Mask inspection

About: Mask inspection is a research topic. Over the lifetime, 1072 publications have been published within this topic receiving 8696 citations.

Reversible photobleachable materials based on nano-sized semiconductor particles and their optical applications

Abstract: Semiconductor nano-particles, due to their specific physical properties, can be used as reversible photo-bleachable materials for a wide spectrum, from far infrared to deep UV. Applications include, reversible contrast enhancement layer (R-CEL) in optical lithography, lithography mask inspection and writing and optical storage technologies.

Wafer inspection as alternative approach to mask defect qualification

Abstract: Defect inspection is one of the major challenges in the manufacturing process of photomasks. The absence of any printing defect on patterned mask is an ultimate requirement for the mask shop, and an increasing effort is spent in order to detect and subsequently eliminate these defects. Current DUV inspection tools use wavelengths five times or more larger than the critical defect size on advanced photomasks. This makes the inspectability of high-end mask patterns (including strong OPC and small SRAF's) and sufficient defect sensitivity a real challenge. The paper evaluates the feasibility of inspecting the printed wafer as an alternative way for the high-sensitivity defect inspection of photomasks. Defects originating in the mask can efficiently be filtered as repeated defects in the various dies on wafer. Using a programmed-defect mask of 65-nm technology, a reliable detection of the printing defects was achieved with an optimized inspection process. These defects could successfully be traced back to the photomask in a semi-automated process in order to enable a following repair step. This study shows that wafer inspection is able to provide a full defect qualification of advanced photomasks with the specific advantage of assessing the actual printability of arbitrary defects.

Development of automated contact inspection system using in-line CD SEM

Abstract: We have developed an automated contact inspection system using an in-line CD SEM and applied it to monitor contact etching processes. As the design rule shrinks, monitoring of the contact etching, which cannot be detected by the conventional optical inspection systems, are becoming one of the most critical issues in semiconductor processing. Though there are e-beam based inspection systems or manual inspection sequence with in-line SEM (Scanning Electron Microscope), monitoring small and electrical defects has a few fundamental limitations. E-beam inspection systems have low throughput and a high price as a mass production tool. In the case of the manual inspection system, the inspection result depends on the operator and it is difficult to quantify the defect data. We have developed an automated contact inspection system to overcome these limitations. The system is composed of a data processing system and an in-line SEM. The automated in-line SEM inspects and stores the images of specified points on the wafer. The data processing system receives and manipulates the images to indicate the etching problem. It was shown that the scanning electron image of the contact is related to failures such as insufficient etching or residuals inside the contact.

Investigation of EUV mask defectivity via full-field printing and inspection on wafer

Abstract: Full-field printing on the ASML Alpha Demo Tool, followed by wafer inspection on a KLA-T 2800, is used to qualify typical defectivity levels of EUV reticles. Mask defects are found as repeaters among multiple dies on wafer. The uniform pattern consists of dense lines and spaces. In a first reticle with 40nm linewidth, high levels of natural defects have been found of which a relatively large share was considered as multilayer (ML) type defects, because they printed as rings. Simulation of ML defects could explain this printing behavior as a function of height, size and slope. The main parameter determining the printing behavior of a ML defect is its height. A local distortion of the upper part of the ML, as thin as ~2nm can already print. On-reticle analysis of the ring defects by SEM showed that the defects are present on the absorber, which already explains the printing result. Yet, still several other defects were found to print on the wafer, whereas they were not visible on the reticle and considered local distortions of the ML. Printing results with a second version of the mask that additionally includes programmed multilayer defects with 3nm height confirmed the pronounced printing impact of ML defects as they were simulated. Encouragingly low numbers of natural defects have been found on a third reticle. With this reticle also a first correlation has become possible between the defect maps obtained from wafer inspection, (direct) mask inspection, and blank inspection. This is a viable method to highlight potential gaps between the capability of these tools and printability of defects.

Method and apparatus to accurately correlate defect coordinates between photomask inspection and repair systems

Abstract: A method and apparatus for calibrating the coordinate systems of photomask processing machines improves processing efficiency and the quality of resulting photomasks. A test pattern is printed on an unproductive area of the photomask. The test pattern is used to calibrate the coordinate system of each processing machine on which the photomask is mounted. Using the test pattern as a common reference point enables points located using one processing machine to be quickly and accurately found on a second processing machine. The test pattern is also used as a reference for other metrology measurements.