【作者】 金占雷；

【导师】 谭久彬；

【作者基本信息】 哈尔滨工业大学 ， 仪器科学与技术， 2008， 博士

【摘要】 衍射光学元件是航天、航空、国防和通信等领域的关键器件之一,随着科学技术的进步,对衍射光学元件的功能和加工精度提出了越来越高的要求,特别是对具有微细结构衍射元件的需求日益迫切。激光直写技术由于无需掩模、加工精度高等优点成为目前衍射光学元件加工的关键技术之一,其中极坐标激光直写是加工圆对称衍射光学元件的主要手段,但该技术存在接头闭合质量低、线宽稳定性差以及加工线条中心的径向漂移等问题,制约了圆对称衍射光学元件加工精度的提高。课题“极坐标激光直写若干控制关键技术研究”的目的是在现有极坐标激光直写技术的基础上,探讨研究一种提高线条制作质量的控制技术,着重通过径向位置补偿消除径向漂移原理误差,通过增加对接区域有效过渡长度减小定位误差对接头质量的影响,通过弱化曝光量误差和曝光阈值误差对线条宽度的影响提高制作线条的稳定性。本课题的研究为解决目前极坐标激光直写过程中的线条对接质量和线宽稳定性提供了一种有效的技术途径,为提高衍射元件的性能、拓宽其应用领域提供技术储备。本文首先从极坐标激光直写的曝光原理出发,对极坐标激光直写曝光量分布进行了深入分析,研究了当扫描半径接近光斑尺寸时,加工线条的展宽和中心向极坐标中心移动的径向漂移,由此建立了线条展宽模型和径向漂移模型,并分析了线条展宽和径向漂移之间的耦合,进而分别建立了线条展宽光功率补偿模型和径向漂移补偿模型。为了提高接头闭合质量,提出基于S曲线光强控制的极坐标激光直写接头光滑闭合方法。在对接区域采用S曲线进行光强控制,利用S曲线斜率渐变的特性增加了对接区域曝光量变化的有效过渡长度,以减小曝光量的变化速率;在此基础上分析了S曲线控制参数变化对曝光量分布的影响,进而在以对接区域曝光量分布恰好存在一个极值点为最优的条件下,对控制参数进行优化,实现了接头的光滑闭合。线宽均匀稳定性是线条质量的重要指标,分析了影响离焦激光直写线宽稳定性的因素,并且提出一种提高离焦激光直写线宽稳定性的光功率控制方法,通过同时调节激光功率和离焦量,使曝光阈值处于线宽对曝光量的变化率较小的位置,从而弱化实际曝光量和曝光阈值等参数变化对线宽的影响,提高离焦直写制作衍射光学元件的线宽稳定性。本文最后对课题所研究的若干关键技术进行实验验证,主要包括:S曲线光强控制接头闭合效果验证,采用稳定线宽方法后的线宽模型验证以及对曝光量误差和曝光阈值误差线宽稳定性验证。更多还原

【Abstract】 Diffraction optical elements are keys to aerospace, aviation, national defense and communications. The diffraction optical elements with high performance and high fabrication precision, especially with minuteness structure, are urgently demanded with the development of science and technology. Laser direct writing is one of the key techniques in diffraction optical elements fabrication due to its maskless and high precision, and polar laser direct writing is the mostly method to manufacture centrosymmetrical diffraction optical elements. However, the shortages of polar laser direct writing such as low joint quality, low linewidth stability and line center radial drift restrict the improvement of centrosymmetrical diffraction optical elements quality.The study of this dissertation is to get a control method to improve the line fabrication quality on the basis of polar laser direct writing technique at present. Concretely, radial drift is eliminated by radial position compensation, the joints quality is improved by increasing valid exposure dose transition length and the linewidth stability is improved by reducing the linewidth sensitivity to exposure dose error and exposure threshold error. The study provides an effective approach to resolve the problem of joints quality and linewidth stability, then to provide technical storage for improvement of diffractive optical elements performance and widen the application fields of diffractive optical elements.In order to reduce the fabrication error during polar laser direct writing process, the exposure dose distribution is profoundly analyzed correspond to exposure principle of polar laser direct writing. The linewidth broadening model and the line center radial drift model are established on the basis of studying the causes that linewidth broadening and radial drift appear. The coupling of linewidth broadening and radial drift is analyzed, and then the linewidth broadening power compensation model and radial drift compensation model are established.In order to improve the joint quality of closed line, an S-curve intensity control smooth close-up method is presented. The intensity of joint area is controlled by S-curve, and the valid transition length of exposure dose variation increases due to the characteristic of S-curve’s slope rate gradual change. Further, the parameters of S-curve is optimized considering it to be optimal when the exposure dose distribution got an extremum at one point, then smooth close-up is realized.Linewidth stability is an important index of line quality. A laser power control method is presented to improve linewidth stability for defocusing laser direct writing on the basis of analyzing the factors which affect the linewidth stability. The writing power and defocusing amount are synchronously adjusted to set photoresist threshold at position where the linewidth variation rate is small, thereby the linewidth sensitivity to variation of actual exposure dose and photoresist threshold is weakened, and then the linewidth stability during defocusing laser direct writing is guaranteed.Finally, experiment are done to validate the methods presented in this dissertation, including validation of close-up effect when use S-curve to control the intensity of joint area, validation of linewidth model and linewidth stability when linewidth stabilizing method is adopted.更多还原