In the last decade much improvement has been achieved for ultra-short pulse lasers with high repetition rates. This laser technology has vastly matured so that it entered a manifold of industrial applications recently compared to mainly scientific use in the past. Compared to ns-pulse ablation ultra-short pulses in the ps- or even fs regime lead to still colder ablation and further reduced heat-affected zones. This is crucial for micro patterning when structure sizes are getting smaller and requirements are getting stronger at the same time. An additional advantage of ultra-fast processing is its applicability to a large variety of materials, e.g. metals and several high bandgap materials like glass and ceramics.
One challenge for ultra-fast micro machining is throughput. The operational capacity of these processes can be maximized by increasing the scan rate or the number of beams – parallel processing. This contribution focuses on process parallelism of ultra-short pulsed lasers with high repetition rate and individually addressable acousto-optical beam modulation. The core of the multi-beam generation is a smooth diffractive beam splitter component with high uniform spots and negligible loss, and a prismatic array compressor to match beam size and pitch. The optical design and the practical realization of an 8 beam processing head in combination with a high average power single mode ultra-short pulsed laser source are presented as well as the currently on-going and promising laboratory research and micro machining results. Finally, an outlook of scaling the processing head to several tens of beams is given.
Direct laser patterning of various materials is today widely used in several micro-system production lines like inkjet
printing, solar cell technology, flat-panel display production, LEDs, OLEDs, semiconductors and medicine. Typically
single-mode solid state lasers and their higher harmonics (e. g. 266, 355, 532 and 1064 nm) are used especially for
machining of holes and grooves. The striking advantages of flat top intensity distributions compared to Gaussian beam
profiles with respect to the efficiency and quality of these processes were already demonstrated. Here we will give an
overview of parameters, methods and applications of Gaussian-to-top-hat beam shaping. The top hat field size can start
from about 30 μm with no upper size limitation in the far field of the optics. Beam shaping for various wavelengths were
realized with field geometries of squares, rectangles and circles. With LIMO's compact Gaussian-to-top-hat converter an
inhomogeneity better than 5% contrast was reached. Special focus is put on the integration of Gaussian-to-top-hat beam
shapers in fast scanning systems employing Galvo mirrors and a specially developed f-Theta lens to avoid destruction of
the top hat profile within the scan field. Results with a 50x50μm2 top hat size (inhomogeneity down to <10%) in a scan
area of 156x156mm² are presented. The minimal distortions of the top hat observed within the scan area make LIMO's
compact Gaussian-to-top-hat converter excellently suited for industrial scanning applications, e.g. for the processing of
solar panels.
Semiconductor lasers play an important role in many applications. Depending on the wavelength of the emitted laser
light in the blue (e.g. 405-445 nm), red (~ 650 nm), near infrared (780 - 1070 nm) and e.g. the eye-safe wavelength
region around 1500 nm a manifold of applications exist. Due to their increasing power and brightness single emitter
devices are becoming increasingly widely used for the assembly and packaging of high power diode lasers. In the near
infrared typical emitter widths are 50, 90 (100) and 200 μm with power levels available > 15 W. Also larger stripes are
available - up to 1000 μm - with power levels > 25W. For highest power laser devices not only the power of the emitter
is important - but of equal importance is the subsequent optics to collect all the emitted power while maintaining the
brightness of the source. High NA acylindrical micro-lenses very well account for the strong asymmetric emitter
characteristics of the fast and slow axis and thus, result in best collimation and coupling efficiencies in contrast to
spherical lenses. LIMO's cost-effective micro-optics wafer technology is most suited for such acylindrical optics. It
allows the manufacture of different materials to cover wavelengths ranges from the UV to the NIR, e.g. 380 - 2000 nm.
Since both sides of a wafer can be structured with crossed cylindrical lenses one single monolithic optical element
simultaneously shapes the fast and slow axis of the emitted light. Additionally, mechanical reference planes can be
integrated in such monolithic optics for precise and simple integration. Application examples for collimation and fiber
coupling optics in the near infrared as well as focussing/pump optics in the blue wavelength range are shown.
Micro-lenses and micro-lens arrays are widely used for various applications. Monolithic arrays of cylindrical lenslets
made of glass, semiconductors or crystals provide great advantages to laser applications, e.g. high efficiency, intensity
stability and very low absorption. However, up to now, mainly symmetrical micro-lens surfaces are utilized in most
applications due to design and manufacturing restrictions. The manufacture and application benefits of asymmetrical
cylindrical-like micro-lens surfaces are enabled by LIMO's unique production technology. The asymmetrical shape is
defined by uneven-polynomial terms and/or an asymmetrical cut-off from an even polynomial surface. Advantages of
asymmetrical micro-lenses are off-axis light propagation, the correction of aberration effects or intensity profile
deformations when the illuminated surfaces are not orthogonal to the optical axis. First application results of such microlens
arrays are presented for beam shaping of high power diode lasers. The generation of a homogeneous light field by a
100 W laser with tilted illumination under an angle of 30-50° is shown. A homogeneity of better than 90% was achieved
for a field size of 270 mm x 270 mm. In laser direct write processes a top hat profile has several advantages compared to
a Gaussian beam profile, especially the throughput of the system and quality of the structures can be improved. Novel
patterning results with TopHat-converted single mode lasers and a special Gaussian-to-TopHat galvo scan system are
demonstrated for solar cell technology.
High power laser sources are used in various production tools for microelectronic products and solar cells, including the
applications annealing, lithography, edge isolation as well as dicing and patterning. Besides the right choice of the laser
source suitable high performance optics for generating the appropriate beam profile and intensity distribution are of high
importance for the right processing speed, quality and yield.
For industrial applications equally important is an adequate understanding of the physics of the light-matter interaction
behind the process. In advance simulations of the tool performance can minimize technical and financial risk as well as
lead times for prototyping and introduction into series production. LIMO has developed its own software founded on the
Maxwell equations taking into account all important physical aspects of the laser based process: the light source, the
beam shaping optical system and the light-matter interaction.
Based on this knowledge together with a unique free-form micro-lens array production technology and patented micro-optics
beam shaping designs a number of novel solar cell production tool sub-systems have been built. The basic
functionalities, design principles and performance results are presented with a special emphasis on resilience, cost
reduction and process reliability.
When it comes to highest power laser applications CO2-lasers are one of the most prominent choices. In most applications the raw laser beam which exhibits a Gaussian or Gaussian-like shape is employed. In contrast, homogeneous top hat profiles or customized beam shapes offer several application-specific advantages. Up to now the possibilities of beam shaping for CO2-lasers were very limited based on traditional approaches only. To make the advantages of homogeneous beam profiles also accessible for CO2 sources LIMO has expanded its range of production capabilities for the manufacturing of ZnSe micro-optics. LIMO's proprietary production technology is based on computer-aided design and no etching technique is involved at all. A Gaussian-to-top-hat converter made of ZnSe is demonstrated. The properties of the micro-lens surface, the generated beam profile with a CO2-laser as well as first application results are shown.
Direct laser patterning of various materials is today widely used in several micro-system production lines like inkjet
printing, solar cell technology, flat-panel display production and medicine. Typically single-mode solid state lasers and
their higher harmonics are used especially for machining of holes and grooves. The most prominent lasers are pulsed
Nd:YAG lasers and their harmonics @ 266, 355 and 532 nm. Recently, the striking advantages of flat top intensity
distributions for the efficiency and quality of these processes were demonstrated. The use of LIMO's compact Gaussian-to-
top-hat converter enables the creation of steeper and sharper edges. Additionally, the higher energy efficiency of
rectangular top hat profiles compared to smooth, circular Gaussian shapes allows for faster patterning. A standard
method to reduce process times is the use of optical scanning systems. Yet, the application of Gaussian-to-top-hat
converters in combination with a scanner was hindered by distortions of the top hat introduced by the F-Theta focussing
lens of the scanners even at very small deflection angles (<2°). We solved this challenge by implementing an alternative
scanning approach (patent pending). Scanning results obtained with a 50x50μm2 top hat field (homogeneity down to
<10%) in a scan area of 156x156mm2 will be presented. The minimal distortions of the top hat observed within the scan
area make LIMO's compact Gaussian-to-top-hat converter excellently suited for industrial scanning applications, e.g. for
the processing of solar panels.
High power laser sources are used in a large variety of applications for material processing, such as ablation, welding,
soldering, cutting, drilling, laser annealing, micro-machining and deep-UV lithography. Using high performance optics
in the laser systems to generate the appropriate beam profile becomes a key factor for getting the best results and
throughput in an application field. Refractive micro-lens arrays made of glass, semiconductors or crystals provide great
advantages in laser applications, by improving efficiency, precision, intensity stability and performance.
With LIMO's unique production technology, free form surfaces on monolithic arrays exceeding 200 mm edge length can
be manufactured with high precision and reproducibility. Each lens of the array can be designed individually and can
also be shaped asymmetrically. The asymmetric shape is defined by
odd- and even-polynomial terms and/or an
asymmetric cut-off from a polynomial surface. Advantages of asymmetric micro-lenses are off-axis light propagation,
the correction of aberration effects, or the correction of the intensity profile deformations when the illuminated surfaces
are not orthogonal to the optical axis.
The applications results of such micro-lens arrays are presented for beam shaping of high power diode lasers. The
generation of a homogeneous light field by a 100 W laser with tilted illumination under an angle of 30°-50° is shown. A
multi-kW line generator based on the superposition of over 50 diode laser bars under different illumination angles is
demonstrated as well.
Novel microoptical beam shapers in lithographic applications reduce the complexity of macrooptics in hyper-NA illumination systems. Extremely uniform intensity distribution can be created without using field lenses or by using simple spherical field lenses instead of complex aspheres.
KEYWORDS: Beam shaping, High power diode lasers, Homogenization, Semiconductor lasers, Lenses, Laser sources, Manufacturing, Laser processing, High power lasers, Semiconductors
Micro-lens arrays are widely used for beam shaping, especially beam homogenization of various laser sources.
Monolithic arrays of cylindrical lenslets made of glass, semiconductors or crystals provide great advantages in laser
applications, e.g. high efficiency, intensity stability and very low absorption. However, up to now, mainly symmetrical
micro-lens surfaces are utilized in most applications due to design and manufacturing restrictions. The manufacture and
application benefits of asymmetrical cylindrical-like micro-lens surfaces are enabled by LIMO's unique production
technology. The asymmetrical shape is defined by uneven-polynomial terms and/or an asymmetrical cut-off from an
even polynomial surface. Advantages of asymmetrical micro-lenses are off-axis light propagation, the correction of
aberration effects or intensity profile deformations when the illuminated surfaces are not orthogonal to the optical axis.
Additionally, the opportunities in simultaneous illumination from numerous light sources to one target are extended by
just geometrical arrangement without the need for collinear beam alignment. First application results of such micro-lens
arrays are presented for beam shaping of high power diode lasers. The generation of a homogeneous light field by a 100
W laser with tilted illumination at an angle of 35° is shown. A multi-kW line generator based on the superposition of
over 50 diode laser bars under different illumination angles is demonstrated as well. Thus, laser material processing like
plastics welding, soldering or annealing becomes much more convenient and less demanding regarding beam steering.
Laser direct micro-machining processes are used in a variety of industries like inkjet printing, semiconductor processing,
solar technology, flat-panel display production and medicine. Various kinds of materials, e.g. ceramics, metals, isolators,
oxides, organics and semiconductors are being structured. In most cases pulsed single mode solid state lasers with an
inhomogeneous Gaussian beam profile are employed, like YAG lasers and their harmonics. However, the quality and functionality of the generated structures and micro-systems as well as the speed of the process can be improved by the utilization of homogeneous top hat profiles. The beam shaping principle of refractive Gaussian-to-top-hat converters is shown. Compact beam shaper modules based on this principle have been developed - supporting most direct laser micro-machining applications. The resulting process advantages are demonstrated by selected application results, namely the drilling of holes and patterning of trenches for different kinds of materials.
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.
High power and high energy laser sources are used in a large variety of industrial and scientific applications for material
processing. The most common are welding, soldering, cutting, drilling, laser thermal annealing, micro-machining,
ablation and micro-lithography. For optimised processes the most important laser sources today are: CO2-lasers, Nd-
YAG lasers, high-power diode lasers, excimer lasers or fiber lasers. Beside the right choice of the suitable laser source
the right choice of high performance optics for generating the appropriate beam profile is of high importance for the
applications. In many cases homogenous top-hat square or rectangular light fields as well as light lines are indispensable
or add strong advantages to the application. This takes into account that gaussian shaped laser foci are not the ideal
solution.
Refractive micro-lenses and micro-lens arrays based on damage resistant materials are an efficient, compact and flexible
solution to achieve adequate intensity distributions on the work piece. LIMO has a unique production technology based
on computer-aided design that enables the manufacture of high-precision microlens arrays with free programmable
surfaces. Thus, specific beam profiles with superior uniformity and efficiency can be generated. Compact beam shaper
modules with prealigned optics have been developed. These modules simply have to be placed into the collimated input
beam and the required intensity profile is generated at the target without any complicated alignment.
High-power laser sources are used in many applications for material processing, like annealing, welding, soldering, printing and micro-machining. Additionally, they are widely used as illumination sources for metrology - e.g. LIDAR - and vision systems based on CCD cameras. In many of these applications homogenous top-hat square or rectangular light fields as well as light lines are indispensable or add strong advantages to the application. LIMO has a unique production technology based on computer-aided design that enables the manufacture of high-precision microlens arrays with free programmable surfaces. Thus, specific beam profiles with superior uniformity and efficiency can be generated. Compact beam shaper modules with prealigned optics have been developed. These modules simply have to be placed into the collimated input beam and the required intensity profile is generated at the target without any complicated alignment. High-power diode laser systems for the NIR spectral region from 1W to several KW are available with application-specific beam shapes due to integrated micro-optics. Special attention is put on compact and solid design for rough environmental conditions.
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