Abstract
SiGe virtual substrate and high-k dielectrics were introduced into Metal Oxide Field Effect Transistor (MOSFET) devices to improve the electrical characteristics. For ultrathin equivalent oxide thickness (EOT), a higher-k dielectric was proposed to solve the leakage current issue. However, a reduction in carrier mobility is also encountered. A promising candidate to solve this issue is to alternate Si channel with high mobility material like Ge, which can offer two times higher electron mobility and four times higher hole mobility than Si. MOSFET with SiGe channel and higher-k gate dielectric are studied. Samples with TaON/HfO2 or TiON/HfO2 stacks show larger drain current, transconductance, and smaller subthreshold swing than that with single HfO2 layer. In addition, the reliability for SiGe MOSFET device is clearly improved with TaON/HfO2 stacks in terms of trans-conductance degradation and Vth shifts after hot-carrier stress. The integration of SiGe channel with TaON higher-k dielectric is useful for high performance MOSFETs. Metal oxide semiconductor (MOS) devices with in-situ remote plasma treatment during high-k dielectric deposition are studied in this thesis. The EOT value and leakage current of the MOS device with in-situ NH3 plasma treated high-k dielectrics can be significantly reduced to 0.83 nm and 1.7x10-3 A/cm2, respectively. The stress-induced flat-band voltage shifts and leakage current are obviously reduced as well. In-situ remote plasma treatment also provides a good approach of nitridation for high-k dielectrics. The oxygen vacancy can be passivated by nitrogen, which suppresses further oxygen diffusion and the formation of the oxygen vacancies. The in-situ NH3 plasma treatment is useful for high performance MOS devices with good reliability. High-k gated MOSFETs with Cl2 and CF4 plasma treatments are studied in this thesis. A higher-k HfON with more tetragonal phase is formed by the halogen plasma treatment on interfacial layer (IL). A low inversion equivalent oxide thickness in MOSFET is obtained with the Cl2 plasma treated IL. In addition, high mobility and transconductance, and low subthreshold swing are obtained by the Cl2 plasma treatment, which therefore is a promising interface engineering for advanced MOSFETs. Ge MOS devices with about 95% Ge4+ in HfGeOx interfacial layer are obtained by H2O plasma process together with in-situ desorption before atomic layer deposition (ALD). The EOT is scaled down to 0.39 nm; the leakage current is decreased as well. The improvement can be attributed to the in-situ Ge sub-oxide desorption process in an ALD chamber at 370 oC. The interface trap density and frequency dispersion need further process development to be reduced. Electrical characteristics of Ge pMOSFETs with HfO2, ZrO2, ZrO2/HfO2, and HfZrOx gate dielectrics are studied in this thesis. A lower EOT is obtained in ZrO2 device, which however has a higher interface trap density (Dit) due to its inferior dielectric/Ge interface. Interestingly, the Dit and sub-threshold swing of Ge pMOSFETs are clearly reduced by ZrO2/HfO2 stack gate dielectric. A peak hole mobility of 335 cm2/V-sec is achieved in ZrO2/HfO2 device thanks to good dielectric/Ge interface. Furthermore, the EOT of ZrO2/HfO2 device is 0.62 nm, and the leakage current is 2x10-3 A/cm2. Therefore, a ZrO2/HfO2 stack gate dielectric is promising for Ge MOSFETs.