JPH0716008B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a gate oxide film having a high dielectric breakdown voltage.

[Conventional technology]

Conventionally, as shown in FIGS. 3 (a) and 3 (b), a gate oxide film of a semiconductor integrated circuit device is formed by opening a thick oxide film by dry etching or wet etching.
It is formed by a thermal oxidation method so as to have a newly designed specified film thickness.

That is, in the conventional gate oxide film, as shown in FIG. 3A, the thick silicon oxide film 31 is first opened by etching to form the diffusion layer region 32, and then the diffusion layer region is directly formed.
A gate oxide film 33 having a designed film thickness is formed on the film 32 by using a thermal oxidation method as shown in FIG.

[Problems to be Solved by the Invention]

However, according to this method, the narrowed portion 34 of the thin gate oxide film 33 is formed at the boundary between the diffusion layer region 32 and the thick oxide film 31. This occurs because the lateral permeation of oxidizing species is blocked by the thick oxide film when the silicon substrate in the diffusion layer region 32 is thermally oxidized, and the lateral oxidation of the substrate is not sufficiently performed at this portion. The phenomenon in which the gate oxide film has a constricted portion and becomes thin as described above causes the dielectric breakdown voltage of the gate oxide film to be lower than the design value, thus significantly lowering the manufacturing yield of the integrated circuit and further improving the reliability during operation. Greatly reduce.

In view of the above situation, an object of the present invention is to provide a method for manufacturing a semiconductor device without forming a thin constriction portion of a gate oxide film at a boundary with a thick oxide film.

[Means for Solving the Problems]

According to the present invention, a method of manufacturing a semiconductor device includes a step of selectively opening a thick silicon oxide film to form a diffusion layer region, and a relatively thick silicon oxide film that exceeds the film thickness of a gate oxide film to be formed. Forming a film on the diffusion layer region, and selectively opening the thick silicon oxide film or the thick silicon oxide film in the relatively thick silicon oxide film excluding the boundary portion with the thick silicon oxide film. A step of selectively ion-implanting high-concentration ions using the mask material used for the above as an ion-implantation mask, and a selective etching step of removing the high-concentration ion-implanted region of the silicon oxide film from the diffusion layer region. And a thermal oxidation step of forming a gate oxide film on the exposed surface of the diffusion layer region.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 1A to 1E are process diagrams of forming a gate oxide film showing an embodiment of the present invention. According to this embodiment, the thickness 6 formed by the chemical vapor deposition method (CVD method) on the silicon substrate
The 000Å thick silicon oxide film 11 is removed by a wet etching method using hydrofluoric acid to form a diffusion layer region 12 (FIG. 1 (a)). Next, a relatively thick silicon oxide film 10 having a film thickness of 800 Å is formed in a combustion atmosphere of hydrogen and oxygen at a temperature of 950 ° C. by a thermal oxidation method. At this time, a first constriction 14 having a thickness of about 500Å is formed at the boundary between the silicon oxide film 10 and the thick oxide film 11 (Fig. 1 (b)). Next, argon ions are ion-implanted under the conditions of an acceleration voltage of 30 keV and a dose amount of 1 × 14 ¹⁴ / cm ² by using a substrate rotating oblique ion implantation method with an incident angle of about 40 ° (FIG. 1 (c)). At this time, the injection beam 15 from the right direction is injected to the entire surface of the silicon oxide film, but the injection beam 16 from the left direction is not injected to the shaded portion 17 of the thick oxide film 11, so the shadowed portion on average. Is smaller than the other portions (Fig. 1 (c)). Next, the entire surface is etched by a wet etching method using hydrofluoric acid. At this time, since the interatomic bonds are disturbed in the partial region of the silicon oxide film 10 into which the ions have been implanted, the etching rate is faster than that of a normal thermal oxide film, so that the ions are shadowed by the implantation beam from the left. The portion where the implantation amount is small remains almost in its original shape even if the portion where the implantation amount is large is removed by etching (FIG. 1 (d)). Wet in the time when such a structure was obtained
Stop etching. At this time, the partial film thickness of the first constriction 14 becomes about 300Å. Here, the gate oxide film 13 is formed to a film thickness of 200 Å in an oxygen atmosphere at a temperature of 900 ° C. by using a thermal oxidation method. At this time, the second constriction 18 is formed at the boundary with the oxide film 10.
However, since the thickness of the oxide film 10 in contact with the gate oxide film 13 is thin and the oxidizing species are sufficiently supplied, its thickness is about
It stays at 180Å (Fig. 1 (e)). According to the conventional method,
Since the oxide film thickness of the constriction 34 is extremely thin at 100 to 120Å, the reduction of the oxide film thickness at this portion is remarkably improved. The oxide film thickness of the first constriction 14 is about 300Å, but since it is thicker than the gate oxide film thickness, the withstand voltage of the gate oxide film 13 is not affected. Further, since the argon used for ion implantation is electrically neutral even when it reaches the temporary silicon substrate, it may affect the electrical characteristics of the MOS transistor or MOS capacitor formed in the diffusion layer region 12. There is no.

2 (a) to 2 (e) are process diagrams of forming a gate oxide film showing another embodiment of the present invention. According to this embodiment, a 2000 Å-thick nitride film is also formed by the CVD method on the thick 6000 Å-thick silicon oxide film 21 formed on the silicon substrate by the CVD method. Next, this nitride film is patterned by dry etching to form a masking nitride film 30, and then the thick oxide film 21 is selectively removed by etching with hydrofluoric acid using the masking nitride film 30 as a mask, and diffusion is performed. A layer region 22 is formed (FIG. 2 (a)). Next, as in the previous embodiment, a relatively thick silicon oxide film 20 having a film thickness of 800 Å is formed by a thermal oxidation method in a combustion atmosphere of hydrogen and oxygen at a temperature of 950 ° C. in this case,
A constriction 24 having an oxide film thickness of about 500Å is formed at the boundary between the thick silicon oxide film 21 and the silicon oxide film 20 (FIG. 2 (b)). Next, using a normal vertical ion implantation method, argon ions 25 are accelerated at a voltage of 30 keV and a dose amount of 1 × 10 5.
Ions are implanted under the condition of ¹⁴ / cm ² (Fig. 2 (c)). At this time, the ion implantation beam 25 of argon is used as the mask nitride film.
Blocked by 30 eaves shadows 26, thick silicon oxide film 21
Does not reach the vicinity of the boundary between the silicon oxide film 20 and the silicon oxide film 20. Then, the entire surface is etched by the wet etching method using hydrofluoric acid. At this time, since the etching rate of the ion-implanted portion of the silicon oxide film 20 is increased, the portion of the mask nitride film 30 shielded by the eaves is shown in FIG. 2 (d).
Remains as shown in. The wet etching is stopped at the time when such a structure is obtained. At this time, the first constriction
The partial film thickness of 24 is about 350Å. Here, after removing the masking nitride film 30 with hot phosphoric acid, the gate oxide film 23 is formed to a film thickness of 200 Å in an oxygen atmosphere at a temperature of 900 ° C. by using a thermal oxidation method. At this time, the oxide film thickness of the second constricted portion 28 is 180Å as in the previous embodiment. That is, the conventional method 100-
The reduction of the oxide film thickness in the constricted part is markedly improved compared with the film thickness of 120Å. The semiconductor film for a mask used in this example is not etched with hydrofluoric acid such as silicon carbide,
In addition, any material that does not deform or disappear in an oxidizing atmosphere can be used instead of the nitride film. Further, since a complicated device such as the substrate rotating oblique ion implantation method used in the previous embodiment is not required, it can be easily carried out.

〔The invention's effect〕

As described above, according to the present invention, an oxide film region thicker than the gate oxide film thickness can be formed at the boundary between the diffusion layer region and the thick silicon oxide film forming the element isolation region. The reduction in the film thickness of the constricted portion of the oxide film can be remarkably improved as compared with the conventional method, and the reduction in the dielectric breakdown voltage of the gate oxide film can be significantly improved.
Therefore, the manufacturing yield of the integrated circuit device can be remarkably improved, and the reliability in the operation thereof can be remarkably improved.

[Brief description of drawings]

1 (a) to 1 (e) are process diagrams of forming a gate oxide film showing an embodiment of the present invention, and FIGS. 2 (a) to 2 (e) are gate oxide films showing another embodiment of the present invention. And FIG. 3A and FIG. 3B are process diagrams of forming a conventional gate oxide film. 11,21… Thick silicon oxide film, 12,22… Diffusion layer region, 13,2
3 ... Gate oxide film, 10, 20 ... Silicon oxide film, 14, 24 ... First constriction, 15 ... Ion implantation beam from right side, 16 ... Ion implantation beam from left side, 17 ... Shadow of ion implantation, 18, 28 ...
Second constriction, 25 ... Argon ion beam, 26 ... Shadow of mask mask eaves, 30 ... Mask nitride film.

Claims (1)

[Claims] 1. A step of selectively opening a thick silicon oxide film to form a diffusion layer region, and a relatively thick silicon oxide film exceeding the film thickness of a gate oxide film to be formed on the diffusion layer region. In the step of forming and in the relatively thick silicon oxide film excluding the boundary with the thick silicon oxide film, the thick silicon oxide film or the mask material used for the selective opening of the thick silicon oxide film is ionized. Using an implantation mask to selectively implant high-concentration ions,
A selective etching step of removing a high-concentration ion implantation region of the silicon oxide film from the diffusion layer region; and a thermal oxidation process of forming a gate oxide film on the exposed surface of the diffusion layer region. Of manufacturing a semiconductor device.