Study of high‐k gate dielectrics by means of positron annihilation

Abstract

PACS 77.55.+f, 78.70.Bj High-dielectric constant (high-k) gate materials, such as HfSiO x and HfAlO x , fabricated by atomic-layerdeposition techniques were characterized using monoenergetic positron beams. Measurements of the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positrons indicated that positrons annihilated from the trapped state by open volumes that exist intrinsically in amorphous structures of the films. The size distributions of the open volumes and the local atomic configurations around such volumes can be discussed using positron annihilation parameters, and they were found to correlate with the electrical properties of the films. We confirmed that the positron annihilation is useful technique to characterize the matrix structure of amorphous high-k materials, and can be used to determine process parameters for the fabrication of high-k gate dielectrics. 1 Introduction According to the international technology roadmap for semiconductors [1], the technology node for mass production of LSI devices will reach the 45-nm level in 2010; as a result, the need to replace SiO 2 with high-dielectric (high-k) materials will be indispensable for fabrication of metal-oxidesemiconductor field effect transistors (MOSFETs). Among many candidates for high-k materials, hafnium (Hf) based oxides (such as HfAlO x and HfSiO x ) have advantages such as a moderately high dielectric constant and high thermal stability in contact with Si [2,3]. Although the electric properties of MOS using metal oxides have been intensively studied, behaviour of the metal oxides during device processing is not fully understood. This might be due to a lack of techniques to characterize very thin films (≤5 nm). Positron annihilation is one established technique for investigating defects in materials [4]. Point defects in transition-metal oxides have been investigated by using positron annihilation [5][6][7][8][9][10][11][12], and the results show that positrons are a useful probe for studying vacancy-type defects in such materials. Thin high-k dielectrics deposited on Si substrates were characterized also using monoenergetic positron beams [13][14][15][16]. In the present study, we used this technique to probe open volumes in thin HfAlO x and HfSiO x films.