Airborne molecular contamination: quality criterion for laser and optical components

Abstract

Airborne molecular contaminations (AMCs) have been recognized as a major problem in semiconductor fabrication. Enormous technical and financial efforts are made to remove or at least reduce these contaminations in production environments to increase yield and process stability. It can be shown that AMCs from various sources in laser devices have a negative impact on quality and lifetime of lasers and optical systems. Outgassing of organic compounds, especially condensable compounds were identified as the main source for deterioration of optics. These compounds can lead to hazing on surfaces of optics, degradation of coating, reducing the signal transmission or the laser signal itself and can enhance the probability of laser failure and damage. Sources of organic outgassing can be molding materials, resins, seals, circuit boards, cable insulation, coatings, paints and others. Critical compounds are siloxanes, aromatic amines and high boiling aromatic hydrocarbons like phthalates which are used as softeners in plastic materials. Nowadays all sensitive assembly steps are performed in controlled cleanroom environments to reduce risks of contamination. We will demonstrate a high efficient air filter concept to remove AMCs for production environments with special AMC filters and methods for the qualification and monitoring of these environments. Additionally, we show modern techniques and examples for the pre-qualification of materials. For assembled components, we provide sampling concepts for a routine measurement for process, component and product qualification. A careful selection of previously tested and certified materials and components is essential to guarantee the quality of lasers and optical devices.

Analysis of laser-induced contamination at 515 nm in the sub-ps/MHz regime

“…This unwanted deposition process, referred as Laser-Induced Contamination (LIC), can be responsible for an accelerated transmission loss and finally non-reversible laser damage of the optical components, possibly causing laser failure. [18][19][20][21][22] This effect is critical for the industrial applications, and it has mainly been studied in the context of space applications: several past spaceflight missions using ns UV lasers proved to be short-lived and unreliable due to this effect, which has initiated an active field of research between space and laser communities. [23][24][25][26][27][28][29][30] LIC effects in the fs/ps regime have not been reported in the opened literature up to now but our investigations on laser components have led us to the 3 conclusion that these effects are also particularly detrimental in this regime and can be a main limitation of short wavelength high average power fs/ps lasers (Figure 1).…”

Investigation of laser-induced contamination on dielectric thin films in MHz sub-ps regime

“…LIC is the result of the interaction between the laser beam, the optical surface, and compounds in the surrounding environment. A contamination layer is typically created by organic compounds or other molecules on optical components that undergo photopolymerization due to laser irradiation (Scurlock, 2005;Wernham et al, 2010;Otto, 2015). Irradiation of the contamination-based layer causes chemical reactions yielding a loss of volatility of the contaminants.…”

Sub-ps MHz green laser-induced contamination on dielectric coatings in air

“…A contamination layer is typically created by organic compounds or other molecules on optical components that undergo photopolymerization due to laser irradiation. [12][13][14] Irradiation of the contaminationbased layer causes chemical reactions yielding a loss of volatility of the contaminants. A thin LIC deposit is thus formed under the beam, which modifies the optical component properties.…”