Yorinobu Kunimune

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...

Dual Damascene Interconnect Technology for 130-nm-node Complementary Metal–Oxide–Semiconductor Devices Using Ladder-Oxide Film

A 0.34-µm-pitch Cu dual damascene interconnect technology using a low-k ladder-oxide film (k=2.9) is developed for 130-nm-node complementary metal oxide semiconductor (CMOS) devices. Photoresist poisoning was improved by adopting the ladder-oxide film with annealing before the photolithography step. The fence structures around via openings caused poor Cu gap filling. The problem was solved by controlling the filling height of a bottom anti-reflective coating and by eliminating the photoresist poisoning. Furthermore, no degradation of the ladder-oxide film upon photoresist stripping was observed. It was demonstrated that these technologies could be applied to a product-level application-specific integrated circuit chip with a seven-level Cu interconnect.

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...

Lateral Diffusion Distance Measurement of 40?80 nm Junctions by Etching/TEM-Electron Energy Loss Spectroscopy Method

A new technique to measure the lateral diffusion distance of boron has been developed by wet-etching combined with TEM and Electron Energy Loss Spectroscopy (TEM-EELS). The position at a dopant concentration of 5×1018 cm-3 can be correctly delineated with a spatial resolution of less than 5 nm. This technique is based on the fact that the gradient of the etched surface changes discontinuously at a dopant concentration of 5×1018 cm-3. This characteristic appeared for all carrier profiles as long as the etching time was sufficiently long. Etching time optimization is needed because an incubation time exists before the etching starts and because the incubation time depends on carrier distribution. Thickness distribution after the etching is measured by TEM-EELS which enables a high spatial resolution measurement. The lateral diffusion distance at the pn junction measured by this technique was about 0.6 times of the vertical diffusion distance for 40–80 nm junctions. These results were compared with those obtained by an electrical C-V measurement, and were consistent.

High resolution secondary ion mass spectrometry analysis of hydrogen behavior in SiO2/SiN/SiO2 films with thermal treatment

The distribution and behavior of hydrogen in a SiO2/SiN/SiO2 (ONO) film stack structure with thermal treatment were investigated by high-resolution secondary ion mass spectrometry analysis. Hydrogen atoms were present in the poly-Si/top-SiO2 interface, SiN layer, and bottom-SiO2/Si-substrate interface. These hydrogen atoms decreased in number with annealing (1000 °C, 60 s) and spike annealing (1000 °C, about 1 s). However, when a SiN cap layer with hydrogen atoms was formed on a poly-Si/ONO film structure, hydrogen atoms in the ONO film did not decrease in number with spike annealing. It was considered that the SiN cap layer mainly performed a supply source of hydrogen into the ONO film during spike annealing, and that hydrogen atoms interdiffused between the SiN cap layer and the SiN layer of the ONO film. These results indicate that the amount of hydrogen in the ONO film can be controlled by annealing and the formation of a SiN cap layer.

Study of strain fields caused by crystallization of boron doped amorphous silicon using scanning transmission electron microscopy convergent beam electron diffraction method

Study of strain fields around boron doped silicon electrodes in silicon devices was carried out with scanning transmission electron microscopy convergent beam electron diffraction. Leak current, which was one of the crucial failures of this kind of structure, depends on boron concentration in the electrodes. Transmission electron microscopy and diffraction analysis showed that the electrodes consist of epitaxial phase and poly-Si phase, and the proportion of these phases depends on the boron concentration in the electrode. Strain distribution obtained with scanning transmission electron microscopy convergent beam electron diffraction revealed that the origin of the strain is volume shrinkage of the epitaxial phase in the electrode, and the poly-Si phase acts as buffer against this strain. Electron energy-loss spectroscopy analyses revealed that boron segregation occurred in samples having a higher boron concentration, and prevented epitaxial growth in the electrodes. As a result, the core of the electrode...

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.

Dopant Drive-in Path Analysis in Poly-silicon Filled in Trench type 3D-MOSFET using Atom Probe Tomography

Dopant drive-in path in nand p-type poly-Si gate of trench structure, one of the 3D device structures, is investigated by atom probe tomography. In the case of P atoms, grain boundary diffusion is dominant. While in the case of B atoms, grain boundary diffusion coefficient seems to be almost same with bulk one.