Etching simultaneous

The writer has found that etching and exami nation with CDTA at successive 15 second inter vals reveals information about relative rates of alite reactivity, for example, when comparing clinkers from different production periods. The polished sections are bound together with a rubber band and etched simultaneously, or the clinkers can be en capsulated in a multichambered container. 

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

Ion-Assisted Processes An alternative use of ion beams generated from low cost sources is to assist particular chemical reactions, or vapour deposition. An example here is in etching processes (Figure 16). The simultaneous use of an argon beam with XeFp gas compared with the use of either separately, to etch silicon produces an etch rate of a factor of at least fourteen. The use of ion beams can also increase the directionality (23) of the process (Figure 17). Examples are given in Table IV of how ion bombardment during film formation modifies the final film. 

In order to assess the accuracy of the present method, we compared it with two other methods. One was the Track Etch detector manufactured by the Terradex Corp. (type SF). Simultaneous measurements with our detectors and the Terradex detectors in 207 locations were made over 10 months. The correlation coefficient between radon concentrations derived from these methods was 0.875, but the mean value by the Terradex method was about twice that by our detectors. The other method used was the passive integrated detector using activated charcoal which is in a canister (Iwata, 1986). After 24 hour exposure, the amount of radon absorbed in the charcoal was measured with Nal (Tl) scintillation counter. The method was calibrated with the grab sampling method using activated charcoal in the coolant and cross-calibrated with other methods. Measurements for comparison with the bare track detector were made in 57 indoor locations. The correlation coefficient between the results by the two methods was 0.323. In the case of comparisons in five locations where frequent measurements with the charcoal method were made or where the radon concentration was approximately constant, the correlation coefficient was 0.996 and mean value by the charcoal method was higher by only 12% than that by the present method. 

Likewise, when Ar impinged on the surface, pure sputtering ( 2 A/min) was noted. However, when the beams were simultaneously directed at the silicon surface, a relatively large (--SS A/min.) etch rate was observed the measured rate was approximately an order of magnitude greater than the sum of the chemical and physical components. Obviously, synergistic effects due to ion bombardment are crucial to this chemical etch process. Unfortunately, the exact nature of these effects is at present undefined. 

Unlike silicon-based materials where selective reactants are of ultimate importance, and III-V and metallic materials where product volatility dominates etching considerations, selective etching of organic films is driven by incorporating the desired reactivity (or lack of it) into the film itself. In device fabrication all types of materials are present simultaneously and the process engineer must be aware of the important aspects of the chemistry of each material in addition to the gas phase reactions that produce chemically active species. It is hoped that the discussions presented here provide a basis for approaching such a complex chemical system and for critically evaluating studies which appear in the literature. 

The mechanism of silicon etching in alkaline solutions is a process of material dissolution with a simultaneous hydrogen evolution. The main soluble product is a silicic anion Si02(0H)2 that can further be condensed to form polysilicic anions. In fact, due to the acido-basic ionization of OH radicals in a highly alkaline solution, Eq. (19) should be modified as follows ... 

Emphasis will also be placed on approaches which lead to the removal of reactive species from the gas phase as well as the special role of energetic positive ions in plasma-surface interactions. Controlled scavenging of critical species from the gas phase and/or at specific surfaces and the degree of positive ion bombardment at a given surface can in fact result in simultaneous polymerizatidn at one surface and etching at another within the same apparatus. 

Fig. 32. Electron-assisted gas-surface chemistry using 1500 eV electrons and XeFj simultaneously incident on SiOj. P(total) = 6x 10 Torr with most of the ambient gas being xenon. Neither exposure to XeF nor an electron beam produced etching by itself. Simultaneous exposure produces an etch rate of 200 A/min. (See Ref. )...

There are numerous metal pretreatment techniques that can be used in addition to solvent degreasing. To obtain metal/polymer systems which exhibit strong initial adhesion it is usually sufficient to wash the metal with a solvent followed by an acid etch or sandblasting technique to remove any weak oxide layers and roughen the surface simultaneously. 

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