Thermally Grown and Reoxidized Nitrides as Alternative Gate Dielectrics
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E3.14.1
Thermally Grown and Reoxidized Nitrides as Alternative Gate Dielectrics Alexandra Ludsteck1, Waltraud Dietl2, Hinyiu Chung2, Joerg Schulze1, Zsolt Nenyei2 and Ignaz Eisele1 1 Institute of Physics EIT 9, University of the Bundeswehr Munich, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany 2 Mattson Thermal Products GmbH, Daimlerstr. 10, 89160 Dornstadt, Germany ABSTRACT The use of high-k materials as gate dielectric still meets a lot of unsolved problems such as thermal instability during post deposition anneals resulting in the formation of interfacial oxide layers or bad process compatibility. As long as these requirements are not accomplished alternative gate dielectrics have to be formed by oxynitrides or gate stacks built of oxynitrides and some high-k material. In order to achieve a low equivalent oxide thickness (EOT) it is necessary to grow homogeneously thin oxynitrides which are nitrogen-rich and which have a high interface quality. Therefore we have studied the growth of thin nitrides and oxynitrides (EOT = 1 - 2nm) formed by rapid thermal nitridation in NH3 and wet reoxidation. By varying the partial pressure of NH3 in the process gas ambient NH3/Ar the nitride quality could be optimized: it was found that an optimized ratio of NH3 and Ar during nitridation improves the electrical properties of the nitrides and oxynitrides significantly. Interface state densities as low as those of dry thermal oxides and leakage current densities reduced by four orders of magnitude compared to SiO2 of the same EOT have been obtained. Due to the high incorporation of nitrogen into the oxynitride by rapid thermal nitridation and following oxidation the leakage current densities are also lower than those of most oxynitrides reported in literature. In addition we present data concerning the suppression of boron diffusion from p+ poly-Si electrodes. In summary the developed oxynitrides are suitable to bridge the gap between common SiO2 and new alternative gate dielectrics or to form gate stacks in combination with high-k materials. INTRODUCTION The required equivalent oxide thickness (EOT) for the coming technology nodes is less than 2 nm [1], which is a thickness range where silicon dioxide will not be suitable as gate dielectric due to high leakage currents and low resistance to boron diffusion from the p+ polysilicon electrode. Promising candidates to bridge the gap between the use of SiO2 and some high-k material are oxynitrides. During the last decades a lot of work has been done to examine oxynitrides formed by different methods like CVD-nitridation with following post nitridation anneals (PNA) in oxygen containing gas ambients [2,3,4,5], rapid thermal oxynitridation in NO or N2O [6,7], rapid thermal nitridation of thin oxides in NH3 [8] or remote plasma nitridation [9,10]. But little work has been done using NH3 in rapid thermal nitridation to form Si3N4, because of the insufficient control of oxygen incorporation. The object of this paper is to present optimized nitrogen-rich (oxy)nitrides formed by rapid th
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