In the calculation, such a structure as to show an effect of the present invention was employed, specifically, the values of T1 of 20 nm, T2 of 20 nm, T3 of 500 nm, T4 of 4,000 nm, T5 of 8,000 nm and (h) of 5 nm (see FIGS. 4A and 4B) in FIG. 3 were employed.