High-K Dielectrics in Metal Insulator Metal (MIM) Capacitors for RF Applications

PHUNG THANH HOA

Publication

High-K Dielectrics in Metal Insulator Metal (MIM) Capacitors for RF Applications

PHUNG THANH HOA

Abstract

The thesis provided some solutions to address the challenges faced by the metal-insulator-metal (MIM) capacitor technology for the radio frequency (RF) and analog-mixed signal (AMS) applications. The MIM capacitors for the RF and AMS applications have requirements of high capacitance densities and low quadratic voltage coefficients of capacitance (VCCs) and leakage currents. To address these conflicting requirements, MIM capacitors using stacked dielectrics of a high-k dielectric on SiO2 were proposed. The MIM capacitors comprising thin film SiO2 formed by atomic layer deposition (ALD) at 200 and 400 ?C were characterized for the first time. The MIM capacitor with 4 nm ALD SiO2 deposited at 400 ?C achieved a low leakage current of 2?10-7 A/cm2 at 3.3 V, a high field strength of 19 MV/cm, and a high operation voltage of 3.6 V for 10-year lifetime. The leakage currents through ALD SiO2 were shown to be at least 10 times smaller than those through SiO2 deposited by PECVD (plasma enhanced chemical vapour deposition). Moreover, the negative quadratic VCC of SiO2 was explained by modeling the polarization in SiO2 as a sum of the electronic, ionic and orientation polarization in which the former 2 are relatively independent of the electric field. The orientation polarization however reduces with increasing electric field, giving rise to the negative quadratic VCC in SiO2. The MIM capacitors with sputtered Er2O3 on ALD SiO2 stacked dielectrics were then demonstrated to have excellent performance. An optimized MIM capacitor with 8.9 nm Er2O3 on 3.3 nm ALD SiO2 deposited at 400 ?C had a capacitance density of 7 fF/?m2, a quadratic VCC of -89 ppm/V2 at 100 kHz, a leakage current of 10-8 A/cm2 at 3.3 V, a dielectric field strength of 8.6 MV/cm and an operation voltage of 5.1 V for a 10-year operation lifetime. With leakage currents of ~10-7 A/cm2 at 3.3 V and ~10-8 A/cm2 at 2 V, the MIM capacitors with capacitance densities of 7.5 and 8.6 fF/?m2 and quadratic VCCs less than 100 ppm/V2 were also demonstrated with the Er2O3 (7 nm)/ALD SiO2 (3.3 nm) (deposited at 400 ?C) and Er2O3 (8.8 nm)/ALD SiO2 (2.3 nm) (deposited at 200 ?C) stack dielectrics. Lastly, the stack dielectrics of Er2O3 on ALD SiO2 were also investigated for the high voltage (20 V) applications. Although the MIM capacitors with single layer Er2O3 or HfO2 demonstrated a notable performance: capacitance density of 2.6 fF/?m2 and low quadratic VCC (less than 20 ppm/V2), the leakage currents were still very high, about 4?10-5 A/cm2 at -20 V. Using the stack dielectric of Er2O3 on ALD SiO2 deposited at 400 ?C, a high capacitance density of 2.5 fF/?m2 and a low leakage current of ~1?10-6 A/cm2 at -20 V was achieved. Having low quadratic VCCs, the capacitance densities obtained in this work were much higher than 0.5-1 fF/?m2 obtained by the Si3N4 MIM capacitors, indicating that the Er2O3/SiO2 stacked dielectric is a potential structure to be used in the MIM capacitors for high precision, high voltage applications.