Development of Thick High Aspect Ratio Plating Resist Technology

Recent evolution in chip integration technologies continues to drive the need for advancement in plating and etch applications. In particular, the rise of fan out wafer level packaging, adaptive patterning, and 3D integration is intensifying requirements for thicker copper features with higher aspect ratios, enabling vertical interconnects and reduced layer counts for cost effective scaling.

Chemically amplified negative tone resist systems that can be easily removable using commercially available removers are attractive due to the potential of obtaining high aspect ratio features. Residue free removability with standard solvent developers is especially valuable, reducing risk of downstream contamination and eliminating the need for costly proprietary strippers.

Fan out and adaptive patterning offers scalability to finer pitch by eliminating capture pad size limitation, mitigates natural variation in die position, and provides superior contact resistance allowing maximum via size on minimum bond pad, while eliminating extra dielectric and metal layers, in turn reducing the cost. Meeting these demands requires lithography materials that combine thickness capability, sharp profile control, and compatibility with widely available exposure tools.

Inherent adoption of this will require thicker copper features with high aspect ratios, which makes resist performance at thicknesses above 50 microns a critical enabler. This is particularly important for vertical copper pillars and vias in 3D stacking, where well defined sidewalls are essential.

KAM offers both negative and positive temporary resists, but current development emphasizes negative tone systems that offer mechanical stability, faster photo speeds, lower operating costs, and better adhesion to most substrates. The new platform demonstrates excellent compatibility with i line and broadband steppers as well as contact aligners, maintaining profile fidelity and resolution across the full thickness range without requiring new lithography infrastructure.

Current positive tone offerings allow patterning and plating up to 40 microns. However, recent development of KAM’s negative temporary resist has demonstrated patterning and plating up to 100 microns with excellent aspect ratio. These advancements directly address critical industry challenges rather than incremental product extension.

The work demonstrates recent R&D advancements in formulation solutions with potential applications in wafer level packaging, such as redistribution layers and copper bump plating. These results also highlight applicability for 3D packaging vertical interconnects, where aspect ratio and thickness performance are key enablers of chiplet and memory on logic architectures.

For instance, the earlier release of the photo patternable TempKoat N provided a product that could be coated in thicknesses ranging from 5 to 15 microns and patterned successfully with a 2:1 aspect ratio, while offering good adhesion to copper and gold, easy removability, and excellent chemical resistance to plating chemistry. Expansion of this product line is focused on coatings from 20 to 75 microns in a single coat and up to 100 microns in a double coat with excellent coat quality. At these thicknesses, the resist maintains sharp sidewall profiles and high-resolution patterning even under contact alignment conditions, making it practical for both legacy and advanced fab environments.

These advancements are made possible by combining new polymer discoveries with advanced formulation strategies. Importantly, these materials can be manufactured without significant changes to current processes and capabilities. Additionally, we prioritize the exclusion of chemicals of concern. All the polymers and formulations discussed here are free from NMP and are 100 percent PFOS/PFOA free. This ensures not only environmental compliance but also long-term process security for manufacturers seeking scalable, high performance temporary plating resist solutions.