High throughput grating qualification of directed self-assembly patterns using optical metrology

• We present an optical metrology technique to quantify grating quality.
• We inspect 14 nm half-pitch directed self-assembly (DSA) line/space gratings.
• The optical technique is automated, non-destructive and over 20× faster than SEM.
• Process windows are in excellent agreement between the optical technique and SEM.
• The optical grating qualification also has resolution right after phase separation.

Directed self-assembly (DSA) of block copolymers (BCP) is a bottom-up patterning technique that can be used to achieve frequency multiplication of optical lithography patterns. As such, DSA could be used to provide the necessary pitch reduction for future semi-conductor manufacturing nodes.In DSA, the figure of merit for setting up and optimizing a process is not CD (critical dimension), as is done in traditional optical lithography, but rather the degree of order of the self-assembled structures that can be achieved. Top-down scanning electron microscopy (SEM) is widely used to obtain the images for the pattern quality inspection, but the data processing is labor-intensive and time-consuming.In this paper we present an optical scatterometer-based metrology technique to quantify the degree of order of line/space patterns formed by DSA, before and after the last step, in which the PMMA block is removed. In a fast and automated way, this technique assigns a grating qualification score based on the light diffracted by the DSA grating. In contrast to scatterometry, this optical technique does not require any model or reconstruction. It has the advantage of measuring at very high throughput with a large spot size, thus collecting more statistical information than with SEM. It also has fast and automated data processing capabilities.We determine the performance of the novel technique for DSA process and material optimizations and anchor the results to the SEM analysis. We obtain excellent agreement between the process windows determined with this optical technique and SEM, taking care, however, to correctly normalize the optical grating qualification score.Therefore, the optical technique is useful for a fast comparison of closely related processes, and is ideally suited for process optimizations, material selections, and monitoring purposes.

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