Download Reliable Integrated MIM Decoupling Capacitors: Higher operating

Reliable Integrated MIM Decoupling Capacitors: Higher operating frequencies and supply
currents in advanced chips like microprocessors result in increased power-line “noise.”
Decoupling capacitors are an effective way to reduce noise, but they have been off-chip discrete
components. This not only takes up precious space, but more capacitance is needed as chips
become more powerful. Thus, decoupling capacitors are increasingly being integrated with chip
circuitry, either on the front-end when transistors are built, or at the back-end when the
interconnect is built. These are MIM (metal-insulator-metal) capacitors. Thin SiN or high-k
dielectric films have been used to build them, but leakage and reliability problems increase as
SiN gets thinner, and most of the high-k materials require expensive processes and pose
contamination issues.
At IITC, an NEC team will describe how they fabricated integrated MIM capacitors with an
ultra-thin tantalum oxide (TaO) insulator in a copper interconnect stack. The keys were a novel
low-temperature process using N2O to oxidize the TaO, and a laminated bottom electrode to
control the microstructure of the initial Ta to be oxidized. The resulting integrated MIM
capacitor demonstrated high breakdown voltage of 10V, high capacitance of 13 fF/µm2 and high
reliability (TDDB lifetime > 10 years).
The image shows a POx/TaO capacitor (13 fF/µm2) integrated into a copper back-end, and
also a magnified image of the MIM stack.
(Paper #11.5, “Low-Temperature Plasma-Oxidation Process for Reliable Tantalum-Oxide (TaO) Decoupling
Capacitors,” I. Kume et al, NEC)