For decades, capacitors have been an important and irreplaceable circuit element used often in electronic circuit designs. For example, capacitors are widely used in applications such as dynamic random access memory (DRAM), active and passive filters, analog-to-digital and digital-to-analog converters (A/D and D/A converters, respectively), operational amplifiers, radio and tuning circuits, oscillators and multivibrator circuits, time critical and time delay circuitry, noise reduction circuitry, charge pumps, power electronics, and many other diverse applications. A capacitor is defined in the simplist terms as a device consisting of two conducting surfaces separated by an insulating material. A capacitor stores electrical charge, blocks the flow of direct current (DC), and permits the flow of alternating current (AC) depending essentially upon the capacitance of the device and the frequency of the incoming current or charge. Capacitance, measured in farads, is determined by three physical characteristics: (1) a thickness or average thickness of the insulating material separating the two conducting surfaces; (2) how much surface area is covered by the two conducting surfaces; and (3) various mechanical and electrical properties of the insulating material and the two conducting surfaces or electrodes.
Many forms of capcitors exist in the semiconductor industry. In the early development and marketing of the above mentioned technologies, parallel plate or parallel electrode capacitors were used as capacitance structures. The parallel electrode capacitor is a capacitor that has a planar top and a planar bottom conducting surface separated by a planar dielectric or insulator. Another capacitor is known as a trench capacitor. The trench capacitor is formed by first etching a deep well, trench, or hole in a substrate surface or a surface overlying the substrate surface. This trench or hole is then used to form and contain two electrodes separated by an insulator. Other known structures such as double box capacitors, crown capacitors, fin capacitors, and the like have been developed.
In the early development of the semiconductor capacitor, a doped substrate formed a first capacitor electrode, silicon dioxide formed a capacitor dielectric, and a metal layer formed a second capacitor electrode. As technology progressed, polysilicon, epitaxial silicon, silicides, salicides, and several metallic conductors, such as osmium, rhodium, platinum, gold, ruthenium metal, and aluminum were developed for use as a capacitor electrode. In addition, improved capacitor dielectric materials were developed such as oxide-nitride-oxide (ONO), tantalum pentoxide (Ta.sub.2 O.sub.5), and lead zirconium titanate (PZT) for use as capacitor dielectrics.
The current conventional and widely accepted electrode materials, such as the above mentioned polysilicon, epitaxial silicon, and several metallic conductors, such as aluminum, are not stable and oxidize in an oxygen ambient. In many cases, special care must be taken to ensure that an oxygen ambient is not exposed to the capacitor electrodes due to this oxidation phenomenon. Therefore, improved or complex processing equipment is required or additional cleaning and etch steps are required to maintain an oxide-free electrode surface. If an oxide-free surface is not achieved as is sometimes the case, electrode electrical contact quality, integrated circuit yield, and/or capacitor performance is reduced.
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