Coating apparatus – Work holders – or handling devices
Reexamination Certificate
1998-09-30
2001-03-27
Crispino, Richard (Department: 1734)
Coating apparatus
Work holders, or handling devices
Reexamination Certificate
active
06206966
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to optical substrates, particularly to optical substrates that contain coated reflective optics, and more particularly to a pedestal type optical substrate that maintains acceptable figure before or after coating, is not sensitive to mount disturbance loads, and demonstrates high dynamic stiffness.
Optics for extreme ultraviolet (EUV) lithography imaging systems, for example, require coated reflective optics that are precisely figured at the angstrom level. In such reflective optics, the optical substrates are first figured, then coated with a film of material that is reflective in the ultraviolet wavelengths. Unfortunately, the coated film has a residual stress that causes the substrate to deform from its desired figure. It has been shown that for a disk-like optical substrate, the nonspherical component of the figure distortion decreases as the aspect ratio (width divided by height) of the substrate increases. Thus, while thinner substrates deform more due to the coating, the deformation is primarily spherical. In many cases an imaging system is relatively insensitive to spherical changes in an individual optic. Thus, a thinner substrate reduces the negative effect of coating residual stress.
The coated optics must be assembled into the imaging system using some form of mechanical attachment. The mechanical attachment, referred to as the optical mount, must physically attach to the substrate. This attachment provides a mechanism through which undesired figure distorting forces and moment can be applied to the substrate. There are many sources of these disturbance inputs, including system temperature changes, distortion of their imaging system structure, and residual stress due to the mounting process. The sensitivity of the optics surface figure is directly related to the mechanical stiffness of the substrate. An infinitely stiff substrate would not deform due to these inputs. A realistic, disk-like substrate will always demonstrate a level of sensitivity to these mount induced disturbance loads. The lower the aspect ratio of a disk-like substrate, the lower the optic's sensitivity to disturbance loads. Thus, a thicker substrate reduces the sensitivity of a substrate to disturbance loads.
Frequently, there is a requirement that an optical substrate demonstrates a high degree of dynamic stiffness. A low aspect ratio substrate generally provides for more favorable (higher) dynamic stiffness.
The problem is that while a thinner substrate reduces negative coating effects, it may not provide the necessary stiffness and insensitivity to mount disturbances. The present invention, which involves a pedestal substrate, addressees the need to have an optical substrate that maintains acceptable figure before or after coating, is not sensitive to mount disturbance loads, and demonstrates high dynamic stiffness. The pedestal substrate of the present invention comprises the basic components: 1) a disk-like optic or substrate section, the top surface of which is to be coated with reflective material, 2) a disk-like base section, and 3) a connecting section between the base and optic or substrate sections. These three sections may be formed as a monolith from a solid piece of material, the optic or substrate section and the connecting section may be formed from a solid piece, or the three sections and being formed individually and secured together. The pedestal substrate approach of the present invention permits the optic component designer to independently control the effects of residue coating film stress, mount disturbance loads, and substrate dynamic stiffness.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved substrate for both coated and uncoated optics.
A further object of the invention is to provide a pedestal substrate for coated optics.
A further object of the invention is to provide a pedestal substrate for coated optics comprising a substrate section, a base section, and a connector section.
Another object of the invention is to provide a pedestal optical substrate that simultaneously provides high substrate dynamic stiffness, low surface figure sensitivity to mechanical mounting hardware inputs, and constrains surface figure changes caused by optical coatings to assume a desired form, for example, spherical.
Another object of the invention is to provide a pedestal substrate which includes a disk-like optic section, a disk-like base section, and a connecting section between the base and optic sections.
Another object of the invention is to provide a pedestal substrate having three sections formed from a solid piece of material.
Another object of the invention is to provide a pedestal substrate containing a substrate section, a base section, and a connector section, wherein the substrate section and connector section are integral.
Another object of the invention is to provide a pedestal substrate having a substrate section, a base section, and a connector section, wherein the connector section is connected to at least the base section, at three equally spaced points.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves a pedestal substrate for coated optics. The pedestal substrate of this invention provides an optical substrate that maintains acceptable figure after coating, is not sensitive to mount disturbance loads, and has high dynamic stiffness. Thus, the present invention provides an optical component for extreme ultraviolet (EUV) lithography imagine systems or any optical system requiring coated optics and/or substrates with reduced sensitivity to mechanical mounts. The invention involves a pedestal substrate composed of three basic elements: 1) a disk-like optic section having a top surface that requires coating, 2) a disklike base section, and 3) a connecting section between the base and optic sections. The connecting section may be a separate component secured to both the optic section and the base section, may be integral with the optic section, or may be integral with the optic and base sections. The connecting section, if separate from the base section, is secured to the base section, at three equally spaced locations, and if separate from the optic section, may be secured thereto at three or more points or may be continuously secured. The connecting section may be triangular, but preferably cylindrical, and may be hollow, and connected to at least the base section by three spaced protruding legs which extend into openings in the base section and bonded or otherwise secured thereto. Also, the connecting section may extend into an opening in the base section with the base section having three spaced protruding members which contact the connecting section and are secured thereto. The connecting section may be similarly secured to the optic section, but preferably the connecting section is integral with the optics section, and may be solid or hollow. The three basic components of the pedestal substrate of the invention are preferably fabricated from a low thermal expansion glass or from low thermal expansion ceramics such as Zerodur, ULE, or Zerodur M.
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Hale Layton C.
Malsbury Terry N.
Patterson Steven R.
Carnahan L. E.
Crispino Richard
Grzybicki Daryl S.
Koch, III George R
The Regents of the University of California
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