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

Abstract

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...

A von Hamos x-ray spectrometer based on a segmented-type diffraction crystal for single-shot x-ray emission spectroscopy and time-resolved resonant inelastic x-ray scattering studies

“…High energy resolution hard x-ray (5-15 keV) emission spectroscopy (XES) is a powerful tool to determine the electronic structure of matter and has found many applications in chemistry, 1 geology, 2 nanotechnology, 3 magnetism, 4 catalysis, 5 and biology, 6 to name of few. At synchrotron sources, hard x-ray emission spectroscopy is used for resonant inelastic x-ray scattering studies (RIXS), 7 high energy resolution fluorescence detected XAS spectroscopy (HERFD-XAS or alternatively called partial fluorescence yield XAS) (Refs.…”

Depth profiles of Al impurities implanted in Si wafers determined by means of the high-resolution grazing emission X-ray fluorescence technique

“…The energy selected for the excitation of the Al-Kα fluorescence line was guided by several considerations. Besides the suppression of the strong Si-Kα fluorescence line and the increased photoabsorption cross-section if an excitation energy just above the Al K-edge is chosen, this excitation energy also resulted in a considerable background reduction as it is explicitly described in [13]. Briefly, the high resolution of our spectrometer allows separating the Si RRS-KL [15] structure, which is usually the limiting factor for the detection limit of Al and whose edge depends directly on the primary beam energy, from the Al-Kα fluorescence line by choosing an energy just above the Al K-edge.…”

“…Monochromatic x-rays from a synchrotron source, the Bremsstrahlung from an x-ray tube, or ionized particles like electrons and ions can be used. In addition focussed and collimated x-ray beams can be used if needed in GEXRF setups which allow performing surface scans as it is shown in [13]. Such surface scans cannot be realized with grazing incidence geometries since the incoming beam spreads over the target surface.…”

Depth profiling of dopants implanted in Si using the synchrotron radiation based high‐resolution grazing emission technique

“…Consequently, low detection limits can be achieved. [18] Furthermore, SR sources can deliver focused and collimated X-ray beams, which can be easily combined with grazing emission setups to realize spatially mm-resolved measurements. Elemental surface maps of the contaminant or dopant distribution in terms of location and concentration can thus be obtained.…”

“…The feasibility of such elemental mapping was demonstrated in. [18] At SR sources, GEXRF can be combined in addition with X-ray absorption spectroscopy that allows to study, for example, the local electronic structure of implanted dopants. [8,19] SR enhances, thus significantly, the versatility of possible GEXRF applications.…”