Abrupt reduction of the partial sputtering yield of copper in silicon due to beam induced oxidation and segregation

Boron‐doped silicon samples with a submonolayer coverage of copper were sputter profiled under O⁺2 bombardment at energies between 4 and 12 keV and impact angles of 2° and 32°. The profiles of Cu⁺ secondary ions showed a peak due to the buildup of oxygen in the sample. Under conditions of incomplete oxidation (at 32°) the Cu⁺ intensity beyond the peak decreased exponentially with a decay length of about 39 nm (8 keV O⁺2). By contrast, beam induced SiO2 formation (at 2°) resulted in a rather abrupt decrease of the Cu⁺ intensity (factor of 10 within a sputtered depth of 1.3–3 nm depending on the beam energy). The effect is attributed to very rapid diffusion of copper away from the surface oxide (beam induced segregation).