Papers

AVS1996 Session AS-MoA: Depth Profiling

Monday, October 14, 1996 1:30 PM in Room 105B

Monday Afternoon

Start	Invited?	Item
1:30 PM		AS-MoA-1 Ion Beam Damage during Sputtering J. Pitts, L. Dake, D. King, A. Czanderna (National Renewable Energy Laboratory) Ion-beam sputtering, combined with surface analysis, is often used to probe buried interfaces in multi-layered systems. The data interpretation requires a complete understanding of the artifacts introduced by the ion beam at and near the interface. We summarize the major categories encountered in our review of about 1000 articles from the last 15 years on ion beam effects on solids. The discussion is restricted to non-reactive ion beams with energies from ca. 0.3 keV to 5 keV, typical of those used for sputter-depth profiling, sample cleaning, and for ISS and SIMS analysis. Topics considered include implantation, knock-on and mixing, preferential sputtering, topographical changes, defect creation, amorphization, reactivity and chemical state changes, redeposition, surface diffusion into the crater, desorption, enhanced reactivity with background gases, impurities, and interactions. Methods to minimize these effects and/or simplify the analysis will also be discussed.
1:50 PM		AS-MoA-2 The Effects of Oxygen Flooding on Sputtering and Ionization Processes during Ion Bombardement C. Tian, W. Vandervorst (IMEC, Belgium) The use of oxygen flooding has gained significant interest in the SIMS-analysis of very shallow profiles. In order to promote its use in quantitative analysis detailed studies regarding the oxygen incorporation and accompanying changes in sputter yield and ionization degree during oxygen and argon bombardement are performed. Evidence for the presence of preferential sputtering is found from the enhancement of the Si\super +\ ion yield sputtered from a thermal SiO\sub 2\ matrix by oxygen flooding under argon as well as under oxygen bombardement and the reduction in erosion rate resp. 40% (argon) and 25% (oxygen) when flooding is added. The larger the angle of incidence, the higher the factor of the reduction. Bombardement of Si with flooding leads to the formation of a thick oxide layer (oxygen) or just a thin oxide layer (argon). When depth profiling through a SiO\sub 2\/Si interface with oxygen flooding, the Si\super +\ ion intensity is increasing slightly although the variations of other ion signals demonstrate a reduction of oxidation occurs. An analysis of the sputter yields shows that with oxygen primaries at an oblique angle of incidence the partial sputter yield of Si can be reduced by a factor larger than 2.15 which would result from the transformation of Si into SiO\sub 2\. These data demonstrate that the interaction is more complex than a simple chemical adsorption and knock-on process. The formation of the thick oxide is related to the reduction of the sputter yield whereas the effects on the thermal oxyde are to be explained in terms of a competition between preferential sputtering and oxygen adsorption.
2:10 PM		AS-MoA-3 Optimized TOF-SIMS Depth Profiling with a Dual Beam Technique K. Iltgen, C. Bendel, E. Niehuis, A. Benninghoven (Physikalisches Institut der Universit\um a\t M\um u\nster, Germany) TOF-SIMS combines quasiparallel mass registration with high sensitivity and high mass resolution. Its application in depth profiling, however, is limited by the low duty cycle of the pulsed primary ion beam.The depth profiling performance of TOF-SIMS can be improved considerably by applying a dual beam technique. In this technique a high erosion rate is achieved by an additional high current density rastered "sputter" ion beam, optimized regarding ion species, energy, and angle of incidence. The properties of the "analytical" ion beam can be selected independently (e.g. a noble gas ion beam for large area, or a fine focused Ga beam for small area depth profiling). This independent setting of "sputter" and "analytical" ion beam allows a most flexible optimization of all parameters determining the quality - depth resolution, sensitivity, time for the analysis - of a TOF-SIMS depth profile.We studied by this dual beam technique the influence of sputter beam parameters on depth resolutions and sensitivities achieved for a wide variety of systems. Emphasis was on the B- and As-profiles in silicon (\delta\-profiles as well as low energy implants), silicon gate oxides, multilayers on magnetic disks, and other microelectronic devices. Optimized depth profiles for these samples will be presented.
2:30 PM		AS-MoA-4 Accurate Concentration Depth Profiling of Alkali Elements in Bulk Glasses by SIMS T. B\um u\y\um u\klimanli, S. Novak, C. Magee (Evans East) Beam induced migration of the alkalis, especially Na, in SiO\sub 2\ thin films and bulk glass have made it difficult to acquire accurate concentration depth profiles by any surface analytical technique. We successfully have used a standardized ion implanted SiO\sub 2\ thin film on Si sample to set up instrument parameters to minimize the alkali element migration due to sample charging. These instrument parameters however, may not be applicable to bulk SiO\sub 2\ or glass samples. Therefore, alkali depth profiling analyses of bulk glass or thin film/glass interfaces requires a standard with known alkali composition distribution both in the bulk and at film/glass interfaces. In order to achieve this goal, bulk glass and SnO\sub 2\ thin films on glass substrates have been ion implanted simultaneously with Si substrate. These samples were characterized using the co-implanted Si sample, which is not subjected sample charging. Instrument was subsequently set up to minimize alkali migration by monitoring their expected SIMS depth profile. These parameters are then used to characterize unknown samples.
2:50 PM		AS-MoA-5 SIMS Analysis of Autodoping of Undoped Oxide in Chambers which Deposit Doped and Undoped Oxides F. Stevie, K. Steiner, M. Twiford, J. Obeng, E. Prather, M. Thoma, W. Cochran (Lucent Technologies) Secondary Ion Mass Spectrometry (SIMS) has been used to detect boron and phosphorus contamination at important steps in silicon semiconductor processing. Doped and undoped Plasma Enhanced Tetraethylorthosilicate (PETEOS) films can be deposited in the same chamber to maximize product throughput. Significant autodoping of the undoped oxide can occur when the deposition of undoped glass immediately follows a doped deposition. SIMS depth profiles were used to identify the extent of boron and phosphorus contamination and to establish the process conditions that reduced the contamination to an acceptable level.
3:10 PM		AS-MoA-6 Role of Desorption Methods on Quantitative Surface Analysis by Laser Postionization Mass Spectrometry C. He, C. Becker (SRI International) Postionization techniques can bring reliable quantitation to surface analysis, while still maintaining the high sensitivity for which secondary ion mass spectrometry (SIMS) has been known. Complete quantitation is influenced by both the way of material is removed from the solid to the gas phase and by the manner of detection of the gas phase atoms and molecules. Commonly used material removal methods are sputtering by kilo-electron volts (keV) noble gas ions and pulsed laser ablation. Recently we have demonstrated that for nonresonant multiphoton ionization of gaseous and ion beam sputtered atoms and molecules, high laser beam quality combined with high power density can lead to uniform ionization of species with quite different ionization potentials. The ejected flux of ion sputtered composite materials preserve their solid phase stoichiometries over a range of kinetic energies of the sputtering ions. Assured by the capability of our uniform ionization and det! ection technique, we studied the quantitation capabilities of using multiphoton ionization with laser ablation. We found that stoichieometric removal of material by laser ablation is hardly possible. The elemental composition of the ablated plume depends critically on laser power density and the thermal properties of the ablated material. Experiments have been performed on standard alloys, semiconductors and insulators. The ablation and photoionization mechanisms will be discussed also.
3:30 PM		AS-MoA-7 AES Depth Profiling- Pitfalls and Work Arounds J. Geller (Geller Microanalytical Laboratory) Depth profiling using electron beam excited Auger emission spectra has gained wide acceptance as a method for characterizing changes in specimen surface composition as the specimen surface is eroded by an incident ion beam. The processes involved are very complex and most are not well understood. With this poor understanding of the fundamentals combined with numerous pitfalls in the experimental procedure we must carefully consider what results can be relied upon. While electron excitation and Auger emission are well understood, the ion sputtering process has been difficult to characterize. Ion sputtering yields are greatly affected by the experimental conditions as are the surface reactions of the in-vacuo specimen while it is being eroded. This talk, illustrated by experimental data, will review many of the elements which contribute towards a reliable depth profile. Amongst others the topics covered will include vacuum conditions (total and partial pressures), ion gun, electron beam, and spectrometer alignment, ion sputtering rates, ion sputter induced roughness and its affect upon sputtering rate, electron enhanced ion sputtering, measurement of Auger peak intensity and quantitative analysis using experimentally derived sensitivity factors.
4:10 PM		AS-MoA-9 Auger Depth Profiling of Deeply Buried Thin Layers M. Menyhard, A. Sulyok, A. Barna (Research Institute for Technical Physics, Hungary) There are several technologically interesting cases when the analysis= =20 of thin layers (in the range of even one monolayer) buried with thick=20 overlayer is necessary. The detection or/and analysis of such layer is only= =20 possible if the depth profiling technique used applies ion etching of proper= =20 conditions. We will show that the most important requirement for achieving= =20 a good depth resolution after removing thick (more than 100 nm) overlayer = =20 is the reduction of the sputtering induced surface roughness. This can be=20 achieved by applying specimen rotation and grazing angle of incidence.=20 Having a relatively smooth surface the major part of the interface=20 broadening, which in fact determines the depth resolution, comes from the= =20 ion mixing. To reduce the broadening effect of ion mixing low energy=20 sputtering should be used (see Ref.). It will be shown that applying =20 sputtering conditions as described, we could observe about one monolayer=20 oxide contamination on a multilayer-substrate interface in a depth of 200= nm.Reference: M. Menyhard, A. Barna, J.P. Biersack, K. J=E4rrendahl, and J-E= =20 Sundgren J. Vac. Sci.Tech., A 13 (1995) 1999.
4:30 PM		AS-MoA-10 XPS Characterization of Semiconductor Thin Films using Simultaneous Mg/Zr Excitation D. Allgeyer (Micron Technology, Inc.) A method for determining the interfacial chemical composition of semiconductor thin films is discussed. Some of the materials and interfaces characterized by this technique include tungsten silicide, titanium nitride, silicon nitride, titanium silicide, and aluminum. These thin film materials are typically supported on conductive (silicon, polysilicon) and non-conductive (BPSG) substrates. The determination of their interfacial chemical compositions are enhanced with the use of the zirconium anode (2042.4 eV). The simultaneous use of the magnesium and zirconium anodes allows the analysis of the photoelectron as well as their corresponding higher energy Auger electrons for such materials as silicon and aluminum whose energies are above the fermi edge of either the magnesium (1253.6 eV) or aluminum (1486.6 eV) anodes. The photoelectron used in conjunction with their Auger electrons provides both line energies necessary for the determination of their Auger parameters which are independent of localized sample charging and provide their chemical identification. Charging is common in many of these materials and is especially prevalent when analyzed using an increasingly common monochromatized aluminum source for excitation. Thus, the simultaneous use of the magnesium (1253.6 eV) and zirconium (2042.4 eV) anodes minimizes sample charging while providing interfacial chemical identification which is discussed in depth in this paper.