Chemistry and Process Considerations for the Removal of Residues for Hybrid Bonding

Protective coatings are used throughout the industry to ensure the wafer surface and circuitry is not damaged during the dicing step. A significant amount of silicon dust and debris is generated during dicing and can land on top of the die if the surface is not protected. Removing dried-on silicon dust from a surface is very challenging, which makes protective coatings even more valuable. These protective coatings can vary greatly between companies but are typically a laminate, photoresist, or spray-coated organic film. Residual temporary bonding material from bonding to a carrier for the die thinning process can also be present on the wafer surface prior to apply the protective coating. Simultaneously removing the protective coating and bonding residues while the diced wafer remains on frame simplifies the process flow and enables subsequent bonding steps.

Careful consideration should be given when removing protective dicing coating and bonding residues. The first consideration is the chemistry used to remove the protective coating. The chemical needs to be capable of removing the coating in a short amount of time, while not attacking the dicing tape the wafer is attached to or any exposed circuitry (metals or dielectrics). The second consideration is the equipment set to be used to remove the protective coating. Some dicing equipment contains a cleaning module with an integrated pressure spray. However, these integrated cleaning modules typically don’t have much functionality and cannot handle any chemicals other than water. As wafer thicknesses approach sub-50 microns, increased functionality is required to ensure the thinned die are not damaged and ensure a residue-free surface. A high throughput and consistent cleaning of diced wafers on tape will enable high volume die package assembly manufacturing. The third consideration is how the wafer will be processed. Three traditional approaches to removing any protective coating are soaking a cassette of wafers in a bath, spraying each wafer individually, or a combination of soak and spray.

In this paper, the simultaneous removal of residual temporary bonding residues after a thinning process and a protective dicing coating was investigated. Cleaning efficiencies of four different chemical dispensing techniques (wall, aerosolized, high pressure, and a combination of high pressure and wall) were compared. The highest yielding technique was then applied to a combination clean of bonding residue and a protective dicing coating. Cleaning on film frame was performed with both 50 micron thick die and 200 micron thick die. Optical microscopy confirmation and bonding yield with electrical data demonstrated a high yielding clean process on both die thicknesses.