JPH06224398A - Slid-state image sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a solid-state image sensor, in which crosstalk is reduced the sensitivity and image quality are improved with the aperture open. CONSTITUTION:A solid-state image sensor comprises a transfer electrode 103, a photoelectric member 102 adjacent to the transfer electrode, and a cap layer 108 (optical path). Between the transfer electrode and the cap layer is provided a low-refraction layer 107 whose refractive index is lower than that of the cap layer 108. The low-refraction layer 107 may be formed of air or inactive gas, such as nitrogen, or a resin having a lower refractive index than the cap layer. To reflect incident light 111 or oblique light 112 sufficiently, the layer 107 preferably has a surface roughness smaller than one fourth of the wavelength of the incident light or oblique light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor,
In particular, the present invention relates to high sensitivity and high image quality of a solid-state image sensor.

[0002]

2. Description of the Related Art Recent solid-state image pickup devices have dramatically improved sensitivity due to the benefit of microlenses. Conventionally, the design of the optical system of the microlens has been performed by so-called paraxial optics with the standard diaphragm of the camera lens in mind. Hereinafter, a conventional solid-state image sensor will be described with reference to FIGS.

FIG. 7A shows a sectional view of a unit pixel of a conventional solid-state image pickup device. That is, here, 701 is a semiconductor substrate, 702 is a photoelectric conversion unit, 703 is a transfer electrode for transferring signal charges, 704 is an insulating film, 705 is a light-shielding film, 706 is a protective film, and 709 is a microlens support layer. A transparent resin layer 710 is a microlens. In FIG. 7A, reference numeral 711 is parallel light that is incident on the solid-state image sensor, forms an image on the photoelectric conversion unit 702, and is converted into signal charges by the photoelectric conversion unit. Also, 712a
Is obliquely incident light that is incident on the solid-state imaging device and does not enter the photoelectric conversion unit 702, and therefore does not contribute much to the signal charge, but rather causes smear. Therefore,
There is also a solid-state image sensor in which the electrode side surface of the transfer electrode 703 is covered with a light shielding film 705 in order to eliminate the above-mentioned smearing cause.

Further, with the recent progress of microfabrication and miniaturization and high resolution of optical systems, high integration of solid-state image pickup devices has been advanced. FIG. 7B shows a cross-sectional view of a unit pixel of a conventional solid-state imaging device that is more highly integrated. Here, each symbol in FIG. 7B has the same meaning as each symbol in FIG. 7A. However, the obliquely incident light 712b not only causes smear, but also acts as light penetrating into adjacent pixels. In the above-mentioned solid-state image pickup device, the reduction in the horizontal direction has progressed considerably with the increase in the degree of integration, but the reduction in the vertical direction has not achieved the progress commensurate with the scaling in the horizontal direction. This is because the thin film material forming the solid-state imaging device has no improvement in proportion to scaling, and problems such as the breakdown voltage of the insulating film and the resistance of the electrode have not been solved. As a result, as the degree of integration increases, the aspect ratio of the photoelectric conversion section of the solid-state image pickup device has increased.

[0005]

By the way, in the movie camera using the solid-state image pickup element, the use of the movie camera is diversified, and the field of low illuminance is used as a selling point with high sensitivity. Since it has been expanded to general-purpose movie cameras, the frequency of using the camera lens of movie cameras with an open aperture, or using a wide-angle lens with an open aperture as a camera lens like a surveillance camera has increased. Therefore, nowadays, when designing an optical system, it is unavoidable to consider oblique incident light, which has not been necessary in the past. That is, FIG.
As shown in (a), there is a problem that the ratio of the obliquely incident light 712a incident on the photoelectric conversion unit 702 is reduced, and the sensitivity is reduced when the aperture is widened or when the wide-angle lens is used.

Further, as the integration progresses, the aspect ratio of the solid-state imaging device becomes higher, and as shown in FIG. 7B, the ratio of the oblique incident light 712b incident on the photoelectric conversion unit 702 decreases. However, there is a problem that the sensitivity is lowered. Regarding the problem that the aspect ratio becomes high, it is conceivable that the microlens has a long focal point and the microlens is accompanied by the expansion of the distance between photoelectric conversion units.
When the distance is expanded, as shown in FIG. 7B,
The proportion of the obliquely incident light 712b incident on the adjacent pixel increases, and a so-called crosstalk phenomenon occurs. as a result,
There was a problem such as resolution deterioration and image quality deterioration.

The present invention aims to solve the above-mentioned conventional problems.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a transfer electrode,
In a solid-state imaging device having a photoelectric conversion unit adjacent to the transfer electrode and an optical path forming unit above the photoelectric conversion unit, a refractive index lower than that of the optical path forming unit is provided between the transfer electrode and the optical path forming unit. It is characterized in that a rate region layer is provided.

The present invention is also characterized in that, in the above solid-state image pickup device, the low refractive index region layer is a resin layer.

Further, in the present invention, in the method for manufacturing a solid-state image pickup device in which the low refractive index region layer is a resin layer, a step of forming the resin layer above the photoelectric conversion section, and a step of forming the photoelectric conversion section A step of removing a part of the upper resin layer,
And a step of deforming the resin layer by heat melting.

The present invention is also characterized in that, in the solid-state image pickup device, the low refractive index region layer is a gas layer.

In the method for manufacturing a solid-state image pickup device in which the low refractive index region layer is a gas layer, the present invention further comprises the step of forming a water-soluble resin layer above the photoelectric conversion section, and the photoelectric conversion section. A step of removing a part of the water-soluble resin layer above, and a step of applying a material to be an optical path forming section so as to cover the water-soluble resin layer, and above the photoelectric conversion section, The method is characterized by including a step of processing the optical path forming portion into a desired pattern to expose the water-soluble resin layer, and a step of removing the water-soluble resin layer.

Further, according to the present invention, a solid-state image pickup device having a plurality of pixels formed of a photoelectric conversion part formed on a semiconductor substrate and a resin layer formed on the semiconductor substrate having the plurality of pixels formed thereon. In the above method, a groove is provided in the resin layer in a portion corresponding to the pixel, and as a method of manufacturing the groove, the resin layer is formed of the first resin layer and the first resin layer. A step of forming a second resin layer having an etching rate lower than that of the first resin layer at the time of forming the groove, and a desired region of the first resin layer and the second resin layer Is removed by dry etching to form the groove.

[0014]

According to the present invention, the light incident on the side surface of the transfer electrode is
Alternatively, the light that enters the adjacent pixels can be made to enter the original photoelectric conversion portion by total reflection, and the sensitivity, resolution, and image quality can be improved.

[0015]

EXAMPLES The present invention will be described in detail below based on examples.

First, a first embodiment of the present invention will be described. FIG. 1 shows a horizontal sectional view of a unit pixel in the first embodiment. That is, here, 101 is a semiconductor substrate, 102 is a photoelectric conversion unit, 103 is a transfer electrode for transferring a signal charge, 104 is an insulating film, 105 is a light shielding film,
106 is a protective film, 107 is a low refractive index layer, 108 is a cap layer made of resin, 109 is a resin layer which is a microlens supporting layer, and 110 is a microlens. Here, the low refractive index layer 107 may be a hollow layer made of air or an inert gas such as nitrogen, or the cap layer 108.
A resin layer having a lower refractive index may be used. Low refractive index layer 107
In order to sufficiently reflect the incident light or the oblique incident light, it is desirable that the surface roughness be about 1/4 or less of the wavelength of the incident light or the oblique incident light. It has flatness. The shape of the low refractive index layer 107 depends on the material and the manufacturing method, but it is preferable that the low refractive index layer 107 has a shape perpendicular to the semiconductor substrate 101, but it may have a slight inclination. Since the cap layer 108 needs to maintain optical continuity, it preferably has a refractive index almost the same as that of the resin layer 109, and the refractive index is usually about 1.6.

Here, the path of the light beam in this embodiment will be described. Reference numeral 111 denotes parallel light that is incident on the solid-state image sensor, forms an image on the photoelectric conversion unit 102, and is converted into signal charges by the photoelectric conversion unit. On the other hand, 112 is oblique incident light incident on the solid-state imaging device, and θ is an angle between the oblique incident light 112 and a surface normal at the interface between the low refractive index layer 107 and the cap layer 108, The incident angle is shown.
The critical angle is θc, and the total reflection condition is expressed as sin θc = (refractive index of low refractive index layer 107) / (refractive index of cap layer 108). For example, the refractive index of the cap layer 108 is 1.6. When the low refractive index layer 107 is formed of air having a refractive index of 1.0, the critical angle is about 39 °, and the low refractive index layer 107 is formed of a resin having a refractive index of 1.3. In that case, the critical angle is about 54 °. Therefore,
The oblique incident light 112 incident at the critical angle or more is reflected at the interface between the low refractive index layer 107 and the cap layer 108, enters the photoelectric conversion unit 102, and contributes to photoelectric conversion. That is,
In the related art, obliquely incident light that does not contribute to photoelectric conversion can be incident on the photoelectric conversion unit by utilizing total reflection, and as a result, the sensitivity, resolution, and image quality of the solid-state image sensor can be improved.

A method of manufacturing the above solid-state image pickup device will be described below with reference to FIGS.

FIG. 2A is a diagram showing an initial manufacturing process according to this embodiment. That is, on the semiconductor substrate 201, a photoelectric conversion unit 202, a structure 203 such as an electrode of an underlying black and white device, a water-soluble polymer layer 204 formed by coating, and a window above the photoelectric conversion unit 202 were opened. A resist layer 205 is formed.

Here, as the water-soluble polymer layer 204,
Polyvinyl alcohol, polyvinyl pyrrolidone, or polymeric pullulan that is a natural polysaccharide can be used.

A problem in the above step is that the water-soluble polymer layer 204 dissolves in the resist developing solution during the development of the resist. The four methods for solving the above problems will be described in detail below.

The first method is to open a window of the resist layer 205 as a plasma developing resist, that is, as a negative image without performing wet development. As is well known, the combination of a polymer having a photosensitive radical-generating group and a silicon compound having a vinyl group,
It becomes a dry phenomenon negative resist. Oxygen plasma 206
Gives a negative image as shown in Figure 2 (a),
The water-soluble polymer layer 204 can be continuously etched. Since the structure 203 usually includes a light-shielding film having high reflectance, in this method, an antireflection dye is mixed in the water-soluble polymer layer itself in order to prevent diffused reflection in the photo process. It is better to keep it.

In the second method, after the water-soluble polymer layer 204 is formed, it is treated with fluorine-based plasma or the like to form fluorocarbon on the surface of the polymer layer to make the surface hydrophobic. In this case, a positive resist can be used for the resist layer 205, and the altered surface can be easily removed by oxygen plasma.

In the third method, after the water-soluble polymer layer 204 is formed, its surface is made insoluble in a resist developing solution as in the second method. That is, after the water-soluble polymer layer 204 is formed, the surface thereof is made of a hydrophobic material such as a fluororesin, and a thin film layer of about several tens nm is formed by a dipping method or the like. The subsequent manufacturing process is similar to that of the second method, but it is better to treat the surface of the water-soluble polymer layer 204 with a surfactant or the like before forming the resist layer 205 in order to improve the adhesiveness of the resist. good.

In the fourth method, a positive resist is applied on the water-soluble polymer layer 204, the exposure amount during photo is controlled, and after development, a thin film of about 100 nm is not formed on the surface of the water-soluble polymer layer 204. It is left as an exposed portion so that the water-soluble polymer layer 204 is not dissolved.
Then, the unexposed portion is removed by oxygen plasma or the like. Of the four methods described above, one of the methods shown in FIG.
As shown in (a), after removing the resist layer above the photoelectric conversion unit 202, the water-soluble polymer layer 204 is removed using the resist layer 205 as a mask. In this embodiment, the photoelectric conversion unit 202 is directly below the water-soluble polymer layer, but as shown in FIG. 1, it may have a protective film or an insulating film. Since the water-soluble polymer layer formed by the above method needs to have a film thickness that fulfills an optical function, it needs to have a film thickness of at least about 100 nm or more.

FIG. 2B is a diagram showing a cap layer forming process according to this embodiment. That is, a resin layer 207 which is a material to be a cap layer is applied, the pixel portion is flattened, and then a resist layer 208 for forming a cap layer is formed for each pixel by a photo technique. It should be noted in this step that the water-soluble polymer layer 204 has a high possibility that the polymer is cross-linked when it is baked at a high temperature and the water solubility is deteriorated.
The point that baking at the time of application of 07 is necessary to be performed at a temperature as low as possible. Therefore, when the material of the resin layer 207 is a thermosetting resin, a resin whose crosslinking start temperature is lowered as much as possible is used, or a photocurable resin (after the cap layer is formed, the resin layer 207 is completely finished). It is possible to bake at a temperature sufficient to effect cross-linking) and to cure by photo-crosslinking instead of baking. Oxygen plasma 209
Thus, the resin layer 207 is removed by dry etching to expose the water-soluble polymer layer 204.

FIG. 2C is a diagram showing a hollow region forming step according to this embodiment. That is, when the resist is removed by the resist developing solution after the dry etching, the water-soluble polymer layer is completely dissolved and the hollow region 211 is formed between the cap layer 210 and the structure 203.

FIG. 2D is a diagram showing a microlens support layer forming step according to this embodiment. That is, after forming the hollow region 211, a resin layer 212 to be a microlens supporting layer is applied and formed. When the resin layer 211 is applied, the application is performed in an atmosphere of an inert gas such as nitrogen and the hollow region 211 is filled with the above gas. Further, as the material of the resin layer 212, a material having a viscosity increased to about 100 CP is suitable so as not to excessively penetrate into the hollow region 211 during application.

Hereinafter, in the solid-state image pickup device according to the first embodiment, a manufacturing method for forming the low refractive index layer with resin will be described with reference to FIGS.

FIG. 3A shows a cross section of an initial manufacturing process according to this embodiment, which has the same structure as that of FIG. 2A. That is, the photoelectric conversion unit 30 is formed on the semiconductor substrate 301.
2, a structure 303 such as an electrode of an underlying black and white device, a low-refractive index resin layer 304 formed by coating, and a resist layer 305 having a window above the photoelectric conversion section 302 formed therein. As a material of the low refractive index resin layer 304, an antireflection film resin for preventing a line width change after development due to multiple reflection in a resist film in a photo process is preferable, and for example, perfluoroalkylpolyether (refractive index 1.29) is used. ) A
Z aquator (AZ is a registered trademark of Hoechst: refractive index 1.41) CYTOP (Cytop is a registered trademark of Asahi Glass Co., Ltd .: refractive index 1.34). Oxygen plasma 30
6, the low-refractive-index resin layer 30 above the photoelectric conversion unit 302
4 is etched and removed.

FIG. 3B is a diagram showing the shape after the etching and after the resist is peeled off. After forming as shown in FIG. 3B, by etching the low-refractive index resin layer 304, steps and damages generated on the surface of the photoelectric conversion portion 302 are alleviated, and an ideal shape for total reflection is formed. In order to obtain it, the low refractive index resin layer 304 is reflowed by high temperature baking. An amorphous fluororesin having a relatively low glass transition point such as CYTOP can be melted within a temperature range that does not adversely affect the underlying element. The low refractive index resin layer needs to have a film thickness of at least about 100 nm or more, as shown in the description of FIG.

FIG. 3C is a diagram showing the state after the microlens support layer is formed in this manufacturing process. That is, the resin layer 30 that will become the microlens support layer after the reflow treatment.
7 is applied and the upper part of the photoelectric conversion unit 302 is planarized and formed. Although the low-refractive-index resin layer above the photoelectric conversion part is removed in this manufacturing process, the removal process of the low-refractive-index resin layer may be omitted. Further, the photoelectric conversion portion is directly below the low refractive index resin layer, but as shown in the description of FIG.
There may be a protective film or an insulating film.

Next, a second embodiment of the present invention will be described. FIG. 4 shows a horizontal sectional view of a unit pixel in the second embodiment. That is, here, 401 is a semiconductor substrate, 402 is a photoelectric conversion unit, 403 is a transfer electrode for transferring signal charges, 404 is an insulating film, 405 is a light-shielding film, 4
Reference numeral 06 is a protective film, 407 is a groove, 408 is a flattening layer for filling a step in a pixel portion, 409 is a resin layer which is a microlens supporting layer, 410 is a microlens, and 413 is a color filter layer. Color filter layer 413
Is necessary in the case of a color solid-state image sensor, and unlike the conventional case, the filters are formed without overlapping the filters of adjacent pixels. In this embodiment, the groove 407 penetrates the flattening layer 408 and the resin layer 409, and when viewed from the top surface of the element, the pixel shape is vertical or horizontal, one pixel row at a time, or one pixel at a time in a grid pattern. Are arranged in. Furthermore, the grooves are usually filled with air or an inert gas such as nitrogen. Here, the path of the light beam in this embodiment will be described. Reference numeral 411 denotes parallel light that is incident on the solid-state image sensor, forms an image on the photoelectric conversion unit 402, and is converted into signal charges by the photoelectric conversion unit. On the other hand, 412 is
The oblique incident light incident on the solid-state imaging device is 412a.
Is the obliquely incident light in the conventional structure without the groove 407, and
12b is light reflected by total reflection at the interface between the groove 407 and the resin layer 409. That is, the refractive index of the groove 407 is 1.0 and the resin layer 40 is the same as the solid-state image sensor of FIG.
When the refractive index of 9 is 1.6, the critical angle is about 39 °, and when the incident angle is more than the critical angle, the groove 407 and the resin layer 4
It is reflected by total reflection at the interface of 09. As a result, it contributes to photoelectric conversion or the light component penetrating into adjacent pixels is reduced, and the sensitivity, resolution and image quality of the solid-state image sensor are improved, and crosstalk is reduced.

A method of manufacturing the above solid-state image pickup device will be described below with reference to FIGS. 5 (a) and 5 (b).

FIG. 5A shows that after the microlenses are formed,
It is a process sectional view before forming a groove. Further, FIG. 5B is a process cross-sectional view in which the resist is removed after the groove is formed. Here, 501 is a semiconductor substrate, 502 is a photoelectric conversion unit, and 503.
Is a structure such as an electrode of an underlying black and white device, 504 is a flattening layer, 505 is a color filter layer, 506 is a lower support layer, 507 is an upper support layer, 508 is a microlens, 5
Reference numeral 09 denotes a resist layer serving as a mask at the time of forming the groove, 510 denotes plasma for forming the groove, and 511 denotes the formed groove.

On the other hand, FIG. 6 shows the shape of the microlens as seen from the upper surface of the element. Here, 601 is a microlens,
Reference numeral 602 is an ineffective area without a microlens. It is important to control the groove size of the groove 511 in FIG. 5 to the same extent as the width of the invalid area 602.
A groove width of less than 0 μm can be formed with good control. That is, the microlens supporting layer has a two-layer structure of the lower supporting layer 506 and the upper supporting layer 507, the resist layer 509 has etching resistance, and the etching conditions for forming the groove are devised. To do. Although it is possible to form a groove without this method, there are some problems in dimensional control and the like.

The upper support layer 507 is made of a polymer having a relatively high etching resistance, for example, a polymer having a high phenyl group content density such as novolac resin or polystyrene, whereas the lower support layer 506 is made a relatively etching resistance. It is a method of suppressing the expansion of the groove width immediately below the microlens by a method of forming a so-called side chain type acrylic resin having a low temperature. In the 1/3 inch 410,000 pixel area sensor, the total thickness of the lower support layer 506 and the upper support layer 507 is about 4 μm, and the upper support layer 5
A suitable thickness of 07 is about 1.5 μm.

Next, since the resist layer 509 serves as a mask when forming a groove, it is necessary to devise a method of increasing the film thickness or improving the selection ratio. That is, the thickness of the resist layer 509 is preferably thicker in the sense that the directivity of ions is increased during dry etching when forming the groove, but if it is thicker, the etching rate is lowered, and therefore it is usually 3 to 4.
About μm is desirable. In addition, the DESIRE process (B. Roland & F. Coopmans: Ex for silylating the resist surface)
t.Abs.of Conf.on SSDM 1986, 33), or a method of increasing the selectivity of the resist itself such as a silicon-containing resist, it is better to increase the selectivity of the mask.

Further, the etching for forming the groove is RI
Dry etching with E is good, and the composition of the gas species based on oxygen plasma is good. Since the directivity of ions is enhanced, etching at low pressure is good. In addition, in order to efficiently remove the reaction product and the reaction product gas at the time of etching from the groove, the etching sequence is
Sequences containing intervals are desirable, and
In the sense of suppressing the adsorption of reaction products gas etc. on the groove side surface,
It is desirable to raise the substrate temperature to about 100 ° C. in order to promote desorption.

In general, many color filter materials use natural proteins or the like, but since they have extremely high etching resistance, it is better to separate them from the groove portion as shown in FIG. desirable.

The resist 509 remaining after the dry etching can be easily removed by an alkaline stripping solution, but at this time, the upper layer support layer 507 and the lower layer support layer 506, which are microlens support layers, have no photosensitivity. It does not dissolve in the alkaline stripper because it is thermoset at high temperature during formation.

Although the present invention has been described above with reference to the first and second embodiments, these two embodiments are combined to form a solid-state image sensor having higher sensitivity and higher performance. It is also possible.

The present invention can be applied not only to black-and-white or color solid-state image pickup devices, but also various modifications can be made within the scope of the claims of the present invention.
The invention is not limited to the above embodiment.

[0044]

As described above in detail, according to the present invention, the oblique incident light which was not the signal light in the past can also be used as the signal light, and the crosstalk can be reduced and the sensitivity and the image quality at the open aperture can be reduced. Can be improved.

Further, since the light shielding film is not necessarily required on the side surface of the transfer electrode, the aperture ratio can be improved. As a result, a solid-state imaging device with higher sensitivity and higher performance can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure in a first embodiment of the present invention.

FIG. 2 is a diagram showing a cross-sectional structure in a manufacturing process according to the first embodiment.

FIG. 3 is a diagram showing a cross-sectional structure in another manufacturing process according to the first embodiment.

FIG. 4 is a diagram showing a sectional structure in a second embodiment of the present invention.

FIG. 5 is a diagram showing a cross-sectional structure in a manufacturing process according to a second embodiment.

FIG. 6 is a diagram showing an invalid area of a microlens.

FIG. 7 is a diagram showing a cross-sectional structure of a solid-state image sensor according to a conventional technique.

[Explanation of symbols]

 101 semiconductor substrate 102 photoelectric conversion unit 103 transfer electrode 104 insulating film 105 light-shielding film 106 protective film 107 low refractive index layer 108 cap layer 109 resin layer 110 microlens

Claims (7)

[Claims] 1. A solid-state imaging device comprising a transfer electrode, a photoelectric conversion part adjacent to the transfer electrode, and an optical path forming part above the photoelectric conversion part, wherein the transfer electrode and the optical path forming part are between the transfer electrode and the optical path forming part. In the solid-state imaging device, a low refractive index region layer is provided on the optical path forming part. 2. The solid-state imaging device according to claim 1, wherein the low refractive index region layer is a resin layer. 3. The method for manufacturing a solid-state image pickup device according to claim 2, wherein a step of forming the resin layer above the photoelectric conversion section and a part of the resin layer above the photoelectric conversion section are performed. A method of manufacturing a solid-state imaging device, comprising: a step of removing the resin layer; and a step of deforming the resin layer by heat melting. 4. The solid-state imaging device according to claim 1, wherein the low refractive index region layer is a gas layer. 5. The method for manufacturing a solid-state imaging device according to claim 4, wherein the step of forming a water-soluble resin layer above the photoelectric conversion section, and the step of forming the water-soluble resin layer above the photoelectric conversion section A step of removing a part, a step of applying a material to be an optical path forming section above the photoelectric conversion section and so as to cover the water-soluble resin layer, and processing the optical path forming section into a desired pattern. And a step of exposing the water-soluble resin layer and a step of removing the water-soluble resin layer. 6. A solid-state imaging device having a plurality of pixels formed of a photoelectric conversion part formed on a semiconductor substrate, and a resin layer formed on the semiconductor substrate having the plurality of pixels formed thereon. A solid-state imaging device, characterized in that a groove is provided in the resin layer at a portion corresponding to the space. 7. The method for manufacturing a solid-state imaging device according to claim 6, wherein the resin layer is formed on the first resin layer and above the first resin layer when the groove is formed from the first resin layer. And a second resin layer having a low etching rate, and a step of removing the desired regions of the first resin layer and the second resin layer by dry etching to form the groove. And a method for manufacturing a solid-state image sensor.