InGaAs has a higher electron mobility and saturation velocity than Si, making it a potential candidate for a channel material of next generation metal-oxide-semiconductor devices. To introduce InGaAs into semiconductor devices as a channel material, a series of chemical mechanical polishing (CMP) processes are required after InGaAs deposition processes [1]. However, silica particles may remain on the InGaAs surface after CMP processes, and the particles reduce the yield of semiconductor manufacturing. In order to remove silica particles from the InGaAs surface, post-CMP cleaning process is required. However, the behavior of silica particles on the InGaAs surface has not been extensively investigated yet. In this study, the behavior of silica particles on the InGaAs surface in ammonium hydroxide (NH₄OH)–hydrogen peroxide (H₂O₂)–H₂O mixture (APM) solution containing cationic surfactant was investigated. Also, the interaction forces between the silica particle and the InGaAs surface in the APM solution with different concentrations of hexadecyltrimethylammonium bromide (CTAB) were examined.

To investigate the behavior of silica particles on the InGaAs surface in the APM solution, silica particles were intentionally contaminated on the InGaAs surface by dipping the InGaAs in the solution where silica particles were dispersed. CTAB was added to the APM solution at the concentrations of 10^-4–10^-2 M to modify the interaction forces between the silica particle and the InGaAs. To estimate the interaction forces (van der Waals force, acid–base force and electrostatic force) between the silica particle and the InGaAs surface in the solution, the surface properties of InGaAs and silica particle, such as zeta potential, surface energy components, acid–base energy constant and Hamaker constant, were examined from the contact angles and surface charges.

As shown in Fig. 1, the number of particles per InGaAs surface area was observed to be 4.5×10⁵ particles/mm² after dipping the InGaAs in particle-dispersed APM solution. When 10^-4 M CTAB was added to the APM solution, the number of particles per InGaAs surface area slightly increased, but it decreased the concentration of CTAB in the APM solution increased to 10^-2 M. It is believed that the addition of CTAB to the APM solution changes the interaction force between silica particles and the InGaAs surface, thereby determining the adhesion behavior of silica particle to the InGaAs surface.

The interaction force between the silica particle and the InGaAs surface in the APM solution is obtained by sum of the attraction (van der Waals) and the repulsions (acid–base and electrostatic). Since van der Waals force, acid–base force and electrostatic force were proportional to Hamaker constant, acid–base energy constant and zeta potential, respectively, the change of each force was estimated from the change of surface property. Compared to their surface properties in the APM solution without CTAB, Hamaker constant, acid–base energy constant and zeta potential were reduced by the addition of 10^-4 M CTAB. The results suggest that van der Waals force, acid–base force and electrostatic force decrease in the APM solution with the addition of 10^-4 M CTAB. However, since the decrement in acid–base force and electrostatic force was larger than that in van der Waals force, the attraction was dominant over the repulsion in the 10^-4 M CTAB-added APM solution. Therefore, the adhesion of silica particles in the APM solution with the CTAB addition of 10^-4 M may be facilitated by attraction force. When 10^-2 M CTAB was added to the APM solution, Hamaker constant, acid–base energy constant and zeta potential increased, indicating that van der Waals, acid–base and electrostatic forces are enhanced. However, since the increments in acid–base force and electrostatic force were larger than that in van der Waals force, the repulsion was dominant over the attraction in the 10^-2 M CTAB-added APM solution. It is suggested that the adhesion of silica particles to the InGaAs surface is suppressed by repulsion force. From the estimation for the change in the interaction forces, it is proposed that the APM solution with the addition of 10^-2 M CTAB capable of suppressing the adhesion of silica particles may be a potential candidate for the InGaAs surface cleaning.

Reference

[1] E. E. Remsen, S. Anjur, D. Boldridge, M. Kamiti, S. Li, T. Johns, C. Dowell, J. Kasthurirangan, P. Feeney, J. Electrochem. Soc., 153, G453–G461 (2006).