| US 7,482,102 B2 | ||
| Photomask having a monitoring pattern with an asymmetrical diffraction grating that includes semi-transparent probing-phase shifters | ||
| Takashi Sato, Kanagawa (Japan); and Takashi Sakamoto, Kanagawa (Japan) | ||
| Assigned to Kabushiki Kaisha Toshiba, Tokyo (Japan) | ||
| Filed on Aug. 27, 2004, as Appl. No. 10/927,320. | ||
| Claims priority of application No. 2003-303479 (JP), filed on Aug. 27, 2003. | ||
| Prior Publication US 2005/0112475 A1, May 26, 2005 | ||
| Int. Cl. G03F 1/00 (2006.01); G03F 1/14 (2006.01) | ||
| U.S. Cl. 430—5 | 13 Claims |
| 1. A photomask having a monitoring pattern configured to obtain information required for adjusting an optical system of a
projection lithography tool, the monitoring pattern comprising:
a mask substrate; and
a first asymmetrical diffraction grating delineated on the mask substrate, configured to generate a positive first order diffracted
light and a negative first order diffracted light in different diffraction efficiencies, the first asymmetrical diffraction
grating including:
a plurality of first probing-phase shifters formed of semi-transparent material, disposed periodically on the mask substrate
in parallel, each of the first probing-phase shifters is implemented by a first asymmetrically recessed ridge having a geometry
defined by:
a strip-shaped first entrance face contacting with the mask substrate, extending along the longitudinal direction of the first
asymmetrically recessed ridge,
a strip-shaped first exit face opposite to the first entrance face implemented by a top surface of a lower step of the first
asymmetrically recessed ridge, the lower step being displaced on one side of the first asymmetrically recessed ridge in a
plan view, extending along the longitudinal direction, and
a strip-shaped first light-shielding face implemented by a top surface of an upper step of the first asymmetrically recessed
ridge, the upper step has a higher horizontal level than the lower step, the upper step being adjacent to the lower step and
displaced on another side of the first asymmetrically recessed ridge in a plan view, extending along the longitudinal direction;
and
an opaque strip disposed on the first light-shielding face for each of the first probing-phase shifters,
wherein a phase difference between the light transmitting through the first probing-phase shifters and the light not transmitting
through the first probing-phase shifters is an integer multiple of a value larger than zero degrees and lower than 180 degrees,
and a width of the first exit face measured perpendicular to the longitudinal direction is 1/R times an interval between the
first probing-phase shifters, where R is an attenuation constant of the light leaving from the first exit face, after the
light propagates through each of the first probing-phase shifters.
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