干涉条纹相位锁定系统

干涉曝光系统中干涉条纹的相位漂移会导致曝光对比度降低,为了有效抑制相位漂移,利用声光调制器对干涉光频率进行实时调制。分析了条纹漂移的特点,指出了主要干扰源是0~5 Hz的空气扰动。应用数值分析法得到了条纹漂移量与曝光对比度的关系曲线,并以此为依据提出了条纹锁定精度的目标值。针对所要达到的锁定精度,给出了系统硬件的选型方法,搭建了基于RTX的干涉条纹相位锁定系统。利用闭环辨识的方法得到了系统的参数模型,完成了反馈控制器的设计,最终实现了实时锁定条纹相位的功能。实验结果表明,在400Hz的控制频率下,干涉锁定系统能够有效抑制0~5Hz的低频扰动,干涉条纹相位漂移的3σ值可以控制在±0.04个条纹周期内,满足干涉光刻的曝光对比度要求。

Interference fringe phase locking system

The phase drift leads to low exposure contrast in interference lithography system. In order to effectively suppress the phase drift of interference fringe, an Acousto-Optic Modulator (AOM) was employed to modulate the frequency of interference beam in real time. The characteristic of phase drift was analyzed, indicating that the main disturbance came from air turbulence with frequency within 0~5 Hz. The relationship between phase drift and exposure contrast was deduced by numerical analysis, and the target phase accuracy of fringe locking system was submitted. In terms of the target accuracy, the experiment devices were picked and the experiment system based on RTX was prepared. Finally the parameter model of system was established by closed-loop identification and a feedback controller was designed, thus realizing the fringe locking function. The experiment results indicated that the low-frequency disturbance ranging from 0 to 5 Hz is suppressed efficiently by the proposed fringe locking system under the control frequency of 400 Hz. The 3σ value of phase drift is within ±0.04 period, which satisfies the exposure contrast requirements of interference lithography.