Yuan Tu

Influence of laser power on atom probe tomographic analysis of boron distribution in silicon.

The relationship between the laser power and the three-dimensional distribution of boron (B) in silicon (Si) measured by laser-assisted atom probe tomography (APT) is investigated. The ultraviolet laser employed in this study has a fixed wavelength of 355nm. The measured distributions are almost uniform and homogeneous when using low laser power, while clear B accumulation at the low-index pole of single-crystalline Si and segregation along the grain boundaries in polycrystalline Si are observed when using high laser power (100pJ). These effects are thought to be caused by the surface migration of atoms, which is promoted by high laser power. Therefore, for ensuring a high-fidelity APT measurement of the B distribution in Si, high laser power is not recommended.

Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices...

Role of W and Mn for reliable 1X nanometer-node ultra-large-scale integration Cu interconnects proved by atom probe tomography

We used atom probe tomography (APT) to study the use of a Cu(Mn) as a seed layer of Cu, and a Co(W) single-layer as reliable Cu diffusion barriers for future interconnects in ultra-large-scale integration. The use of Co(W) layer enhances adhesion of Cu to prevent electromigration and stress-induced voiding failures. The use of Cu(Mn) as seed layer may enhance the diffusion barrier performance of Co(W) by stuffing the Cu diffusion pass with Mn. APT was used to visualize the distribution of W and Mn in three dimensions with sub-nanometer resolution. W was found to segregate at the grain boundaries of Co, which prevents diffusion of Cu via the grain boundaries. Mn was found to diffuse from the Cu(Mn) layer to Co(W) layer and selectively segregate at the Co(W) grain boundaries with W, reinforcing the barrier properties of Co(W) layer. Hence, a Co(W) barrier coupled with a Cu(Mn) seed layer can form a sufficient diffusion barrier with film that is less than 2.0-nm-thick. The diffusion barrier behavior was pres...

Boron distributions in individual core–shell Ge/Si and Si/Ge heterostructured nanowires

Ge/Si and Si/Ge core-shell nanowires (NWs) have substantial potential for application in many kinds of devices. Because impurity distributions in Ge/Si and Si/Ge core-shell NWs strongly affect their electrical properties, which in turn affect device performance, this issue needs urgent attention. Here we report an atom probe tomographic study of the distribution of boron (B), one of the most important impurities, in two kinds of NWs. B atoms were doped into the Si regions of Ge/Si and Si/Ge core-shell NWs. It was found that the B atoms were randomly distributed in the Si shell of the Ge/Si core-shell NWs. In the Si/Ge core-shell NWs, on the other hand, the B distributions depended on the growth temperature and the B2H6 flux. With a higher growth temperature and an increased B2H6 flux, the B atoms piled up in the outer region of the Si core. However, the B atoms were observed to be randomly distributed in the Si core after decreasing both the growth temperature and the B2H6 flux.

Effect of carbon on boron diffusion and clustering in silicon: Temperature dependence study

Atom probe tomography and secondary ion mass spectrometry were used to investigate the effects of carbon (C) co-implantation and subsequent annealing at 600 to 1200 °C on the behavior of implanted boron (B) atoms in silicon. When B alone was implanted, annealing at 600 to 800 °C caused it to form clusters in the peak region (1020 cm−3) of the concentration profile, and diffusion only occurred in the low-concentration tail region (<1018 cm−3), which is thought to be the well-known transient enhanced diffusion. However, when co-implantation with C was performed, this diffusion was almost completely suppressed in the same annealing temperature range. In the absence of C implantation, annealing at 1000 °C caused B clusters to begin to dissolve and B to diffuse out of the peak concentration region. However, this diffusion was also suppressed by C implantation because C atoms trapped B atoms in the kink region found at the B concentration level of 2 × 1019 cm−3. At 1200 °C, B clusters were totally dissolved and a strong B diffusion occurred. In contrast to lower annealing temperatures, this diffusion was actually enhanced by C implantation. It is believed that Si interstitials play an important role in the interaction between B and C. This kind of comprehensive investigation yields important information for optimizing ion implantation and annealing processes.Atom probe tomography and secondary ion mass spectrometry were used to investigate the effects of carbon (C) co-implantation and subsequent annealing at 600 to 1200 °C on the behavior of implanted boron (B) atoms in silicon. When B alone was implanted, annealing at 600 to 800 °C caused it to form clusters in the peak region (1020 cm−3) of the concentration profile, and diffusion only occurred in the low-concentration tail region (<1018 cm−3), which is thought to be the well-known transient enhanced diffusion. However, when co-implantation with C was performed, this diffusion was almost completely suppressed in the same annealing temperature range. In the absence of C implantation, annealing at 1000 °C caused B clusters to begin to dissolve and B to diffuse out of the peak concentration region. However, this diffusion was also suppressed by C implantation because C atoms trapped B atoms in the kink region found at the B concentration level of 2 × 1019 cm−3. At 1200 °C, B clusters were totally dissolved and...

Blocking of deuterium diffusion in poly-Si/Al2O3/HfxSi1−xO2/SiO2 high-k stacks as evidenced by atom probe tomography

Hydrogen (H) plays an important role in determining the reliability and performance of HfO2- and Al2O3-based high-k dielectric electronic devices. In order to understand H behavior, deuterium (D), an isotope of H, was introduced into the poly-Si cap of Al2O3/HfxSi1−xO2/SiO2 high-k stacks by ion implantation. Atom probe tomography was used to image the D distribution in samples annealed under different conditions. The results clearly demonstrated that the D atoms were trapped at the interface of poly-Si and Al2O3 after annealing at 900 K for 10 min. Thus, it is possible that Al2O3 blocks the H atoms at the surface, preventing them from diffusing into the high-k dielectrics during the H2 annealing process in current fabrication technology. The current work also exhibits an example of investigating H behavior in semiconductors by atom probe tomography.

Revisiting room-temperature 1.54 μιη photoluminescence of ErO x centers in silicon at extremely low concentration

Luminescence of erbium in silicon has been intensively explored in the past in the high power emission regime, but its employment for manufacturability of active components for silicon photonics proved unfeasible. We explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of ErOx in Si for accessing few photon regime towards single photon emission. We achieve countable photon regime and we assess the lower-bound number of detectable emission centers by micron scale implanted dots, whose emission is collected by an inverted confocal microscope.

Atom probe study of erbium and oxygen co-implanted silicon

It has been reported that erbium (Er) is a source of optical emission at λ=1.54 pm due to ⁴I<inf>13/2</inf> →⁴I<inf>15/2</inf> transition of Er³⁺. A method of oxygen (O) codoping with Er has attracted attention as a candidate for obtaining more efficient optical gain by forming Er:O complex. Although several simulations predict the equilibrium structure of Er:O complex, it is difficult to understand experimentally how related between these implanted ions followed by annealing for optical activation. In this workshop, we reported the preliminary results on three-dimensional distributions of Er and O co-implanted into Si investigated by atom probe tomography.

1.54 μm photoluminescence from Er:O x centers at extremely low concentration in silicon at 300 K

The demand for single photon sources at λ = 1.54 μm, which follows from the consistent development of quantum networks based on commercial optical fibers, makes Er:Ox centers in Si still a viable resource thanks to the optical transition of Er3+: I13/2 → I15/2. Yet, to date, the implementation of such system remains hindered by its extremely low emission rate. In this Letter, we explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of Er:Ox in Si. The emitted photons, excited by a λ = 792 nm laser in both large areas and confined dots of diameter down to 5 μm, are collected by an inverted confocal microscope. The lower-bound number of detectable emission centers within our diffraction-limited illumination spot is estimated to be down to about 104, corresponding to an emission rate per individual ion of about 4 ×103 photons/s.The demand for single photon emitters at λ=1.54  μm, which follows from the consistent development of quantum networks based on optical fiber technologies, makes Er:Ox centers in Si a viable resource, thanks to the I13/24→I415/2 optical transition of Er3+. While its implementation in high-power applications is hindered by the extremely low emission rate, the study of such systems in the low concentration regime remains relevant for quantum technologies. In this Letter, we explore the room-temperature photoluminescence at the telecomm wavelength from very low implantation doses of Er:Ox in Si. The lower-bound number of optically active Er atoms detected is of the order of 102, corresponding to a higher-bound value for the emission rate per individual ion of about 104  s-1.

Atom probe tomographic assessment of the distribution of germanium atoms implanted in a silicon matrix through nano-apertures

Ion implantation through nanometer-scale apertures (nano-apertures) is a promising method to precisely position ions in silicon matrices, which is a requirement for next generation electronic and quantum computing devices. This paper reports the application of atom probe tomography (APT) to investigate the three-dimensional distribution of germanium atoms in silicon after implantation through nano-aperture of 10 nm in diameter, for evaluation of the amount and spatial distribution of implanted dopants. The experimental results obtained by APT are consistent with a simple simulation with consideration of several effects during lithography and ion implantation, such as channeling and resist flow.