Ion-Implanted Photoresist Stripping by Using Organic Solvents

Abstract

In the ion implantation process, accelerated ions attack not only target materials but also photoresist, causing deformation of the molecular structure of the photoresist. It is difficult to remove crust layer formed by ion implantation in the standard photoresist removal methods. A typical method of removing high-dose ion-implanted photoresist is to use plasma ashing followed by the treatment in the mixture of hot sulfuric acid and hydrogen peroxide [1]. However, this process etches III-V semiconductors and dielectric materials [2]. Therefore, in this study, organic solvent-based mixtures were developed to remove high-dose ion-implanted photoresist without damaging the substrate. Trench-patterned GaAs was used as a substrate and KrF photoresist was coated on trench patterned GaAs. Then, P+ ion implantation with a dose of 5×1015 ions/cm2 was conducted on the photoresist. A mixed solution of dimethyl sulfoxide (DMSO) and acetonitrile (AcN) (DMSO: AcN = 6: 4) was used to remove the ion-implanted photoresist and 1 vol% HCl or HF was used as an additive. Photoresist removal was measured using an optical microscope and in-situ MIR-FTIR. When a mixed solvent of DMSO and AcN was used to remove ion-implanted photoresist, the photoresist was not completely removed and the residue and crust remained on the trench-pattern (Fig. 1). In order to improve the removal efficiency of ion-implanted photoresist, 1 % HCl or HF was added to DMSO+AcN solution. When 1 % HCl was added to the DMSO+AcN solution, the ion-implanted photoresist with an implantation energy of 30 and 50 keV was completely removed without residue. However, when the ion implantation energy was 70 keV, the photoresist crust was not removed in DMSO+AcN+HCl solution. When 1 % HF was added to DMSO+AcN solution, the ion-implanted photoresists was completely removed regardless of the ion implantation energy. Removal performance was quantitatively analyzed by in-situ MIR-FTIR as shown in Fig. 2. First, the ion-implanted photoresist was not removed more than 40 % for 10 min in DMSO. In DMSO+AcN solution, most of the photoresist was removed in 6 min, and all photoresist was removed in 4 min when DMSO+AcN+HCl was used. In the case of DMSO+AcN+HF, all of the ion-implanted photoresists were completely removed in 2 min and 30 s. Therefore, it is confirmed that DMSO+AcN+HF solution removes ion-implanted photoresist more quickly and effectively than other solutions used in this study. In addition, it is suggested that the largest interaction energy between DMSO+AcN+HF and the ion-implanted photoresist resulted in improvement of the removal efficiency of the photoresist.