Friction Properties and Mechanism of Aluminum Sheets Under an Eco-Friendly CMCS Lubrication Condition

The eco-friendly tendency in the aluminum (Al) chemical mechanical polishing (CMP) process urgently requires a nontoxic, biodegradable, and cost-effective lubricant. To solve this challenge, Carboxymethyl chitosan (CMCS) lubricant was introduced into the polishing slurry. The wear mechanism of the Al sheet under dry friction, water lubrication, and CMCS lubrication conditions were investigated. The friction experiments were conducted with a Si₃N₄ ball sliding on the surface of the Al sheet under three different conditions. Adhesive wear was found to be prominent under dry friction and water lubrication conditions. Moreover, materials spalling leads to wear under CMCS lubrication condition. More specifically, a molecule-scale material removal mechanism was confirmed under the condition of a minimum wear depth of 0.315 nm per single scratch and a corresponding minimum wear rate of 0.1702 × 10⁻⁶ mm³/s, when CMCS lubrication was applied. Consequently, when CMCS lubrication at the pressure of 1.0 psi was exploited, the surface roughness (Ra) of the Al sheet after CMP was observed to be 0.22 nm, and such a result further implied that an Al-CMP induced, eco-friendly CMCS solution at low pressure contributes to the low-damaged planarization.