MEMS Device

MEMS devices require extremely careful preparation due to their complex multi-layer structure and fine features. Use precision diamond saws and diamond abrasives throughout. The material is prone to delamination between layers, so gentle handling and appropriate mounting are essential.

Use precision diamond saw with continuous coolant flow. Diamond saws are essential for cutting hard, brittle MEMS materials. Standard diamond blade (0.3-0.5 mm thickness) is appropriate. Use adequate coolant flow to prevent overheating and minimize thermal shock. Cutting speed: 100-200 RPM for most diamond saws. Apply very light pressure - the brittle, multi-layer material requires extremely careful handling to avoid delamination and cracking. Avoid forcing the cut which can cause layer separation. Leave adequate allowance (~1-2 mm) for grinding away any damage from cutting.

Cold mounting with low-viscosity epoxy resin is essential to avoid heat that could cause delamination or introduce thermal stress. Use a low-shrinkage epoxy resin for best edge retention. Vacuum impregnation may be necessary to ensure complete penetration into any porosity. Ensure complete cure before grinding to prevent edge rounding and maintain sample integrity. The multi-layer structure requires careful handling during mounting to avoid delamination.

The hardness and multi-layer structure require careful grinding with diamond abrasives. Use diamond grinding papers or diamond lapping films with adequate water lubrication. Disc speed: 200-300 RPM. Apply very light pressure (15-25 N per 30 mm sample) - the brittle, multi-layer material is prone to delamination if too much pressure is applied. Use sharp, fresh diamond papers to minimize deformation and prevent layer separation.

Grinding sequence:

• 240 grit diamond: Remove sectioning damage (30-60 seconds). Use very light pressure to avoid delamination.
• 320 grit diamond: Remove previous scratches (30-60 seconds). Monitor for any layer separation.
• 400 grit diamond: Remove previous scratches (30-60 seconds). Ensure complete scratch removal.
• 600 grit diamond: Remove previous scratches (30-60 seconds). Ensure complete scratch removal.
• 800 grit diamond: Final grinding step (30-60 seconds). Prepare surface for polishing.

Always rotate the specimen holder 90° between steps to ensure complete scratch removal. Use complementary rotation (platen and holder same direction, different speeds) rather than contra-rotation to minimize deformation. Adequate water lubrication is critical - avoid drying during grinding which can cause chipping or delamination.

The multi-layer structure requires careful polishing with diamond abrasives. Use diamond polishing with appropriate polishing pads for each stage. Apply very light pressure throughout to prevent delamination and deformation.

Diamond polishing sequence:

• 6μm diamond: 3-5 minutes on a soft synthetic pad (e.g., TEXPAN) with very light pressure (15-25 N per 30 mm sample). Start with 6μm to minimize damage. Monitor constantly for delamination.
• 3μm diamond: 3-5 minutes on a soft synthetic pad (e.g., TEXPAN) with very light pressure (12-20 N). Continue removing scratches from previous step. Monitor for layer separation.
• 1μm diamond: 2-4 minutes on a soft synthetic pad with very light pressure (12-20 N). These pads provide gentle material removal suitable for multi-layer structures.
• 0.05μm colloidal silica: 1-2 minutes on a soft final polishing pad (e.g., MICROPAD) with very light pressure. This removes any remaining fine scratches and prepares the surface for examination. Monitor for relief between layers - reduce polishing time if excessive relief develops.

Use appropriate polishing lubricants. The multi-layer structure means polishing times should be sufficient but not excessive - avoid over-polishing which can cause relief between layers and affect layer integrity. Monitor the surface frequently under the microscope to check for delamination, chipping, or excessive relief.

MEMS devices typically do not require etching for general microstructural examination. For specific layer analysis, specialized etchants may be used depending on the materials present:

Wright Etch (Chemical Etching) - For silicon layers:

• Composition: 60ml HF (49%), 30ml HNO₃ (70%), 30ml CrO₃ (5M), 60ml Cu(NO₃)₂ (1M), 60ml acetic acid, 60ml H₂O
• Application: Immerse sample for 10-30 seconds. Use in fume hood with excellent ventilation.
• Reveals: Silicon layer structure and defects.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.
• Note: HF is highly toxic - use proper PPE and fume hood.

Etching Strategy:

• Most MEMS devices do not require etching for general examination
• Use specialized etchants only when specific layer analysis is required
• Always clean and degrease before etching
• Use short initial etch times, check under the microscope, repeat if needed
• Be aware that different layers may etch at different rates

Safety: All etchants containing HF require proper PPE (gloves, safety glasses, lab coat), proper fume hood, and HF-specific safety measures. HF can cause severe burns and is toxic.