Fabrication of wear-resistant silicon microprobe tips for high-speed surface roughness scanning devices

Abstract

Silicon microprobe tips are fabricated and integrated with piezoresistive cantilever sensors for high-speed surface roughness scanning systems. The fabrication steps of the high-aspect-ratio silicon microprobe tips were started with photolithography and wet etching of potassium hydroxide (KOH) resulting in crystal-dependent micropyramids. Subsequently, thin conformal wear-resistant layer coating of aluminum oxide (Al 2 O 3 ) was demonstrated on the backside of the piezoresistive cantilever free end using atomic layer deposition (ALD) method in a binary reaction sequence with a low thermal process and precursors of trimethyl aluminum and water. The deposited Al 2 O 3 layer had a thickness of 14 nm. The captured atomic force microscopy (AFM) image exhibits a root mean square deviation of 0.65 nm confirming the deposited Al 2 O 3 surface quality. Furthermore, vacuum-evaporated 30-nm/200-nm-thick Au/Cr layers were patterned by lift-off and served as an etch mask for Al 2 O 3 wet etching and in ICP cryogenic dry etching. By using SF 6 /O 2 plasma during inductively coupled plasma (ICP) cryogenic dry etching, micropillar tips were obtained. From the preliminary friction and wear data, the developed silicon cantilever sensor has been successfully used in 100 fast measurements of 5-mm-long standard artifact surface with a speed of 15 mm/s and forces of 60-100 µN. Moreover, the results yielded by the fabricated silicon cantilever sensor are in very good agreement with those of calibrated profilometer. These tactile sensors are targeted for use in high-aspect-ratio microform metrology.

High-speed microprobe for roughness measurements in high-aspect-ratio microstructures

“…They offer a high level of hardness and wear resistance as well as a low friction coefficient [8]. In a previous work [9] we have described the fabrication steps for the coating of silicon microprobe tips using the atomic layer deposition (ALD) technique. Alumina (Al 2 O 3 ) was chosen as a coating material.…”

In-Line Measurement of the Surface Texture of Rolls Using Long Slender Piezoresistive Microprobes

“…A disadvantage is potential breakage of the probe when the deflection surpasses its range of 1 mm [ 14 , 15 ]. Novel microprobe designs have improved wear resistance by using diamond tips [ 10 ] or hard coatings for the tip [ 16 ].…”