离心法曲面涂胶的胶层厚度研究

Research on resist-layer thickness by spin-coating on curved substrate

曝光工艺中经离心涂敷后抗蚀剂胶层的均匀性对曝光线宽有很大的影响。为了得到高速旋转下抗蚀剂胶体在凹面衬底上所形成膜层厚度的均匀性,在凹面衬底上建立了非牛顿流体微元经离心旋转的流体动力学模型。根据对应的边界条件、非牛顿流体的本构方程和连续性方程,推导并得到了流体性质、曲面面形、旋转速度和时间等因素与最终厚度的关系式。使用流变仪对950 K PMMA C 2%抗蚀剂的流体性质进行标定,在凹面衬底上以旋转速度为单一变量进行离心涂胶实验,使用光谱椭圆偏振仪测量离心后随矢量半径变化的胶体厚度,并与理论推导进行对比。实验结果表明:旋转速度在2000 r/min时,理论厚度为267 nm,实验所测厚度为230 nm,偏差比率为13.86%;旋转速度在3000 r/min时,理论厚度为178 nm,实验所测厚度为172 nm,偏差比率为3.37%。考虑到涂胶后,前烘工艺会进一步减小胶层厚度,偏差在正常范围内。本文建立的数学模型具有较好的预见性,可以对胶体经旋转离心后的均匀性提供理论指导。

In lithography,the uniformity of resist coating considerably affects the consistency of line width after spin-coating.To obtain homogeneity of the resist-layer thickness on the upper surface of a curved substrate,a hydrodynamic model of a non-Newtonian fluid element is first established on the surface of the curved substrate under spin-coating.According to the corresponding boundary conditions and constitutive equation and continuity equation of the non-Newtonian fluid,the relationship between the nature of the fluid,curvature radius of the surface,horizontal vector radius,rotation speed and time,and the final thickness of the fluid is deduced and obtained.Second,a rheometer is used to calibrate the fluid viscosity of 950 K PMMA C 2%resist.A spin-coating experiment is conducted on a curved substrate using rotational velocity as a single variable.After centrifugation,the thickness was measured by ellipsometry.The relationship between the resist-layer thickness and the change in the vector radius is obtained and demonstrated with theoretical results.Experimental results show that when the spin speed is 2000 r/min,the theoretical thickness is 267 nm,measured thickness is 230 nm,and deviation ratio is 13.86%.When the spin speed is 3000 r/min,the theoretical thickness is 178 nm,measured thickness is 172 nm,and deviation ratio is 3.37%.After spin-coating,the soft-bake will further reduce the thickness of the resist-layer,and the deviation is within the normal range.Therefore,the mathematical model can provide a theoretical guidance for homogeneity after spin-coating,and the established model has a good predictability.