Method for fabricating CMOS image sensor
View Patent ↗A method for fabricating a CMOS image sensor forms silicon nitride (SiN) layer on a pad. Microlenses, having a minimum height and footprint according to a desired packing density of the lenses, are fabricated of an oxide film and a nitride film deposited on the silicon nitride. Since the lenses have a low height, a refractive index of the lenses may be improved. A sidewall spacer type inner lens may be additionally formed below a main lens curvature to aid in overcoming problems caused by a single-lens structure.
1. A method for fabricating a CMOS image sensor, comprising:
forming a metal line pattern;
forming a pad film on the metal line pattern;
forming a passivation film on the pad film;
forming a recess by etching the passivation film using a photoresist mask for forming a microlens having a desired shape;
sequentially depositing a high-density plasma oxide film and an O 3 tetra-ethyl-ortho-silicate film on the etched passivation film, wherein depositing the high-density plasma oxide film provides a conic microlens structure of photoresist on a microlens base; and
etching back the high density plasma oxide film and the O 3 tetra-ethyl-ortho-silicate film to form a main lens curvature on a surface of the etched passivation film and a sidewall spacer type lens at inner sidewalls of the recess of the etched passivation film, thereby forming a dual-lens structure.
2. The method of claim 1 , wherein the passivation film is formed of silicon nitride (SiN).
3. The method of claim 2 , wherein after the etching of the passivation film, a predetermined thickness of the silicon nitride as an etched recess in an original surface of the silicon nitride remains.
4. The method of claim 1 , wherein the etching back process is performed under conditions of etchant flow rates of approximately 20-200 sccm for Ar, approximately 5-20 sccm for C 4 F 8 , approximately 30-50 sccm for CH 3 F, and approximately 20-500 for O 2 , a top RF power of approximately 200-300 W; a bottom RF power of approximately 50-150 W; and a pressure of approximately 100-200 mTorr.
5. The method of claim 1 , further comprising:
forming a sublayer below the pad film;
forming a metal line having an opening on the sublayer; and
forming an aluminum pad on a portion of a lower surface of the pad film to correspond to the opening.
6. The method of claim 1 , wherein depositing O 3 tetra-ethyl-ortho-silicate provides a curved upper surface to the conic microlens structure.
7. The method of claim 6 , wherein a dual-lens structure is formed by etching back the conic microlens structure to form a sidewall spacer type microlens.
8. The method of claim 7 , wherein the etching back is performed under conditions of etchant flow rates of approximately 20-200 sccm for Ar, approximately 5-20 sccm for C 4 F 8 , approximately 30-50 sccm for CH 3 F, and approximately 20-500 sccm for O 2 , a top RF power of approximately 200-300 W, a bottom RF power of approximately 50-150 W, and a pressure of approximately 100-200 mTorr.