Hisashi Takamizawa

Dopant distributions in n-MOSFET structure observed by atom probe tomography

The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted.

Dopant distribution in gate electrode of n- and p-type metal-oxide-semiconductor field effect transistor by laser-assisted atom probe

Three dimensional dopant distributions in polycrystalline Si gate of n-type (n-) and p-type (p-) metal-oxide-semiconductor field effect transistor (MOSFET) structure were investigated by laser-assisted three dimensional atom probe. The remarkable difference in dopant distribution between n-MOSFET and p-MOSFET was clearly observed. In n-MOSFET gate, As and P atoms were segregated at grain boundaries and the interface between gate and gate oxide. No diffusion of As and P atoms into the gate oxide was observed. On the other hand, in p-MOSFET, no segregations of B atoms at grain boundaries or the interface were observed, and diffusion of B atoms into the gate oxide was directly observed.

Origin of characteristic variability in metal-oxide-semiconductor field-effect transistors revealed by three-dimensional atom imaging

The greater variability in the electrical properties of n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) compared with those of p-type MOSFETs poses problems for scaling of silicon based large-scale integration technology. We have elucidated the origin of the variability difference between n- and p-type transistors by using laser-assisted atom probe tomography to directly count the number of discrete atoms in local regions. We found that ion implantation and activation annealing for source/drain extension fabrication enhances anomalous dopant fluctuations of boron atoms in n-MOSFET channel regions, interpreted by fast migration of boron atoms.

Depth and lateral resolution of laser-assisted atom probe microscopy of silicon revealed by isotopic heterostructures

We report on a direct comparison of the depth and lateral resolution of the current state-of-the-art laser-assisted atom probe microscopy analysis of single-crystalline silicon. The isotopic heterostructures composed of 5–15 nm-thick S28i- and S30i-enriched layers were measured to reconstruct three-dimensional images of S28i and S30i stable isotope distributions in the surface perpendicular and parallel directions for the analysis of the depth and lateral resolution, respectively. The decay length experimentally obtained for the lateral direction is only about twice longer than in the direction, meaning that the lateral resolution is higher than obtained by secondary ion mass spectrometry.

Correlation between threshold voltage and channel dopant concentration in negative-type metal-oxide-semiconductor field-effect transistors studied by atom probe tomography

The correlation between threshold voltage (VT) and channel boron concentration in silicon-based 65 nm node negative-type metal-oxide-semiconductor field-effect transistors was studied by atom probe tomography (APT). VT values were determined for one million transistors in a single chip, and transistors having a ±4σ deviation from the median VT were analyzed using APT. VT and the channel boron concentration were positively correlated. This is consistent with the relationship between the average boron concentration of wafers implanted with different channel doses and the median VT of the million transistors. APT is suitable for the study of dopant-distribution-based device failure mechanisms.

Dopant characterization in self-regulatory plasma doped fin field-effect transistors by atom probe tomography

Fin field-effect transistors are promising next-generation electronic devices, and the identification of dopant positions is important for their accurate characterization. We report atom probe tomography (APT) of silicon fin structures prepared by a recently developed self-regulatory plasma doping (SRPD) technique. Trenches between fin-arrays were filled using a low-energy focused ion beam to directly deposit silicon, which allowed the analysis of dopant distribution by APT near the surface of an actual fin transistor exposed to air. We directly demonstrate that SRPD can achieve a boron concentration above 1 × 1020 atoms/cm3 at the fin sidewall.

Phosphorus and boron diffusion paths in polycrystalline silicon gate of a trench-type three-dimensional metal-oxide-semiconductor field effect transistor investigated by atom probe tomography

The dopant (P and B) diffusion path in n- and p-types polycrystalline-Si gates of trench-type three-dimensional (3D) metal-oxide-semiconductor field-effect transistors (MOSFETs) were investigated using atom probe tomography, based on the annealing time dependence of the dopant distribution at 900 °C. Remarkable differences were observed between P and B diffusion behavior. In the initial stage of diffusion, P atoms diffuse into deeper regions from the implanted region along grain boundaries in the n-type polycrystalline-Si gate. With longer annealing times, segregation of P on the grain boundaries was observed; however, few P atoms were observed within the large grains or on the gate/gate oxide interface distant from grain boundaries. These results indicate that P atoms diffuse along grain boundaries much faster than through the bulk or along the gate/gate oxide interface. On the other hand, in the p-type polycrystalline-Si gate, segregation of B was observed only at the initial stage of diffusion. After f...

Impact of carbon coimplantation on boron behavior in silicon: Carbon–boron coclustering and suppression of boron diffusion

Coimplantation of heterogeneous dopants in materials can be used to control the principal dopant distribution. We used atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) to investigate the impact of coimplanted carbon on boron diffusion in silicon. After annealing, three-dimensional APT analysis of dopant distributions revealed the presence of carbon–boron coclusters around the projection range of boron. In addition, SIMS depth profiles revealed enhanced boron concentration around the projection range of carbon. These results suggest that the carbon–boron interaction suppresses boron diffusion in silicon.

Atomic-scale characterization of germanium isotopic multilayers by atom probe tomography

We report comparison of the interfacial sharpness characterization of germanium (Ge) isotopic multilayers between laser-assisted atom probe tomography (APT) and secondary ion mass spectrometry (SIMS). An alternating stack of 8-nm-thick naturally available Ge layers and 8-nm-thick isotopically enriched 70Ge layers was prepared on a Ge(100) substrate by molecular beam epitaxy. The APT mass spectra consist of clearly resolved peaks of five stable Ge isotopes (70Ge, 72Ge, 73Ge, 74Ge, and 76Ge). The degree of intermixing at the interfaces between adjacent layers was determined by APT to be around 0.8 ± 0.1 nm which was much sharper than that obtained by SIMS.

Three-Dimensional Elemental Analysis of Commercial 45 nm Node Device with High-k/Metal Gate Stack by Atom Probe Tomography

Laser-assisted atom probe tomography (APT) was successfully applied to analyze the elemental distributions in a high-k/metal gate stack of a commercially available 45 nm node real device. APT revealed the multilayer structure of the high-k/metal gate stack with nearly atomic-scale resolution, and successfully detected small amounts of Zr in the thin layer of high-k HfO2 dielectrics and H in the Ti layer of the metal gate. The present results demonstrate the usefulness of APT as a tool of elemental analysis in nanoscale multilayer device structures.