248nm Bandpass Filter

Context: Optical projection lens system used in microlithography (the process of printing circuit patterns onto semiconductor wafers).

Usage of Filter: The bandpass filter (often part of a line-narrowing module or spectral purity filter) is placed in the optical path of the KrF excimer laser source before the light enters the projection lens.

Function: It strictly limits the spectral bandwidth of the illumination light to 248 nm, typically narrowing it to a fraction of a picometer (pm).

Result: This prevents chromatic aberration in the projection lens (which is made of a single material, fused silica, and cannot correct for color focus shifts), allowing the system to print extremely fine features (sub-micron) with perfect focus.

Context: Excimer laser inspection system for detecting defects on semiconductor wafers.

Usage of Filter: The filter is used in the illumination arm or the detection path to isolate the specific 248 nm laser line from background noise or broadband emission.

Function: It acts as a spectral selector, ensuring that only the high-energy Deep UV (DUV) light interacts with the sample or reaches the detector, while blocking longer wavelengths (visible/IR) that might reduce contrast.

Result: High-speed detection of "sub-wavelength" defects (defects smaller than the light itself) on the wafer surface is achieved with high signal-to-noise ratio.

Context: Native Fluorescence Detection for Protein Analysis (specifically in Capillary Electrophoresis systems).

Usage of Filter: The bandpass filter is positioned after the light source (often a laser-driven plasma or frequency-doubled laser) to "clean" the excitation beam before it hits the capillary tube.

Function: It selects the specific Deep UV excitation wavelength (such as 248 nm or similar deep UV lines) and blocks any stray stray light or other harmonic frequencies that could interfere with the delicate fluorescence signal.

Result: The system successfully excites native fluorophores (like the amino acid tryptophan) inside proteins without requiring external dye labels, achieving extremely high sensitivity (Limit of Detection in the 10-20 nM range).