Mark Kawaguchi

Wafer Surface Charging Model for Single-Wafer Wet-Spin Processes

Wet chemical processes in integrated circuit (IC) manufacturing are used in many applications, e.g., post-etch residue removal and pre-deposition surface treatment. While advanced single-wafer wet spin tools are part of the critical tool-set for advanced IC fabrication, non-optimized tool hardware and/or process may induce different types of wafer surface charging issues. In this paper, a physical model to fundamentally explain surface charging induced by a single-wafer wet spin tool is described. The model is based on the advection of surface charges from wafer-center to wafer-edge resulting from the shear flow of the liquid. The charge distribution in the diffuse layer adjacent the wafer surface is calculated by solving the coupled Poissons and current continuity equations. As often practiced in the industry in characterizing this type of wafer surface charging, a thermally grown silicon dioxide surface is used as the model surface and de-ionized water as the liquid medium. Good agreement is obtained between experimental and calculated surface charging potentials for radial positions extending from wafer-center to approximately 130 mm on standard 300 mm diameter wafers. The observed charging potential trends with respect to radial position, wet process time, and wafer spin speed are well explained by the current model.

Factors Influencing Drying Induced Pattern Collapse

The collapse of high aspect ratio features is a daunting challenge facing the semiconductor industry. The complex physics and dynamics that govern this process are not entirely understood. Through the use of optical video imaging we have observed pattern collapse in real time. It was found that the liquid meniscus reconfigures itself laterally along the length of the structure as opposed to the expected top-to-bottom drying. Herein, we report on our observations and the physics of drying high aspect ratio structures.

Minimizing Wafer Surface Charging for Single-Wafer Wet Cleaning for 10 nm and beyond

Wafer charging has become an issue since single-wafer wet clean has been introduced and multiple aspects could be potential root causes. In chemistry and DIW process factors, typical process parameters; flow rate and time were re-evaluated. As an alternative solution, dilute NH4OH could reduce the wafer surface charging. Hardware parts were also investigated and wafer holding chuck-pin material was revealed to become a risk of discharging failure at edge of wafer. Ionizer has been known to discharge wafer surface; however, it is not enough to remove pre-existing charge from post DIW rinsed wafer. Soft X-ray is challenged to remove pre-existing charge and obtained initial positive result.