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The demand for ever smaller features in integrated circuit manufacturing continues to put more stringent requirements on photomask fabrication, particularly with respect to critical dimension (CD) control. A high resolution process for making attenuated-phase-shift masks (attPSM) for the 45nm node with a negative-tone chemically amplified resist (nCAR), utilizing a new precision bake system, was evaluated. This process showed a significant performance improvement in critical dimension uniformity (CDU), respective to an established process based on an APB5500 system. A CD-uniformity improvement from 2.1nm CD 3σ to 1.3nm CD 3σ (40%) was achieved on a demanding layout. The new precision bake system utilizes an improved multi-zone hotplate design and control algorithm, which enables highly precise temperature controllability, facilitating a superior temperature ramp-up performance, as well as significantly improved temperature setpoint stability, as has been measured with a 25-point sensor mask for a 95°C bake process. The new precision bake system shall now be introduced to the market within the HamaTech MaskTrack series.

Several haze studies were conducted in a test environment where UV lamps and test chambers were used to simulate a wafer fab environment. This study was designed to investigate reticles experiencing different cleaning processes in a real wafer production environment. A split test was carried out to benchmark two different fabs: an 8" R & D fab and an 8" memory production fab. Reticles cleaned with UV treatment and hot DI water were exposed on ArF scanners for up to 80 hours over a period of two months. Starlight inspection before and after laser exposure confirmed no significant defect count increase after exposure. Ion chromatography (IC) results from masks cleaned on a new Steag MaskTrack cleaner suggest that hydrogenated water (H2-H2O) and ozonated water (O3-H2O) processes can further reduce the sulfate and ammonium ion residual count by 40%. UV + hot water cleaning also shows advantages in phase and transmission preservation where less than a 0.2 degree phase angle loss per clean can be achieved.

Progress towards 65 nm next-generation lithography requires unprecedented global CD uniformity, with the actual ITRS 2002 roadmap proposing 4.2 nm 3/spl sigma/ (dense lines) for 65 nm binary masks. Since resolution requirements are satisfied only by using chemically amplified resists (CARs), exposure and post-exposure bake (PEB) are key processes to successful mask making, both introducing global CD errors. Develop and etch processes potentially contribute further global CD errors. The global CD uniformity can be improved significantly by adaptive PEB, especially for CARs showing moderate to strong PEB sensitivity, like NEB22. With the 25-zone hotplate of the APB5500 bake system, facilitated through a novel calibration mask with 25 equidistant temperature sensors within the resist plane, an appropriate temperature profile can be applied during PEB. This temperature profile is automatically calculated by an adaptive optimization algorithm, based on 2-dimensional spline fitting of a CD measurement. A CD-uniformity improvement (dense lines) from 4.8 nm 3/spl sigma/ to 3.9 nm 3/spl sigma/ (/spl cong/20%) on a state-of-the-art production mask is achieved for the chrome layer (ASI, after strip inspection).

Negative-tone chemically amplified resists (nCARs), like NEB22 are promising candidates for next-generation lithography, e.g. 90 nm and 65 nm technology node and next-generation lithography. For these resists, e-beam exposure and post-exposure bake (PEB) are most critical processes, since these resists show a strong sensitivity to post-exposure delay (PED) in vacuum during e-beam writing of about 0.5 nm/h, and in air while waiting for PEB. Further, such resists show a strong PEB temperature sensitivity of up to 8 nm/K. The multi-zone hotplate approach of the APB AFB 5500 bake system with its use prior temperature uniformity results in excellent global CD-uniformity already. However, all kinds of systematic large area effects of processes, e.g. blank coat/bake, exposure, PED, the PEB itself, etch loading, etc. may transfer in additional systematic CD-errors. Such systematic, repeatable errors can be reduced during PEB by superimposing an appropriate non-uniform temperature profile onto the regular, optimized uniform bake temperature profile, thereby compensating for such CD-non-uniformities. The required temperature profile can automatically be calculated from a suitable gobal CD measurement, determined in a typical process flow. The compensation of CD-errors resulting from vacuum PED and hotplate temperature characteristics is demonstrated here, by using automated temperature profile calculation. The global CD uniformity was improved significantly, the achieved results show a typical reduction of about 20-30%, from a total global range of about 9nm to about 6-7nm on leading-edge production photomasks.

Negative-tone chemically amplified resists MES-EN1G (JSR), FEN-270 (Fujifilm ARCH), EN-024M (TOK) and NEB-22 (Sumitomo) were evaluated for binary mask making. The investigations were performed on an advanced tool set comprising a 50kV e-beam writer Leica SB350, a Steag Hamatech hot/cool plate module APB5000, a Steag Hamatech developer ASP5000, an UNAXIS MASK ETCHER III and a SEM LEO1560 with integrated CD measurement option. We investigated and compared the evaluated resists in terms of resolution, e-beam sensitivity, resist profile, post exposure bake sensitivity, CD-uniformity, line edge roughness, pattern fidelity and etch resistance. Furthermore, the influence of post coating delay and post exposure delay in vacuum and air was determined.