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本文叙述了用于投影光刻机中的一种掩模对准技术。在片子与掩模的对准中,通过一种锁相干涉法确定其偏移量。此方法采用的对准图形是一种交叉的栅格,用氦氖激光束照明。经过衍射和干涉后得到了一种谐波强度信号,信号的相位表示了掩模与片子的相对位移。用一个电流计扫描仪驱动一块可倾斜的玻璃片来实现相位调制和精密对准。包括套准和精密对准在内总的对准操作用一个PC单元控制,具有毫微米的套准精度和低于0.3秒的对准周期。此方法特别适用于缩小步进投影光刻机中的逐场对准。最后讨论了其理论研究与试验的结果。
This article describes a mask alignment technique used in projection lithography. In the alignment of the film with the mask, its offset is determined by a phase-locked interferometry method. The alignment pattern used in this method is a crossed grid that is illuminated with a helium-neon laser beam. A harmonic intensity signal is obtained after diffraction and interference. The phase of the signal indicates the relative displacement of the mask and the film. A galvanometer scanner drives a tiltable glass sheet for phase modulation and fine alignment. The total alignment including registration and precision alignment is controlled with one PC unit with registration accuracy of nanometers and alignment cycles of less than 0.3 seconds. This method is especially useful for field-by-field alignment in a reduced step-projection lithography machine. Finally, the theoretical research and experimental results are discussed.