Study On Real-time Focusing Technology For High-precision Lithography On Curved Surface

Laser scribing is a kind of integrated front technology, because of its ultra-high-precision in lithography, it has a great value in either commercial or military field. But the effective focal depth of the laser beam can not always focus on the surface owing to the factors caused by nonuniformity of the photoresist spreaded on the surface, installation error and mechanical relative motion etc. these factors can cause scoring errors. More defocusing amount can be caused due to the existing dip, which is formed by the curved surface, when the laser beam is used to scribe on the cured surface and the influencing factors are the same as mentioned. So there is a higher demand for the performance of the real-time focusing system.In this paper, the whole project of photolithography system on curved surface is given. It simply analysed the principle and advantages and disadvantages of the focus detecting methods which are often used. It emphatically analysed the principle of differential critical angle. The design scheme of the real-time focusing system which is based on differential critical angle is also given. The dual-quadrant photodiode (S5870) with high sensitivity and low dark current is used as photodetector, and the piezoelectric ceramics and the driver with high resolution are used as micro-driving device in order to guarantee the system performance.The real-time focusing controller for laser scribing on curved surface with the core of high -speed DSP chip TMS320VC5416 is designed. According to the requirement of the surface scoring system, the hardware circuit and its necessary software system have been provided. The hardware circuit takes DSP as the core, including signal pretreatment electric circuit, the data acquisition circuit, the smallest DSP system circuit, the serial port communication circuit and the self-starting electric circuit etc. The signal processing and control of every part of the system are performed by DSP. The DSP system software is realized on the platform of CCS2.0 provided by TI. The controlling arithmetic and software flow are presented in the paper and, the signal gathering controls, serial port correspondence, self-starting etc. are completely realized. The real-time focusing control interface is designed on the platform of VC.The factors which may influence the sensitivity are analysed in this paper. It also analysed the nonlinear exist in the curve, which is about defocusing amount and the output signal, and the curve fitting method to be used for the nonlinear correction.The verification experiments indicate that the precision and real-time performance of the system can meet the primitive demands.