The present invention relates to a solid-state image pickup device which can increase light-gathering efficiency to a light receiving sensor unit to enhance the sensitivity characteristic thereof.
Recently, solid-state image pickup devices have made further progress in a compact design and a high-density design of pixels, and this progress in the microstructure design has caused reduction in the light receiving area in which light is received, thereby inducing degradation of characteristics such as reduction in sensitivity, etc. As a countermeasure to the reduction in sensitivity, it has been proposed and practically used to provide an on-chip lens or an in-layer lens to enhance the light gathering efficiency at the light receiving sensor unit.
However, a solid-state image pickup device in which an in-layer lens is formed of material having high refractive index has the following problem.
In the case where the in-layer lens is formed of Pxe2x80x94SiN having a refractive index of about 2.0 (silicon nitride based on the plasma CVD method), since a color filter layer formed on the in-layer lens usually has a refractive index of about 1.6, there is large difference in refractive index between the in-layer lens and the color filter layer, and thus reflection occurs at the interface between the in-layer lens and the color filter layer, so that the sensitivity characteristic is reduced. The reflection due to the difference in refractive index is inherently introduced from the wave equation.
An interlayer film which is subjected to a reflow treatment, etc. is formed under the in-layer lens, and BPSG (boron phosphorus silicate glass) having a refractive index of 1.45 or the like is normally used as the interlayer film because it is subjected to the reflow treatment, etc. Accordingly, as in the case of the refractive index difference between the in-layer lens and the color filter layer, the large difference in refractive index occurs between the in-layer lens and the interlay film and reflection also occurs at the interface therebetween, so that the sensitivity characteristic is reduced.
The present invention has been implemented in view of the foregoing situation, and has an object to provide a solid-state image pickup device which can prevent reflection between an in-layer lens and an upper layer or lower layer thereon or thereunder to enhance the light gathering efficiency, thereby enhancing the sensitivity.
In order to attain the above object, according to a first aspect of the present invention, a solid-state image pickup device comprises: a light receiving sensor portion which is provided in a surface layer portion of a substrate and performs photoelectric conversion; an in-layer lens which is provided in a layer above the light receiving sensor portion and converges incident light to the light receiving sensor portion, and a color filter layer which is provided through an antireflection film on the in-layer lens, wherein the antireflection film is formed of material having a refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the color filter layer.
The solid-state image pickup device may further include a charge transfer portion which is provided in the surface layer portion of the substrate and transfers signal charge read out from the light receiving sensor portion, and a transfer electrode which is provided through an insulation film on the substrate so as to be located substantially just above the charge transfer portion.
The solid-state image pickup device may further include an on-chip lens at the upper side of the color filter layer.
The solid-state image pickup device may further include an interlayer film which is provided below the in-layer lens through another antireflection film below the in-layer lens, wherein the other antireflection film is formed of material having a refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the interlayer film.
According to the solid-state image pickup device of the first aspect of the present invention, the upper antireflection film is formed between the color filter layer and the in-layer lens, the film being formed of the material having the refractive index which is an intermediate value between the refractive index of the color filter and the refractive index of the in-layer lens. Therefore, even when the difference in refractive index between the color filter layer and the in-layer lens is large, the color filter layer and the in-layer lens are not directly bonded to each other. Accordingly, there is no interface therebetween, and there exist only the interface between the color filter layer and the upper antireflection film, the refractive index difference of which is smaller than the refractive index difference between the color filter layer and the in-layer lens, and the interface between the upper antireflection film and the in-layer lens, the refractive index difference of which is also smaller than the refractive index difference between the color filter layer and the in-layer lens. Accordingly, by providing the upper antireflection film, the interface having a large refractive index difference is changed to the interface having a small refractive index difference, so that there does not occur any reflection which would occur if the interface having the large refractive index difference exists.
According to a second aspect of the present invention, a solid-state image pickup device includes: a light receiving sensor portion which is provided in a surface layer portion of a substrate and performs photoelectric conversion; an interlayer film formed on the light receiving sensor portion; and an in-layer lens which is provided on the interlayer film and converges incident light through an antireflection film to the light receiving sensor portion, wherein the antireflection film is formed of material having a refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the interlayer film.
The solid-state image pickup device may further include a charge transfer portion which is provided in the surface layer portion of the substrate and transfers signal charge read out from the light receiving sensor portion, and a transfer electrode which is provided through an insulation film on the substrate so as to be located substantially just above the charge transfer portion.
The solid-state image pickup device may further include a color filter layer disposed above the in-layer lens.
The solid-state image pickup device may further include an on-chip lens disposed above the in-layer lens.
In the solid-state image pickup device, the color filter layer is provided through another antireflection film on the in-layer lens, and the other antireflection film is formed of material having a refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the color filter layer.
According to the solid-state image pickup device of the second aspect of the present invention, the lower antireflection film is formed between the in-layer lens and the interlayer film, the lower antireflection film being formed of the material having the refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the interlayer film. Therefore, even when the difference in refractive index between the in-layer lens and the interlayer film is large, the in-layer lens and the interlayer film are not directly bonded to each other. Accordingly, there is no interface therebetween and there exist only the interface between the lower antireflection film and the in-layer lens, the refractive index difference of which is smaller than the refractive index difference between the in-layer lens and the interlayer film, and the interface between the lower antireflection film and the interlayer film, the refractive index difference of which is also smaller than the refractive index difference between the in-layer lens and the interlayer film. Accordingly, by providing the lower antireflection film, the interface having a large refractive index difference is changed to the interface having a small refractive index difference, so that there does not occur any reflection which would occur if the interface having the large refractive index difference exists.
According to a third aspect of the present invention, a method of manufacturing a solid-state image pickup device comprises the steps of: forming in a surface layer portion of a substrate a light receiving sensor portion for performing photoelectric conversion, a charge transfer portion for transferring signal charge read-out from the light receiving sensor portion, and forming a transfer electrode through an insulation film substantially just above the charge transfer portion on the substrate; depositing an interlayer film so as to cover the transfer electrode; conducting a heat treatment under a predetermined condition to form a recess portion; and forming an antireflection film along the upper portion of the portion, wherein the antireflection film is formed of material having a refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the interlayer film, and wherein the in-layer lens is formed on the antireflection film so that the lens material is filled in the recess portion, and then the surface thereof is flattened.
In the above method, a color filter layer may be formed above the in-layer lens.
In the above method, an on-chip lens may be formed above the in-layer lens.
The above method may further comprises the steps of forming another antireflection film on the in-layer lens, and forming a color filter layer on the other antireflection film, wherein the antireflection film is formed of material having a refractive index which is an intermediate value between the refractive index of the in-layer lens and the refractive index of the color filter layer.