JPH0329293B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a semiconductor device in which a gate oxide film is formed on a semiconductor substrate, such as a semiconductor integrated device or a semiconductor storage device.

[Technical Background of the Invention] Conventionally, in order to form a capacitor in, for example, a dRAM (dynamic RAM), a thin gate oxide film is first grown on the surface of a semiconductor substrate in an oxidation furnace. Next, with this gate oxide film exposed, photolithography and ion implantation were performed to form a metal diffusion layer within the substrate, and the resist film was removed and the substrate surface was cleaned with RCA. Thereafter, a polysilicon conductive layer serving as an electrode material is deposited on the gate oxide film to form a capacitor.

[Problems with the Background Art] However, in the manufacturing process of semiconductor devices as described above, the gate oxide film, which requires the highest level of cleanliness, is exposed to the atmosphere containing ions such as Na and K for a long period of time. In addition, the substrate surface is exposed to metal contamination during photoetching or resist stripping processes, ion implantation, etc., so even if the substrate surface is not chemically exposed to the surface before depositing the electrode material,
Even if RCA cleaning is performed, the above contamination cannot be sufficiently removed. For this reason, no matter how much the film quality of the gate oxide film itself is improved, it is difficult to maintain the film quality. For example, the more the gate oxide film is exposed to the above contamination, the more Problems arise, such as deterioration of the breakdown voltage characteristics.

[Purpose of the Invention] This invention was made in view of the above-mentioned problems, and it is a method of applying various treatments such as photoetching, ion implantation, resist peeling, or cleaning to the surface of a semiconductor substrate after forming a gate oxide film. An object of the present invention is to provide a method for manufacturing a semiconductor device that can prevent deterioration of device characteristics without causing deterioration in the film quality of the gate oxide film, even in the case of a semiconductor device.

[Summary of the Invention] In other words, the method for manufacturing a semiconductor device according to the present invention is such that immediately after forming a gate oxide film on the surface of a semiconductor substrate, a thin film of polysilicon is deposited on the surface in advance to a thickness that does not interfere with the next process. After forming and performing various necessary steps, a polysilicon conductive layer is formed with a predetermined thickness on the surface of the polysilicon thin film, and the polysilicon thin film prevents contamination caused by the various steps described above. This is to prevent deterioration in the quality of the gate oxide film.

[Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings.

FIGS. 1A to 1D each show the manufacturing process of the semiconductor device. First, a silicon semiconductor substrate 11 as shown in FIG. 1A is oxidized in a clean oxygen atmosphere, and the surface is A gate oxide film 12 is formed as shown. This gate oxide film 12
Since the electrode is extremely sensitive to external contamination, a thin film 13 of polysilicon, which is an electrode material, is formed on the surface immediately after its formation, as shown in FIG. 1C. In this case, the polysilicon thin film 13
If the film thickness is increased, a large ion accelerating voltage will be required when forming the anti-inversion ion implantation layer, channel ion implantation layer, or source and drain layers in the next process.
In contrast to the method of directly implanting As ions onto the gate oxide film 12, the polysilicon thin film 13 described above is
After forming a film with a thickness of 500 Å, ion implantation is performed,
To obtain an injection layer equivalent to the above, the accelerating voltage Vacc
=170 to 180keV is required. Here, since the current acceleration voltage limit of ion implantation equipment is 200 keV, the thickness of the polysilicon thin film 13 is
This means that it is less than 1000Å.

Thereafter, through a photo-etching process, for example, As ions are implanted into the semiconductor substrate 11 from above the polysilicon thin film 13 to form an As ion-implanted layer 14. Thereafter, the resist film (not shown) formed as a mask for photoetching is peeled off and the substrate is cleaned. In this case, metal contamination due to photoetching, ion implantation, resist peeling, and substrate cleaning, or contamination due to contact with the atmosphere, is mostly blocked by the polysilicon thin film 13, and the gate, which is sensitive to contamination, is blocked by the polysilicon thin film 13. There is no adverse effect on the oxide film 12. Thereafter, a polysilicon conductive layer 15, which is essentially required as an electrode, is formed by polymerization on the surface of the polysilicon thin film 13 to a predetermined thickness determined in consideration of the thickness of the polysilicon thin film 13.

That is, in such a manufacturing process, since the gate oxide film 12 is covered with the polysilicon thin film 13 immediately after its formation, it is protected from contamination from photoresist in subsequent steps and metal contamination during ion implantation. It becomes like this. Thereby, the quality of the gate oxide film 12 is always maintained at the same quality as when it was formed. Figures 2A and 2B show a conventional manufacturing method in which various treatments are directly applied to a 120 Å gate oxide film, and
This figure shows a comparison of the breakdown voltage distribution characteristics of a semiconductor device when using the manufacturing method according to the present invention in which the above-mentioned treatment is performed after coating with a polysilicon thin film 13. Here, in the case of the device manufactured by the conventional method shown in FIG. 2A, first the electric field is
Initial failures were observed below 1 MV/CM, and as the electric field increased, the failure rate gradually increased.
All of them were destroyed at 8.5MV/CM. On the other hand, in the case of the device manufactured by the method of the present invention shown in FIG. / CM suddenly leads to destruction. Therefore, by applying the method of the present invention, it is possible to form elements using a gate oxide film with extremely few defects, and it is possible to improve the yield and reliability of semiconductor products using this gate oxide film.

[Effects of the Invention] As described above, according to the present invention, immediately after forming a gate oxide film on the surface of a semiconductor substrate, a thin polysilicon film is formed on the surface in advance to a thickness that does not interfere with the next process. Then, after performing various necessary steps, a polysilicon conductive layer is formed with a predetermined thickness on the surface of the polysilicon thin film, so that the film quality of the gate oxide film is not deteriorated. It becomes possible to prevent deterioration of element characteristics.

[Brief explanation of the drawing]

1A to 1D are cross-sectional configuration diagrams showing the manufacturing process of a semiconductor device according to an embodiment of the present invention, and FIGS. 2A and 2B are diagrams showing the breakdown voltage of the device according to the conventional manufacturing method and the manufacturing method according to the present invention, respectively. FIG. 3 is a diagram showing a comparison of distribution characteristics. 11... Semiconductor substrate, 12... Gate oxide film, 13
...Polysilicon thin film, 14...Ion implantation layer, 15
...Polysilicon conductive layer.

Claims (1)

[Claims] 1. A step of forming a gate oxide film on the surface of a semiconductor substrate, a step of forming a polysilicon thin film on the surface of the gate oxide film immediately after forming the gate oxide film, and a step of forming a polysilicon thin film on the surface of the gate oxide film. a step of performing one or more of photoetching, resist stripping, or wafer cleaning, including at least ion implantation, on the semiconductor substrate whose surface is covered with the polysilicon thin film; forming a polysilicon conductive layer, and the polysilicon thin film is formed as a protective film to protect the gate oxide film from contamination caused by photoetching, ion implantation, resist stripping, or wafer cleaning. However, the method of manufacturing a semiconductor device is characterized in that the film is formed to a thickness that allows ion implantation into the semiconductor substrate through the polysilicon thin film.