Paper AS-ThP3
Silicon Wet Etching Using NH4OH Solution For Texturing of Silicon Micro-Channels

Thursday, October 24, 2019, 6:30 pm, Room Union Station B

This work presents the surface texturing of the horizontal wall of silicon micro-channels (SiMCs) using the NH4OH solution. The micro-channels are obtained on the backside of Si substrates, where the solar cells are fabricated. The micro-channels are used as heat sinks through which fluid will flow, such as water or alcohol. The texturing results in the micro-channels with roughness (in micro-pyramid shape) on horizontal surface. The roughness assists in the dilution of bubbles that can occur inside the fluid, because if the bubble excess occurs into the fluid, this can difficult the transport into the SiMC. The texturing is based on the formation of micro-pyramids with the use of NH4OH (ammonium hydroxide) alkaline solution etching, which is anisotropic. Our NH4OH solution etching can control the size of micro-pyramids on the surface into the SiMC This occurs because the etch rates are different for three [100], [110] and [111] Si crystal planes. The Si etching is due to the presence of the OH- (hydroxyl) in the NH4OH solution that reacts with Si. The micro-pyramids occurs because the (100) mono-crystalline substrates have a lower Si surface density of the plane than the (110) plane. The difference in density causes the etch rate for (100) plane to be greater than (110), which in turn, is greater than for (111). Thus, since it is a surface with lower density is easier penetration of the solution, which facilitates the Si reaction with hydroxyl (OH -). Anisotropic etching is obtained by alkaline solution of monocrystalline Si substrate, with (100) surface orientation. Exposure of [111] crystal plans occurred, forming the micro-pyramids. The obtained values of micro-pyramid height of 770 nm and 920 nm, when compared with a desired micro-channel depth of 200 µm, represent a ratio (between roughness and channel depth) lower than 5%. This ratio is considered suitable to reduce a significant impact on micro-channel performances.