| 摘要 |
An alignment simulation method simulates the signal waveform for an alignment mark using various alignment methods as well as the signal strength for an alignment mark, which is useful in optimizing the thickness of one or more layers as well as the geometry of the mark. The simulation of signal strength is also useful in optimizing the thickness of a layer for artifact wafers. The alignment simulation method includes accurately modeling the alignment mark, including one or more layers of various thicknesses and materials. The accurate modeling of the alignment mark includes such things as smoothing regions of the alignment mark and generating lateral shifts of the layers. The model of the alignment mark is a series of small pixels, each including the thickness of the layers and the layers indices of refraction. Using scalar diffraction, a complex reflectivity is generated for each pixel and a fast fourier transform is performed on the series of pixels. The results of the fast fourier transform are used to simulate the diffraction intensities for the alignment mark alignment systems, such as LIA or LSA as well as the signal waveforms. The LSA signal waveform, however, requires additional modeling of the alignment mark. An FIA image is generated by removing appropriate orders from the fast fourier transform result and performing an inverse fast fourier transform and repeating the process at different light wavelengths and illumination angles. The signal strength is the maximum value of the image minus the minimum. |
