To date, the semiconductor manufacturing industry has relied on optical lithography to enable the scaling of devices to ever smaller dimensions. Developers use extreme UV lithography to print very small features, but this technology has suffered numerous technical delays and is still not feasible for high-volume manufacturing. The industry is therefore pursuing new schemes, such as multiple patterning, that are intended to improve 193nm immersion lithography (the technique that uses a liquid with a relatively high refractive index to enhance resolution). These approaches have enabled successful fabrication of features smaller than the resolution limit of the 193nm immersion tools. However, their drawbacks are increased process complexities and higher costs. One potentially lower-cost alternative for generating smaller structures is the directed self-assembly (DSA) of block copolymers (BCPs),where a BCP is deposited and aligned and one block is removed to form a pattern.
DSA of BCPs is a promising technology for extending semiconductor device scaling. Lam Research Corporation have fabricated BCP structures down to 5nm, in part by understanding how these materials interact with different RIE plasmas. future work will focus on integrating select silicon-containing BCPs into DSA flows and also studying how different plasma processes affect pattern roughness.
Scanning electron microscope (SEM) image of a cross-section of self-assembled poly(styrene-block-methyl methacrylate) (PS-b-PMMA) with 21nm domains prior to PMMA removal (a) and post reactive ion etch (RIE) removal of PMMA domains (b). Minimal mask loss of polystyrene was observed.
Figure 2. Tilted SEM image of poly(styrene-block-4-pentamethyldisilylstyrene) (PS-b-PDSS) with 10nm domains. Polystyrene domains were removed with carbon dioxide (CO2) RIE plasma.