Planar techniques

To meet these requirements, a local and global planarization technique for the disk substrates becomes neces-... 

The preparative (or nonlinear) adsorption TLC has never attracted enough attention from the side of theoreticians of the planar technique to result in a codified system of rules, helpful in an efficient carrying out of micropreparative isolation of individual compoimds or compoimd groups. Normally, it is taken for granted that to the preparative (i.e., nonlinear) adsorption TLC, the same rules ean be applied as to the analytical (i.e., linear) variant, although it is also known in advance that performance of these rules in the former case is considerably worse than in the latter one. 

The major attribute that distinguishes planar techniques from column chromatography is that in the former separation and detection are discontinuous ( offline )- In column chromatography analytes are carried through the entire column and monitored at the end, usually by flow-through detectors measuring changes in some physical characteristics of the effluent (optical... 

Much effort has been made over the past 15 years to replace planar techniques with modern column-based techniques. The advantages of columns are many including reproducibility, speed, selectivity, and ease of use among others. Another advantage of columns is that they are much easier, in almost all cases, to interface to detectors such as mass spectrometers. 

The process sequence for several multi-level resist schemes involving planarization techniques. 

Planar techniques can tolerate application of either solutions or suspensions. In addition, the solvent used to dissolve the sample need not be compatible with the TLC mobile phase as is the case for HPLC methods. 

A process for the production of photodiodes by a planar technique is presented in US-A-3988774. A thin transition layer is formed between the substrate and a dielectric masking layer necessary for local diffusion to increase the shunt resistance of the photodiodes. The... 

The data obtained by planar techniques are reported as Rf values, which were defined and discussed in Chapter 5. Extensive bibliographies have been published.1,2 Stahl, who first used the name TLC, has written an interesting account of his 20 years in the field3 as well as a useful laboratory handbook.4... 

All of these uncontrollable factors make it difficult to operate the planar techniques by the best theoretical principles, and their development has been more empirical than the column methods. However, the rate equation predicts that small particle sizes should increase efficiency, and that has been found to be true for TLC. Until a few years ago, the particle size of the silica gel in common TC plates was typically greater than 10 ixm in diameter, yielding a few hundred plates for a typical run. 

There is another difference between column techniques and planar techniques in LC. It is the way that the retention ratio is expressed. In Chapter 1, the retention ratio Rr was defined for column techniques as... 

There is a parameter used in the planar techniques that has not been defined. It was suggested by Martin in 1949 as a way to relate an analyte s structure and its free energy for chromatographic partitioning. It is called Rm and its definition is... 

TLC is the more popular of the two planar techniques. It is used for fast screening of mixtures and for surveying methods for use in columns. Quantitative analysis is better accomplished by column LC, but quantitative TLC is increasing in popularity as the instrumentation improves. Table 4 contains a summary of the advantages and disadvantages of the planar methods. 

Davari B, Koburger CW, Schulz R, Wamock JD, Furukawa T, lost M, Taur Y, Schwittek WG, DeBrosse JK, Kerbaugh ML, Mauer JL. A new planarization technique using a combination of RIE and chemical mechanical polish (CMP). lEDM Technical Digest Dec 1989. p 61-64. 

As mentioned in Chapter 1, the present state of CMP is the result of the semiconductor industry s needs to fabricate multilevel interconnections for increasingly complex, dense, and miniaturized devices and circuits. This need is related to improving the performance while adding more devices, functions, etc. to a circuit and chip. This chapter, therefore, discusses the impact of advanced metallization schemes on the performance and cost issues of the ICs. Our discussions start with the impact of reducing feature sizes on performance and the need of various schemes to counter the adverse effect of device shrinkage on the performance of interconnections. An impact of continued device shrinkage on circuit delay is discussed. Then the need of low resistivity metal, low dielectric constant ILD, and planarized surfaces is established leading to the discussion of CMP. Finally various planarization techniques are compared to show why CMP is the process that will satisfy the planarity requirements of the future. 

J. Olsen and F. Moghadam, Planarization Techniques, in Multilevel Metallization for Integrated Circuits, eds. S.R. Wilson, C.J. Tracy, and J.L. Freeman, Noyes Publications, Park Ridge, NJ (1993). 

Several examples are known in which the separation itself was done by using a planar technique, and the detection by using direct visualisation. X-ray detection or mass spectrometry after transfer of the spots to another plane. In one example the separation was done by two-dimensional (2D) slab electrophoresis and then applied to 2D-TLC directly combined with mass spectrometry 111. -115]. The methods cannot be directly applied for 2D polyacrylamide gel electrophoresis because an essential portion (S-Ll f) of the polyacrylamide gel is water, and therefore a 9 x 1.1 cm plate of polyacrylamide contains 15 ml water 1116. This is the reason that the gel cannot be directly inserted into the high-vacuum source of the mass spectrometer. To avoid the complications of freeze-drying and other methods of removing the water and to keep the substances in the gel as well as the form of the gel, the separated substances should be transferred to a plate. Nitrocellulose was found to have the properties required and this method was used to detect bradykinin and dynorphine using SIMS (Secondary /on Mass Spectrometry). A detailed description is given for TLC-SIMS (115]. 

Substrate planarization is a critical requirement in the fabrication technology of state-of-the-art integrated circuits (ICs). After a brief review of the existing planarization techniques the use of spin-on glass (SOG) films, which have the inherent quality of planarizing underlying topography, as an interlevel dielectric is described. The physical, chemical, and dielectric properties of two SOG materials,... 

Planar imaging techniques are used to obtain a 2-D, full-field view of flames [32]. Acquired images provide useful information on fhe sfructure of fhe entire flow field. There are two major planar techniques applicable for fhe study of TDFCF (i) planar image velocimefry (PIV) and... 

B. Davari et at., A new planarization technique, using a combination of RIE and chemical mech anical polish (CMP), Tech. Dig. IEEE Int. Electron Devices Meet., p. 61 (1989). 

The planarity of the surface above a narrow CVD-filled trench may be quite good, provided a sufficient amount of CVD material has been deposited. The specific planarity will depend directly on the trench width and the CVD film thickness. This relationship is shown in Figure 20. Surface planarity will not be achieved for wider trenches. Such major surface irregularities cannot be tolerated as a final surface structure, and a post-CVD surface planarization technique must be employed to assure a sufficiently planar surface prior to a subsequent back-etching process step. 

The development of LC was rapid with the appearance of several different methods and techniques. Some trends are outlined. Liquid-liquid chromatography (LLC) was introduced in 1941. In this case, both the stationary phase and mobile phase are immiscible liquids. The stationary phase is a porous material (support) covered with a thin film of liquid. A variation of LLC is paper chromatography (PC), where the stationary phase is paper with the water included in its pores. PC was the first planar technique. The term planar comes from the fact that the stationary phase (paper) is a two-dimensional bed. A subsequent planar technique is thin-layer chromatography (TLC). In this case, the stationary phase is a thin layer of solid material, composed of small particles, spread on a glass plate or an aluminum sheet. 

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