Sputtered Material

The processes in the case of sputtering chemical compounds, such as oxides, are more complex than those of metals. As already mentioned, the impact energy often causes dissociation of chemical compounds, releases oxygen from oxides, and thus considerably alters the composition of the target, and the sputtered species may contain variable amounts of molecular fragments. 

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AES analysis is done in one of four modes of analysis. The simplest, most direct, and most often used mode of operation of an Auger spectrometer is the point analysis mode, in which the primary electron beam is positioned on the area of interest on the sample and an Auger survey spectrum is taken. The next most often used mode of analysis is the depth profiling mode. The additional feature in this mode is that an ion beam is directed onto the same area that is being Auger analyzed. The ion beam sputters material off the surface so that the analysis measures the variation, in depth, of the composition of the new surfaces, which are being continu-... 

In Dynamic Secondary Ion Ma s Spectrometry (SIMS), a focused ion beam is used to sputter material from a specific location on a solid surface in the form of neutral and ionized atoms and molecules. The ions are then accelerated into a mass spectrometer and separated according to their mass-to-charge ratios. Several kinds of mass spectrometers and instrument configurations are used, depending upon the type of materials analyzed and the desired results. 

The atom flux sputtered from a solid surface under energetic ion bombardment provides a representative sampling of the solid. Sputtered neutral mass spectrometry has been developed as method to quantitatively measure the composition of this atom flux and thus the composition of the sputtered material. The measurement of ionized sputtered neutrals has been a significant improvement over the use of sputtered ions as a measure of flux composition (the process called SIMS), since sputtered ion yields are seriously affected by matrix composition. Neutral panicles are ionized by a separate process after sputter atomization, and SNMS quantitation is thus independent of the matrix. Also, since the sputtering and ionization processes are separate, an ionization process can be selected that provides relatively uniform yields for essentially all elements. 

Useful yield provides an overall measure of the extent to which the sputtered material is used for analysis. It is a quantity employed to estimate the sensitivity of the mass spectrometric method. Values of Y (X (A)) for elements typically range from 10 to 10 in TOF SIMS. The number of sputtered particles A per incident primary ion (sputtering yield) can be measured from elemental and multielemental standards under different operational conditions and can, therefore, by judicious interpolation between standards, be estimated with reasonable accuracy for the material being analyzed. 

Figure 3.37 gives an example of the depth resolution routinely achieved with both e-beam and HF-plasma SNMS on suitable samples. If Eq. (3.21) is applicable, i.e. all sputtered material has been recorded with Hi, then YeollA,y equals Sli/Si [3.75], and depths 2 can be calculated according to ... 

Hence, Tct is seen to increase with pore density and pore radius. However, a problem appears at a porous substrate when thin films are to be deposited during metallization to form interconnections, thin-film capacitors, etc.335 Sputtered material falls deep into the pores, which affects the planarity of the deposited layer and the electrical resistivity of the oxide layer underneath.335 To cope with this effect, the porous oxide should be padded by inorganic (A1203 and Si02) or organic (polyimide, negative photoresist) layers. 

The Mg isotopic measurements were performed with a modified AEI IM-20 ion microprobe [13,14]. Secondary ions were generated by bombarding the sample with a focussed ion beam to excavate a small volume of the sample. A fraction of the sputtered material is ionized during the sputtering process and is drawn off into the mass spectrometer. A duoplasmatron ion source produces a... 

In secondary-ion mass spectrometery (SIMS) and its sister technique fast atom bombardment mass spectrometry (FARMS), a surface is bombarded with energetic particles, and the kinetic energy of the particles converts substrate and chemisorbed atoms and molecules to gas-phase species. The ejected (or sputtered) material is subsequently interrogated using various analytical tools, such as lasers and mass spectrometers, to indirectly deduce information about the initial surface. The relationships between sputtered material and the surface, however, are not always clear, and erroneous conclusions are easily made. Computer simulations have demonstrated that a fundamental understanding of the sputtering process is required to interpret experimental data fully ... 

A number of advantages exist for ion milling compared to plasma etching or RIE. Because of the collimated beam of ions, essentially vertical profiles are possible. Also, profile tapering can be achieved by tilting the substrate relative to the ion beam. In addition, ion milling is performed at pressures at least 100 times lower than those used in plasma etching or RIE. Therefore, redeposition of sputtered material is reduced. 

Only a small fraction of the sputtered material will actually be ionized. The ionization probability depends on the element species and on the matrix material. 

The theoretical basis for sputtering has been known for a long time but more recently commercial methods have been developed along lines similar to those in vacuum evaporation just described. Essentially, a discharge of argon gas plasma is established between an anode and cathode electrode in this instance, the source material is the cathode, and the work piece the anode. Gas ions charged positively are attracted to the cathode, where they collide with it and remove atoms of the source material—which in turn travel to the anode and form a coating of sputtered material on the work piece. 

The combination of magnetron sputtering and inductively coupled plasma excitation (ICP) is a technique which allows enhanced ionization of the sputtered material. The combination of transition mode process control of the reactive sputtering and ICP plasma excitation is described in [112]. However, the resistivity of ZnO Al films sputtered from a Zn 1.5 wt% A1 target is in the of 1,000 gH cm at T = 150 °C, which is inferior to results from conventional sputter processes under similar conditions. 

One final factor which can influence stoichiometry has been described by Stupp . He reported that fresh molybdenum disulphide compacts initially emit sulphur faster than molybdenum. As a result the target surface becomes molybdenum-rich. As sputtering continues, sulphur diffuses to the surface at a rate which balances the removal of sputtered atoms, so that an equilibrium is established and the composition of the sputtered material remains constant. The problem of the initial variation in composition is overcome by a preliminary sputtering of the target before the specimen substrate is exposed to the sputtered particles. 

Type II films appear to be more reliably produced by certain co-sputtered materials, and by ion beam bombardment, and these are discussed in Section 10.7. 

A combined LEISS-AES-EC study was earlier undertaken at crystalline PtsCo and PtsNi alloy surfaces. It was reported that, when PtsCo and PtsNi were annealed at 1000 K, only Pt atoms existed on the outermost layer the latter was referred to as a Pt skin. This particular observation is not in agreement with the result here that Co actually co-exists with Pt at the outermost layer. Interestingly, when the PtsCo surface in the earlier study was lightly sputtered, approximately 25% of the sputtered material was Co this result suggests that Co is in fact present at the topmost layer. Why a discrepancy exists between the LEISS and depth-profile studies is unclear. But, for the difference between the present and previous LEISS work, the possibility exists that the interfacial be-... 

As mentioned earlier, the process that utilizes the deposition of sputtered material is often termed sputter coating. The material is sputtered from a target by plasma, and the sputtered material is deposited onto a substrate, which is usually placed out... 

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