Improvement of Tantalum Pentoxide Metal-Insulator-Metal Capacitors For SiGe RF-BiCMOS Technology
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Improvement of Tantalum Pentoxide Metal-Insulator-Metal Capacitors For SiGe RFBiCMOS Technology Hongjiang Sun1, Ka Man Lau1, Eyup Aksen2, Nancy Bell1, 1 Philips Semiconductors, P.O. Box 1279, Hopewell Junction, NY 12533 2 Philips Research Leuven, Kapeldreef 75, B-3001 Leuven, Belgium Tel. (845) 902-1555, Fax. (845) 902-1805, [email protected] Abstract 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 270C – 1500C 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/0C with a negligible TC2. The leakage current density is 3.1x10-3 A/cm2 at 1250C 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. Introduction
High performance MIM capacitors have received a lot of attentions in recent years for two main reasons. First, reduced circuit area is an economic driver of the microelectronics revolution. Indeed, high-k materials help to reduce the chip area by decreasing for instance the size of the storage capacitor of DRAM but also meet the requirements for RF applications. Second, high-frequency telecommunications need a material that has a high-k value, low temperature coefficient and better linearity. Due to the parasitic capacitance between the passive device and the underlying substrate, polysilicon capacitors and oxide capacitors degrade as the frequency increases, which is unacceptable in high-frequency range applications. But increasing the separation between the passive component and the underlying conductive substrate, the parasitic can be significantly reduced. The tantalum pentoxide Ta2O5 Metal-Insulator-Metal (MIM) capacitor with a capacitance of 5fF/µm2 was developed and fully integrated into our existing SiGe RF BiCMOS technology1,2. It has been reported that the surface roughness of the lower and upper electrode was important to the magnitude of the leakage current density3. The leakage is directly related to the Ta2O5 quality and the dielectric/electrode interface4. A better leakage was observed for the lowest deposition rates7 but post deposition treatments in oxygen plasmas demonstrate superior leakage5. This pape
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