Etching of semiconductors

In the case of irradiated semiconductor suspensions, the monoacid is formed in a one-hole transfer reaction as given by the lower path in the reaction scheme. This reaction is of great interest because the monoacid described here is difficult to synthesize by ordinary chemical methods. Many other reactions have been investigated [118]. 

Si02 is dissolved by HE The electrochemical etching is characterized by hole transfer. Taking GaAs as an example, the dissolution at low pH can be described by [120]  

When etching is carried out at open-circuit potentials, these holes must be supplied by an oxidizing agent of a fairly positive standard potential such as Ce [121]. We have then 

Since this process occurs via the valence band it works for a p-type electrode as well as for an n-type material. This is an etching process which occurs at metal electrodes in the same way. 

Accordingly, a surface state (surface radical) is formed which acts as an effective electron trap, i.e. 

Photoetching is of special interest, because the semiconducting material can be locally etched away by focussing a light beam on a certain spot (or by using 

Light-sensitive etching with polarization from an external source is called photoanodic etching, and that in an oxidizing solution, photochemical etching. 

Light-sensitive etching is based on the change, due to illumination, in the minority-carrier concentration, which determines the rate of anodic dissolution and corrosion of semiconductors. For example, under illumination of an n-type semiconductor in the anodic polarization regime, the etching rate can be limited by the rate of hole supply to the electrode surface. In darkness, a certain. 

Illumination of a semiconductor under open-circuit conditions in an etching (oxidizing) solution gives rise to corrosion even in darkness. In the simplest case where the cathodic partial reaction of a corrosion process proceeds exclusively through the conduction band and the anodic one through the valence band, the corrosion rate for specimens of any conductivity type is limited by the minority-carrier supply to the surface and is therefore low in darkness. Illumination accelerates corrosion processes. Comparison with the case considered above shows that here the chemical polarization of the semiconductor by an oxidizer introduced into the solution acts as anodic polarization. 

In simple cases but ones that are important for practical applications, the theory of laser etching yields an analytical expression for the characteristics of the relief produced as a function 

the resolution of light-sensitive etching, i.e., the maximal value d attained, is not determined, in accordance with the above consideration, by the diffusion length Lp, as might be expected a priori (a — Lp), but is much higher. 

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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. 

Zalm P C 1986 Ion-beam assisted etching of semiconductors Vacuum 36 787-97... 

Uses. The chemical inertness, thermal stability, low toxicity, and nonflammability of PFCs coupled with their unusual physical properties suggest many useflil applications. However, the high cost of raw materials and manufacture has limited commercial production to a few, small-volume products. Carbon tetrafluoride and hexafluoroethane are used for plasma, ion-beam, or sputter etching of semiconductor devices (17) (see loN implantation). Hexafluoroethane and octafluoropropane have some applications as dielectric gases, and perfluorocyclobutane is used in minor amounts as a dielectric fluid. Perfluoro-1,3-dimethyl cyclohexane is used as an inert, immersion coolant for electronic equipment, and perfluoro-2-methyldecatin is used for... 

Born in London, Paul May grew up in Redditch, Worcestershire. He went on to study at Bristol University, where he graduated with a first class honours in chemistry in 1985. He then joined GEC Hirst Research Centre in Wembley where he worked on semiconductor processing for three years, before returning to Bristol to study for a PhD in plasma etching of semiconductors. His PhD was awarded in 1991, and he then remained at Bristol to co-found the CVD diamond research group. In 1992 he was awarded a Ramsay Memorial Fellowship to continue the diamond work, and after that a Royal Society University Fellowship. In October 1999 he became a full-time lecturer in the School of Chemistry at Bristol. He is currently 36 years old. His scientific interests include diamond films, plasma chemistry, interstellar space dust, the internet and web technology. His recreational interests include table-tennis, science fiction, and heavy metal music. 

Another example comes from the field of semiconductor photoelectrochemistry. Semiconductors in contact with aqueous solutions can drive chemical reactions when irradiated. This is the basis for the photoelectrochemical etching of semiconductors in the electronic industry and for much research aiming at... 

Advances in Gas Phase Ion Chemistry is different from other ion chemistry series in that it focuses on reviews of the author s own work rather than give a generai review of the research area. This allows for presentation of some current work in a timely fashion which marks the unique nature of this series. Emphasis is placed on gas phase ion chemistry in its broadest sense to include ion neutral, ion electron, and ion-ion reactions. These reaction processes span the various disciplines of chemistry and include some of those in physics. Within this scope, both experimental and theoretical contributions are included which deal with a wide variety of areas ranging from fundamental interactions to applications in real media such as Interstellar gas clouds and pleismas used in the etching of semiconductors. The authors are scientists who are leaders in their fields and the series will therefore provide an up-to-date analysis of topics of current importance. This series is suitable for researchers and graduate students working in ion chemistry and related fields and will be an invaluable reference for years to come. The contributions to the series embody the wealth of molecular information that can be obtained by studying chemical reactions between ions, electrons and neutrals in the gas phase. 

Among the methods of anodic and chemical etching of semiconductors, widely used both in the production of semiconductor devices and in investigations (see, for example, Schnable and Schmidt, 1976 Turner and Pankove, 1978), the so-called light-sensitive etching is of great importance. It is based on the variation, under illumination, of the concentration of minority carriers, which often determines, as was shown above, the rate of anodic dissolution and corrosion of semiconductors. 

In recent years the surface science approach has led to a dramatic increase in our knowledge of the surface chemistry and kinetics. Processes that have been studied using the surface science approach include the deposition and etching of semiconductors (e.g., Si, Ge,... 

Electrolytic etching of semiconductors is used to remove damaged surface layers on single crystal material and/or shape... 

The electrochemistry of the anodic etching of semiconductors is similar in most respects to the anodic dissolution of metals. The main difference in the electrolytic behavior of metals and semiconductors is in the electrode material itself. 

This leads us to another important category of multi-electron photoprocesses involving the semiconductor itself. While photocorrosion is a nuisance from a device operation perspective, it is an important component of a device fabrication sequence in the microelectronics industry. Two types of wet etching of semiconductors can be envisioned [290]. Both occur at open-circuit but one involves the action of chemical agents that cause the simultaneous rupture and formation of bonds. This is exemplified by the action of H2O2 on GaAs [291] ... 

The etching of semiconductors in the manufacture of computer chips is another important solid-liquid dissolution reaction, see Problem P5-12 and Section 12.10). The dissolution of the semiconductor MnOj was studied using a number of different acids and salts. The rate of dissolution was found to be a function of the reacting liquid solution redox potential relative to the energy-level conduction band of the semiconductor. It was found that the reaction rate could be increased by a factor of 10 simply by changing the anion of the acid From the data below, determine the reaction order and specific reaction rate for the dissolution of Mn02 in HBr. 

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