Depth profile of thin layers

A depth profile analysis of trace and matrix elements (B, Na, Ni, Fe, Mg, V, A1 and C) in a 26p.m Si layer on a SiC substrate measured by GDMS, yielded impurity profiles, for example, with constant Ni contamination in the Si layer and enrichment at the interface layer.45 However, with respect to depth profiling of thin layers using dc GDMS with a depth resolution between 50 and 500 nm, this technique plays a subordinate role compared to the commercially available and cheaper GD-OES (glow discharge optical emission spectrometry). 

Applied Spectroscopy 51,No.8,Aug.l997,p.l238-44 PHASE-RESOLVED DEPTH PROFILING OF THIN-LAYERED PLASMA POLYMER FILMS BY STEP-SCAN FOURIER TRANSFORM INFRARED PHOTOACOUSTIC SPECTROSCOPY... 

The emission of secondary ions of both polarities from instrument construction materials produced as a by-product of ion source operation was first observed by Amot [86,87] and was developed into an analytical instrument by Herzog and Viebock [88]. Inspired by these experiments, an early SIMS instrument was constructed in the 1960s to analyze lunar rocks from NASA s Apollo missions. Much of the breakthrough of SIMS for i) bulk analysis of solids, ii) depth profiling of thin layers, Hi) imaging, and iv) monolayer analysis is also the merit of the Ben-ninghoven group [82,84,89,90]. 

Instruments based on GD-MS coupling have been employed most commonly for the quantitative analysis of trace and ultratrace amounts in high-purity materials. However, it has been demonstrated that, as in GD-OES, quantitative depth profile analysis by GD-MS is possible [33]. At present, a GD-MS prototype which allows the depth quantification of thin layers on conducting or insulating materials is being developed for commercial purposes [34]. 

A practical definition could finally also be derived from the capabilities of the instrumentation in use. For instance, SIMS, the most widespread MS technique, applied to surface and thin films can be operated in static mode (giving information from the first atomic layers of a nearly undamaged surface) or dynamic mode (depth profile of the layer). When the material to be analyzed is sputtered, this sputtering could be very slow, providing a practical limit (often in the micrometer range for SIMS) to the thickness range achievable in a reasonable amount of time. 

There are several MS-based techniques that can provide chemical information for thin and thick layers [12]. For very thin layers (sub to 1-2 monolayers), nondestructive techniques such as static SIMS [13], ion scattering MS [14], or MS of recoiled ions [15] are suitable. These techniques are also the best adapted for examining surface contamination. They are all based on surface interactions of an ion beam with the solid surface. For depth profiling of thin and thick layers, MS is associated with a destructive source of neutrals or ions dynamic SIMS, secondary neutron mass spectroscopy (SNMS), glow discharge mass spectroscopy (GD-MS), matrix-enhanced SIMS, laser desorption/ionization MS, and desorption electrospray ionization (DESI) MS [16]. Ions are either desorbed from the solid surface or generated by postionization of neutrals sputtered off the surface. 

Muller F, Bimer A, Gosele U, Lehmann V, Ottow S, Foil H (2000) Structuring of macroporous silicon for applications as photonic crystals. J Porous Mater 7 201-204 Nassiopoulu AG, Kaltsas G (2000) Porous silicon as an effective material for thermal isolation on bulk crystalline silicon. Phys Stat Solidi (a) 182 307 Nava R, de la More MB, Taguena-Martinez J, del Rio JA (2009) Refractive index contrast in porous silicon multilayers. Phys Stat Solidi C6 1721-1724 Pettersson L, Hultman L, Arwin H (1998) Porosity depth profiling of thin porous silicon layers by variable angle spectroscopic ellipsometry a porosity graded layer model. Appl Optics 37(19) 4130 136... 

Parratt LG (1954) Surface studies of solids by total reflection of X-rays. Phys Rev 95 359 Pettersen LA, Hultman L, Arwin H (1998) Porosity depth profiling of thin porous silicon layers by use of variable angle spectroscopic ellipsometry a porosity graded-layer model. Appl Opt 37 4130... 

Ellipsometry measurements can provide infomiation about the thickness, microroughness and dielectric ftinction of thin films. It can also provide infomiation on the depth profile of multilayer stmctiires non-destmctively, including the thickness, the composition and the degree of crystallinity of each layer [39]. The measurement of the various components of a complex multilayered film is illustrated m figure Bl.26.17 [40]. 

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.

Depth profiling of single airborne particles has been reported by Carson et al. (1995, 1997a), who showed that the use of variable laser fluences in single-particle laser ionization mass spectrometry can be used to probe thin films on particles in laboratory systems. At low laser intensities, only the surface layer is volatilized and ionized, whereas the entire particle can be vaporized and detected at higher intensities. 

EPMA consists of a combination of a scanning electron microscope with several dispersive X-ray spectrometers. This technique is essentially an analysis of X-rays emitted from the sample which is being probed with an electron beam. The method is particularly useful for measuring the surface composition and the depth profile of alloy thin layers. However, it is also relatively poor in detecting light elements. 

W. Theia, M. Wemke, and V. Offermaim, Depth profiling of porous silicon layers by attenuated total reflection spectroscopy. Thin Solid Films 255, 181, 1995. 

Product analysis Time resolved measurements such as pulse radiolysis system were described in the previous section. For product analysis, most of ordinary analyzing procedures in traditional radiation chemistry can be applied, such as changes in molecular weight, gel fraction, infrared or ultra-violet spectroscopy. In the case of ion beam, elaboration to characterize surface or very thin layers has been tried. For example, development of spin coated thin film is used for monitoring gel fraction [42]. Another characteristic may be depth dependent phenomena. Depth-profile of optical absorption is performed as... 

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