Programmable spatial filter for wafer inspection
First Claim
1. An optical inspection system for inspecting a sample, comprising:
- a light source for directing an incident light beam onto said sample;
an objective element having a back focal plane and operative to form an image of said sample from light collected from said sample; and
a programmable spatial filter positioned at said back focal plane, said programmable spatial filter comprising an array of Micro-Electro-Mechanical System (MEMS) devices, at least some of said MEMS devices having switched configurations which are alternately generally optically transmissive and optically blocking.
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Accused Products
Abstract
A programmable spatial filter for use as a Fourier plane filter in dark field wafer inspection systems, based on the use of MEMS (Micro-Electro-Mechanical Systems) devices. In comparison with prior art systems, especially those using LCD'"'"'s, the use of MEMS devices provide a number of potential advantages, including good transmission in the UV, a high fill factor, polarization independence and a high extinction ratio since the shutter is opaque when closed. The MEMS devices can be flap devices, artificial eyelid, or double shutter devices. Additionally, a novel spatial light modulator (SLM) assembly having a double layer of SLM arrays is described, in which the fill factor is increased in comparison to a single layer SLM using the same devices, by positioning the dead areas of the elements of both arrays collinearly in the modulated beam. This SLM assembly can be implemented using pixelated LCD arrays or MEMS arrays.
135 Citations
31 Claims
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1. An optical inspection system for inspecting a sample, comprising:
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a light source for directing an incident light beam onto said sample;
an objective element having a back focal plane and operative to form an image of said sample from light collected from said sample; and
a programmable spatial filter positioned at said back focal plane, said programmable spatial filter comprising an array of Micro-Electro-Mechanical System (MEMS) devices, at least some of said MEMS devices having switched configurations which are alternately generally optically transmissive and optically blocking. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of optically inspecting a sample, comprising the steps of;
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illuminating said sample with a beam of incident light;
forming an image of said sample by means of an objective element, said objective element having a back focal plane;
positioning at said back focal plane, a programmable spatial filter comprising an array of Micro-Electro-Mechanical System (MEMS) devices, at least some of which have switched alternate configurations which are generally optically transmissive and optically blocking; and
adjusting said programmable spatial filter to a pattern such that information related to selected features of said sample is blocked. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A filter for controlling the spatial transmission of a light beam, comprising:
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at least a first optical shutter comprising a section switchable between optically transmissive and optically blocking states, and an unswitchable dead area; and
at least a second optical shutter comprising a section switchable between optically transmissive and optically blocking states, and an unswitchable dead area;
wherein said at least second optical shutter is disposed in the path of said light beam serially to said at least first optical shutter and is aligned such that in the path of said light beam, said dead area of said at least second optical shutter overlaps said dead area of said at least first optical shutter, and said at least first and at least second optical shutters are mutually aligned such that in a plane perpendicular to said light beam, said switchable section of said at least first optical shutter and said switchable section of said at least second optical shutter face opposite directions relative to said overlapping dead areas. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31)
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20. A filter for controlling the spatial transmission of a light beam, comprising:
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at least a first optical shutter comprising a section switchable between optically transmissive and optically blocking states, and an unswitchable dead area; and
at least a second optical shutter comprising a section switchable between optically transmissive and optically blocking states, and an unswitchable dead area;
wherein said at least second optical shutter is disposed in the path of said light beam serially to said at least first optical shutter and is aligned such that in the path of said light beam, said dead area of said at least second optical shutter overlaps said dead area of said at least first optical shutter, and said at least first and at least second optical shutters are mutually aligned with their planes generally parallel, and rotated in said planes at essentially 180°
to each other. - View Dependent Claims (21, 22, 23)
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Specification