JP2826324B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a multilayer capacitive element.

(Prior Art) An element in which a low-resistance polysilicon containing high-concentration impurities is used as a base electrode, an insulating film is formed on the surface thereof, and an upper electrode is formed thereon is widely used as a capacitance element in a semiconductor device. . Recently, miniaturization of device dimensions has been advanced for higher integration. Under such circumstances, it is strongly required to reduce the thickness of the insulating film in order to secure a sufficient capacity.
Conventionally, a method of forming an insulating film on polysilicon has been performed by directly thermally oxidizing or thermally nitriding polysilicon containing impurities. However, there is a disadvantage that impurities remain in the insulating film formed by this method, and the withstand voltage and the life characteristics of dielectric breakdown are deteriorated. Journal of Electrochemical Society: Solid State Science and Technology (Journal Electrochem.
Soc .: Solid-State Science and Technology) 1983/7
March, pages 1597 to 1603, Ramp Breakdown Study of Double Polysilicon Rams as Function of Fabrication Parameters
dy of Double Polysilicon RAM ′s as a Function of F
As shown in a paper entitled "Abrication Parameters", there is a drawback that as the concentration of phosphorus contained in the underlying polysilicon increases, impurities are taken into the insulating film and the breakdown voltage deteriorates.

(Problems to be Solved by the Invention) As an attempt to reduce the impurity concentration in the insulating film, a high aspect ratio by continuous formation of an in-situ phosphorus-doped / undoped polycrystalline Si film was reported in the spring 1988 Abstracts of the Japan Society of Applied Physics 31a-V-8 As shown in FIG. 2, a report published under the title "Embedment of trench" shows that the upper surface of a polysilicon lower electrode containing impurities was formed (3).
In FIG. 1, a polysilicon (4) containing no conductive impurities is deposited, and the polysilicon is oxidized to form a capacitive insulating film (5). However, the insulating film formed by this method has a problem in that a reliable film cannot be obtained, for example, the breakdown voltage distribution becomes broad due to the influence of polysilicon grains, particularly, the unevenness of the polysilicon surface.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a capacitor having a highly reliable thin insulating film while eliminating the conventional problems.

(Means for Solving the Problems) According to the present invention, there is provided a step of forming a low-resistance polysilicon serving as a lower electrode containing a high-concentration impurity, Depositing amorphous silicon, and thermally oxidizing or thermally nitriding the surface of the thin amorphous silicon layer to form at least one insulating film;
A step of performing a heat treatment after the formation of the insulating film to diffuse impurities in the low-resistance polysilicon into portions of the thin amorphous silicon that are not oxidized or nitrided, and at the same time, polycrystallize the non-oxidized or nitrided portions of the amorphous silicon. And forming an upper electrode before or after the impurity diffusion and polycrystallization steps.

(Function) In a film formed by thermally oxidizing or thermally nitriding silicon having a high impurity concentration, the insulating property of the original film may be deteriorated due to the influence of the incorporation of the impurities and the like into the film. According to the method of the present invention, a highly reliable capacitive insulating film can be obtained by oxidizing or nitriding a silicon layer containing no impurity or having a low impurity concentration. In the present invention, since the amorphous silicon layer is used as the silicon layer, there is no grain in the silicon layer to be oxidized or nitrided. For this reason, when performing thermal oxidation or thermal nitridation, there is little surface orientation dependency and film unevenness such as polysilicon, and a uniform insulating film can be formed.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1A to 1D are sectional views sequentially showing a method of forming a capacitive insulating film according to an embodiment of the present invention.

First, as shown in FIG. 1 (a), a silicon oxide film (2) is formed on a silicon substrate (1) having a trench formed thereon, and polysilicon (3) is deposited on the silicon oxide film to form phosphorus, arsenic, or boron. And high concentration thermal diffusion. In order to reduce the resistance of the polysilicon (3), thermal diffusion of impurities is performed here. However, other methods for obtaining low-resistance polysilicon include ion implantation and doped polysilicon such as phosphorus and arsenic boron. There is deposition.

Next, as shown in FIG. 1B, an amorphous silicon layer (4) containing no impurities is deposited on the polysilicon layer.

Next, as shown in FIG. 1C, the amorphous silicon layer (4) is thermally oxidized to form a capacitance insulating film (5). After the operation of forming the insulating film is completed, impurities are diffused from the polysilicon layer (3) by annealing into the non-oxidized portion of the layer (4) to reduce the resistance and use the electrode as an electrode. At this time, the amorphous silicon layer (4) is crystal-grown to be polysilicon.

Next, as shown in FIG. 1 (d), polysilicon 6 serving as an upper electrode is deposited on the capacitive insulating film (5), and phosphorus, arsenic, and boron are diffused to form an upper electrode. However,
The above-mentioned phosphorus indentation may be performed after forming the upper layer polysilicon ((6) in FIG. 1 (d)).

In this embodiment, a thermal oxide film is used as a capacitor insulating film. However, a multilayer capacitor film having a CVD nitride film (33) formed thereon as shown in FIG. 3 (a) may be used. Thus, the surface of the CVD nitride film (33) may be oxidized (34). Further, as shown in FIG. 3C, a non-doped amorphous silicon (4) may be thermally nitrided to form a thermal nitride film (35), or as shown in FIG. May be.

[Brief description of the drawings]

FIGS. 1A to 1D are schematic cross-sectional views of a semiconductor chip shown in the order of steps for explaining a manufacturing method according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of a semiconductor chip illustrating a conventional example. 3 (a) to 3 (d) are schematic cross-sectional views showing various capacitor insulating film structures. DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Silicon oxide film 3 ... Polysilicon in which phosphorus, arsenic, and boron are diffused 4 ... Non-doped amorphous silicon 4 '... Phosphorus, arsenic, and boron are diffused from polysilicon. Layer 5: Silicon oxide film 6: Upper polysilicon 32: Thermal oxide film 33: CVD nitride film 34: A film obtained by oxidizing a nitride film 35: Thermal nitride film 36: A film obtained by nitriding a thermal oxide film

Claims (1)

(57) [Claims] A step of forming a low-resistance polysilicon to be a lower electrode containing a high-concentration impurity in the multilayer capacitor; and forming a thin amorphous silicon having a low impurity concentration or no impurity on the low-resistance polysilicon. Depositing, thermally oxidizing or thermally nitriding the surface of the thin amorphous silicon layer to form at least one insulating film, and performing heat treatment after the insulating film formation to remove impurities in the low-resistance polysilicon. A step of diffusing the non-oxidized or nitrided portion of the thin amorphous silicon and simultaneously polycrystallizing the non-oxidized or nitrided portion of the amorphous silicon; and A method for manufacturing a semiconductor device, comprising a step of forming an electrode.