Abstract
Ge possesses two times electron mobility and four times hole mobility compared to Si. So we use Ge substrate and high-k material to obtain ultra-thin EOT, to achieve high mobility and drain current. However, using Ge material will face many challenges. It is easy for Ge oxide to be volatilized and hydrolyzed at 4000C. Ge out-diffusion induced gate leakage and Ge oxide quality is our first priority which is needed to be improved immediately. In this thesis, different buffer layer is deposited by ALD (Atomic Layer Deposition System) to improve the electrical characteristics of Ge MOS devices. In the first part, We use ZrO2 as high-k material, and deposit Hf-rich and Zr-rich buffer layer between ZrO2 dielectric and GeO2 interfacial layer on Ge MOSCAPs. For Ge MOSCAPs with Zr-rich buffer layer, the EOT is the thinnest, 4.3 Å, but the gate leakage current is increased, around 10-1 A/cm2, and the interfacial quality between Ge substrate and GeO2 interfacial layer is poor. For Ge MOSCAPs with Hf-rich buffer layer, the EOT is increased to 4.9 Å, but the gate leakage current can be reduced, and better interfacial quality can be achieved. From XPS, we consider that Zr-rich buffer layer will seriously consume GeO2 interfacial layer, and cause the gate leakage current increased, and poor interfacial quality. However, Hf-rich buffer layer will incorporate into GeO2 interfacial layer, and then form a thicker and denser HfGeOX interfacial layer, so it can achieve lower gate leakage current and better interfacial quality. Ge MOS devices with Hf-rich and Zr-rich buffer layer can also achieve small hysteresis and good reliability characteristics. In the second part, we use different temperature to deposit ZrO2 dielectric, 2500C, 3000C and 3500C, respectively, and then discuss the difference between the electrical characteristics of Ge MOSCAPs with ZrO2 dielectric at different temperature. For ZrO2 dielectric deposited at 3000C, EOT is about 4.7 Å, although the gate leakage current is increased, the characteristics of hysteresis, stress induced flat-band voltage shift, and SILC is obviously better than ZrO2 dielectric deposited at 2500C and 3500C due to higher oxygen content, fewer oxide traps, and better intermixing between GeO2 interfacial layer and ZrO2 dielectric. In the third part, we combine the results of the above two experiments, and use 3000C to deposit ZrO2 dielectric with Hf-rich and Zr-rich buffer layer on Ge MOSFETs, and then discuss the difference of the electrical characteristics. For ZrO2 dielectric with Hf-rich buffer layer, the electrical characteristics are better than ZrO2 dielectric with Zr-rich buffer layer and without buffer layer, it can achieve higher saturation drain current and lower off current, the mobility is about 350 cm2/V-s, and it can also achieve good reliability characteristics.