JP2005333066A - Solid-state image pickup element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable and durable solid-state image pickup element in which the area of a light receiving part is highly precisely specified, and disconnection of metal wiring by deposition of boron and phosphorous can be prevented. <P>SOLUTION: The solid-state image pickup element is provided with a photoelectric converter and a charge transmitter having a charge transmission electrode transmitting a charge caused in the photoelectric converter. The element is also provided with an adhesion layer 71 having an opening in the photoelectric converter and covering the charge transmitter and a shielding film 72 formed to cover a whole surface including side walls of the adhesion layer 71. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly to a structure of a light-shielding film that defines a light-receiving region of a photoelectric conversion unit of the solid-state imaging device.

  A solid-state imaging device using a CCD used for an area sensor or the like includes a photoelectric conversion unit such as a photodiode and a charge transfer unit including a charge transfer electrode for transferring a signal charge from the photoelectric conversion unit. A plurality of charge transfer electrodes are arranged adjacent to each other on a charge transfer path formed on the semiconductor substrate, and are sequentially driven.

In recent years, with the increase in the number of pixels of a CCD, the demand for higher resolution and higher sensitivity is increasing in solid-state imaging devices, and the number of imaging pixels is increasing to more than gigapixels. In particular, the lateral shrinkage of the solid-state image sensor is prominent.
However, the vertical shrinkage has slowed down, and the aspect ratio tends to increase. Increasing the aspect ratio tends to generate reflected light and scattered light at the light shielding film covering the charge transfer electrode, reducing the margin with respect to the light incident angle in the CCD, resulting in difficulty in optical path design.

When miniaturization progresses in this way, when patterning the light-shielding film, the unevenness of the base is large, so that the sensor aperture area fluctuates due to halation, which may adversely affect sensitivity and smear.
In order to solve this problem, various proposals have been made to reduce the surface irregularities and prevent the incidence of light from an oblique direction.

  For example, after forming the charge transfer electrode, an interlayer insulating film is formed, a groove is formed in the interlayer insulating film, and a light shielding film is filled in the groove, thereby defining a photoelectric conversion unit. It has been proposed (Patent Document 1).

  Further, the first light-shielding film having a window so as to surround the light-receiving part is covered, and the periphery of the light-receiving part is covered with a second light-shielding film, and the light-receiving part is defined by the first and second light-shielding films, A structure that reduces the occurrence of smear due to incident light from an oblique direction has been proposed (Patent Document 2).

  In general, a BPSG (borophospho silicate glass) film or a PSG (phospho silicate glass) film is used as an interlayer insulating film between the charge transfer electrode and a wiring layer such as aluminum formed on the upper layer. A recess is formed right above the photoelectric conversion portion, and a silicon nitride film is buried in the recess by a CVD method to form an in-layer lens structure.

  However, in such a structure, it cannot be sufficiently thinned, and requires a high-temperature heat treatment step for producing heat fluidity, and thus precipitates are likely to precipitate on the surface in this high-temperature heat treatment step, There has been a problem that there is a risk of disconnection of the metal wiring in the contact portion.

JP 2000-340783 A JP-A-7-326726

As described above, in the conventional solid-state imaging device, as the miniaturization progresses, in the photolithography process, the aperture area that defines the light receiving portion fluctuates due to halation caused by the unevenness of the base, which adversely affects sensitivity and smear characteristics. There was a problem of affecting.
In addition, after forming the light shielding film, a high temperature heat treatment step for flattening the BPSG film to be filled in the light receiving portion is required, thereby causing a problem of disconnection of the metal wiring in the contact portion due to precipitates.
The present invention has been made in view of the above circumstances, and an object thereof is to define the area of a light receiving portion with high accuracy.
It is another object of the present invention to provide a solid-state imaging device that can prevent disconnection of metal wiring due to precipitation of boron or phosphorus, and has a long life and high reliability.

  Therefore, the present invention provides a solid-state imaging device including a photoelectric conversion unit and a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit, and the photoelectric conversion unit has an opening. And an adhesion layer covering the charge transfer portion, and a light shielding film formed so as to cover the entire surface including the side wall of the adhesion layer.

  According to the above configuration, since the light shielding film can be formed without requiring a photolithography process, the pattern accuracy is not deteriorated due to halation. In addition, since the photoelectric conversion part has an opening and is formed so as to cover the entire surface including the side wall of the adhesion layer that covers the charge transfer part, it prevents the incidence of light from an oblique direction and is highly sensitive and stable. It is possible to form a solid-state imaging device having smear characteristics.

  In the invention, it is preferable that the light shielding film is a conductive film formed on the surface of the adhesion layer by selective growth.

  According to the above configuration, since the light shielding film is formed on the surface of the adhesion layer by selective growth, it is possible to form a highly accurate and highly reliable light shielding layer without variation in pattern accuracy due to halation.

  In the invention, the adhesion layer includes an aluminum thin film.

  According to the above configuration, a film having low resistance and high adhesion can be obtained. Therefore, it can be used as a light-shielding film, and can also be used as a low-resistance wiring layer at a required location. The adhesion layer is not limited to aluminum, but is preferably a thin film having a specific resistance comparable to that of an aluminum thin film.

  In the invention, the light shielding film includes a tungsten film.

  According to the above configuration, a highly reliable tungsten film can be formed on the aluminum thin film pattern.

  Further, the present invention comprises a planarization film that is formed so as to cover a part of the light shielding film from the surface of the photoelectric conversion part, and is filled in the photoelectric conversion part so that the surface is substantially flat, The planarization film includes a film having a higher refractive index than the surface of the light shielding film.

  According to the above configuration, the interlayer insulating film such as the BPSG film formed so as to cover the surface of the solid-state imaging device is selectively filled only in the concave portion as the planarizing film, and the charge transfer is in contact with the planarizing film. Since the electrode surface is covered with a light-shielding film, shrinking in the vertical direction is facilitated, and the planarizing film has a condensing function as an in-layer lens. An imaging element can be formed.

  Moreover, this invention contains what the said planarization film | membrane is a coating film.

  According to the above configuration, a reflow process is not required, and a flat film can be formed without going through a high temperature process. Therefore, even when a low melting point thin film such as aluminum is used as the adhesive layer, the wiring resistance is low and the service life is long. Thus, a highly reliable solid-state imaging device can be obtained.

In the invention, the planarization film is an SOG film.
According to the above configuration, a flat insulating film that can be formed at a low temperature can be obtained.

The present invention includes one in which the planarizing film is an SOD film.
According to the above configuration, a flat insulating film that can be formed at a low temperature can be obtained.

The present invention includes the field insulating film characterized in that the surface of the field insulating film is below the surface of the charge transfer electrode.
With this configuration, the surface can be flattened.

The present invention includes a step of forming a photoelectric conversion unit on the surface of a semiconductor substrate, and a charge including a charge transfer electrode disposed in the vicinity of the photoelectric conversion unit so as to transfer the charge generated in the photoelectric conversion unit A step of forming a transfer portion, a step of forming an adhesive layer having an opening in the photoelectric conversion portion and covering the charge transfer portion, and a step of forming a light shielding film on the adhesive layer by selective growth And a step of forming a planarizing film on the upper layer.
According to this configuration, after patterning the adhesive layer, the light-shielding film can be formed by selective growth of the metal film, and it is possible to provide a solid-state imaging device with high accuracy, high sensitivity, and high reliability. Become. Here, by selecting a flattening film that can be formed at a low temperature, a material that can be easily processed and used as a base for selective growth, such as aluminum, can be used for the adhesive layer.

In the present invention, the step of forming the adhesive layer includes a step of forming an aluminum or aluminum alloy thin film and a step of patterning the thin film by photolithography.
According to this configuration, since aluminum or an aluminum alloy is patterned by photolithography, a highly accurate pattern can be obtained. Here, aluminum or an aluminum alloy has a low resistance and is extremely effective as an adhesive layer. Further, according to the method of the present invention, this adhesion layer is effective because it can be formed without passing through a high temperature step in the flattening film forming step even when it is a low melting point thin film having a melting point of 500 ° C. or less.

In the present invention, the step of forming the light shielding film includes a selective growth step.
According to this configuration, the film can be formed with good controllability so as to cover the side wall of the adhesive layer without requiring photolithography.

In the present invention, the step of forming the planarizing film includes a step of forming a coating film.
Aluminum can be selectively grown and is an effective material. However, when a low melting point thin film such as aluminum is used as the adhesive layer, there is a problem that it deteriorates after a high temperature process. Thus, a highly reliable film can be formed.

In the present invention, the step of forming the planarizing film includes a step of applying an SOG (Spin on Glass) film.
With this configuration, a highly reliable planarizing film can be obtained at a low temperature.

In the present invention, the step of forming the planarizing film includes a step of applying an SOD (Spin on Dielectric) film.
With this configuration, a highly reliable planarizing film can be obtained at a low temperature.

  The planarization step includes a resist etch back step.

  Further, the planarization step includes a step of planarizing by chemical mechanical polishing (CMP).

According to the present invention, the step of forming the planarizing film includes a step of forming a BPSG film.
By using an atmospheric pressure CVD method or the like, a film with high flatness can be formed at a low temperature.

Further, the step of forming the planarizing film includes a step of forming a TEOS (silicon oxide film) film by HDP plasma CVD.
According to this method, the film can be flattened by CMP or the like after film formation, and the insulating film can be formed with good flatness at 350 to 400 ° C. Therefore, the reliability of the element region is not deteriorated. A high solid-state image sensor can be obtained.

Furthermore, it is desirable to form the inter-element insulating film (field insulating film) so as to be at a lower level than the electrode surface.
When the height of the field insulating film protrudes, the flatness is lost. However, according to the above structure, a solid image-receiving element surface with high flatness can be obtained.

According to the solid-state imaging device of the present invention, since the photoelectric conversion unit has an opening and is formed so as to cover the entire surface including the side wall of the adhesion layer that covers the charge transfer unit, incident light from an oblique direction Therefore, it is possible to form a solid-state imaging device having high sensitivity and stable smear characteristics.
In addition, according to the method for manufacturing a solid-state imaging device of the present invention, the light-shielding film can be formed without the need for a photolithography process even when miniaturization is performed, and thus the reliability of the pattern is improved without causing deterioration in pattern accuracy due to halation. Can be measured.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
As shown in FIGS. 1 and 2, the solid-state imaging device includes a photoelectric conversion unit 30 and a charge transfer unit 40 including a charge transfer electrode that transfers charges generated by the photoelectric conversion unit 30. An adhesion layer (adhesion layer) 71 made of an aluminum thin film having an opening of the photoelectric conversion portion and a light shielding layer 72 made of a tungsten thin film formed by selective growth so as to cover the upper layer from the side wall of the adhesion layer. Tungsten and a flat layer formed on the light shielding layer 72, formed so as to cover a part of the light shielding layer from the surface of the photoelectric conversion unit, and filled in the photoelectric conversion unit so that the surface is substantially flat. And a filter 50 and a lens 60 are formed on the planarizing film through a protective film 74 made of polyimide resin. Than it is.
The flattening film 73 has a higher refractive index than the surface of the light shielding film 72, and acts to enhance the light collecting property.
As a result, the surface can be satisfactorily flattened, and the thickness can be greatly reduced.

  The gate oxide film 2 is composed of a three-layer structure film of a silicon oxide film, a silicon nitride film, and a silicon oxide film.

  1 is a schematic cross-sectional view, and FIG. 2 is a schematic plan view. 1 is a cross-sectional view taken along line AA of FIG. A plurality of photodiode regions (photoelectric conversion units) 30 are formed on the silicon substrate 1, and a charge transfer unit 40 for transferring signal charges detected in the photodiode region 30 is formed between the photodiode regions 30. The The element region formed in the silicon substrate 1 is omitted.

  Although not shown in FIG. 2, the charge transfer channel through which the signal charge transferred by the charge transfer electrode moves is formed in a direction crossing the direction in which the charge transfer unit 40 extends.

  In FIG. 2, the description of the interelectrode insulating film formed near the boundary between the photodiode region 30 and the charge transfer portion 40 is omitted.

  As shown in FIG. 1, a photodiode region 30, a charge transfer channel, a channel stop region (not shown), and a charge readout region (not shown) are formed in the silicon substrate 1. The gate oxide film 2 is formed. On the surface of the gate oxide film 2, an interelectrode insulating film 4 made of a silicon oxide film and a charge transfer electrode 3 (a first electrode made of a first layer doped amorphous silicon film 3a, a second layer doped amorphous silicon film 3b, Second electrode) is formed to form a multi-electrode structure.

  Although the charge transfer unit 40 is as described above, an intermediate layer 70 is formed on the upper surface of the charge transfer electrode of the charge transfer unit 40 as shown in FIG. Except for the photodiode region 30, an adhesive layer made of an aluminum thin film and a light shielding film 72 made of a tungsten film are provided, and a planarizing film 73 made of an SOG film is formed in the recess. A passivation film 74 made of a transparent resin film is provided as an upper layer. As the passivation film, a silicon nitride film formed by a plasma CVD method may be used.

A color filter 50 and a microlens 60 are further provided above the intermediate layer 70. Further, a flattening layer made of an insulating transparent resin or the like may be filled between the color filter 50 and the microlens 60 as necessary.
In this example, a so-called honeycomb-structured solid-state imaging device is shown, but it goes without saying that the present invention can also be applied to a square lattice type solid-state imaging device.

Next, the manufacturing process of this solid-state imaging device will be described in detail with reference to FIGS.
First, a charge transfer electrode having a multi-electrode (two-layer electrode) structure is formed by a normal method. That is, a 15 nm-thickness silicon oxide film, a 50 nm-thickness silicon nitride film, and a 10 nm-thickness silicon oxide film are formed on the surface of an n-type silicon substrate 1 having an impurity concentration of about 1.0 × 10 ¹⁶ cm ^−3. Then, a gate oxide film 2 having a three-layer structure is formed.

Subsequently, a phosphorus-doped first layer doped amorphous silicon film having a thickness of 0.4 μm is formed on the gate oxide film 2 by a low pressure CVD method using SiH ₄ added with PH ₃ and N ₂ as a reactive gas. 3a is formed. The substrate temperature at this time shall be 500-600 degreeC.

Thereafter, the first layer doped amorphous silicon film 3a is patterned by photolithography to form a first electrode located on the lower layer side, and the surface of the first electrode is thermally oxidized to thereby form a silicon oxide film having a thickness of 15 nm. A film 4 is formed. In this patterning, reactive ion etching using a mixed gas of HBr and O ₂ is performed to form wirings for the first electrode and the peripheral circuit. Here ECR (Electron cyclotron resonance: Electron Cycrotoron Resonance) system or ICP (Inductively Coupled Inductively Coupled Plasma) side is preferable to use an etching apparatus such as a formula.

Similarly, a 0.4 μm-thick phosphorus-doped second-layer doped amorphous silicon film 3b is formed by a low pressure CVD method using SiH ₄ added with PH ₃ and N ₂ as a reactive gas. Then, patterning is performed by photolithography to form a second electrode. Further, an HTO film is formed on the upper layer after thermal oxidation to form a silicon oxide film 5 having a thickness of 50 nm (FIG. 3A).

  Then, for example, an aluminum thin film is formed as the adhesive layer 71 by the CVD method using trimethylaluminum (organoaluminum) as the upper layer (FIG. 3B). A PVD method or a sputtering method may be used. Here, an aluminum thin film was used as a thin film containing a material having a low melting point (low melting point thin film).

  Subsequently, a positive resist is applied to the upper layer so as to have a thickness of 0.5 to 1.4 μm, exposed by photolithography using a desired mask, developed, and washed with water to form a resist pattern R1. (FIG. 3C).

  Then, using this resist pattern R1 as a mask, the aluminum thin film as the adhesive layer 71 is patterned (FIG. 3D).

Next, the resist pattern R1 is removed by ashing (FIG. 4A), and a film is formed on the surface of the adhesive layer 71 by a selective CVD method using tungsten hexafluoride (WF ₆ ) and silane (SiH ₄ ). A tungsten thin film having a thickness of 100 to 300 nm is formed (FIG. 4B).

  Then, as shown in FIG. 4C, an SOG film as the planarizing film 73 is applied to planarize the surface.

Further, a planarizing layer 74 made of a transparent resin film is formed on this upper layer (FIG. 4D).
Thereafter, a color filter 50, a microlens 60, and the like are formed to obtain a solid-state imaging device as shown in FIGS.

  According to this method, the light shielding film 72 is formed by selectively growing tungsten with respect to the pattern of the adhesive layer 71 made of an aluminum thin film. A light-shielding film is formed with high pattern accuracy so as to surround the image sensor, and a highly sensitive and reliable solid-state imaging device can be realized without adversely affecting smear characteristics.

Further, since the planarization film can be formed by coating without passing through a high temperature process, the metal wiring is not deteriorated due to the precipitation of impurities as in the case of using the BPSG film.
Furthermore, when a BPSG film is used, planarization is performed by reflow. However, since the SOG film is formed by a coating method, a reflow process is not necessary. Therefore, there is no deterioration of aluminum.
Further, since the light shielding layer has a two-layer structure of a light shielding film made of tungsten and an adhesive layer made of aluminum, it is used as a wiring pattern having low resistance and high reliability in a region where wiring is necessary.
In the above embodiment, the SOG film is used as the planarizing film, but an SOD film may be used.
In addition to aluminum, titanium nitride, titanium, and the like can be applied as the adhesive layer, but these films have a high melting point.

(Second Embodiment)
In the first embodiment, SOG is used as the planarizing film. However, as the second embodiment of the present invention, as shown in FIG. 5, a BPSG film is used as the planarizing film 73S, and this is reflowed. A flattened one is used.
At this time, the adhesive layer 71S is composed of a two-layer film of titanium nitride and titanium.
The other configurations are the same as those in the first embodiment.
With this configuration, it is possible to obtain a thin solid-state imaging device that is thin and has higher light collection efficiency.

(Third embodiment)
In the first and second embodiments, the solid-state imaging device having a charge transfer electrode having a multi-electrode structure has been described. However, the present embodiment also applies to a solid-state imaging device having a charge transfer electrode having a single-layer electrode structure. Is possible.
FIG. 6 shows a solid-state imaging device having a charge transfer electrode having a single-layer electrode structure.
In this embodiment, the second layer silicon conductive film may be planarized by CMP to form a charge transfer electrode having a single layer electrode structure. In the present embodiment, the field insulating film 80 for element isolation has a buried structure, and the surface level of the photoelectric conversion portion and the field insulating film 80 are substantially the same. Other parts are the same as those in the first and second embodiments.

  According to this structure, there is no protrusion to the surface due to the presence of the field insulating film 80, so that it is possible to obtain a solid-state imaging device that is thinner and has high light collection efficiency.

  As described above, in the present invention, since the surface can be flattened and thinned, it is possible to form a small-sized, high-accuracy and highly reliable solid-state imaging device, which is effective for application to a small camera. .

It is sectional drawing which shows the solid-state image sensor of the 1st Embodiment of this invention. It is a top view which shows the solid-state image sensor of the 1st Embodiment of this invention. It is a figure which shows the manufacturing process of the solid-state image sensor of the 1st Embodiment of this invention. It is a figure which shows the manufacturing process of the solid-state image sensor of the 1st Embodiment of this invention. It is a figure which shows the solid-state image sensor of the 2nd Embodiment of this invention. It is a figure which shows the solid-state image sensor of the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Gate oxide film 3a 1st electrode (1st layer doped amorphous silicon film)
3b Second electrode (second layer doped amorphous silicon film)
3 Charge Transfer Electrode 4 Silicon Oxide Film 5 Silicon Nitride Film 30 Photodiode Region 40 Charge Transfer Section 50 Color Filter 60 Microlens 70 Intermediate Layer 71 Adhesive Layer 72 Light-shielding Film 73 Flattening Film 74 Passivation Film

Claims (15)

In a solid-state imaging device including a photoelectric conversion unit, and a charge transfer unit including a charge transfer electrode that transfers charges generated in the photoelectric conversion unit,
An adhesion layer having an opening in the photoelectric conversion unit and covering the charge transfer unit;
A solid-state imaging device, comprising: a light-shielding film formed so as to cover the entire surface including the side wall of the adhesion layer. The solid-state imaging device according to claim 1,
The solid-state imaging device, wherein the light shielding film is a conductive film formed on the surface of the adhesion layer by selective growth. The solid-state imaging device according to claim 1 or 2,
The adhesion layer is a solid-state imaging device including an aluminum thin film. The solid-state imaging device according to any one of claims 1 to 3,
The solid-state imaging device, wherein the light shielding film is a tungsten film. The solid-state imaging device according to any one of claims 1 to 4,
A flattening film that is formed so as to cover a part of the light-shielding film from the surface of the photoelectric conversion unit and is filled in the photoelectric conversion unit so that the surface is substantially flat;
The solid-state imaging device, wherein the planarizing film has a higher refractive index than the surface of the light shielding film. A solid-state imaging device according to any one of claims 1 to 5,
The solid-state imaging device, wherein the planarizing film is a coating film. The solid-state imaging device according to claim 6,
The solid-state imaging device, wherein the planarizing film is an SOG film. The solid-state imaging device according to claim 6,
The solid-state imaging device, wherein the planarizing film is an SOD film. A solid-state imaging device according to any one of claims 1 to 8,
A solid-state imaging device, wherein the surface of the field insulating film is below the surface of the charge transfer electrode. Forming a photoelectric conversion part on a semiconductor substrate surface;
Forming a charge transfer unit including a charge transfer electrode disposed in proximity to the photoelectric conversion unit so as to transfer the charge generated in the photoelectric conversion unit;
Forming an adhesive layer having an opening in the photoelectric conversion unit and covering the charge transfer unit;
Forming a light-shielding film by selective growth on the adhesive layer;
And a step of forming a planarizing film on the upper layer. It is a manufacturing method of the solid-state image sensing device according to claim 10,
The step of forming the adhesive layer includes a step of forming an aluminum or aluminum alloy thin film and a step of patterning the thin film by photolithography. It is a manufacturing method of the solid-state image sensing device according to claim 11,
The method of manufacturing a solid-state imaging device, wherein the step of forming the light shielding film is a selective growth step. A method for producing a solid-state imaging device according to any one of claims 10 to 12,
The step of forming the planarizing film includes a step of forming a coating film. It is a manufacturing method of the solid-state image sensing device according to claim 13,
The step of forming the planarizing film includes a step of applying an SOG film. It is a manufacturing method of the solid-state image sensing device according to claim 13,
The step of forming the planarizing film includes a step of applying a SOD film.

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