LiDepoWetPro - Wet clean process simulation for 450mm wafers

The distribution of a process liquid as a thin film driven by centrifugal forces is a well- established concept for the controlled wetting of the processed surface of silicon wafers. The permanent drive to increase productivity and to reduce the consumption of chemicals, as well as the ongoing miniaturization of the surface structures (22nm-technology) make it more and more difficult to attain the desired quality of the process and produced results. An important prerequisite to master this challenging task is a reliable description of the detailed transport phenomena in the region of liquid impact and inside the film spreading out on the rotating substrate. The prospective transition to larger disk sizes suggests a locally distributed dispense of the process liquid supplied by several jets (e.g. using several individual single-jet dispensers, or one manifold-like multi-jet dispenser) to ensure a most uniform continuous wetting of the surface. Based on theoretical/analytical and experimental investigations for varying operating conditions and wettabilities of the wafer surface the most relevant parameters for a continuous wetting shall be identified. These parameters shall be combined to appropriate non-dimensional groups, which are used to demarcate the critical regimes, where film breakup has to be expected. Numerical flow simulations shall be carried out for single-jet and multi-jet dispense to determine the sub-domains where the flow conditions significantly affect the species mass transfer. The analysis of the numerical results is specially focussed on the transport of mass and momentum in the region of impingement, the bow wave, and the neighbouring thin film region. The obtained findings shall help to develop an appropriate concept for the liquid dispense, in particular regarding the position(s) of the impinging jet(s). The numerical results will also be used to evaluate the scope and the limits of the thin film approximation, whose accuracy strongly depends on realistically assumed profile functions for all flow variables inside the liquid film. A further topic is devoted to the initial wetting of a dry substrate, where the mass transfer near the three-phase contact line shall be investigated using highly resolved numerical simulations. The numerical study considers a spatially limited domain applying well established existing models for the dynamics of the contact line to keep the computational costs on an acceptable level. The computational investigations shall provide valuable insight into the temporal and spatial evolution of the transfer rates in the vicinity of the contact line, which is practically not accessible to experiments. The experimentally and computationally obtained results of the present project will strongly contribute to better understand, describe, and finally to further optimize the thin film based wet processing of silicon wafers. The extended knowledge shall in particular help to identify critical aspects already in an early phase of process development and to derive adequate solutions or improvements.