A New Approach to Tackle Wafer Contact Mark Contamination Issues in Marangoni Drying
Authors: Chen Gim , Nemeth Dennis , Kashkoush Ismail 
Published: February 2020

Introduction

Wafer drying is the last and critical step in wet wafer surface preparation processes for a product finished with clean and dry surfaces (1). Among various wafer drying technologies, Marangoni drying has been the most commonly used application nowadays due to its advantages in many aspects (1-3). However, surface tension gradients generated by Marangoni effect might not be able to fully overcome the capillary force existing at the tight geometry of the contact area between wafers and a wafer holder, resulting in contact mark contamination issues, especially under an inspection condition with reduced wafer edge exclusion (Figure 1). In this paper, we demonstrate the application of a technological approach to enhance a complete drainage of water droplets at the wafer/holder contact points to significantly mitigate the contact mark contamination issue.

Experimental

Experiments were conducted on a GAMATM wafer cleaning station in NAURA-Akrion’s Applications Lab, in which a LuCIDTM dryer is used for the wafer drying process. The dryer was set to run a typical Marangoni process at fixed parameters, with the in-tank wafer holder as the only variable. Various numbers of 200mm bare Si test wafers, sandwiched with clean dummy wafers to serve a full loading condition, were placed to various slots of a full pitch process carrier for a test batch. To ensure a consistent degree of hydrophilic state of Si surfaces during the drying process, each wafer batch was processed with an SC1/QDR/Dry instead of a Dry Only recipe. Before and after a process run, test wafers were inspected with a KLA-Tencor SP1 at ≥100nm particle threshold with 2mm edge exclusion.

Results

Wafer contact mark incidence was evaluated by overlapping the “pre” and “post” wafer map of each test wafer to identify the specific contact mark signature. Figure 2 highlights the incidence with respect to frequency and severity of contact mark occurrence. The former indicates how many test wafers in a testing batch show contact mark contamination, while the latter presents the extent of particle clustering in a contact mark. It can be seen from Fig.2 that both the frequency and severity of contact mark contamination were significantly reduced with appropriate liquid drainage at the contact area between the test wafers and a modified in-tank holder.

Conclusion

Experiments were conducted to tackle the wafer contact mark issue in a Marangoni drying process. The capillary effect holding liquid droplets at wafer/holder contact points can be overcome by a drainage technology to significantly reduce the contact mark incidence. With the technological solution, the Marangoni process window can be broadened and, in turn, the robustness and performance of the drying process are enhanced.

References

D.C. Burkman, et. al., in Handbook of Semiconductor Wafer Cleaning Technology (ed.. W. Kern), Noyes Publications, Westwood, NJ, 1993, pp. 131-134.

A.F.M. Leenaars, et. al., Marangoni Drying: A New Extremely Clean Drying Process, Langmuir, 1990, 6 (11), pp. 1701-1703.

T. Vukosav, Substrate Drying Using Surface Tension Gradient Technology, R&D Magazine, 7/16/2013. https://www.rdmag.com/article/2013/07/substrate-drying-using-surface-tension-gradient-technology

Figure 1