Gray Scale Mask Produced by Optical Pick-up Head
|Keywords:||光學讀取頭;底片;optical pick-up head;gray scale|
|Abstract:||灰階光罩有許多不同的光罩製作方式，因為微影製程簡單，近年來備受矚目，有半階光罩、HEBS玻璃灰階光罩、雷射直寫(Laser Direct Write)玻璃灰階光罩。由於HEBS玻璃灰階光罩和LDW玻璃灰階光罩價格昂貴，在本論文採用專業底片搭配光學讀取頭，來產生灰階底片光罩，以求降低灰階光罩的成本。
本論文的光學讀取頭內有聚焦致動器、循軌致動器、透鏡、光感測器、及雷射二極體等元件。聚焦致動器可驅動透鏡垂直移動，當底片和透鏡的距離太遠或太近，藉由光感測器產生的聚焦誤差訊號及PI控制器來補償誤差，可使得透鏡產生的光點聚焦在底片上。循軌致動器可驅動透鏡平行移動，由於在底片上無資料軌道，無法產生循軌誤差訊號，因此僅藉循軌驅動電路來控制透鏡的平行移動量，其最小的移動量為4.68 μm。雷射二極體，經由雷射二極體驅動電路，提供不同強度的雷射光，由於透鏡的NA (numerical aperture)值為0.67,所以照射在底片上的最小光點大小為0.617 μm。灰階底片光罩產生步驟如下:循軌致動器平行移動透鏡至一個特定位置後，雷射二極體發射特定時間及強度的雷射光，經過透鏡，聚焦在底片上。重複上面的步驟，底片上的每個位置接收到不同的曝光量。曝光過的底片，經過顯影步驟，灰階的情形便會產生在底片上，藉此，完成灰階底片光罩。
There are many different gray scale mask fabrication processes in gray scale mask, such as half tone mask, high energy beam sensitive (HEBS) glass gray scale mask, and laser direct write (LDW) glass gray scale mask. They are attractive recently due to the simple photolithography process. Because the price of the HEBS glass and LDW glass is too expensive, the professional film is used to produce the gray levels by a DVD optical pick-up head. The DVD optical pick-up head in this thesis is composed of the tracking actuator, the focusing actuator, the objective lens, the photo detector, the laser diode, and so on. The focusing actuator can drive the objective lens in the vertical direction. When the distance is not in focus, the focusing error signal is produced by the photo detector and the PI controller compensates the error. Then, the distance is focused. The tracking actuator driven by the driving circuit actuates the objective lens in the horizontal direction. Because there is no data track in the film, there is no tracking error. Therefore, the movement of the objective just can be controlled by the driving circuit, and the smallest movement is 4.68 μm. The laser diode driven by the driving circuit can emit the different intensity of the laser. Because the numerical aperture of the objective lens is 0.67, the smallest spot size in the film is 0.617 μm. The tracking actuator moves the objective lens to a specific position, and the specific emitting time and power of the laser is emitted by the laser diode. Then, the laser passes through the objective lens, and the spot is focused on the film. The above steps are repeated, and the different value of exposure is received in every position of the film. Gray scale levels are produced in the exposed film through the processing. The target of the thesis is to produce the gray scale film mask within a 500μm range. the gray scale view can be analyzed by the optical microscope and Matlab.
|Appears in Collections:||Thesis|