Composite substrate applied to direct type backlight LED chip and preparation method of composite substrate

The invention discloses a composite substrate applied to a direct type backlight LED chip and a preparation method of the composite substrate. The composite substrate applied to the direct type backlight LED chip comprises a sapphire substrate, nano-micron patterns are arranged on the sapphire substrate, and the nano-micron patterns are arranged on the sapphire substrate. Each nano-micron pattern comprises a hexagonal pyramid reflecting layer and a dielectric insulating layer which are arranged on the sapphire substrate. According to the composite substrate, the light emitting efficiency of light can be remarkably improved, and the brightness of an LED is improved. The preparation method of the composite substrate applied to the direct type backlight LED chip comprises the steps of cleaning, reflective layer coating, gluing, primary dry etching, cleaning, dielectric insulation layer deposition, primary gluing, exposure, development, secondary dry etching, secondary gluing, exposure, development, DBR reflectiv