As2S3 - Wet Etching

As2S3 - Wet Etching

Material Name: As2S3
Recipe No.: 8514
Primary Chemical Element in Material: As
Sample Type: Thin film
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: To investigate the etch-response, UV-exposed and unexposed films were immersed in a solutions from of 0.05 mol-% to 0.90 mol-% diisopentylamine (DIPA) dissolved in dimethylsulfoxide (DMSO) and monitored visually with a camera to identify the time required to remove both the exposed and unexposed material. UV-exposed films were prepared by irradiating samples for two minutes in a Zeta Loctite UV flood chamber equipped with high-pressure mercury lamps that emit broad-band UV radiation (65 mW/cm2). Photo-patterned arrays of nano-structures were etched using a solution of 0.05 mol-% DIPA in DMSO. The sample was immersed into the etchant for 60 to 300 seconds then rinsed with acetone. After etching, the As2S3 structures were imaged by scanning electron microscopy (SEM). The SEM images were used to determine the dimensions and shapes of the features so these could be correlated with film composition and processing conditions.
Procedure (Condition): No data
Note: As2S3 is a ChG that is transparent in the IR (620 nm to 11 µm) with applications in IR sensors, photonics waveguides, and acousto-optics6 As2S3 can be thermally deposited as thin films. Such films can be photo-patterned, like polymeric photo-resists, then chemically etched to obtain a targeted structure.

Deposition: As2S3 was deposited onto polished silicon wafers by thermal evaporation of the bulk glass. Two different deposition rates were used to explore its effect on the film composition and photo-response. The temperature of the substrate was not controlled. Films #1 and #5 were deposited at a rate of 80 Å s-1. Film #1 had a final thickness of 171 nm ± 11 nm and appeared pink in color. Film #5 had a thickness of 204 nm ± 16 nm and appeared blue. Films #2, #3, and #4 were deposited at a rate of 25 Å s-1. Films #2 had a thickness of 204 nm ± 24 nm and appeared pinkish/blue. Films #3 and #4 had a thickness of 170 nm ± 17 nm and 169 nm ± 11 nm, respectively, and both appeared pink. Films #6 was deposited at a rate of 27 Å s-1, had a thickness of 1075 nm ± 0.8 nm, and appeared pink. The films were transported in petri dishes wrapped with aluminum foil and stored in an amber desiccator in a cupboard to prevent unintended exposure to ambient light.

Photo-patterning: DLW was performed using a continuous-wave mode-locked femtosecond laser (Coherent-Mira, 800-nm center wavelength, 120-fs pulse duration, 76 MHz repetition rate). The film exposure was controlled using a mechanical shutter and the power was controlled using a half-wave plate/polarizer combination. The beam was routed through beam expanders to a 100x/1.4 Numerical Aperture (NA) oil-immersion objective (Nikon) which focused the beam into the film/substrate interface. An arbitrary coordinate system is defined so that the substrate lies in the xy-plane and the beam focuses along the z-axis. The average power used to cross-link the films was measured at the exit aperture of the objective with an integrating sphere and ranged from 0.05 mW to 0.20 mW. The sample was translated at a speed of 50 µm s-1 in the x-, y-, and z-axes relative to the laser beam to define the pattern. Arrays of single-point, nano-scale features were photo-patterned by locating the beam to a targeted (x,y)-position, opening the shutter, then translating the sample in the z-direction over a distance of 6 µm, to ensure that the feature was exposed throughout the entire thickness of the film.
Reference: Casey M. Schwarz, et al., Processing and properties of arsenic trisulfide chalcogenide glasses for direct laser writing of 3D micro-structures, Proceedings of SPIE - The International Society for Optical Engineering 8974, February 2014, pp. 1-13.