JPH0294568A - Manufacture of solid-state image sensing device - Google Patents

Abstract

PURPOSE:To enhance the accuracy of a position even in a region of the lower part of a transfer electrode by ion implanting a thick silicon oxide film at the opening of a silicon nitride film thereby to form a predetermined region such as a vertical charge transfer unit or the like in a self-alignment manner with a channel stopper region. CONSTITUTION:A thick silicon oxide film 5 is formed in the region of the opening 3a of a silicon nitride film 3 on the surface of a silicon substrate 11 by selective oxidation. A channel stopper region 12 is formed under the film 5 by ion implanted impurity. The film 5 is disposed partly in the opening 3b formed at the film 3 on the surface of the substrate 1. That is, the region including the thick film 5 is opened. With the film 3 having the opening 3b and the film 5 as masks it is ion implanted. Since the implantation for forming a vertical charge transfer unit 13 is conducted with the film 5 as part of the mask, the unit 13 is formed in a self-alignment manner with the region 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a solid-state imaging device in which a thick silicon oxide film is formed by a selective oxidation method.

[Summary of the Invention] The present invention provides a method for manufacturing a solid-state imaging device in which a thick silicon oxide film is formed on a semiconductor substrate by selective oxidation, in which the silicon nitride film used for selective oxidation is re-irradiated with i! By removing a large portion of the thick silicon oxide film and exposing a portion of the thick silicon oxide film to the inside of the opening, ion implantation is performed in a self-aligned manner using this as a mask to prevent misalignment of the ion implanted region and improve the device. This prevents deterioration of characteristics.

[Prior art] Interline type, frame interline type CCD
The device has a vertical charge transfer section (V register) adjacent to the light receiving section via the readout section, and a channel stopper region is placed on the substrate surface in order to separate pixels and separate the vertical charge transfer section. It is formed.

By the way, in conventional processes, mask alignment for forming each region on the surface of a semiconductor substrate is performed using a certain target mark on the wafer as a reference.

There is also a known technique in which a thick silicon oxide film is formed by a selective oxidation method, and ions are implanted using the thick silicon oxide film as a mask to form an overflow drain region with a self-alignment line (for example, 6
(See Publication No. 131111).

[Problem to be solved by the invention]

However, when trying to increase the resolution of solid-state imaging devices, even more precise mask alignment technology is required, and as elements become smaller in size these days, misalignment can lead to variations in characteristics. become. Although the alignment of the area is improved by using the Selfa line technology, it is possible to form a light receiving part with the transfer electrode formed on the vertical charge transfer part via an insulating film and the Selfa line.
It is difficult to form the readout section and channel stopper region using the vertical charge transfer section and the self-alignment line using the current process.

SUMMARY OF THE INVENTION In view of the above-mentioned technical problems, it is an object of the present invention to provide a method for manufacturing a solid-state imaging device in which each region is formed with high positional accuracy.

[Means to solve the problem]

In order to achieve the above-mentioned object, the method for manufacturing a solid-state imaging device of the present invention starts by sequentially laminating a silicon oxide film and a silicon nitride film on a semiconductor substrate such as a silicon substrate. Next, a mask layer is formed on the silicon nitride film, and ion implantation is performed to form a channel stopper region reflecting the pattern of the mask layer. This ion implantation may be performed before or after the silicon nitride film is vacuumed.

Next, using the silicon nitride film selectively removed from the pattern of the mask layer as a mask, a thick silicon oxide film is formed on the semiconductor substrate. Then, the silicon nitride film is selectively removed again so that at least the thick silicon oxide film faces into the opening. The opening can correspond, for example, to the area of the vertical charge transfer section.

Next, ion implantation is performed using the silicon nitride film and the thick silicon oxide film as masks. For example, a vertical charge transfer section can be formed by this ion implantation, and after the ion implantation, the silicon nitride film and the thick silicon oxide film may be removed.

[Operation] Ion implantation is performed to form a channel stopper region in the region where the silicon nitride film is selectively removed by the mask layer, and then oxidized, so that the selectively formed thick oxide layer is removed. A channel stopper region will be formed under the silicon film. Next, by selectively removing the silicon nitride film again so that at least the thick silicon oxide film faces into the opening, the thick silicon oxide film can be used as a part of the mask, resulting in a channel stone bar region. This means that a region for ion implantation can be obtained using the self-alignment line.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

This embodiment is an example of a CCD imager, and a vertical charge transfer portion is formed by a channel stopper region and a self-aligned line using a thick silicon oxide film formed by selective oxidation. Hereinafter, this embodiment will be explained according to its steps with reference to FIGS. 1a to 1e.

(a) First, as shown in FIG. 1a, a silicon oxide film 2 is formed on the entire surface of a silicon substrate 1. This silicon oxide film 2 is a so-called pad oxide film.

Then, ion implantation is performed on the entire surface. This ion implantation is performed to set the potential of the readout section. In the figure, the region from the substrate surface to the dotted line 11 indicates the region into which impurities have been introduced.

Next, as shown in FIG. 1, a silicon nitride film 3 is formed over the entire surface of the silicon oxide film 2. This silicon nitride film 3 functions as an oxidation-resistant film.

A mask N4 made of a photoresist material is formed on the silicon nitride film 3 to a desired thickness. This mask layer 4 is patterned by selective exposure, development, etc.
A window portion 4a is formed. The pattern of the window portion 4a corresponds to the channel stopper area, as will be described later. By etching, the silicon nitride film 3 is selectively removed from the pattern of the mask layer 4, and the window portion 4a is removed.
An opening 3a that reflects this is obtained. Ion implantation is then performed using these mask layer 4 and silicon nitride film 3 as masks to form an impurity region on the surface of silicon substrate 1 for forming channel stopper SJ[[12. Here, for example, boron or the like is used as the impurity.

(C) Next, the mask layer 4 is removed, and as shown in FIG. 1C, selective oxidation is performed to form the silicon nitride film 3.
A thick silicon oxide film 5 is formed on the surface of the silicon base Fil in the region of the opening 3a. This thick silicon oxide film 5
A channel stopper region 12 is formed below by ion-implanted impurities.

(dl Next, as shown in FIG. 1d, the silicon nitride film 3 is patterned again using the photoresist layer 6. At this time, in a part of the opening 3b formed in the silicon nitride film 3, The thick silicon oxide film 5 faces the surface of the silicon substrate I.

In other words, a region including the thick silicon oxide film 5 is opened.

Next, ion implantation is performed using the silicon nitride film 3 having the opening 3b and the thick silicon oxide film 5 as a mask.
Note that if the photoresist layer 6 remains, the photoresist layer 6 functions as a part of the mask. By this ion implantation, impurities for forming the vertical charge transfer section 13 are introduced into the opening 3b. Since the thick silicon oxide film 5 is used as a part of the mask for ion implantation to form the vertical charge transfer section 13, the vertical charge transfer section 13 is formed by the channel stomper region 12 and the self-alignment line. . Therefore, there is no need for a margin for mask alignment between the channel stopper region 12 and the vertical charge transfer section 13, and the two can be formed with good matching.

(e) Next, the silicon nitride film 3 used as a mask is removed twice: selective oxidation of the photoresist layer 61 and ion implantation, and then the silicon oxide film 2 on the surface is removed.
5 is removed to expose the surface of the silicon substrate 1. At this time, the vertical charge transfer section 13 and the channel stopper region 12 have already been formed with good alignment by the above-mentioned self-alignment line, and since the readout section uses the potential that is initially implanted into the entire surface, the vertical charge transfer section 13. The channel stomper region 12 and the readout section 14 are each formed with high positional accuracy.

Subsequently, an insulating film 7 is formed over the entire surface including the recessed portion where the thick silicon oxide film 5 was formed. This insulating film 7 is an oxide film or has, for example, an ONO (oxide film-nitride oxide film) structure. Next, a polysilicon layer 8 that will become a transfer electrode is formed. Although not shown, this polysilicon layer 8 has a two-layer structure, and an interlayer insulating film is formed between the first layer and the second Nth layer, and is patterned into a desired electrode shape. Then, using the polysilicon layer 8 as a mask, ion implantation is performed to form a light receiving section 15. Thereafter, the necessary wiring, passivation, etc. are performed to complete the device.

In this way, in the manufacturing method of the solid-state imaging device of this embodiment, since the vertical charge transfer section 13 is formed in a self-aligned manner using the thick silicon oxide film 5 as a part of the mask, Channel stopper region 12 and vertical charge transfer section 13 formed using the same mask
are formed with good positional accuracy. Therefore, since the positional accuracy is improved, it is possible to prevent variations in the characteristics of the element.

〔Effect of the invention〕

In the method for manufacturing a solid-state imaging device of the present invention, ions are implanted with the thick silicon oxide film facing the opening of the silicon nitride film, so that required regions such as vertical charge transfer regions are formed in the channel stopper region and the self-alignment line. will be done. Therefore, even in the region below the transfer electrode, positional accuracy can be improved and variations in the characteristics of the element can be prevented, which is particularly advantageous when miniaturizing the element and increasing resolution.

...Silicon nitride film ...mask layer ...thick silicon oxide film ...Polysilicon layer 2...Channel stopper area 3...Vertical charge transfer section 4...Reading section 5... Light receiving section

Claims (1)

[Claims] A step of sequentially laminating a silicon oxide film and a silicon nitride film on a semiconductor substrate, forming a mask layer on the silicon nitride film, and forming a channel stopper region reflecting the pattern of the mask layer. a step of performing ion implantation to remove the silicon nitride film; a step of forming a thick silicon oxide film on the semiconductor substrate using the selectively removed silicon nitride film as a mask; and a step of selectively removing the silicon nitride film again. manufacturing a solid-state imaging device, comprising: a step of making at least a thick silicon oxide film face into the opening; and a step of performing ion implantation using the silicon nitride film and the thick silicon oxide film as a mask. Method.