Investigation of room temperature deposited silicon dioxide thin films for surface texturisation of monocrystalline {100} silicon

Abstract

In the fabrication of crystalline silicon-based solar cells, silicon surface is usually texturised by wet anisotropic etchant without using any masking pattern. This method provides randomly oriented upright pyramids (or hillocks) of varying sizes. However, a surface textured with inverted pyramids yields high efficiency compared with the one textured with normal pyramids. Silicon dioxide thin films synthesised using anodic oxidation technique at room temperature are explored as etch mask in KOH solutions to texturise the Si{100} surface with inverted pyramids without patterning of the oxide layer using lithography. Oxide films of ∼50 nm thickness are synthesised in different compositions of the electrolyte under potentiodynamic regime. Thickness uniformity and refractive index of the as-grown oxide films are measured using spectroscopic ellipsometry. Scanning electron microscope is primarily used to inspect the etched surface morphology. The composition of the electrolyte, KOH concentration and etching time are optimised for the maximum surface coverage of inverted pyramids. The surface texturing process demonstrated is very simple and economic as it utilises anodic silicon dioxide as an etch mask, which is deposited by a simple experimental setup and the process does not involve any lithography step.

Pyramid textured Si{100} surface with low reflectivity in CMOS compatible solution

“…In surface texturing, the Si surface is intentionally made rough to increase the optical path length by multiple internal reflections, which results in more photon generation and thus increase the efficiency [2]. Surface texturing is usually done by wet etching, dry etching, and lithography [3–23]. For generating anti‐reflective structures on Si surface, many techniques based on lithographies such as photolithography, electron‐beam lithography, and nanoimprint lithography have been used.…”

“…Potassium hydroxide and tetramethylammonium hydroxide (TMAH) are the two most extensively used alkaline solutions for surface texturing of silicon [5, 8, 12–14, 24]. Out of these two etchants, TMAH is popular because it provides better etch selectivity between silicon and silicon dioxide and offers compatibility with the CMOS process [3, 8, 12, 14–16, 24]. In wet etching, final etched surface morphology is defined by many parameters, i.e.…”

“…Among all, wet etching is a low cost, high throughput, and easy handling procedure, which brings a good balance between the efficiency and cost of the solar cells [2,11,24]. Potassium hydroxide and tetramethylammonium hydroxide (TMAH) are the two most extensively used alkaline solutions for surface texturing of silicon [5,8,[12][13][14]24]. Out of these two etchants, TMAH is popular because it provides better etch selectivity between silicon and silicon dioxide and offers compatibility with the CMOS process [3,8,12,[14][15][16]24].…”