Contactless Evaluation Of The Stress In X-Ray Mask Wafers (SiN/Si) Using A Laser/Microwave Method.

Highly accurate X-ray masks are strongly required to establish SR lithography technology. X-ray masks must be produced as accurately as the LSI devices, because a one-toone projection aligner system is used. To minimize the in-plane mask distortion, it is desirable to estimate the value of the stress and the non-uniformity in the membrane fabrication (SiN) process. The values of the stress were estimated from the measurement of the warpage and the calculation. It is very difficult to obtain the stress distribution in the SiN/Si wafer. Thus, we measured the minority carrier lifetime distribution using the non-contact laser/microwave method. The carrier injection was done by a 774nm or 904nm semiconductor laser diode, and their beam was focused to about 500 μmφ. The surface lifetime, τ s, of the SiN/Si wafer with the stress over ˜ 108dyn/cm2 decreased to 60–70% of that of the bare Si wafer. Thus, the contactless laser/microwave system can be adaptable for the characterization in the X-ray mask process.