Silicon nitride surface characterization

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... 

Although CVD and plasma deposited films offer excellent properties as a passivation layer, the inability to reproduce chemical and physical properties has been a problem. Depending on gas flow rates and deposition conditions, free Si, H, C and 0 may be Incorporated into the films. Characterization of these films has been restricted almost exclusively to surface analytical techniques and ellipsometry. AES and XPS have been used to determine the C, N, 0, and Si content of CVD silicon nitride. 

A new alternative to solve this problem is atomic force microscopy (AFM) which is an emerging surface characterization tool in a wide variety of materials science fields. The method is relatively easy and offers a subnanometer or atomic resolution with little sample preparation required. The basic principle involved is to utilize a cantilever with a spring constant weaker than the equivalent spring between atoms. This way the sharp tip of the cantilever, which is microfabricated from silicon, silicon oxide or silicon nitride using photolithography, mechanically scans over a sample surface to image its topography. Typical lateral dimensions of the cantilever are on the order of 100 pm and the thickness on the order of 1 pm. Cantilever deflections on the order of 0.01 nm can be measured in modem atomic force microscopes. 

Surface moisture is a problem of concern in ceramic powders, and IR has been used to characterize the surface groups of -OH and -H [58,63,64]. IR was also applied to characterize chemically bound hydrogen in chemical vapor-deposited silicon nitride at various ammonia-silane ratios [65]. Surface silicon dioxide on SiC powders was determined by photoacoustic IR and diffuse reflectance IR spectroscopy [66,67]. IR spectroscopy was also used to study the surface oxidation of SiC and SisN4 [68,69]. 

With respect to evenness and plane parallelism, the attainable accuracies are comparable to those of lapped parts. Ground parts, however, exhibit a surface structure with curved grinding traces superimposing in all directions. Lapped surfaces on the other hand are characterized by a microscopic crater structure that does not reveal any directional dependencies. If surface isotropy is a necessary quality criterion as, e.g., in optical applications, then surface grinding with lapping kinematics cannot be used. The various removal mechanisms and resulting surface patterns are shown in Figure 16.2 for the example of a silicon nitride sample. 

Very recently, many studies have been conducted to identify new reinforcing systems. These systems are similar to silica compounds and characterized by the use of a coupling agent to chemically bond elastomer chains to filler surface. Many reinforcing systems have been patented alumina oxyhydroxide and oxide [18,19], titanium oxides [20], and silicon nitride/carbide [21]. 

RBS has also been used to characterize palladium and tin catalysts on polyetherimide surfaces [229], titanium nitride thin films [230], silicon oxynitride films [231], and silicon nitride films [232]. and to study the laser mixing of Cu-Au -Cu and Cu - W - Cu thin alloy films on Si3N4 substrates [233], and the annealing behavior of GaAs after implantation with selenium [234]. 

D. K. McNamara is a scientist at Martin Marietta Laboratories. He joined the Laboratories in 1973, having previously worked at Mound Laboratory and Brookhaven National Laboratory in instrumentation and vacuum system design. His interest in structural characterization has involved research into such diverse materials as silicon nitride, metal- and polymer-based composites, and metal carbides. He has studied extensively the role of surface preparations in adhesive bonding, from both theoretical and practical standpoints. 

In previous papers we demonstrated that the same nitridation approach can be also successfully applied for the incorporation of nitrogen into the framework of different Y zeolites, this making possible the preparation of porous basic catalysts active in the Knoevenagel condensation reaction [13-14]. The present work was undertaken in order to understand the modifications induced by nitridation and to provide a picture of the chemical rearrangements that occur upon nitrogen incorporation into ultrastable Y zeolite (Si/Al ratio of 13). Since catalysis is a surface phenomenon we choose to characterize the local environments of nitrogen, silicon and aluminum by X-ray photoelectron spectroscopy (XPS). A clear identification of these modifications is essential to allow a control of the preparation parameters for more efficient basic catalysts. 

---