The shrink of semiconductor fabrication ground rule continues to follow Moore's law over the past years. However, at the 100 nfl node, the fabrication cost starts to rise rapidly. This is mainly due to the increase of complexity in the fabrication process, including the use of hard masks, planarization, resolution enhancement techniques, etc. Smaller device sizes require higher alignment tolerances. Also, higher degree of complexity makes alignment detection more difficult. For example, planarization techniques may destroy mark topography; hard masks may optically bury alignment marks; and more film layers makes the alignment signal more susceptible to process variations. Therefore, in order to achieve reliable alignment, it is absolutely critical to develop an accurate and fast simulation software that can characterize alignment performance based on the film stack structure. In this paper, we will demonstrate that we have built an extremely fast alignment signal simulator for both direct imaging and diffractive detection systems based on simple optical theory. We will demonstrate through examples using our advanced DRAM products that it is capable of accurately mapping the multi-dimensional parameter space spanned by various film thickness parameters within a short period of time, which allows both on-the-fly feedback in alignment performance and alignment optimization.
The impact of alignment mark structure, mark geometry, and stepper alignment optical system on mark signal contrast was investigated using computer simulation. Several sub-wavelength poiy silicon recessed film stack alignment targets of advanced memory products were studied. Simulated alignment mark signals for both darkfield and bright-field systems using the rigorous electromagnetic simulation program TEMPEST showed excellent agreement with experimental data. For a dark-field alignment system, the critIcal parameters affecting signal contrast were found to be mark size and mark recess depth below silicon surface. On the other hand, film stack thickness and mark recess depth below/above silicon surface are the important parameters for a bright-field alignment system. From observed simulation results optimal process parameters are determined. Based on the simulation results some signal enhancement techniques will be discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.