Derek Coon

Experimental study on nonlinear multiple-exposure method

Non-linear multiple exposure (NOLMEX) method for forming a fine line and space pattern is described. The combination of the resist with non-linear photosensitivity and multiple exposures allows us to exceed the optical cut-off frequency, which has never been realized in the field of photolithography. In this paper, a new approach for NOLMEX method utilizing an ordinary resist instead of the non- linear resist is introduced. In the experimental results, 0.19 micrometers L/S pattern was resolved with a commercial i-line stepper using ordinary illumination, which indicates the potential of NOLMEX method.

High-speed alignment simulator for Nikon steppers

It is an unfortunate fact that most wafer processing steps degrade the quality of the stepper alignment marks rather than improve it. One example is the severe planarization requirements used in many VLSI processes. Furthermore, process development time, especially with respect to wafer alignment, has been reduced due to fab streamlining and cost of ownership issues. With these problems in mind Nikon has developed a commercially available alignment simulator to reduce stepper usage in alignment process development. The simulator can simulate Nikons three different wafer alignment sensor and has five different simulation modes. The simulated alignment mark can have up to ten different process layers, the thicknesses of which can be varied simultaneously if need be. In addition, the geometry of each process layer can be made quite intricate so that complicated processes can be simulate.d The simulator uses scalar diffraction theory for high speed calculations, but which is still accurate when the mark width is larger than optimization which previously took weeks can now be done in days.