Reduction of surface roughness and aperture size effect for etching of Si with XeF₂

Abstract

Low etching pressure and high silicon substrate temperature successfully decrease the etched surface roughness and the aperture size effect, which represent challenges to the application of silicon etching with XeF2 to the fabrication of microelectromechanical systems (MEMS). The etched roughness and aperture size effect are extremely high and limit factors for the design rules of MEMS devices. In order to express the extent of the aperture size effect, a uniformity of etched depth is defined as follows: (depth at 25 μm)/(depth at 175 μm) × 100%. By lowering the charge pressure from 390 to 65 Pa, the etched roughness decreased from 870.8 and 174.4 Å and the uniformity improved from 71.3 to 88.7%. By increasing the substrate temperature from 300 to 440 K, the etched roughness decreased from 151.4 and 44.5 Å and the uniformity increased from 71.3 to 91.6%. These results will allow us to design with fewer constraints and to expand the field of applications of XeF2 etching to MEMS.

Real-Time Glucose Sensing Using a MEMS-Based Bi-Material Deflecting Membrane

“…Si islands are then patterned from the bottom side of the die using PR, followed by coating the top surface with an intermediate PDMS layer. In the final step the last few microns of Si below the polymer membrane are removed using a XeF 2 vapor etch [4] , leaving released islands of Si attached to the PDMS membrane. The XeF 2 vapor phase etch method prevents damage to the polymer membrane while releasing the Si island.…”

Effects of focused MeV ion beam irradiation on the roughness of electrochemically micromachined silicon surfaces

“…For many applications such as low loss silicon photonic components, highly reflective surfaces, high quality-factor microcavities, one needs to produce as smooth a surface as possible. 12,13 Therefore, it is important to study the underlying causes of surface roughness. Different applications typically use differing resistivity of p-type silicon as the starting material, e.g., silicon-based photonic devices normally use low-doped material ͑1-10 ⍀ cm͒ to minimize optical losses due to free carrier scattering, whereas moderately doped material ͑0.02 ⍀ cm͒ is preferred for machining surface relief patterns with multiheight steps, micromirrors, and holographic surfaces since it is easier to machine a range of differing step heights.…”

The Effect of Temperature on the Etch Rate and Roughness of Surfaces Etched With XEF2

“…Some researchers have noted that roughness occurs because etching begins at etch sites which expand out to meet each other [12]. Faster etch rates and longer etch times make these non-uniformities become larger, and the surface becomes rougher [13]. Optimization of the XeF 2 etching process requires achieving an intelligent balance between cost, etch rate, and surface roughness.…”