Infrared characterisation of semiconductors

Abstract

A theoretical and experimental investigation of the optical properties of ion-implanted silicon over the wavelength range 2 μm to 3 cm has been performed. Twelve samples were supplied by Hughes Microelectronics Ltd. and a further two from Plessey Research Caswell. In the near infrared (short wavelength region) plasma edge features are seen for implants of 10¹⁵ions / cm² and above. The feature shape is sensitive to the donor implant distribution and this allows contactless characterisation through the use of a computer model developed in chapters 1 and 2. In the far infrared interference fringes are seen with modulation close to theory and the total transmission is sensitive to implant dose. Millimeter quasi optical results are in close agreement with the theory. The near infrared is limited to doses of 10¹⁵ions / cm² and above for implant distribution measurements, whilst at centimeter wavelengths a 4 x difference between the transmission at 10¹⁵ions / cm² and zero dose should allow an implant as low as 2x10¹⁴/cm² to be identified. At centimeter wavelengths the absolute fit between theory and experiment is not as good as in the millimeter and shorter wavelengths due to standing waves in the experimental arrangement. The possibility exists for tuning out these reflections with matching stubs and, with appropiate modeling, achieving even higher sensitivity in transmission to implant doses below 2x10¹⁴/cm². Level crossing effects in Zeeman split donor states in GaAs were investigated. Ho conclusive evidence for these was found within the limits of sensitivity of the experiments indicating that any amplitude is below 10% of the main transition intensity.