EUV Illumination Optical Unit with Disjoint Reflective Facet Groups
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Solution Overview
Problem
Current microlithography projection exposure systems face limitations in achieving a wide range of angle-dependent intensity distributions at the object field, which restricts the minimum feature size that can be imaged, especially when using extreme ultraviolet (EUV) radiation.
Innovation Solution
The illumination optical unit incorporates a first optical element with multiple reflective facet elements and a second optical element with disjoint groups of reflective facet elements, allowing for various angle-dependent intensity distributions by adjusting the positions and orientations of the facet elements, enabling flexible illumination patterns in the exit pupil plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If exclusively reflective optical elements are used for EUV imaging, then the system can operate at EUV wavelengths (5-15 nm), but the ability to provide varied angle-dependent intensity distributions is limited
Solution Approach 1:
The reflective optical elements are divided into multiple facet elements with different orientations. Each facet element reflects radiation into a specific angular range, allowing the system to generate different angle-dependent intensity distributions by selectively activating different facet elements or groups thereof.
Solution Approach 2:
The illumination optical unit incorporates movable optical elements that can be positioned in different states. By changing the position of the first optical element relative to the second optical element, the system can dynamically adjust which facet elements are active, thereby providing varied angle-dependent intensity distributions at the object field.
2Manufacturing precision
If the minimum feature size is reduced, then higher imaging resolution is achieved, but the requirements for angle-dependent intensity distribution coordination become more stringent
Solution Approach 1:
Different regions of the illumination optical unit are designed with specific facet element configurations tailored to particular imaging requirements. Each facet element or group is optimized to provide specific angular distributions suitable for different feature sizes and patterns on the mask, enabling precise control over the illumination characteristics at the object field.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for a large number of different angle-dependent intensity distributions at the object field, enhancing imaging resolution and flexibility, particularly in EUV microlithography, by optimizing the illumination patterns in the exit pupil plane.
Implementation Method 1
a first optical element having a plurality of first reflective facet elements and a second optical element having a plurality of second reflective facet elements
Data Source
AI summary
An illumination optical unit for EUV microlithography includes a first optical element having a plurality of first reflective facet elements and a second optical element having a plurality of second reflective facet elements. Each first reflective facet element from the plurality of the first reflective facet elements has a respective maximum number of different positions which defines a set—associated with the first facet element—consisting of second reflective facet elements in that the set consists of all second facet elements onto which the first facet element directs radiation in its different positions during the operation of the illumination optical unit. The plurality of second reflective facet element forms a plurality of disjoint groups, wherein each of the groups and each of the sets contain at least two second facet elements, and there are no two second facet elements of a set which belong to the same group. This construction makes it possible to provide an illumination optical unit which can be used to provide a large number of different angle-dependent intensity distributions at the location of the object field.