Hdp-cvd sion films for gap-fill

A method of forming a plurality of image sensors over a substrate, the method comprising:

• forming a plurality of optical arrangements on a substrate, each of the optical arrangements comprising an optical via formed over an optical detector;
• wherein the optical vias are formed by:
• etching a trench in a silicon oxide insulating layer formed over the optical detector;
• growing a first lining layer comprising predominantly silicon dioxide in the trench by forming a high density plasma from a process gas comprising a silicon source and an oxygen source while maintaining a mean pressure within the chamber of about 15 mTorr or less and maintaining a mean substrate temperature of 500° C. or less;
• growing a second lining layer comprising predominantly silicon oxynitride over the first lining layer by forming a high density plasma from a process gas comprising a silicon source, an oxygen source and a nitrogen source while maintaining a mean pressure within the chamber of about 15 mTorr or less and maintaining a mean substrate temperature of 500° C. or less, wherein a deposition-to-sputter ratio during growth of the second lining layer is at least 50:1;
• growing a bulk gap-fill layer comprising predominantly silicon oxynitride over the second lining layer by forming a high density plasma from a process gas comprising a silicon source, an oxygen source and a nitrogen source while maintaining a mean pressure within the chamber of about 15 mTorr or less and maintaining a mean substrate temperature of 500° C. or less, wherein a deposition-to-sputter ratio during growth of the bulk gap-fill layer is between about 2:1 and 6:1.