Scanning silicon nitrides

TappingMode scanning techniques, (3) improved AFM probes (such as standard silicon nitride probes modified by electron beam deposition and... 

Nagy, P. B. and Adler, L. (1989). On the origin of increased backward radiation from a liquid-solid interface at the Rayleigh angle. J. Acoust. Soc. Am. 85,1355-7. [116] Narita, T., Miura, K., Ishikawa, I., and Ishikawa, T. (1990). Measurement of residual thermal stress and its distribution on silicon nitride ceramics joined to metals with scanning acoustic microscopy. /. Japan. Inst. Metals 54,1142-6. [148]... 

Fig. 31. Scanning electron micrograph (SEM) and scanning Auger element maps for an array of four strips of gold numbers 1,3,6, and 8) and four of aluminum/alumina (numbers 2, 4, 5, and 7) on a silicon nitride substrate that was exposed to a mixture of HS(CH2),, C1 and CF3(CF2)8C02H in isooctane. The SEM and element maps are for the array viewed from above the schematic of the device (the height of the strips is not drawn to scale) is a side view [175]...

Atomic force microscopy (AFM) has become a standard technique to image with high resolution the topography of surfaces. It enables one to see nanoscopic surface features while the electrode is under potential control. This powerful probe microscopy operates by measuring the force between the probe and the samples (56,57). The probe consists of a sharp tip (made of silicon or silicon nitride) attached to a force-sensitive cantilever. The tip scans across the surface (by a piezoelectric scanner), and the cantilever deflects in response to force interactions between the tip and the substrate. Such deflection is monitored by bouncing a laser beam off it onto a photodetector. The measured force is attributed to repulsion generated by the overlap of the electron cloud at the probe tip with the electron cloud of surface atoms. 

Fig. 40 Conducting film, plasma polymerised from 2-iodothiophene, on silicon. Left topography contrast (shaded pseudo-3D-image) with 405 nm corrugation. Middle real part (conductivity), with a contrast of 2.8 nA. Right imaginary part (capacity), with a contrast of 270 pA, the a.c. currents shown in the middle and in the right image were simultaneously measured together with the topography. The cantilever is made of silicon nitride coated with gold. The excitation is 0.8 V at 60 kHz, the scan speed is 4.17 pm/s...

Atomic Force Microscopy Atomic force microscopy is a direct descendant of STM and was first described in 1986 [254], The basic principle behind AFM is straightforward. An atomically sharp tip extending down from the end of a cantilever is scanned over the sample surface using a piezoelectric scanner. Built-in feedback mechanisms enable the tip to be maintained above the sample surface either at constant force (which allows height information to be obtained) or at constant height (to enable force information to be obtained). The detection system is usually optical whereby the upper surface of the cantilever is reflective, upon which a laser is focused which then reflects off into a dual-element photodiode, according to the motion of the cantilever as the tip is scanned across the sample surface. The tip is usually constructed from silicon or silicon nitride, and more recently carbon nanotubes have been used as very effective and highly sensitive tips. 

The scanning electron microscope (SEM) in Fig. 13.10a shows the representative results after HSS BKM 2. The SEM image in Fig. 13.10a was taken just after CMP and illustrates minimal dishing and SiN loss. The SEM in Fig. 13.10b was taken after the silicon nitride strip. It shows that the isolated oxide is more than 500 A above the level of the active silicon that will become the transistor. It is critical to keep the dishing low and the step height over the active silicon consistent for the sake of proper device performance. 

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. 

The AFM used in this study was a Nanoscope II system (Digital Instrument Inc.) operated at ambient conditions. Two AFM scan heads (700 nm range and 8000 nm range) with silicon nitride probes were employed. The AFM was operated in the height imaging mode and at low scan frequency (< 2 Hz). AFM analysis was conducted ex-situ on the fresh film, after H2 pretreatment, after S addition, and after the catalytic reaction. Four areas from each piece of catalysts were imaged before and after each reaction. The areas scanned varied from 100 xlOO nm to 4000 x 4000 nm. ... 

Atomic force microscopy (AFM) allows the topography of a sample to be scanned by using a very small tip made from silicon nitride. The tip is attached to a cantilever that is characterised by its spring constant, resonance frequency, and a quality factor. The sample rests on a piezoceramic tube which can be moved horizontally x,y motion) and vertically (z motion). Displacement of the cantilever is measured by the position of a laser beam reflected from the mirrored surface on the top side of the cantilever, whereby the reflected laser beam is detected by a photodetector. AFM can be operated in either contact or a noncontact mode. In contact mode the tip travels in close contact with the surface, whereas in noncontact mode the tip hovers 5-10 nm above the surface. 

Four examples were given in the patent, all using supercritical propane with polysilane and aluminum isopropoxide, so-called precursor ceramic materials. In one instance scanning electron microscopy was used to demonstfate that polysil me was deposited as a smooth surtace film on the alumina fibers and fine silicon nitride whiskers. A silicon carbide material with internal pore openings as small as 10 microns was penetrated by supercritical propane laden with aluminum isopropoxide. Weight gains of up to 43% can be obtained depending on the density of the initial host ceramic. 

The photodiode-lever separation can be measured sufficiently accurately to ensure that it is a negligible source of error. The value of this distance varies slightly om scan to scan, depending on the beam alignment, but is typically 12.0 mm. Finally one must consider the geometrical and mechanical properties of the cantilever. Because the stoichiometry of the cantilevers can vary from that of bulk amorphous silicon nitride, the values of the Young s modulus and Poisson ratio are not very accurately known. We have used quoted values for bulk silicon nitride, but the accuracy of these values is hard to assess. As mentioned earlier, the quoted thickness of the levers was checked by measuring the lever resonant frequency, and frie width of the levers is accurately known (10 pm). 

On the basis of our results using scanning force microscopy such as S VM and LFM, we claim that the mobility at the surface of PS films is not the same as that in the bulk. However, in such measurements, a probe tip made of silicon or silicon nitride makes contact with the surface to be measured. This may induce some artifacts in the results. If an effect of tip contact on the surface dynamics cannot be negligible, our conclusion must be reconsidered. Thus, T is here discussed on the basis of coarse-grained molecular dynamics simulation using a bead-spring model of Grest... 

Figure 8.80 Silicon carbide inclusion that acted as a fracture origin in silicon nitride scanning electron micrograph.

Fig. 5 Scanning electron micrographs of a silica microsphere glued with polymer glue to the end of a silicon nitride cantilever (a). The polystyrene particle shown to the right was sintered at 120°C to the cantilever (b).

Fig. 7.2. Scanning electron micrograph of a microfabricated silicon nitride cantilever commonly used for force measurements. (A polystyrene microsphere glued at the end of the V-shaped cantilever can be seen pointing upward. The scale bar corresponds to 10 pm.) Reprinted from [10]. Copyright 1992, with kind permission from the American Chemical Society...

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