Negative resistance, utilization

John A. Copeland and Stephen Knight, Applications Utilizing Bulk Negative Resistance F.A. Padovani, The Voltage-Current Characteristics of Metal-Semiconductor Contacts P.L. Hower, W.W. Hooper, B.R. Cairns, R.D. Fairman, and D.A. Tremere, The GaAs Field-Effect Transistor Marvin H. White, MOS Transistors... 

Although the single-layer negative resists commonly utilized are simple, they typically do not resolve narrow (0.5 ftm) gaps between wide lines or pads due to proximity effects from backscatter from the substrate during electron beam (E-beam) exposure. Further, there are variations in linewidth which occur when images are written in a single-layer resist which overlies steps in the substrate. 

J. A. Copeland and S. Knight, Applications Utilizing Bulk Negative Resistance... 

It was indicated earlier that swelling limits resolution in solvent-developed negative resists. It was also intimated that swelling effects could be minimized if there were a sufficient polarity change between the exposed and non-exposed areas of the type mentioned in the previous discussion of the PBOCST system. A similar principle was utilized by Hofer et al., (145-146) at IBM, based on ion pair formation. The resist consists of a polystyrene polymer to which tetrathiofulvalene (TTF) units have been attached. When spun down with an acceptor such as CBr4, a complex is formed which, on irradiation, undergoes an electron transfer reaction to form an ion pair ... 

Many reports have been published on negative electron-beam resists. Most of these resists utilize radiation-induced gel-formation as the insolubilzation reaction. However, a major problem with these resists, is that their resolution is limited by swelling which is induced by the developer during development. 

The concepts of positive or negative systems are by no means a strict classification since modifications of the original pre-polymer with additives, with suitable changes In the development processes can be utilized to obtain positive resists whilst the unmodified material Is a negative resist. For example, tetra-chloro dlazo cyclopentadienes in general are polymerisable by UV light to obtain negative resist systems. 

An aqueous base developable negative resist for use in 193 nm lithography was developed by combining NBHFA and norbornene bearing a pendant vic-diol (Fig. 118) [352]. One problem in the design of 193 nm resists is that the benzylic stabilization effect cannot be utilized to drive the acidolysis reactions and two kinds of ketone can be formed in this case. 

Acid-catalyzed silanol condensation to form insoluble networks has been also utilized in the design of aqueous base developable negative resist systems [419]. An aqueous base soluble silicone polymer was synthesized by a sol-gel reaction of a mixture of phenyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane. This polymer contained a high concentration of silanol OH groups and thus was soluble in aqueous base. 

In theory, the antidigestive properties of Pi s combined with the above enzyme-based defenses should provide "double-barrel negative resistance, since the first increases the need for sulphur amino acids, and the second has the potential to decrease the availability of these and other amino acids. However, in order to jointly utilize these two defenses effectively, a deeper knowledge of their chemical interrelationships is necessary. Potential complications in the use of proteinase inhibitors will be discussed below. 

The band edges are flattened when the anode is illuminated, the Fermi level rises, and the electrode potential shifts in the negative direction. As a result, a potential difference which amounts to about 0.6 to 0.8 V develops between the semiconductor and metal electrode. When the external circuit is closed over some load R, the electrons produced by illumination in the conduction band of the semiconductor electrode will flow through the external circuit to the metal electrode, where they are consumed in the cathodic reaction. Holes from the valence band of the semiconductor electrode at the same time are directly absorbed by the anodic reaction. Therefore, a steady electrical current arises in the system, and the energy of this current can be utilized in the external circuit. In such devices, the solar-to-electrical energy conversion efficiency is as high as 5 to 10%. Unfortunately, their operating life is restricted by the low corrosion resistance of semiconductor electrodes. 

Many diseases, including anthrax, are most effectively treated before actual manifestation of the symptoms is observed. Presently a presumptive identification of Bacillus anthracis can be made in about 3 hours however, if a full laboratory response network (LRN) confirmation procedure is utilized, the theoretical time increases substantially to approximately 48 hours. During the recent anthrax cases 72 to 96 hours were common to complete the entire LRN protocol. In the meantime antibiotics were administered as a precaution based on the presumptive results to individuals thought to be exposed to B. anthracis spores or with anthrax symptoms. The mass administering of antibiotics from a cost standpoint, as well as from medical prudence to prevent the rise of antibiotic-resistant strains, is not the optimal answer to the anthrax infection problem. Therefore it is important that early tests be rapid and reliable with a minimum number of false positive and false negative results. 

C The Epoxy Resists. The first negative tone electron beam resist materials with useful sensitivity were based on utilizing the radiation chemistry of the oxirane or epoxy moiety. The most widely used of these materials, COP (Figure 32) is a copolymer of glycidyl methacrylate and ethyl acrylate and was developed at Bell Laboratories (43,44). COP has found wide applicability in the manufacturing of photomasks. The active element... 

---