Dry etching

Physical etching uses beams of ions, electrons, or photons to bombard on the material surface. The ions are accelerated in an electric field and bombarded on the surface of a target. The ions knock out the atoms from the substrate surface due to the high kinetic energy, that is, the etching action takes place due to the physical action of the incident ion flux. 

Physical dry etching is carried out in low pressures, and the ejected material must be transported out before undergoing redeposition. The target, that is, the substrate to be etched, is coupled with electrode. The plasma produced by the electrodes is directed to the target. The 

2Xep2 -I- Si = 2Xe -l- Sip4 (volatile) where xenon and Sip4 are the volatile components which desorb. 

Physicochemical dry etching also known as reactive ion etching (RIE) is an important technique for micromachining. Here, the reactant gases are excited to ions. The ions are bombarded on the substrate activating the reaction. The basic conflguration is that the object, that is, the target to be etched, is placed on the cathode of a cold plasma, which is made up of reactive species. The movement of the ions is ballistic at low pressure. The ions 

In sputter etching (ion etching or ion beam etching) the workpiece is placed into a plasma reactor. The removal of material is a real physical process. A plasma is defined as a partially or fully ionised but spatially neutral gas, which contains electrons, ions and eventually uncharged species. Such species are atoms, molecules and radicals. A plasma is ignited using for instance an RF power source generating ions that are accelerated towards the workpiece 

Process Mechanism of effect Selectivity Profile of geometry Pressure (Pa) 

Barrel etching Chemical Excellent anisotropic Isotropic 100 

Additionally to the above mentioned processes, magnetically enhanced and chemically assisted processes have been developed. Further information can be found in the literature [342]. 

Selectivity Poor to good (dependent on the special process) Good 

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In corrosion, adsorbates react directly with the substrate atoms to fomi new chemical species. The products may desorb from the surface (volatilization reaction) or may remain adsorbed in fonning a corrosion layer. Corrosion reactions have many industrial applications, such as dry etching of semiconductor surfaces. An example of a volatilization reaction is the etching of Si by fluorine [43]. In this case, fluorine reacts with the Si surface to fonn SiF gas. Note that the crystallinity of the remaining surface is also severely disrupted by this reaction. An example of corrosion layer fonnation is the oxidation of Fe metal to fonn mst. In this case, none of the products are volatile, but the crystallinity of the surface is dismpted as the bulk oxide fonns. Corrosion and etching reactions are discussed in more detail in section A3.10 and section C2.9. 

Dry etching is a commonly used teclmique for creating highly anisotropic, patterned surfaces. The interaction of gas phase etchants with surfaces is of fundamental interest to understanding such phenomena as undercutting and the dependence of etch rate on surface structure. Many surface science studies aim to understand these interactions at an atomic level, and the next section will explore what is known about the etching of silicon surfaces. 

In order to design and optimize anisotropic dry etching processes, severai issues must be understood ... 

In what may be the single most influential experiment in the field of dry etching, Jolm Cobum and Eiarold Winters of the IBM Almaden Research Centre in San Jose, CA, USA demonstrated that the rate of the F-Si thennal etching... 

Gillis H P, Choutov D A and Martin K P 1996 The dry etching of Group Ill-Nitride wide bandgap semiconductors J. Mater. 48 50-5... 

Etch Mechanisms. Most wet etches for the compound semiconductors employ oxidation of the semiconductor followed by dissolution of the oxide. For this reason, many wet etches contain the oxidant hydrogen peroxide, although nitric acid can also be used. One advantage of wet etching over dry is the absence of subsurface damage that is common with dry etching. Metal contacts placed on wet-etched surfaces exhibit more ideal characteristics than dry-etched surfaces. 

Polyimides, both photodefinable and nonphotodefinable, are coming iato iacreased use. AppHcatioas iaclude planarizing iatedayer dielectrics oa iategrated circuits and for interconnects, passivation layers, thermal and mechanical stress buffers ia packagiag, alpha particle barriers oa memory devices, and ion implantation (qv) and dry etching masks. 

Non-selective films are easily pattemable by wet or dry etching technology. 

Initial studies of the dry-etch resistance of these resists showed that PFEMA had an etching rate in a CCl plasma (p = 0.2 torr, P = 600 W) about threeotimes lower (i.e. 380 X/min) than that of aluminum (i.e. 1200 A/min). 

The passivation of dry-etching damage by low energy hydrogen implantation from a Kaufman ion source (0.4 keV) has also been reported (Singh et al., 1984b). The Si samples were either initially bombarded with a... 

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