TiN layers

detailed analysis of the chemical structure and composition of TiN layers is of prime importance. The obvious choice for this analysis is XPS. as reflected in the numerous papers published recently [42—481. 

The bulk of the literature shows that the energy of the Ti 2p doublet exhibits large chemical shifts (up to 4 eV) and considerable alterations of peak. shape due to changes in the chemical environment around the Ti atoms, e.g.. due to partial oxidation. This has led to the erroneous conclusion that chemical-state determination can be performed in a quantitative manner with relative ea.se by using a simple peak-synthesis procedure on the Ti 2p envelope. As will be shown, a complex evaluation procedure should be applied to the quantitative analysis and the assignment of the chemical states of Ti, making the characterization of TiN more reliable. 

One TiN layer, polycrystalline PVD, was prepared by dc bias reactive sputtering onto (100) oriented Si substrates at 570 K [42], while another was obtained by dc plasma nitriding of chemically pure titanium at 970 K [43]. Both layers had a columnar structure with preferred (111) orientation. The PVD layer proved to be nearly stoichiometric when examined by RBS. while TiN, Ti N, a-Ti and traces of TiOi phases were revealed by XRD in the sample prepared by the dc plasma method. 

For reference purpo.ses a stoichiometric single-crystalline TiN layer was prepared by reactive (Ar+ + Np sputtering onto a single-crystal MgO substrate as described in [49. The composition and the chemical state of this reference sample after wet chemical etching (HF H2O=l 20, 5 min), followed by a moderate (1 keV, 1 lA-cnr-, 5 min) Ar+ cleaning were taken to be repre.sentative of stoichiometric TiN virtually unaffected by ion sputtering. 

The position of the Ti 2pj/i line, determined from the stoichiometric single-crystal TiN layer was found to be 454.7 0.1 eV (42). The latter value was derived by referencing the. spectra to the CFl, type C l.s line at BE=284.6 eV. corresponding also to the position of the Au line at BE=84.0 eV. The position of the Ar 2pyp line of the implanted argon was found to be 242.6 0.2 eV, which can also be 

---

An imponant component of the complex metallizations for both semiconductor devices and magnetic media is the diffusion barrier, which is included to prevent interdiffiision between layers or diffusion from overlyii layers into the substrate. A good example is placement of a TiN barrier under an Al metallization. Figure 7a illustrates the results of an SNMSd high-resolution depth profile measurement of a TiN diffusion barrier inserted between the Al metallization and the Si substrate. The profile clearly exhibits an uneven distribution of Si in the Al metallization and has provided a clear, accurate measurement of the composition of the underlying TiN layer. Both measurements are difficult to accomplish by other means and dem-... 

Figure 7 Quantitative high depth resolution profile of the major elements in the thin-film structure of Al /TIN /Si, comparing the annealed and unannealad structures to determine the extent of interdiffusion of the layers. The depth profile of the unannealed sample shows excellent depth resolution (a). The small amount of Si in the Al is segregated toward the Al/TiN interface. After annealing, significant Ti has diffused into the Al layer and Al into the TIN layer, but essentially no Al has diffused into the Si (b). The Si has become very strongly localized at the Al / TIN interface.

To ensure maximum continuity of the tin-iron compound layer between tin and steel. This layer is itself corrosion resistant and appears to act as a nearly inert screen limiting the area of steel exposed as tin is removed by corrosion. Its effectiveness is measured by the Alloy-Tin Couple (A.T.C.) test, in which the current flowing is measured between a sample of tinplate from which the unalloyed tin layer has been removed, and a relatively large tin electrode immersed in an anaerobic fruit juice. ... 

In order to assign an oxidation number to the adsorbed species, knowledge of the number of Pt sites occupied by one tin adatom, S, is necessary. This was calculated by different authors. Motoo [97] and Sobkowski [98] reported a value of 2, while Szabo found a value of 2.2 [96]. The method used by Sobkowski has the advantage, for our purposes, of making no assumption on the oxidation state of the adsorbed tin layer. The number of electrons associated with the formation of adsorbed tin, n, can be calculated as follows ... 

Whether SnFLt is a symmetric or spherical top was discussed based on the rotational spectrum of the sixth stretching vibrational overtone, obtained by photoacoustic spectroscopy107. The IR band at vgn ]q 1844 cm-1 served to investigate the kinetics and mechanism of chemical vapour deposition of a thin tin layer, by thermolysis of trimethylstannane at 378-503 K108. 

If iron is covered with a protective layer of a metal that is less reactive than iron, there can be unfortunate results. A tin can is actually a steel can coated with a thin layer of tin. While the tin layer remains intact, it provides effective protection against rusting. If the tin layer is broken or scratched, however, the iron in the steel corrodes faster in contact with the tin than the iron would on its own. Since tin is less reactive than iron, tin acts as a cathode in each galvanic cell on the surface of the can. Therefore, the tin provides a large area of available cathodes for the small galvanic cells involved in the rusting process. Iron acts as the anode of each cell, which is its normal role when rusting. 

In electronic applications, where it is common to deposit copper and/or copper alloy and tin in sequence, with a nickel diffusion barrier layer, 0.5 fim thick, between the layers present, no failure occurs. Without the nickel layers between bronze/-copper/tin layers themselves, for instance, intermetaUic brittle layer(s) and Kirkendall voids are formed, leading eventually to separation of the coated system and substrate. 

In reflectometry, the light passes through the films to be measured. Beneath the transparent films, there must be an opaque substrate through which light does not pass. The substrate characteristics must be modeled correctly to calculate the thicknesses of the films above. In silicon processing, theoretically, any of the commonly used metal materials, such as the titanium nitride (TiN), aluminum (Al), and tungsten (W), can be used as substrates. However, in reality, whereas a PMD oxide can be measured on the polysilicon material used in poly interconnections, an ILD oxide can not be measured directly on TiN, because the TiN layer used is too thin to be opaque. TiN is semitransparent if its thickness is less than 1000 A. A thin... 

The above mixture with the addition of 20-50 wt% TiN or pure TiN (layers with index 2, bulk tensile stress). 

Thin ( 2 /mi) layers of nickel and tin are electroplated over the silver termination, the former to act as a barrier preventing dissolution of the silver during the subsequent wave-soldering operation when the chips are surface-mounted onto a substrate. The tin layer ensures good wetting of the termina tion by the solder. In the case of the BME capacitor (see below) the termination is copper fired on under reducing conditions and covered with an electroplated layer of nickel. 

The first study of Sn deposition on Pt( 111) was reported by Paffet and Windham in 1989 [42] and a subsequent one on the same system was published by Campbell in 1990 [1]. In both studies, two LEED patterns were observed after annealing a 2x2 and a ( /3x v ) R30°. Both superstructures were interpreted in terms of incorporation of the tin layer in the first platinum layer, but only a qualitative examination of the LEED pattern was performed. Subsequently the results of low energy alkali ion scattering spectroscopy ALISS [43, 21] could be quantitatively interpreted as due to ordered, single atomic layer surface alloys. The ion scattering results have been confirmed and expanded by a quantitative LEED study [34]. The atomic structure of both phases corresponds exactly to that of the topmost layer of the phases with the same periodicity observed on the on PtsSnflll). The LEED and ALISS results for the Sn/Pt(lll) system were confirmed by a recent STM study reported by Batzill et al. [44]. Even though atomic resolution was not attained in this study (only the surface unit mesh could be observed), the results are closely comparable to the atomically resolved ones obtained on the PtaSn(l 11) surface [35]. 

An identical procedure can be applied for vias to WSix or W. In these cases the TiN layer is not needed since the conversion will stop on the metal automatically. Contact resistivities were measured and were very acceptable lxlO 8 Ocm2 for the vias and 2xl0 7 for n+ and 4xl0 7 Hem2 for p+ mono-... 

Microwave-assisted fabrication of ceramic coatings on fibers and powders can be done at intermediate temperatures. For example, at temperatures of about 800-900° C, carbon fibers have been coated with thin TiN layers using a microwave plasma-assisted fluidized bed with the precursor vapor (TiCU in this case) being introduced into the reactor by the fluidizing gas. ... 

This in situ formed TiN layer on GaN is of the form of textured polycrystals with their (111) planes parallel to the GaN (0001) plane [23]. The crystalline nature of the porous TiN is also confirmed by the selective area diffraction (SAD) pattern in our TEM analysis. 

Figure 6.19 Surface of porous-TiN layers on (a) CVD481 and (b) CVD489 the surface of 3 pm thick GaN layers on the porous TiN of (c) CVD481 and (d) CVD489 Reproduced from Fu Y. et al., Journal of Applied Physics 99(3) Art. No. 033518 Copyright (2006), with permission from the American Institute of Physics...

An iron container can be covered with a layer of another metal such as tin or zinc. A tin can is made by applying a thin layer of tin over iron. Rust formation is prevented as long as the tin layer remains intact. However, once the surface has been scratched, rusting occurs rapidly. If we look up the standard reduction potentials, we find that iron acts as the anode and tin as the cathode in the corrosion process ... 

The possibility of applying copper deposition directly on top of TiN barrier via electrochemical method was studied. Previous report of using contact displacement to deposit copper was found chemically questionable. The copper deposition observed could be due to reaction between cupric ion and silicon underneath through cracks in the intermediate TiN layer. 

Then wafer samples covered with TiN layer were dipped in each of the solution, respectively. The samples came from two sources, designated as A and B. Furthermore, we also dipped bare Si and TiN powder in the test solution for comparison. The results is as follows,... 

---