Method to adjust multilayer film stress induced deformation of optics
First Claim
1. A multilayer reflective optical element, comprising:
- a substrate,a multilayer system of a first composition deposited on the substrate, anda multilayer system of a second composition deposited on the first deposited multilayer system,a switch-over point from the first composition to the second composition being at about one half of a total thickness of an overall multilayer system,each of said multilayer systems having opposite stresses, whereby overall stress on the substrate is near-zero.
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Accused Products
Abstract
Stress compensating systems that reduces/compensates stress in a multilayer without loss in reflectivity, while reducing total film thickness compared to the earlier buffer-layer approach. The stress free multilayer systems contain multilayer systems with two different material combinations of opposite stress, where both systems give good reflectivity at the design wavelengths. The main advantage of the multilayer system design is that stress reduction does not require the deposition of any additional layers, as in the buffer layer approach. If the optical performance of the two systems at the design wavelength differ, the system with the poorer performance is deposited first, and then the system with better performance last, thus forming the top of the multilayer system. The components for the stress reducing layer are chosen among materials that have opposite stress to that of the preferred multilayer reflecting stack and simultaneously have optical constants that allow one to get good reflectivity at the design wavelength. For a wavelength of 13.4 nm, the wavelength presently used for extreme ultraviolet (EUV) lithography, Si and Be have practically the same optical constants, but the Mo/Si multilayer has opposite stress than the Mo/Be multilayer. Multilayer systems of these materials have practically identical reflectivity curves. For example, stress free multilayers can be formed on a substrate using Mo/Be multilayers in the bottom of the stack and Mo/Si multilayers at the top of the stack, with the switch-over point selected to obtain zero stress. In this multilayer system, the switch-over point is at about the half point of the total thickness of the stack, and for the Mo/Be--Mo/Si system, there may be 25 deposition periods Mo/Be to 20 deposition periods Mo/Si.
54 Citations
23 Claims
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1. A multilayer reflective optical element, comprising:
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a substrate, a multilayer system of a first composition deposited on the substrate, and a multilayer system of a second composition deposited on the first deposited multilayer system, a switch-over point from the first composition to the second composition being at about one half of a total thickness of an overall multilayer system, each of said multilayer systems having opposite stresses, whereby overall stress on the substrate is near-zero. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for fabricating a stress compensating system that reduces total multilayer thickness without loss in reflectivity, comprising:
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providing a substrate, depositing on the substrate a multilayer system composed of two different multilayer material combinations having opposite stress; and switching from one of the two multilayer material combinations to another one of the two multilayer material combinations at about one half of the overall thickness of the multilayer material thickness. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
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20. A multilayer reflective element comprising:
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two multilayer systems, one of said two multilayer systems being composed of alternating layers of Mo and Be, another of said two multilayer systems being composed of alternating layers of Mo and Si, said two multilayer systems having opposite stress for reducing the total stress of the reflective element to near zero. - View Dependent Claims (21, 22, 23)
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Specification