The Passivation And Performance Of High-k Gate Dielectric / Semiconductor Substrate Interface Is Improved

With the rapid development of microelectronics industry, the feature size of CMOS device is scaling down continuously, traditional based silicon dioxide/Si system has reached to its limited thickness as gate dielectric. On the one hand, when the thickness of SiO2 is reduced to the atomic scale, the leakage current will become so serious that make the device useless because of quantum tunneling. In that case, we have no choice but to choose high-kappa dielectric material to replace the SiO2. Among various high-k materials, hafnium oxide (HfO2) is regarded as one of the most promising candidate materials due to its moderate dielectric constant(～25), big bandgap(～5.6eV) and band alignment(△Ec= 1.5eV,△Ev=1.7eV), and superior thermal stability with Si etc., but HfO2 still has some problems to be solved. In order to perform as a successful gate dielectric, high-k material/Si system must match a set of criterias. Therefore, it should have some similar characteristics with SiO2/Si system, also has to be compatible with the current semiconductor manufacture technology. The summary of criteria for the selection of high-k gate dielectric includes:(1).high dielectric constant and band alignment; (2). remain morphology under the thermal process; (3).good thermal stability; (4). excellent interface quality; (5).compatible with process, etc.On the other hand, the demand of high speed devices poses a challenge to the carrier mobility of the substrate.Ⅲ-Ⅴgroup semiconductor (GaAs etc.), Ge and GeSi are extensively studied because of their high carrier mobility. But their native oxides can not protect the substrate effectively like the SiO2 layer on the silicon. To the contrary, it will introduce a high interface state density. The progress on the passvation process is one of the core technologies which make it possible to fabricate high performance MOS device on the GaAs substrate.The mainly work of this paper is arranged into two parts:1. We use the advanced ALD to deposit Al2O3 and HfAlO high-k gate dielectric on the Si (100) substrate. The precusors of Al, Hf and O are TMA, TEMAH and H2O respectively. We analysis the electrical properties of the structures which use Al2O3 buffer layer between the Si and HfAlO (with a 30 ALD cycles), the ALD Al2O3 cycles of two samples are 5 and 10. The pre-treatment of TMA precursor before depositing HfAlO is also analyzed and compared. The accumulative capacitance density of TMA-treated,5-ALD Al2O3 cycles and 10-ALD Al2O3 cycles is 0.813,1.143, 0.772μF/cm2 respectively. And the Dit in the center of band gap is 7.09×1011, 5.01×1011 and 8.12×1011(cm-2.eV-1) respectively. Though the HfAlO/Si MOS capacitor without Al2O3 buffer layer has the highest accumulative capacitance density, its performance on the interface density and frequence dispersion is relatively poor. Both two kinds of HfAl0/Al203/Si structures have small frequency dispersion under 100 KHz and 1MHz tested signals, also have relatively low and little difference on the leakage current, while the CET of the former is 1.4nm less than the latter's. In conclusion,5-ALD Al2O3 cycle is enough to keep the balance between low leakage current and CET. The thermal stability and the ability of withstand detrimental impurities were greatly improved after using Al2O3 buffer layer, it can also suppress the crystallization of gate dielectric.2. We employ the sulfur wet passivation process in order to eliminate the native oxides and elemental arsenic from GaAs surface, thereby suppresses the formation of antisite defects AsGa and leaves compact GaS on the surface to avoid oxidation. CH3CSNH2 and (NH4)2S solution were used as sulfur-passivation solution, so as to deposit Al2O3 high quality gate dielectric on the GaAs. From the XPS results and analysis of those two surface pretreatments, we can notice that most native oxides and elemental As were removed effectively from the Al2O3/GaAs interface, but the Ga-0 and As-As bond can not be removed completely. It also reveals that surface pretreatment can form Ga-S bond at the GaAs interface, CH3CSNH2 has a better passvation effect than (NH4)2S from further comparison of these two pretreatments. TMA pretreatment before high-k dielectric deposition can leave a better surface. We study the electric properties of TMA pretreatment and these two sulfur passivation samples. Among them, CH3CSN2-treated sample shows the highest accumulation capacitance density and the best interface state intensity. The accumulation capacitance density of sulfur-treated samples were increased because of the densitification of Al2O3.after PDA at 500℃N2 ambient for 5 min. It confirms sulfur-treatment can enhance the stability of Al2O3/GaAs system.