JP3154134B2 - Solid-state imaging device - Google Patents

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,
In particular, the present invention relates to a solid-state imaging device in which a micro condenser lens is formed on a light receiving unit.

[0002]

2. Description of the Related Art In a solid-state image pickup device, for example, a CCD solid-state image pickup device, when the relationship between signal charge and noise in the CCD and illuminance on an image surface is viewed, noise (shot noise) due to fluctuation of signal charge on the low illuminance side. It is known that the influence of dark noise increases.

The shot noise can be reduced by increasing the aperture ratio of the light receiving portion. However, with the recent trend toward miniaturization, there is a limit to the increase in the aperture ratio. Therefore, a structure in which a micro condenser lens is formed on a light receiving unit has been proposed. In the case of the structure in which the micro condenser lens is formed, the light utilization rate increases, the sensitivity in the light receiving section can be improved, and this is effective in reducing the shot noise (the formation of the micro condenser lens). The method is described in, for example, JP-A-60-53073 and
-10666 publication).

In a conventional CCD solid-state imaging device, as shown in FIG. 8, a transfer electrode 43 made of a polycrystalline silicon layer is selectively formed on a silicon substrate 41 via a gate insulating film 42 made of SiO2 or the like. An Al light-shielding film 45 is selectively formed on these transfer electrodes 43 via an interlayer film 44, and a flattening film 46 is formed on the entire surface including the Al light-shielding film 45.
Are stacked, and a micro condenser lens 47 is formed on the flattening film 46.

Here, a portion where the transfer electrode 43 is not formed is a light receiving portion 48, and the Al light shielding film 45 is removed on the light receiving portion 48. A micro condenser lens 47 is formed.

Incidentally, the micro condenser lens 47
When only parallel light is considered as incident light, the shape may be such that light is surely condensed in the light receiving unit 48. Therefore, conventionally, as shown in FIG. 9A, when the aperture diameter of the camera objective lens 49 is minimized (that is, when the F-number is maximized), the spot of the incident light (parallel light) on the light receiving unit 48 is reduced. The radius of curvature r (see FIG. 8) of the micro condenser lens is selected so that the diameter is equal to or smaller than the opening width W (see FIG. 8) of the light receiving section 48. In another example, a method of changing the refractive index of the micro condenser lens 47 has been proposed.

As described above, by selecting the radius of curvature r of the micro condenser lens 47, the micro condenser lens 47 is selected.
Can be maximized (sensitivity with micro condenser lens / sensitivity without micro condenser lens).
It is possible to improve the sensitivity of the CD solid-state imaging device.

[0008]

However, the incident angle component of the light incident on the light receiving section 48 changes depending on the aperture diameter (F value) of the camera objective lens 49. For example, when the aperture of the camera objective lens 49 is moved to the open side, for example, as shown in FIG. Light having an appropriate angle is incident. Therefore, in the case of the shape of the micro-condensing lens 47 that is optimally condensed by the parallel light, the oblique light incident component out of focus increases when the F value is minimum.

[0009] In this case, as shown in FIG.
The light is shielded at the shoulder of the Al light shielding film 45,
There is a problem that a sufficient light-collecting effect cannot be obtained. That is, as the F-number of the camera objective lens 49 decreases, the light collection rate of the micro light collection lens 47 decreases. For this reason, it is practically very difficult to keep the light-collecting effect constant at all aperture positions.

The present invention has been made in view of such a problem, and an object of the present invention is to improve the F-number dependency of the light collection rate while maximizing the light collection rate. An object of the present invention is to provide a solid-state imaging device capable of sufficiently exhibiting the sensitivity improvement which is an original effect of a micro condenser lens.

[0011]

According to the present invention, there is provided a semiconductor substrate comprising:
A large number of light receiving portions 3 are formed separately from each other, a condenser lens 14 is formed on each light receiving portion 3, and the radius of curvature r of the condenser lens 14 is changed to a value corresponding to the incident light on the light receiving portion 3. In the solid-state imaging device selected so that the spot diameter is equal to or less than the opening width W of the light receiving unit 3, the refracted light L ₁ of the oblique light condensing lens 14 when the F value of the camera objective lens is minimized. The angle between the vertical line m and the vertical line m is θ ₁ , the angle between the parallel light converging lens 14 and the refracted light L _{2 on} the vertical line m when the F value is maximized is θ ₂ , Light L ₁
The incident position on the surface of the semiconductor substrate 1 in the same point of incidence of the distance between the incident position of the semiconductor substrate 1 in the refracted light L ₂ d, on the condenser lens 14 of the parallel light and the oblique light When the distance between the surfaces of the semiconductor substrate 1 is h, d = (tan θ ₁ -tan θ ₂ ) · h is satisfied, and when the opening width of the light receiving section 3 is W, d ≦ W is satisfied. I do.

[0012]

According to the configuration of the present invention described above, the parallel light receiving portion 3 when the F-number of the camera objective lens is maximized.
The spot diameter on the light receiving section 3 and the spot diameter on the light receiving section 3 of the oblique light when the F value is minimized
, The oblique light is not blocked by the light-shielding film 11, so that not only parallel light but also oblique light can be efficiently condensed on the light receiving portion 3, and the F value is reduced. As a result, it is possible to improve the F-number dependency of the light-collecting rate, that is, the light-collecting rate of the light-collecting lens 14 decreases. As a result, the improvement in sensitivity, which is the original effect of the condenser lens 14, can be sufficiently exhibited.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a cross-sectional view illustrating a main part of the CCD solid-state imaging device according to the present embodiment.

As shown in FIG. 1, the CCD solid-state imaging device includes an N-type light receiving portion 3, a vertical register 4, and a P-type channel stopper region in a first P-type well region 2 on an N-type silicon substrate 1. 5 are formed. Also, the light receiving unit 3
A P-type positive charge accumulation region 6 is formed on the surface, and a second P-type well region 7 is formed immediately below the vertical register 4.

Further, a transfer electrode 9 of a polycrystalline silicon layer is selectively formed on the first P-type well region 2 via a gate insulating film 8, and an interlayer insulating film 10 is formed on the transfer electrode 9.
An Al light shielding film 11 is formed through the
A flattening film 12 and a color filter layer 13 are sequentially laminated on the entire surface including the substrate 1, and a micro condenser lens 14 is formed on the color filter layer 13 to constitute a CCD solid-state imaging device.

Then, a large number of the light receiving sections 3 are arranged in a matrix to form an image area. The P-type low-concentration region 1 formed between the light receiving unit 3 and the vertical register 4
5 is a read gate. FIG. 2 shows a layout around a light receiving section of the CCD solid-state imaging device.

The Al light-shielding film 11 is selectively etched away on the light receiving portion 3, and light is incident on the light receiving portion 3 through the light receiving portion opening 11a formed by this etching removal. ing.

In this embodiment, the radius of curvature r of the micro condenser lens 14 is optimized, and the height between the micro condenser lens 14 and the light receiving section 3 is reduced.

That is, when the F value of the camera objective lens (not shown) is maximized (when the aperture diameter is minimized), the spot diameter of the parallel light on the light receiving portion 3 is determined by the aperture of the light receiving portion 3. The radius of curvature r of the micro condenser lens 14 is selected so as to be equal to or less than the width W (this is conventionally performed). In this case, it is preferable to set the radius of curvature r of the micro condenser lens 14 so that the parallel light is almost just focused on the light receiving unit 3.

In this embodiment, the refracted light L ₁ (shown by a solid line) of the oblique light in the micro condenser lens 14 when the F value is further minimized (when the aperture diameter is maximized).
Angle of theta ₁ between the vertical line m, the angle between the vertical line m of the refracted light L ₂ (shown in phantom) in the micro-condenser lens 14 of the parallel light in the case of maximizing the F value To θ ₂ ,
The incident position on the surface of the silicon substrate 1 in the refracted light L _1, the refracted light L d the distance between the incident position on the surface of the silicon substrate 1 in the _2, the micro-condenser lens 14 above the parallel light and the oblique light Incident point and silicon substrate 1
When the distance between the surfaces is h, d = (tan θ ₁ -tan θ ₂ ) · h is satisfied, and when the opening width of the light receiving unit 13 is W, d ≦ W (more preferably, d ≦ W / 2) It is configured to satisfy the following.

With this configuration, the spot diameter of the parallel light on the light receiving portion 13 when the F value of the camera objective lens is maximized, and the oblique light reception when the F value is minimized. Since the spot diameter on the portion 13 is equal to or less than the opening width W of the light receiving portion 3, the oblique light is not blocked by the Al light shielding film 11, and not only parallel light but also oblique light is transmitted to the light receiving portion 3. Light can be collected efficiently.

FIG. 3 shows a CCD solid-state image pickup device according to the above-described embodiment (example; indicated by a curve) and a CCD solid-state image pickup device in which only the radius of curvature r of the micro condenser lens 14 is optimized (Comparative Example 1, curve ) And the micro condenser lens 1
4 shows the F-number dependence of each light-collecting rate in a CCD solid-state imaging device (Comparative Example 2; indicated by a curve) in which the curvature radius r is not optimized.

From this figure, it can be seen that the light collection efficiency generally decreases as the F-number decreases, but in the case of the embodiment, the decrease is smaller than in the other comparative examples 1 and 2. . That is, in the case of the example, it is understood that the F-number dependency of the light collection rate is improved.

Therefore, according to the configuration of the above-described embodiment, the sensitivity improvement, which is the original effect of the micro condenser lens 14, can be sufficiently exhibited, and as a result, the effective aperture ratio of the light receiving section 3 can be improved. In addition, miniaturization of the pixel area can be promoted.

In the above embodiment, the micro condenser lens 14
It is important to shorten the distance between the light receiving unit 3 and the light receiving unit 3, but various measures are required to realize this configuration. As one of the ideas, there is a configuration shown below.

That is, as shown in FIG. 4, a plurality of color filters R, G, B formed between the micro condenser lens 14 and the light receiving section 3 are usually provided with a flattening interlayer film (prevention film). 21 and 22, which also function as a dye film, are formed. This is for facilitating the formation of the color filters R, G, and B and improving the uniformity of the filter characteristics in the screen. However, in this case, there is a problem that the thickness of the color filter layer 13 is increased, and the distance between the micro condenser lens 14 and the light receiving unit 3 is unnecessarily long.

Therefore, in this embodiment, as shown in FIG. 5, the total thickness t of the color filter layers is reduced by removing the interlayer films 21 and 22 between the color filters R, G and B. In this way, the distance between the micro condenser lens 14 and the light receiving section 3 can be reduced. 4 and 5, reference numeral 23 denotes a protective layer, and reference numeral 24 denotes a transfer electrode 9 and Al.
2 shows a film including a light shielding film 11.

Next, an example of a method for reducing the total thickness t of the color filter layers by removing the interlayer films 21 and 22 between the color filters R, G and B will be described with reference to FIGS.

First, as shown in FIG. 6A, after a flattening film 12 is formed on the entire surface of the film 24 including the transfer electrode and the Al light-shielding film, gelatin or casein is formed on the flattening film 12.
A photosensitive dyeing material layer 31 made of a mixture with ammonia bichromate or the like is applied.

Thereafter, the first material layer 31 is
A known dyeing method of performing selective exposure corresponding to a color, for example, a green color filter pattern, developing and patterning the same, and immersing the patterned material layer 31 in a green dye solution. Then, a green color filter G is formed as shown in FIG. 6B.

Thereafter, the color filter G is subjected to a fixing process, that is, a tannic acid immersion and a tartaric acid immersion, and thereafter, a process of forming a hardened layer on at least the surface thereof is performed. In this treatment, for example, the color filter G itself is immersed in, for example, an aqueous formaldehyde solution or slaked lime to sufficiently cure and cure at least the surface of the color filter G itself. Then, it heat-drys and performs immersion in tannic acid, immersion in tartaric acid, and washing and drying.

Next, as shown in FIG. 6C, the same material layer 31 as described above is applied to the entire surface including the green color filter G. Thereafter, the dyeing material layer 31 is subjected to selective exposure corresponding to a second color, for example, a red color filter pattern, developed and patterned, and the patterned dyeing material layer 31 is removed. A known dyeing method of immersing in a red dyeing solution is performed to form a red color filter R as shown in FIG. 7A. Thereafter, the same fixing process and curing process as described above are performed on the color filter R.

Next, as shown in FIG. 7B, the same coloring material layer 3 as described above is formed on the entire surface including the two types of color filters R and G.
1 is applied. Thereafter, the dyeing material layer 31 is subjected to selective exposure corresponding to a third color, for example, a blue color filter pattern, developed and patterned, and the patterned dyeing material layer 31 is removed. A known dyeing method of immersion in a blue dyeing solution is performed to form a blue color filter B as shown in FIG. 7C. After that, each color filter R,
A protective layer 32 is formed on the entire surface including G and B. These color filters R, G, B and the protective layer 32 form a color filter layer 13.
Is configured.

In this manner, the first to third colors, that is, green, red and blue color filters R, G, and B are arranged and formed substantially in one plane.

In the above-mentioned manufacturing method, the lower color filters R, G, and B are each subjected to a curing treatment so that at least the surface thereof is cured.
Even if the interlayer films 21 and 22 (see FIG. 4) are not formed thereon, the lower color filter (R or G) is not stained with another color again in the dyeing process of each color.

Further, since the respective color filters R, G, B are arranged and formed substantially in one plane, as shown in FIG.
The formation layer of the color filters R, G, B, that is, the color filter layer 13
Of the micro condenser lens 1 can be reduced.
It is possible to reduce the distance between 4 and the light receiving unit 3.

[0037]

According to the solid-state imaging device of the present invention, it is possible to improve the dependence of the light-collecting rate on the F-number while maximizing the light-collecting rate, and to achieve the sensitivity which is the original effect of the micro light-collecting lens Can be sufficiently exhibited.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a main part of a CCD solid-state imaging device according to an embodiment.

FIG. 2 is a plan view showing a layout of a main part of the CCD solid-state imaging device according to the embodiment.

FIG. 3 is a characteristic diagram showing the F-number dependence of the light collection rate in a micro light collection lens.

FIG. 4 is an explanatory diagram (normal example) showing a state of forming a color filter according to the embodiment.

FIG. 5 is an explanatory diagram (present example) illustrating a state of forming a color filter according to the present example.

FIG. 6 is a process chart (1) showing a method of forming a color filter layer according to the present embodiment.

FIG. 7 is a process diagram (part 2) illustrating the method for forming the color filter layer according to the present embodiment.

FIG. 8 is a sectional view showing a main part of a CCD solid-state imaging device according to a conventional example.

FIG. 9 is an explanatory diagram showing a light incident mode according to an F value of a camera objective lens.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon substrate 2 first P-type well region 3 light-receiving section 4 vertical register 5 channel stopper region 6 positive charge accumulation region 7 second P-type well region 8 gate insulating film 9 transfer electrode 10 interlayer film 11 Al light-shielding film 12 Flattening film 13 Color filter layer 14 Micro condenser lens 15 Read gate

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 27/14-27/148 H04N 5/335

Claims (2)

(57) [Claims] 1. A semiconductor substrate having a plurality of light receiving portions formed separately from each other, a condenser lens formed on each light receiving portion, and a radius of curvature of each of the condenser lenses being different from that of the incident light on the light receiving portion. the spot diameter in the selected solid-state imaging device to be equal to or less than the opening width of the light receiving portion, the oblique light in the case where the F value of the objective lens for the camera to minimize the refracted light L ₁ in the condenser lens ₁ the angle between the vertical line theta, the angle of theta ₂ between the vertical line of the refracted light L ₂ in parallel light of the condenser lens in the case of maximizing the F value, the in the refracted light L ₁ and the incident position on the semiconductor substrate surface, the same point of incidence of the distance between the incident position in the semiconductor substrate surface in the refracted light L ₂ d, on the condensing lens of the parallel light and the oblique light and the semiconductor When the distance between the substrate surfaces is h, d = (tan _{1 -tanθ 2)} · h satisfied, and when the opening width of the light receiving portion and is W, the solid-state imaging device which satisfies the d ≦ W. 2. The solid-state imaging device according to claim 1, wherein when a color filter is provided between each of said light receiving sections and said corresponding condensing lens, no interlayer film is formed between said color filters. .