Spectroscopic EUV metrology for nanoscale gratings

半导体制造中不断减小的特征尺寸导致对生产过程中使用的计量的需求不断增加。纳米尺度光栅结构的关键尺寸测量是其核心任务之一，由于目前使用的红外、可见光和紫外光谱测量方法对极小特征尺寸的灵敏度已经达到极限，因此正在探索替代测量方法。特别是使用X射线的计量方法在过去几年中得到了广泛的测试。然而，这些不能提供足够小的测量点，并且仅展示有限的吞吐量。另一方面，EUV光谱范围内的计量方法具有克服上述缺点的潜力。因此，极紫外计量作为纳米级光栅计量方法的适用性应在计划的项目中进行理论和实验研究。在掠入射角下的光谱极紫外反射测量将用于确定不同几何形状（线宽，梯形角）的纳米级光栅的极紫外反射率的对比。为此，将通过严格的电磁衍射模拟进行理论研究。之后，模拟结果将用于提取光谱范围和照明设置，对于这些光谱范围和照明设置，不同几何形状的光栅之间的对比度将特别高。基于这些结果，将制造一组具有相关几何形状变化的样品。随后，将在申请人现有的用于光谱EUV反射计的实验装置中通过实验确定所制造的样品的EUV反射率。在进一步的步骤中，光栅几何参数将通过模拟反射率值与实验测量反射率值的迭代拟合从实验获取的EUV反射率值重建。最后，将评估纳米级光栅的EUV计量的理论极限，考虑到真实的测量不确定性，并包括光谱范围和照明设置，在实验中不能直接访问。最后，与现有的测量方法进行了比较，以确定其在未来半导体制造中的应用前景。该项目的成功结果表明，即使是最小的半导体特征尺寸，EUV测量也具有必要的灵敏度。因此，EUV计量可以成为未来半导体制造中质量保证和工艺控制的组成部分。

Constantly decreasing feature sizes in semiconductor manufacturing lead to increasing demands on the metrology used in the production process. The metrology of nanoscale grating structures for the determination of the critical dimension is one of the core tasks.Since currently used spectroscopic metrology methods using infrared, visible and ultraviolet light are reaching their limits with respect to the sensitivity to very small feature sizes, alternative metrology methods are being explored. Especially metrology methods using X-rays have been extensively tested over the last years. However, these do not provide sufficiently small measuring spots and demonstrate only limited throughput. Metrology methods in the EUV spectral range, on the other hand, have the potential to overcome the mentioned disadvantages. The applicability of EUV metrology as a metrology method for nanoscale gratings should therefore be theoretically and experimentally investigated within the planned project.Spectroscopic EUV reflectometry at grazing angles of incidence will be used to identify contrasts in EUV reflectance of nanoscale gratings of different geometries (line width, trapezoidal angle). For this purpose, theoretical investigations will be carried out by means of rigorous electromagnetic diffraction simulations. After that, the simulation results will be used to extract spectral ranges and illumination settings for which particularly high contrasts between gratings of different geometries are expected. Based on these results, a set of samples with relevant geometry variations will be fabricated. Subsequently, the EUV reflectance of the fabricated samples will be determined experimentally in the applicant’s existing experimental setup for spectroscopic EUV reflectometry. In a further step, the grating geometry parameters will be reconstructed from the experimentally acquired EUV reflectance values by an iterative fit of simulated reflectance values to the experimentally measured ones. Conclusively, the theoretical limits of EUV metrology for nanoscale gratings will be evaluated, taking into account real measurement uncertainties, and including spectral ranges and illumination settings that are not directly accessible in the experiment. Finally, a comparison to the already existing metrology methods will be made with respect to the applicability to future feature sizes in semiconductor manufacturing.A successful outcome of the project will show that EUV metrology has the necessary sensitivity even for the smallest semiconductor feature sizes. EUV metrology can thus become an integral part of quality assurance and process control in future semiconductor manufacturing.