Exploring Modified Flow for Advanced Wet-Cleaning in Semiconductor Processing

Microchips are embedded in nearly every aspect of modern life, from computers and phones to cars and household appliances.   

Fabrication of a microchip relies on the successive deposition and selective removal of materials on thin silicon disks called wafers, to create the patterned multilayered structures required for integrated circuits.  Material removal in these steps is commonly performed with liquid chemicals in so-called wet processes, where fluids are applied to the wafer to selectively etch materials or clean away the contaminants to prepare the surfaces for subsequent layer depositions. In a conventional wet processing step, a wafer either spins on a rotating chuck while chemicals are dispensed from a nozzle onto its surface (continuous process) or remains stationary while being immersed in a chemical bath (batch process).  

These traditional types of liquid dispensing suffer from several drawbacks, including inhomogeneous flow and excessive inefficient chemical consumption. The short residence time of the liquid on the wafer surface results in the high consumption of often hazardous and environmentally harmful chemicals. 

In this thesis, we investigate a new liquid-dispense configuration, modifying the flow over the wafer, which increases the chemical residence time and enables improved control of the flow over the wafer. 

To investigate this concept, we use a lab-scale setup on a rheometer to study model systems and assess its effectiveness compared to the traditional process. In particular, the first part of this topic will investigate alternative configurations of the current system, like a flow with multiple liquid injection points or the injection of a fixed volume of liquid, in the attempt to replicate both batch and continuous configurations, allowing us to compare their efficiencies for a model etching system. The implementation of subsequent rinsing and drying steps in these configurations will also be explored.

In the second part of the thesis, we will apply the modified flow to facilitate the removal of particle contamination. Particle contamination is a major challenge in microchip fabrication, particularly as device dimensions continue to shrink. Particles comparable in size to critical features can cause device short-circuits, degrade device performance, and disrupt subsequent deposition steps or introduce unwanted elemental impurities. Removing such particles without damaging the exposed layer is difficult. In this work, we investigate viscoelastic polymer solutions as potential cleaning agents capable of overcoming the attractive forces between particles and the wafer surface. When subjected to flow, these solutions generate elastic forces that can induce particle sliding or lift off, enhancing cleaning efficiency. This thesis will investigate the efficiency of the modified flow in comparison to regular wet processing dispense configuration.  

The project involves the use of advanced characterization techniques, including SEM, ellipsometry, and optical microscopy to verify the efficiency of the different setup configurations. The student will also have access to both at the SMaRT (KU Leuven) and imec facilities.