B. Gautier

Deconvolution of SIMS depth profiles of boron in silicon

We have measured the depth resolution function of the SIMS analysis of boron in silicon for different experimental conditions and fitted this function with an analytical expression initially proposed by Dowsettet al. We use this analytical depth resolution function for the implementation of an iterative deconvolution algorithm, taking into account several properties of the signal, such as positivity and regularity. This algorithm is described precisely. n nThe algorithm is tested on several theoretical structures and then implemented for the deconvolution of real structures of boron-doped silicon layers in silicon. In particular, a sample constituted by six consecutive delta layers and a 75 A thick layer are deconvolved. It is shown that the asymmetry of the profiles is completely removed and that the full width at half-maximum of the deconvolved delta layers can be reduced down to 41 A. It is also shown that a layer whose real thickness is smaller than the measured width of the resolution function can be easily distinguished from a delta layer, and its thickness estimated.

Quantification of germanium and boron in heterostructures Si/Si1−xGex/Si by SIMS

Abstract The use of secondary ions mass spectrometry (SIMS) generally leads to very high sensitivity and depth resolution for silicon-based components. Low concentration elements such as dopants, are easy to quantify in silicon, whereas high concentration elements are subject to “matrix effects”, i.e. the intensity does not vary linearly with the concentration. Matrix effects are presently studied in SiGe alloys using two primary beams O 2 + and Cs + and a CAMECA IMS4F instrument. Rapid thermal chemical vapor deposition grown Si/Si 1− x Ge x /Si multilayer structures with x varying from 0 to 23.5% are preliminarily characterized by Rutherford backscattering spectrometry (RBS) in thickness and atomic composition. The linear variation of the SIMS intensity ratio I Ge + / I Si + with the RBS concentration ratio x /(1− x ) is confirmed for both O 2 + and Cs + beams. However, the linearity does not imply the absence of matrix effects. A variation of the ionization yields with Ge concentration and a similar behavior for τ Ge+ and τ Si+ actually lead to an exact compensation of the intensity ratio variation. At any energy, O 2 + experiments systematically over-estimate the real Ge concentration, whereas matrix effects under Cs + beam are weak. For polyatomic MCs + ions, strong matrix effects are observed in Si 1− x Ge x alloys. A quantitative analysis of major constituents and a dopant (boron) is used to determine the depth profiles of a thin base of a SiGe HBT heterostructure. Two different procedures are used depending on the primary beam. Consistent results are obtained for the concentrations of the major elements. The fully autonomous SIMS analysis with the Cs + beam is still penalized by the lack of sensitivity for boron in the secondary positive mode.

Influence of the ferroelectric polarization on the electronic structure of BaTiO3 thin films

Micron scale ferroelectric (FE) domains have been written into a 20-nm-thick epitaxial thin film of BaTiO3 (001) [BTO(001)] on a Nb-doped SrTiO3 substrate using a piezoforce microscope (PFM). The domain-dependent electronic structure has been studied using fully energy-filtered photoemission electron microscopy (PEEM) and synchrotron radiation. Shifts, induced by FE polarization, of up to 300 meV were observed in the work function of the sample. The surface is Ba-O terminated. Polarization-induced distortion of the electronic structure was observed in the valence band and on the Ba 3d, Ti 2p and O 1s core levels of BTO. Polarization-dependent surface adsorption was observed. A simple electrostatic model based on net surface charge is not sufficient to explain the observed modifications in the electronic levels. Copyright

SIMS depth profile correction for the study of the first step of the diffusion of boron in silicon

Abstract The analysis by secondary ions mass spectrometry (SIMS) is a powerful tool for the study of the diffusion of boron in silicon. It has been extensively used in order to determine diffusion coefficients. Most of the time, the SIMS profiles used to calculate the diffusion coefficients are sufficiently large so that the SIMS analysis do not modify the real concentration distribution in a significant manner. But more and more, the first steps of the diffusion are to be considered in order to obtain very thin diffused structures. In that case, where very thin layers are analyzed by SIMS, it is no more possible to measure directly the real concentration distribution because the SIMS analysis modify it rather significantly. When the real width or the real shape of the analyzed layers is needed, the measured profile has to be corrected in some way. We show that in the case of Gaussian original profiles, the SIMS profiles can be efficiently corrected, and the exact second order moment of the profile determined from the measured profile until the original second order moment is as low as 20 A. This can be done by the study of the properties of the convolution of the profiles by the SIMS analysis response function. In the case of non-Gaussian profiles, the real shape and width of the profiles can be determined by a deconvolution procedure that we have previously described. (B. Gautier, J.C. Dupuy, G. Prudon, J.P. Vallard, C. Dubois, Proceedings of SIMS X, The International Conference on Secondary Ion Mass Spectroscopy and Related Techniques, Wiley, Chichester, 1996, pp. 443; B. Gautier, R. Prost, J.C. Dupuy, G. Prudon, Surface and Interface Analysis 24 (11) (1996) 733). This procedure is applied to the case of the SIMS measurement of δ-doped layers of boron in silicon before and after rapid thermal annealing (RTA).

Single crystal PZT thin film membrane with highly conductive electrodes

Piezoelectric membrane based on single crystalline Pb(Zr0.52Ti0.48)O3 (PZT) thin film on (001) Si substrate is reported in this paper. To obtain epitaxial single crystalline PZT thin film, SrTiO3 (STO) buffer layer was grown by Molecular Beam Epitaxy on Si substrate, which has been proven as an effective way to increase the crystalline quality. 70nm-thick PZT thin film was deposited on STO-buffered Si substrate by the sol-gel method. 100nm-thick Ru top electrode was patterned by wet etching and subsequently 200nm-thick SiO2 elastic layer was deposited on the top of the stack in order to mechanically strengthen the final membrane. Deep reactive ion etching was therefore used to release the membrane from the backside. Finally, 100nm-thick Au bottom electrode was deposited on the backside of the membrane. Two types of membrane structures were realized, i.e. piezoelectric actuator and resonator. The resonances were studied by an impedance meter and the hysteresis loop of the electromechanical response was characterized by a Wyko profilometer.