X Blasco

Enhanced electrical performance for conductive atomic force microscopy

A new configuration of a conductive atomic force microscopy (CAFM) is presented, which provides enhanced electrical specs and performance while keeping the nanometer spatial resolution. This is achieved by integrating in the same measurement system a CAFM and a semiconductor parameter analyzer (SPA). The CAFM controls the tip position and scanning parameters, and the SPA is used for sample biasing and measurement. To test this set up, thin SiO2 gate oxides of MOS devices have been characterized. For current measurements, the resulting dynamic range was from 1 pA up to 1 mA. The good performance of the conductive tip at such high currents is demonstrated.

Nanoscale post-breakdown conduction of HfO/sub 2//SiO/sub 2/ MOS gate stacks studied by enhanced-CAFM

An enhanced conductive atomic force microscope has enabled a measurement of the conduction through a HfO/sub 2//SiO/sub 2/ gate stack until breakdown (BD) in a single measurement, with nanometer resolution. Before the stack BD, the current-voltage characteristic shows several conduction modes. After BD, switchings between different conduction states were observed, showing that BD is a reversible phenomenon.

Ultra thin films of atomic force microscopy grown SiO2 as gate oxide on MOS structures: conduction and breakdown behavior

Abstract Electrical conduction modes and breakdown of atomic force microscopy (AFM) grown SiO2 as gate oxide in metal–oxide–semiconductor (MOS) structures are studied, and the results are compared to those obtained from MOS capacitors with thermally grown SiO2. Gate current vs. gate voltage characteristics were obtained from standard electrical characterization techniques, i.e. wafer prober plus semiconductor parameter analyzer. To obtain suitable samples, AFM oxidation has been integrated in a CMOS microelectronic process. This characterization showed larger current levels and lower breakdown voltages for AFM grown gate oxides than for thermally grown gate oxides. On the other hand, I–V curves collected at a nanometric range by means of a conductive-AFM show a closer behavior for both kinds of oxides.

Breakdown spots of ultra-thin (EOT < 1.5 nm) HfO2/SiO2 stacks observed with enhanced—CAFM

Abstract In this work, the (gate) current versus (gate) voltage ( I – V ) characteristics and the dielectric breakdown (BD) of an ultra-thin HfO 2 /SiO 2 stack is studied by enhanced conductive atomic force microscopy (ECAFM). The ECAFM is a CAFM with extended electrical performance. Using this new set up, different conduction modes have been observed before BD. The study of the BD spots has revealed that, as for SiO 2 , the BD of the stack leads to modifications in the topography images and high conductive spots in the current images. The height of the hillocks observed in the topography images has been considered an indicator of structural damage.

Topographic characterization of AFM-grown SiO2 on Si

In order to establish whether atomic force microscope (AFM) grown SiO2 is appropriate for use as a gate oxide in nanoelectronics, a characterization of these films needs to be performed. In this paper results on AFM fabrication and topographical characterization of large-area SiO2 patterns are presented. This paper is centred around the SiO2 surface and SiO2-Si interface roughness, due to its importance in relation to the quality of ultrathin dielectrics. Our results show quite similar values to those obtained for thermal oxides and thus we suggest that AFM-grown SiO2 is a suitable candidate for gate oxide applications in nanodevices.

Characterising the surface roughness of AFM grown SiO2 on Si

Abstract The reliability of AFM grown SiO 2 as a gate oxide needs to be examined if nanodevices fabricated from the oxide are to be integrated into standard microelectronic technology. In this article we present our preliminary results on AFM fabrication and topographical characterisation of large area oxide, electrical characterisation is to follow. Roughness is the central issue of this work due to its importance in relation to the quality of ultra thin dielectrics.

Electrical characterization and fabrication of SiO2 based metal?oxide?semiconductor nanoelectronic devices with atomic force microscopy

Atomic force microscopy (AFM) has been used to fabricate and electrically characterize SiO2 films as gate dielectrics of metal–oxide–semiconductor (MOS) electronic devices. The electrical properties of the AFM grown oxide (3 nm thick) have been determined at a nanometric scale and compared to those of thermal gate oxides (GOXs). The results show a similar electrical behaviour of both kinds of oxide. Furthermore, the broken down GOX locations (breakdown spots) induced in microelectronic-sized devices have been located and electrically characterized with AFM. The results indicate that AFM is a suitable tool for the fabrication and reliability analysis of present and future Si/SiO2 based MOS nanoelectronic devices.

Pre- and post-breakdown switching behaviour in ultrathin SiO2layers detected by C-AFM

Ultrathin SiO2 films (3-6 nm) have been electrically characterized with a conductive atomic force microscope. This technique allows the electrical characterization of areas of ~100 nm2, which are comparable to the area of breakdown spots. Sequences of voltage ramps on fixed oxide locations have been applied to induce the oxide degradation and its conduction properties have been analysed within the nanometre scale range. In particular, on-off fluctuations before and after breakdown are reported on single breakdown spots.

Local current fluctuations before and after breakdown of thin SiO2 films observed with conductive atomic force microscope

Abstract Very thin SiO 2 films (3–6 nm) have been characterized with a conductive atomic force microscope (C-AFM). The set-up allows the electrical characterization of 30–50 nm 2 areas, which are of the order of single breakdown spots. Voltage ramps have been repeatedly applied to induce the degradation. On these spots, the phenomenology observed is quite similar to that during conventional electrical tests. In particular, on–off fluctuations before and after breakdown are reported on single breakdown spots. The results confirm the C-AFM as a suitable tool for the analysis of the gate oxide electrical properties and degradation dynamics at a nanometer scale.

Electrical characterization of atomic-force-microscopy grown SiO2

Atomic Force Microscopy (AFM) has been demonstrated to be one of the most powerful tools for nanoelectronic fabrication and characterization. However, AFM grown SiO2 has not been yet used as the gate dielectric, and its electrical behavior remains still unknown. After a topographic characterization, in this paper the conduction modes of AFM grown gate oxide (AFM-GOX) MOS structures are studied from measurements of their current-voltage (IV) characteristics. The results are compared to those obtained for thermally grown SiO2 (T-GOX), which is used as quality reference. Two types of structures have been used to study the conduction through AFM-GOX: a) MOS capacitors with polysilicon deposited gate, for standard electrical characterization and b) MOS structures without deposited gate, because the conductive AFM tip acts as gate terminal, for Conductive-AFM (C-AFM) measurements. Qualitatively, the fabrication process of the poly-Si gated structures consisted of: a field oxidation of the Si wafers, opening of windows in the field oxide to reach the substrate, then AFM oxidation was performed (4nm thick oxide), and as a last step a polysilicon gate was deposited. For the reference structures, AFM gate oxidation process was replaced by thermal oxidation with thickness of 3.5 and 4.5nm. The substrate was n-type Si. The standard electrical characterization, reveals that the dielectric breakdown of T-GOX happens at higher voltage than for AFM-GOX. Moreover, the current level through AFM GOX at voltages below the breakdown value is several orders of magnitude larger than that measured at same voltages for thermal oxides. These differences could be caused by defects introduced during the AFM oxidation, performed in ambient air. However, a comparison between the IV curves of AFM-GOX and T-GOX measured by C-AFM shows that at a nanometer scale both oxides behave similarly.