文档介绍：Lecture 4 Micro-process technology Etching process
清華大學材料科學與工程系
廖建能教授
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Etching process
Basic Concepts of Etching
Wet Etching
Specific Wet Etches
– Silicon
– Silicon Dioxide
– Aluminum
Dry (Plasma) Etch Mechanisms
– Chemical Etching
– Physical Etching (sputtering)
– Ion Enhanced Etching
Plasma Reactors
Dry Etch Chemistry
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Introduction
Etching: using photoresist or SiO2/Si3N4 as mask layer to selectively remove part of the materials
Etching is done either in “dry” or “wet” methods
- Wet etching uses liquid etchants with wafers immersed in etchant solution.
- Dry etching uses gas phase etchants in a plasma.
Wet Etch: chemical process only
Dry Etch: chemical and physical (sputtering) process
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Basic Concepts
Etching is consisted of 3 process:
– Mass transport of reactants (through a boundary layer) to the surface to be etched
– Reaction between reactants and the film(s) to be etched at the surface
– Mass transport of reaction products from the surface through the surface boundary layer
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Types of Etching Processes
Isotropic (等向性):
Best to use with large geometries, when sidewall slope does not matter, and to undercut the mask
Quick, easy, and cheap
Anisotropic (非等向性):
Best for making small gaps and vertical sidewalls
Typically more costly
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Wet Etching
Diffusion reactive species from the liquid bulk through the boundary layer to the surface of wafer
Reaction of species at the surface to form solvable species
Diffuse reaction products away from the surface through the boundary layer into the bulk of the liquid
Advantages: High selectivity because it is based on chemical
processes
Disadvantages: Isotropic, poor process control and particulates
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Wet Etching 2
The etch rate can be controlled by any of the three serial processes
Preference is to have reaction rate controlled process because
– Etch rate can be increased by temperature
– Good control over reaction rate –temperature of a liquid is easy to control
Mass transport