Improvement activities were made in fully integrated Metal-Insulator-Metal (MIM) capacitors (>5fF/μm2) used in the advanced SiGe RF BiCMOS technology. By changing the process sequence of the lower metal electrode and the MIM capacitor, an improved MIM capacitor has achieved a lower leakage density with a better voltage linearity at 27°C − 150°C temperature range and a lower temperature dependency from −6V to +6V. Voltage coefficients VC1 and VC2 are 187ppm/V and 24ppm/V2 respectively, and temperature coefficient of capacitance TC1 is 99 ppm/°C with a negligible TC2. The leakage current density is 3.1×10−3 A/cm2 at 125°C for 5.5V with a breakdown voltage of 20V.
To increase capacitance density while maintaining low leakage, an ozone treatment after tantalum pentoxide film deposition has been investigated. A capacitance density as high as 10.3fF/μm2 has been achieved with a leakage density one order lower than the standard process. The fact that the extracted dielectric constant increased from 28 to 32 as well as the significant changes of the voltage and temperature coefficients clearly indicated that the ozone treatment has changed the intrinsic property of the tantalum pentoxide film as well as the top dielectric surface.
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