Bottom antireflective coating films

The absorption parameter, k, and the refractive index, n, were measured using variable angle spectrophotometric ellipsometry. The bottom antireflective coating of test solutions were spin coated onto primed silicon wafers and baked to get selected film thickness. The coated wafers were then measured using an ellipsometer to obtain and n values. 

The resist formulation was spin-coated onto a silicone wafer on which a bottom antireflective coating had been previously applied and then soft-baked for 60 seconds at 90°C on a hot plate to obtain a film thickness of 1000 nm. The resist film was then exposed to i-line radiation of 365 nm through a narrowband interference filter using a high-pressure mercury lamp and a mask aligner. Experimental samples were then baked for 60 seconds at 90°C on a hot plate and developed. The dose to clear, E0, which is the dose just sufficient to completely remove the resist film after 60 seconds immersion development in 2.38% aqueous tetramethyl ammonium hydroxide, was then determined from the measured contrast curve. Testing results are provided in Table 1. 

Another methodology to obtain antireflective coatings is the superposition of films with different refraction index according to the so called bottom antireflective coating technique. In these cases, the coating design is made in such a way that the refraction index gradually decreases from the layer closest to the substrate towards the outer layer. 

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