Alignment in chromeless masks

Moitreyee Mukherjee-Roy; Navab Singh; Sohan Singh Mehta; Hideki Suda; Takao Kubota; Yasuki Kimura; Hiroshi Kinoshita

doi:10.1117/12.538224

24 May 2004 Alignment in chromeless masks

Moitreyee Mukherjee-Roy, Navab Singh, Sohan Singh Mehta, Hideki Suda, Takao Kubota, Yasuki Kimura, Hiroshi Kinoshita

Proceedings Volume 5375, Metrology, Inspection, and Process Control for Microlithography XVIII; (2004) https://doi.org/10.1117/12.538224
Event: Microlithography 2004, 2004, Santa Clara, California, United States

Abstract

One of the contributions to pattern placement/misalignment may come from the mask making process itself, in chromeless masks. This contribution will be important at 90 nm and smaller nodes. Hence it is necessary to estimate this contribution and find ways to minimize this. In this paper an effort has been made to measure this misalignment accurately. A series of box in box structures for overlay measurement, on KLA and CD SEM, were designed on the reticle. The structures had an outer box of etched chrome and an inner box with 180 degree phase. The edge of the chrome was used as the edge of the outer box. The line printed at the phase intersection was used as the edge of the inner box. Each of these structures were put in with a pre-determined value of X and Y misregistrations. The CD SEM structures were smaller in size but designed the same way as KLA structures. Such structures were put at 4 corners of the die. Overlay measurements were carried out using the optical overlay machine as well as CD SEM. An average misalignment of 11 nm and 1 nm were found in the X and Y directions respectively. When the results from each die corner was analyzed, it was found that the X misalignment had two different distributions. Also, exposure parameters such as focus and partial coherence for best misalignment measurement points were investigated. It is concluded that for obtaining accurate misalignment data, measurements should be conducted at a focus where the two opposite phase edges pattern at similar width. Also, a higher partial coherence is recommended as aberrations such a coma have more profound influence at lower partial coherence and this could contaminate the true misalignment data.

Citation Download Citation

Moitreyee Mukherjee-Roy, Navab Singh, Sohan Singh Mehta, Hideki Suda, Takao Kubota, Yasuki Kimura, and Hiroshi Kinoshita "Alignment in chromeless masks", Proc. SPIE 5375, Metrology, Inspection, and Process Control for Microlithography XVIII, (24 May 2004); https://doi.org/10.1117/12.538224

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KEYWORDS

Scanning electron microscopy

Overlay metrology

Monochromatic aberrations

Optical lithography

Photomasks

Reticles

Etching

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