By forming a microlens of negative photoresist, economical microlens fabrication processes may be used which, in some embodiments, may achieve microlenses having good optical clarity and high thermal stability. In one embodiment, a positive photoresist may be used as a pattern mask to transfer a pattern to the negative photoresist. The microlenses may be formed by dry etching the positive photoresist which acts as a mask to transfer a pattern to the underlying negative photoresist. At the same time a scratch protection layer may be formed over regions not overlying optical sensors.