The Stripping Behavior of High-Dose Ion-Implanted Photoresists in Supercritical CO₂Formulations

Abstract

A new type of high-dose ion-implanted photoresist (HDI PR) stripping method was reported based on supercritical CO 2 (scCO 2 ) microemulsions consisting of branched hydrocarbon surfactant 2-ethyl hexanol polyoxyethylene-polyoxypropylene (EH-3) and co-solvent dimethylsulfoxide (DMSO). The optimized concentration of EH-3 and DMSO in scCO 2 were 3 wt% and 2 vol.%, respectively, and the ratio of H 2 O and EH-3 is 1:1. The post-etch HDI PRs containing crust polymer were removed in the scCO 2 microemulsions under the pressure of 10-25 MPa at 40-80 • C for 10 min. The results revealed that the stripping efficiency increased with the pressure and temperature when the temperature is lower than 60 • C. The 94% removal efficiency was achieved at 60 • C and 20 MPa and then it gradually decreased as the temperature is higher than 60 • C due to the lower scCO 2 density at higher temperature. The magnetic agitation and pressure pulsation were favorable to HDI PR removal. The optimum stripping parameters were determined to be 60 • C and 25 MPa for 20 min at which 100% photoresist removal efficiency was achieved in EH-3/DMSO/scCO 2 microemulsions. This environmentally benign method provides a promising alternative to effectively strip the HDI PR for nano-sized devices in microelectronics processing.The complete and effective stripping of high-dose ion-implanted photoresist (HDI PR) in IC manufacturing has become more challenging as the level of photoresist has increased while the allowable material loss and surface damage has decreased with the chip size downscaling. The heavily implanted photoresist is extremely difficult to be removed because an amorphous carbonized crust is formed due to the reaction of the implanted cation with the photoresist polymer as ion-implant dose is greater than 5 × 10 14 atoms/cm 2 and this crust is insoluble in wet chemicals. Usually, this kind of HDI PR removal has been achieved through a combination of dry plasma ashing and a subsequent wet chemical treatment with sulfuric acid and hydrogen peroxide mixture at elevated temperature. 1,2 These physical and chemical approaches cannot only lead to the increase in material loss and surface damage but also are troublesome at present, such as chemicals and disposals cost, ultrapure water consumptions, environmental burdens, etc. 3 Furthermore, as the feature size for integrated circuits continues to shrink down, the removal of HDI PR and postetch residues in the trenches/vias with high aspect ratio structure is extremely difficult in aqueous-based cleaning solutions due to their high surface tension and capillarity. The residues at the bottom of the trenches/vias will increase the contact resistance of interconnects, which will affect the subsequent process and eventually degrade the device performance. To fabricate smaller devices, low conductivity (ρ) copper and low dielectric constant (k) insulator are usually required to replace Al and SiO 2 as interconnects and inter-metal dielectrics, respectively, to minimize the resistance-capacitance (RC) coupli...

Removal of ion-implanted photoresists on GaAs using two organic solvents in sequence

“…It is known that photoresist components react with implanted cations to afford highly cross-linked polymers during the ion implantation process [12,13]. In addition, when the implantation dose is above 1 × 10 15 atoms/cm 2 , the cross-linked photoresist produces an amorphous carbonized crust and residue [12,14] that are not easily removed using conventional organic solvents [15,16].…”