RESUMEN
A scanning tunneling microscope (STM) was used to investigate tip-induced chlorine desorption and lithographic patterning of Cl-terminated Si(100)-(2 × 1) surfaces from 4 to 600 K in ultrahigh vacuum. Until now, STM lithography has exclusively focused on hydrogen-based chemistry for donor device fabrication. As the initial step in developing halogen-based chemistries for STM fabrication of acceptor-based devices, we substituted the hydrogen resist with chlorine. We found that chlorine can be selectively desorbed by the STM tip using both electron and hole injection. Observations show that targeted chlorine was not driven into the surface but desorbed completely as both individual and pairs of atoms. Chlorine depassivation lithography is demonstrated using both field-emission patterning to desorb chlorine from large areas with high efficiency (0.83(1)) and atomic-precision patterning to desorb one to two dimer rows at a time, resulting in 1.5 nm wide lines. Further, varying the experimental parameters for lithography revealed a positive correlation between pattern line widths and both positive sample bias voltage (1.7(2) nm/V) and total electron dose (0.15(2) nm/(mC/cm)), demonstrating that the energy and total number of electrons play a role in desorption from multiple sites.
RESUMEN
Atomic precision advanced manufacturing (APAM) leverages the highly reactive nature of Si dangling bonds relative to H- or Cl-passivated Si to selectively adsorb precursor molecules into lithographically defined areas with sub-nanometer resolution. Due to the high reactivity of dangling bonds, this process is confined to ultra-high vacuum (UHV) environments, which currently limits its commercialization and broad-based appeal. In this work, we explore the use of halogen adatoms to preserve APAM-derived lithographic patterns outside of UHV to enable facile transfer into real-world commercial processes. Specifically, we examine the stability of H-, Cl-, Br-, and I-passivated Si(100) in inert N2and ambient environments. Characterization with scanning tunneling microscopy and x-ray photoelectron spectroscopy (XPS) confirmed that each of the fully passivated surfaces were resistant to oxidation in 1 atm of N2for up to 44 h. Varying levels of surface degradation and contamination were observed upon exposure to the laboratory ambient environment. Characterization byex situXPS after ambient exposures ranging from 15 min to 8 h indicated the Br- and I-passivated Si surfaces were highly resistant to degradation, while Cl-passivated Si showed signs of oxidation within minutes of ambient exposure. As a proof-of-principle demonstration of pattern preservation, a H-passivated Si sample patterned and passivated with independent Cl, Br, I, and bare Si regions was shown to maintain its integrity in all but the bare Si region post-exposure to an N2environment. The successful demonstration of the preservation of APAM patterns outside of UHV environments opens new possibilities for transporting atomically-precise devices outside of UHV for integrating with non-UHV processes, such as other chemistries and commercial semiconductor device processes.
RESUMEN
We use scanning tunneling microscopy to show that Cl2 dosing of Cl-saturated Si(100)-(2x1) surfaces at elevated temperature leads to uptake beyond "saturation" and allows access to a new etching pathway. This process involves Cl insertion in Si-Si dimer bonds or backbonds, diffusion of the inserted Cl, and ultimately desorption of SiCl2. Investigations into the etch kinetics reveal that insertion occurs via a novel form of Cl2 dissociative chemisorption that is mediated by dangling bond sites. Upon dissociation, one Cl atom adsorbs at the dangling bond while the other can insert.