JPS5911664A - Manufacture of capacitor for semiconductor device - Google Patents

Abstract

PURPOSE:To advance oxidation uniformly, to relax stress due to cubic expansion in case of oxidation and to reduce leakage currents by forming ultra- thin silicon nitride films between tantalum oxide films and silicon substrates and using oxide films obtained by oxidizing multilayered films in which tanalum oxide film layers and silicon nitride films layers are laminated alternately. CONSTITUTION:The four layer films in which tantalum films 3, 3' and the tantalum oxide films 4, 4' are laminated alternately are formed 2 by periodically introducing sufficient oxygen into the chamber of a sputtering device in an argon gas atmosphere through a sputtering method while using tantalum as a target electrode on ultra-thin silicon nitride films 2. The four layer films 3, 4, 3', 4' on the ultra-thin silicon nitride film 2 are converted into the uniform tantalum oxide film 6 through heat treatment in a dried oxygen atmosphere at 525 deg.C. The sudden progress of oxidation is suppressed by the tantalum oxide film layers by using the multilayered films alternately laminated, and oxidation can be advanced equally on the silicon substrate 1.

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 film is attached to a metal or semiconductor, and an electrode made of metal or the like is further attached. Films such as silicon dioxide (Si(1)), alumina (A1203), and silicon nitride (Si3N4) have been used as insulating films. There has been a demand for an extremely thin dielectric film with a large dielectric constant.A method for forming a thin film capacitor with a tantalum oxide dielectric is described in the Proceedings of the 1981 Spring Conference of the Japan Society of Applied Physics, page 588. In the above method, a thin film of tantalum is deposited by R-F spacing onto a silicon substrate that will become the first capacitor electrode. The silicon substrate with the tantalum film is then heated to 525°C. All of the tantalum is converted to tantalum oxide. A second capacitor electrode is deposited on top of the tantalum oxide film. The disadvantage of the above method is that this Capacitors have a large leakage current.In the above method, a tantalum thin film is heat-treated in an oxygen atmosphere at 525°C to convert it into tantalum oxide, and then further heat-treated in an oxygen atmosphere at 1000°C to form a tantalum oxide film. It is stated that a thin silicon oxide film is formed between the tantalum oxide film and the silicon substrate, thereby reducing leakage current.However, the silicon oxide film newly formed at the interface between the tantalum oxide film and the silicon substrate has a low dielectric constant. Since it is small, it has the disadvantage that the overall capacity is lower than that of a tantalum oxide film alone.

The present invention completely prevents direct interaction between the tantalum oxide film and the silicon substrate by forming an ultra-thin silicon nitride film between the tantalum oxide film and the silicon substrate, and reduces the leakage current of the tantalum oxide film. Furthermore, by using a tantalum oxide film obtained by oxidizing a multilayer film in which tantalum oxide film layers and tantalum film layers are alternately stacked, rapid oxidation of the tantalum film can be prevented, and the tantalum film can be uniformly deposited over the entire surface of the silicon substrate. The leakage current is reduced by allowing complete oxidation to proceed, and also by relaxing the stress caused by the volume expansion during oxidation of the tantalum film, and by forming an ultra-thin silicon nitride substrate film with a higher dielectric constant than a silicon oxide film. It is an object of the present invention to provide a method for controlling a capacitor for a semiconductor device, which eliminates the above-mentioned drawbacks by reducing the decrease in overall capacitance.

Embodiments of the present invention will be described below with reference to all of FIGS. 1 to 5. First, as shown in Figure 1, 30 cmO
Using an N-type silicon semiconductor substrate 1 with a specific resistance of 100% (
N)-13) The surface of the silicon semiconductor substrate 1 is heated to about 30°C by heating at 1200°C for 11 hours in a gas as shown in FIG.
A portion with a thickness of A is converted into an ultra-thin silicon nitride film 2. Next, as shown in Figure 3.

The tantalum film 3 and 3' and tantalum oxide films 4 and 4' are stacked alternately to form a four-layer film. In Figure 3, we first show the ultra-thin silicon nitride waist.
2, a tantalum film layer 3 with a thickness of 10 OA is deposited in an argon gas atmosphere, then a tantalum oxide film layer 4 with a thickness of 10 OA is deposited in an argon and 10% oxygen mixed gas atmosphere, and then a tantalum oxide film layer 4 with a thickness of 10 OA is deposited on the argon gas atmosphere. A tantalum film 3' with a thickness of 10OA is deposited on the surface in a gas atmosphere, and finally a tantalum oxide film 4 with a thickness of 100A is deposited on the surface in an argon and 10% oxygen mixed gas atmosphere.
The figure shows the case where the entire four-layer film is formed by depositing . Furthermore, the last layer formed on the surface after laminating the fc layers may be a tantalum film or a tantalum film instead of a tantalum oxide film layer.

The number of layers in the multilayer film can range from a two-layer film in which one tantalum oxide film layer and one tantalum film layer are laminated to a multilayer film with more than that. Further, the thickness of the tantalum film layer and the thickness of the tantalum oxide film layer may be different. The substrate with this multilayer film was then heat treated in a dry oxygen atmosphere at 525°C for 30 minutes to produce a
0λ thick tantalum film) Wt 3 and 3' are all converted into tantalum oxide film layers. 4-layer film on ultra-thin silicon nitride film 2 3. 4. 3' and 4' are converted into a uniform tantalum oxide film 5. When a tantalum film is heat-treated at 525°C in a dry oxygen atmosphere to convert it into a tantalum oxide film, the tantalum film is converted into a tantalum oxide film with approximately twice the thickness, so the volumetric expansion at this time results in an ultra-thin silicon nitride film. A slight stress is applied to the interface 5 between the film 2 and the tantalum film layer 3, but when oxidizing a four-layer film in which tantalum film layers 3 and 3' and tantalum oxide film layers 4 and 4' are alternately laminated, , the stress applied to the interface 5 can be reduced compared to the case of forming a single layer of tantalum +V without having a multilayer structure. Furthermore, since the oxidation rate of tantalum film is very fast, by using a multilayer film in which tantalum film layers and tantalum oxide film layers are alternately laminated as in the present invention, rapid progress of oxidation can be suppressed in the tantalum oxide film layer. Therefore, oxidation can proceed uniformly on the silicon substrate. The above heat treatment also reduces non-stoichiometric oxygen deficiency in the tantalum oxide film layers 4 and 4'. As shown in FIG. 5, aluminum with a thickness of 1 μm is deposited on the insulating film 2.6 and patterned to form the electrode 7. Next, heat treatment is performed for 10 minutes in a N2 atmosphere at 400''C to form a capacitor.

The capacitor manufactured by the above method has an ultra-thin silicon nitride film between the tantalum oxide film and the silicon semiconductor substrate, which causes problems when using only the tantalum oxide film (8) and the problem of reducing leakage current. In addition, as a method for forming a tantalum oxide film, a multilayer film in which tantalum oxide film layers and tantalum film layers are laminated alternately is heat-treated to form a uniform tantalum oxide film. The progress of assimilation is suppressed and oxidation progresses uniformly over the entire surface of the silicon substrate.

Furthermore, by using the above multilayer film, the stress applied to the interface between the tantalum oxide film and the ultra-thin silicon nitride film is reduced due to body N expansion when the tantalum film is oxidized and converted into a tantalum oxide film, thereby reducing leakage current. I can do it. In addition, in a known method of reducing 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. The capacitance value does not change and the formation of tantalum silicide can be prevented.
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 performs full heat treatment on a multilayer film in which tantalum oxide film layers and tantalum film layers are alternately laminated. By forming a uniform tantalum oxide film, a capacitor with high capacitance density and low leakage current can be obtained.

[Brief explanation of drawings]

1 to 5 are cross-sectional views illustrating the manufacturing process of a capacitor according to the present invention in order of process. In the figure, ]...Silicon semiconductor substrate, 2...Ultra-thin silicon nitride film, 3 and 3'...Tantalum film layer, 4 and 4'... ...Tantalum oxide film layer, 5...
...Interface between tantalum oxide film and ultra-thin silicon nitride film, 6
. . . Tantalum oxide film, 7 . . . Metal electrode.

Claims (1)

[Claims] A silicon substrate, which will become the first electrode of the capacitor, is heat-treated in an atmosphere containing all nitrogen atoms to form an ultra-thin silicon nitride film on the surface of the silicon substrate, and tantalum tartar is applied to the surface of the ultra-thin silicon nitride film. After forming a multilayered film in which tantalum film layers and tantalum oxide film layers were alternately stacked by periodically introducing sufficient tungsten into the snow ivy gas atmosphere using the sputtering method using k, A method for manufacturing a capacitor for a semiconductor device, comprising heat-treating the structure in an oxygen atmosphere to convert all of the tantalum film layers into tantalum oxide film layers, and depositing a second electrode of the capacitor on the insulating film. .