Lithography
In directed self-assembly (DSA), what mainly determines the period of the stripes that a block copolymer forms on its own?
- AThe molecular length (molecular weight) of the block copolymer
- BThe wavelength of the exposure tool
- CThe resist development time
Show answer and explanation
Answer: A. The molecular length (molecular weight) of the block copolymer
A block copolymer joins chains of two different polymers end to end. On annealing, the two blocks try to separate but, being joined, cannot separate far, so they form a pattern whose period is set by the molecular length. The period can be tuned by molecular weight, and how fine it can go depends on the χ parameter, which expresses how strongly the blocks separate. In directed self-assembly (DSA), guides made by lithography align the pattern's position and orientation.
- A. Correct. The size of the molecules sets the period.
- B. The wavelength sets the resolution of the guides, not the stripe period.
- C. The self-assembly period is not set by development conditions.