Lithographic Exposure Illumination Unit for Sub-250 nm Resolution
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Solution Overview
Problem
Conventional lithographic methods face limitations in achieving high lateral structure resolution due to diffraction effects and the need for expensive optical systems, particularly in photolithography, which restricts the smallest structure size that can be transmitted to around 0.5 µm for contact printing and a few micrometers for proximity printing.
Innovation Solution
A device for lithographic exposure utilizing an illumination unit with a high-pressure Hg lamp, collimating optics, and double-sided lens arrays to homogenize intensity and angular distributions, combined with the Talbot effect for achieving self-imaging of periodic structures, allowing for precise control of illumination and enabling structure widths less than 250 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mask aligner with photomask and illumination optics is used, then lateral structure resolution is limited to 0.5 µm for contact printing or a few micrometers for proximity printing due to diffraction effects, but the system is relatively simple and cost-effective
Solution Approach 1:
The illumination system is segmented into multiple independent components: a light source, a first double-sided lens array, a second double-sided lens array, and a diaphragm. Each component performs a specific function in homogenizing the illumination, allowing the system to achieve high resolution without requiring a single complex optical system
Solution Approach 2:
The patent introduces intermediate optical elements (double-sided lens arrays and diaphragm) between the light source and the photomask to homogenize the illumination. These intermediaries transform the non-uniform light distribution into a uniform one, enabling better diffraction-limited resolution without direct contact between light source and mask
2Manufacturing precision
If imaging optics are used to image the mask structure onto the radiation-sensitive polymer layer, then lateral resolution is improved, but the system becomes significantly more expensive and complex than mask aligners
Solution Approach 1:
The patent extracts the essential function of imaging optics by using only the necessary components (double-sided lens arrays and diaphragm) to homogenize illumination, rather than implementing a complete imaging system. This extraction achieves sufficient resolution improvement while removing unnecessary complexity and cost
Solution Approach 2:
The patent changes the illumination parameters (intensity distribution and angular distribution) by using double-sided lens arrays to transform the light field. This parameter transformation enables the system to achieve imaging-quality resolution without requiring complex imaging optics, as the homogenized illumination naturally produces the desired image quality
3Manufacturing precision
If the photomask is brought into direct contact with the radiation-sensitive polymer layer for contact printing, then the lateral resolution is limited by diffraction, but the device structure is simple
Solution Approach 1:
The patent introduces a new dimension to the illumination system by using double-sided lens arrays that operate in both the object space and image space. This dimensional approach allows the system to homogenize illumination from multiple angles simultaneously, achieving better resolution without requiring the photomask to be in direct contact with the polymer layer
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
The device achieves improved lateral structure resolution, exceeding conventional mask aligner capabilities by a factor of 2.5 for contact printing and over 10 for proximity printing, while minimizing the risk of photomask defects by avoiding direct contact with the radiation-sensitive polymer layer.
Implementation Method 1
As a result of the diffraction of the illumination light occurring at the mask structure, the intensity distribution behind the photomask is no longer sharply delimited
Implementation Method 2
A first double-sided lens array follows the light source in the beam path... The purpose of the first double-sided lens array arranged downstream of the light source is in particular to homogenize the intensity distribution of the illumination light
Implementation Method 3
a radiation-sensitive polymer layer (resist) is exposed to a laterally varying dose distribution of a specific type of radiation... The radiation dose introduced changes the polymer properties in such a way that in a subsequent development step only the irradiated (positive resist) or only the unirradiated (negative resist) areas of the polymer layer are selectively dissolved
Data Source
Figure 1
Figure 2A~2C
AI summary
The illuminating unit (13) has a light source (5) e.g. mercury high pressure lamp, for radiating an illuminating light (7). A lens (3) e.g. collective lens, is arranged adjacent to a double sided lens array (1). Another double sided lens array (2) is arranged in a focal plane of the lens. Another lens (4) is arranged adjacent to the latter lens array. A substrate (11) is coated with a radiation-sensitive polymer layer (10). A spacing (L) between a photomask (9) and the polymer layer is defined by a relationship based on a period of a periodical mask pattern (9b) and a wavelength of the light.