Accurate Junction-Depth Measurements Using Chemical Staining

The characterization of ultrashallow junctions after implantation and subsequent rapid thermal processing (RTP) annealing is usually done in two ways. The sheet resistance of the junction is measured with a four-point probe and junction depth and dose are evaluated via secondary ion mass spectrometry (SIMS). After ultralow energy beamline implantation in a Varian VIISta 80 single wafer high current implanter the subsequent spike anneal for maximum activation and minimal diffusion was carried out on a Mattson 3000 Plus equipped with the flash-anneal controller. Junction depth profiling was done to monitor the influence of implant conditions and RTP annealing parameters. Measurements of junction depth, total dose, activated dose and uniformity were carried out on FEI Quadrupole SIMS tools. Queued measurements were performed on full wafers and small samples. Calibration of both junction depth and retained dose will be discussed. At very low beam energies (250 eV, oxygen, normal incidence) valuable information about depth profile shape, near surface concentration, and activated dose were obtained.

Shallow arsenic implants were activated by furnace and rapid thermal annealing (RTA). Comparisons of junction depths measured by secondary ion mass spectrometry (SIMS) and spreading resistance (SR) showed SIMS values 50–90nm deeper than SR values, due to ion knock-on during SIMS profiling.

Secondary ion mass spectrometry (SIMS) has become an established method for the analysis of trace elements in semiconductor and other materials. The flexibility of this technique has led to its use in a wide variety of materials analysis problems. It is routinely used to determine dopant and trace contaminant levels in semiconductor devices of micron and submicron dimensions. It is used to determine isotopic abundances in mineral phases and it is used to study the localization of trace elements in biological tissues. Time-of-flight SIMS is becoming a standard tool for the analysis of polymeric and other high-mass materials. SIMS is a complementary technique for methods such as Auger electron spectroscopy and photoemission spectroscopy, discussed in Chapters 4 and 9 in this volume, respectively, and for the technique of laser ionization mass spectrometry, discussed in Chapter 10. This chapter will outline basic principles of the SIMS technique, the equipment used for the technique, and several closely related techniques (SIMS variants). Information which can be obtained by SIMS will be discussed and several examples presented.

The technique of dynamic secondary ion mass spectrometry (SIMS) has, during the 1980s, become a firmly established tool in the microanalytical and microstructural characterization of dental hard tissues. SIMS has proved to be outstandingly suited for charting the distributions of most elements, even at extremely low concentrations, in tooth and bone materials. In-depth concentration profiles as well as surface distribution maps of elements have been recorded with excellent (sub-micron) morphologic resolution. In spite of documented success, only relatively few teams, in a handful of countries, are presently engaged, to any significant extent, in conducting tooth or bone research by the application of SIMS. For dental-medical-surgical laboratories, a partial reason for non-communication is a lack of information about SIMS and its particular assets. Another reason may be connected with an essentially groundless reputation, among non-specialists, of SIMS being an exclusive and expensive technique. Among SIMS laboratories, on the other hand, the inertia in tackling biomineralization is partly due to some particular artifacts of analysis, hitherto not generally known and controlled. The present paper briefly sketches the chief principles of modern SIMS, emphasizing factors of special relevance in the characterization of biomineralized tissues. Examples of recent applications are provided. Present procedures and their limitations are discussed, especially with regard to elemental quantification and imaging. Suggestions for relatively simple modifications to existing routines are offered with the aim of enhancing the ease and availability of SIMS in odontological and surgical research.

This article discusses the utilization of profiling data from an end-user’s viewpoint and emphasizes some requirements of profiling techniques for the modeling of present and future integrated circuit technologies. In the development and characterization of diffusion model, we have to fit both the measured profile shape and integrated dose for each dopant. We will present the evaluation of secondary ion mass spectrometry (SIMS) and spreading resistance (SRP) profiling techniques against this criterion and the selection of SIMS data as the standard for model parameter extraction. We will then discuss the methodology and results of model characterization which is a step-by-step application of SIMS data for the calibration of SUPREM III model parameters. To validate the characterized model for technology development, we will talk about the checking against available SRP, sheet resistance, C–V, and device I–V data. Finally, we want to bring up the need of profiling data for the characterization of two-dimensional shallow junctions and dopant diffusion in polysilicon.

P was diffused into p-type Si wafers containing B at 1100/spl deg/C for six different times using a solid state source and a standard pre-deposition process. Secondary ion mass spectrometry (SIMS) provided profiles of dopant concentration versus wafer depth from which both the surface concentration and the junction depths for the six wafers were determined. These profiles were fitted acceptably well by the constant supply model of diffusion in the dilute tail region identified by Fair, although indications of concentration-dependent diffusion were observed. Two independent determinations of the sheet resistivity of each sample were made. The results confirmed the correct operation of our custom-built sheet resistivity system. The resulting data allow us to predict the junction depth within 0.2 /spl mu/m over a range from 1.0 to 2.0 /spl mu/m. A plot of the dopant surface concentration, N/sub 0/, versus the product of the sheet resistivity and the junction depth, R/sub s/x/sub j/, agrees well with data from the Irvin plot.

Secondary Ion Mass Spectrometry

High-sensitivity U–Pb rutile dating by secondary ion mass spectrometry (SIMS) with an O2+ primary beam

It's difficult to measure junction depth because the junction is not in horizontal direction in textured silicon solar cells. In this paper a new, accurate junction depth measurement technique for textured silicon solar cells is investigated. Both experience and experimental data indicate that the measurement technique we used is feasible.

Heavily n-doped epitaxially grown Si layers are of great importance for source/drain (S/D) application in advanced node nMOS devices. For contact resistivity reduction, the dopant activation level is very important. Various techniques are being used to evaluate dopant activation in Si:P layers. Among these two methods are Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM). SSRM uses an atomic force microscope equipped with a hard conductive probe that is scanned in contact mode on the cross-sectioned sample’s surface and measures spreading resistance. Measured resistance values as a function of depth are converted into resistivity and carrier concentration depth profiles using calibration measurements and conversion relationships. DHEM provides depth profiles of mobility, resistivity and carrier concentration through a semiconductor layer by making successive sheet resistance (Rs) and Hall voltage measurements using Hall effect/Van der Pauw techniques, as the electrically active thickness of the layer is reduced through successive oxidation steps. Controlled oxidation is achieved by electrochemical anodization. Data collected can then be processed to yield the depth profiles. In this contribution we have carried out SSRM and DHEM measurements on Si:P epi layers subjected to different processing conditions including annealing and ohmic contact fabrication. Secondary Ion Mass Spectrometry (SIMS) was used to measure the total (active + inactive) dopant profiles through the films. Effects of these processes on dopant diffusion and activation were studied and the results from DHEM and SSRM were compared.In-situ phosphorus (P) doped Si epi-layers were grown over 300mm diameter boron doped monitor wafers. While one set was kept as the reference, a second set was treated by a spike-annealing process at 1000 °C. In a third set a Ti/TiN contact fabrication process was carried out and the contact was removed before analysis. In the fourth set contact process was applied to the spike annealed wafer before removal of the Ti/TiN layers. Bulk sheet resistance measurements were made using 4-point probe (4PP) for all the samples. SSRM measurements were carried out at IMEC. Cross-shaped Van der Pauw test-patterns were formed on 8mmx8mm areas on the samples and DHEM measurements were performed at ALP. Figure below shows the dopant depth profiles obtained by SIMS and the carrier concentration profiles from DHEM and SSRM techniques for samples D02 (as deposited Si:P) and D03 (spike annealed). One can make some general observations from the data in this figure. The total dopant concentration as measured by SIMS is ~ 1.4E21/cm3. There is only a small difference in the total dopant distribution profiles (SIMS) between the as deposited sample and the spike annealed sample. However, the spike annealed sample shows much higher dopant activation as measured by DHEM. Carrier concentration is ~2.5x higher in sample D03 (~5E20/cm3) compared to sample D02 (~2E20/cm3). Activation levels measured by SSRM, however, are lower for both samples, and the peak carrier concentration value increases only slightly upon spike annealing, going from ~2E20/cm3 in sample D02 to ~2.2E20/cm3 in sample D03. DHEM clearly indicates the sharp interface between the p-type substrate and the n-type epi-layer and its depth calibration agrees well with the expected thicknesses of the epi layers. The tail of the SSRM data is much more graded. Data from other samples will be presented and discussed in the final manuscript. Figure 1

Electrolytic hydrogenation and its isotope effect in Zr and Pd studied by ERDA and SIMS techniques

Accurate determination of F in minerals is a difficult task even when high F concentrations are present. Fluorine usually is determined by means of electron micro-probe analysis (EMPA) standardized on non-silicate-matrix compounds (e.g., fluorite), and some previous work has revealed the difficulties in determining F at high concentrations such as found in the humite-group minerals. Moreover, when both single-crystal structure refinement (SREF) and EMPA are available for the same crystal, the two estimates do not always agree. On the other hand, the secondary ion mass spectrometry (SIMS) technique is not easily applied at high F concentrations due to the existence of matrix effects related to the chemical composition and structure of the sample as well as to the concentration of the element itself. We tested the agreement among these analytical techniques in the estimation of high F contents and propose an analytical procedure for the analysis of fluorine. Our results indicate that careful selection of working conditions for EMPA of F together with appropriate correction, can yield accurate fluorine concentrations in minerals. Fluorine data extracted from refined site occupancies are systematically overestimated. New accurate working curves have been worked out for SIMS analysis of F taking Si and Mg, in turn, as the reference element for the matrix. Humite-group minerals show SIMS matrix effects on the order of ~10%. In analyzing fluoborite in the most unfavorable cases, the difference in Ion Yield (F/Mg) between “disoriented” humite-group minerals and “oriented” fluoborite samples can reach ~27%. Finally, a lower than expected IY(F/Si) from the F/Si working curve (made with humite minerals) is shown by topaz, which can be ascribed to chemical matrix effects, as well as to the covalent-type bonding between F and the major element in the matrix (Al).

The carrier concentration‐depth profiles of ultrathin boron layers in Si, grown by molecular beam epitaxy, are determined by the electrochemical capacitance‐voltage (ECV) and the spreading resistance (SR) profiling techniques. Secondary ion mass spectrometry (SIMS) is employed as a base for the comparison of the results. It has been shown that, under carefully chosen conditions, both ECV and SR techniques are able to resolve ultrathin layers including a delta layer, however ECV match better with the results of SIMS than that of SR. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High detection sensitivity in bulk analysis or depth profiling by secondary ion mass spectrometry (SIMS) can only be achieved, for positively charged ions, if the nearsurface regions of the sputter eroded sample are fully oxidized. Using oxygen primary ions, a stationary oxidation state is established after some time of bombardment during which period the sputtering yield decreases and the ionization probability increases. The physical and chemical processes occurring during the transient period are reviewed with emphasis on the results for impurity analysis in silicon, i.e. the matrix material that has been studied most thoroughly in the past. The transient decrease in sputtering yield gives rise to a depth scale offset and an associated apparent shift of impurity profiles towards the surface. The effect is largest at normal beam incidence, ca. 1 nm /keV (O + 2 ), in which case silicon is fully oxidized. The transition depth, i.e. the depth sputtered before achieving a stable ion yield is about twice as large and increases as the impact angle is turned away from normal. The shift and the depth scale offset can be measured safely using thin (delta) layers of isotopically pure tracers, for example 30 Si in 28 Si. Boron delta layers can serve as secondary standards because this impurity behaves almost the same as the host silicon atoms. The profile shift observed with other common dopants may contain contributions due to unidirectional relocation, often driven by segregation away from the surface. At O + 2 energies below about 0.7 keV the transition depths fall below the thickness of typical native oxides, so that the transient changes in sputtering yield and ionization probability can disappear. The transient phenomena may be described by a simple sputtering-oxidation model that connects the depth scale offset to other observable parameters like the initial and final sputtering yield, the transition fluence and the oxide thickness.

The knowledge of Li diffusion in lithium silicide (LixSi) is nowadays of importance for the Li-ion battery (LIB) research and development community. About twenty times more charge (Li+) can be stored per Si atom (Li3.75Si) than per C atom (LiC6), while carbon is still the main storage material in commercial LIBs. Consequently, huge effort is made to replace carbon by silicon in LIBs. Unfortunately, the diffusion of high amounts of Li+ into silicon during LIB operation is accompanied by a huge volume expansion of up to 400 % leading to a pulverization of the silicon electrode due to stress. Li diffusion in the interior of the electrode plays an important role for a fundamental understanding and for an optimization of application relevant properties like charging/discharging rates, maximum capacity, self-discharge, and cycling stability. This contribution reports about the realization of Li diffusion experiments in electrochemically lithiated amorphous silicon. Li diffusion was investigated at room temperature using the technique of secondary ion mass spectrometry (SIMS) in depth profile and in line scan mode in combination with stable 6Li isotope tracers. Experiments were done on 200 nm thin Si electrodes with a Li+ insertion stage of about 30 % and 80 % of full capacity. SIMS line scan data were successfully obtained, which will allow to measure fast Li diffusion on electrodes over macroscopic distances in the mm range, which is not possible using SIMS depth profiling mode.