A Groundbreaking First: China’s New Advance within the Semiconductor Area

Lithography is a core driver behind the continual miniaturization of built-in circuit chip manufacturing processes.

Lately, a staff led by Professor Hailin Peng from the Faculty of Chemistry and Molecular Engineering at Peking College, in collaboration with different researchers, has achieved a big breakthrough. For the primary time, they used cryo-electron tomography (cryo-ET) to resolve the microscopic 3D construction, interface distribution, and entanglement conduct of photoresist molecules of their native liquid state. This pivotal discovery has guided the event of an industrial resolution that considerably reduces lithography defects. The associated findings have been revealed in Nature Communications.

“Growth,” an important step in lithography, includes utilizing a developer to dissolve the uncovered areas of the photoresist, exactly transferring the circuit sample onto the silicon wafer. The motion of photoresist within the developer instantly determines the accuracy and high quality of this “circuit drawing,” finally impacting chip yield.
Traditionally, the microscopic conduct of photoresist throughout improvement has been a “black field,” forcing the trade to depend on repetitive trial-and-error for course of optimization—a serious bottleneck for bettering yields on the 7nm node and past.

To deal with this, the staff pioneered the appliance of cryo-ET in semiconductor analysis. After customary lithography publicity on a wafer, they quickly extracted a pattern of the developer containing photoresist polymers onto an EM grid. This pattern was then vitrified inside milliseconds, “freezing” the photoresist in its true liquid state.

Subsequently, researchers tilted the frozen pattern contained in the cryo-electron microscope, accumulating a collection of 2D projection photos from completely different angles. Utilizing computational 3D reconstruction algorithms, they merged these photos right into a high-resolution 3D visualization with a decision higher than 5 nanometers. This methodology concurrently overcomes the three main limitations of conventional methods: the lack to carry out in-situ, three-dimensional, high-resolution remark.

This method led to a number of important discoveries. As corresponding creator Professor Yiqin Gao defined, whereas it was beforehand assumed that dissolved photoresist polymers have been dispersed inside the liquid bulk, the 3D photos revealed they primarily adsorb on the air-liquid interface. The staff additionally instantly noticed “cohesive entanglement” of those polymers, held collectively by weak forces or hydrophobic interactions. Moreover, polymers at this interface have been extra susceptible to entanglement, forming aggregated clusters averaging about 30nm in dimension. These clusters are potential defect sources, as they will deposit onto intricate circuit patterns, inflicting unintended connections.

The staff proposed two sensible options to manage entanglement: optimally rising the post-exposure bake temperature to suppress polymer entanglement and cut back massive aggregates, and optimizing the event course of to take care of a steady liquid movie on the wafer floor, serving to to clean away polymers and stop deposition. Combining these methods efficiently eradicated sample defects attributable to photoresist residue on 12-inch wafers, decreasing defect counts by over 99%.

Professor Peng highlighted that cryo-ET offers a robust software for resolving varied liquid-phase interfacial reactions on the atomic/molecular scale. A deeper understanding of polymer construction and conduct in liquids can advance defect management and yield enchancment in important processes like lithography, etching, and moist cleansing for superior manufacturing nodes.