Yasutaka Kikuchi

Characterization of binary and attenuated phase shift mask blanks for 32nm mask fabrication

During the development of optical lithography extensions for 32nm, both binary and attenuated phase shift Reticle Enhancement Technologies (RETs) were evaluated. The mask blank has a very strong influence on the minimum feature size and critical dimension (CD) performance that can be achieved on the finished reticle and can have a significant impact on the ultimate wafer lithographic performance. Development of a suitable high resolution binary mask making process was particularly challenging. Standard chrome on glass (COG) binary blanks with 70 nm thick chrome films were unable to support the required minimum feature size, linearity, and through pitch requirements. Two alternative mask blank configurations were evaluated for use in building high resolution binary masks: a binary (BIN) mask blank based on the standard attenuated PSM blank and an Opaque MoSi on Glass (OMOG) mask blank consisting of a newly- developed opaque MoSi [1]. Data comparing the total process bias, minimum feature size, CD uniformity, linearity, through pitch, etch loading effects, flatness, film stress, cleaning durability and radiation durability performance of the different binary and attenuated PSM mask blanks are reported. The results show that the new OMOG binary blank offers significant mask performance benefits relative to the other binary and attenuated PSM mask blanks. The new OMOG blank was the opaque mask blank candidate most capable of meeting 32nm binary mask fabrication requirements..

Impact of transmitted and reflected light inspection on mask inspectability, defect sensitivity, and mask design rule restrictions

The application of aggressive optical proximity correction (OPC) has permitted the extension of advanced lithographic technologies. OPC is also the source of challenges for the mask-maker. Sub-resolution features, small shapes between features and highly-fragmented edges in the design data are difficult to reproduce on masks and even more difficult to inspect. Since the inspection step examines every image on the mask, it is required to guarantee the total plate quality. The patterns themselves must be differentiated from defects, and the ability to recognize small deviations must be maintained. In other words, high inspectability at high defect sensitivities must be achieved simultaneously. This must be done without restricting necessary OPC designs features. Historically, transmitted light has been deployed for mask pattern inspection. Recently, the inspection challenge has been both enhanced and complicated by the introduction of reflected light pattern inspection. Reflected light reverses the image contrast of features, creating a new set of design limits. This paper introduces these new reflected inspection limits. Multiple platform capabilities will be incorporated into the study of reflected and transmitted inspection capability. The benefits and challenges of integrating a combination of transmitted and reflected light pattern inspection into manufacturing will be explored. Aerial Image Measurement System (AIMS) analysis will be used to help understand how to leverage the enhanced inspection capability while avoiding unnecessary restrictions on OPC.

Development of refined cleaning technique focusing on an ecological viewpoint

In this paper, we focused on the refined cleaning process with minium use of chemicals. We developed a cleaning tools and process using high-concentration ozonic water generated by the high-efficiency ozonizing apparatus (OW00345, Mitsubishi Electric Corp. Industrial Systems), as chemicals substitution. To optimize a cleaning process, we have evaluated the removal and decomposition efficiency of organic compounds on the mask surface, the optical degradation of Cr and Siliside materials and so on.

Defect printability and inspection capability for tri-tone PSM

The KrF12% tri-tone PSM (phase shift mask) was designed with the programmed defects on the chrome (Cr) and phase shift (PS) layers. From the lithography simulation, the PS defects, generated on the PS layer, were estimated to fluctuate the CD of the contact holes on the wafer more than the defects in the same size on the conventional EAPSM (half-tone PSM). The printability of the PS defects and Cr defects on the contact holes were investigated by the print-test on the wafer. The Cr residues on the PS layer slightly changed the CD of the contact holes on the wafer. The PS defects showed the great influence to the CD variation of the contact holes. The light calibration of the defect inspection was optimized to detect the PS and Cr defects. For the detection of the PS defects in the die-to-die inspection mode, the UV inspection system SLFX7 showed the high performance with the PS/SiO2 calibration, in which the boundary of the PS layer and SiO2 substrate was used as the light calibration point. The SLFX7 also available to detect the Cr defects in the die-to-die mode. For the die-to-database mode to detect the Cr defect, the KLA351, the visible light inspection system, was available by the Cr/PS calibration. The sensitivity of the SLFX7 and KLA351 was adequate for the Cr defects, however, that was not enough to the specification of the PS defects estimated from the print-test. The sensitivity of the SLFX7 showed a slight difference between the tri-tone and binary layout in the specific defect types.

New repair of clear defects on half-tone PSM using Ga implantation

The new repair of the clear defects on the half-tone PSM (EAPSM) was proposed. The Ga (gallium) ions were implanted by the FIB on the area adjacent to the carbon films formed on the clear defects. The Ga ion implanted area on the SiO2 substrate showed the semi-transparency at the KrF and ArF wavelengths. The lithography simulations of the layouts designed for the defect-repaired area endorsed the concept of the new repair. The Ga ion implantation was optimized to the new repair by using the AIMS and AFM measurements for the transmittance and etched depth of the SiO2 surface. The authors applied this method to the clear defects programmed on the KrF and ArF EAPSMs. The AIMS analysis showed that the deviation of the CD (critical dimension) of the defect-repaired regions on the wafer was within +/-5% to the non-defective reference at every defocused point. The new repair moderated the specification of the edge placement accuracy of the FIB processing compared to the conventional carbon film deposition.

Improvement of critical dimension stability of chemically amplified resist by overcoat II

The critical dimensions (CD) change by the process delay is the most critical issue to apply the chemically amplified resists (CAR) for photomask fabrication. In the photomask fabrication processes, the resist should have both post coating delay (PCD) and post exposure delay (PED) stability, while keeping higher sensitivity. To achieve this requirement, overcoat process has been examined for the purpose of CD stabilization in CAR process for photomask manufacture. The material, which consists of hydrophobic polymer and PAG, was used for the overcoat in this study. Consequently, it has become clear that pattern formations have been possible without unnecessary thickness loss. Moreover, it has been proved that the overcoat shows the effect of controlling CD change and improvement of CD uniformity. From these results, it is thought that the overcoat process is promising for the size stabilization in photomask manufacture for devices less than 90 nm.