JPH0730091A - Manufacture of solid-state image sensing device - Google Patents

Abstract

PURPOSE:To reduce a dark current in a solid-state image sensing device by a method wherein after a silicon nitride film on the charge storage part of a photodiode is removed by wet etching, ions are implanted in an impurity region and the film thickness of an insulating film on the upper part of the photodiode is uniformly formed. CONSTITUTION:An N-type impurity region 2 of a charge storage part of a P-N junction photodiode and an N-type impurity region 3 of a charge transfer part of the photodiode are formed in a P-type silicon substrate 1. Moreover, a first silicon oxide film 4, a silicon nitride film 5 and a second silicon oxide film 6 are formed as a gate insulating film and a polycrystalline silicon film 7 of a charge transfer electrode is formed on the film 6. Then, a dry etching is performed using a photoresist film 8 and the film 5 is partially left without removing completely the film 5. Moreover, after a thermal oxide film 10 is grown, the film 5 is removed by wet etching. Then, boron ions are implanted via the film thickness (a) of the film 4 to form a P<++> buried region 9 on the photodiode part. The uniformity of the concentration of the region 9 is also improved in combination with the uniformity of the film thickness (a).

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 image pickup 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 image pickup 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 unit and an N-type impurity region 3 of a charge transfer unit of a PN junction photoelectric conversion device (hereinafter referred to as a photodiode). To form. Further, a first silicon oxide film 4, a silicon nitride film 5, and a second silicon oxide film 6 are formed as a gate insulating film on the P-type silicon substrate 1, and a polycrystalline silicon film 7 of a charge transfer electrode is formed thereon. To do.

Next, as shown in FIG. 4B, 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 formed by dry etching on the silicon oxide film 4
Is etched up to. The film thickness d of the gate insulating film left by etching changes according to the change of the etching time and the etching selection ratio. In addition, the film thickness d is 1 on the wafer surface.
A variation of about 5 nm occurs, and the variation further increases between lots.

Next, as shown in FIG. 4C, by implanting boron (B ⁺ ) ions through the residual film d of the gate insulating film, a P ^{+ +} type buried region (impurity region) is formed immediately above the photodiode portion. ) 9 is formed. When the film thickness d becomes thin, P ⁺⁺
The depth e of the embedded region of the mold becomes deep. According to the LSS theory, when boron is implanted into a silicon oxide film, the film thickness is 10n.
The increment of m corresponds to the increment of ion implantation energy of 5 KeV.

[0005]

However, in the conventional method for manufacturing a solid-state image pickup device, the thickness of the gate insulating film above the photodiode changes due to the change in the dry etching amount 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 the boron implantation above the photodiode. The P ⁺⁺ type buried region 9 is formed in order to suppress surface recombination by making the vicinity of the surface of the N type photodiode a non-depleted region. Therefore, the depletion region expands in a region where the P ⁺⁺ type buried region 9 has a low concentration, and when reaching the silicon surface, a dark current occurs due to the influence of the silicon interface state. The dark current becomes a noise signal and deteriorates the S / N ratio, and at the same time, it looks like a white flaw in the output image and remarkably deteriorates 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 implantation, and further causes a dark current.

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

[0007]

According to another aspect of the present invention, there is provided a method of manufacturing a solid-state image pickup device, wherein a charge storage 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 the charge accumulation part is formed on the semiconductor substrate. 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 photoresist is used as a mask to transfer the charge transfer electrode and the second silicon oxide film. The film is selectively etched, the charge transfer electrode is thermally oxidized, the silicon nitride film above the charge storage part is removed by wet etching, and an impurity region of one conductivity type is formed directly above the charge storage part by ion implantation. It is a thing.

According to a second aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device, wherein a charge storage 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 film are formed using a photoresist as a mask.
The silicon oxide film and the silicon nitride film are selectively etched, the first silicon oxide film above the charge storage part is removed by wet etching, and the silicon oxide film is formed above the charge storage part of the semiconductor substrate to accumulate the charge. One conductivity type impurity region is formed immediately above the portion by ion implantation.

According to a third aspect of the present invention, there is provided a solid-state image pickup device manufacturing method, wherein a charge storage 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. An insulating film is formed by sequentially growing a silicon nitride film and a second silicon oxide film, a charge transfer electrode is formed on the insulating film, and 90% or more of the film thickness of the silicon nitride film is left by using a photoresist as a mask to charge the film. The transfer electrode and the second silicon oxide film are selectively etched, an impurity region of one conductivity type is formed by ion implantation immediately above the charge storage part, and a light shielding film is formed in a region other than above the charge storage part. The silicon nitride film above the storage portion is etched.

[0010]

According to the method of manufacturing the solid-state imaging device of claim 1,
When ion-implanting the impurity region of one conductivity type into the charge storage portion of the photoelectric conversion device, the first silicon oxide film remains in perfect condition on the semiconductor substrate, and the film thickness of the insulating film above 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 second aspect, when the impurity region of one conductivity type is ion-implanted into the charge storage portion of the photoelectric conversion device, the silicon oxide film is formed on the semiconductor substrate. The thickness of the insulating film on the photodiode is uniform, and the concentration of the impurity region formed in the charge storage portion is also uniform. According to the method of manufacturing a solid-state imaging device of 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 complete state on the semiconductor substrate, The thickness of the insulating film on the photodiode is uniform, and the concentration of the impurity region formed in the charge storage portion is also uniform.

[0012]

【Example】

First Embodiment A method for manufacturing a solid-state imaging device according to the first embodiment of the present invention will be described.
It will be described with reference to FIG. In FIG. 1A, an N-type impurity region 2 of a charge storage part of a PN junction photodiode and an N-type impurity region 3 of a charge transfer part 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 a gate insulating film on the P-type silicon substrate 1, and a polycrystalline silicon film 7 of a charge transfer electrode is formed thereon. To do.

Next, as shown in FIG. 1B, the polycrystalline silicon film 7 is dry-etched by the photoresist film 8 and the silicon nitride film 5 is partially removed without being completely removed. Further, as shown in FIG. 1C, after the thermal oxide film 10 is grown on the polycrystalline silicon film 7, the silicon nitride film 5 on the photodiode is removed by wet etching.
In the embodiment, phosphoric acid is used to remove the silicon nitride film 5.
Since the selection ratio of phosphoric acid to the silicon oxide film is very large, the underlying silicon oxide film 4 is hardly etched during etching. Further, since the silicon oxide film 4 is directly grown on the silicon substrate 1, the silicon oxide film 4 is
The film thickness a of the film has a good uniformity within 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 film thickness a of the silicon oxide film 4. ) 9 is formed. Since the film thickness a has a good uniformity within the wafer surface of about 5 nm, the uniformity of the concentration of the P ^{+ +} -type buried region 9 is also due to the dry etching residual film d.
The variation is reduced to about 1/3 or less as compared with (see FIG. 4).

Second Embodiment A method for manufacturing a solid-state image pickup 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 patterned by selective dry etching with a photoresist film 8. At this time, the insulating film above the photodiode is etched to the silicon oxide film 4 by dry etching.

Next, as shown in FIG. 2C, the residual film b (FIG. 2B) of the silicon oxide film 4 formed by the dry etching of the polycrystalline silicon film 7 is completely removed by wet etching. . In the example, the silicon oxide film 4 was etched with buffered hydrofluoric acid. Next, as shown in FIG. 2D, the silicon oxide film 11 is grown again on the silicon substrate 1. At this time, the thickness c of the silicon oxide film 11 is good because the silicon oxide film 11 is grown directly on the silicon substrate 1, so that the uniformity within the wafer surface is about 5 nm. After that, boron (B ⁺ ) ions are implanted through the silicon oxide film 11 to form the P ⁺⁺ type buried region 9 immediately above the photodiode portion.

Third Embodiment A method of manufacturing a solid-state image pickup 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 which 90% or more of the film 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 of FIG. 3B, HBr-based polysilicon etching gas is used,
The selection ratio of the silicon nitride film to the silicon oxide film is increased to leave 90% or more of the film thickness of the silicon nitride film 5.

Next, as shown in FIG. 3 (c), boron (B ⁺ ) ions are implanted through the first silicon oxide film 4 and the silicon nitride film 5 to form P on the photodiode portion.
^{A ++} type embedded region 9 is formed. Further, as shown in FIG. 3D, after the insulating interlayer film 12 is formed, the aluminum light-shielding film 13 is formed, and the pattern of the light entrance opening is formed by dry etching. At the same time, by removing the silicon nitride film 5 by etching, the reduction of the transmitted light due to the silicon nitride film 5 is also eliminated.

[0019]

According to the method of manufacturing a solid-state image pickup device of the present invention, since the film thickness of the insulating film on the photodiode is made uniform, the concentration of the P ^{+ +} type buried region of the photodiode becomes uniform and the photo The effect that the surface recombination of the diode is suppressed and the dark current can be reduced is obtained.

[Brief description of drawings]

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

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

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

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

[Explanation of symbols]

1 P-type silicon substrate (semiconductor substrate) 2 N-type impurity region (charge storage part 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 the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 31/10 8617-4M H01L 21/265 J 9272-4M 21/306 S 8422-4M 31/10 A (72) Inventor Shinichi Uchida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd.

Claims (3)

[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 a first silicon oxide film, a silicon nitride film, and a second silicon film on the semiconductor substrate. A step of growing an oxide film in order to form an insulating film; a step of forming a charge transfer electrode on the insulating film; and a step of selectively etching the charge transfer electrode and the second silicon oxide film using a photoresist as a mask. A step of thermally oxidizing the charge transfer electrode, a step of removing the silicon nitride film above the charge storage portion by wet etching, and an impurity region of one conductivity type being ion-implanted immediately above the charge storage portion. And a step of forming by injection. 2. 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 a first silicon oxide film, a silicon nitride film, and a second silicon film on the semiconductor substrate. Growing an oxide film in order to form an insulating film; forming a charge transfer electrode on the insulating film; and using the photoresist as a mask, the charge transfer electrode, the second silicon oxide film, and the silicon nitride film. Selectively etching the first silicon oxide film above the charge storage portion by wet etching, and forming a silicon oxide film above the charge storage portion of the semiconductor substrate. A step of 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 part 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. A step of growing an oxide film in order to form an insulating film, a step of forming a charge transfer electrode on the insulating film, and a step of using the photoresist as a mask to leave 90% or more of the film 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 directly above the charge storage portion by ion implantation; and a region other than above the charge storage portion. A method of manufacturing a solid-state imaging device, comprising: forming a light-shielding film; and etching the silicon nitride film above the charge storage portion.