Mask inspection

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

Illumination control in lensless imaging for EUV mask inspection and review

Abstract: Coherence control and flexible pupil fill play a key role in the imaging of EUV reticles. This is also true for lensless metrology applications based on coherent diffraction imaging. We describe the concept and the key components of a Fourier synthesis illuminator designed to provide the RESCAN microscope with flexible illumination capabilities and to improve its resolution limit. In particular, we discuss the characteristics of the three mirrors of the new illuminator and the requirements for their multilayer coating.

MEEF-based mask inspection

Abstract: Mask making yield is seriously affected by un-repairable mask defects. Up to now, there is only one size specification for critical defects, which has to be applied to any defect found. Since recently, some mask inspection tools offer the capability to inspect different features on one mask with different sensitivity. Boolean operations can be used to segregate mask features into more and less critical. In this paper we show the MEEF (Mask Error Enhancement Factor), which determines from the mask / wafer pattern transfer the actual effectiveness of mask errors, as an objective and relatively easily determinable parameter to assess the printability of mask defects. Performing OPC, a model-based OPC tool is aware of the MEEF, and can also provide the capability for the additional information handling, which is needed to supply the mask maker with a set of data layers of different defect printability for one mask layer.

X-Ray Mask Inspection Using Replicated Resist Patterns

Abstract: A new X-ray mask inspection method using replicated resist patterns is proposed. It is able to detect fatal opaque defects on the back surface of the mask and at the bottom of the hole pattern, in addition to those on the front surface. It can also ignore transparent defects on the mask. This method is useful even for defect detection on a single-die mask through die-to-die comparison. For the false process defects occurring during the replication process, a discrimination procedure using a 2-step die-to-die comparison is proposed. In inspection tests with SEMSpec, we investigate the relation between the detection sensitivity to small resist defects and the conductive-coating thickness on them.

Aerial image based mask defect detection in dense array structures

Abstract: For leading mask technologies the mask inspection for finding critical defects is always a difficult task. With the introduction of chrome-less, high-transmission and alternating mask types, new absorber material and the possibility of quartz defects the defect inspection and -classification becomes even more challenging. To decide whether a defect is critical or a repair is successful, the Zeiss AIMS tool is used to classify defects. For conventional imaging the optical settings are usually chosen such that resolution is maximized, for example a dipole illumination is used for imaging a dense line-space array at an optimum contrast. In this paper we will do the opposite and reduce the optical resolution, such that we can filter out the array pattern and study the resulting defect image. This technique allows using a simple threshold detector to find and classify defects.

AIMS D2DB simulation for DUV and EUV mask inspection

Abstract: AIMS™ Die-to-Die (D2D) is widely used in checking the wafer printability of mask defects for DUV lithography. Two AIMS images, a reference and a defect image, are captured and compared with differences larger than certain tolerances identified as real defects. Since two AIMS images are needed, and since AIMS system time is precious, it is desirable to save image search and capture time by simulating reference images from the OPC mask pattern and AIMS optics. This approach is called Die-to-Database (D2DB). Another reason that D2DB is desirable is in single die mask, where the reference image from another die does not exist. This paper presents our approach to simulate AIMS optics and mask 3D effects. Unlike OPC model, whose major concern is predicting printed CD, AIMS D2DB model must produce simulated images that match measured images across the image field. This requires a careful modeling of all effects that impact the final image quality. We present a vector-diffraction theory that is based on solid theoretical foundations and a general formulation of mask model that are applicable to both rigorous Maxwell solver and empirical model that can capture the mask 3D-effects. We demonstrated the validity of our approach by comparing our simulated image with AIMS machine measured images. We also briefly discuss the necessary changes needed to model EUV optics. Simulation is particularly useful while the industry waits for an actinic EUV-AIMS tool.