JPS5911663A - Manufacture of capacitor for semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the leakage currents of a tantalum oxide film by forming an ultra-thin silicon nitride film between the tantalum oxide film and a silicon substrate, forming a nitrogen-concentration gradient, and reducing stress in the interface between the tantalum oxide film and the ultra-thin silicon nitride film. CONSTITUTION:A direct interaction between the tantalum oxide film 4 and the silicon semiconductor substrate 1 is obstructed owing to the ultra-thin silicon nitride film 2, and leakage currents are reduced. The nitrogen concentration gradient of which nitrogen concentration in the tantalum oxide film 4 increases in the interface 5 in the film thickness direction and decreases gradually toward the surface 6 of the tantalum oxide film and gradually increases again and reaches the surface 6 of the tantalum oxide film can be formed through heat treatment for two hrs. at 1,100 deg.C in NH3 gas, and tantalum oxide film layers 7, 7' of high nitrogen concentration are each formed. The oxide film layer 7 functions as a buffer layer relaxing stress resulting from the difference of thermal expansion coefficients because it has an intermediate thermal expansion coefficient of the tantalum oxide film 4 containing no nitrogen and the ultra-thin silicon nitride film 2, and leakage currents in the tantalum oxide film can be reduced.

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing a capacitor for a semiconductor device.

Conventionally, capacitors for semiconductor devices have a structure in which an insulating layer is entirely attached to a metal or semiconductor, and an electrode made of metal or the like is further attached. Films such as silicon dioxide (8i0z), alumina (A[203), and silicon nitride (8i3N4) have been used as the insulating film. Since it is desired to increase the packaging density, a dielectric film having a larger dielectric constant than those of these insulating films and an extremely thin dielectric film has been required. , page 588 of the Proceedings of the 1981 Spring Academic Conference of the Japan Society of Applied Physics, describes a method for forming a thin film capacitor having a tantalum oxide dielectric. In the above method, a tantalum thin film is deposited on a silicon substrate, which will become a first capacitor electrode, by R-F spacing. The silicon substrate with this tantalum thin film was then rated at 525"oLve.
It is treated in an elementary atmosphere. All tantalum is converted to Qantalum oxide. A second capacitor electrode is deposited over the tantalum oxide film.

A disadvantage of the above method is that this capacitor has a high leakage current.

In the above method, after the tantalum thin film is heat-treated in an oxygen atmosphere at 525°0 to convert it into tantalum oxide,
It has been reported that when heat treatment is performed in an oxygen atmosphere at 000°C, a thin silicon oxide film is formed between the tantalum oxide film and the silicon substrate, thereby reducing leakage current. However, since the silicon oxide film newly formed at the interface between the tantalum oxide film and the silicon substrate has a small dielectric constant, there is a drawback that the overall capacitance is lower than in the case of only the tantalum oxide film.

The present invention prevents direct mutual reaction between the tantalum oxide film and the silicon substrate and reduces leakage current of the tantalum oxide film by forming an ultra-thin silicon film between the tantalum oxide film and the silicon substrate. Furthermore, the total concentration of ♀ elements in the tantalum oxide film gradually decreases in the film thickness direction at the interface between the tantalum oxide film and the ultra-thin silicon nitride film, and gradually increases again toward the tantalum oxide film surface. The leakage current of the tantalum oxide film is reduced by reducing the stress at the interface between the tantalum oxide film and the ultra-thin silicon nitride film by creating a nitrogen concentration gradient leading to The present invention provides a method for manufacturing a capacitor for a semiconductor device, which eliminates the above-mentioned drawbacks by reducing the overall capacitance drop by using a film.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 6.

First, as shown in Fig. 1, an N-type silicon semiconductor substrate 1 with a specific resistance of 30 cmO is heated in 100% (NH3) gas for 1200'0.1 hour to form a silicon semiconductor substrate as shown in Fig. 2. A portion of the surface of the substrate 1 having a thickness of about 3080' is converted into an ultra-thin silicon nitride film 2.

Next, as shown in FIG. 3, a tantalum film 3 having a thickness of 30 nm is entirely deposited on the ultra-thin silicon nitride film 2 by a sputtering method.

The substrate with this two-layer film was then heat treated in a dry oxygen atmosphere at 525°C for 30 minutes to form a three-layer structure as shown in FIG.
The entire tantalum film with a thickness of 0OA is converted into tantalum oxide film 4. At this time, direct interaction between the tantalum oxide film 4 and the silicon semiconductor substrate 1 is prevented due to the ultra-thin honey silicon nitride BK2 between the tantalum oxide film and the silicon semiconductor substrate, and the tantalum oxide film 4 has conductivity. Formation of silicide can be prevented and leakage current of the tantalum oxide film can be reduced. Next, convert the above structure to 100
% (NHa) gas for 12 hours at 1100°C, the nitrogen concentration in the tantalum oxide film 4 exceeds that of the tantalum oxide film 4 in the film thickness direction due to accelerated diffusion through the grain boundaries of the tantalum oxide film. At the interface 5 of the thin silicon nitride film 2, a nitrogen concentration gradient is formed which gradually decreases toward the tantalum oxide film surface 6 and then gradually increases again to reach the tantalum oxide film surface 6. As a result, as shown in FIG. 5, near the interface 5 between the tantalum oxide film and the ultra-thin silicon nitride film,
tantalum oxide film layers 7 and 7 with high nitrogen content near the
' are formed, and a tantalum oxide film layer 8 with a low nitrogen concentration is formed between them. This tantalum oxide film layer 7 with a high concentration of nitrogen has a coefficient of thermal expansion between the tantalum oxide film 4 which does not contain nitrogen and the ultra-thin silicon nitride film 2. It acts as a buffer layer to relieve stress caused by the difference in thermal expansion coefficient between the two. For this reason, leakage current in the tantalum oxide film can be reduced.

Both tantalum oxide film layers 7 and 7' with high nitrogen content concentration are effective in reducing leakage current, but as the nitrogen content concentration in the tantalum oxide film increases, the dielectric constant of the tantalum oxide film decreases. For the purpose of the present invention, the nitrogen content of the tantalum oxide film layer 7 with a high nitrogen content concentration is increased, and the tantalum liquefied film layer 7 with a high nitrogen content concentration is
It is desirable to keep the nitrogen concentration of ' as low as possible. .

As shown in FIG. 6, aluminum with a thickness of 1 μm is deposited on the insulating films 2, 7, 8, 7' and patterned to form electrodes 9. Next, heat treatment is performed for 10 minutes in a N2 atmosphere at 400° C. to form a capacitor.

Since the capacitor manufactured by the above method has an ultra-thin silicon nitride film between the tantalum oxide film and the silicon semiconductor substrate, it is possible to reduce leakage current, which has conventionally been a problem when using only a tantalum oxide film. Furthermore, since there is a tantalum oxide film layer with a high concentration of nitrogen near the interface between the tantalum oxide film and the ultra-thin silicon nitride film in the tantalum oxide film, stress at the interface between the tantalum oxide film and the ultra-thin silicon nitride film is alleviated. Leakage current can be completely eliminated. Furthermore, in the known method of reducing the total leakage current by forming a silicon dioxide film between a tantalum oxide film and a silicon semiconductor substrate by heat treatment in an oxygen atmosphere, as the heat treatment time increases, the silicon dioxide film The thickness increases so that the overall capacitance value decreases over time. Furthermore, when heat-treated at high temperatures, a thin silicon dioxide film cannot prevent the formation of tantalum silicide, which is a drawback. The value does not change, the formation of tantalum silicide can be prevented, and a capacitor with low leakage current can be obtained.

As explained in detail above, the present invention forms an ultra-thin silicon nitride film at the interface between a tantalum oxide film and a silicon semiconductor substrate, and then oxidizes the tantalum oxide film near the interface between the tantalum oxide film and the ultra-thin silicon nitride film and near the surface of the tantalum oxide film. By converting to a tantalum oxide film layer with a high total nitrogen content concentration, a capacitor with a large capacitance density and a small leakage current can be obtained.

[Brief explanation of drawings]

1 to 6 are cross-sectional views illustrating the manufacturing process of a capacitor according to the present invention in order of process. In the figure, 1... silicon semiconductor substrate, 2... ultra-thin silicon nitride film, 3... tantalum film, 4...
... Tantalum oxide film % 5 ... Interface between tantalum oxide film and ultra-thin silicon nitride film, 6 ... Tantalum oxide film surface, 7 and 7' ... Nitrogen content Tantalum oxide film layer with high concentration, 8... Tantalum oxide film layer with low nitrogen content concentration, 9 11111Ichibanii□□□□□□Jijiru□ 283- Ichino Houki I Figure 2 /4 77' /3 1/ 77' =≦ Kayaotsu figure -/

Claims (1)

[Claims] A silicon substrate, which will become the first electrode of the capacitor, is heat-treated in an atmosphere containing nitrogen as a constituent atom to form an ultra-thin silicon nitride film on the entire surface of the silicon substrate, and tantalum is deposited on the surface of the ultra-thin silicon nitride film. After the above structure is heat-treated in a total oxygen atmosphere to convert all the tantalum into a tantalum oxide film, the above-mentioned structure is heat-treated in an ammonia atmosphere, and the desired element content concentration in the tantalum oxide film is determined by its film thickness. With respect to the direction, at the interface between the tantalum oxide film and the ultra-thin silicon nitride film, the oxide concentration gradually decreases toward the surface of the tantalum oxide film, gradually increases again, and reaches the surface of the tantalum oxide film. A method for manufacturing a capacitor for a semiconductor device, which is characterized in that a second electrode of a capacitor is attached to the capacitor.