Refractive beam shaping: from Maxwell's Equations to products and applications in laser materials processing

Abstract

High power laser sources are used in a large variety of applications for materials processing. The most common are welding, soldering, cutting, drilling, laser annealing, micro-machining, ablation and micro-lithography. Beside the right choice of the suitable laser source adequate high performance optics for the generation of the appropriate beam profile are essential. Widely used geometries are square, rectangular light fields or light lines with homogeneous intensity distributions. The whole devolution from optical design and engineering to products and applications is demonstrated. LIMO has developed powerful software tools founded on Maxwell's Equations taking into account all important physical aspects of the beam shaping task. Various beam shaping principles, e.g. phase shifting for single-mode lasers, beam mixing for multi-mode lasers and other beam transformation schemes are discussed. Based on LIMO's unique production technology with computer-aided design free-form micro-lens surfaces can be structured cost-effectively on wafer-basis. Thus, the theoretically optimized surfaces can be transformed with high precision into a large range of materials. Typical products, their beam profiles and the respective application results are exemplarily shown for optical micro-lithography, micro-machining with Nd:YAG lasers and their harmonics as well as a-Si thin film annealing for flat panel display production.

Beam shaping: top hat and customized intensity distributions for semiconductor manufacturing and inspection

“…The analysis of microlens profiles that are produced by LIMO [11] shows, that this technology can be applied for fabrication of continuous periodic micro reliefs with a very fine lateral structure, for example of 10 μm. Previously we have reported on the continuous diffractive structures designed as 1:3 and 1:5 beam splitters at 1064 nm manufactured in BK7 glass [14].…”

“…It turns out that this seemingly straight forward approach is not as simple as it may appear at first glance. In conventional laser scribing systems a scanning systemeither a Galvo scanner for two dimensional tasks or a polygon scanner for one dimensional task's -is utilized in combination with a F-theta lens [11]. In the typical setup, the collimated laser beam is deflected by the scanner mirror, and the deflected beam is afterwards focused by the F-Theta lens to a focal spot in the micro meter scale at the target plane.…”

“…LIMO's manufacturing technology for free form micro-lenses and arrays has been developed and continuously improved over the last 18 years [9][10][11][12][13]. Recently, this technology was further improved in order to produce high efficiency free form diffractive micro-optics.…”

Detailed illuminator design for full-field ArF lithography system with a method based on the fly's eye

“…The cylindrical microlens array had been widely used by Nikon 5 , Canon 6 and LIMO 7 . LIMO has reported that the microlens array can reach φ 150mm with about 30000 micro lenses 8 . And the pitch of the micro lens can reach 500 m μ even smaller.…”

One-dimensional reflective diffuser for line beam shaper with microlens array homogenizer

“…1,2) The architecture shown in Fig. 1 has been proposed for the line beam shaper, in which the microlens array serves as the homogenizer.…”