Structural devices
Structural devices

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Structural devices

7 Deposition

7.1 Introduction

Micro fabrication often involves multiple layers of different materials, each following a sequence of process steps, usually deposition/lithography/etching. The microelectronics industry has been a driver for many of these techniques and that momentum has carried over into the MEMS community. The treatment that follows covers examples from both industries.

The appropriate deposition technique depends on the purpose of the layer – a thin insulating barrier layer in a transistor or capacitor will have very different requirements from a metal plug filling a hole for a contact between layers. The capabilities of different techniques are outlined in Table 2.

Table 2 Aptitudes of different deposition techniques

Pure metals Alloys Semiconductors Compounds Polymers Rate Film purity Composition control Step coverage Wafer heated
Electroplating Y *** * * *** N
Evaporation Y (Y) *** ** * * (Y)
Sputtering (PVD) Y Y (Y) ** *** ** ** (Y)
Laser ablation deposition Y Y Y Y *** * ** ** (Y)
Reactive PVD Y ** *** ** ** (Y)
Chemical vapour deposition (CVD) (Y) Y Y Y ** * ** *** Y
PECVD Y Y Y ** * ** ** (Y)
Spin-on/flowfill Y Y *** * ** ** N
Atomic layer deposition (ALD) Y * ** ** *** (Y)
Molecular beam epitaxy (MBE) Y Y Y (Y) * *** *** ** Y
Key: Y means yes, N means no. Brackets indicate under some circumstances. The more stars, the better.

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