Since the birth of integrated circuitry about thirty five years ago, microelectronics design and manufacturing technologies have evolved toward higher integration density with smaller design rules. As the semiconductor industry moves into ultra-large-scale integration (ULSI), device geometries continue to shrink into the sub-half-micron region while circuit densities increase to optimize reliability and improve performance. The resulting demands on interconnect technologies necessitate the exploitation of all development avenues: design, materials, and manufacturing.Emerging sub-half-micron technologies require multilevel metallization (MLM) design schemes that reduce interconnection lengths and lead to lower signal transmission delays and enhanced device speeds. MLM schemes also permit increased device density, due to the ability to use the third (vertical) dimension, and easier signal routing because of higher flexibility in architectural design. These schemes, in turn, demand interconnect metals that can handle the higher current densities resulting from the decreasing size of device features, without the loss of electrical and structural integrity, and deliver the sheet resistance needed to meet performance demands. They also require reliable deposition techniques to successfully fabricate the increasingly complex architectures as lateral feature sizes are scaled down more rapidly than conductor or insulator thicknesses.
We describe chemical mechanical polishing (CMP) of blanket and patterned aluminum films employing a polyurethane pad and a slurry based on alumina particles as the abrasive and hydrogen peroxide as the oxidizer. The experiments were conducted at pressures from 19 to 47 kPa and at linear velocities from 26 to 48 m/min, and yielded Al removal rates from 80 to 250 nm/min. The oxidant concentration has a weak effect on the removal rate of Al. Polishing selectivities of Al to silicon dioxide as high as 130:1 were obtained with the maximum selectivities being observed at regions of low pressures and low velocities. The Preston equation fails to describe the dependence of the removal rate on pressure and velocity, and a power function is proposed instead. X-ray photoelectron spectroscopy was used to examine the surface of Al before and immediately after CMP. These experiments provided information on the thickness of the oxidized Al layer. We found that larger removal rates correlated with a smaller Al-oxide thickness.
Chemical mechanical polishing (CMP) studies of blanket aluminum, patterned aluminum, and SiO 2 thin films using a commercial slurry based on Al 2 O 3 abrasive particles are presented. Both silicon dioxide and aluminum blanket films were polished with two pads of different hardness and structure. The removal rate and the dependence of the removal rate on pressure and linear velocity for both materials varies significantly with pad type. For the softer pad, the Al removal rate depends critically on the surface saturation of the pad with Al 2 O 3 slurry particles. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to study the texture and chemical composition of the soft pad after different polishing conditions. We found saturation of the pad surface with Al 2 O 3 particles but no metallic aluminum on the pad after CMP. Pad reconditioning causes the removal of the abrasive particles from the pad surface. Patterned aluminum samples with a TiN barrier layer were polished in alumina slurry with and without hydrogen peroxide using the soft pad. During CMP of microstructures, both Al and TiN must be removed at similar rates. The removal rate of the TiN film is dramatically enhanced when H 2 O 2 is incorporated into the slurry, whereas polishing of aluminum thin films showed that the oxidizer has no effect on the Al removal rate. Passive soaking of TiN in H 2 O 2 slurry revealed that TiN readily dissolves in the presence of a strong oxidizer, which increases the chemical component of the CMP process.
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