基于Mueller矩阵椭偏仪的纳米压印模板与光刻胶光栅结构准确测量

摘要

在纳米压印工艺中，对模板和压印结构的几何参数进行快速、低成本、非破坏性地准确测量具有非常重要的意义。与传统光谱椭偏仪只能改变波长和入射角2个测量条件并且在每一组测量条件下只能获得振幅比和相位差2个测量参数相比， Mueller矩阵椭偏仪可以改变波长、入射角和方位角3个测量条件，而且在每一组测量条件下都可以获得一个4×4阶Mueller矩阵共16个参数，因此可以获得更为丰富的测量信息。通过选择合适的测量条件配置，充分利用Mueller矩阵中的测量信息，有望实现更为准确的纳米结构测量。基于此，本文利用自主研制的Mueller矩阵椭偏仪对硅基光栅模板和纳米压印光刻胶光栅结构进行了测量。实验结果表明，通过对Mueller矩阵椭偏仪进行测量条件优化配置，并且在光学特性建模时考虑测量过程中出现的退偏效应，可以实现压印工艺中纳米结构线宽、线高、侧壁角以及残胶厚度等几何参数更为准确的测量，同时对于纳米压印光刻胶光栅结构还可以直接得到光斑照射区域内残胶厚度的不均匀性参数。%In order to control nanoimprint lithography (NIL) processes for achieving good fidelity, the fast, low-cost, non-destructive and accurate measurement of geometric parameters of templates and imprinted grating structures is of great importance. Compared with conventional ellipsometric scatterometry, which only obtains two ellipsometric angles and has 2 changeable measurement conditions, i.e., the wavelength and the incidence angle, Mueller matrix ellipsometry (MME) can provide up to 16 quantities of a 4 × 4 Mueller matrix in each measurement with 3 changeable measurement conditions, i.e., the wavelength, the incidence angle and the azimuthal angle. Therefore, MME can acquire much more useful information about the sample. It is expected that much more accurate measurements of nanostructures can be achieved by choosing proper measurement configurations and completely using the rich information hidden in the measured Mueller matrices. Accordingly, the templates and imprinted grating structures in NIL processes are measured using an in-house developed Mueller matrix ellipsometer. We experimentally demonstrate that more accurate quantification of geometric parameters, such as line width, line height, sidewall angle and residual layer thickness, can be achieved by performing MME measurements in the optimal configuration and meanwhile by incorporating depolarization effects into the optical model. Moreover, as for the imprinted grating structures, the residual layer thickness variation over the illumination spot can also be directly determined by MME. The comparison between MME-extracted template and imprinted resist profiles also indicates an excellent fidelity of the nanoimprint pattern transfer process.