JP2002141490A - Solid-state imaging device and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To improve both characteristics of a photodiode part and a vertical CCD part, and to be unaffected by an uncertain amount of electric charge injected into an antireflection film at the time of device formation. The characteristics of the signal charge readout from the section to the vertical CCD section are improved, and the sensitivity of the solid-state imaging device is increased. SOLUTION: An anti-reflection film 6 for increasing the sensitivity of a solid-state imaging device is formed on a photodiode section 16 as a photoelectric conversion element section formed on a semiconductor substrate 11, and a vertical CCD section as a vertical charge transfer section. 17 is covered with the light shielding film 4, and the potential of the light shielding film 4 is set to be the same as the potential of the semiconductor substrate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device, and more particularly to a film structure of a photoelectric conversion element on a solid-state imaging device and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a layer above a photoelectric conversion element portion (photodiode portion) of a solid-state imaging device, Japanese Patent Laid-Open No. 4-206 is disclosed.
As shown in Japanese Patent Application Laid-Open No. 571-571 and Japanese Patent Application Laid-Open No. 4-152677, an antireflection film is formed for the purpose of improving sensitivity.

FIG. 8 is a cross-sectional view showing the structure of a photoelectric conversion element (photodiode) of a solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 4-206571.

As shown in FIG. 8, a photodiode section 42 as a photoelectric conversion element section is formed on the surface of a silicon semiconductor substrate 41, and an insulating film 43 and a silicon semiconductor substrate 41 are formed above the photodiode section 42. A thin intermediate refractive index film 44 having an intermediate refractive index is formed via an insulating film 43, and a protective film 45 is formed on the intermediate refractive index film 44.
And the flattening film 46 were formed.

Further, the intermediate refractive index film 44 and the insulating film 43 are connected to the photodiode section 42 and a vertical CCD section 47 described later.
Are formed in common over the formation region of

On the other hand, a vertical C for transferring the signal charges stored in the photodiode section 42 to a horizontal CCD section (not shown)
As described above, the CD portion 47 is formed on the silicon semiconductor substrate 41.
An intermediate refractive index film 44 is formed thereon via an insulating film 43,
A gate electrode (transfer electrode) 4 is formed on the intermediate refractive index film 44.
8, an interlayer insulating film 49, a light shielding film 50 made of Al or W,
The protective film 45 and the flattening film 46 were sequentially formed.

FIG. 9 is a sectional view showing the structure of a photoelectric conversion element section (photodiode section) of a solid-state imaging device disclosed in Japanese Patent Application Laid-Open No. 4-152677.

The upper layer structure of the photodiode section 42 as the photoelectric conversion element section shown in FIG. 9 is almost the same as the structure shown in FIG. 8, but the vertical CCD section 47 shown in FIG.
In the upper layer structure, a part of the intermediate refractive index film 44 and the insulating film 49 are formed.
And a part of the gate electrode (transfer electrode) 48 is formed in a state of being superimposed on a part of the gate electrode (transfer electrode) 48.

In the solid-state imaging device shown in FIGS. 8 and 9, the refractive index difference between the silicon semiconductor substrate 41 on which the photodiode portion 42 is formed and the insulating film 43 is large, and the difference between the silicon semiconductor substrate 41 and the insulating film 43 is large. Since the reflection at the boundary surface increases, the intermediate refractive index film 44 having an intermediate refractive index between the silicon semiconductor substrate 41 and the insulating film 43 is formed as an antireflection film. The reflection of the incident optical signal on the boundary surface between the silicon semiconductor substrate 41 and the insulating film 43 is suppressed.

[0010]

In the structure of the solid-state imaging device shown in FIG. 8, an insulating film 43 and an intermediate refractive index film 44 are formed in common over the photodiode section 42 and the vertical CCD section 47. Are the insulating film 43 and the intermediate refractive index film 44
Is to enhance the anti-reflection effect of the photodiode section 42,
This is used to increase the charge transfer efficiency of the vertical CCD unit 47.

However, the thickness of the insulating film 43 and the intermediate refractive index film 44 for enhancing the anti-reflection effect in the photodiode section 42 and the thickness of the insulating film 43 for increasing the charge transfer efficiency in the vertical CCD section 47 are different. Although it is necessary to set the dimensions to be different from the thickness of the intermediate refractive index film 44, the insulating film 4
3 and the intermediate refractive index film 44 are formed in common over the photodiode section 42 and the vertical CCD section 47, the anti-reflection effect of the photodiode section 42 and the vertical CCD section 47.
However, there is a problem that it is difficult to achieve characteristics such as sufficient transfer charge amount and good transfer efficiency.

In the structure of the solid-state imaging device shown in FIG. 9, the light shielding film 50 covering the vertical CCD section 47 needs to have an opening for light incidence at the photodiode section 42. Light-shielding film 5
When the 0 is etched, the light-shielding film 50 is charged up and becomes a high potential, and the charge at the time of etching is injected into the intermediate refractive index film 44, and the signal charge for reading the signal charge from the photodiode portion 42 to the vertical CCD portion 47 is read. There has been a problem that the potential of the reading unit varies due to the influence of an uncertain amount of charges injected into the intermediate refractive index film 44 during device formation.

An object of the present invention is to improve both the anti-reflection effect of the photodiode section and the transfer efficiency of the vertical CCD section, and to improve the vertical CCD section from the photodiode section.
An object of the present invention is to provide a solid-state imaging device having improved characteristics of reading charges from a D section and a method of manufacturing the same.

[0014]

In order to achieve the above object, a solid-state imaging device according to the present invention is a solid-state imaging device having a photoelectric conversion element section and a charge transfer section on a semiconductor substrate, wherein the photoelectric conversion element An anti-reflection film for increasing the sensitivity of the solid-state imaging device is formed on the portion, and the charge transfer portion is covered with a light-shielding film, and the potential of the light-shielding film is set to be the same as the potential of the semiconductor substrate.

The anti-reflection film is formed on the semiconductor substrate with an insulating film interposed therebetween.
It is formed directly on the semiconductor substrate.

Further, the antireflection film formed on the photoelectric conversion element portion and the insulating film provided below the transfer electrode of the charge transfer portion are formed separately. The insulating film is an oxide film of a material forming the semiconductor substrate.

The signal charge reading section for reading the signal charges stored in the photoelectric conversion element section into the charge transfer section is a second conductive semiconductor covering the photoelectric conversion element section formed on the first conductive semiconductor substrate. A part of the polarity of the region is replaced, and a voltage is applied to the transfer electrode of the charge transfer portion to lower the potential of the portion of the second conductivity type semiconductor region in which the polarity has been replaced. And reading out signal charges from said portion to said charge transfer portion.

Further, according to the present invention, there is provided a method for manufacturing a solid-state imaging device having a photoelectric conversion element section and a charge transfer section on a semiconductor substrate, wherein the solid-state imaging element is provided on the photoelectric conversion element section. Forming an anti-reflection film for improving the sensitivity of the light-emitting device, covering the charge transfer portion with a light-shielding film, and setting the potential of the light-shielding film to the same potential as the potential of the semiconductor substrate. Patterning step.

Further, according to the present invention, there is provided a method of manufacturing a solid-state imaging device having a photoelectric conversion element section and a charge transfer section on a semiconductor substrate, wherein the photoelectric conversion element section outputs an optical signal. Accumulating as charges, the charge transfer unit transfers signal charges read from the photoelectric conversion element unit, and forming a transfer electrode on an insulating film of the charge transfer unit formed on the semiconductor substrate; Forming the anti-reflection film on the photoelectric conversion element portion formed on the semiconductor substrate after the transfer electrode is formed, and covering the charge transfer portion after the anti-reflection film is formed. Forming a light-shielding film; and, after forming the light-shielding film, patterning the light-shielding film in a state where the potential of the light-shielding film is the same as the potential of the semiconductor substrate.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a solid-state imaging device according to one embodiment of the present invention, and FIG. 2 is a plan view showing a solid-state imaging device according to one embodiment of the present invention. FIG. 3 is a sectional view showing a method of manufacturing a solid-state imaging device according to an embodiment of the present invention in the order of steps, and FIGS. 4, 5 and 6 are characteristic diagrams showing the relationship between the thickness of the antireflection film and the reflectance. It is.

In FIGS. 1 and 2, the solid-state imaging device according to the present invention has a photoelectric conversion element portion and a charge transfer portion on a semiconductor substrate 11.

The solid-state imaging device shown in FIGS. 1 and 2 accumulates an incident optical signal as a signal charge in a photoelectric conversion element portion.
In this method, a signal charge stored in a photoelectric conversion element unit is read by a signal charge reading unit, and the read signal is transferred by a charge transfer unit. The charge transfer unit includes a vertical charge transfer unit that transfers a read signal from the signal charge read unit, and a horizontal charge transfer unit that receives and transfers the read signal transferred by the vertical charge transfer unit.

In the example shown in FIGS. 1 and 2, a photodiode section 16 is used as a photoelectric conversion element section, a vertical CCD section 17 is used as a vertical charge transfer section, and a horizontal CCD section 24 is used as a horizontal charge transfer section. .

In the solid-state imaging device according to the embodiment of the present invention shown in FIGS. 1 and 2, the sensitivity of the solid-state imaging device is increased above the photodiode section 16 as the photoelectric conversion element section formed on the semiconductor substrate 11. A vertical CCD section 17 as a vertical charge transfer section is covered with a light shielding film 4, and the potential of the light shielding film 4 is set to be the same as the potential of the semiconductor substrate 11. It is.

The antireflection film 6 is formed on the semiconductor substrate 11 via an insulating film (silicon oxide film) 7.
Alternatively, the antireflection film 6 is formed directly on the semiconductor substrate 11. As the insulating film 7, the semiconductor substrate 11
May be used.

Since an optical signal is reflected when entering a medium having a different refractive index, the transmittance can be increased by forming an antireflection film on a boundary between the media having different refractive indexes. As a general antireflection film, a λ / 4 film, λ / 4-λ
/ 4 film and the like. Here, λ means the wavelength of light.

For example, considering reflection of light having a wavelength λ of 550 nm, the refractive index of the silicon oxide film 7 shown in FIG. 1 is about 1.5, and the refractive index of the silicon substrate (semiconductor substrate) 11 is about 3. 5, the photodiode section 16
Oxide film 7 and silicon substrate 1 in the formation region of silicon
The reflection at the boundary with 1 is large.

Therefore, the anti-reflection film 6 is formed at the boundary between the silicon oxide film 7 and the silicon substrate 11 in the region where the photodiode portion 16 is formed so that the reflection on the surface of the silicon substrate 11 is reduced and the transmittance is increased. By doing so, the sensitivity of the solid-state imaging device, in particular, the sensitivity of the photodiode section 16 can be improved.

FIGS. 4A and 4B show the vertical incident light when the antireflection film 6 is directly formed on the silicon substrate 11 without forming the silicon oxide film 7 on the silicon substrate 11 shown in FIG. FIG. 4 is a diagram showing the reflectance with respect to. Here, the reflectivity means the sum of the reflectivities of all the films existing between the air layer and the silicon substrate 11. In FIG. 4, a film having a refractive index of 2.0 and having no light absorption is used as the antireflection film 6.

In FIG. 4, since it is assumed that a film having a refractive index n of 2.0 and no light absorption is used as the antireflection film 6, (1-reflectance n) reaches the silicon substrate 11. . The total thickness of the insulating films (the interlayer insulating film 5, the cover film 3, and the flat film 2) above the antireflection film 6 is about 4 μm, and it is considered that visible light does not interfere therewith. Is substantially the same as the insulating film, the total thickness of the insulating film (interlayer insulating film 5, cover film 3, flat film 2) and the microlens 1 is: It is absolutely larger than the thickness of the anti-reflection film 6 as a thin film, and can be handled as if an insulating film having an infinite thickness is formed on the anti-reflection film 6.

The dashed lines in FIGS. 4A and 4B indicate the case where the anti-reflection film 6 is not formed, that is, the anti-reflection film 6.
3 shows the reflectance when the film thickness d is 0 nm.

On the other hand, the solid line represents a substance having a refractive index of about 2.0 and having no absorption (eg, SiO, silicon nitride, TaO ₂ , Ti).
O ₂ ) shows the reflectance when the anti-reflection film 6 is formed, and shows that the reflectance is reduced by forming the anti-reflection film 6 having an appropriate thickness. That is, as shown in FIG.
When the wavelength is increased from 0 nm to 50 nm, the reflectance decreases,
Further, as shown in FIG.
, The reflectance is further reduced.

FIGS. 5A and 5B show a substance (for example, SrTi) having a refractive index n of 3.0 and having no absorption as the anti-reflection film 6.
FIG. 9 is a diagram showing the reflectance when O ₃ is used.

In this case, comparing FIG. 5A and FIG. 5B, when the film thickness of the antireflection film 6 is small (d = 10 to 50 nm) as shown in FIG. Area (400-7
00 nm) is particularly reduced.

FIG. 6 shows the silicon substrate 11 and the antireflection film 6.
As shown in FIG. 1, a silicon oxide film 7 is formed to a thickness of 100 ° on a silicon substrate 11 and an antireflection film 6 is formed on the silicon oxide film 7 in order to improve the interface state with the silicon oxide film 7. FIG. 4 is a diagram showing the reflectance of the present invention. FIG. 6 corresponds to FIG. 4. In FIG. 6, a film having a refractive index of 2.0 and having no light absorption is used as the antireflection film 6.

FIG. 6 also shows the refractive index n of the anti-reflection film 6.
It can be understood that the reflectance can be reduced by adjusting the thickness d.

Although one anti-reflection film 6 is provided in FIG. 1, even if the anti-reflection layer 6 is formed in multiple layers, the sensitivity of the solid-state imaging device can be improved. In addition, as shown in FIG.
The anti-reflection film 6 is formed on the silicon substrate 11 in which is present, and the anti-reflection film 6 is formed so as to extend toward the vertical CCD unit 17 and partially overlap the gate electrode 8 of the vertical CCD unit 17. I have. This facilitates the etching of the anti-reflection film 6 and reduces the level difference between the surface of the anti-reflection film 6 of the base film and the gate electrode 8 when the interlayer insulating film 5 is formed and flattens the surface. It is. As the antireflection film 6, a silicon nitride film, tantalum oxide, titanium oxide, strontium titanate, or the like can be used.

Here, with respect to the vertical CCD section 17 as a charge transfer section, one of the parameters affecting the characteristics such as the transfer charge amount and the transfer efficiency is located below the gate electrode (transfer electrode) 8 of the vertical CCD section 17. It is known that the thickness is the thickness of the gate insulating film 9 to be formed.

Therefore, in the present invention, an antireflection film 6 formed on a photodiode section 16 as a photoelectric conversion element section and a gate electrode (transfer electrode) 8 of a vertical CCD section 17 as a charge transfer section are provided below the layer. The gate insulating film (insulating film) 9 to be formed is formed separately.

In the present invention, the anti-reflection film 6 formed on the photodiode section 16 and the gate insulating film 9 provided below the gate electrode 8 of the vertical CCD section 17 are formed as separate bodies. In addition, the refractive index, the film thickness of the antireflection film 6, the number of steps (single layer or multilayer), etc. can be optimized independently of the gate insulating film 9 to improve the sensitivity of the solid-state imaging device. The thickness of the insulating film 9 is changed to the antireflection film 6
Independent of the above, the characteristics such as the amount of transfer charge and the transfer efficiency of the vertical CCD unit 17 can be improved.

The signal charge reading section 18 for reading the signal charges stored in the photoelectric conversion element section (photodiode section 16) to the charge transfer section (vertical CCD section 17) includes a first conductivity type semiconductor substrate (n-type). The polarity of a part of the second conductivity type semiconductor region (P ⁺ region 15) covering the photoelectric conversion element portion (photodiode portion 16) formed on the silicon substrate 11) is replaced (P ⁻ region 13), A voltage is applied to the transfer electrode (gate electrode 8) of the charge transfer section (vertical CCD section 17) to lower the potential of the portion of the second conductivity type semiconductor region (P ⁻ region 13) where the polarity has been replaced. The signal charges are read out from the photoelectric conversion element section (photodiode section 16) to the charge transfer section (vertical CCD section 17).

Therefore, the charge transfer section (vertical CCD section 1)
7) The light-shielding film 4 is etched when the light-receiving opening 4a is formed in the light-shielding film 4 covering the light-shielding film 4 by etching.
Is charged up, and charges are injected into the antireflection film 6 from the semiconductor substrate region in which the photodiode section 16 is formed, under the influence of the charges, the signal charges from the photoelectric conversion element section by the signal charge reading section 18 are affected. P ^- region 1 when reading data
The potential of No. 3 varies.

In order to avoid this, in the present invention, the potential of the light shielding film 4 is set to be the same as the potential of the semiconductor substrate 11.
More specifically, as shown in FIG. 2 and FIG.
^The light shielding film 4 and the surface of the semiconductor substrate (P ⁺ region 20) of the photodiode section 16 are brought into contact with the ⁺ region 20 to have the same potential.

Therefore, in the present invention, when the light incident opening 4a is formed in the light shielding film 4 covering the charge transfer portion (vertical CCD portion 17) by etching, as shown in FIGS. Is in contact with the P ⁺ region 20 and the light-shielding film 4 and the semiconductor substrate surface (P ⁺
Since the region 20) is at the same potential, the light-shielding film 4 does not charge up when the light-shielding film 4 is etched, and charges are injected into the antireflection film 6 from the semiconductor substrate region where the photodiode portion 16 is formed. And the potential of the P ⁻ region 13 does not vary when the signal charge reading unit 18 reads the signal charge of the photoelectric conversion element unit. Can be accurately read and transferred to the vertical CCD unit 17.

Next, a method for manufacturing a solid-state imaging device according to an embodiment of the present invention will be described with reference to FIG. First, FIG.
As shown in FIG. 3, the insulating film 30 extends over the photodiode region and the vertical CCD region on the silicon substrate 11.
To form

Next, as shown in FIG.
In the part forming region, the insulating film 30 is left on the silicon substrate 11, and the insulating film 30 is used as the gate insulating film 9, and the gate electrode 8 of the vertical CCD unit 17 is formed on the gate insulating film 9.

On the other hand, in the photodiode portion forming region,
The insulating film 30 on the silicon substrate 11 is completely removed by dry etching and refreshing when the gate electrode 8 is etched, or a thin oxide film is left on the surface of the silicon substrate 11 from which the insulating film 30 has been removed.

Next, a silicon oxide film having a desired thickness is formed on the surface of the silicon substrate 11 on which the photodiode portion 16 is formed, on which the insulating film 30 is completely removed, or on the surface on which the thin oxide film is left. 7 and its silicon oxide film 7
An anti-reflection film 6 is formed thereon by a silicon nitride film or the like.
Thus, the antireflection film 6 is formed on the photodiode section 16.

After the oxide film 30 is completely removed during the etching of the gate electrode 8, no new oxide film is formed.
The antireflection film 6 may be directly formed on the silicon substrate 11.

Next, an interlayer insulating film 5 is formed on the silicon substrate 11 in the photodiode section forming area and the vertical CCD section forming area.

Here, referring to FIG. 1 and FIG. 2, the photodiode section 16 formed in the image section 23 and the vertical C
The relationship with the CD unit 17 will be described. Image part 23
The inside shows only the P ⁺ region 20, the P ^- region 13, and the light shielding film 4. In FIG. 2, the region with a diagonally upward slant is the P ⁺ region 2
0, and the photodiode P ⁺ region 19 in the P ⁺ region 20, channel stop P ⁺ region 15, which contains an image portion upper P ⁺ region 27, the surface layer of the P ⁺ regions 15, 19 are the silicon substrate 11 These P ⁺ regions 15, 19, 20, and 27 are electrically connected to each other. (2) is the P ^- region 13.

Also, as shown in FIG.
The portions 17 are respectively covered with the light-shielding films 4, and the light-shielding films 4 are provided at openings corresponding to the photodiode portions 16.
An opening a is formed by etching, and light is incident on each photodiode 16a of the photodiode section 16 through the opening 4a of the light shielding film 4. The arrangement rows of the vertical CCD units 17 and the number of the photodiodes 16a are not limited to those shown in the figure.

Photodiode P ⁺ region 1 in FIG.
Each photodiode 16a of the photodiode section 16 is constituted by a pn junction of the N well 9 and the N well 14,
As shown in FIG. 2, a photodiode 16a formed by a pn junction between the photodiode P ⁺ region 19 and the N well 14
Is surrounded by a channel stop P ⁺ region 15,
Eight are arranged vertically in FIG. 2 while being separated from each other, and a vertical CCD is arranged along eight photodiodes 16a.
The portions 17 are formed adjacent to each other. Since the periphery of the photodiode 16a is partitioned by the channel stop P ⁺ region 15, the photodiode 16a
Is prevented from being trapped to cause a problem such as an afterimage. Further, when a bias is applied to the gate electrode 8 for reading charges from the photodiodes 16a to the vertical CCD unit 17, the P ⁻ region 13 which serves as a path for the charges from the photodiodes 16a to the vertical CCD unit 17 is formed in each photodiode. 16a.

The signal charge photoelectrically converted by each photodiode 16a of the photodiode section 16 is applied to the vertical CCD section 1
7. The data is transferred to the horizontal CCD unit 24 and taken out through the output amplifier 25. The bus line 26 of the vertical CCD section 17 is usually located on the side of the image section 23.

After forming the interlayer insulating film 5 as described above, a contact hole 21 reaching the P ⁺ region 20 is opened in the interlayer insulating film 5.

Next, the light shielding film 4 is formed on the interlayer insulating film 5,
A part thereof is filled in the contact hole 21 of the interlayer insulating film 5 to electrically connect the light shielding film 4 to the P ⁺ region 20. As a result, the light-shielding film 4 comes into contact with the P ⁺ region 20 and both have the same potential. Since the P ⁺ region 20 is formed on the surface layer of the silicon substrate 11, the light shielding film 4 comes into contact with the P ⁺ region 20 and has the same potential as the silicon substrate 11.

Next, the light-shielding film 4 is patterned by etching in a state where the light-shielding film 4 is set to the same potential as that of the silicon substrate 11, and a light incident opening 4a is formed by etching in a portion corresponding to the photodiode portion 16. I do.

Finally, a cover film 3 and a flattening film 2 are formed on the interlayer insulating film 5, and the microlenses 1 are formed corresponding to the respective photodiodes 16a.

As described above, according to the production method of the present invention,
When the light incident opening 4a is formed in the light shielding film 4 covering the charge transfer section (vertical CCD section 17) by etching,
As shown in FIG. 3, since the light shielding film 4 is in contact with the P ⁺ region 20 and the light shielding film 4 and the silicon substrate surface (P ⁺ region 20) of the photodiode section 16 have the same potential, the light shielding film 4 is etched. Sometimes, the light-shielding film 4 does not charge up, so that charges can be prevented from being injected into the antireflection film 6 from the semiconductor substrate region where the photodiode portion 16 is formed. There is no variation in the potential of the P ⁻ region 13 when reading out the signal charges of the element section, and the signal charge reading section 18 can accurately read out the signal charges of the photoelectric conversion element section and transfer it to the vertical CCD section 17. .

(Example) Next, an example of the present invention will be described in detail. A P well 10 is formed on an NSub 11 a of a silicon substrate 11, and an N well 14 of a photodiode unit 16 and an N well 1 of a vertical CCD unit 17 are formed on the P well 10.
2, a P ⁺ region 19 of the photodiode section 16, a channel stop P ⁺ region 15 and a P ^- region 13 are formed.

The gate insulating film 9 (for example, silicon oxide film 29-silicon nitride film 28-silicon oxide film 27 in FIG.
ONO structure), a gate electrode 8 (n-doped polysilicon), and an interlayer oxide film 5 (SiO ₂ ) are formed, respectively.
A light-shielding film 4 (tungsten or aluminum) is formed thereon.
And a cover film 3 (SiO ₂ ) are formed so as to cover the vertical CCD section 17, and a flattening film 2 (SiO ₂₎
Or resin).

A silicon oxide film 7 and a silicon nitride film (anti-reflection film) 6 are formed on the silicon substrate of the photodiode portion 16 above the silicon substrate, and the interlayer oxide film 5, the cover film 3, the planarization film 2, Micro lenses 1 are respectively formed.

The thicknesses of the silicon oxide film 7 and the silicon nitride film 6 are designed so that the sensitivity of the photodiode section 16 is high. In the embodiment, the thickness of the silicon oxide film 7 is Is set to 30 nm, but is not limited to this value.

In the vertical CCD section 17, the silicon nitride film 6
And the underlying silicon oxide film 7 partially overlaps the upper layer of the polysilicon gate electrode 8.

In the image portion 23, only the P ⁺ region 20, the P ^- region 13 and the light shielding film 4 are shown. The signal charges photoelectrically converted in the photodiode section 16 are transferred to the vertical CCD section 1
7. The data is transferred to the horizontal CCD unit 24 and taken out through the output amplifier 25 to the outside. The bus line 26 of the vertical CCD section 17 is usually located on the side of the image section 23.

The feature of the present invention is that the light-shielding film 4 is charged up during the patterning of the light-shielding film 4, and an indefinite amount of charge is injected from the silicon substrate 11 of the photodiode portion 16 into the anti-reflection film 6. Gate electrode 8 for reading charges from the vertical CCD section 17
When a bias is applied to the P ⁻ region 13, the charge passes from the photodiode unit 16 to the vertical CCD unit 17.
Of the signal charge readout unit 18
In order to prevent the read voltage from fluctuating, a contact is made between the P ⁺ region 27 above the image portion 23 and the light shielding film 4 when the light shielding film 4 is formed, and the P ⁺ region 20, ie, the silicon substrate surface of the photodiode portion 16 is contacted. The point is that patterning is performed after the light shielding film 4 is set to the same potential.

At the time of patterning the light shielding film 4, the P ⁺ region 20
Since the light-shielding film 4 and the light-shielding film 4 have the same potential, no charge is injected into the antireflection film 6 even if the light-shielding film 4 is charged up. In FIG. 2, the light-shielding film 4 is in contact with a P ⁺ region 27 provided above the image portion 23, and the upper P ⁺ region 27 is connected to the channel stop P ⁺ region 15 and the photodiode P ⁺ region 19 in series. And have the same potential. The upper P ⁺ region 27 is connected to the wiring 28 via the contact hole 22, and the wiring 28 is grounded.

Next, the manufacturing method of the present invention will be described in the order of steps. First, as shown in FIG.
A P well 10 is formed on b11a, and an N well 14 of a photodiode section 16 and a vertical CCD are formed on the P well 10.
N-well 12 of section 17 and photodiode section P ⁺ region 1
9, a channel stop P ⁺ region 15 and a P ⁻ region 13 are formed.

Next, a gate insulating film 30 is formed on the silicon substrate 11 as shown in FIG. 3A, and a gate electrode 8 is formed as shown in FIG. 3B. Vertical CCD section 17
When the gate electrode 8 is etched and left, the gate electrode 8 on the photodiode portion 16 is completely removed. The gate insulating film 30 corresponds to the gate insulating film 9 shown in FIG. 1, and has an ONO structure of a silicon oxide film 27, a silicon nitride film 28, and a silicon oxide film 29.

Further, as shown in FIG. 3B, a 20 nm-thick silicon oxide film 7 and a 30 nm-thick silicon nitride film are formed on the silicon substrate 11 of the photodiode section 16 to form an antireflection film 6. The diode section 16 is covered with the antireflection film 6.

The silicon oxide film 7 is formed on the gate insulating film 3
When 0 is an ONO film, a gap is not formed between the silicon nitride film and the silicon nitride film 6 constituting the ONO film of the gate insulating film 30 unless the thermal oxide film is used to form the CVD film instead of the thermal oxide film.
The effect of the hydrogen alloy cannot be exerted, and the dark current increases. Therefore, the silicon oxide film 7 is made of O.sub.
In the case of an NO film, it is formed by a CVD film.

Next, as shown in FIG. 3C, the antireflection film 6 is vertically etched on the gate electrode 8 in a stripe shape. If the entire surface is covered with the antireflection film 6 without performing this processing, the effect of the hydrogen alloy does not occur. Thereafter, an interlayer oxide film 5 is formed, and a contact hole 21 with the P ⁺ region 27 is opened in the interlayer insulating film 5 above the image portion of the solid-state imaging device (the position shown in FIG. 2).

Next, as shown in FIG. 3D, the light-shielding film 4 is formed of tungsten, and the light-shielding film 4 and the P ⁺ region 20 are brought into contact with each other through the contact hole 21 to have the same potential. 4 is patterned to open a light incident opening 4a.

Thereafter, a cover film 3 and a flattening film 2 are formed, and a microlens 1 is formed (FIG. 1).

FIG. 6 shows the sensitivity of the photodiode section 16 depending on the presence or absence of the antireflection film 6 in the structure of the embodiment shown in FIG. In FIG. 6, the antireflection film 6 is shown.
3 shows the sensitivity of the photodiode section 16 when no photodiode is provided. On the other hand, the thickness of the underlying silicon oxide film 7 is 20 n
m, the thickness of the antireflection film (silicon nitride film) 6 is 20
The sensitivities when set to nm, 30 nm, and 40 nm are shown as,. In each case, an improvement in sensitivity of about 10% is observed.

[0077]

As described above, according to the present invention, both the characteristics of the photodiode section and the vertical CCD section are improved, and the uncertain amount of electric charge injected into the antireflection film at the time of device formation is improved. The signal charge readout characteristics from the photodiode section to the vertical CCD section can be improved without being affected, and an anti-reflection film is formed on the upper layer of the photodiode section of the solid-state imaging device, thereby improving the sensitivity of the solid-state imaging device. Can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a solid-state imaging device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a solid-state imaging device according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a method for manufacturing a solid-state imaging device according to an embodiment of the present invention in the order of steps.

FIG. 4 is a characteristic diagram showing a relationship between the thickness of the antireflection film and the reflectance.

FIG. 5 is a characteristic diagram showing a relationship between the thickness of the antireflection film and the reflectance.

FIG. 6 is a characteristic diagram showing a relationship between the thickness of the antireflection film and the reflectance.

FIG. 7 is a characteristic diagram illustrating sensitivity of a photodiode unit depending on the presence or absence of an antireflection film.

FIG. 8 is a cross-sectional view showing a solid-state imaging device according to a conventional example.

FIG. 9 is a cross-sectional view showing a solid-state imaging device according to a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Micro lens 2 Flattening film 3 Cover film 4 Light shielding film 5 Interlayer insulating film 6 Antireflection film 7 Insulating film (silicon oxide film) 8 Gate electrode 9 Gate insulating film 13 P ^- region 16 Photodiode part 17 Vertical CCD part 18 Signal Charge readout section 20 P ⁺ area 23 Image section 24 Horizontal CCD section 25 Output amplifier

Claims (8)

[Claims] 1. A solid-state imaging device having a photoelectric conversion element portion and a charge transfer portion on a semiconductor substrate, wherein an anti-reflection film for increasing the sensitivity of the solid-state imaging device is formed on the photoelectric conversion element portion, and A solid-state imaging device, wherein the charge transfer unit is covered with a light-shielding film, and a potential of the light-shielding film is set to be the same as a potential of the semiconductor substrate. 2. The solid-state imaging device according to claim 1, wherein the antireflection film is formed on the semiconductor substrate via an oxide film. 3. The solid-state imaging device according to claim 1, wherein the anti-reflection film is formed directly on the semiconductor substrate. 4. The method according to claim 1, wherein the antireflection film formed on the upper layer of the photoelectric conversion element section and the insulating film formed on a lower layer of the transfer electrode of the charge transfer section are formed separately. Item 2. The solid-state imaging device according to Item 1. 5. The semiconductor device according to claim 2, wherein the insulating film is an oxide film of a material constituting the semiconductor substrate.
3. The solid-state imaging device according to item 1. 6. A signal charge reading section for reading a signal charge stored in the photoelectric conversion element section into the charge transfer section,
A part of the polarity of the second conductivity type semiconductor region covering the photoelectric conversion element portion formed on the conductivity type semiconductor substrate is replaced,
A voltage is applied to the transfer electrode of the charge transfer unit to lower the potential of the portion of the second conductivity type semiconductor region where the polarity has been replaced, and the signal charge is read from the photoelectric conversion element unit to the charge transfer unit. The solid-state imaging device according to claim 1, having a structure. 7. A method for manufacturing a solid-state imaging device having a photoelectric conversion element portion and a charge transfer portion on a semiconductor substrate, wherein an anti-reflection film for increasing the sensitivity of the solid-state imaging device is formed on the photoelectric conversion element portion. And covering the charge transfer portion with a light-shielding film, and patterning the light-shielding film in a state where the potential of the light-shielding film is the same as the potential of the semiconductor substrate. Of manufacturing a solid-state imaging device. 8. A method for manufacturing a solid-state imaging device having a photoelectric conversion element unit and a charge transfer unit on a semiconductor substrate, wherein the photoelectric conversion element unit stores an optical signal as signal charge,
Forming a transfer electrode on an insulating film of the charge transfer unit formed on the semiconductor substrate, wherein the charge transfer unit transfers a signal charge read from the photoelectric conversion element unit; and After the formation, a step of forming an anti-reflection film on the photoelectric conversion element portion formed on the semiconductor substrate; After the anti-reflection film is formed, forming a light-shielding film covering the charge transfer portion And a step of patterning the light-shielding film in a state where the potential of the light-shielding film is the same as the potential of the semiconductor substrate after the light-shielding film is formed. Production method.