(5bm) Single Molecule Chemically Amplified Photoresists for Nanolithography

The shrinking of feature sizes in microelectronics is the primary driving force for smaller, faster, more powerful, more energy efficient computers and electronics. The critical enabling factor for the reduction in feature size is advances in photolithography, the process wherein well-defined areas are patterned onto a semiconductor substrate. Current state-of-the-art semiconductor manufacturing prints features as small as 45 nm. To continue shrinking feature sizes toward the molecular scale, multiple improvements must be made in photoresists.

Our design approach for next generation chemically amplified photoresists is termed single molecule resists. The name does not imply that the entire resist film is made of a single molecule, but rather that the film is composed of multiple copies of a single molecule that contains all the functionality desired in a chemically amplified resist. This differs radically from conventional photoresists which are composed of blends of polydisperse co-polymers, small molecule photoacid generators (PAGs), and small molecule base quenchers. Single molecule resists combine the advantages of multiple types of resists and have additional unique advantages. Since they are small molecules instead of polymers, they are purely monodisperse, can be made with full synthetic control of stereochemistry and regiochemistry, and have much smaller molecular size relative to the features being printed. Additionally, since there are no physically blended additives, this approach allows for a molecularly homogeneous resist.

We have taken a combined experimental/modeling approach in the design and synthesis of single molecule resists. Mesoscale modeling of the lithographic process suggests that using very high PAG loading, such as in our system, provides the best combination of resolution, sensitivity, and pattern fidelity. The modeling also shows the trade-off between photoacid diffusion length and number of protecting groups which directs synthetic design for performance. Experimentally, multiple different families of single molecule resists have been designed, synthesized, and exercised lithographically. Results have shown that resolution can be maintained and even improved by this approach, while providing significant enhancement in pattern fidelity. Two completely different single molecule designs have shown a line-edge-roughness of 3.9 nm, a significant improvement over the limit of 5 nm found in conventional designs. The single molecule resist approach shows great promise to provide a path forward in photoresist design, leading to ever smaller and faster integrated circuits.