The material property of CLEARCERAM®-Z series, which is the low thermal expansion glass-ceramics products by
Ohara Inc., with an integrated product size of Dia.1.4meter was investigated along with confirmation of the surface
finish performances. The material property investigation for the Dia.1.4meter CLEARCERAM®-Z HS indicated the
mean CTE of 0.01×10-7/degree C, the CTE uniformity (CTEmax.-CTEmin.) of 0.10×10-7/degree C based on developed
precision CTE measurement system with 2ppb/degree C repeatability and the maximum stress birefringence of
4.4nm/cm within the disk, which are meeting the mirror substrate material specification for near future large telescope
project (Thirty Meter Telescope project). From the experiments to determine surface finish performance, no practical
change was observed for the surface profile in millimeter scan filed per Ion Beam Figuring processing. Also the
surface robustness against acid solutions, which are used at mirror cleaning, was proved from dipping tests using
Hydrochloric acid and Nitric acid. With the material property based on the precision metrology and the surface finish
performances, the suitability of CLEARCERAM®-Z for telescope mirror substrate application was presented.
Material properties and performances for near future applications were studied for low thermal expansion glass-ceramics; CLEARCERAM series produced by OHARA Inc. In the material study, the improved CTE characteristics of CLEARCERAM-Z HS over conventional CLEARCERAM-Z were shown with interferometric CTE metrology system with 2ppb/degree C repeatability. Also the material uniformity was evaluated by means of refractive index homogeneity. In the application study, the capabilities of CLEARCERAM-Z HS for near future precision applications, Extreme Ultra Violet Lithography (EUVL) system component and extremely large telescope mirror applications were discussed by reviewing actual data prepared in accordance with the existing specifications for each application. For EUVL system component application, inter lot CTE uniformity and surface finish data meeting the SEMI P37 specification were presented and the performance was evaluated. For extremely large telescope mirror application, intra disk uniformity of CTE and stress birefringence for Dia.780mm CLEARCERAM-Z HS meeting mirror blanks specification of existing extremely large telescope project were demonstrated and the potential performance of CLEARCERAM-Z HS for the application was shown with the on-going integration of the size availability at OHARA Inc.
The material capability of CLEARCERAM-Z series for EUVL components (Mask, Mirror and Structural application) was investigated. Data for an existing specification and key characteristics for each application were collected and the material performances were evaluated. For mask substrate application, the inter lot and intra block CTE uniformity to meet Class A in SEMI P37 standard with a statistical confidence, and the surface roughness & flatness to meet the SEMI specifications were demonstrated for CLEARCERAM-Z HS. For mirror application, the size availability up to Dia.780mm and the material uniformity equivalent to optical glass were confirmed for CLEARCERAM-Z HS products. Also ion beam figuring results showed a linear removal controllability by processing time and no practical change in the base line profile in mid spatial frequency roughness region of the post figured surface. For structure application, demonstrative processing tests by utilizing possible techniques to produce the structural components for EUVL were done. In the R&D activities for new materials, advantageous improvements on CTE stability over temperature and smoother surface finish than conventional CLEARCERAM-Z series were presented with a material uniformity equivalent to the conventional products.
CLEARCERAM®-Z HS is a low thermal expansion glass-ceramics and has been used in semiconductor industry field as well as for various precision applications. Extreme Ultra Violet Lithography (EUVL) is one of the applications, in which future utilization of CLEARCERAM®-Z HS can be expected. Previous reports revealed that CLEARCERAM®-Z HS met the material requirements in the SEMI spec. This paper refers to the latest investigation results on the CTE & surface finish performance of CLEARCERAM®-Z HS relative to the SEMI spec. Also the data obtained from the development of new CLEARCERAM®-Z, which is designed for more fit with EUVL applications, will be presented and its advantageous potential for EUVL Photomask substrate application is to be discussed.
The material property and processability of the low thermal expansion glass-ceramics product by Ohara Inc. called CLEARCERAM-Z were studied for telescope mirror substrate application. For material property, numbers of the key properties for the application, such as Coefficient of Thermal Expansion (CTE) characteristic in wide temperature range, Stress Birefringence and Mechanical strengths were intensively investigated focusing on the blank uniformity. The mean CTE of +0.15x10-7/degree C in wide temperature range (-50 to +150degree C) with the standard deviation (Std.) of 0.03x10-7/degree C and Young’s Modulus & Poisson Ratio data with the coefficient of variation less than 1% were obtained for the blanks with the size up to Dia.670mm. The maximum Stress Birefringence was 3nm/cm within a 400mm square blank. For processability, the surface finish data of AFM Rms 0.15nm, the Power Spectral Density profile in the same level of low expansion amorphous glass and three dimensional structured samples were demonstrated. The comparison of the obtained data with known blanks specification for past and future telescope projects revealed that CLEARCERAM-Z has capability to meet material property requirements for telescope mirror substrate application in the size up to Dia.670mm. Also for the precision metrology to support the material technology, CTE measurement system developed at OHARA was described.
The Coefficient of Thermal Expansion (CTE) uniformity and the surface finish performance of the low expansion glass-ceramic material produced by Ohara called CLEARCERAM-Z HS were investigated relative to the SEMI P37 specifications for Extreme Ultraviolet Lithography (EUVL) Photomask Substrates. The study on the CTE uniformity utilizing precision CTE measurement system based on Fizeau Interferometry with a single ppb/degree C level repeatability revealed that the standard deviation of the latest product CTE (+19 to +25degree C) data was 0±10ppb/degree C, which meets the Class B CTE specification in the SEMI P37 with statistical confidence and was improved from the previous report (0±15ppb/degree C, Class C). For the surface finish performance, the flatness data less than 100 nm (meeting Class A in the SEMI P37) and the roughness of 0.15nm Rms (Conforming to the SEMI P37) were demonstrated. Additionally the roughness uniformity was investigated and shown to be 1% in the coefficient of variation. By reviewing the data and performances from actual measurements, the suitability of CLEARCERAM-Z HS for EUVL Photomask Substrate material is discussed and updated. Also, preliminary R&D data of a new CLEARCERAM-Z material now under developing to response to the further requirements from EUVL community are introduced.
The Coefficient of Thermal Expansion (CTE) properties and surface finish values of a low expansion glass-ceramic material produced by Ohara called CLEARCERAM were measured and compared to the SEMI P37 EUVL specifications, which include dL/L profiles, CTE variation, surface roughness, and flatness. The results showed that CLEARCERAM-Z HS, a derivation from the conventional CLEARCERAM material, had the CTE (+19 to +25C) variation of 0±15 ppb/degree C in standard deviation with the intra block uniformity of Delta CTE = 3 ppb/degree C in the 40x40mm, which corresponds to the CTE specification of Class C in the SEMI standard P37 for Extreme Ultraviolet Lithography (EUVL) Photomask Substrates. Also polishing experiments targeting the surface specifications in SEMI P37 were performed. Surface flatness less than 100 nm (meeting Class A in SEMI P37) and surface roughness of 0.15 nm Rms (Conforming to the SEMI P37) were obtained and reviewed. The results of the CTE property and polished surface evaluations suggest that CLEARCERAM-Z HS is a suitable candidate material to meet SEMI standard P37 for EUVL Photomask Substrates, while further improvements of CTE measurement accuracy and polishing processes are necessary to fully meet the current specifications.