Undercut Removal of Micrometer-Scale Particles from Surfaces

• Published in: Journal of the Electrochemical Society Vol. 153; no. 2; pp. G175 - G181
• Main Authors: Kumar, G., Beaudoin, S.
• Format: Journal Article
• Language: English
• Published: 2006
• ISSN: 0013-4651
• DOI: 10.1149/1.2149224

Effective removal of particulate contaminants from wafer surfaces during semiconductor manufacturing is essential for high-yield processing. To improve cleaning effectiveness, experimental and theoretical evaluations of undercut cleaning were conducted. A model system of polystyrene latex (PSL) spheres being removed from a tetraethyl ortho-silicate (TEOS)-sourced silicon dioxide surface was examined. 7 and 15 mm PSL particles were spray deposited on wafer surfaces and allowed to settle for 24 h. Undercutting was then carried out using 20:1 buffered hydrofluoric acid to etch the silicon dioxide under nonflow conditions. Preand postetch scans of the wafer surface were obtained using a Tencor SP1 Surfscan in the laboratories of SEZ America in Phoenix, AZ. The percentage of particles that remained adhered to the surface after etching for varying lengths of time was monitored. A model for undercut removal of particles from surfaces was proposed. Chemical etching of the silicon dioxide surface was assumed to cause a reduction in the particle-wafer contact area. Undercut removal was hypothesized to occur due to a subsequent reduction in the van der Waals force of adhesion and an increase in the area over which repulsive electrostatic forces were dominant. Interactions between the PSL and the silicon dioxide were calculated based on computer simulation of a van der Waals adhesion model and an electrostatic force model. Particle and surface morphology, mechanical properties, and geometry were included in the van der Waals calculation, and the electrostatic force calculation considered the particle and silicon dioxide zeta potentials and local separation distance. The model and experiments agreed to within 10%.