《Chapter10_introduce_to_etching_图文》由会员分享，可在线阅读，更多相关《Chapter10_introduce_to_etching_图文（23页珍藏版）》请在金锄头文库上搜索。
1、Chapter 10 Etching,Introduction to etching.Wet chemical etching: isotropic.Anisotropic etching of crystalline Si.Dry etching overview.Plasma etching mechanism.Types of plasma etch system.Dry etching issues.Dry etching method for various films.Deep Si etching (can etch through a wafer).,1,NE 343: Mic
2、rofabrication and thin film technologyInstructor: Bo Cui, ECE, University of Waterloo; http:/ece.uwaterloo.ca/bcui/Textbook: Silicon VLSI Technology by Plummer, Deal and Griffin,Material removal: etching processes,Etching is done either in “dry” or “wet” methods:Wet etching uses liquid etchants with
3、 wafers immersed in etchant solution.Wet etch is cheap and simple, but hard to control (not reproducible), not popular for nanofabrication for pattern transfer purpose.Dry etch uses gas phase etchants in plasma, both chemical and physical (sputtering process).Dry plasma etch works for many dielectri
4、c materials and some metals (Al, Ti, Cr, Ta, W).For other metals, ion milling (Ar+) can be used, but with low etching selectivity. (as a result, for metals that cannot be dry-etched, it is better to pattern them using liftoff),Figures of merit: etch rate, etch rate uniformity, selectivity, and aniso
5、tropy.,Etching is consisted of 3 processes:Mass transport of reactants (through a boundary layer) to the surface to be etched.Reaction between reactants and the film to be etched at the surface.Mass transport of reaction products from the surface through the surface boundary layer.,2,Figures of meri
6、t: selectivity,Etching with mask erosion,Etching selectivity:The ratio of etching rate between different materials, usually the higher the better. Generally, chemical etching has high selectivity, physical etching (sputtering, milling) has low selectivity.For fabrication, the selectivity is usually
7、between film material and mask material, and is defined by Sfm. (f: film; m: mask),Temperature affects selectivity,3,Selective over-etch of different materials,The film is etched through to the bottom, plus over-etch to etch laterally for under-cut profile.,4,Figures of merit: anisotropy,Isotropic:
8、etch rate is the same along all directions.Anisotropic: etch rate depends on direction, usually vertical vs. horizontal.,For isotropic, RI=1. For complete anisotropic, RI=0.,CD: critical dimension,5,Generally speaking, chemical process (wet etch, plasma etch) leads to isotropic etch; whereas physica
9、l process (directional energetic bombardment) leads to anisotropic etch.Isotropic:Best to use with large features when sidewall slope does not matter, and to undercut the mask (for easy liftoff).Large critical dimension (CD, i.e. feature size) loss, generally not for nano-fabrication.Quick, easy, an
10、d cheap.Anisotropic:Best for making small features with vertical sidewalls, preferred pattern transfer method for nano-fabrication and some micro-fabrication.Typically more costly.,Figures of merit: anisotropy,6,Chapter 10 Etching,NE 343: Microfabrication and Thin Film TechnologyInstructor: Bo Cui,
11、ECE, University of Waterloo, bcuiuwaterloo.caTextbook: Silicon VLSI Technology by Plummer, Deal, Griffin,Introduction to etching.Wet chemical etching: isotropic.Anisotropic etching of crystalline Si.Dry etching overview.Plasma etching mechanism.Types of plasma etch system.Dry etching issues.Dry etch
12、ing method for various films.Deep Si etching (can etch through a wafer).,7,Wet etching,Wet etching was used exclusively till 1970s when feature size 3um.For small scale features, large etch bias leads to significant CD (critical dimension) loss.For todays IC industry, wet etching is used for noncrit
13、ical feature sizes.Advantages: high selectivity, relatively inexpensive equipment, batch system with high throughput, etch rate can be very fast (many m/min).Disadvantages: generally isotropic profile, high chemical usage, poor process control (not so reproducible), excessive particulate contaminati
14、on.,The etch rate can be controlled by any of the three serial processes: reactants transport to the surface (depends on chemical concentration and stirring), reaction rate (depends on temperature), reaction products transport from the surface (depends on stirring).Preference is to have reaction rat
15、e 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 control will result in non-uniform etch rate: edge etches faster. Etchant is often stirred to minimize boundary layer and make etching more
16、 uniform.,8,Isotropic wet etching (silicon dioxide),Etch is isotropic and easily controlled by dilution of HF in H2O.Thermally grown oxide etches at 120nm/min in 6H2O:1HF 1 m/min in 49 wt% HF (i.e. undiluted as purchased HF).Faster etch rate for doped or deposited oxide. High etch selectivity (SiO2/Si) 100 Buffered HF (BHF) or buffered oxide etchant (BOE) provides consistent etch rate In regular HF etches, HF is consumed and the etch rate drops.HF buffered with NH4F to maintain HF concentration, typically 6NH4F : 1HF NH4FNH3+ HF,
