Yoshihiro Koga

Erratum: “Proximity gettering of C3H5 carbon cluster ion-implanted silicon wafers for CMOS image sensors: Gettering effects of transition metal, oxygen, and hydrogen impurities”

A new technique is described for manufacturing silicon wafers with the highest capability yet reported for gettering transition metallic, oxygen, and hydrogen impurities in CMOS image sensor fabrication. It is demonstrated that this technique can implant wafers simultaneously with carbon and hydrogen elements that form the projection range by using hydrocarbon compounds. Furthermore, these wafers can getter oxygen impurities out-diffused from the silicon substrate to the carbon cluster ion projection range during heat treatment. Therefore, they can reduce the formation of transition metals and oxygen-related defects in the device active regions and improve electrical performance characteristics, such as dark current and image lag characteristics. The new technique enables the formation of high-gettering-capability sinks for transition metals, oxygen, and hydrogen impurities under device active regions of CMOS image sensors. The wafers formed by this technique have the potential to significantly reduce dark current in advanced CMOS image sensors.

Study of Carrier Emission and Capture Processes at Electron Traps in 3C-SiC

The n-type 3C-SiC grown on Si(001) substrates by chemical vapor deposition was characterized by deep-level-transient spectroscopy (DLTS). DLTS peaks appeared near 160 K and 260 K with the emission rate being 26 s-1. For the shallower level, the activation energy Ea is 0.34 eV and the capture cross section at infinite temperature σ∞ is 6.0×10-17 cm2. For the deeper level, Ea=0.52 eV and σ∞=9.5×10-18 cm2. The capture cross section at the peak temperature was obtained by changing the injection pulse width, and it was found that the energy barrier of electron capture is negligibly small for these two traps.

Trapping and diffusion kinetic of hydrogen in carbon-cluster ion-implantation projected range in Czochralski silicon wafers

We investigated the diffusion behavior of hydrogen in a silicon wafer made by a carbon-cluster ion-implantation technique after heat treatment and silicon epitaxial growth. A hydrogen peak was observed after high-temperature heat treatment (>1000 °C) and silicon epitaxial growth by secondary ion mass spectrometry analysis. We also confirmed that the hydrogen peak concentration decreased after epitaxial growth upon additional heat treatment. Such a hydrogen diffusion behavior has not been reported. Thus, we derived the activation energy from the projected range of a carbon cluster, assuming only a dissociation reaction, and obtained an activation energy of 0.76 ± 0.04 eV. This value is extremely close to that for the diffusion of hydrogen molecules located at the tetrahedral interstitial site and hydrogen molecules dissociated from multivacancies. Therefore, we assume that the hydrogen in the carbon-cluster projected range diffuses in the molecular state, and hydrogen remaining in the projected range forms complexes of carbon, oxygen, and vacancies.

Gettering Mechanism in Carbon-cluster-ion-implanted Epitaxial Silicon Wafers using Atom Probe Tomography

The difference in agglomerate defects formed by carbon-cluster-ion-implanted Czochralski (CZ)-Si and epitaxial Si has been investigated using atom probe tomography. In the previous work, we reported on the strong gettering capability in implanted epitaxial Si. We found that the distribution of O and C atom concentrations on agglomerates differs between CZ-Si and epitaxial Si. This suggests that a C agglomerate, which grows without including O atoms, results in strong gettering efficiency for Fe.

Effect of dose and size on defect engineering in carbon cluster implanted silicon wafers

Carbon-cluster-ion-implanted defects were investigated by high-resolution cross-sectional transmission electron microscopy toward achieving high-performance CMOS image sensors. We revealed that implantation damage formation in the silicon wafer bulk significantly differs between carbon-cluster and monomer ions after implantation. After epitaxial growth, small and large defects were observed in the implanted region of carbon clusters. The electron diffraction pattern of both small and large defects exhibits that from bulk crystalline silicon in the implanted region. On the one hand, we assumed that the silicon carbide structure was not formed in the implanted region, and small defects formed because of the complex of carbon and interstitial silicon. On the other hand, large defects were hypothesized to originate from the recrystallization of the amorphous layer formed by high-dose carbon-cluster implantation. These defects are considered to contribute to the powerful gettering capability required for high-performance CMOS image sensors.