Characterization, film stress

Characterization of Stresses in Polymer Films for Microelectronics Applications... 

The flocculation and coalescence processes of a polydis-persed lamella or film can be divided into two processes film drainage and film rupture. To model the film-mpture process of polydispersed emulsions, film stress-relaxation experiments were carried out. In these experiments, the film was quickly expanded and then the relaxation of the film was measured. To characterize the film-drainage process, dynamic film-tension measurements were conducted in which the film was continuously and slowly expanded while the film tension was monitored. Single interfaces were also studied by forming a drop at the eapillary (7). 

The preceding section has described a useful technique for characterizing blown film bubbles based on easfly calculated processing values. However, as indicated, the technique is generalized and only provides qualitative information about the degree of melt stretching imparted on the film. Many comprehensive studies have been performed to develop more sophisticated models that characterize bubble stresses and kinematics (shape and velocities). For more detailed reading on this subject, the reader is referred to additional resources [17—28]. 

The Mullins effect is characterized by stress softening. In order to demonstrate the presence of the Mullins effect in NR nanocomposites, three successive tensile cycles were performed for each sample. For the unfilled NR matrix, curves corresponding to the successive cycles were perfectly superposed, to a few per cent (6-8%) (Figure 14.22(a)).For nanocomposites, a significant decrease in G o can be observed between the first and the second cycle, for films reinforced with 30 wt% starch nanocrystals (Figure 14.22(b)).Similar to the Payne effect, the magnitude of the Mullins effect also increases with filler content. Furthermore, this increase was almost proportional to the filler content. 

Properties may be general, for example thickness, or may vary locally, for example presence of pinholes in the film or small areas of high film stress. The general properties of the film may not be uniform over a large surface area or may not be constant from one area to another on the holding fixtures (i.e. there may not be position equivalency). Often variations may be due to substrate conditions, deposition parameters, etc. This means that some care must be taken in selecting the material to be characterized and the sampling statistics must take into consideration the possibility of such variations with position. 

Residual film stress during deposition by deflection of a thin beam. l The result of in situ characterization should be noted on the traveler. 

Witness plate (characterization) A substrate that is not a part of the production batch but is used for characterizing some portion of the process or some film property such as film thickness, film stress, film adhesion, etc. Also called a Monitor plate. 

Physical Properties. Raman spectroscopy is an excellent tool for investigating stress and strain in many different materials (see Materlals reliability). Lattice strain distribution measurements in siUcon are a classic case. More recent examples of this include the characterization of thin films (56), and measurements of stress and relaxation in silicon—germanium layers (57). 

Elastohydrodynamic Lubrication (EHL). Lubrication needs in many machines ate minimized by carrying the load on concentrated contacts in ball and toUet beatings, gear teeth, cams, and some friction drives. With the load concentrated on a small elastically deformed area, these EHL contacts ate commonly characterized by a very thin separating hydrodynamic oil film which supports local stresses that tax the fatigue strength of the strongest steels. 

The Metravib Micromecanalyser is an inverted torsional pendulum, but unlike the torsional pendulums described eadier, it can be operated as a forced-vibration instmment. It is fully computerized and automatically determines G, and tan 5 as a function of temperature at low frequencies (10 1 Hz). Stress relaxation and creep measurements are also possible. The temperature range is —170 to 400°C. The Micromecanalyser probably has been used more for the characterization of glasses and metals than for polymers, but has proved useful for determining glassy-state relaxations and microstmctures of polymer blends (285) and latex films (286). 

Characterization. The proper characterization of coUoids depends on the purposes for which the information is sought because the total description would be an enormous task (27). The foUowiag physical traits are among those to be considered size, shape, and morphology of the primary particles surface area number and size distribution of pores degree of crystallinity and polycrystaUinity defect concentration nature of internal and surface stresses and state of agglomeration (27). Chemical and phase composition are needed for complete characterization, including data on the purity of the bulk phase and the nature and quaHty of adsorbed surface films or impurities. 

Stress in crystalline solids produces small shifts, typically a few wavenumbers, in the Raman lines that sometimes are accompanied by a small amount of line broadening. Measurement of a series of Raman spectra in high-pressure equipment under static or uniaxial pressure allows the line shifts to be calibrated in terms of stress level. This information can be used to characterize built-in stress in thin films, along grain boundaries, and in thermally stressed materials. Microfocus spectra can be obtained from crack tips in ceramic material and by a careful spatial mapping along and across the crack estimates can be obtained of the stress fields around the crack. ... 

One of the apparent results of introducing couple stress is the size-dependent effect. If the problem scale approaches molecular dimension, this effect is obvious and can be characterized by the characteristic length 1. The size effect is a distinctive property while the film thickness of EHL is down to the nanometre scale, where the exponent index of the film thickness to the velocity does not remain constant, i.e., the film thickness, if plotted as a function of velocity in logarithmic scale, will not follow the straight line proposed by Ham-rock and Dowson. This bridges the gap between the lubrication theory and the experimental results. 

Experiments like those described above have been performed to evaluate sodium ion barrier properties of Hitachi PIQ and DuPont PI 2540 polyimide films. Also included in the comparison were silicon nitride coatings plasma deposited in both tensile and compressive stress modes. The structure of the samples is illustrated in Figure 9. N-type, (111) oriented silicon substrates were cleaned and oxidized in dry oxygen ambient at 1100°C to form a 1060 A Si02 film. Wafers intended for polyimide characterization were coated with an organic silane film (gamma glycidal amino propyl trimethoxysilane) to promote adhesion of the polyimide to the oxide surface. The polyimide resins were spun onto the wafers at speeds to produce final... 

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