EUV mask black border evolution

Abstract

The black border is a frame created by removing all the multilayers on the EUV mask in the region around the chip. It is created to prevent exposure of adjacent fields when printing an EUV mask on a wafer. Papers have documented its effectiveness [1] . As the technology transitions into manufacturing, the black border must be optimized from the initial mask making process through its life. In this work, the black border is evaluated in three stages: the black border during fabrication, the final sidewall profile, and extended lifetime studies.This work evaluates the black border through simulations and physical experiments. The simulations address concerns for defects and sidewall profiles. The physical experiments test the current black border process. Three masks are used: one mask to test how black border affects the image placement of features on mask and two masks to test how the multilayers change through extended cleans. Data incorporated in this study includes: registration, reflectivity, multilayer structure images and simulated wafer effects.By evaluating the black border from both a mask making perspective and a lifetime perspective, we are able to characterize how the structure evolves. The mask data and simulations together predict the performance of the black border and its ability to maintain critical dimensions on wafer. In this paper we explore what mask changes occur and how they will affect mask use.

Evaluation of multilayer defect repair viability and protection techniques for extreme ultraviolet masks

“…The degradation also showed the etching of molybdenum, as comb-like silicon fingers can be seen in the middle of side wall, consistent with past observations. 16 The repaired site with treatment [ Fig. 9(b)] showed reduced degradation as compared to the untreated result.…”

“…In particular, exposed multilayer sidewalls have been shown to significantly degrade after several mask cleans. 16 In order to quantify any potential imaging impact from cleans, a variety of repairs, guided by rigorous three-dimensional (3-D) electromagnetic field (EMF) simulations, were performed on the EUV multilayer, and actinic aerial image critical dimensions (CDs) before and after cleans were experimentally measured and compared. Several protection methodologies were experimentally evaluated to quantify their effectiveness in preventing degradation from cleans.…”

Overview of stitching for high NA: imaging and overlay experimental and simulation results

“…From this cross-section, we see a straight profile of the ML wall with a small undercut which can be estimated as <10 nm on mask. From publications we know that the ML wall in the black border trench can be impacted by mask cleaning [7], say, max 20 nm per 25 mask cleans as follows from this publication of 2014. We can assume that there have been improvements in mask cleaning and thus, the impact has become less.…”

Impact of thermal expansion coefficient on the local tilt angle of extreme ultraviolet pellicle

“…(3). Wrinkles within 3 mm of the border were excluded as they did not affect the imaging performance owing to the black border of the mask, 40 and the modeled wrinkle profiles were plotted as a 10 mm × 100 mm XY-plane contour graph with a grid size of 100 μm.…”