Optimization of EDP solutions for feature size independent silicon etching

The etching of single crystal silicon in ethylenediamine-pyrocatechol-water solutions (EDP) has been studied as a function of the composition of the etching solution. The solution with a constant composition of 7.5ml of ethylenediamine (with 6g of pyrazine per liter) and 1.2g of pyrocatechol is used, and the water content is varied from 0ml to 4ml. Etch rate dependence on the active etching area is examined using three mask patterns having significantly different areas. It has been observed that etch rate depends significantly on the feature size in the solutions with higher water concentration and is almost independent of the area when the water content is 1ml and below. Surface morphology was the other important criteria considered while optimizing the solution. It is found that the hillocks formation on surface is dependent on the etchant composition. Hillock density has been measured by etching the samples in different compositions to a constant depth of 45μm. It is found to be high when the water content is above 2ml and also when the amount of water is reduced below 0.5ml. Minimal Hillock density is obtained when the water content is 0.5ml. The optimized EDP solution containing 0.5ml of water results in an etch rate of 44μm/hr, independent of feature size and also good surface finish with hillock density less than ∼103/cm2.