JP4281132B2 - Solid-state image sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solid-state imaging device having a concave lens structure formed therein, for example.
[0002]
[Prior art]
In recent years, in color solid-state imaging devices, with the miniaturization of the device, a color filter is formed in the device, and a so-called on-chip lens structure in which a microlens is further formed on the color filter is employed. The sensitivity of the sensor (light receiving unit) is improved by condensing the light with the microlens.
[0003]
[Problems to be solved by the invention]
In some solid-state imaging devices having the above-described on-chip lens structure, a second lens structure having a condensing characteristic is further provided between the surface microlens and the light receiving unit.
Examples of the second lens structure include a concave lens structure in which a boundary surface between two layers having different refractive indexes is a concave surface and a concave lens is formed here.
[0004]
FIG. 7 shows a schematic diagram of an example of a solid-state imaging device in which a concave lens structure is formed between the surface layer and the light receiving unit.
In the solid-state imaging device 50, a sensor (light receiving unit) 52 is formed in a semiconductor substrate 51, and a transfer electrode 54 is formed on the semiconductor substrate 51 other than the light receiving unit 52 via an insulating film 53. A light shielding film 56 is formed on the transfer electrode 54 via an interlayer insulating film 55, and the light shielding film 56 prevents light from entering the transfer electrode 54. The light shielding film 56 is provided with an opening on the light receiving portion 52 so that light enters the light receiving portion 52.
Then, for example, a BPSG (boron phosphorus silicate glass) film 57 is formed so as to cover the light shielding film 56, and the BPSG film 57 has irregularities on the surface corresponding to the level difference due to the light shielding film 56, and is a part on the light receiving portion 52. Is a recess.
[0005]
On the BPSG film 57, a high refractive index layer 58 made of, for example, a SiN film (refractive index n = 1.9 to 2.0) is formed, and a concave lens structure (so-called intralayer lens) is formed here.
[0006]
The upper surface of the high refractive index layer 58 is flattened, and a color filter 60 is formed via a passivation film 59. Further, a microlens 61 is formed on the color filter 60.
[0007]
In this case, the refractive index of the BPSG film 57 and the high refractive index layer 58 so that the light incident on the concave lens surface, that is, the boundary surface between the two layers of the BPSG film 57 and the high refractive index layer 58 is collected on the light receiving unit 52. It is necessary to adjust the relationship.
In general, considering a concave lens, in order to collect light on the light receiving portion 52, the refractive index of the upper high refractive index layer 58 is higher than the refractive index of the underlying BPSG film 57 with the lens surface as a boundary. The rate is adjusted to be larger.
[0008]
However, when light is incident on the concave lens surface from an oblique direction, depending on the incident angle, the light may be incident on the concave lens surface at a large angle, which is not the case with a structure that does not form a concave lens structure.
For this reason, depending on the incident angle, it can be predicted that light is totally reflected on the surface of the concave lens, which may result in insufficient improvement in sensitivity.
[0009]
In order to solve the above-described problems, the present invention provides a solid-state imaging device having high sensitivity by guiding incident light to be widely incident on a light receiving unit.
[0010]
[Means for Solving the Problems]
Solid-state imaging device of the invention, the layer having a concave structure between the outermost surface layer is formed from the sensor opening, grooves are dug structure in the bottom portion is provided in the concave structure, within this groove dug structure In addition, a high refractive index material layer constituting the concave lens structure is formed.
[0011]
According to the above-described configuration of the solid-state imaging device of the present invention, the structure in which the groove is dug in the bottom of the concave lens structure is provided, so that light entering the bottom of the concave lens structure at a large incident angle is not totally reflected and the groove is formed. Since it is guided to the sensor opening by the excavated structure , the amount of light received by the sensor can be increased .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a layer having a concave lens structure is provided between the sensor opening and the outermost surface layer, and a grooved structure is provided at the bottom of the concave lens structure. Is a solid-state image sensor formed by forming a high refractive index material layer .
[0018]
The present invention, in a solid-state imaging device, including a groove is dug structure, passivated film on the surface of the interlayer insulating layer formed under the concave lens structure is formed, constitutes a concave structure on the passivation film The high refractive index material layer is formed .
[0019]
The present invention, in a solid-state imaging device, a higher refractive index material layer is a structure made of a resin.
According to the present invention, in the solid-state imaging device, the passivation film is a SiN film.
According to the present invention, in the solid-state imaging device, an etching stopper film is formed so as to face the bottom of the grooved structure.
[0021]
A solid-state imaging device 20 shown in FIG. 1 is a cross-sectional view of an element corresponding to one pixel of an embodiment of the solid-state imaging device of the present invention.
[0022]
In this solid-state imaging device 20, a sensor (light receiving unit) 2 is formed in a semiconductor substrate 1, and a transfer electrode 4 is formed on the semiconductor substrate 1 other than the light receiving unit 2 through an insulating film 3. A light shielding film 6 is formed on the transfer electrode 4 via an interlayer insulating film 5, and this light shielding film 6 prevents light from entering the transfer electrode 4. The light shielding film 6 is provided with an opening on the light receiving portion 2 so that light enters the light receiving portion 2.
Further, similarly to the example shown in FIG. 7 described above, for example, BPSG (refractive index n = 1.4 to 1.5) or the like that covers the light shielding film 6 and has irregularities on the surface corresponding to the steps due to the light shielding film 6. An interlayer insulating layer 7 made of is formed.
[0023]
In the present embodiment, a well-like digging structure 21 is formed on the light receiving portion 5 of the interlayer insulating layer 7 made of BPSG or the like.
The peripheral portion of the well-shaped digging structure 21 has a concave lens structure (so-called intra-layer lens) as in the example shown in FIG. That is, a well-shaped digging structure 21 is formed at the bottom of the center of the inner lens.
On the interlayer insulating layer 7, a high refractive index layer 8 made of, for example, a SiN film (refractive index n = 1.9 to 2.0) or the like is formed, and light is refracted at the interface between these two layers 7 or 8. Total reflection.
Also in this case, in order to collect light on the light receiving portion 2, the refractive index of the upper high refractive index layer 8 is adjusted to be larger than the refractive index of the interlayer insulating layer film 7.
[0024]
Furthermore, in the present embodiment, the etching stopper film 12 is formed at a position facing the bottom of the well-shaped digging structure 21 on the sensor 2.
[0025]
The etching stopper film 12 is formed of a material that can have an etching selectivity with respect to the interlayer insulating layer 7, and has a depth at which the etching is stopped when the well-shaped digging structure 21 is formed in the interlayer insulating layer 7. Keep it constant.
As a result, the depth h (see FIG. 2) of the well-shaped digging structure (hereinafter referred to as well structure) 21 is regulated to a certain depth.
[0026]
When the interlayer insulating layer 7 is formed by, for example, BPSG as described above, the etching stopper film 12 is formed by, for example, SiN, so that the etching selectivity is sufficient, and the etching can be stopped here.
Furthermore, the surface of the sensor 2 is not damaged during etching.
[0027]
Further, when the etching stopper film 12 is formed of a material having a low reflectance with respect to incident light such as SiN, the etching stopper film 12 can have a function as a low reflection film.
[0028]
Thereafter, similarly to the above-described example, the upper surface of the high refractive index layer 8 is flattened, and the color filter 10 is formed via the passivation film 9. Further, a microlens 11 is formed on the color filter 10.
[0029]
The depth h of the well-like digging structure 21 is desirably dug deeply until the distance from the insulating film 3 below the well structure 21 is about several hundred nm or less. Accordingly, the film thickness of the etching stopper film 12 is preferably about several hundred nm or less.
[0030]
Further, in order to make the incident angle of light entering the well structure 21 as large as possible with respect to the side wall 21a of the well structure 21, as shown in FIG. 2, the aspect ratio of the well structure 21, that is, the well structure 21 It is necessary to increase the ratio h / d between the depth h and the width d in the substrate surface direction as much as possible.
Accordingly, at this time, the width d in the substrate surface direction of the well structure 21 is desirably smaller than the opening width w of the light shielding film 6 on the light receiving portion 2.
[0031]
When the well structure 21 is formed with a high aspect ratio h / d as described above, the incident angle of light incident on the well structure 21 is higher than the side wall 21a of the well structure 21 because the aspect ratio h / d is high. It becomes easy to cause total reflection.
[0032]
Further, once total reflection occurs at the side wall 21a of the well structure 21, the refractive index of the material of the two layers 7 and 8 constituting the well structure 21 and the aspect ratio h / d of the well structure 21 are taken into consideration. 2, it is considered that the total reflection is repeated until the incident light L that has undergone total reflection at the side wall 21 a reaches the bottom 21 b of the well structure 21. That is, a kind of waveguide can be formed by the well structure 21.
Then, by forming the well structure 21 by digging it up to the vicinity of the light receiving portion 2, it is possible to guide the light incident into the well structure 21 to the light receiving portion 2 without leaking as much as possible.
[0033]
Further, the increase in the total reflection component described above reduces the rate of transmission through the interlayer insulating layer 7 and incident on the light shielding film 6.
Therefore, it is possible to suppress a decrease in sensitivity due to reflection of light incident on the light shielding film 6.
[0034]
In general, the intralayer lens has a function of guiding incident light L ₂ that is originally incident on the light shielding film 56 onto the light receiving portion 52, as shown in FIG. is there.
[0035]
As shown in FIG. 3, the well structure 21 in the above-described embodiment can also guide the incident light L ₂ incident on the light shielding film 6 to the light receiving unit 2, and does not impair the effect of the above-described intralayer lens. .
[0036]
On the other hand, in FIG. 8, in the intralayer lens, there is the light L ₃ that is not incident on the sensor due to total reflection on the concave surface of the lens, but according to the above-described embodiment, the entrance of the well structure 21 is present there. For this reason, the incident light L ₃ is not totally reflected and enters the well structure 21. Therefore, the amount of light incident on the light receiving portion is increased as compared with the in-layer lens structure, and the sensitivity of the solid-state imaging device is improved. Is planned.
[0037]
In order to further increase the sensitivity, if a reflective film such as Al or W is formed on the side wall of the well structure 21, the sensitivity can be increased by eliminating a component that transmits the side wall. Such a reflective film can be formed, for example, by leaving the reflective film as a thin film on the entire surface and then performing anisotropic etching to leave only the sidewall of the well structure.
[0038]
The well structure 21 described above can be formed as follows.
First, each region (not shown) such as the light receiving portion 2, the charge transfer portion, and the channel stop region is formed inside the semiconductor substrate 1 by a conventionally known method, and the gate insulating film 3 on the surface of the semiconductor substrate 1, A transfer electrode 4, an interlayer insulating film 5, and a light shielding film 6 are sequentially formed thereon, and then an opening is formed in a corresponding portion of the light shielding film 6 on the light receiving portion 2.
[0039]
Next, an etching stopper film 12 such as a SiN film is formed in the opening portion of the light shielding film 6 on the light receiving portion 2.
[0040]
Subsequently, an interlayer insulating layer 7 such as a BPSG film (refractive index n = 1.4 to 1.5) is deposited on the entire surface so as to cover the light shielding film 6 and the etching stopper film 12.
Thereafter, the interlayer insulating layer 7 is reflowed, for example, by heat treatment, thereby forming an in-layer lens shape having irregularities corresponding to the steps due to the light shielding film 6 and having concave portions formed on the light receiving portion 2.
[0041]
In the structure shown in FIG. 7, immediately after this, a material having a refractive index higher than that of the interlayer insulating layer 7, such as a silicon nitride film, is formed in order to obtain lens characteristics.
On the other hand, in this embodiment, the interlayer insulating layer 7 is patterned here, and the anisotropic etching is performed on the portion of the concave and convex portions of the interlayer insulating layer 7 that has been reflowed, where the concave portion has the lowest height. Thus, a well structure 21 having a bottom facing the etching stopper film 12 is formed by digging vertically until reaching the etching stopper film 12 previously formed.
[0042]
Next, the well structure 21 is filled, and the high refractive index layer 8 is formed on the interlayer insulating layer 7 to form a concave lens structure of an in-layer lens.
Thereafter, the surface of the high refractive index layer 8 is flattened, and the color filter 10 is formed via the passivation film 9.
Further, a layer made of the material of the microlens 11 is formed on the color filter 10 and reflowed to adjust the lens shape of the microlens 11.
In this way, the structure of the solid-state imaging device 20 shown in FIG. 1 can be formed.
[0043]
Next, FIG. 4 shows a cross-sectional view of an element corresponding to one pixel of another embodiment of the solid-state imaging element of the present invention.
In this solid-state imaging device 30, in particular, the passivation film 9 is formed on the surface of the interlayer insulating layer 7 including the inside of the well structure 21, and the high refractive index layer 8 is formed on the passivation film 9.
A color filter 10 is formed directly on the high refractive index layer 8.
[0044]
For the high refractive index layer 8 constituting the in-layer convex lens structure, for example, a heat-melting transparent resin such as a polyimide resin can be used in addition to the SiN mentioned in the previous embodiment.
[0045]
When the high refractive index layer 8 is formed of such a heat-meltable transparent resin, the high refractive index layer 8 can be formed by a coating method such as spin coating.
Further, by forming by spin coating, the surface of the high refractive index layer 8 can be easily flattened simultaneously. Therefore, the color filter 10 can be formed directly on the high refractive index layer 8.
[0046]
Further, when the interlayer insulating layer 7 is formed of, for example, BPSG as described above, it is difficult to form such a resin directly on the interlayer insulating layer 7.
Therefore, for example, a passivation film 9 made of SiN made of plasma is formed on the interlayer insulating layer 7 including the inside of the well structure 21, and a high refractive index layer 8 made of resin is formed thereon.
By forming the high refractive index layer 8 made of resin through the passivation film 9 in this manner, the high refractive index layer 8 can be easily formed in a good film formation state.
[0047]
The other configuration is the same as that of the solid-state imaging device 20 of the embodiment shown in FIG.
[0048]
In the solid-state imaging devices 20 and 30 of the above-described embodiments, the uniformity of anisotropic etching of the interlayer insulating layer is improved by adopting a configuration in which the etching stopper film 12 facing the bottom of the well structure 21 is formed. The reproducibility of the depth of the well structure 21 can be improved.
Therefore, the depth h of the well structure 21 can be made uniform with no variation at each pixel or each position in the semiconductor wafer, and as a result, the solid-state imaging devices 20 and 30 having good characteristics can be obtained.
[0049]
On the other hand, even if there is a slight variation in the depth of the well structure 21 at each pixel or at a position in the semiconductor wafer, the entire solid-state imaging device is required to have an effect on various characteristics of the solid-state imaging device caused by this variation. However, the depth of the well structure 21 does not necessarily have to be uniform.
In this case, the etching stopper film 12 can be omitted.
[0050]
The configuration of the solid-state imaging device in this case is shown in FIG.
As shown in FIG. 5, in this solid-state imaging device 41, the interlayer insulating layer 7 remains between the bottom of the well structure 21 and the insulating film 3.
[0051]
The characteristics of each pixel of the solid-state image sensor are affected by the thickness of the interlayer insulating layer 7.
Preferably, the well structure 21 is formed by performing anisotropic etching so that the thickness of the interlayer insulating layer 7 remaining between the bottom of the well structure 21 and the insulating film 3 is about 100 nm or less.
[0052]
Further, in contrast to the configuration of FIG. 5 in which the etching stopper film 12 is omitted, a solid-state imaging device 42 having a configuration in which a passivation film 9 is formed on the surface of the interlayer insulating layer 7 as in the embodiment shown in FIG. Shown in
Also in this case, like the solid-state imaging device 30 shown in FIG. 4, the high refractive index layer 8 made of resin can be formed in a favorable film formation state through the passivation film 9.
[0053]
In the configuration of FIG. 6, the well structure 21 is formed so as to reach the insulating film 3 on the sensor 2 substantially. By using the above-described plasma SiN film as the passivation film 9 with such a configuration, the passivation film 9 can also function as a low reflection film.
[0054]
The solid-state imaging device and the manufacturing method thereof according to the present invention are not limited to the above-described embodiments, and various other configurations can be taken without departing from the gist of the present invention.
[0055]
【The invention's effect】
According to the above-described solid-state imaging device according to the present invention, in the solid-state imaging device provided with the concave lens structure on the sensor opening, the well-shaped digging structure is provided at the bottom of the concave lens, thereby preventing total reflection at the bottom of the concave lens, Since the light incident on the bottom can be guided to the light receiving unit, the amount of received light can be increased, and the sensitivity can be improved.
[0057]
Further, according to the present invention described above, an interlayer insulating layer is formed by forming a passivation film on the surface of the interlayer insulating layer and forming a high refractive index material layer thereon including the inside of the well-like digging structure. A high refractive index material layer can be formed on the film in a favorable film formation state.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram (a cross-sectional view of one pixel) of an embodiment of a solid-state imaging device according to the present invention.
FIG. 2 is a diagram for explaining a well structure in FIG. 1;
3 is a diagram illustrating a propagation path of incident light in the solid-state imaging device of FIG. 1;
FIG. 4 is a schematic configuration diagram (cross-sectional view of one pixel) of another embodiment of a solid-state imaging device according to the present invention.
FIG. 5 is a schematic configuration diagram (cross-sectional view of one pixel) of a solid-state imaging device having a configuration in which an etching stopper film is omitted.
FIG. 6 is a schematic configuration diagram (cross-sectional view of one pixel) of another solid-state imaging device having a configuration in which an etching stopper film is omitted.
FIG. 7 is a schematic configuration diagram (a cross-sectional view of one pixel) of an example of a solid-state imaging device in which an in-layer lens is formed.
8 is a diagram illustrating a propagation path of incident light in the solid-state imaging device of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 Light-receiving part (sensor), 3 Insulating film, 4 Transfer electrode, 5 Interlayer insulating film, 6 Light shielding film, 7 Interlayer insulating layer, 8 High refractive index layer, 9 Passivation film, 10 Color filter, 11 Micro lens , 12 Etching stopper film, 20, 30, 41, 42 Solid-state imaging device, 21 Well structure, 50 Solid-state imaging device, 51 Semiconductor substrate, 52 Light receiving portion (sensor), 53 Insulating film, 54 Transfer electrode, 55 Interlayer insulating film, 56 light shielding film, 57 BPSG film, 58 high refractive index layer, 59 passivation film, 60 color filter, 61 microlens, L, L ₁ , L ₂ , L ₃ incident light, d well structure width, h well structure high , W Width of the light shielding film opening

Claims (5)

In a solid-state imaging device provided with a layer having a concave lens structure between the sensor opening and the outermost surface layer,
A structure in which a groove is dug in the bottom of the concave lens structure is provided,
A solid-state imaging device comprising a high refractive index material layer that forms the concave lens structure including the inside of the structure in which the groove is dug . A passivation film is formed on the surface of the interlayer insulating layer formed under the concave lens structure including the structure in which the groove is dug, and a high refractive index material layer constituting the concave lens structure is formed on the passivation film. The solid-state imaging device according to claim 1. The solid-state imaging device according to claim 2 , wherein the high refractive index material layer is made of a resin. The solid-state imaging device according to claim 2, wherein the passivation film is a SiN film. The solid-state imaging device according to claim 1, wherein an etching stopper film is formed facing the bottom of the structure in which the groove is dug.

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