JP3036747B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly, to a method for manufacturing a charge-coupled device (CCD) having a two-layer polycrystalline silicon structure.

[Conventional technology]

Conventionally, this type of solid-state imaging device using a charge-coupled device having a two-layer polycrystalline silicon electrode structure is shown in FIG.
FIG. 4A is a cross-sectional view taken along the line II ′ of FIG. 3, and FIG.
As shown in the sectional view taken along the line II-II 'of FIG. 3, a plurality of photoelectric converters 2 formed by a PN junction on a P-type semiconductor substrate 1 and an N-type region 6 for transferring signal charges. , Gate insulating film
A charge transfer section 3 composed of 10 and two layers of polycrystalline silicon films 11 and 12; and a photoelectric conversion section 2 adjacent to a transfer gate section 4 for reading signal charges from the photoelectric conversion section 2 to the charge transfer section 3.
And a channel stop 5 for electrically separating the charge transfer unit 3.

FIG. 5 is an example of a cross-sectional view of a charge transfer section in main manufacturing steps of a conventional solid-state imaging device. After selectively forming a photoelectric conversion unit 2, an N-type layer 6 serving as a buried channel of a charge transfer unit 3 and a high-concentration P-type layer 7 serving as a channel stop 5 in a P-type semiconductor substrate 1, The substrate 1 is oxidized to form a first gate insulating film 8, a first polycrystalline silicon film 11 is deposited, the specific resistance of the first polycrystalline silicon film is reduced, and the back surface of the P-type semiconductor substrate 1 is formed. Then, phosphorus is diffused into the first polycrystalline silicon film 11 in order to perform high gettering by intentionally generating crystal defects on the back surface by adding high concentration phosphorus (FIG. 5A).

Next, the first photolithography and plasma etching methods are used.
Is patterned, and the first gate insulating film 8 is etched down to the substrate surface with a hydrofluoric acid-based etchant (FIG. 5B). A second insulating film 9 is formed by oxidizing the P-type semiconductor substrate 1 and the first polycrystalline silicon film 11 (FIG. 5C). A second polycrystalline silicon film 12 is deposited and patterned by photolithography and plasma etching in the same manner as in the case of the first polycrystalline silicon film 11 described above (FIG. 5D). ). Thereafter, an interlayer silicon oxide film 15 is formed by a normal pressure CVD method, and an aluminum wiring 16 and a protective silicon oxide film 17 are applied to obtain the solid-state imaging device shown in FIGS.

[Problems to be solved by the invention]

In the above-described conventional solid-state imaging device, after the first polycrystalline silicon film 11 is patterned and the first gate insulating film 8 is etched to the surface of the P-type semiconductor substrate 1,
Since the first polycrystalline silicon film 11 is thermally oxidized to form the second gate insulating film 9, the second gate insulating film 9
At the time of formation, phosphorus (out diffusion) that has jumped out of the first polycrystalline silicon film 11 and the back surface of the P-type semiconductor substrate 1 adheres to the N-type layer 6 of the photoelectric conversion unit 2 or the charge transfer unit 3 on the substrate surface. Since the N ⁺ layer is locally formed, a point defect on the reproduction screen occurs when the N ⁺ layer adheres to the photoelectric conversion unit 2, and when the N ⁺ layer adheres to the N-type layer 6 of the charge transfer unit 3, the concentration at the point of attachment occurs. is the surface potential for the point of forming a thick N ⁺ layer than the other points, the charge came deeply be transferred becomes the form which is trapped a portion at that point, there is a drawback that results in the transfer charge loss Was.

[Means for solving the problem]

The method for manufacturing a solid-state imaging device according to the present invention includes a method of manufacturing a solid-state imaging device, comprising: a photoelectric conversion portion of a second conductivity type region provided on a surface of a first conductivity type semiconductor substrate containing phosphorus on a back surface; a first gate insulating film; , A second gate insulating film, a second polycrystalline silicon electrode and a charge transfer section including a second conductivity type region, and a charge transfer section from the photoelectric conversion section to the charge transfer section. A transfer gate for performing charge transfer;
In the method of manufacturing a solid-state imaging device having a high-concentration first conductivity type channel stop region that electrically separates the respective regions, the second gate insulating film forms a silicon oxide film by a plasma CVD method. And a step of thermally oxidizing the silicon oxide film.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a charge transfer section in a main manufacturing process according to one embodiment of the present invention.

After selectively forming an N-type layer 6 serving as an embedded channel of the photoelectric conversion unit 2 and the charge transfer unit 3 and a high-concentration P-type layer 7 serving as a channel stop 5 in the P-type semiconductor substrate 1, 1 is oxidized to form a first gate insulating film 8,
A first polycrystalline silicon film 11 is deposited to reduce the specific resistance of the first polycrystalline silicon 11 and high-concentration phosphorus is added to the back surface of the P-type semiconductor substrate 1 to intentionally generate crystal defects on the back surface. In order to perform gettering, phosphorus is diffused into the first polycrystalline silicon film 11 (FIG. 1A).

Next, the first polycrystalline silicon film 11 is patterned by photolithography and plasma etching, and the first gate insulating film 8 is etched to the substrate surface with a hydrofluoric acid-based etchant (FIG. 1 (b)). )).

Approximately 10nm to 50n silicon oxide film 13 using plasma CVD
m is deposited (FIG. 1 (c)).

The silicon oxide film 13 deposited by the plasma CVD method is subjected to thermal oxidation to form a second gate insulating film 9 (FIG. 1 (d)).

A second polycrystalline silicon film 12 is deposited and patterned by photolithography and plasma etching as in the case of the first polycrystalline silicon film 11 described above (FIG. 1E).

Thereafter, an interlayer oxide film layer is formed by a normal pressure CVD method, and an aluminum wiring and a protective oxide film are applied to obtain a solid-state imaging device.

FIG. 2 is a cross-sectional view of the charge transfer section in the main manufacturing process of the reference example of the present invention.

2 (c) is the same as the embodiment shown in FIG. 1 except that the silicon nitride film 14 is deposited to a thickness of about 10 to 30 nm by the plasma CVD method.

In FIG. 2E, after the patterning of the second polycrystalline silicon film 12 is completed, an interlayer oxide film layer is formed by a normal pressure CVD method, and an aluminum wiring and a protective oxide film are applied to obtain a solid-state imaging device.

〔The invention's effect〕

As described above, according to the present invention, in the manufacturing process of the solid-state imaging device, the second gate insulating film is formed by thermally oxidizing the silicon oxide film formed by the plasma CVD method. At the time of film formation, phosphorus outdiffused from the back surface of the first polycrystalline silicon film and the P-type semiconductor substrate forms N in the photoelectric conversion portion or the charge transfer portion on the substrate surface.
It is possible to suppress the formation of a local N ⁺ layer by adhering to the mold layer, and when used as a television camera system, a point defect and a charge on the reproduction screen caused by the local N ⁺ layer. There is an effect that rod-like defects due to transfer damage can be suppressed.

[Brief description of the drawings]

1 (a) to 1 (e) are cross-sectional views of a charge transfer section in a main manufacturing process according to an embodiment of the present invention, and FIGS. 2 (a) to 2 (e).
FIG. 9 is a cross-sectional view of a charge transfer section in a main manufacturing process according to another embodiment of the present invention. FIG. 3 is a plan view of a solid-state image pickup device using a charge-coupled device having a two-layer polycrystalline silicon electrode structure as an example of the prior art, FIG. 4 (a) is a cross-sectional view taken along the line II 'of FIG. FIG. 4 (b)
FIG. 3 is a cross-sectional view taken along the line II-II 'of FIG. 3, and FIG. 5 is a cross-sectional view of a charge transfer section in main manufacturing steps of a conventional solid-state imaging device. DESCRIPTION OF SYMBOLS 1 ... P-type semiconductor substrate, 2 ... Photoelectric conversion part, 3 ... Charge transfer part, 4 ... Transfer gate part, 5 ... Channel stop, 6 ... N-type layer, 7 ... P-type layer, 8 ... 1st
Gate insulating film, 9 ... second gate insulating film, 10 ... gate insulating film, 11 ... first polycrystalline silicon film, 12 ... second
Polycrystalline silicon film, 13 ... Plasma CVD silicon oxide film, 1
4 ... Plasma CVD silicon nitride film, 15 ... Normal pressure CVD interlayer silicon oxide film, 16 ... Aluminum wiring, 17 ... Protective silicon oxide film.

Claims (1)

(57) [Claims] A second conductive type region provided on a surface of a first conductive type semiconductor substrate containing phosphorus on a back surface thereof; a first gate insulating film; A crystalline silicon electrode, a second gate insulating film, a charge transfer portion including a second polycrystalline silicon electrode and a second conductivity type region, and a transfer gate for transferring charge from the photoelectric conversion portion to the charge transfer portion And a method of manufacturing a solid-state imaging device having a high-concentration first-conductivity-type channel stop region that electrically separates the respective regions, wherein the second gate insulating film is formed of a silicon oxide film by a plasma CVD method. A method for manufacturing a solid-state imaging device, comprising: a forming step; and a step of thermally oxidizing the silicon oxide film.