JPH025476A - Manufacture of schottky type image sensor - Google Patents

Abstract

PURPOSE:To obtain a large effective photodetecting region by implanting other conductivity type impurity with second oxide film and a resist film as masks to form a channel stopper at the boundary between a charge coupled element active region and a photodetector guard ring region. CONSTITUTION:After the implantation of an impurity for forming a charge coupled element active region and the implantation of an impurity for forming the guard ring of a Schottky diode are simultaneously conducted with an antioxidation film 3a as a mask, a thick oxide film 4a is formed on the active region and the guard ring by thermally oxidizing. Thereafter, the film 3a is removed, and a thin film 2 at the center of the diode are covered with a resist film 7. With the films 4a, 7 as masks an impurity for a channel stopper is implanted. Since the film 4a on the guard ring and the film 7 perform sufficient functions as masks at the time of implanting the impurity for the stopper if they are superposed, an excess margin for forming the Schottky diode effective photodetecting region may not be considered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a Schottky image sensor.

[Conventional technology]

As an example of a Schottky image sensor.

Figures 3(a) to 3(d) show cross-sectional views of a semiconductor chip in the main manufacturing process of a back-illuminated image sensor that combines a charge-coupled device and a Schottky diode (a plan view thereof is shown in Figure 2). ).

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 using a photoresist method. A CCD active region 20 and a light receiving element area are defined, and a resist film 16 is provided in the center of the light receiving element area to define a photodiode guard ring area 21b.Thereafter, as shown in FIG. A type impurity 1, for example, phosphorus, is ion-implanted and thermally oxidized to form an N-type buried channel 5, an N-type guard ring 6a, and a second silicon oxide 1114b.Next, as shown in FIG.
), a P-type impurity such as boron is ion-implanted to form a channel stopper 8. No.],
After removing the second silicon oxide film, a silicon oxide film of a predetermined thickness is grown, and polysilicon is deposited thereon. By patterning this silicon oxide film and polysilicon, gate oxide film 9 and gate electrode 10 of a charge coupled device are formed. A resist 1 to a film 11 having a predetermined shape is formed. Thereafter, N type impurity 7, for example, phosphorus, is ion-implanted to form N+ region 12. next,
As shown in FIG. 3(d), after removing the resist film 11, an insulating film 1, for example, a PSG film is stacked, and an insulating film pattern 1.3 is formed by a photoresist method. metal layer,
For example, a platinum layer is deposited, heat treated, and then etched with a predetermined etching solution to form the Schottky diode metal electrode layer 14b.

Incidentally, after removing the silicon oxide films 2 and 4b, irregularities are formed on the surface, but these are not shown in FIG. 3(c) for convenience. or,
The N area 12 is the shoulder diode metal electrode 1.
4b, and are provided at several locations inside the guard ring 6b. Further, FIG. 2 shows the state before the interlayer insulating film 16, reflective electrode 17, and cover film 18 are attached.

[Problem to be solved by the invention]

However, the conventional Schottky image sensor manufacturing method requires alignment for providing a photoresist film within the light receiving element region separated by the silicon nitride film 3b to define the photodiode guard ring region. Therefore, patterning must be performed using an effective light-receiving area pattern that takes into account the misalignment that occurs at this time (typically about 0.3 μm per side).
There was a drawback that the effective light-receiving area could not be enlarged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a Schottky image sensor that can eliminate the above-mentioned drawbacks and ensure a large effective light-receiving area.

[Means to solve the problem]

The method for manufacturing a Schottky image sensor of the present invention includes:
- After forming a first oxide film on the surface of a conductive semiconductor substrate, selectively forming an oxidation-resistant film on the first oxide film to define a charge coupled device active region and a light receiving device guard ring region; , using the oxidation-resistant film as a mask, impurities of other conductivity type are introduced into the charge-coupled device active region and the light-receiving device guard ring region, and then selective oxidation is performed to form a predetermined region on the device active region and the light-receiving device guard ring region. After forming a second oxide film with a certain 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,
The method includes the step of introducing impurities of other conductivity type 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. .

[Effect]

In the present invention, the introduction of impurities to form the active region of the charge coupled device and the introduction of impurities to form the guard ring of the Schottky diode are simultaneously performed using an oxidation-resistant film as a mask, and then the charge coupled device is activated by thermal oxidation. Form a thick oxide layer over the area and card ring. after that,
The oxidation-resistant film is removed, and the thin oxide film at the center of the Schottky diode is covered with a resist film. Using the thick oxide film and the resist film as a mask, impurities for a channel stopper are introduced. In this step, if the thick oxide film on the guard ring overlaps with the resist film, it sufficiently functions as a mask when introducing impurities for the channel stopper. Therefore, there is no need to consider an extra alignment margin for forming an effective light-receiving area of the Schottky diode, which was necessary in the conventional manufacturing method. In the manufacturing method of the present invention, by designing and manufacturing the Schottky diode guard ring to have the minimum necessary area, it is possible to secure a large effective light receiving area of the Schottky diode.

〔Example〕

FIGS. 1(a) to 1(d) show cross-sectional views of a semiconductor chip in main manufacturing steps for explaining embodiments of the present invention.

First, as shown in FIG. 1(a), P-type silicon]/substrate 1
A first silicon oxide film 2. After growing a silicon nitride film 3a (oxidation-resistant film), patterning is performed using a photoresist method to define a CCD active region 20 and a photodiode card ring region 21,a. Next, N-type impurity 9 (for example, phosphorus) is ion-implanted, and as shown in FIG. A mold guard ring 6a is formed. 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 a resist film 7.
After covering with a P-type impurity 1 (for example, boron), a channel stopper 8 is formed as shown in FIG. 1<c). After removing the first silicon oxide film and the second silicon oxide film, a silicon oxide film of a predetermined thickness is grown, and polysilicon is deposited thereon. Gate oxide film 9 and gate electrode 10 of a charge coupled device are formed by patterning this silicon oxide film and polysilicon. A resist film 11 having a predetermined pattern is formed. Thereafter, an N-type impurity 2 such as phosphorus is ion-implanted to form a Ng@ region 12. Next, Figure 1 (
As shown in d), an insulating film 1 such as a PSG film is deposited,
An insulating film pattern 13 is formed by a photo-strengthening method. A metal film 1, such as a platinum film, is deposited, heat treated, and then patterned using a predetermined etching solution to form a Schottky diode metal electrode layer 1.4a.

〔Effect of the invention〕

In the Schottky image sensor, the dark current is #,i,>
At the same time, it is necessary to form a Schottky diode with a large effective light-receiving area.4 In order to reduce dark current, it is necessary to form a guard ring, but in order to ensure a large effective light-receiving area, the guard ring area must be must be reduced. According to the manufacturing method of the present invention, since the channel stopper 8 and the Schottky diode effective light-receiving area 15 are patterned using the same mask, the guard ring is formed to have the minimum necessary area without considering extra alignment margin. A large effective light receiving area can be secured.

[Brief explanation of the drawing]

FIGS. 1(a) to (d) are cross-sectional views of a semiconductor chip shown in the order of steps to explain an embodiment of the present invention, and FIG. 2 is a plan view of a semiconductor chip showing an example of a Schottky image sensor. , and FIGS. 3(a) to 3(d) are cross-sectional views of semiconductor chips arranged in the order of steps to explain a conventional example. Note that FIGS. 1 and 3 show cross-sectional portions taken along line xx' in FIG. 2. DESCRIPTION OF SYMBOLS 1... P-type silicon substrate, 2... First silicon oxide film, 3a, 3b-... Silicon nitride film, 4a, 4b...
...Second silicon oxide film, 5...Buried channel, 6
a, 6b... Guard ring, 7... Resist film, 8
...Channel stopper, 9...Gate oxide film, 10
...Gate electrode, 1]...Resist film, ], 2...
N+ region 1.3...Insulating film pattern, 1.4a
14b-. Schottky diode metal electrode layer, ]5... Schottky diode effective light receiving area, 16... interlayer insulating film, 17... reflective electrode, 18... cover film, 19-1
．． 1.9-2... Vertical transfer electrode, 20... CCD active region, 21a, 21b... Photodiode guard ring region, 22a, 22b... Photodiode region.

Claims (1)

[Claims] After forming a first oxide film on the surface of a semiconductor substrate of one conductivity type, an oxidation-resistant film is selectively formed on the first oxide film to define a charge coupled device active region and a light receiving device guard ring region. , using the oxidation-resistant film as a mask, impurities of other conductivity type are introduced into the charge-coupled device active region and the light-receiving device guard ring region, and then selective oxidation is performed to form a predetermined region on the device active region and the light-receiving device guard ring region. After forming a second oxide film with a certain 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,
The method includes the step of introducing an impurity of a different conductivity type 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. A method for manufacturing a Schottky image sensor.