Process for manufacturing a semiconductor device having a contact window defined by an inclined surface of a composite film

A method of manufacturing a semiconductor device, said method comprising:

• providing a semiconductor substrate;
• forming a composite film, having an index of refraction that varies serially over the thickness thereof, over a surface of the semiconductor substrate, said composite film consisting of a lower film of silicon nitride having a first refractive index, a middle film of silicon nitride having a refractive index that increases over the thickness thereof in a direction toward the lower film, and an upper film of silicon nitride-oxide having a refractive index that increases over the thickness thereof in a direction toward the middle layer;
• forming a photoresist in a pattern over the insulating film;
• forming a contact window extending through the composite film and defined by a vertically extending sidewall thereof by subjecting the structure formed by performing the preceding steps to a reactive ion etching process in which the photoresist is used as a mask;
• exposing the structure formed by performing the preceding steps to an etchant capable of etching the composite film so as to etch the vertically extending sidewall into an inclined surface due to the variation in the index of refraction of the insulating film;
• removing the photoresist;
• and
• forming a conductive film over the composite film including the inclined surface thereof and over a surface of the substrate exposed at the bottom of the contact window.