| Summary: | 博士 === 國立交通大學 === 電子工程系所 === 97 === According to International Technology Roadmap for Semiconductor (ITRS), continuous increasing the capacitance density is required to scale down the device size and the cost of Metal-Insulator-Metal (MIM) capacitors which are widely for Analog, RF and DRAM functions. However, they often occupy a large fraction of circuit area. To meet these requirements, high dielectric constant (k) materials provide the only solution since decreasing the dielectric thickness (tk) degrades both the leakage current and ΔC/C performance. To achieve this goal, the only choice is to increase the k value of the dielectrics, which have evolved from SiON (k~4-7), Al2O3 (k=10), HfO2 (k~22), Ta2O5 (k~25) to Nb2O5 (k~40).
To further achieve the properties of MIM such as low leakage current, low voltage coefficient of capacitance and low temperature coefficient of capacitance. Thus, we have developed novel process and high-k dielectric materials, such as TiNiO (k~30-40), TiPO (k~26-32) and SrTiO3 (k>50) to achieve this technology. To further improve the small bandgap (EG) of these dielectrics, we apply the higher work-function Pt (5.7 eV) and Ir (5.3 eV) top electrode are used to give better device performance.
Although SrTiO3 has large dielectric (k~50-200), the small conduction band offset (ΔEc) and bandgap leading to larger leakage current is a larger drawback. Besides, SrTiO3 shows its higher k values by forming nano-crystals, which is only practicable at a higher process temperature > 450oC. Furthermore, the high voltage coefficient of capacitance of SrTiO3 is also an important issue. Because Ta2O5 has very low voltage coefficient of capacitance and can considerably suppressed the leakage current, the overall electrical characteristics of MIM device could be improved by doping Ta2O5 into SrTiO3 MIM capacitor. Otherwise, we have developed a plasma treatment on dielectric to repair the defect of the dielectric to improve leakage current, voltage coefficient of capacitance and temperature coefficient of capacitance at the same time. Therefore, not only high capacitance and low leakage current, but also small voltage/temperature dependence of capacitance are obtained under limited thermal budget for back-end-integration.
In addition to the measurement of capacitance at low frequency and the leakage current, the measurement of the S-parameters to investigated the characteristics of the MIM capacitors at RF regime are also demonstrated. By using the simulation software, the capacitance density of MIM capacitors at different frequencies was extracted. Besides, the related factors such as understandings of the mechanism of conductivity, the voltage/temperature dependence of capacitances, barrier height, and interfacial layer were investigated, and these are also useful in the development of advanced MIM capacitors.
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