| Inferior resist adhesion causes lifting of the resist starting from the resist edges, with subsequent underetching. In exothermic etching solutions, this resist lifting is promoted by local heating and may further be promoted by mechanical forces if e.g. H2 evolution occurs. Resist adhesion can be improved by i) using a suited resist (we recommend the AZ® 1500 and 4500 positive resist series, or TI image reversal resists in image reversal mode), ii) a proper substrate pretreatment (e.g. TI PRIME), and iii) optimized processing (sufficient softbake, image reversal bake). On glass and ceramics, a hardbake is not generally recommended due to the different heat expansion coefficients of resist and substrate, which might cause crackles in the resist.In isotropic etch media, even optimized resist adhesion results in underetching. If convection and diffusion of the etched medium is not the etch rate bottleneck, the lateral underetching near the substrate/resist interface is comparable to the etched depth.In HF-containing etching solutions, F-ions diffuse through the resist to the substrate. With the resist film too thin, and/or the etching time too long, the substrate covered by the resist is also etched with large-scale resist ablation as a consequence either during etching or the subsequent rinsing. In this case, either i) a higher resist film thickness, or/and ii) an increased etching rate at fixed HF-concentration by adjusting the HF/HNO3-ratio to the specific substrate will help. |
Resists and Etchants
Optimized Substrate Pretreatment