Yes, SILLS is a Scrabble word!

Letter values in Scrabble US: S 1, I 1, L 1, L 1, S 1.

Is it a valid word?

SILLS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

United States operatic soprano (born in 1929)
structural member consisting of a continuous horizontal timber forming the lowest member of a framework or supporting structure
(geology) a flat (usually horizontal) mass of igneous rock between two layers of older sedimentary rock

Also: beverly sills, belle miriam silverman.