Abstract
Atomic layer deposition (ALD) is one of the backbones for today's electronic device fabrication. A critical property of ALD is the layer-by-layer growth, which gives rise to the atomic-scale accuracy. However, the growth rate - or growth per cycle - can differ significantly depending on the type of system, molecules used, and several other experimental parameters. Typically, ALD growth rates are constant in subsequent ALD cycles, making ALD an outstanding deposition technique. However, contrary to this steady-state - when the ALD process can be entirely decoupled from the substrate on which the material is grown - the deposition's early stage does not appear to follow the same kinetics, chemistry, and growth rate. Instead, it is to a large extent determined by the surface composition of the substrate. Here, we present evidence of oxygen relocation from the substrate-based oxide, either the thermal or native oxide of InAs, to the overlayer of HfO2 in the initial ALD phase. This phenomenon enables control of the thickness of the initial ALD layer by controlling the surface conditions of the substrate prior to ALD. On the other hand, we observe a complete removal of the native oxide from InAs already during the first ALD half-cycle, even if the thickness of the oxide layer exceeds one monolayer, together with a self-limiting thickness of the ALD layer of a maximum of one monolayer of HfO2. These observations not only highlight several limitations of the widely used ligand exchange model, but they also give promise for a better control of the industrially important self-cleaning effect of III-V semiconductors, which is crucial for future generation high-speed MOS.
Highlights
The future development of semiconductor technology is intimately connected to the development of faster and smaller devices, with a reduced power consumption
We investigate eight InAs samples prepared with varying oxide thickness ranging from a few Å to a few nanometres by ambient pressure X-ray photoelectron spectroscopy (AP-XPS), a method which allows the real-time monitoring of the deposition process[8,21,22]
We find a linear correlation between the thickness of InAs oxide before deposition and the thickness of HfOx at the end of the first half cycle of Atomic layer deposition (ALD), self-limited though to a maximum of one monolayer of HfOx
Summary
The future development of semiconductor technology is intimately connected to the development of faster and smaller devices, with a reduced power consumption. The research efforts towards this goal are intensive, not least in relationship to the metal oxide semiconductor field-effect transistor (MOSFET). Substituting the silicon channel material with a IIIV semiconductor has often been suggested as another promising step towards faster MOSFET devices[2,5]. Among the III-V semiconductors, InAs plays a important role, since it has a narrow band gap compared to that of silicon and an electron mobility that is around 20 times higher than that of silicon[6]; these properties make InAs suitable for the a.Division of Synchrotron Radiation Research, Department of Physics, Lund University, 221 00 Lund, Sweden b.NanoLund Center for Nanoscience, Lund University, 221 00 Lund, Sweden c. MAX IV Laboratory, Lund University, 221 00 Lund, Sweden d.Department of Electrical and Information Technology, Lund University, 221 00
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