Focus measurement with a simple pattern design
| Autor: | Hwang-Kuen Lin, Tan Fu Lei, Chin-Yu Ku |
|---|---|
| Rok vydání: | 2008 |
| Předmět: |
Depth of focus
business.industry Bar (music) Scanning electron microscope Computer science Materials Science (miscellaneous) Astigmatism medicine.disease Curvature Industrial and Manufacturing Engineering Tilt (optics) Optics Position (vector) medicine Business and International Management Focus (optics) business Lithography Petzval field curvature |
| Zdroj: | Applied optics. 40(16) |
| ISSN: | 1559-128X |
| Popis: | The increasingly smaller depth of focus of advanced lithographic tools requires that the position of best focus be determined to ensure accuracy and efficiency. We present what we believe is a novel bar in bar that is drawn on a conventional chrome binary mask to translate focal errors into center-to-center shifts of outer and inner bars. An overlay measurement tool can easily measure this shift. A symmetrical center-to-center shift against best focus is created during defocus, and this shift can be well fitted by a second-order polynomial equation. Simply differentiating the fitted equation leads to an accurate and reliable focus value, with a maximum error of less than 0.05 microm. The proposed technique can also be employed to evaluate the tilt, field curvature, and astigmatism of advanced lithographic tools. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
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