Aluminum impurities in silicon: Investigation of x-ray Raman scattering in total reflection x-ray fluorescence spectroscopy

Baur, Katharina; Kerner, Jonathan A.; Brennan, S.; Singh, Andy; Pianetta, P.

doi:10.1063/1.1312848

Cited by 25 publications

(32 citation statements)

References 13 publications

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“…2 However, the latter can be overcome by tuning the primary x-ray energy to an excitation energy below the Si K absorption threshold which also increases the photo absorption cross-section for Al [5,6]. This results in a minimum detection limit of 2.4 x 10 9 atoms/cm 2 as will be shown below.…”

Section: Introductionmentioning

confidence: 99%

“…This background is due to resonant inelastic x-ray Raman scattering which is an inelastic x-ray scattering process [10,11,12]. It has been shown that the asymmetric shape of the x-ray Raman scattering dominates the background of the Al fluorescence line.In order to accurately determine the minimum detection limit, the spectra have to be deconvoluted taking the specific shape of the resonant Raman scattering profile into account [6].In this paper we demonstrate that this data analysis can also be extended for the deconvolution of TXRF spectra from conventional systems which so far only subtract the background as measured from a clean Si wafer. A deconvolution of the Al spectra would make this step unnecessary and could increase the accuracy in determining the Al concentration on Si wafer surfaces.…”

mentioning

confidence: 99%

“…In order to accurately determine the minimum detection limit, the spectra have to be deconvoluted taking the specific shape of the resonant Raman scattering profile into account [6].…”

Section: Introductionmentioning

confidence: 99%

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Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Baur

Brennan

Burrow³

et al. 2001

Spectrochimica Acta Part B: Atomic Spectroscopy

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Having established detection limits for transition elements exceeding current requirements of the semiconductor industry, our recent efforts at the Stanford Synchrotron Radiation Laboratory (SSRL) have focused on the improvement of the detection sensitivity for light elements such as Al. Data analysis is particularly challenging for Al, due to the presence of the neighboring Si signal from the substrate. Detection limits can be significantly improved by tuning the excitation energy below the Si-K absorption edge. For conventional TXRF systems this can be done by using a W-Mα fluorescence line (1.78 keV) for excitation.At a synchrotron radiation facility energy tunability is available. However, in both cases this results in a substantial increase in background due to resonant x-ray Raman scattering. This scattering dominates the background under the Al Kα fluorescence line, and consequently limits the achievable sensitivity for the detection of Al surface contaminants. In particular, we find that for a precise determination of the achievable sensitivity, the specific shape of the continuous Raman background must be taken into account in the data analysis. The data deconvolution presented here opens a new perspective for conventional TXRF systems to mitigate this background limitation. This results in a minimum detection limit of 2.4 x 10 9 atoms /cm 2 for Al. 1Based on these results it will also be demonstrated that by improving the detector resolution, the minimum detection limit can be improved significantly. For a detector resolution of 15 eV as predicted for novel superconducting tunnel junction detectors, an improvement in minimum detection limit of about a factor of 3 can be estimated. Keywords:Total reflection X-ray fluorescence, low Z elements, Stanford Synchrotron Radiation Laboratory IntroductionExploiting the unique capabilities of synchrotron radiation, total reflection x-ray fluorescence spectroscopy (TXRF) has been successfully applied to detect very low concentrations of impurities on Si wafer surfaces [1,2,3,4]. Synchrotron radiation offers several advantages over conventional x-ray tubes: It provides a high incident flux, especially from insertion devices, it is both low-divergence and linearly polarized, which leads to an increased fluorescence signal while reducing the elastically scattered background. In addition, tuning the x-ray energy to a characteristic absorption threshold of a typical element present in the wafer surface increases the excitation cross-section for this element which leads to higher fluorescence intensities. With these combined capabilities we routinely achieve an minimum detection limit of < 9 x 10 7 atoms/cm 2 for transition metals on Si wafer surfaces for a 1000 second spectrum.On the other hand, the detection of low Z elements such as Al is challenging because of the lower fluorescence yield as compared to transition metals. In addition, the detection of Al on Si wafers is difficult because of the presence of the much stronger Si substrate signal which tends to dominat...

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Baur

Brennan

Burrow³

et al. 2001

Spectrochimica Acta Part B: Atomic Spectroscopy

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“…In this case, as reported earlier, 6,14,15 the DL for Al is affected by the presence of the x-ray resonant Raman scattering ͑RRS͒ process in Si. Indeed, for photon beam energies tuned below the Si K-edge in order to avoid the strong K␣ fluorescence line, the x-ray RRS profile overlaps with the weak fluorescence line from Al impurities.…”

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confidence: 53%

Application of the high-resolution grazing-emission x-ray fluorescence method for impurities control in semiconductor nanotechnology

Szlachetko

Banaś

Kubala‐Kukuś

et al. 2009

Journal of Applied Physics

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We report on the application of synchrotron radiation based high-resolution grazing-emission x-ray fluorescence ͑GEXRF͒ method to measure low-level impurities on silicon wafers. The presented high-resolution GEXRF technique leads to direct detection limits of about 10 12 atoms/ cm 2 . The latter can be presumably further improved down to 10 7 atoms/ cm 2 by combining the synchrotron radiation-based GEXRF method with the vapor phase decomposition preconcentration technique. The capability of the high-resolution GEXRF method to perform surface-sensitive elemental mappings with a lateral resolution of several tens of micrometers was probed.The production of ultraclean silicon wafers is one of the most important issues for Si-based microelectronics technology. According to the International Technology Roadmap for Semiconductors ͑ITRS͒ ͑Ref. 1͒, a sensitivity below the level of 10 9 atoms/ cm 2 for transition metals on Si wafer surfaces is needed. At present, the total reflection x-ray fluorescence ͑TXRF͒ method 2-5 combined with intense synchrotron radiation ͑SR͒ sources offers the best possibilities for measuring very low concentration of impurities on Si surfaces. Using SR beams, a sensitivity level of 10 8 atoms/ cm 2 for direct detection of Cu was achieved. 6 On the other hand, in the case of low Z impurities, such as Al, the achieved detection limits ͑DLs͒ by means of the SR-TXRF technique are still above the ITRS requirements. 1,7,8 Moreover, the SR-based TXRF technique, which employs the grazing incidence geometry, cannot benefit from the available microfocused x-ray beams at synchrotrons in order to perform high-spatial resolution two-dimensional ͑2D͒ surfaces mapping. Therefore, further development of new direct techniques to measure metallic impurities on Si wafers is still a challenging problem. In this context, the application of the SR based grazing-emission x-ray fluorescence ͑GEXRF͒ technique for measuring x-ray emission from Si-wafer impurities can be regarded as a good alternative. In the GEXRF technique, which is a kind of inverse of TXRF, the excited x-ray fluorescence is observed at grazing emission angles exit smaller than the critical angle c . 9-12 Such a geometry results in a relative enhancement of the characteristic fluorescence emission from the surface with respect to the substantially decreased fluorescence signal from the bulk substrate.In this paper, we report on a high-resolution GEXRF technique developed for the detection of low-level impurities on Si surfaces. In this method the grazing emission geometry is combined with a wavelength-dispersive spectrometer. The measurements were performed at the European Synchrotron Radiation Facility ͑ESRF͒ in Grenoble, France, at the beamline ID21, employing a von Hamos-type crystal spectrometer 13 for the high-resolution detection of the fluorescence x rays from the impurities deposited on Si wafers. As for small grazing emission angles exit , the photon beam spot on the target, observed in the direction defined by the Bragg angle Bragg , appear...

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“…The cross-section for X-ray Raman scattering is generally low compared to the elastic Rayleigh or inelastic Compton scattering, but it can become significant due to resonant enhancement if the incident photon energy is close to a major absorption edge of the sample matrix. Figure 3 shows a typical fluorescence spectrum (dots) from a wafer intentionally contaminated with 3 ϫ 10 11 atoms/cm 2 aluminum obtained for an excitation energy of 1730 eV and an angle of incidence of 0.1°(critical angle = 0.9°) for 10,000 s. The figure also contains the deconvolved contribution from the elastically scattered signal at 1730 eV, the aluminum K␣ line, and the calculated continuous Raman background (18). This figure demonstrates that it is the inelastic Raman scattering that ultimately determines the minimum detection limit for aluminum, which has been derived for a bending magnet beamline to be 2.4 ϫ 10 9 atoms/cm 2 for a 10,000-s count time, corresponding to 7.6 ϫ 10 9 atoms/cm 2 for a standard 1000-s count time.…”

Section: Sensitivitymentioning

confidence: 99%

Peer Reviewed: Looking at Trace Impurities on Silicon Wafers with Synchrotron Radiation

Baur¹,

Brennan²,

Pianetta³

et al. 2002

Anal. Chem.

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Aluminum impurities in silicon: Investigation of x-ray Raman scattering in total reflection x-ray fluorescence spectroscopy

Cited by 25 publications

References 13 publications

Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Application of the high-resolution grazing-emission x-ray fluorescence method for impurities control in semiconductor nanotechnology

Peer Reviewed: Looking at Trace Impurities on Silicon Wafers with Synchrotron Radiation

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