Large-Scale and Localized Laser Crystallization of Optically Thick Amorphous Silicon Films by Near-IR Femtosecond Pulses

Abstract

Amorphous silicon (α-Si) film present an inexpensive and promising material for optoelectronic and nanophotonic applications. Its basic optical and optoelectronic properties are known to be improved via phase transition from amorphous to polycrystalline phase. Infrared femtosecond laser radiation can be considered to be a promising nondestructive and facile way to drive uniform in-depth and lateral crystallization of α-Si films that are typically opaque in UV-visible spectral range. However, so far only a few studies reported on use of near-IR radiation for laser-induced crystallization of α-Si providing less information regarding optical properties of the resultant polycrystalline Si films demonstrating rather high surface roughness. The present work demonstrates efficient and gentle single-pass crystallization of α-Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of laser-annealed films by atomic-force microscopy, optical, micro-Raman and energy-dispersive X-ray spectroscopy, as well as numerical modeling of optical spectra, confirmed efficient crystallization of α-Si and high-quality of the obtained films. Moreover, we highlight localized laser-induced crystallization of α-Si as a promising way for optical information encryption, anti-counterfeiting and fabrication of micro-optical elements.

Au-Hyperdoped Si Nanolayer: Laser Processing Techniques and Corresponding Material Properties

“…This effect is well-studied and described in many works, for example, [ 23 ]. Thus, according to the above study results, as well as the smoothing of the crystalline peak in silicon [ 24 ] on the Raman spectra ( Figure 7 ), it can be judged that silicon after processing appears in the form of polycrystals (poly-Si) [ 25 ].…”

Ultrabroadband, High Color Purity Multispectral Color Filter Arrays

“…The optimized color filters with dimensions of 50 × 50 μm are fabricated using standard CMOS processes (see fabrication process in Figure S6 in the Supporting Information). Polysilicon is obtained through furnace annealing of PECVD-deposited amorphous silicon, which can be replaced by laser annealing (to make it back-end CMOS compatible and make using other CMOS-compatible metals feasible). , To ensure stability at high temperatures, platinum has been selected as the inserted metal layer, as most refractory metals tend to react with both SiO 2 and silicon under high temperatures. , To prevent the reaction between Pt and polysilicon during the annealing step, two 15 nm silicon dioxide buffer layers sandwiching the Pt layer are employed (see Figure S7 in the Supporting Information) . An antireflection layer and protection layer of 110 nm SiO 2 are deposited above the color filter (Figure a).…”

“…The whole fabrication process is CMOS compatible. To make the fabrication of the filters compatible with the CMOS backend process, a potential alternative to the high-temperature annealing method is the use of pulsed laser annealing, which is an industry-standard. , The design principles demonstrated in this work can be easily transferred to other wavelength ranges such as near-infrared (NIR) and infrared (IR) by reoptimizing the thin film thicknesses and materials. − At longer wavelengths, this approach can offer a larger wavelength range with easier fabrication than that we demonstrated. Additionally, by exploring the freedom in the metal location, cavity, and distributed Bragg reflector (DBR) phase manipulation, and introducing tunable materials, this design principle can be utilized not only for multispectral color filter arrays but also for more customized and even actively tunable color filters with various applications in imaging and display technologies. − …”

“…To make the fabrication of the filters compatible with the CMOS backend process, a potential alternative to the high-temperature annealing method is the use of pulsed laser annealing, which is an industry-standard. 47,48 The design principles demonstrated in this work can be easily transferred to other wavelength ranges such as nearinfrared (NIR) and infrared (IR) by reoptimizing the thin film thicknesses and materials. 52−54 At longer wavelengths, this approach can offer a larger wavelength range with easier fabrication than that we demonstrated.…”

Monolithic broadband multispectral color filter array

“…We anneal amorphous silicon at 700°C for 2 hours to crystalize it into polysilicon. This process can be back-end CMOS compatible by replacing the furnace anneal with laser annealing 10 . Most refractory metals will react with silicon or silicon dioxide over 600°C.…”