JP2005322833A - Solid-state imaging pickup element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve sensitivity in an element, by thinning and flattening the interlayer insulating film between a charge transfer electrode and a wiring layer, and vertically shrinking the solid-state imaging element. <P>SOLUTION: The solid-state imaging element comprises a photoelectric conversion section, and a charge transfer section having the charge transfer electrode for transferring the charge generated at the photoelectric conversion section. An opening is provided at the photoelectric conversion section; and there are a light-shielding film for covering the charge transfer and a planarization film that is formed on the upper layer of the light-shielding film, is formed while one portion of the light-shielding film is formed from the surface of the photoelectric conversion section, and is filled in the photoelectric conversion so that the surface becomes nearly flat. The planarization film has a refractive index that is higher than that of the surface of the light-shielding film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device and a method for manufacturing the same, and particularly relates to a structure of an incident portion 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 on the light-shielding film covering the charge transfer electrode, reducing the margin for the light incident angle in the CCD, and there is a problem that the optical path design is difficult.
One example of such a solid-state imaging element is a BPSG film (as a interlayer insulating film 17 between a charge transfer electrode and an aluminum wiring layer (not shown) formed thereon as shown in FIG. Using the thermal fluidity of borophospho silicate glass (PSG) or PSG film (phospho silicate glass), a recess is formed directly above the photoelectric conversion part, and the silicon nitride film 18 is embedded in this recess by the CVD method to collect light in the layer. A structure is formed (Patent Document 1).

  For this reason, the above-described configuration has a problem that it is difficult to cope with further improvement in sensitivity.

JP 2002-135811 A

As described above, in the conventional solid-state imaging device, the aspect ratio (aspect ratio) tends to increase with respect to the shrinkage in the vertical direction, and the light-shielding film that covers the charge transfer electrode due to the increase in the aspect ratio. The reflected light and scattered light are likely to be generated, and the margin for the light incident angle in the CCD is reduced, making it difficult to design the optical path.
The present invention has been made in view of the above circumstances, and by reducing the thickness and flattening of the interlayer insulating film between the charge transfer electrode and the wiring layer, and performing vertical contraction of the solid-state imaging device, the sensitivity of the device is increased. The purpose is to plan.

  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. A light-shielding film having at least a light-shielding function that covers the charge transfer unit, and is formed on the light-shielding film, and is formed so as to cover a part of the light-shielding film from the surface of the photoelectric conversion unit. And a flattening film filled in the photoelectric conversion portion so as to be substantially flat.

According to the above configuration, the interlayer insulating film such as the BPSG film that has been 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 electric charge in contact with the planarizing film Since the transfer electrode surface is covered with a light-shielding film, shrinking in the vertical direction is facilitated, the allowable light incident angle is widened, and a highly sensitive solid-state imaging device can be formed. Here, a part of the surface of the light-shielding film is exposed from the planarizing film, and the surface of the light-shielding film is brought into contact with the filter directly or via a protective film, so that the thickness can be further reduced.
Note that, when the planarizing film is made of a material having a higher refractive index than the light-shielding film, a light condensing effect can be obtained and a further increase in the allowable incident angle can be achieved.

The present invention also includes the light-shielding film configured such that the top surface thereof and the top surface of the planarization film are substantially flush with each other.
According to the above configuration, a part of the light-shielding film surface is exposed from the planarization film, and the planarization film is configured to substantially coincide with the top surface of the light-shielding film, so that the vertical shrinkage is enhanced. Therefore, the thickness can be further reduced.

  Moreover, this invention includes what the said light-shielding film is a two-layer film of a metal light-shielding layer and an antireflection layer.

According to the above configuration, since the anti-reflection layer is provided, when the light-shielding film pattern is patterned, the mask pattern may be formed on the upper layer in a state where the metal light-shielding layer and the anti-reflection layer are laminated. Therefore, it becomes possible to realize highly accurate patterning.
Note that a metal film such as TiN may be used as the antireflection layer.

In the invention, it is preferable that the antireflection layer contains silicon nitride.
With this configuration, it acts as an antireflection film during patterning of the light-shielding film pattern, and acts as an etching stopper during planarization, so that a highly reliable pattern can be formed.
Further, it is only necessary to form hydroxynitride SiONH.

In the invention, the planarization film is a BPSG film.
With this configuration, it is possible to form a flat film having a high refractive index and without undergoing a high temperature process.
Note that a PSG film or a BSG film may be used as the planarizing film. Further, NSG may be used when performing planarization by CMP or etchback.

In the invention, it is preferable that the planarizing film is a silicon oxide film using TEOS.
With this configuration, a flat film can be efficiently formed at a low temperature by an atmospheric pressure CVD method or the like.

The solid-state imaging device manufacturing method of the present invention includes a step of forming a photoelectric conversion unit on a semiconductor substrate surface, and a proximity of the photoelectric conversion unit so as to transfer charges generated in the photoelectric conversion unit. Forming a charge transfer part including a charge transfer electrode, forming a light-shielding film having an opening in the photoelectric conversion part and covering the charge transfer part, and having at least a light shielding function, and an upper layer thereof Including a step of forming a planarizing film and a step of planarizing the surface by removing the planarizing film until the part of the light shielding film is exposed using the light shielding film as an etching stopper.
With this configuration, it is possible to easily shrink in the vertical direction by flattening a flattened film made of an insulating film or the like using the light-shielding film as an etching stopper. In addition, the allowable incident angle can be increased.

  In the present invention, the planarization step may be a resist etch back step.

  In the present invention, the planarization step may include 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.
Since flattening can be easily performed, a highly flat film can be formed.

According to the present invention, the step of forming the planarizing film includes a step of forming a silicon oxide film by an atmospheric pressure CVD method using TEOS.
According to this method, since an insulating film can be formed with good flatness at 350 to 400 ° C., a highly reliable solid-state imaging device can be obtained without causing deterioration of the device region.

In the present invention, the step of forming the light-shielding film includes a step of forming a light-shielding metal film and a step of forming a silicon nitride film on the metal film.
According to this method, since reflection can be prevented in the photolithography process for forming the mask pattern, high-accuracy patterning is possible, and the pattern accuracy can be increased.
Further, a metal film such as TiN can be applied as the antireflection layer, and a laminated structure of TiN and a silicon nitride film may be used.

  Preferably, the step of forming the charge transfer electrode includes a step of forming a pattern of a first layer silicon-based conductive film constituting the first electrode on the surface of the semiconductor substrate on which the gate oxide film is formed; Forming an insulating film to be an inter-electrode insulating film on at least the side wall of the electrode; and a second layer constituting the second electrode on the surface of the semiconductor substrate on which the first electrode and the inter-electrode insulating film are formed Forming a silicon-based conductive film.

  When the multi-electrode structure film is formed on the first layer electrode so as to overlap the second electrode, the height in the vertical direction is increased. However, since the planarization film is directly formed by this method, Thus, the effect of the present invention is remarkable.

  Further, the second-layer silicon-based conductive film may be planarized by CMP to form a charge transfer electrode having a single-layer electrode structure.

  In addition, by performing a surface treatment step with an alkaline chemical solution after CMP, the surface treatment with an alkaline chemical solution is performed on the surface of the silicon-based conductive film, particularly the second layer silicon-based conductive film. Damages such as surface depressions formed after the CMP treatment can be removed, and local thinning, disconnection, and short-circuiting of the electrode due to surface roughness can be suppressed. In addition, if the surface treatment step includes an oxidation treatment step and a surface treatment step using a solution containing fluorine ions, a better surface state can be obtained.

According to the method of the present invention, the interlayer insulating film between the charge transfer electrode and the wiring is flattened and thinned, thereby ensuring a wide allowable incident angle of the solid-state imaging device and forming a highly sensitive solid-state imaging device. It becomes possible.
In addition to having the antireflection layer in addition to the light shielding layer, the pattern accuracy during photolithography can be improved due to the presence of the antireflection layer.

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. The photoelectric conversion part of the photoelectric conversion part has an opening and is formed on a light-shielding film (light-shielding layer 71 and antireflection layer 72) covering the charge transfer part and on the antireflection layer 72, and the photoelectric conversion A BPSG film as a flattening film 73 formed so as to cover a part of the light-shielding film from the surface of the portion and filled in the photoelectric conversion portion so that the surface is substantially flat. The filter 50 and the lens 60 are formed on the conversion film via a passivation film 74 made of polyimide resin.
As a result, a part of the light-shielding film is in direct contact with the filter 50 via the passivation film 74, and the solid-state imaging device is extremely thin. Therefore, according to this solid-state imaging device, 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.

  Here, FIG. 1 is a schematic cross-sectional view, and FIG. 2 is a schematic plan view. FIG. 1 shows an AA cross section of FIG. A plurality of photodiodes 30 are formed on the silicon substrate 1, and a charge transfer unit 40 for transferring signal charges detected by the photodiodes 30 is formed between the photodiodes 30.

  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 and the charge transfer portion 40 is omitted.

  As shown in FIG. 1, a photodiode 30, a charge transfer channel (not shown), a channel stop region (not shown), and a charge readout region (not shown) are formed in the silicon substrate 1. A gate oxide film 2 is formed on the surface of the substrate 1. 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 (a first electrode made of a first layer doped amorphous silicon film 3a and a second layer doped amorphous silicon film 3b) A second electrode) is formed, forming a multiple electrode structure.

  Although the charge transfer unit 40 is as described above, an intermediate unit 70 is formed on the upper surface of the charge transfer electrode of the charge transfer unit 40 as shown in FIG. A light shielding layer 71 and an antireflection layer 72 made of a silicon nitride film are provided except for the photodiode 30 portion, and a planarizing film 73 made of a BPSG film is formed in the recess. A passivation film 74 made of a silicon nitride film is provided as an upper layer. Furthermore, a planarizing layer using a transparent resin may be formed on the silicon nitride film.

A color filter 50 and a microlens 60 are further provided above the intermediate portion 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, it is desirable to use an etching apparatus such as ECR or ICP.

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, a silicon nitride film 5 having a thickness of 50 nm is formed on this upper layer by low pressure CVD (FIG. 3A).

  Then, a light shielding layer 71 made of a titanium nitride (TiN) layer and W (tungsten) is formed on this upper layer by sputtering (FIG. 3B).

  Subsequently, a silicon nitride film 72 as an antireflection layer is formed on the upper layer by plasma CVD. Then, a positive resist is applied to the upper layer so as to have a thickness of 0.5 to 1.4 μm, exposed by using a desired mask by photolithography, developed and washed with water to form a resist pattern R1 (FIG. 3). (C)). Here, a silicon nitride film is used as the antireflection layer. However, an inorganic antireflection film suitable for the exposure wavelength for resist pattern formation for processing the light-shielding film may be formed to have a desired thickness.

  Then, using the resist pattern R1 as a mask, the antireflection layer 72 and the light shielding layer 71 are patterned (FIG. 3D).

  Next, the resist pattern R1 is removed by ashing (FIG. 4A), and a pattern of the light shielding film (antireflection layer 72 and light shielding layer 71) is obtained.

Then, as shown in FIG. 4B, a non-doped silicon oxide film (not shown) is formed as a boron phosphorus diffusion preventing film by plasma CVD, and then a BPSG film as a planarizing film 73 is formed by atmospheric pressure CVD. Form by the method.
Then, after the planarization film 73 is fluidized and planarized by heat treatment at 850 ° C. for 30 minutes, the surface is planarized by resist etch back as shown in FIG.

Further, a passivation film 74 made of silicon nitride is formed on this upper layer.
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 solid-state imaging device, the surface of the charge transfer electrode and the surface of the flattening film are configured to be substantially the same level, and the allowable light incident angle with respect to the light receiving surface is widened by the vertical shrink, thereby achieving high sensitivity. be able to.

In addition, since the charge transfer portion is covered with a light-shielding film and the light receiving portion is defined with high accuracy, the allowable margin for the incident angle can be increased.
According to this method, when patterning the light-shielding film, photolithography is performed in a state where the surface of the light-shielding layer 71 composed of a two-layer film of TiN and W is covered with silicon nitride as an antireflection layer. There is no degradation of pattern accuracy due to halation.
Here, the measurement result of the relationship between the reflectance and the wavelength when the antireflection layer is formed on the surface of the light shielding layer 71 is shown by a straight line in FIG. Note that the reflectance when the antireflection layer is not formed is indicated by a dotted line.

  In this way, there is no deterioration of pattern accuracy due to halation, a light-shielding film is formed with good pattern accuracy so as to surround the photoelectric conversion part, and a highly sensitive and highly reliable solid-state imaging device without adversely affecting smear characteristics Can be realized.

In addition, since the silicon nitride film as the antireflection layer is effective for end point detection in the resist etch-back process for planarization, film loss can be prevented. This may be effective in planarization by CMP.
As the antireflection layer, a silicon nitride (SiN) film, a plasma silicon nitride (SiN) film, a silicon oxynitride (SiON) film, or the like, which is formed by a CVD method, is etched or BPSG film. Any material with polishing selectivity may be used. In addition, a condition may be selected such that a light shielding layer is used for the end point detection. In this case, the antireflection layer may be removed by etching. However, since the light shielding layer has etching selectivity, film loss due to overpolishing can be prevented.
Furthermore, the planarizing film is not limited to the BPSG film but may be a PSG film.
In the above embodiment, BPSG is used as the planarizing film, but an SOG film or an SOD film may be used.
Further, by using a material having a higher refractive index than the surface of the light shielding layer 71 as the planarizing film 73, the light condensing property can be further enhanced.

(Second Embodiment)
In the first embodiment, a BPSG film is used as the planarizing film. However, as a second embodiment of the present invention, as shown in FIG. 5, a BPSG film is used as the planarizing film 73. After flattening by reflow and CMP treatment, a desired resist pattern is formed on the photoelectric conversion portion and isotropic etching treatment is performed, whereby a convex lens surface can be formed with good controllability.
The other configurations are the same as those in the first embodiment.

(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. The second layer doped amorphous silicon 3b is flattened by CMP, and is the same as the first embodiment except that the second layer doped amorphous silicon 3b is arranged in parallel with the first layer doped amorphous silicon 3a.
In this embodiment, the second-layer silicon-based conductive film is planarized by CMP to form a charge transfer electrode having a single-layer electrode structure. Other parts are the same as those in the first and second embodiments.

  As described above, according to the present invention, the interlayer insulating film is prevented from becoming higher than the level of the light-shielding film covering the surface of the charge transfer portion, so that the vertical shrinkage can be achieved and the light incident Since the margin for the corner can be reduced, it is effective for forming a fine and highly sensitive solid-state imaging device such as 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. It is a figure which shows the result of having measured in relation to exposure wavelength and a reflectance in the case of photolithography of the light shielding layer of this invention and a prior art example. It is a figure which shows the solid-state image sensor of a prior art example.

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)
4 Silicon oxide film 5 Silicon nitride film 30 Photodiode section 40 Charge transfer section 50 Color filter 60 Micro lens 70 Insulating film 71 Light shielding layer 72 Antireflection layer 73 Planarization film 74 Passivation film

Claims (12)

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,
A light-shielding film having an opening in the photoelectric conversion unit and having at least a light-shielding function formed so as to cover the charge transfer unit;
A flattening film formed on the light-shielding film, formed so as to cover a part of the light-shielding film from the surface of the photoelectric conversion part, and filled in the photoelectric conversion part so that the surface is substantially flat A solid-state imaging device comprising: The solid-state imaging device according to claim 1,
The light-shielding film is a solid-state imaging device configured such that a top surface of the light-shielding film and a top surface of the planarizing film are substantially flush with each other. The solid-state imaging device according to claim 1 or 2,
The light-shielding film is a solid-state imaging device that is a two-layer film of a light-shielding layer and an antireflection layer. The solid-state imaging device according to claim 3,
The antireflection layer is a solid-state imaging device containing silicon nitride. The solid-state imaging device according to any one of claims 1 to 3,
The solid-state imaging device, wherein the planarizing film is a BPSG film. The solid-state imaging device according to any one of claims 1 to 3,
The solid-state imaging device, wherein the planarizing film is a TEOS film. 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 a light-shielding film having an opening in the photoelectric conversion unit and covering the charge transfer unit;
Forming a planarization film;
And a step of planarizing the surface by removing the planarizing film until a part of the light shielding film is exposed using the light shielding film as an etching stopper. It is a manufacturing method of the solid-state image sensing device according to claim 7,
The planarization step is a method for manufacturing a solid-state imaging device, which is a resist etch-back step. It is a manufacturing method of the solid-state image sensing device according to claim 7,
The method of manufacturing a solid-state imaging device, wherein the planarizing step is a step of planarizing by chemical mechanical polishing (CMP). A method for manufacturing a solid-state imaging device according to any one of claims 7 to 9,
The step of forming the planarizing film is a method of manufacturing a solid-state imaging device, which is a step of forming a BPSG film. A method for manufacturing a solid-state imaging device according to any one of claims 7 to 9,
The step of forming the planarizing film is a method of manufacturing a solid-state imaging device, which is a step of forming a silicon oxide film by atmospheric pressure CVD using TEOS (tetraethoxysilane). It is a manufacturing method of the solid-state image sensing device according to any one of claims 7 to 11,
The step of forming the light-shielding film includes a step of forming a light-shielding metal film and a step of forming a silicon nitride film on the metal film.

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