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We investigated STM-induced chlorine desorption and lithographic patterning of Cl-terminated Si(100)-(2×1) surfaces at sample temperatures from 4 K to 600 K. STM lithography has previously focused on hydrogen-based chemistry for donor device fabrication. Here, to develop halogen-based chemistries for fabricating acceptor-based devices, we substituted the hydrogen resist with chlorine. Lithographic patterning was explored using both field emission patterning to desorb chlorine from large areas as well as atomic precision patterning to desorb chlorine along one to two dimer rows at a time. We varied the experimental parameters for lithographic patterning and found a positive correlation between pattern line widths and both sample bias voltage and total electron dose. Finally, the use of chlorine, bromine, and iodine as lithographic resists to broaden the range of available chemistries for future device fabrication utilizing halogen-based dopant precursors is discussed. arXiv:1808.05690v2 [cond-mat.mes-hall]

The reactivity of liquid hydrazine (N 2 H 4 ) with respect to H-, Cl-, and Br-terminated Si(100) surfaces was investigated to uncover the principles of nitrogen incorporation into the interface. This process has important implications in a wide variety of applications, including semiconductor surface passivation and functionalization, nitride growth, and many others. The use of hydrazine as a precursor allows for reactions that exclude carbon and oxygen, the primary sources of contamination in processing. In this work, the reactivity of N 2 H 4 with H-and Cl-terminated surfaces prepared by traditional solvent-based methods and with a Brterminated Si(100) prepared in ultrahigh vacuum was compared. The reactions were studied with X-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy, and the observations were supported by computational investigations. The H-terminated surface led to the highest level of nitrogen incorporation; however, the process proceeds with increasing surface roughness, suggesting possible etching or replacement reactions. In the case of Cl-terminated (predominantly dichloride) and Br-terminated (monobromide) surfaces, the amount of nitrogen incorporation on both surfaces after the reaction with hydrazine was very similar despite the differences in preparation, initial structure, and chemical composition. Density functional theory was used to propose the possible surface structures and to analyze surface reactivity.

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.

Spontaneous desorption of Cl, Br, and I from n-and p-type Si͑100͒-͑2 ϫ 1͒ was studied with scanning tunneling microscopy at temperatures of 620-800 K where conventional thermal bond breaking should be negligible. The activation energies and prefactors determined from Arrhenius plots indicate a novel reaction pathway that is initiated by the capture of electrons which have been excited by phonon processes into Si-halogen antibonding states. This configuration is on a repulsive potential energy surface, and it is sufficiently long lived that desorption can occur, constituting phonon-activated electron-stimulated desorption. Surprisingly, the Arrhenius plots for differently doped samples crossed and, above a critical temperature, the reaction with the largest activation energy had the highest rate. This is explained by large entropy changes associated with the multiphonon nature of the electronic excitation. For Cl desorption from p-type Si, these entropy changes amounted to 34k B . They were 19k B , 13k B , and 8k B for Br desorption from p-type, lightly doped n-type, and heavily doped n-type Si, respectively. The desorption rates for I were nearly three orders of magnitude larger than the rates observed for Cl and Br. Here, the Si-I antibonding states overlap the conduction-band minimum, so that conduction-band electrons with this energy can be captured by the Si-I antibonding states. Together, these results reveal that a complex relationship exists between phonons and electronic excitations during chemical reactions at surfaces.