Study for low-temperature formation of high-quality STNO high-k films for non-volatile memories

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The purpose of this research project is to develop film formation process technologies for high-quality high-k films (Sr_2(Ta_<1-x>, Nb_x)_2O_7 : STNO) with excellent uniformity within ±2 % over large diameter wafers at very low-temperatures below 500 ℃ by utilizing a microwave excited high-density plasma with a radial line slot antenna.By using the conventional high-k film formation methods such as sol-gel, PE-CVD (plasma enhanced chemical vapor deposition), CVD, and sputtering, it is difficult to form uniform high-quality gate insulator with high-rate at low-temperatures. In this research project we have developed following novel high-k gate insulator formation technologies. The process sequence is as follows. At first, a high-quality ultra-thin silicon nitride film as a barrier film is formed on a silicon substrate at low temperature of 500 ℃ by utilizing the microwave excited high-density plasma to mitigate the reaction between the high-k film and the silicon substrate. Then a Sr, … More Ta, Nb alloy film are formed on the substrate by using a novel sputtering technology with balanced electron drift magnetron plasma utilizing low-energy ion bombardment. Then, high-k film is formed by direct oxidation in the microwave excited high-density plasma equipment.We have succeeded to form high-quality silicon nitride gate insulator films with excellent barrier ability, very low leakage current (3 order of magnitude lower than the conventional thermally grown gate oxide films), very low 1/f noise (2 order of magnitude lower than the conventional gate oxide films), and excellent strength for current stress (Qbd : 100 C/cm^2) by low-temperature direct-nitridation process with NH^* radicals. Furthermore, we have succeeded to form oxide films with excellent electric properties by directly oxidizing the single-crystal silicon with every surface orientation, poly silicon, and metal involving the Sr, Ta, Nb alloys. These results lead not only to the realization of ultrahigh-speed devices with high-k gate FET but also to the establishment of a number of advanced processing technologies which certainly will become the main stream in microelectronics in sub- 100 nm era, impacting greatly the semiconductor manufacturing technology in future. Less