US 7,492,510 B2
Optical element having antireflection film, and exposure apparatus
Seiji Kuwabara, Utsunomiya (Japan)
Assigned to Canon Kabushiki Kaisha, Tokyo (Japan)
Filed on Nov. 08, 2006, as Appl. No. 11/557,573.
Claims priority of application No. 2005-325307 (JP), filed on Nov. 09, 2005.
Prior Publication US 2007/0103769 A1, May 10, 2007
Int. Cl. G02B 5/20 (2006.01)
U.S. Cl. 359—359  [359/580; 359/586; 355/71] 8 Claims
OG exemplary drawing
 
1. An optical element comprising:
a substrate that transmits a light having a central wavelength in a wave range between 150 nm and 250 nm; and
an n-layer antireflection film that is formed on the substrate, and includes, from said substrate, an n−2-th layer made of a high refractive index material, an n−1-th layer made of an amorphous material containing AlF3, and an n-th layer made of a low refractive index material, each of the high and low refractive index materials containing a crystalline material, wherein n is an integer greater than or equal to 4.