Abstract. The paper reviews recent progress and current challenges in implementing high-k dielectrics in microelectronics. Logic devices, non-volatile-memories, DRAMs and low power mixedsignal components are found to be the technologies where high-k dielectrics are implemented or will be introduced soon. Two gate architectures have to be considerd: MOS with metal as gate electrode and MIM. In particular, Hf-silicates for logic and NVM devices in conventional MOS architecture and ZrO 2 for DRAM cells in MIM architecture are discussed.
Fields of applicationsThe breakthrough and thus the enormous growth of the microelectronics, especially in the Information Technology, in the past few decades is based, to a large extend, on the SiO 2 /Si system which was therefore called "a simple gift of nature". Gate dielectrics consisting of ultra thin silicon dioxide layers are the key element in conventional silicon based microelectronic devices. In the very beginning of the microelectronics, the thickness of the SiO 2 gate oxide was a few hundred nanometers. Nowadays, state-of-the-art MOSFETs (metal oxide semiconductor field effect transistor) require gate oxide thicknesses of just a few atomic layers. Until recently, the continuous scaling of the ULSI (ultra large scale integration) devices has been accomplished by shrinking physical dimensions. Physical gate oxides with physical thicknesses in the range of 1.6 nm are currently fabricated and thicknesses below 1.0 nm will be requested for future device generations [1]. In this thickness range, key dielectric parameters degrade, like gate leakage current, channel mobility, reliability etc. [2,3,4]. Thus, the necessity arises to replace the SiO 2 with a dielectric of higher permittivity [5,6]. Application of oxides with a higher dielectric constant (high-k) allows for a physically thicker insulating layer with the same capacitance per unit area as that required for SiO 2 . The so-called equivalent oxide thickness (EOT) is defined as follows: EOT = d high-k · k SiO2 / k high-k .(1) d high-k is the physical oxide thickness, k SiO2 and k high-k are the dielectric constant of the silicon dioxide and the high-k oxide, respectively. But, the high-k dielectric has to satisfy several requirements to fulfil all the demands of state-of-the-art gate dielectrics. First, it has to be thermodynamically stable in contact with silicon [7], it must be process compatible with CMOS (complementary MOS) and withstand source/drain implant annealing, oxygen diffusion should be low to prevent generation of a sizeable SiO 2 interface layer (IL) or trapping defects [8], and it must have sufficiently high band offsets to act as barrier for electrons and holes [9]. Also, the high-k oxide has to show a high quality interface to silicon, with only few interface or defect states within the silicon band gap, be- Online: 2008-03-24 ISSN: 1662-9752, Vols. 573-574, pp 165-180 doi:10.4028/www.scientific.net/MSF.573-574.165 © 2008 This is an open access article under the CC-BY 4.0 license (https://creativecomm...