JP2874071B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device having a fine pattern and capable of arranging highly integrated elements.

[0002]

2. Description of the Related Art In order to increase the degree of integration of semiconductor devices, as typified by, for example, 16 MDRAMs, miniaturization of the semiconductor devices is progressing. The area occupied by the element itself is determined by the required dimensions of each layer determined by the electrical characteristics, the resolution in photolithography, and the overlay accuracy. Among them, particularly, a margin for superposition is a necessity that requires a considerable amount.

In the process of manufacturing many devices such as DRAMs, it is necessary to remove a portion of the polysilicon at the bottom of the hole and connect the underlying substrate or conductive film to the upper wiring layer. is there. FIG. 2 shows a process for forming an opening in the polysilicon layer at the bottom of such a hole by a conventional method. In the figure, 1 is a silicon substrate, 2A is a thin oxide film, 2B is a silicon nitride film, and 3 is a BPSG (Borond
oped Phospho-Sillicate Glass) film, 4 is a polysilicon film, and 5 is a photoresist film. In this case, FIG.
As shown in FIG. 6, after the pattern of the opening is formed by the photoresist film 5, the lower polysilicon film 4 is etched. According to this method, a margin for alignment is required between the opening pattern of the photoresist film 5 and the side wall of the hole. This amount is about 0.2 μm using a current stepper.

[0004]

In such a conventional configuration, the above-mentioned alignment margin becomes a great hindrance in improving the degree of integration of fine devices such as a 16 MDRAM.

The present invention solves such a conventional problem, and provides a method of manufacturing a semiconductor device by a self-aligned opening method on the bottom surface of a polysilicon film which does not require any alignment margin. It is the purpose.

[0006]

In order to achieve the above object, the present invention comprises a step of forming a polysilicon film in a region including a hole formed in a predetermined portion of a film such as a BPSG film on the surface of a semiconductor substrate; Forming a silicon oxide film and a silicon nitride film on the surface of the polysilicon film, and forming an organic resin film such as a photoresist only in the hole so as to cover at least the silicon nitride film formed on the bottom surface of the hole. Using the organic resin film as a mask, removing the other silicon nitride film while leaving at least the silicon nitride film formed on the bottom surface of the hole, and removing the silicon nitride film after removing the organic resin film. Forming a silicon oxide film on the formed polysilicon film by thermal oxidation, and etching the polysilicon film formed on the bottom of the hole by using the silicon oxide film as a mask. By at least a structure and a step for himself consistent removed.

[0007]

According to the above construction, since the polysilicon film on the bottom surface of the hole can be opened over the entire bottom surface, there is no need for a margin for overlapping the side surface of the hole and the opening of the polysilicon film.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view showing a step of opening a polysilicon film at a bottom portion of a hole in a method of manufacturing a semiconductor device according to the present invention. After forming a 20 nm oxide film 2A on the silicon substrate 1 as shown in FIG.
m silicon nitride film 2B was formed by low pressure CVD. After that, a BPSG film 3 having a thickness of 800 nm is formed by atmospheric pressure CVD.
Formed by the method. At this time, the boron concentration in the BPSG film was 3 wt%, and the phosphorus concentration was 6 wt%. Then, after a heat treatment at 900 ° C. for 30 minutes in nitrogen, the diameter is 1.6 μm.
A hole m was formed by dry etching using a resist as a mask. Next, a polysilicon film 4 having a thickness of 300 nm was deposited thereon by a low pressure CVD method. This polysilicon film 4 contains phosphorus and has a sheet resistance of 20Ω / □.

Thereafter, a process which is a feature of the present invention is started. That is, the silicon oxide film 11 having a thickness of 20 nm is formed on the polysilicon film 4 by decompression CV by thermal decomposition of dichlorosilane gas.
Formed by the D method, and further formed by the reduced pressure CVD method.
A 0 nm silicon nitride film 12 was formed thereon. Next, Shipley S-1400 type photoresist was applied to a thickness of 1.2 μm.
After coating with m, the film is exposed to 436 nm ultraviolet light of 80 mJ / cm ² by a stepper, and further developed with NMD-3 type developer manufactured by Tokyo Ohka Kogyo Co., Ltd. for 45 seconds, as shown in FIG. Then, the photoresist film 13 was left only inside the hole. Next, FIG. 1 CHF ₃ as (b)
The silicon nitride film 12 outside the hole is removed by performing dry etching with a gas, and then the photoresist film 13 in the hole is removed. 200 nm silicon oxide film 14
Was selectively formed. Then, as shown in FIG. 3C, the silicon nitride film 12 in the trench is removed by hot phosphoric acid, and the underlying silicon oxide film is removed by a mixed solution of hydrofluoric acid and ammonium fluoride. Anisotropic dry etching of the polysilicon film 4 is performed using HBr as a mask.
And it could be self-aligned manner opening the polysilicon film 4 on the bottom portion of the hole by making with respect to the side surface of the hole by a gas mixture of O _2. In this embodiment, the exposure by the stepper is performed as a method of leaving the photoresist film 13 only in the hole, but the same effect can be obtained by the etch-back method.

After the bottom polysilicon film 4 is opened, a contact hole for the silicon substrate 1 and an upper wiring layer is further formed in the polysilicon film 4.
When the thickness is 6 μm, in this method, the overlapping margin is 0.2 μm on one side.
m, the diameter of the opening of the BPSG film of the above embodiment is 1.6 μm (0.6 μm of opening + polysilicon film 2 ×
0.3 μm + alignment margin 2 × 0.2 μm).

If a polysilicon film opening is formed on the bottom surface by using a photoresist mask and a contact hole is formed in the polysilicon film as in the prior art, the diameter of the opening of the BPSG film is at least 2.0 μm (opening 0.2 mm). 6 μm +
Polysilicon film 2 x 0.3 µm + alignment margin 4 x
0.2 μm). According to the present invention, it is possible to significantly reduce the occupied area.

[0012]

As is apparent from the above embodiments, the present invention has a structure in which, when an opening is formed in a polysilicon film formed in a region including a hole, the polysilicon film at the bottom of the hole is removed in a self-aligned manner. Therefore, it is not necessary to have a margin for overlapping the side surface of the hole and the opening of the polysilicon film, the widest opening area can be obtained, and a semiconductor device which improves the degree of integration by reducing the area occupied by the opening can be provided. .

[Brief description of the drawings]

FIG. 1 is a process sectional view illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention;

FIG. 2 is a process cross-sectional view for explaining a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate (semiconductor substrate) 2A oxide film 2B silicon nitride film 3 BPSG film 4 polysilicon film 11 silicon oxide film 12 silicon nitride film 13 photoresist film (organic resin film) 14 silicon oxide film

Claims (3)

(57) [Claims] A step of forming a polysilicon film in a region including a hole formed in a predetermined portion of a film such as a BPSG film on a surface of a semiconductor substrate; and forming a silicon oxide film and a silicon nitride film on the surface of the polysilicon film. Forming an organic resin film such as a photoresist so as to cover at least the silicon nitride film formed on the bottom of the hole only in the hole, and using the organic resin film as a mask, Removing the other silicon nitride film while leaving the silicon nitride film formed on the bottom surface of the hole, and thermally oxidizing the silicon oxide film on the polysilicon film from which the silicon nitride film has been removed after removing the organic resin film. At least a step of forming a film and a step of self-aligningly removing the polysilicon film formed on the bottom of the hole by etching using the silicon oxide film as a mask are described. The method of manufacturing a semiconductor device which is characterized in that. 2. The method according to claim 1, wherein the step of forming an organic resin film such as a photoresist so as to cover at least the silicon nitride film formed on the bottom surface of the hole only in the hole is performed. 2. The method according to claim 1, wherein after the film is applied, the entire surface of the organic resin film is dry-etched to retreat the surface of the organic resin film, and the organic resin film is formed only in the hole. A method for manufacturing a semiconductor device. 3. An organic resin film such as a photoresist is formed on the entire surface including the inside of the hole instead of forming an organic resin film such as a photoresist so as to cover at least the silicon nitride film formed on the bottom surface of the hole only in the hole. 2. The method for manufacturing a semiconductor device according to claim 1, wherein after the film is applied, a predetermined portion of the organic resin film is exposed and developed to form an organic resin film only in the hole.