Anisotropic etch profiles

Low energy electron-enhanced etching (LE4) uses a DC plasma in which electrons with energies <15 eV and reactive species at thermal velocities are incident on a sample. The sample is also heated at temperatures ranging from 50 to 250°C. Gillis et al [26,27] used hydrogen and chlorine plasmas to produce highly anisotropic etch profiles and smooth etch surfaces, at etch rates of 50 - 70 nm/min. 

Figure 1.5 Isotropic and anisotropic etch profiles created by wet and dry etchings.

Figure 14. Etch profiles for isotropic, tapered, and anisotropic etching of a film. Sq, Wq and Sf, Wf represent mask dimensions before etching and feature dimensions after etching, respectively. The degree of undercutting (dfj) and wall taper (6) are indicated for etching to a depth (dy) that exposes just the initial mask dimensions in the substrate. (Reproduced with permission from Ref. 11J...

Figure 1. Cross sections of films etched with liquid or plasma etchants. The isotropic profile is the result of zero overetch and can be generated with liquid or plasma etch techniques. The anisotropic (vertical) profile requires plasma or dry-etch processes. W is the width of the resist pattern. (Reproduced from reference 2. Copyright 1983 American Chemical Society.)...

Ion bombardment can be used to enhance resist etch rates and thus achieve anisotropic resist profiles. Reactive sites produced by bombardment permit more rapid attack by oxygen species in the plasma. Multilevel processing (181,182), in which an etch-resistant layer serves as a mask to pattern... 

Sputter or ion etching (IE) is also a physical etching method with inert ions (such as Ar+) from a plasma which are accelerated towards the substrate. In this case the substrate is in contact with the plasma. The etching profile is anisotropic, the selectivity is poor. 

Plasma etching. (PE) Physical-chemical etching with free radicals, supported by ions. Etching profile anisotropic-isotropic, good selectivity. 

FIGURE 8.6 The cross section of a weir-type filter (not to scale). The channels in the silicon substrate are anisotropically etched using EPW. This gives the characteristic V-shaped grooves. This profile is critical to preventing surface tension lock. The barrier or weir is etched in a different step from the channels and can be anywhere from 0.1 pm to a few micrometers from the lid. The lid is Pyrex glass and is attached to the substrate by anodic bonding [836]. Reprinted with permission from Elsevier Science. 

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