JP2928058B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device.

[0002]

2. Description of the Related Art FIG. 4 is a schematic sectional view of a unit pixel portion of a conventional solid-state imaging device. A conventional method for manufacturing a solid-state imaging device will be described with reference to FIG. In FIG. 4A, on the surface of a P-type silicon substrate 1, an N-type impurity region 2 of a charge storage portion of a PN junction photoelectric conversion device (hereinafter referred to as a photodiode) and an N-type impurity region 3 of a charge transfer portion are provided. And are formed. Further, a first silicon oxide film 4, a silicon nitride film 5, and a second silicon oxide film 6 are formed as gate insulating films on the P-type silicon substrate 1, and a polycrystalline silicon film 7 of a charge transfer electrode is formed thereon. I do.

[0003] Next, as shown in FIG. 4 (b), the polycrystalline silicon film 7 is selectively dry-etched with a photoresist film 8 to form a pattern. At this time, the insulating film above the photodiode is subjected to dry etching to form a silicon oxide film 4.
Etched until. The thickness d of the gate insulating film remaining after etching varies according to the variation of the etching time and the etching selectivity. The film thickness d is 1 in the wafer plane.
A variation of about 5 nm occurs, and the variation further increases between lots.

Next, as shown in FIG. 4C, a P ⁺⁺ type buried region (impurity region) is formed immediately above the photodiode portion by boron (B ⁺ ) ion implantation through the remaining film d of the gate insulating film. ) 9 is formed. When the film thickness d becomes thin, P ⁺⁺
The depth e of the mold buried region is increased. According to the LSS theory, when boron is implanted into a silicon oxide film,
The increase in m is equivalent to the increase in ion implantation energy of 5 KeV.

[0005]

However, in the conventional method of manufacturing a solid-state imaging device, the thickness of the gate insulating film above the photodiode changes due to the change in the amount of dry etching of the polycrystalline silicon film 7. The variation in the thickness of the silicon oxide film 4 on the photodiode causes a difference in the concentration of the P ⁺⁺ type buried region 9 due to boron implantation above the photodiode. The P ⁺⁺ type buried region 9 is formed to suppress the surface recombination by making the vicinity of the surface of the N-type photodiode a non-depleted region. Therefore, the depletion region expands in the region where the concentration of the P ⁺⁺ type buried region 9 is low, and when reaching the silicon surface, a dark current is generated under the influence of the silicon interface state. The dark current becomes a noise signal, deteriorating the S / N ratio, and at the same time, looks like white flaws in the output image and significantly impairs the image quality. As described above, the concentration of the P ⁺⁺ type buried region 9 is greatly affected by the thickness of the insulating film before boron is implanted, and further causes dark current.

An object of the present invention is to provide a method for manufacturing a solid-state imaging device in which dark current is extremely reduced.

[0007]

According to a first aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device, comprising: forming a charge accumulation portion of a photoelectric conversion device of another conductivity type on a main surface of a semiconductor substrate of one conductivity type; A first silicon oxide film, a silicon nitride film, and a second silicon oxide film are sequentially grown to form an insulating film, a charge transfer electrode is formed on the insulating film, and the charge transfer electrode and the second silicon oxide film are formed using a photoresist as a mask. The film is selectively etched, the charge transfer electrode is thermally oxidized, the silicon nitride film above the charge storage portion is removed by wet etching, and an impurity region of one conductivity type is formed immediately above the charge storage portion by ion implantation. Things.

According to a second aspect of the present invention, there is provided a method for manufacturing a solid-state imaging device, wherein a charge accumulation portion of a photoelectric conversion device of another conductivity type is formed on a main surface of a semiconductor substrate of one conductivity type, and a first silicon oxide film is formed on the semiconductor substrate. A silicon nitride film and a second silicon oxide film are sequentially grown to form an insulating film, a charge transfer electrode is formed on the insulating film, and the charge transfer electrode and the second
The silicon oxide film and the silicon nitride film are selectively etched, the first silicon oxide film above the charge storage portion is removed by wet etching, and a silicon oxide film is formed above the charge storage portion of the semiconductor substrate to store the charge. An impurity region of one conductivity type is formed immediately above the portion by ion implantation.

According to a third aspect of the present invention, there is provided a method for manufacturing a solid-state imaging device, wherein a charge accumulation portion of a photoelectric conversion device of another conductivity type is formed on a main surface of a semiconductor substrate of one conductivity type, and a first silicon oxide film is formed on the semiconductor substrate. A silicon nitride film and a second silicon oxide film are sequentially grown to form an insulating film, a charge transfer electrode is formed on the insulating film, and a charge is left using a photoresist as a mask while leaving 90% or more of the thickness of the silicon nitride film. The transfer electrode and the second silicon oxide film are selectively etched, an impurity region of one conductivity type is formed immediately above the charge storage portion by ion implantation, and a light shielding film is formed in a region other than above the charge storage portion. This is for etching the silicon nitride film above the accumulation part.

[0010]

According to the method for manufacturing a solid-state imaging device of the first aspect,
When the impurity region of one conductivity type is ion-implanted into the charge storage portion of the photoelectric conversion device, the first silicon oxide film remains in a complete state on the semiconductor substrate, and the thickness of the insulating film on the photodiode becomes uniform. Also, the concentration of the impurity region formed in the charge storage portion becomes uniform.

According to the method of manufacturing a solid-state image pickup device of the present invention, a silicon oxide film is formed on a semiconductor substrate when ion-implanting an impurity region of one conductivity type into a charge storage portion of a photoelectric conversion device. The thickness of the insulating film over the photodiode becomes uniform, and the concentration of the impurity region formed in the charge storage portion becomes uniform. According to the method of manufacturing a solid-state imaging device according to claim 3, when the impurity region of one conductivity type is ion-implanted into the charge storage portion of the photoelectric conversion device, the silicon nitride film remains in a perfect state on the semiconductor substrate, The thickness of the insulating film over the photodiode becomes uniform, and the concentration of the impurity region formed in the charge storage portion becomes uniform.

[0012]

【Example】

First Embodiment A method for manufacturing a solid-state imaging device according to a first embodiment of the present invention will be described.
A description will be given based on FIG. In FIG. 1A, an N-type impurity region 2 of a charge storage portion of a photodiode having a PN junction and an N-type impurity region 3 of a charge transfer portion are formed on a surface of a P-type silicon substrate (semiconductor substrate) 1. . Further, a first silicon oxide film 4, a silicon nitride film 5, and a second silicon oxide film 6 are formed as gate insulating films on the P-type silicon substrate 1, and a polycrystalline silicon film 7 of a charge transfer electrode is formed thereon. I do.

Next, as shown in FIG. 1B, the polycrystalline silicon film 7 is dry-etched with a photoresist film 8 to leave a part of the silicon nitride film 5 without completely removing it. Further, as shown in FIG. 1C, after growing a thermal oxide film 10 on the polycrystalline silicon film 7, the silicon nitride film 5 on the photodiode is removed by wet etching.
In the embodiment, phosphoric acid was used to remove the silicon nitride film 5.
Since phosphoric acid has a very high selectivity with respect to the silicon oxide film, the underlying silicon oxide film 4 is hardly etched during etching. Since the silicon oxide film 4 is grown directly on the silicon substrate 1, the silicon oxide film 4
Has a good uniformity in the wafer surface of about 5 nm.

Next, as shown in FIG. 1D, a P ⁺⁺ type buried region (impurity region) is formed on the photodiode portion by boron (B ⁺ ) ion implantation through the thickness a of the silicon oxide film 4. ) 9 is formed. Since the uniformity of the film thickness a in the wafer surface is as good as about 5 nm, the uniformity of the concentration of the P ⁺⁺ type buried region 9 is also improved by the residual film d of the dry etching.
The variation is reduced to about 1/3 or less as compared with (see FIG. 4).

Second Embodiment A method of manufacturing a solid-state imaging device according to a second embodiment of the present invention will be described.
This will be described with reference to FIG. FIG. 2A is the same as FIG. 1A. In FIG. 2B, the polycrystalline silicon film 7 is selectively dry-etched with a photoresist film 8 to form a pattern. At this time, the insulating film above the photodiode is etched down to the silicon oxide film 4 by dry etching.

Next, as shown in FIG. 2 (c), the remaining film b (FIG. 2 (b)) of the silicon oxide film 4 generated by dry etching of the polycrystalline silicon film 7 is completely removed by wet etching. . In this embodiment, the silicon oxide film 4 is etched with buffered hydrofluoric acid. Next, as shown in FIG. 2D, a silicon oxide film 11 is grown on the silicon substrate 1 again. Since the silicon oxide film 11 is grown directly on the silicon substrate 1, the thickness c of the silicon oxide film 11 at this time is as good as about 5 nm in uniformity on the wafer surface. After that, a P ⁺⁺ type buried region 9 is formed immediately above the photodiode portion by boron (B ⁺ ) ion implantation through the silicon oxide film 11.

Third Embodiment A method of manufacturing a solid-state imaging device according to a third embodiment of the present invention will be described.
This will be described with reference to FIG. This embodiment is a method of manufacturing a solid-state imaging device in a case where 90% or more of the thickness of the silicon nitride film 5 is left when the polycrystalline silicon film 7 is etched in the first embodiment. FIG. 3A is the same as FIG. 1A.
At the time of dry etching of the polycrystalline silicon film 7 in FIG. 3B, an HBr-based polysilicon etching gas is used.
The selectivity of the silicon nitride film to the silicon oxide film is increased, and 90% or more of the thickness of the silicon nitride film 5 is left.

Next, as shown in FIG. 3C, boron (B.sup. ⁺ ) Ions are implanted through the first silicon oxide film 4 and the silicon nitride film 5 so that P
^{The ++} type buried region 9 is formed. Further, as shown in FIG. 3D, after forming the insulating interlayer film 12, an aluminum light-shielding film 13 is formed, and a pattern of a light incident opening is formed by dry etching. At the same time, by removing the silicon nitride film 5 by etching, the decrease in transmitted light due to the silicon nitride film 5 is also eliminated.

[0019]

According to the method of manufacturing a solid-state imaging device of the present invention, the thickness of the insulating film on the photodiode is made uniform, so that the concentration of the P ⁺⁺ type buried region of the photodiode becomes uniform, The effect of suppressing the surface recombination of the diode and reducing the dark current can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a manufacturing process of a solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is a sectional view illustrating a manufacturing process of a solid-state imaging device according to a second embodiment of the present invention;

FIG. 3 is a cross-sectional view illustrating a manufacturing process of a solid-state imaging device according to a third embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a manufacturing process of a conventional solid-state imaging device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 P-type silicon substrate (semiconductor substrate) 2 N-type impurity region (charge storage portion of photoelectric conversion device) 4 first silicon oxide film 5 silicon nitride film 6 second silicon oxide film 7 polycrystalline silicon film (charge transfer electrode) 8 Photoresist film 9 P ⁺⁺ type buried region (impurity region) 10, 11 Silicon oxide film (thermal oxide film) 12 Insulating interlayer film 13 Aluminum light shielding film

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shinichi Uchida 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electronics Corporation (56) References JP-A-5-6992 (JP, A) JP-A-4- 56273 (JP, A) JP-A-4-335572 (JP, A) JP-A-3-181171 (JP, A) JP-A-60-28270 (JP, A) JP-A-4-263469 (JP, A) JP-A-4-286361 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 27/148 H01L 21/265 H01L 21/306 H01L 31/10

Claims (3)

(57) [Claims] 1. A step of forming a charge storage portion of a photoelectric conversion device of another conductivity type on a main surface of a semiconductor substrate of one conductivity type, and forming a first silicon oxide film, a silicon nitride film, and a second silicon film on the semiconductor substrate. Forming an insulating film by sequentially growing an oxide film; forming a charge transfer electrode on the insulating film; and selectively etching the charge transfer electrode and the second silicon oxide film using a photoresist as a mask. Performing the step of thermally oxidizing the charge transfer electrode; removing the silicon nitride film above the charge storage section by wet etching; and ion-implanting one conductivity type impurity region immediately above the charge storage section. A method of manufacturing a solid-state imaging device including a step of forming by injection. 2. A step of forming a charge accumulation portion of a photoelectric conversion device of another conductivity type on a main surface of a semiconductor substrate of one conductivity type, and a first silicon oxide film, a silicon nitride film, and a second silicon film on the semiconductor substrate. Forming an insulating film by sequentially growing an oxide film, forming a charge transfer electrode on the insulating film, using the photoresist as a mask, the charge transfer electrode, the second silicon oxide film, and the silicon nitride film. Selectively etching, the step of removing the first silicon oxide film above the charge storage section by wet etching, and the step of forming a silicon oxide film above the charge storage section of the semiconductor substrate. Forming an impurity region of one conductivity type directly above the charge storage portion by ion implantation. 3. A step of forming a charge storage portion of a photoelectric conversion device of another conductivity type on a main surface of a semiconductor substrate of one conductivity type, and forming a first silicon oxide film, a silicon nitride film, and a second silicon film on the semiconductor substrate. Forming an insulating film by sequentially growing an oxide film, forming a charge transfer electrode on the insulating film, and using a photoresist as a mask to leave 90% or more of the thickness of the silicon nitride film. A step of selectively etching the transfer electrode and the second silicon oxide film; a step of forming an impurity region of one conductivity type immediately above the charge storage portion by ion implantation; and a step of forming an impurity region other than above the charge storage portion. A method for manufacturing a solid-state imaging device, comprising: forming a light-shielding film; and etching the silicon nitride film above the charge storage portion.