Wet & Dry Etching / DRIE
Precision material removal — from single-digit nanometer dielectric etches to through-wafer silicon structures. Bosch DRIE, cryogenic, KOH, RIE, and HF vapor release for MEMS and semiconductor fabrication.
Overview
Etching — both wet and dry — is the subtractive process that defines three-dimensional structures in semiconductor and MEMS devices. From the sub-nanometer precision of reactive ion etching for gate stack patterning to the deep through-wafer etching of Bosch DRIE for MEMS proof masses and TSVs, etch process selection directly determines device geometry, yield, and performance.
GINECHIP operates a comprehensive etch bay spanning six distinct technologies: Bosch DRIE for high-aspect-ratio silicon microstructures, cryogenic DRIE for smooth-sidewall photonic structures, anisotropic wet etching (KOH/TMAH) for bulk micromachining, HF vapor etching for stiction-free MEMS release, standard RIE for dielectric and metal pattern transfer, and wet chemical etching for blanket film removal and wafer thinning. Each process is qualified with dedicated test structures and monitored via SPC.
Etching Technologies
DRIE — Deep Reactive Ion Etching (Bosch Process)
The Bosch process alternates between SF₆ isotropic silicon etch and C₄F₈ passivation deposition cycles to achieve high-aspect-ratio anisotropic silicon etching. This is the workhorse etch technique for MEMS fabrication — enabling through-wafer vias, comb-drive actuators, inertial sensor proof masses, and microfluidic channel definition with aspect ratios exceeding 30:1.
Cryogenic DRIE
Low-temperature (−100°C to −130°C) silicon etching in SF₆/O₂ plasma. The cryogenic temperature suppresses sidewall chemical etching, producing smooth sidewalls without the characteristic Bosch scalloping. Preferred for optical MEMS, photonic structures, and applications requiring ultra-smooth vertical surfaces.
KOH / TMAH Wet Anisotropic Etching
Alkaline wet etching that exploits the dramatic etch rate difference between silicon crystal planes — 〈100〉 etches ~100× faster than 〈111〉. Enables V-groove formation, membrane release with precise thickness control using electrochemical etch-stop techniques, and bulk micromachining of silicon wafers.
HF Vapor Etching — Sacrificial Release
Anhydrous HF vapor etching for sacrificial oxide removal without liquid surface tension — eliminating stiction (capillary adhesion) of released MEMS structures. The process used for releasing cantilevers, membranes, and comb-drive structures after DRIE without the yield loss associated with wet release and drying.
RIE — Reactive Ion Etching (Dielectrics & Metals)
Standard RIE for anisotropic etching of dielectric and metal thin films. Processes include SiO₂ etching (CF₄/CHF₃/Ar), Si₃N₄ etching (CF₄/O₂ or SF₆), polymer/photoresist etching (O₂ plasma ashing), and metal etching (Cl₂/BCl₃ for Al, Ar ion milling for Au/Pt). Suitable for pattern transfer from photoresist into underlying films.
Wet Chemical Etching (Isotropic)
Isotropic wet etching using acidic mixtures for blanket or patterned removal of thin films. HNA (HF:HNO₃:CH₃COOH) for isotropic silicon etching, BOE (buffered oxide etch) for SiO₂ removal, hot H₃PO₄ for Si₃N₄ stripping, and various metal etchants (Al etch type A, Au/KI etchant, Cr etchant). Also used for wafer thinning and damage removal post-grinding.
Typical Applications
DRIE etching of comb-drive structures, proof masses, and suspension springs for accelerometers and gyroscopes. HF vapor release of SOI device layer structures with zero stiction yield loss.
High-aspect-ratio silicon via etching for 2.5D/3D packaging. Bosch process to achieve 10:1 AR TSVs (10μm × 100μm) with SiO₂ liner isolation and Cu electroplating fill.
DRIE for deep channel etching (50–200μm) in silicon and glass. KOH anisotropic etching for V-groove channel formation. Through-wafer via etching for fluidic interconnects.
Cryogenic DRIE for smooth-sidewall silicon waveguide etching. RIE for Si₃N₄ and SiO₂ waveguide pattern transfer. HF vapor release for suspended photonic membrane structures.
DRIE for SiC mesa isolation etching in power MOSFETs and Schottky diodes. RIE plasma etching for GaN gate recess in HEMT fabrication. Wet etch for damage removal post-implantation.
Isotropic silicon wet etching (HNA) for wafer thinning to < 50μm. Post-grinding stress relief etch to remove subsurface damage and microcracks from mechanical backgrinding.
Etch Selectivity & Mask Selection
Successful etching depends on choosing the right masking material and understanding selectivity ratios. Key mask systems include: photoresist (simplest, limited to shallow Si etches < 50μm due to erosion), SiO₂ hard mask (Si:SiO₂ selectivity ~100:1 in Bosch process, ideal for deep DRIE), Si₃N₄ hard mask (excellent for KOH etching — Si:Si₃N₄ selectivity > 1000:1), and metal hard masks (Al or Cr for deep RIE of dielectrics). Our process engineers can recommend the optimal mask strategy for your specific etch depth, feature size, and substrate material combination.
Metrology & Process Control
Post-etch metrology includes: profilometry (Dektak or optical) for etch depth and step height measurement, SEM cross-section for sidewall angle, scalloping size, and aspect ratio verification, AFM for sidewall roughness quantification (particularly for cryogenic and KOH etches), and optical microscopy for etch uniformity, undercut, and defect inspection. In-process monitoring includes optical emission spectroscopy (OES) for endpoint detection and laser interferometry for real-time depth measurement during DRIE.
Critical Point Drying (CPD)
For wet-released MEMS structures where HF vapor is not suitable, we offer critical point drying (CPD) using CO₂ to eliminate surface-tension-induced stiction during drying. The process transitions the rinse liquid (typically IPA or methanol) to supercritical CO₂ and then vents the CO₂ as a gas — avoiding the liquid-vapor interface that causes capillary adhesion. Essential for high-aspect-ratio, low-stiffness MEMS structures.
Need Precision Etching for Your Devices?
Specify your substrate material, etch depth, feature size, and required sidewall profile — our etch process engineers will recommend the optimal technology and provide a quotation within 24 hours.