Research On Film Thickness Evolution And Distribution Of Spincoated Thin Films On Rectangular Substrates

Photolithography is widely used in aerospace,optical engineering,biomedicine and other fields.The preparation of photoresist film as the pre-process of photolithography is a key step to ensure the performance of the final device.In recent years,the demand for photoresist film preparation is no longer limited to traditional circular workpieces,and the demand for photoresist film preparation on the surface of rectangular workpieces such as gratings is also increasingly widespread.As a thin film preparation process with a wide range of film thickness,simple operation and high efficiency,spin coating is widely used in photoresist film formation.The spin-coating method is a complex fluid flow process.Due to the non-axial symmetry of the rectangular substrate,the characteristics of the spin-coating film are more difficult to define,which limits the application of the spin-coating method on the rectangular substrate.Therefore,it is necessary to study the film thickness law and film thickness distribution characteristics of spin-coated thin films on rectangular substrates.In this paper,the viscosity-temperature characteristics,density,contact angle and surface tension coefficient of the photoresist solution used in the spin-coating film-forming experiment were tested first,and the parameters were provided for the subsequent spin-coating filmforming simulation model.The transient model of spin-coating process was established,and the film thickness evolution,film thickness distribution and edge bead effect of spin-coating films on rectangular substrates were studied through the development process of spin-coating films in the simulation combined with the experimental results of spin-coating films.The research contents of this paper are as follows:(1)The effects of substrate geometry,air shear,solvent volatilization,and substrate size on the film thickness evolution were investigated by experiments and simulations.In the 3D simulation model,the difference between the film thicknesses on the circular and rectangular substrates at each moment is extremely small,and there is no linear law,and the substrate geometry has no effect on the spin-coating film thickness.The thickness of the liquid film in the two-phase flow simulation of spin-coating film formation and the prediction results of the analytical model without considering air shear is basically the same at each time,and air shear is not the main factor affecting the evolution of spin-coating film thickness.Combining the experimental results and simulation results,it is found that the size of the substrate has no effect on the film thickness development.The designed experiment found that the volatilization of the solvent is the key factor affecting the film thickness development.(2)According to the characteristics of air flow field and film thickness distribution in the3 D spin coating simulation model,the influence of air shear on the film thickness distribution of spin-coated thin films on rectangular substrates is discussed.The film thickness distribution characteristics of radial reduction and edge accumulation of thin films on rectangular substrates are summarized,and the formation mechanism of film thickness distribution characteristics is analyzed and studied based on the experimental and simulation results,and the root cause of the formation of film thickness distribution characteristics on rectangular substrates is determined.The research results show that by improving the air flow field and suppressing the Bernoulli effect during the spin coating process,the distribution characteristics of the film can be weakened and the film thickness uniformity can be improved.It is also possible to fundamentally weaken the film thickness distribution characteristics of spin-coated thin films on rectangular substrates by inhibiting solvent evaporation.(3)The influence of the chamfering angle φ of the substrate and the chamfering width c of the substrate on the effect range of the edge bead is studied through experiments.In Fluent,the VOF two-phase flow model is used to establish a two-dimensional axisymmetric simulation model for the edge bead effect of the spin-coated film.Influence mechanism of chamfer width c on edge bead effect.The research shows that a larger chamfering angle φ and a substrate chamfering width c that is close to the edge bead size of the liquid film are beneficial to reduce the edge bead effect.