Ryo Hirose

Dependence of Absorption Coefficient and Acid Generation Efficiency on Acid Generator Concentration in Chemically Amplified Resist for Extreme Ultraviolet Lithography

The absorption coefficient and acid generation efficiency are elemental key factors for the design of chemically amplified resist because the acid distribution in resist films is primarily determined by these two factors. In this study, the number of acid molecules generated in a model system of chemically amplified extreme ultraviolet (EUV) resists [poly(4-hydroxystyrene) film dispersed with triphenylsulfonium-triflate (TPS-tf)] was evaluated using an acid sensitive dye. The absorption coefficient and acid generation efficiency were evaluated by changing film thickness. The acid generation efficiency was 1.7 (5 wt % TPS-tf), 2.5 (10 wt % TPS-tf), and 3.1 per photon (20 wt % TPS-tf), respectively. The absorption coefficient of the model film was 3.8±0.2 µm-1. The effect of acid generator concentration on the absorption coefficient of resist films was negligible within the concentration range of 0–20 wt %.

Dependence of Acid Generation Efficiency on Molecular Structures of Acid Generators upon Exposure to Extreme Ultraviolet Radiation

The trade-off between resolution, sensitivity, and line edge roughness (LER) is the most serious problem for the development of sub-30 nm resists based on chemical amplification. Because of this trade-off, the increase in acid generation efficiency is essentially required for high-resolution patterning with high sensitivity and low LER. In this study, we investigated the dependences of acid generation efficiency on the molecular structure and concentration of acid generators upon exposure to extreme ultraviolet (EUV) radiation. The acid generation efficiency (the number of acid molecules generated by a single EUV photon) was obtained within the acid generator concentration range of 0–30 wt % for five types of ionic and nonionic acid generators.

Difference between Acid Generation Mechanisms in Poly(hydroxystyrene)- and Polyacrylate-Based Chemically Amplified Resists upon Exposure to Extreme Ultraviolet Radiation

Chemically amplified resists have been used in the mass production of semiconductors. Poly(hydroxystyrene)-based resists have been extensively developed for KrF lithography. After KrF lithography, polyacrylate-based resists have been developed for ArF lithography and used in sub-60 nm fabrication. Both types of resist are candidate platforms of extreme ultraviolet (EUV) resists. In this study, the acid generation mechanisms induced by EUV radiation in both types of resist were investigated from the viewpoint of the deprotonation of polymer radical cations using poly(4-hydroxystyrene), poly(methyl methacrylate), and poly(methyl methacrylate-co-4-hydroxystyrene) as model polymers. The dependence of the quantum efficiencies on the molecular structures and acid generator concentration indicated that the deprotonation mechanisms induced by EUV radiation is the same as those induced using an electron beam.

Dependence of acid generation efficiency on acid molecular structure and concentration of acid generator in chemically amplified EUV resist

The trade-off between resolution, sensitivity, and line edge roughness (LER) is the most serious problem for the development of sub-30 nm resists based on chemical amplification. Because of this trade-off, the increase in acid generation efficiency is essentially required for high resolution patterning with high sensitivity and low LER. Under such circumstances, the absorption coefficient and the acid generation efficiency are elemental key factors for the design of chemically amplified extreme ultraviolet (EUV) resist because the acid distribution in resist films is primarily determined by these two factors. In this study, we investigated the dependence of acid generation efficiency on the molecular structure and concentration of acid generators in chemically amplified EUV resists. The acid generation efficiency (the number of acid molecules generated by a single EUV photon) was obtained within the acid generator concentration range of 2-30 wt % for several kinds of ionic and nonionic acid generators.

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.

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.

Dependence of Absorption Coefficient and Acid Generation Efficiency on Acid Generator Concentration in Chemically Amplified EUV Resist

In this study, the number of acid molecules generated in a model system of chemically amplified EUV resist was evaluated using an acid sensitive dye. Also, the absorption coefficient is a critical factor for the resist design. A convenient method to estimate the absorption coefficient of resists was proposed.