (CVD), plasma enhanced deposition, dry etching, atomic layer deposition, laser ablation etc. will remain critical to the assembly and processing of nanostructures. Leveraging these technologies to nano-scale precision places an unprecedented demand on process control, optimization, and scalability.
Similarly, in MEMS manufacturing, although only at the micron scale, the current technologies need further development in order to handle materials with different mechanical properties, custom designs, or complex three dimensional microstructures, and still simultaneously offer high yield, repeatability, and low cost. Figure 3. Variation of species densities in a plasma enhanced CVD of carbon nanotube.
Previous experience has shown that multi-scale modeling and simulation of these processes offers a significant advantage toward achieving these necessary goals in a cost effective manner.