SAN FRANCISCO - During the International Electron Device Meeting (IEDM) here, Applied Materials Inc. and Stanford University said that they have demonstrated block copolymer lithography-or self-assembly-in the lab.
Block copolymer lithography is capable of realizing feature sizes and pitches beyond access of incumbent optical lithography. Directed self-assembly uses lithographically defined pre-patterns to guide the formation of self-assembled features so that the pre-pattern is subdivided in a precise way.
''CMOS devices and circuits featuring block copolymer patterned 18-nm contact holes were demonstrated at IEDM '09,'' according to a paper from Applied and Stanford.
''In this paper, we experimentally demonstrate a new paradigm: the use of guiding templates close to the natural length scale of the block copolymer can effectively control the size, shape, and pitch of the self-assembled features for random logic circuit layouts,'' according to the paper. ''An example of a 22 nm SRAM contact hole layout using block copolymer lithography is presented.''
According to the paper, the process is based on a graphoepitaxy process. ''It uses a physical confinement such as a small topography (e.g. 40 nm) on a wafer. Graphoepitaxy is an interplay of the surface-block interaction and phase separation force of the block copolymers,'' according to the paper.
''When the block copolymer is confined within a trench, the composition fluctuation first occurs at the trench boundaries, then the phase separation gradually extends toward the center of the trench promoting defect-free, long range ordering,'' according to the paper.
''This surface-block interaction, which is an additional driving force for the microphase separation that results in regular periodic patterns in the absence of other driving forces, direct the self-assembled features to form in desired, aperiodic locations,'' according to the the paper.
''When graphoepitaxy is applied in this manner, it can be viewed as an extension of double exposure combining a coarse optical and a fine self-assembly lithography. However, directed self-assembly does not require a second mask as double exposure does. Herein a diblock copolymer of PS-b-PMMA is dissolved in PGMEA to make 0.5 wt% solutions. The natural size of the self-assembled hexagonally close-packed holes is 18 nm in diameter with 42 nm center to center distances,'' it added.