UHV high temperature surface cleaning and piranha treatment for preserving atomically flat, hydrogen-passivated Si(100) surfaces

This paper demonstrates a significant advance in creating ultra-flat Si(100) surfaces suitable for low thermal budget device fabrication. This is achieved by a two-step pre-flash and protect (PFP) process that locks in an atomically flat surface that survives subsequent device processing steps. The first PFP step is a high-temperature flash in ultra-high vacuum (UHV) that creates an atomically flat surface. The second PFP step is a Piranha solution treatment that preserves the surface with a thin oxide shortly after removal from UHV. This oxide can then be easily removed with buffered oxide etchant (BOE) as needed during subsequent device fabrication. Following BOE, a surface with angstrom-level flatness is recovered, obviating the need for more aggressive thermal or chemical surface flattening processes. With this new process no aggressive chemical cleaning, such as RCA cleaning, is needed and no high-temperature surface cleaning or flattening is required for nanoscale device fabrication. This method offers promising opportunities for device fabrication and other applications that require clean and atomically flat Si(100) surfaces and low thermal budget device processing.