JPH07120777B2 - Schottky type image sensor manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a Schottky type image sensor.

[Conventional technology]

As an example of a Schottky type image sensor, a back illuminated image sensor in which a charge coupled device and a Schottky diode are combined (a plan view thereof is shown in FIG. 2).
3 (a) to 3 (d) are cross-sectional views of the semiconductor chip in the main manufacturing steps of FIG.

First, as shown in FIG. 3 (a), a first silicon oxide film 2 and a silicon nitride film 3a (oxidation resistant film) are grown on a P-type silicon substrate 1 and then patterned by a photoresist method. A CCD active region 20 and a light receiving element region are partitioned, and a resist film 16 is provided in the center of this light receiving element region to partition a photodiode guard ring region 21b. After that, the third
As shown in FIG. 2B, N-type impurities, for example, phosphorus are ion-implanted and thermally oxidized to form N ⁻ -type buried channels 5 and N ^−.
A mold type guard ring 6a and a second silicon oxide film 4b are formed. Next, as shown in FIG. 3C, ion implantation of P-type impurities such as boron is performed to form the channel stopper 8. After removing the first and second silicon oxide films, a silicon oxide film having a predetermined thickness is grown, and polysilicon is deposited thereon. By patterning the silicon oxide film and the polysilicon, the gate oxide film 9 and the gate electrode 10 of the charge coupled device are formed. A resist film 11 having a predetermined shape is formed. Then, N type impurities such as phosphorus ions are implanted to form the N ⁺ region 12. Next, as shown in FIG. 3D, the resist film 11
After removing, the insulating film, for example, the PSG film is deposited, and the insulating film pattern 13 is formed by the photoresist method. After depositing a metal layer, for example, a platinum layer, and subjecting it to heat treatment, etching is performed with a predetermined etching solution to form a Schottky diode metal electrode layer 14b.

After removing the silicon oxide films 2 and 4b, irregularities are formed on the surface, but this is not shown in FIG. 3 (c) for convenience. Further, the N ⁺ region 12 is for making ohmic contact with the Schottky diode metal electrode 14b, and it is assumed that a number of places are provided inside the guard ring 6b. Further, FIG. 2 shows a state before the interlayer insulating film 16, the reflective electrode 17, and the cover film 18 are attached.

[Problems to be Solved by the Invention]

However, the conventional method of manufacturing the Schottky image sensor requires alignment for providing the photoresist film in the light receiving element region partitioned by the silicon nitride film 3b to partition the photodiode guard ring region. Therefore, patterning must be performed using an effective light receiving region pattern that takes into account misalignment (typically about 0.3 μm per side) at this time, and there is a drawback that the effective light receiving region cannot be made large.

It is an object of the present invention to provide a method of manufacturing a Schottky type image sensor which can eliminate the above-mentioned drawbacks and can secure a large effective light receiving area.

[Means for Solving the Problems]

The manufacturing method of the Schottky type image sensor of the present invention is
After forming a first oxide film on the surface of the one conductivity type semiconductor substrate, an oxidation resistant film is selectively formed on the first oxide film to partition the charge coupled device active region and the light receiving device guard ring region. , A predetermined oxidation is performed on the element active region and the light receiving element guard ring region by introducing another conductivity type impurity into the charge coupled device active region and the light receiving element guard ring region by using the oxidation resistant film as a mask. After forming a second oxide film having a thickness and removing the oxidation resistant film, the first oxide film on the light receiving element region surrounded by the light receiving element guard ring region is covered with a resist film, and then,
And a step of forming a channel stopper at a boundary between the charge coupled device active region and the light receiving device guard ring region by introducing another conductivity type impurity using the second oxide film and the resist film as a mask. .

[Action]

In the present invention, the impurity for forming the charge coupled device active region and the impurity for forming the guard ring of the Schottky diode are simultaneously introduced using the oxidation resistant film as a mask, and then the charge coupled device is activated by thermal oxidation. A thick oxide film is formed on the area and the card ring. afterwards,
The oxidation resistant film is removed and the thin oxide film in the central part of the Schottky diode is covered with a resist film. Impurities for the channel stopper are introduced using the thick oxide film and the resist film as a mask. In this step, if the thick oxide film on the guard ring and the resist film overlap each other, they sufficiently function as a mask for introducing the impurities for the channel stopper. Therefore, it is not necessary to consider an extra alignment margin for forming the Schottky diode effective light receiving region, which is required in the conventional manufacturing method. In the manufacturing method of the present invention, the Schottky diode guard ring is designed and manufactured to have the necessary minimum area, and thus a large Schottky diode effective light receiving region can be secured.

〔Example〕

1 (a) to 1 (d) are cross-sectional views of a semiconductor chip in main manufacturing steps for explaining an embodiment of the present invention.

First, as shown in FIG. 1A, a first silicon oxide film 2 and a silicon nitride film 3a (oxidation resistant film) are grown on a P-type silicon substrate 1 and then patterned by a photoresist method. A CCD active area 20 and a photodiode guard ring area 21a are defined. Next, an N-type impurity, for example, phosphorus is ion-implanted, and as shown in FIG. 1B, the second silicon oxide film 4a and the buried channel 5 having a predetermined thickness and the N ⁻ -type guard are formed by thermal oxidation. Form the ring 6a. After removing the silicon nitride film, the first silicon oxide film 2 on the photodiode region 22a surrounded by the buried channel 5 and the guard ring 6a is covered with the resist film 7, and then ion implantation of P-type impurities such as boron is performed. Then, as shown in FIG. 1C, the channel stopper 8 is formed. After removing the first silicon oxide film and the second silicon oxide film, a silicon oxide film having a predetermined thickness is grown, and polysilicon is deposited thereon. By patterning the silicon oxide film and the polysilicon, the gate oxide film 9 and the gate electrode 10 of the charge coupled device are formed. A resist film 11 having a predetermined pattern is formed. Then, N type impurities such as phosphorus ions are implanted to form the N ⁺ region 12. next,
As shown in FIG. 1D, an insulating film, for example, a PSG film is deposited and a pattern 13 of the insulating film is formed by a photoresist method. A metal film, for example, a platinum film is deposited, heat-treated, and then patterned by a predetermined etching solution to form a Schottky diode metal electrode layer 14a.

〔The invention's effect〕

In a Schottky type image sensor, it is necessary to form a Schottky diode that has a small dark current and a large effective light receiving area. In order to reduce the dark current, it is necessary to form a guard ring, but in order to secure a large effective light receiving area, the guard ring area must be reduced. According to the manufacturing method of the present invention, since the patterning of the channel stopper 8 and the Schottky diode effective light receiving region 15 is performed by the same mask, the guard ring is formed in a necessary minimum area without considering an extra alignment margin, A large effective light receiving area can be secured.

[Brief description of drawings]

1 (a) to 1 (d) are cross-sectional views of a semiconductor chip shown in the order of steps for explaining an embodiment of the present invention, and FIG. 2 is a plan view of the semiconductor chip showing an example of a Schottky image sensor. 3A to 3D are cross-sectional views of semiconductor chips arranged in the order of steps for explaining a conventional example. Incidentally, FIGS. 1 and 3 show a cross-sectional portion taken along the line XX 'in FIG. 1 ... P-type silicon substrate, 2 ... first silicon oxide film, 3a, 3b ... silicon nitride film, 4a, 4b ... second silicon oxide film, 5 ... buried channel, 6a, 6b ... ... Guard ring, 7 ... Resist film, 8 ... Channel stopper, 9 ...
… Gate oxide film, 10 …… Gate electrode, 11 …… Resist film, 12 …… N ⁺ region, 13 …… Insulating film pattern, 14a, 14b
...... Schottky diode metal electrode layer, 15 ...... Schottky diode effective light receiving area, 16 …… Interlayer insulating film, 17
...... Reflecting electrode, 18 ...... Cover film, 19-1, 19-2 ...... Vertical transfer electrode, 20 ...... CCD active area, 21a, 21b ...... Photodiode guard ring area, 22a, 22b ...... Photodiode area.

Claims (1)

[Claims] 1. A charge-coupled device active region and a light-receiving device guard by forming a first oxide film on a surface of a one conductivity type semiconductor substrate and then selectively forming an oxidation resistant film on the first oxide film. A ring region is defined, and another conductive type impurity is introduced into the charge coupled device active region and the light receiving device guard ring region using the oxidation resistant film as a mask, and then selective oxidation is performed to perform the device active region and the light receiving device guard ring. A second oxide film having a predetermined thickness is formed on the region, the oxidation resistant film is removed, and then the first oxide film on the light receiving element region surrounded by the light receiving element guard ring region is formed by a resist film. Then, another conductive type impurity is introduced using the second oxide film and the resist film as a mask to form a channel stopper at the boundary between the charge coupled device active region and the light receiving device guard ring region. Manufacturing method of the Schottky type image sensor which comprises a step of forming.