Significance of coating stress on substrate bow in large areaprocessing of MCM

摘要

The substrate bow in a large area processing (LAP) was simulatedusing a finite element analysis (FEA). The structures considered werealuminum (Al) and glass substrates of various thicknesses, and a coatingfrom photosensitive film thickness. It was found that the deflection ofa large area substrate, e.g. 400 mm square, could not always be obtainedfrom the linear, small deflection theory even if the curvature might besmall and the stress-strain behavior in the linear elastic regime. Inthis case, the nonlinear, large deflection theory had to be adopted.Also, the gravity effect on the weight of substrate turned out to bevery significant and had to be incorporated as well. The simulationincorporating these two factors agreed well with the experimental data,which was generated by spin coating and curing the BCB formulation on Alsubstrates, 400×400×1.27 mm. As a means of flattening outthe curvature, subjecting a vacuum underneath the substrate wassimulated. Significant reduction of the substrate deflection wasobserved by applying only a very small vacuum. This result suggestedthat the use of double-stick tape on the bottom of the substrate, forexample, might also be feasible to completely eliminate the bow