Universal threshold for the steam laser cleaning of submicron spherical particles from silicon

The efficiency of the steam laser cleaning process is examined. For the investigation of the physics of particle removal from the particularly interesting surface of silicon we have deposited well-characterized spherical polymer and silica particles of different diameters ranging from several tens to hundreds of nanometers on commercial wafers. As a result of our systematic study we observe a sharp threshold of the steam cleaning process at 110 mJ/cm2 (h=532 nm, FWHMD=7 ns) which is independent of the size (for particles with diameters as small as 60 nm) and material of the particles. An efficiency above 90% after 20 cleaning steps is reached at a laser fluence of 170 mJ/cm2. Experiments with irregularly shaped alumina particles exhibit the same threshold as for spherical particles

with nanosecond time resolution

An optical setup for the measurement of acoustic shock waves is demonstrated experimentally. This sensor, which is based on surface plasmon excitation, provides ns time resolution as well as mm lateral resolution. Initial experiments with laser-induced plasma generation in a water cell already show that in a simple geometry high lateral resolution gives new insight into the ongoing processes

Laser cleaning of silicon wafers : prospects and problems

The removal of particle contamination from surfaces is one of the crucial prerequisites for a further increase in the integration density of ICs and for the progress in nanotechnology. At all stages of the production of ICs, e.g., from the bare Si wager to the patterned chip, particles even smaller than 100 nm in size can cause a damage to the produced structure and hence be responsible for the failure of the final device. In the late 1980s, the experts in the field of cleaning technology predicted that traditional cleaning methods such as ultrasonics and wet techniques would reach their limit of capability (1,2). In addition these traditional techniques were and still are harmful to the environment as they consume large quantities of aggressive chemicals and water. Although the traditional methods have been continuously improved (3), still particle contamination causes considerable production losses (4), and with further shrinking of line widths (5) there is a definite need to replace traditional methods by new cleaning technologies

Surface acceleration during dry laser cleaning of silicon

We report on measurements of the surface acceleration for the application of dry laser cleaning. For that purpose, industrial silicon samples were irradiated by a frequency-doubled Q-switched Nd:YAG laser. The surface displacement was measured by a heterodyne interferometer and recorded by a digital storage oscilloscope. Several hundreds of shots were averaged to give smooth displacement curves which could be derived numerically. The experiments show that the highest accelerations, which are thought to be responsible for the cleaning, occur on the time scale of the laser pulse. Simple theoretical models are in good agreement with the experimental data. The maximal displacement depends only on the deposited energy, while the maximal acceleration shows also a strong dependence from the temporal pulse shape. This knowledge allows one to optimize the pulse shape for the cleaning process

Steam laser cleaning of silicon surfaces : laser-induced gas bubble nucleation and efficiency measurements

The removal of dust particles from semiconductor surfaces requires new cleaning strategies such as Steam Laser Cleaning (SLC). It is based on laser-induced explosive evaporation of a liquid layer applied on the surface. We have investigated the laser-induced nucleation and growth of gas bubbles at silicon/water, silicon/isopropanol and silver-film/water - interfaces by light scattering and surface plasmon spectroscopy. The achieved superheating of the liquid before bubble nucleation sets in strongly depends on the substrate roughness. On rough metal films it is only about 30 K in water, compared to about 150 K on smooth silicon surfaces. Isopropanol (IPA) on smooth silicon surfaces could be heated to 116° C, corresponding to a superheating of 36 K. In combination with numerical calculations it was possible to determine the heat transfer coefficients silicon-water (x = 3 ·107 W/m2 K) and silicon IPA (x = 1 ·107 W/m2 K). Using optical techniques we have measured the pressure wave created by the growing bubbles and the bubble growth velocities. For a quantitative study of the efficiency of SLC we deposited spherical colloidal particles on industrial silicon wafers. We observed a sharp threshold for particle removal at 110 mJ/cm2 (laser l = 532 nm, FWHM = 8 ns) which is independent of the size (diameter 800 nm down to 60 nm) and material of the particles and efficiencies above 90% for particle removal. On the basis of our results we discuss the validity of the existing SLC models and the perspective of the application of SLC as an industrial cleaning tool

Gefahren der Übertragung von Krankheitserregern durch Schildzecken in Deutschland

Durch Zecken übertragbare Krankheitserreger haben eine große Bedeutung für die Gesundheit der deutschen Bevölkerung. Viren wie das Frühsommer-Meningoenzephalitis-Virus (FSMEV), das Uukuniemi-Virus, das Tribec-Virus und das Eyach-Virus oder Bakterien wie Borrelien, Rickettsien, Francisella tularensis, Anaplasma phagocytophilum, Candidatus Neoehrlichia mikurensis (CNM) oder Coxiella burnetii wurden in der in Deutschland häufigsten Zecke, der Schildzecke Ixodes ricinus, nachgewiesen. Während allgemein bekannt ist, dass Zecken FSMEV und Borrelien übertragen können, ist selbst in Fachkreisen nicht bekannt, dass sie auch die anderen oben genannten Erreger tragen und ggf. entsprechende Infektionen verursachen können. Auch wenn in Deutschland in Einzelfällen Erkrankungen nach Übertragung der zuletzt genannten Erreger durch Zecken bereits beschrieben wurden, fehlen systematische Untersuchungen über ihr Vorkommen und ihre pathogenen Eigenschaften. So ist weitgehend unklar, welche Bedeutung neu entdeckte Infektionserreger wie Candidatus Neoehrlichia mikurensis oder auch lange bekannte Erreger wie Rickettsien spielen, die sich bisweilen in einem Fünftel der untersuchten Zecken nachweisen lassen. Ob Klimaänderungen zur weiteren Ausbreitung der Zecken und der Infektionserreger beitragen, bedarf ebenfalls weiterer Untersuchungen. Die Initiativen zur Schaffung natürlicher Lebensräume und der Trend zum häufigeren Aufenthalt in der Natur im Rahmen von Freizeitaktivitäten verstärkt die Gefahr, in Kontakt mit Zecken und ihren Infektionserregern zu kommen. Folglich kann in Zukunft mit dem Auftreten weiterer, bisher nicht bekannter Erkrankungen durch die Übertragung diese Erreger gerechnet werden.Tick-transmitted diseases are of great importance for the general health of the German population. Several viruses, such as tick-borne encephalitis virus (TBEV), Uukuniemi virus, Tribec virus, Eyach virus or bacteria, such as Borrelia, Rickettsiae, Francisella tularensis, Anaplasma phagocytophilum, Candidatus Neoehrlichia mikurensis (CNM) and Coxiella burnetii were detected in the most prominent tick in Germany, the hard tick Ixodes ricinus. While infections, such as TBE and Lyme disease are well known, other infections are hardly known even among experts. Although there have been a few descriptions of isolated cases in Germany, a systematic investigation regarding the distribution and the pathogenic potential of these pathogens is still lacking. In particular elderly people and people with underlying diseases seem to be mostly affected. The importance of new infectious disease agents, such as Candidatus Neoehrlichia mikurensis but also of long known pathogens, such as Rickettsiae still remains unclear, while some of them could be detected in 20 % of investigated ticks. Whether climate change contributes to the further distribution of these infectious agents remains unclear and requires further investigation. The increasing initiatives to create natural environments and the trend towards spending more time in nature for recreational activities will increase the danger of coming into contact with ticks and the respective infectious agents. Considering these circumstances an increase of diseases caused by these pathogens is to be expected

<i>Borrelia</i> Infections in Ageing Ticks: Relationship with Morphometric Age Ratio in Field-Collected <i>Ixodes ricinus</i> Nymphs

In Europe, Ixodes ricinus plays a major role as a vector of Borrelia burgdorferi sensu lato (s.l.) spirochaetes, the causative agents of Lyme borreliosis, among other pathogens. In unfed ticks, Borrelia spirochaetes experience prolonged nutrient restriction. However, only few studies exist with regard to Borrelia infections in unfed ticks of different physiological ages. Changing body dimensions of unfed ticks, due to the consumption of energy reserves, allow physiological age estimation. The present study investigated the relationship of morphometric age with Borrelia prevalence and spirochaete load in 1882 questing I. ricinus nymphs, collected at two different locations in northern Germany in 2020. In addition, Borrelia species composition was investigated by employing a reverse line blot (RLB) probe panel suitable for the detection of ten different B. burgdorferi s.l. species, as well as the relapsing-fever spirochaete B. miyamotoi. Overall, Borrelia prevalence was 25.8% (485/1882). Whilst there was no statistically significant difference in Borrelia prevalence between the different morphometric age groups, Borrelia infection intensity as determined by probe-based quantitative real-time PCR significantly declined with increasing morphometric age. Borrelia species differentiation by RLB was successful in 29.5% of positive ticks, and revealed B. afzelii as the dominating species (65.0% of the differentiated infections). Additionally, B. garinii, B. valaisiana, B. burgdorferi sensu stricto, B. spielmanii, and B. miyamotoi were detected

Laser cleaning of silicon wafers : mechanisms and efficiencies

Laser Cleaning (SLC) process. Using a frequency doubled, Q-switched Nd:YAG laser (FWHM=8 ns) we removed polystyrene (PS) particles with diameters from 110-2000 nm from industrial silicon wafers by the DLC process. The experiments have been carried out both in ambient conditions as well as in high vacuum (10-6 mbar) and the cleaned areas have been characterized by atomic force microscopy for damage inspection. Besides the determining the cleaning thresholds in laser fluence for a large interval of particle size we could show that particle removal in DLC is due to a combination of at least three effects: thermal substrate expansion, local substrate ablation due to field enhancement at the particle and explosive evaporation of adsorbed humidity from the air. Which effect dominates the process is subject to the boundary conditions. For our laser parameters no damage free DLC was possible, i.e. whenever a particle was removed by DLC we damaged the substrate by local field enhancement. In our SLC experiments we determined the amount of superheating of a liquid layer adjacent to surfaces with controlled roughness that is necessary for bubble nucleation. On smooth surfaces high superheatins were necessary, in good agreement with theoretical predictions. Rough surfaces exhibited only a much smaller superheating