山川 進二

In 2019, EUV lithography technology with a wavelength of 13.5 nm was used for the mass production of semiconductor logic devices with 7 nm node. As with small feature size of electronic circuits in semiconductor device will be required in the future, beyond EUV (BEUV) lithography with exposure wavelength around 6.7 nm is a candidate for the next generation lithography. In BEUV, the developments of high-reflective multilayers, high-sensitive resists, and high-power light sources are critical issues. Thus, we have developed BEUV evaluation tools in NewSUBARU synchrotron light facility. Accurate BEUV reflectometry is significant for the development of high-reflective BEUV multilayer. For the accurate reflectometry, higher-diffraction-order generated from a monochromator should be suppressed. At the BL10 beamline at NewSUBARU, the components of second and third-diffraction-order light are 7% mixed into the BEUV measurement light. Mo transmission filter with a 200-nm-thick was previously used to suppress the higher-order light to 1/10, which was insufficient for target accuracy of 0.1%. We have developed a high-order-light cutting unit consisting of two mirrors with TiO2 coating, which suppressed the high-order light to 1/100.

At EUV lithography, an EUV mirror can be easily contaminated with carbon. This carbon contamination causes the reflectance drop of the Mo/Si multilayer mirror. For the carbon-contamination cleaning, hydrogen gas is introduced at a pressure of a few Pascal in the EUV exposure tool. However, during this process, the hydrogen damage would be caused on a Mo/Si multilayer, which would decrease EUV reflectance of the multilayer. The cleaning rate and damage threshold of hydrogen pressure and EUV dose were not well known. Therefore, an EUV irradiation tool in hydrogen atmosphere is developed and installed at the BL09 beamline of the NewSUBARU synchrotron light facility to evaluate the irradiation durability and cleaning effect of the Mo/Si multilayer under these conditions. The EUV-irradiation intensity was up to 6 W/cm2, and hydrogen pressure was up to 70 Pa. The contamination was occurred at the low-hydrogen-pressure conditions from 0 to 5 Pa. The contamination was not occurred at the high-hydrogen-pressure condition of 20 and 68 Pa. In addition, the sample with many particles on the surface was damaged by the EUV-induced plasma.

Extreme ultraviolet lithography was started to use for the production of 7-nm node-logic-semiconductor devices in 2019. And it was adapted to use for high volume manufacturing (HVM) of 5-nm logic devices in 2020. EUVL is required to be extended to use in 1.5-nm-node-device fabrications. However, it still has many technical issues. Especially, for EUV resists, simultaneous achievement of high sensitivity and low line edge width are required. To solve the EUV resist issue, the fundamental work using synchrotron in soft X-ray region is necessary. The fundamental evaluation study of EUV resist at NewSUBARU synchrotron light facility is described in this paper.

In extreme ultraviolet (EUV) lithography development, the reduction of line width roughness (LWR) is a one of the significant issues. It has been reported that the LWR of photoacid generator (PAG) bounded resist is lower than that of PAG blended resist. It is considered that the chemical composition distribution of PAG bounded resist is more uniform than PAG blended resist. However, it has not been evaluated systematically and experimentally. In this study, we introduced the contact angle measurement method for the evaluation of the chemical composition distribution between PAG blended resist and PAG bounded resist. It is clarified that the resist thin film has a different chemical composition distribution from the center to the outside of wafer regardless of the type of resists. In particular, the chemical composition distribution of the bounded resist showed the opposite behavior to that the blended one.

Since 2019, EUV lithography has started to be used for the mass production of 7-nm-node-logic devices. However, many significant issues on EUV lithography still remain in the fabrication of future devices. The technical issues are the development technologies of resist, mask, and EUV light source. Therefore, many significant fundamental researches have been carried out at our facility. Here the EUV mask technologies is highlighted. It is described the fundamental research activities on EUV lithography at NewSUBARU synchrotron light facility, which is related with EUV mask technologies.

© 2019SPST. We examined the synthesis and resist properties of tellurium-containing molecular resist materials. By the condensation reaction of anisol, phenol, and 2-phenylphenol with tellurium tetrachloride (TeCl4), dichloro di(4-hydroxyphenyl) telluride (CHPT), dichloro di(4-hydroxy-3-phenylbenz) telluride (CHBT), di(4-hydroxyphenyl) telluride (HPT), and di(4-hydoxy-3-phenylbenz) telluride (HBT) were synthesized. These were reacted with 2-methyl-2-adamantyl bromo acetate, yielding corresponding compounds CHPT-AD, CHBT-AD, HPT-AD, and HBT-AD, respectively. By the examination of resist properties (thickness loss property, resist sensitivity, and etching durability), CHBT-AD could be good candidate for higher resolution EUV resist material.