PE2-5.3 Microfabrication & Packaging

Work through these

• Wafer processing and photolithography

  The starting sequence, shared with ordinary chip making. If the VLSI technology material is familiar this is revision until the micromachining items.

• Ion implantation and oxidation

  Two more shared steps, for doping and for growing insulator. Included so the process flow is complete.

• Chemical vapour deposition and physical vapour deposition

  Adding material, from a gas or from a target. The stress in the deposited film is what decides whether a released structure curls, which is specific to this field.

• Deposition by epitaxy

  Growing a crystalline layer on a crystalline surface, which gives the best material quality. Used where the mechanical properties have to be predictable.

• Etching

  Removing material, which is where this field starts diverging from ordinary fabrication. The distinction between attacking equally in all directions and preferentially is about to matter enormously.

• Bulk micromachining

  Cutting into the substrate itself, using the fact that the etch attacks some crystal planes far faster than others. The characteristic sloped walls are a consequence of the crystal, not the tool.

• Surface micromachining and the sacrificial release step

  Building on top instead and then dissolving a layer underneath to free the structure. The release step is the moment the device becomes mechanical and the moment it most often fails.

• The LIGA process

  Making tall structures with X-rays and electroplating, which reaches aspect ratios the other methods cannot. Expensive, and used where nothing else works.

• Packaging technology; system level packaging

  Getting the finished device into something usable, which is harder here because it may need to be exposed to what it measures. Packaging is frequently the majority of the cost.

• Single and multichip packaging; interfacing in microsystem packaging

  The remaining packaging questions, including combining several dies and getting signals in and out. It closes the fabrication sequence.