Picciotto Carl, Gao Jun, Yu Zhaoning, Wu Wei
Hewlett Packard Labs, Palo Alto, CA 94304, USA.
Nanotechnology. 2009 Jun 24;20(25):255304. doi: 10.1088/0957-4484/20/25/255304. Epub 2009 Jun 2.
We present a low-cost overlay alignment metrology solution for nanoimprint lithography that uses optical microscopy, displacement-sensing algorithms, and specially-designed imprint molds that include shallow alignment marks that are visible to the optical system but do not pattern the wafer. This innovation reduces measurement distances to near zero, the optimal distance for displacement-sensing algorithms, and allows for alignment marks to occupy the same piece of wafer real estate without interfering in any way, thus saving silicon area. Additionally, the method we present does not require the comparison of alignment marks between the wafer and the mold, thus removing process variations as a variable. We fabricate the shallow-mark molds, show that the shallow alignment marks indeed do not leave a mark on the wafer, and, implementing our nDSE (nanoscale displacement sensing and estimation) techniques, we demonstrate nanoscale alignment to a precision of 35 nm, 1-sigma. Given sufficient engineering refinement, we would fully anticipate achieving alignment errors down to the 1 nm range using these methods.
我们提出了一种用于纳米压印光刻的低成本重叠对准计量解决方案，该方案使用光学显微镜、位移传感算法以及专门设计的压印模具，这些模具包含浅对准标记，光学系统可以看到这些标记，但不会在晶圆上形成图案。这一创新将测量距离减小到接近零，这是位移传感算法的最佳距离，并允许对准标记占据同一块晶圆区域而不会产生任何干扰，从而节省了硅面积。此外，我们提出的方法不需要比较晶圆和模具之间的对准标记，从而消除了作为变量的工艺变化。我们制造了浅标记模具，证明浅对准标记确实不会在晶圆上留下痕迹，并且通过实施我们的nDSE（纳米级位移传感和估计）技术，我们展示了精度为35nm（1σ）的纳米级对准。如果进行足够的工程优化，我们完全预期使用这些方法可实现低至1nm范围的对准误差。
