Proof of damage-free selective removal of thin dielectric coatings on silicon wafers by irradiation with femtosecond laser pulses

Abstract

The microstructural impact of selective femtosecond laser ablation of thin dielectric layers from monocrystalline silicon wafers was investigated. Various spots opened by 280 fs laser pulses at lambda = 1.03 µm wavelength and 50 fs pulses at 800 nm, respectively, were analyzed in detail using Raman and transmission electron microscopy. The results show clearly that the thin dielectric films can be removed without any detectable modification of the Si crystal structure in the opened area. In contrast, in adjacent regions corresponding to laser fluence slightly below the breaking threshold, a thin layer of amorphous silicon with a maximum thickness of about 50 nm is found at the Si/SiO2 interface after laser irradiation. More than one pulse on the same position, however, causes structural modification of the silicon after thin film ablation in any case

Quantized structuring of transparent films with femtosecond laser interference

“…due to this thin heating zone underpins the physics for blistering and ejection of film as reported in references [7][8][24][25][26][27] over varying film thickness without evidence of internal structuring of the transparent film. However, such interface machining was found together with the first evidence of internal structuring of the film as shown in Figure 1c by the SEM images for the present 500 nm thick film exposed at a threshold incident intensity of I avg 59310 12 W cm…”

Ultrafast laser direct hard-mask writing for high efficiency c-Si texture designs

“…During KOH etching, the smallest ablation craters in 100 nm thick SiN x /SiO x films did not etch to form inverted-pyramids. This is attributed to the high fluence ( 0.96 J/cm 2 ) used to delaminate 100 nm thick films that crystallographically damages the underlying Si and thus rendering it unetchable in KOH [16]. The results show that the thinnest possible dielectric film is favoured to yield the smallest ablation crater diameter with minimum Si damage.…”

Optimized scribing of TCO layers on glass by selective femtosecond laser ablation

“…In contrast, the linear absorption is apparently not the mechanism relevant for ablation in the femtosecond regime. Instead, as has been discussed previously [3,4], strongly nonlinear absorption will create a high carrier density already within the pulse duration. These carriers are becoming very quickly the main source of -then quasi-metallic -absorption concentrating the dissipation of the major part of pulse energy within an ultrathin layer adjacent to the interface.…”

“…When the critical carrier density is exceeded within this layer, (nonthermal) vaporization of the TCO starts. The resulting high pressure at the interface then relaxes by bulging and finally blasting away the thin TCO layer [4]. Adiabatic expansion of the evaporated material and the kinetic energy of the ejected TCO disk consume a large amount of the absorbed energy, mostly before thermalization and heat conduction can transport it into the neighborhood.…”

“…Therefore, the zone being inactive with respect to charge separation typically reaches a width of 100 µm or more, because the scribes of the subsequent layer have to be clearly separated from the previous scribes to guarantee electrical functionality [2]. In contrast, ultrashort pulses which work in the real "cold ablation" range (< 1 ps) allow for a scribing of much narrower trenches without HAZ [3] when the processing is done not too far above the ablation threshold [4].…”