Spectroscopic EUV metrology for nanoscale gratings

半导体制造中特征尺寸的不断减小导致对生产过程中使用的计量的需求不断增加。用于确定临界尺寸的纳米级光栅结构的测量是核心任务之一。由于目前使用的红外、可见光和紫外光的光谱测量方法对于非常小的特征尺寸的灵敏度已经达到极限，人们正在探索替代的测量方法。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，这些方法不能提供足够小的测量点，并且只能显示有限的吞吐量。另一方面，在EUV光谱范围内的计量方法有可能克服上述缺点。因此，EUV计量学作为纳米级光栅计量方法的适用性应该在计划的项目中进行理论和实验研究。掠入射角下的光谱EUV反射率将被用于识别不同几何形状(线宽、梯形角)的纳米级光栅的EUV反射率的对比度。为此，将通过严格的电磁绕射模拟进行理论研究。之后，模拟结果将被用于提取光谱范围和照明设置，对于这些范围和照明设置，不同几何形状的光栅之间的对比度特别高。基于这些结果，将制作一组具有相应几何变化的样品。随后，将在申请人现有的光谱EUV反射率测量的实验装置中通过实验确定制作的样品的EUV反射率。在进一步的步骤中，将通过模拟反射率值与实验测量值的迭代拟合，从实验获得的极紫外光反射率值重建光栅的几何参数。最后，将考虑到实际测量的不确定性，并包括实验中无法直接获取的光谱范围和照明设置，来评估纳米级光栅的EUV计量学的理论极限。最后，就半导体制造中未来特征尺寸的适用性与现有的测量方法进行比较。该项目的成功结果将表明，即使对于最小的半导体特征尺寸，极紫外光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不可或缺的一部分。

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.