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Complementary metal-oxide-semiconductor (CMOS) image sensors have widely been used in internet of thinking (IoT) devices such as smartphones, smart watch and personal computer tablets [1] . The consumer market strongly requires higher sensitivity and higher speed image data processing to realize high functional CMOS image sensors such as three dimensionally stacked back-side-illuminated CMOS image sensors (3D-CIS) [2] . However, there are some serious technological issues in the fabrication of advanced CMOS image sensors as shown in Fig. 1 .

The gettering behavior in a hydrocarbon molecular (C3H5) ion implanted region was investigated using atom probe tomography (APT) with the aim of improving electrical properties of CMOS image sensors (CISs) and stacked CISs. APT clarified the formation of carbon atom agglomerates with copper and oxygen gettering capability in the C3H5 ion implanted region. However, there were no oxygen atoms near the copper atoms in the C3H5 ion implanted region. In addition, the copper gettering capability of each carbon atom agglomerates decreased with increasing ratio of the number of oxygen atoms to that of carbon atoms in the carbon atom agglomerates. The copper and oxygen gettering mechanism was considered to involve the formation of a complex with carbon-containing gettering sites. Oxygen degrades the copper gettering capability of carbon atom agglomerates by the formation of stable complexes with carbon-containing gettering sites, which can also act as copper gettering sites. Consequently, the oxygen concentration in the C3H5 ion implanted regions is an important factor in improving the electrical properties of CISs and stacked CISs.

Gettering sinks for metallic impurities formed by carbon-cluster ion implantation in epitaxial silicon wafers have been investigated using technology computer-aided design and atom probe tomography (APT). We found that the defects formed by carbon-cluster ion implantation consist of carbon and interstitial silicon clusters (carbon-interstitial clusters). Vacancy-type clusters are not dominant gettering sinks for metallic impurities in the carbon-cluster ion implanted region. APT data indicated that the distribution of oxygen atoms in the defects differs between Czochralski-grown silicon and epitaxial silicon wafers. The high gettering efficiency observed in carbon-cluster ion implanted epitaxial silicon wafers in comparison with Czochralski-grown silicon wafers is due to the distribution of oxygen atoms in the defects. Defects not containing O atoms provide strong gettering sinks for metallic impurities. These defects are formed by only carbon-interstitial clusters. Oxygen atoms inside the defects modify the amount of carbon-interstitial cluster formation on the defects. It is suggested that the gettering efficiency for metallic impurities in carbon-cluster ion implanted epitaxial silicon wafer is determined by the amount of carbon-interstitial clusters.

We developed silicon epitaxial wafers with high gettering capability by using hydrocarbon&ndash, molecular&ndash, ion implantation. These wafers also have the effect of hydrogen passivation on process-induced defects and a barrier to out-diffusion of oxygen of the Czochralski silicon (CZ) substrate bulk during Complementary metal-oxide-semiconductor (CMOS) device fabrication processes. We evaluated the electrical device performance of CMOS image sensor fabricated on this type of wafer by using dark current spectroscopy. We found fewer white spot defects compared with those of intrinsic gettering (IG) silicon wafers. We believe that these hydrocarbon&ndash, ion&ndash, implanted silicon epitaxial wafers will improve the device performance of CMOS image sensors.

We investigate the amorphous formation behavior on hydrocarbon molecular ion implantation conditions such as hydrocarbon molecular ion size by X-ray photoelectron spectroscopy (XPS). The cross-sectional radius of the amorphous region was obtained from the peak intensity of the amorphous component in Si 2p spectra analyzed by XPS, and using columnar formula for a model. We confirmed that the cross-sectional radius of the amorphous region formed by hydrocarbon molecular ions differs greatly from that formed by monomer carbon ions, and increases by 0.078 nm as the number of carbon atoms composing the hydrocarbon molecular ion increases. The dependence of amorphous formation on the hydrocarbon molecular size is related to the C–C binding distance, and the ratio of increase in the amorphous cross-sectional radius corresponds to half of the C–C binding distance. Therefore, the collision behavior of hydrocarbon molecular ions during implantation predominantly influence the size of hydrocarbon molecular ions.

The metallic impurity gettering capability of hydrocarbon molecular ion-implanted silicon wafers was demonstrated by using a complementary metal-oxide-semiconductor (CMOS) image sensor that provides floating diffusion amplifier voltage (V dark ) output signals under dark conditions. It was found that the V dark output signals of hydrocarbon molecular ion implanted p/p− and p/p+ silicon wafers did not increase after intentional contamination with Fe, Cu, Ni and Co metallic impurities. This indicates that the hydrocarbon molecular ion implanted silicon wafers were able to getter metallic impurities in the projection range of hydrocarbon molecular ion implantation during CMOS device fabrication. It was also found that the hydrocarbon-molecular-ion-implanted silicon wafers had improved electrical device performance factors, such as pn-junction leakage current, in actual device process lines. This gettering technique has no dependence on the silicon wafer substrates such as whether it is composed of bulk por p+ boron doped silicon crystals. We believe that the hydrocarbon-molecular-ion-implanted silicon wafers will be advantages for advanced CMOS image sensor fabrication.

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.

We describe the effect of microwave heating on C 3 H 5 carbon cluster ion implanted epitaxial wafers using a high dose amount of carbon cluster ion implantation condition. A high dose amount condition of C 3 H 5 carbon cluster ion implantation generates implantation-related defects, such as stacking faults, after epitaxial growth. Therefore, we investigated the control and reduction of stacking faults using the microwave heating technique. We revealed that this technique can control and reduce stacking faults by selectively heating of the carbon cluster ion implantation projection range.

CMOS image sensor has been widely used for ubiquitous devices. However, CMOS image sensor devices performance is dramatically influenced by process induced defects such as metallic impurities contamination at devices active region during CMOS devices process. Thus, it is extremely important to study metallic impurities influence on CMOS image sensor devices performance and to develop effectiveness metallic impurities gettering techniques. We introduce our new proximity gettering technique for advanced CMOS image sensor using carbon cluster ion implantation technique. Furthermore, we demonstrated that the carbon cluster ion implanted silicon wafer has high gettering capability of metal, oxygen and hydrogen impurity during CMOS image sensor devices fabrication process.

Complementary metal oxide semiconductor (CMOS) image sensors have become widely used ubiquitous devices such as smart phone and personal computer type tablets. Consumer markets strongly demands more high sensitivity imaging and more high speed image data processing for achieving advanced CMOS image sensor fabrication. However, there are some serious improvement technical issues in CMOS image sensor fabrication process. Extremely important technical issue is metallic impurity contaminated device active region during device fabrication process such as high temperature rapid thermal annealing, dry etching and plasma heat treatment. Metallic impurities formed deep energy level defects in the silicon band-gap. Thus, these deep energy level defects strongly affects electrical device characteristic such as pn-junction leakage current, recombination lifetime and gate oxide breakdown voltage. Another technical issue is oxygen impurity out-diffused to the device active region from a Czochralski (CZ) grown silicon substrate during device heat process. Oxygen impurity formed oxygen related deep energy level defects in the device active region of photo-diode space charge region and transfer transistor gate channel region. These oxygen related defects strongly influenced on electrical device performance such as image lag. Therefore, in recent years, CMOS image sensor manufacturers have strongly demanded silicon wafers with the highest metal and oxygen impurities gettering capability during CMOS device processes. In response, we have developed a novel gettering wafer production concept using a hydrocarbon molecular ion implantation technique for advanced CMOS image sensors [1][2][3]. This technique can implant a silicon wafer surface simultaneously with carbon and hydrogen elements that form the projection range using a hydrocarbon compound molecular gas source. In our previous study, it was found that a hydrocarbon molecular ion implanted silicon wafer had three unique characteristics for high performance of advanced CMOS image sensors. First, a hydrocarbon molecular ion projection range has high gettering capability of metallic impurities [1][2][4]. Second, this projection range also has a diffusion barrier effect for oxygen impurities out-diffusing to the device active region from a CZ grown silicon wafer substrate [5]. Third, it is expected that diffusing hydrogen to the device active region from the hydrogen of hydrocarbon molecular ions gettered in the projection range during the device fabrication process will have a passivation effect on unreconstructed surface dangling bonds and Si/SiO2 interface state densities such as local oxidation of silicon or shallow trench isolation [6][7]. Moreover, we achieved more improvement for gettering capability of hydrocarbon molecular ion implanted silicon wafer which formed epitaxial layer without epitaxial growth process using room temperature direct bonding technique. In this presentation, we demonstrate that a hydrocarbon molecular ion implanted silicon wafers using room temperature direct bonding technique has high gettering capability characteristics for transition metal and light element impurities such as oxygen, and hydrogen during the CMOS image sensor fabrication process. References [1] K.Kurita, et al , Jpn. J. Appl. Phys. 55,121301(2016)/DOI.org/10.7567/JJAP.55.121301. [2] K.Kurita, et al , Phys.Status.Solidi A, 1700216(2017)/DOI 10.1002/pssa.201700216. [3] R.Okuyama, et al: Jpn. J. Appl. Phys. 57,011301(2018)/DOI.org/10.7567/JJAP.57.011301. [4] A.Onaka, et al: Jpn. J. Appl. Phys. 57,021304(2018)/DOI.org/10.7567/JJAP.57.021304. [5] K.Kurita, et al , J. Surf. Sci. Soc. Jpn.,Vol.37,p104(2016)/DOI.org/10.1380/jsssj.37.104. [6] R.Okuyama, et al: Jpn. J. Appl. Phys. 56,025601(2017)/DOI.org/10.7567/JJAP.56.02560. [7] R.Okuyama, et al , Phys.Status.Solidi C, 1700036(2017)/DOI 10.1002/pssc.201700036.

We propose a fabrication process for silicon wafers by combining carbon-cluster ion implantation and room-temperature bonding for advanced CMOS image sensors. These carbon-cluster ions are made of carbon and hydrogen, which can passivate process-induced defects. We demonstrated that this combination process can be used to form an epitaxial layer on a carbon-cluster ion-implanted Czochralski (CZ)-grown silicon substrate with a high dose of 1 × 1016 atoms/cm2. This implantation condition transforms the top-surface region of the CZ-grown silicon substrate into a thin amorphous layer. Thus, an epitaxial layer cannot be grown on this implanted CZ-grown silicon substrate. However, this combination process can be used to form an epitaxial layer on the amorphous layer of this implanted CZ-grown silicon substrate surface. This bonding wafer has strong gettering capability in both the wafer-bonding region and the carbon-cluster ion-implanted projection range. Furthermore, this wafer inhibits oxygen out-diffusion to the epitaxial layer from the CZ-grown silicon substrate after device fabrication. Therefore, we believe that this bonding wafer is effective in decreasing the dark current and white-spot defect density for advanced CMOS image sensors.

The effect of oxygen (O) concentration on the Fe gettering capability in a carbon-cluster (C3H5) ion-implanted region was investigated by comparing a Czochralski (CZ)-grown silicon substrate and an epitaxial growth layer. A high Fe gettering efficiency in a carbon-cluster ion-implanted epitaxial growth layer, which has a low oxygen region, was observed by deep-level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS). It was demonstrated that the amount of gettered Fe in the epitaxial growth layer is approximately two times higher than that in the CZ-grown silicon substrate. Furthermore, by measuring the cathodeluminescence, the number of intrinsic point defects induced by carbon-cluster ion implantation was found to differ between the CZ-grown silicon substrate and the epitaxial growth layer. It is suggested that Fe gettering by carbon-cluster ion implantation comes through point defect clusters, and that O in the carbon-cluster ion-implanted region affects the formation of gettering sinks for Fe.

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.

A new technique is described for manufacturing advanced silicon wafers with the highest capability yet reported for gettering transition metallic, oxygen, and hydrogen impurities in CMOS image sensor fabrication processes. Carbon and hydrogen elements are localized in the projection range of the silicon wafer by implantation of ion clusters from a hydrocarbon molecular gas source. Furthermore, these wafers can getter oxygen impurities out-diffused to device active regions from a Czochralski grown silicon wafer 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 the dark current, white spot defects, pn-junction leakage 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 improve electrical devices performance characteristics in advanced CMOS image sensors.

The trapping and diffusion behaviour of hydrogen in projection range of carbon-cluster was investigated by using a technology computer aided design (TCAD) simulation for high performance complementary metal–oxide–semiconductor (CMOS) image sensors. The hydrogen behaviour seemingly contributes to passivating the interface state density of the isolation region and process-induced defects during the CMOS image sensor fabrication process. This hydrogen behaviour was simulated by a TCAD simulation assuming a reaction model in which the cluster of carbon and silicon self-interstitial (carbon-interstitial cluster) binds to hydrogen. We found that the hydrogen profiles of TCAD agreed with the secondary ion mass spectrometry (SIMS) results after epitaxial growth and high-temperature heat-treatment, thus suggesting that the hydrogen in the projection range of the carbon cluster forms a binding state with the carbon-interstitial cluster. In addition, hydrogen gradually diffused out from the projection range of the carbon-cluster after high-temperature heat-treatment. Therefore, the hydrogen behaviour in projection range of the carbon-cluster is considered to contribute to the CMOS image sensor fabrication process to achieve high electrical performance.

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.

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.