Curable organopolysiloxane compositions curable by the hydrosilation reaction are used as protective coating materials for semiconductor elements in optical semiconductor devices such as photocouplers, light-emitting diodes, solid-state image pickup elements, etc. For the above-mentioned elements to emit light or receive light, it is required that such protective coating materials for semiconductor elements should not absorb light or scatter it.
A curable organopolysiloxane composition comprising an organopolysiloxane containing silicon bonded phenyl groups and silicon bonded alkenyl groups, an organohydrogencyclosiloxane, and a hydrosilation reaction catalyst (refer to Japanese Laid-Open (Kokai or Unexamined) Patent Application Number Hei 8-176447 (176447/1996)); a curable organopolysiloxane composition comprising a solid or liquid organopolysiloxane with a viscosity of 10,000 cp and above at 25° C., and containing silicon bonded phenyl groups and silicon bonded alkenyl groups, an organohydrogenpolysiloxane having at least two silicon bonded hydrogen atoms per molecule, and a hydrosilation reaction catalyst (refer to Japanese Laid-Open (Kokai or Unexamined) Patent Application Number Hei 11-1619 (1619/1999)); and a curable organopolysiloxane composition comprising an organopolysiloxane having at least two alkenyl groups bonded to silicon atoms per molecule and having aryl groups bonded to silicon atoms, an organopolysiloxane having at least two hydrogen atoms bonded to silicon atoms per molecule, and a complex of platinum and an aryl-containing organosiloxane oligomer (refer to Japanese Laid-Open (Kokai or Unexamined) Patent Application Number 2003-128922 (128922/2003)) are suggested as examples of the curable organopolysiloxane compositions that can be cured by the hydrosilation reaction to form cured products of a large refractive index and high light transmittance.
However, the problem was that these curable organopolysiloxane compositions had high viscosity, poor filling properties, or formed cured products with poor adhesive properties that easily peeled off substrates.
It is an object of the present invention to provide a curable organopolysiloxane composition of low viscosity, excellent filling properties, and excellent curability that cures to form a soft cured product of a large refractive index, high light transmittance, and high adhesion to substrates, as well as a semiconductor device of superior reliability, whose semiconductor elements are coated with the cured product of the above-mentioned composition.