Japanese Patent Laid-Open No. 05-235313 discloses a technique which aims to increase the light-collecting efficiency by forming a total reflection structure inside an image sensor. FIG. 17 shows a structure based on an embodiment in Japanese Patent Laid-Open No. 05-235313. In this structure, the value of D/L which is the ratio of the pitch to the depth of the image sensor is 1, and an angle θ of an inclined total reflection surface is about 26.5°. This structure makes it possible to collect light without lowering the light-concentrating efficiency around the center of an imaging plane even when no microlens is used.
Also, Japanese Patent Laid-Open No. 06-224398 discloses a structure for efficiently collecting light incident on an image sensor. FIG. 18 shows a structure based on an embodiment in Japanese Patent Laid-Open No. 06-224398. A resin cap layer 10 is made of a material having a refractive index of about 1.6. A low refractive index layer 9 is made of resin having a refractive index lower than that of the cap layer 10, and has a hollow (filled with air or an inert gas such as nitrogen). Light traveling from the cap layer 10 to the low refractive index layer 9 is totally reflected by the interface when the light exceeds the critical angle. Accordingly, slant incident light can be collected.
Unfortunately, the above conventional examples have the following problems.
In the structure as shown in FIG. 17, of the light totally reflected by the total reflection surface, light directly reaching a light-receiving portion can be received with no problem. However, when light by which the F number of a lens is small is to be collected, light from the periphery of the pupil of the lens sometimes passes through the total reflection surface, without being reflected, when the light is incident on the total reflection surface, since the light does not exceed the critical angle. Also, even when this light is totally reflected, it sometimes passes through a total reflection surface on the opposite side when the light is incident on this total reflection surface, since the light does not exceed the critical angle. To control this state, it is necessary to properly design the dimensional relationship between, e.g., the height of the inclined surface, the incident aperture, and the exit aperture.
Also, in the structure as shown in FIG. 18, the incident side of the high refractive index cap layer 10 is an arc having a small radius. Therefore, when the angle of slant incident light increases, light incident on this arc portion is not totally reflected but passes through it, and enters another pixel.
USPTO Backgrounds
USPTO Backgrounds