SnO₂ thin films grown by atomic layer deposition using a novel Sn precursor

SnO₂ thin films were grown by atomic layer deposition (ALD) with dimethylamino-2-methyl-2-propoxy-tin(II) (Sn(dmamp)₂) and O₃ in a temperature range of 100-230°C. The ALD window was found to be in the range of 100-200°C. The growth per cycle of the films in the ALD window increased with temperature in the range from 0.018 to 0.042 nm/cycle. Above 230°C, the self-limiting behavior which is a unique characteristic of ALD, was not observed in the growth because of the thermal decomposition of the Sn(dmamp)₂ precursor. The SnO₂ films were amorphous in the ALD window and exhibited quite a smooth surface. Sn ions in all films had a single binding state corresponding to Sn⁴⁺ in SnO₂. The concentration of carbon and nitrogen in the all SnO₂ films was below the detection limit of the auger electron spectroscopy technique and a very small amount of carbon, nitrogen, and hydrogen was detected by secondary ions mass spectroscopy only. The impurity contents decreased with increasing the growth temperature. This is consistent with the increase in the density of the SnO₂ films with respect to the growth temperature. The ALD process with Sn(dmamp)₂ and O₃ shows excellent conformality on a hole structure with an aspect ratio of ∼9. This demonstrates that the ALD process with Sn(dmamp)₂ and O₃ is promising for growth of robust and highly pure SnO₂ films.