A novel approach to mask defect inspection

Amir Sagiv; Yuri Shirman; Shmoolik Mangan

doi:10.1117/12.802200

17 October 2008 A novel approach to mask defect inspection

Amir Sagiv, Yuri Shirman, Shmoolik Mangan

Proceedings Volume 7122, Photomask Technology 2008; 71223E (2008) https://doi.org/10.1117/12.802200
Event: SPIE Photomask Technology, 2008, Monterey, California, United States

Abstract

Memory chips, now constituting a major part of semiconductor market, posit a special challenge for inspection, as they are generally produced with the smallest half-pitch available with today's technology. This is true, in particular, to photomasks of advanced memory devices, which are at the forefront of the "low-k₁" regime. In this paper we present a novel photomask inspection approach, that is particularly suitable for low-k₁ layers of advanced memory chips, owing to their typical dense and periodic structure. The method we present can produce a very strong signal for small mask defects, by suppression of the modulation of the pattern's image. Unlike dark-field detection, however, here a single diffraction order associated with the pattern generates a constant "gray" background image, that is used for signal enhancement. We define the theoretical basis for the new detection technique, and show, both analytically and numerically, that it can easily achieve a detection line past the printability spec, and that in cases it is at least as sensitive as high-resolution based detection. We also demonstrate this claim experimentally on a customer mask, using the platform of Applied Material's newly released Aera2^TM mask inspection tool. The high sensitivity demonstrates the important and often overlooked concept that resolution is not synonymous with sensitivity. The novel detection method is advantageous in several other aspects, such as the very simple implementation, the high throughput, and the relatively simple pre- and post-processing algorithms required for signal extraction. These features, and in particular the very high sensitivity, make this novel detection method an attractive inspection option for advanced memory devices.

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Amir Sagiv, Yuri Shirman, and Shmoolik Mangan "A novel approach to mask defect inspection", Proc. SPIE 7122, Photomask Technology 2008, 71223E (17 October 2008); https://doi.org/10.1117/12.802200

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KEYWORDS

Inspection

Photomasks

Signal detection

Acquisition tracking and pointing

Airborne remote sensing

Defect detection

Modulation

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