Austin, Texas - IBM Microelectronics is about to roll out a high-k dielectric metal-insulator-metal capacitor based on tantalum pentoxide. The MIM capacitor, which is due for launch in the third quarter, is destined for use in the suite of passives that combines silicon germanium devices with 130-nanometer CMOS transistors in IBM's next-generation BiCMOS technology.
High-k dielectrics are needed to achieve high capacitance and to reduce parasitics in the MIM capacitors used in analog and mixed-signal devices, said Ebeneezer Eshun, a staff researcher at IBM Microelectronics.
They are needed to replace silicon nitride and silicon dioxide (SiO2) in passives and CMOS devices to curb the current leakage that occurs when thin dielectrics are used for device scaling. Continued thickness reduction of SiO2 also results in reliability degradation. High-k dielectrics can be made thicker than conventional dielectric materials, with the same equivalent capacitance, thereby reducing leakage.
High-k dielectrics are characterized by small bandgaps and high leakage currents, however, resulting in poor reliability compared with the traditional SiO2 and silicon nitride materials.
Eshun said high-k MIM dielectrics are needed for applications including de-coupling of integrated circuits from power supplies, analog functions for RF/wireless applications and termination of transmission lines. Circuit designers need MIM capacitors with good capacitance-voltage linearity, low leakage, high capacitance, a high Q (quality) factor, good device matching, low dielectric loss and 100,000 hours of power-on (POH) reliability with low failure rates, Eshun said.
In addition, the high-k-based MIM capacitor should be compatible with both aluminum and copper back-end processing. High-k dielectrics also require the purchase of a new tool set. Eshun said any new capacitor must be able to be used for older technology generations, requiring a reliability of 100,000 POH at 5 volts or higher.
The IBM MIM high-k dielectric reached 100,000 POH of reliability, at a failure rate of 1 part per million at 10 V, with a capacitance density of 4 femtofarads per square micron for a single MIM capacitor. "To the best of our knowledge, this is the highest operating voltage ever extracted for a high-k-dielectric MIM capacitor," said Eshun. The 10-V reliability is two times higher than the operating voltage of 5 V required for older 250- and 350-nm technologies. For newer technology generations ranging down to 65 nm, the 10-V reliability is about three to four times higher than that required by the operating voltages of 3.3 V and lower.
"The implication of this high-reliability MIM," Eshun said, "is that the high-k dielectric can be scaled down to achieve a higher capacitance" of 10 to 15 fF/micron2 for a single MIM capacitor, while maintaining the 100,000 POH at the minimum-use voltage over several generations. "With IBM's dual-MIM process, further increases in capacitance of 20 to 30 fF/micron2 can be achieved," he said.
Details will be presented at two September conferences: the 2004 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems and the Bipolar/BiCMOS Circuits and Technology Meeting.