Digital Etching of InP by Intermittent Injection of Phosphorous Precursors in Ultra-high Vacuum

Abstract

Intermittent injections of phosphorous precursors, i.e. tris-dimethylaminophosphorus (TDMAP) and tertiarybutylphosphine (TBP), have been applied for the selective etching of InP (001) substrates in order to study surface adsorption/decomposition mechanism of phosphorous precursors on the InP surface in ultra-high vacuum. Digital etching, in which the etching depth is controlled by the number of injection cycles of etching gases and the etch rate is independent of the injection time and pressure of the etching gas in a self-limiting fashion, is achieved for both precursors. The etch rate is well described by a modified Langmuir-type equation. The TBP molecules stick seven times faster than the TDMAP molecules on the InP surface and both precursors prevent the decomposition of InP resulting from the phosphorus loss during an evacuation time of over 5 s. On S-doped substrate grown by a vapor pressure controlled Czochralski method, the activation energy of the digital etching with TBP significantly decreases to 7 kcal/mol. Therefore, excellent uniformity and controllability of the etch rate is expected. A specular etched surface is achieved and well controlled digital etching is realized at an etching temperature as low as 304°C.