Post-CMP Cleaners for Tungsten at Advanced Nodes

Abstract

We discuss several mechanistic approaches and experimental data for improving post-CMP cleaning of W plugs with TiN as barrier liner, and dielectric substrates SiO2 and Si3N4 for use at the 10 nm technology node (metal pitch of 40 nm). Particle charge in the low pH, W CMP slurries are usually positive, and the W surface is always negatively charged at pH >3. Therefore, a strong electrostatic attraction is expected to occur between the W surface and the residual particles during post-CMP cleaning. Two main approaches were chosen to break down the strong particles-W surface post-CMP electrostatic interactions, as well as particles dispersion and prevention of redeposition: (1) using cleaning additives able to adsorb at the W surface and reverse the W surface charge; (2) using organic additives to reverse the particle charge. The latter approach results in two strongly negative charged surfaces, which are able to repulse each other, and leads to the best cleaning.

Post-CMP Cleaners for Tungsten Advanced Nodes: 10nm and 7nm

“…We start from our legacy W PCMP cleaner PlanarClean® AG-W100, which shows low organic defects, and limited corrosion. [6] After CMP + cleaning with PlanarClean AG-W100, SiO 2 surfaces show a metal surface contamination of ~2 x 10 12 atoms/cm 2 , which originates from the metal-containing H 2 O 2 activator. In this work, we aim at reducing the metal surface contamination of our legacy W PCMP cleaner while maintaining the same cleaning performance and corrosion properties.…”

“…Meeting all these requirements using commodity cleans, such as diluted ammonia (dAmmonia) or standard clean 1 (SC1) [5], seems to be impossible: SC1 and dAmmonia cause W recess and show inefficient cleaning of particles and organics on Si 3 N 4 surfaces. [6] In the following paragraphs we will discuss our approach to design formulated cleans that overcome the previously mentioned challenges, and that meet the specifications listed in Table 1.…”

Review—Post-Chemical Mechanical Planarization Cleaning Technology

“…7. The main contaminants after CMP of W are organic residue, metal cations, pad debris, and abrasive particles 151 with defects such as local chemical attack (corrosion), galvanic corrosion, watermark, W recess, voids in the middle of W structure. 12 Tungsten CMP is less expected to develop scratches on W structures than on the dielectric material as the density of W (19.3 g cm −13 ) is lower than the nearby oxide (SiO 2 :2.65 g/cm 3 , Si 3 N 4 :3.17 g cm −13 ) or dielectric material.…”

“…Whereas, with basic chemistry, corrosion inhibitor and/or complexing agent is added to suppress HM formation. 153 Effective removal of surface impurities without W corrosion is required for post-CMP cleaning of W. The selection of conventional or unconventional cleaning solutions for post-CMP cleaning depends on the major cleaning requirements for W. 151 Table IV shows the cleaning requirement employed for W post-CMP. 151 Oxidizer such as hydrogen peroxide, ferric nitrate [Fe (NO 3 ) 3 ] 154,155 carried over from the previous polishing step of CMP makes W more susceptible to corrosion.…”

“…153 Effective removal of surface impurities without W corrosion is required for post-CMP cleaning of W. The selection of conventional or unconventional cleaning solutions for post-CMP cleaning depends on the major cleaning requirements for W. 151 Table IV shows the cleaning requirement employed for W post-CMP. 151 Oxidizer such as hydrogen peroxide, ferric nitrate [Fe (NO 3 ) 3 ] 154,155 carried over from the previous polishing step of CMP makes W more susceptible to corrosion. 153 Although H 2 O 2 is corrosive in nature, it is commonly used due to its cleanliness (nonmetallic slurry) and results in less contamination.…”