Luigi Scaccabarozzi

Investigation of EUV pellicle feasibility

EUV defectivity has been an important topic of investigation in past years. Today, the absence of a pellicle raises concerns for particle adders on reticle front side. A desire to improve defectivity on reticle front side via implementation of a pellicle could greatly assist in propelling EUV into high volume manufacturing. In this paper, we investigate a set of pellicle requirements and potential EUV pellicle materials. Further, we present experimental results of pellicle performance results and imaging results.

Progress on EUV pellicle development

As EUV approaches high volume manufacturing, reticle defectivity becomes an even more relevant topic for further investigation. Current baseline strategy for EUV defectivity management is to design, build and maintain a clean system without pellicle. In order to secure reticle front side particle adders to an acceptable level for high volume manufacturing, EUV pellicle is being actively investigated. Last year ASML reported on our initial EUV pellicle feasibility. In this paper, we will update on our progress since then. We will also provide an update to pellicle requirements published last year. Further, we present experimental results showing the viability and challenges of potential EUV pellicle materials, including, material properties, imaging capability, scalability and manufacturability.

Particle cleaning of EUV reticles

Due to absorption of EUV light, EUV reticles are not likely to have pellicles for particulate contamination protection, thus even nanosize particles on the reticle could result in fatal defects in every printed die. Consequently, measures must be taken to detect and remove particles above a certain critical size that are deposited on the reticle in the course of its use. In this paper we first present the very stringent requirements that a cleaning technique must satisfy in order to be employed for EUV reticle cleaning. The main challenges consist in the capability of removing very small particles (sub-100 nm), in principle of any type (organic/inorganic) and without damage to the reticle. We then focus on two of the techniques that we are investigating, laser shockwave cleaning (LSC) and high voltage cleaning (HVC). Both of them are dry techniques, which is a necessary requirement in view of their potential integration in the lithography tool. We finally present cleaning and damage tests results, including cleaning of 40-nm polystyrene-latex (PSL) spheres on large areas.

Grid-supported EUV pellicles: A theoretical investigation for added value

EUV pellicle membranes are being pursued to protect scanner images from repeating defects caused by reticle fall-on particle defects. Because most materials highly absorb EUV, pellicle membranes must be ultrathin. In an attempt to increase the strength of the ultrathin membranes, grid-supported pellicle membranes have been proposed. In this study we compare grid-supported pellicles (GSP) over free-standing pellicles (FSP). We considered imaging, thermal, mechanical, and thermo-mechanical characteristics. Finite Element Methods (FEM) was used to investigate the thermal, and (thermo-)mechanical behavior of pellicles. The maximum temperature reached under operational conditions by the pellicle film was determined. Using a thermo-mechanical analysis wrinkling behavior was quantified. The mechanical analysis considered the influence of grid structures on the sagging behavior, on crack propagation, on the pellicle film resistance to collision with solid particles, and on the resistance to shocks on the pellicle frame. The analysis shows that GSP that meets imaging requirements will not bring any advantages over FSP.