JPH10209409A - Solid-state image pick up element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pick up element, which is high in sensitivity and has little irregularity in sensitivity in each pixel. SOLUTION: The focal point P of an upper layer of an on-chip lens 18 is positioned on the side upper than a lower layer of an on-chip lens 21 under the lens 18, and when the distance between the focal point P and the lens 21 is assumed Ln and the focal length of the lens 21 is assumed fl, the fl and the Ln are used on the condition of fl<Ln. Owing to this, while a divergence of light 19 is inhibited by the lenses 18 and 21 of the upper and lower layers, this light 19 can be led to a sensor and it is possible to lead the light 10 to the sensor without generating the eclipse of the light 19 due to a light-shielding film 15 or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device having an on-chip lens on a sensor.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional example of the present invention. In this conventional example, a sensor (not shown) and a transfer unit (not shown) of each pixel are formed in a semiconductor substrate 11, and a gate insulating film 12 is formed on the surface of the semiconductor substrate 11. . A transfer electrode 13 is formed on the gate insulating film 12, and the transfer electrode 13 is covered with an insulating film 14 or the like.

The insulating film 14 and the like are covered with a light-shielding film 15, and an opening 15 is formed in a portion of the light-shielding film 15 above a sensor.
a is formed. The light-shielding film 15 and the like are covered with the flattening film 16, and the color filter layer 17 and the on-chip lens 18 are sequentially formed on the flattening film 16. In such a conventional example, the light 1 is
Since 9 is collected in the sensor, the sensitivity is higher than a structure in which the on-chip lens 18 is not provided.

[0004]

However, even if the area of each pixel is reduced, the transfer electrode 1 is required to prevent the resistance of the transfer electrode 13 from increasing and the light-shielding ability of the light-shielding film 15 from decreasing.
It is difficult to reduce the thickness of the third light-shielding film 15 and the like. For this reason, the ratio of the height of the light shielding film 15 and the like to the size of the opening 15a is increasing, and as a result, as shown in FIG.
Light 19, which was not guided to the sensor due to being shaken by 5 or the like, was likely to occur.

For this reason, it was difficult to obtain high sensitivity in the conventional example shown in FIG. Further, the pattern of the light-shielding film 15 varies from pixel to pixel, and furthermore, the incidence angle of the light 19 differs depending on the pixel and the rate of shading differs. It was easy for unevenness to occur.

[0006]

The solid-state image pickup device according to the present invention has a plurality of layers of on-chip lenses, and the focus of the upper-layer on-chip lens is higher than that of the lower-layer on-chip lens. Located on the side
The distance between the focal point and the lower-layer on-chip lens is Ln, and the focal length of the lower-layer on-chip lens is f
When l, fl <Ln.

[0007] The solid-state imaging device according to the present invention preferably satisfies Ln <2fl.

In the solid-state imaging device according to the present invention, it is preferable that fl <fu if the focal length of the upper-layer on-chip lens is fu.

In the solid-state imaging device according to the present invention, the focal point of the upper-layer on-chip lens among the multiple-layer on-chip lenses is located on the upper layer side with respect to the lower-layer on-chip lens. Since the distance between the focal point of the chip lens and the lower-layer on-chip lens is longer than the focal length of the lower-layer on-chip lens, the light that is once converged by the upper-layer on-chip lens and then diverges by the lower-layer on-chip lens. It converges again.

For this reason, the light can be guided to the sensor while suppressing the divergence of the light by the on-chip lenses of the respective layers. Therefore, even if the ratio of the height of the light-shielding film to the size of the opening of the light-shielding film on the sensor is relatively large, this light can be guided to the sensor without causing light shading by the light-shielding film or the like. it can.

If the distance between the focal point of the upper-layer on-chip lens and the lower-layer on-chip lens is smaller than twice the focal length of the lower-layer on-chip lens, the diameter of the lower-layer on-chip lens becomes smaller. Also, among the light diverged after being once converged by the upper-layer on-chip lens, there is little light that does not enter the lower-layer on-chip lens.

If the focal length of the lower-layer on-chip lens is shorter than the focal length of the upper-layer on-chip lens,
Even if the diameter of the lower-layer on-chip lens is small, of the light that is once converged by the upper-layer on-chip lens and diverges, there is little light that does not enter the lower-layer on-chip lens.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows the present embodiment. In the present embodiment, an on-chip lens 21 different from the on-chip lens 18 is provided between the sensor and the on-chip lens 18, and the on-chip lenses 18 and 21 have two layers.

Assuming that the focal length of the on-chip lens 18 is fu, the light 1 that is vertically incident on the surface of the solid-state imaging device
9 converges on a focal point P at a distance of fu from the on-chip lens 18. The thickness and the like of the flattening film 16 are selected so that the focal point P is located at a height near the upper surface of the light shielding film 15.

When the focal length of the on-chip lens 21 is fl and the distance from the focal point P to the on-chip lens 21 is Ln, the relationship of fl <Ln <2fl fl <fu is satisfied. Except for the above points, this embodiment also has a configuration substantially similar to that of the conventional example shown in FIG.

In this embodiment, as is clear from FIG. 1, the light 19 is once converged to the focal point P by the on-chip lens 18, and the light 19 diverging through the focal point P is also transmitted to the on-chip lens 21. It is incident and converged again. That is, the light 19 is guided to the sensor while the divergence of the light 19 is suppressed by the on-chip lenses 18 and 21.

Further, the focal point P at which the light 19 is converged by the on-chip lens 18 is located at a height near the upper surface of the light shielding film 15. Therefore, even if the ratio of the height of the light shielding film 15 and the like to the size of the opening 15a of the light shielding film 15 is large, the light 19 can be guided to the sensor without causing the light 19 to be shaken by the light shielding film 15 and the like. it can.

On the other hand, if fl = Ln, contrary to the above condition satisfied by the present embodiment, as shown in FIG.
Since the light 19 transmitted through the on-chip lens 18 is not converged but becomes parallel light, the light
The light 19 is more likely to be shaken in a portion close to. Note that f
If l> Ln, the light 19 transmitted through the on-chip lens 18 becomes divergent light, so that the light 19 is more likely to be blurred.

If Ln.gtoreq.2fl contrary to the above condition, as a practical matter, as shown in FIG. 5, the light 19 which is once converged to the focal point P by the on-chip lens 18 and then diverges.
Of these, most of the light 19 does not enter the on-chip lens 21. The light 19 that does not enter the on-chip lens 21 in this manner
Is incident on the upper surface or the like of the light shielding film 15 and does not contribute to the sensitivity.

If fl ≧ fu contrary to the above condition, also in this case, as a practical problem, the on-chip lens 1
Of the light 19 diverged after being once converged to the focal point P at 8, there are many light 19 that do not enter the on-chip lens 21. The light 19 not incident on the on-chip lens 21 is incident on the upper surface of the light-shielding film 15 or the like, and does not contribute to the sensitivity.

FIG. 2 shows a first method of manufacturing a solid-state imaging device having a plano-convex on-chip lens 21. Even in the first manufacturing method, as shown in FIG. 2A, a conventionally known process is performed until the opening 15a is formed in the light shielding film 15. However, in the first manufacturing method, the light shielding film 15
Are covered with a flattening film 16, and as shown in FIG.
A recess 16 a is formed in a portion of the flattening film 16 above the opening 15 a of the light shielding film 15.

Next, as shown in FIG.
A resin layer 22 having a refractive index higher than 6 is applied flat on the flattening film 16, and the recess 16 a is filled with the resin layer 22. After that, as shown in FIG. 2D, the color filter layer 17 is formed on the resin layer 22 and the on-chip lens 21 is formed by the resin layer 22 in the concave portion 16a, and as shown in FIG. The on-chip lens 18 is formed on the color filter layer 17.

FIG. 3 shows a second method of manufacturing a solid-state imaging device having a biconvex on-chip lens 21. Also in this second manufacturing method, as shown in FIGS. 3A to 3C, until the resin layer 22 is applied on the flattening film 16, substantially the same as the first manufacturing method shown in FIG. A similar process is performed.

However, according to the second manufacturing method, as shown in FIG.
The portion other than the portion above 6a is etched to leave the resin layer 22 having a trapezoidal cross section on the concave portion 16a. Then, as shown in FIG. 3E, the resin layer 22 having a trapezoidal cross section and the planarizing film 16 are formed.
Another flattening film 23 is applied thereon to form the on-chip lens 21 with the resin layer 22. Although not shown, the color filter layer 17 and the on-chip lens 18 are further formed.

Although the on-chip lenses 18 and 21 have two layers in the above embodiment, three or more on-chip lenses can be provided in the solid-state imaging device. Also in this case, the light diverged after being once converged by the upper-layer on-chip lens is sequentially converged by the lower-layer on-chip lens.

[0026]

In the solid-state imaging device according to the present invention, even if the ratio of the height of the light-shielding film to the size of the opening of the light-shielding film on the sensor is relatively large, light is not blocked by the light-shielding film. Since this light can be guided to the sensor without generation, the sensitivity is high and the sensitivity unevenness of each pixel is small.

If the distance between the focal point of the upper-layer on-chip lens and the lower-layer on-chip lens is shorter than twice the focal length of the lower-layer on-chip lens, the diameter of the lower-layer on-chip lens becomes smaller. Also, the sensitivity is further increased because, of the light diverged after being once converged by the upper-layer on-chip lens, light that does not enter the lower-layer on-chip lens is small.

If the focal length of the lower-layer on-chip lens is shorter than the focal length of the upper-layer on-chip lens,
Even if the diameter of the lower-layer on-chip lens is small, there is little light that does not enter the lower-layer on-chip lens among the light diverged after being once converged by the upper-layer on-chip lens.
Higher sensitivity.

[Brief description of the drawings]

FIG. 1 is a conceptual side sectional view of an embodiment of the present invention.

FIG. 2 is a side sectional view showing a first manufacturing method of one embodiment in the order of steps.

FIG. 3 is a side sectional view showing a second manufacturing method of one embodiment in the order of steps.

FIG. 4 is a side sectional view for explaining a problem when the configuration is different from that of the embodiment.

FIG. 5 is a side sectional view for explaining a problem in another case having a different configuration from the embodiment.

FIG. 6 is a side sectional view of a conventional example of the present invention.

[Explanation of symbols]

 18, 21 On-chip lens P Focus

Claims (3)

[Claims] 1. An on-chip lens having a plurality of layers, wherein a focal point of the upper-layer on-chip lens is located closer to the upper layer than the lower-layer on-chip lens, and the focal point and the lower layer Let Ln be the distance from the on-chip lens and f be the focal length of the lower-layer on-chip lens.
1 is a solid-state imaging device, wherein fl <Ln. 2. The solid-state imaging device according to claim 1, wherein Ln <2fl. 3. The solid-state imaging device according to claim 1, wherein fl <fu, where fo represents a focal length of the upper-layer on-chip lens.