Kazunori Iwamoto

Mask blanks warpage at 130-nm node

Semiconductor device technology is now making transition from 150 to 130 nm node. Lithography tools for 130 node that employ KrF and ArF as light sources have finished being developed. Also, mask drawing and inspection tools are ready. However, for actual processes, there is an issue to be solved from realistic DOF or overlay accuracy acquisition point of view.

New scanners for the 100 nm era

Step and scan exposure tools for 300 mm wafers are being introduced to more fabs aimed at volume production of semiconductor devices with sub 150 nm features. We have developed a KrF scanner for 130 nm applications, and an ArF scanner for the 110 nm generation. High NA, ultra-low aberration projection lenses developed for these tools provide imaging performance that meets requirements of the respective generations, with improved critical dimension (CD) uniformity and low distortion. These achievements have resulted from lens manufacturing that employs higher order Zernike coefficient lens tuning. The scanners incorporate a common platform designed to meet increasing accuracy requirements in 130 nm and 100 nm processes. Compared to previous models, the new platform reduces the impact of vibrations on the floor by receiving the stage drive reaction force with a structure of high damping capability. The wafer stage mounted on the platform simultaneously improves throughput and synchronization accuracy, through increased rigidity of its mechanism. A higher magnification alignment scope with shorter baseline is introduced to achieve high overlay accuracy. We also incorporate a new type focus sensor with self-thermal compensation functionality to improve focus-leveling performance. This paper explores the effects of moving standard deviation (MSD) upon CD uniformity and contrast, and proposes a measure to evaluate the effects on a quantitative basis. It also attempts to clarify synchronization accuracy budget for each technology generation, and introduces a new platform that can satisfy the accuracy required for the 100 nm generation and beyond. The proposed platform can remarkably enhance synchronization accuracy and throughput with wafer and reticle stages of high control performance and high-efficiency high-output linear motors. For this platform, we have developed a new mechanism that cancels the stage drive reaction force within the system and prevents it from being transferred to the floor. This paper shows that applying this system not only improves stage performance but also allows permissible vibration level of the floor to be considerably relaxed.

Imaging performance of scanning exposure systems

Relative position between the projected image on the wafer and the wafer itself changes during exposure. Factors of change are, for example, stage control error, difference of scanning direction between wafer stage and reticle stage (skew) and distortion of projection optics. We can define a kind of probability density function (PDF) concerning these changes of relative position. Fourier transform of this PDF is the transfer function of image transformation by relative motion. In this paper, we call this transfer function MoTF. The modulation of MoTF becomes a barometer of image contrast and the phase of MoTF gives position deviation (distortion). By analytical study of MoTF, standard deviation and expected value of said PDF are found to be the key parameters. Derived approximate equation in this paper agree with a computer simulation result of image contrast deterioration by vibration. With these studies, we can establish adequate specifications of scanning stage control demanded by imaging performance. Canon has developed a new stage structure for scanning exposures. By this structure the wafer stage is separated from main body on which projection optics and measurement systems are mounted so that reaction forces of stage acceleration can not be transferred directly to the maim body. With this structure we achieved excellent stage performance which has achieved imaging performance below 0.18 micrometer with high speed scanning.