Etch Rate Retardation of Ga + -Ion Beam-Irradiated Silicon

Surface chemistry during wet chemical etching in alkaline KOH solution and dry etching in <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub><mml:mo>∕</mml:mo><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>SF6∕O2 plasma of high-dose <mml:math display="inline"><mml:msup><mml:mi mathvariant="normal">Ga</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math>Ga+ -implanted Si has been investigated by means of secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). During wet chemical etching in a <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">K</mml:mi><mml:mi mathvariant="normal">O</mml:mi><mml:mi mathvariant="normal">H</mml:mi><mml:mo>∕</mml:mo><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>KOH∕H2O solution a thin layer of <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math>GaOx of <mml:math display="inline"><mml:mrow><mml:mo><</mml:mo><mml:mn>1</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>nm</mml:mi></mml:mrow></mml:math><1nm thickness is formed, which has been investigated in more detail by angle-resolved XPS. In the case of dry reactive ion etching (RIE) the surface chemistry is quite different. In this case a more enhanced oxidation of Ga takes place due to the high reactivity of atomic oxygen from the <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:msub><mml:mi mathvariant="normal">F</mml:mi><mml:mrow><mml:mn>6</mml:mn></mml:mrow></mml:msub><mml:mo>∕</mml:mo><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>SF6∕O2 plasma. SIMS results show that during RIE a Ga-rich surface layer forms, and therefore an enhanced Ga oxidation takes place, leading to a thicker <mml:math display="inline"><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math>GaOx layer compared to wet chemical treatment. XPS depth profiling reveals a stoichiometry of almost completely oxidized Ga <mml:math display="inline"><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi mathvariant="normal">Ga</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:math>(Ga2O3) layer free from Si with a thickness of about <mml:math display="inline"><mml:mrow><mml:mn>5</mml:mn><mml:mo>–</mml:mo><mml:mn>10</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi>nm</mml:mi></mml:mrow></mml:math>5–10nm . The etch rate lowering in <mml:math display="inline"><mml:msup><mml:mi mathvariant="normal">Ga</mml:mi><mml:mo>+</mml:mo></mml:msup></mml:math>Ga+ as-implanted silicon is ascribed to the formation of gallium oxide at the Si surface during the etch processes.