Modeling and Simulation of SU-8 Thick Photoresist Lithography

Comprehensive Simulations for Ultraviolet Lithography Process of Thick SU-8 Photoresist

“…Several research groups have reported their efforts to develop comprehensive simulation systems and to use the simulation systems for device design and process optimization. Zhou et al have been developing comprehensive 2D and 3D simulation systems for UV lithography of the SU-8 for several years [ 37 , 41 , 44 , 47 ], and a series of 2D and 3D simulations have be implemented for vertical, inclined, and multi-directional lithography methods. Figure 9 shows the 2D simulation and experimental results of the inclined UV lithography of the SU-8 for 23.5° UV incident angle on bare silicon wafer [ 44 ].…”

“…One category is based on scalar diffractive theory [ 29 , 30 , 31 , 38 , 41 , 47 , 59 ] and the other is based on rigorous electromagnetic field theory [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 ]. The former can be further divided into models based on the Fresnel diffraction [ 27 , 28 , 29 , 30 , 31 , 59 ], Fresnel–Kirchhoff diffraction [ 38 , 40 , 41 , 47 ], diffractive angular spectrum theory [ 33 ], and so on. While the latter can be further divided into models based on the finite difference time domain (FDTD) method [ 60 , 61 , 62 ] and waveguide method [ 63 , 64 , 65 , 66 , 67 ].…”

“…Furthermore, the dissolution rate of the SU-8 is depth-dependent [ 38 , 88 ], and the swelling effect will also affect the size of pattern edges and sidewall profiles of the SU-8 [ 38 , 42 ]. Although no accurate physical models for these effects are available, it is necessary to adopt the depth-dependent dissolution rate effect, and the swelling model, to improve the simulation accuracy for some cases [ 38 , 41 , 88 ]. We notice that the swelling effect seems more significant for the original SU-8 resist series than for its newer formulations (SU-8 2000 series and SU-8 3000 series) [ 2 , 44 ].…”

“…However, lithography process simulations of thick photoresist such as SU-8 cannot be accurately implemented by the software specified for thin photoresist, because there are some differences between these two lithography processes [ 28 , 29 ], such as nonlinear factors, the special exposure method for thick SU-8 lithography process, and so on. To overcome this problem, some specified researches for the UV lithography simulations of thick photoresists have been reported during the past several years [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ].…”

Methods for latent image simulations in photolithography with a polychromatic light attenuation equation for fabricating VIAs in 2.5D and 3D advanced packaging architectures

“…This approximation introduces significant error for off-axis points in the near aperture/occulter condition, the exception being a long rectangular diffractor. Consequently, many latent image simulation papers report formulae for aperture geometries, including an infinite straight edge 20 , a single long slit [21][22][23][24] and a rectangle [25][26][27][28] , while robust simulation platforms use a range of formulae, including versions of the Fresnel, Kirchoff and Rayleigh-Sommerfeld diffraction integrals [29][30][31][32][33] . Reported methods require rectangular geometries in the ultra-near aperture/occulter condition, where the Fresnel number, F, is much greater than one, as is commonly observed in photolithography.…”