JPH05235265A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing semiconductor, which forms an extremely thin natural oxide film between a CVD silicon nitride film and a substrate at the time of forming a composite insulating film composed of two or more insulating films with the CVD silicon nitride film at the bottom, forms a thin film when the composite insulating film is formed as a capacitor insulating film, ensures the charge accumulating quantity and prevents the deterioration of electrical pressure resistance and the deterioration of the insulating film reliability. CONSTITUTION:At the time of forming a composite insulating film 17, which is composed of two or more layers of insulating films with a CVD silicon nitride film 15 at the bottom, on the single crystal silicon substrate or an impurity doped polycrystal silicon film 12 of a semiconductor wafer 11, the natural oxide film on the wafer is nitrified thermal nitriding so as to form CVD silicon nitride film on the wafer after cleaning the wafer, the surface of the CVD silicon nitride film is oxidized and a silicon oxide film 16 is grown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a composite of two or more insulating films having as a lowermost layer a CVD silicon nitride film formed by a CVD (chemical vapor deposition) method. The present invention relates to a method for forming an insulating film.

[0002]

2. Description of the Related Art In a semiconductor integrated circuit, for example, an insulating film used for a capacitor of a memory cell is a thin film in order to secure the capacity as much as possible even if the size of the capacitor is reduced due to high integration. And high dielectric constant are required. A silicon nitride film is known as an insulating film having a dielectric constant higher than that of a silicon oxide film.

Generally, since the film quality of the silicon nitride film is not sufficient, it is rarely used as a single layer, and it is used by being laminated with a silicon oxide film. Recently, in order to reduce the thickness of the insulating film, a composite insulating film having a two-layer structure in which the surface of the silicon nitride film is oxidized to grow a silicon oxide film has been put into practical use.

Generally, when forming a silicon nitride film,
After performing a wafer cleaning process using a chemical, it is deposited on the single crystal silicon substrate or on the polycrystalline silicon film doped with impurities by the CVD method under reduced pressure. Then, a silicon oxide film is laminated on the CVD silicon nitride film.

By the way, when the above-described double-layered composite insulating film is formed on a silicon substrate, a natural oxide film of about 1 nm may grow between the CVD silicon nitride film and the base (silicon substrate). Are known. Further, when the composite insulating film is formed on the polycrystalline silicon film on the silicon substrate, it is known that a natural oxide film of about 2 nm grows between the CVD silicon nitride film and the base (polycrystalline silicon film). ing. This point will be described in detail with reference to FIGS. 4A to 4C, taking a case where the composite insulating film is formed as an insulating film of a capacitor of a memory cell as an example.

In FIG. 4A, 41 is a silicon substrate (wafer), 42 is deposited on this silicon substrate,
It is a polycrystalline silicon film (charge storage layer of a capacitor) doped with impurities. Immediately before forming a silicon nitride film using this polycrystalline silicon film as a base, a wafer cleaning process is performed using a chemical. In this case, a natural oxide film (first natural oxide film) 43 of about 1 nm grows on the polycrystalline silicon film when the wafer is washed with water.

After that, the wafer is put into a reaction furnace for forming a silicon nitride film, and a silicon nitride film 45 is formed by a low pressure CVD method as shown in FIG. 4B. At this time, since the temperature inside the furnace is kept at about 700 ° C. when the wafer is put into the reaction furnace before the silicon nitride film is formed, the outside air is entrained in the CVD furnace so that the first natural oxide film 43 is further covered by 1 nm. Natural oxide film (second natural oxide film) 4
4 grows. That is, a natural oxide film (4 nm) of about 2 nm between the silicon nitride film 45 and the lower polycrystalline silicon film 42 is formed.
3, 44) will exist.

Next, as shown in FIG. 4C, the surface of the silicon nitride film 45 is oxidized in a heat treatment furnace to grow a silicon oxide film 46, thereby forming a composite insulating film 47 having a two-layer structure. After that, a capacitor plate electrode 48 made of a polycrystalline silicon film is formed on the composite insulating film 47 to complete the formation of a capacitor using the composite insulating film 47 for inter-electrode insulation.

However, as described above, when the natural oxide film (43, 44) having a thickness of about 2 nm is present in the lower layer of the composite insulating film 47, the thickness of the capacitor insulating film is increased by about 2 nm from the desired value. The increase amount reaches 30% of the whole, for example. This greatly hinders the thinning of the capacitor insulating film, resulting in a decrease in the charge storage amount of the capacitor. This is a big problem now, and it will be an increasingly serious problem in the future.

Further, if the above-mentioned natural oxide film is present, the film quality of the capacitor insulating film may change, which may lead to deterioration of electric breakdown voltage and deterioration of reliability of the insulating film. In particular, as described above, the second natural oxide film 44 generated by the entrainment of the outside air into the CVD furnace has a higher probability of taking in impurities than the silicon oxide film 46 formed by the reaction of a highly pure gas, and thus the capacitor This causes deterioration of the film quality of the insulating film.

[0011]

As described above, according to the conventional method for forming a composite insulating film, since the composite insulating film is formed in a state where the natural oxide film existing between the base and the base is thick, the film quality of the insulating film is high. If a composite insulation film is formed as a capacitor insulation film, it will significantly hinder the thinning of the film, which will lead to a decrease in the amount of accumulated charge, which may result in deterioration of the electrical breakdown voltage and deterioration of the reliability of the insulation film. There was a problem that there is.

The present invention has been made to solve the above problems, and is present between a base and a composite insulating film formed of two or more insulating films having a CVD silicon nitride film as the lowermost layer. The natural oxide film can be formed as thin as possible, and when the composite insulating film is formed as a capacitor insulating film, it can be made thinner, the charge storage amount can be secured sufficiently, the film quality of the insulating film deteriorates, and An object of the present invention is to provide a method for manufacturing a semiconductor device capable of preventing the deterioration of the withstand voltage and the reliability of the insulating film.

[0013]

According to a method of manufacturing a semiconductor device of the present invention, a CV is formed on a single crystal silicon substrate of a semiconductor wafer or a polycrystalline silicon film doped with impurities.
When forming a composite insulating film composed of two or more insulating films having a D silicon nitride film as the lowermost layer, after the wafer cleaning treatment,
The native oxide film on the wafer is converted into a nitride by thermal nitriding, a CVD silicon nitride film is formed on the wafer, and the surface is oxidized to grow the silicon oxide film.

[0014]

Before the silicon nitride film is formed, the natural oxide film is changed to the nitride by rapid thermal nitriding of the wafer with the natural oxide film grown on the wafer. This nitride has a higher dielectric constant than the native oxide film,
Converting the film thickness into a thermal oxide film, the film thickness is about half that of the existing silicon nitride film. Moreover, there is almost no natural oxide film that grows on the nitride when the wafer is placed in the reactor before the silicon nitride film is formed.

Therefore, the composite insulating film can be formed in a state where the natural oxide film existing between the base and the substrate is made as thin as possible. Also,
Since there is almost no natural oxide film that grows on the nitride when the wafer is placed in the reaction furnace before forming the silicon nitride film, it prevents deterioration of the insulation film quality, electrical breakdown voltage, and insulation reliability. be able to.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention will be described in detail below with reference to the drawings.

FIGS. 1A to 1E are cross-sectional views showing an example of a process for forming a composite insulating film composed of two insulating films having a CVD silicon nitride film as a lower layer, as an insulating film of a memory cell capacitor. It is a figure.

In FIG. 1A, 11 is a semiconductor wafer (silicon substrate), and 12 is a polycrystalline silicon film (charge storage layer of a capacitor) deposited on this silicon substrate and doped with impurities.

Immediately before forming a silicon nitride film using this polycrystalline silicon film 12 as a base, a wafer cleaning process is carried out to remove impurities by immersing the wafer in a chemical (eg, a solution containing hydrochloric acid and hydrogen peroxide). To do. In this case, when the wafer is washed with water, as shown in FIG.
A natural oxide film 13 having a thickness of about 1 nm is formed on the polycrystalline silicon film.
Grows.

After that, the wafer is put into a reaction furnace, heated rapidly to about 1200 ° C. by a lamp annealing method, and ammonia gas is caused to flow for about 10 seconds to react the ammonia gas with the natural oxide film 13. This allows
As shown in FIG. 1C, a nitride (which is considered to be composed of polyoxynitride and polynitride) 14 is formed on the polycrystalline silicon film.

After that, the wafer cleaning process is performed again, and the wafer is placed in a reaction furnace for forming a silicon nitride film. At this time, when the wafer is put in the heat treatment furnace, the temperature in the furnace is 700.
Since it is kept at a low temperature of around ℃, there is almost no natural oxide film grown on the nitride. Then, in order to improve the uniformity of the thickness of the deposited film, a CVD silicon nitride film 15 is formed as shown in FIG. 1D by a low pressure CVD method using a reaction of dichlorosilane gas and ammonia gas, for example. ..

Next, the wafer is heated at 800 ° C. in a heat treatment furnace.
It is placed in an oxidizing atmosphere maintained at 950 ° C., and as shown in FIG. 1E, the silicon oxide film 16 is oxidatively grown on the surface of the silicon nitride film 15 to form a composite insulating film 17 having a two-layer structure. After that, a capacitor plate electrode 18 made of a polycrystalline silicon film is formed on the composite insulating film 17 to complete the formation of a capacitor using the two-layer insulating film 17 for interelectrode insulation.

FIG. 2 shows a two-layer insulating film (when an impurity-doped polycrystalline silicon film is used as a base) formed in the above embodiment and a method similar to that in the above embodiment, for example, 10 ¹⁵ atos / cm 2. ³ The measurement results of the respective film thicknesses of the two-layer insulating film (when the silicon substrate is used as the base) formed on the single crystal silicon substrate containing the above impurities are shown.

Further, for comparison, the measurement result of the film thickness of the two-layer insulating film formed by the method of the conventional example (however, the thickness of the CVD silicon nitride film is the same as that in the above-mentioned embodiment) is shown as follows. It shows a case where a polycrystalline silicon film doped with impurities is used as a base and a case where a silicon substrate is used as a base.

As can be seen, the two-layer insulating film using the silicon substrate as a base has a film thickness of 4 angstroms when formed by the method of the above-described embodiment than when formed by the method of the conventional example. It is thin. On the other hand, a two-layer insulating film using a polycrystalline silicon film as a base,
The thickness of the film formed by the method of the above embodiment is 15 angstroms thinner than that formed by the conventional method.

FIG. 3 shows a capacitor using the two-layer insulating film formed by the method of the above embodiment for inter-electrode insulation and a capacitor using the two-layer insulating film formed by the method of the conventional example for inter-electrode insulation. Each TDDB (Time Depen
dent Dielectric Breakdown) measurement results. In this case, a region of about 62 chips was formed on one wafer, and a voltage stress of 11 MV / cm was applied between the capacitor electrodes.

As can be seen here, the capacitor formed by the method of the above-mentioned embodiment has a much smaller occurrence of accidental defects than the capacitor formed by the method of the conventional example, and also has a poor wear. It has decreased and has a long life.

That is, according to the method of the above-described embodiment, the natural oxide film is changed into the nitride by rapid thermal nitriding of the wafer with the natural oxide film grown on the wafer before forming the silicon nitride film. I am letting you. This nitride has a higher dielectric constant than the natural oxide film, and when converted into a film thickness of a thermal oxide film, the film thickness is about half that of an existing silicon nitride film. Moreover, there is almost no natural oxide film that grows on the nitride when the wafer is placed in the reaction furnace before the silicon nitride film is formed.

Therefore, the two-layer insulating film can be formed in a state where the natural oxide film existing between the base and the base is made as thin as possible. In this case, as can be seen from FIG. 2, the polycrystalline silicon film doped with impurities is more effective as a substrate material for the underlayer of the two-layer insulating film than the silicon substrate. ..

Also, since there is almost no natural oxide film that grows on the nitride when the wafer is placed in the reaction furnace before the formation of the silicon nitride film, the quality of the insulating film is deteriorated, the electrical breakdown voltage is deteriorated, and the reliability of the insulating film is improved. Sexual deterioration can be prevented. In addition,
The present invention is not limited to the above-described embodiments, but can be applied to the case of forming a composite insulating film including two or more insulating films having a CVD silicon nitride film as the lowermost layer.

[0031]

As described above, according to the method of manufacturing a semiconductor device of the present invention, when a composite insulating film composed of two or more insulating films having a CVD silicon nitride film as the lowermost layer is formed,
The natural oxide film that exists between the base and the base can be formed as thin as possible, and when the composite insulating film is formed as the capacitor insulating film, it is possible to reduce the thickness and ensure a sufficient amount of charge storage to ensure electrical conductivity. It is possible to prevent deterioration of breakdown voltage and deterioration of reliability of the insulating film.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a step of forming a two-layer insulating film for a capacitor insulating film according to an embodiment of the method for manufacturing a semiconductor device of the present invention.

FIG. 2 is a diagram showing the measurement results of the film thickness of a two-layer insulating film formed by the method of FIG. 1 and the film thickness of a two-layer insulating film formed by the conventional method.

FIG. 3 shows TDDB measurement results of a capacitor using a two-layer insulating film formed by the method of FIG. 1 for inter-electrode insulation and a capacitor using a two-layer insulating film formed by a conventional method for inter-electrode insulation. FIG.

FIG. 4 is a cross-sectional view showing a process of forming a conventional composite insulating film for a capacitor insulating film.

[Explanation of symbols]

11 ... Semiconductor wafer, 12 ... Impurity-doped polycrystalline silicon film (charge storage layer of capacitor), 13
... natural oxide film, 14 ... nitride, 15 ... CVD silicon nitride film, 16 ... silicon oxide film, 17 ... two-layer insulating film, 18
... Capacitor plate electrode (polycrystalline silicon film).

Claims (3)

[Claims] 1. When forming a composite insulating film composed of two or more insulating films having a CVD silicon nitride film as a lowermost layer on a single crystal silicon substrate of a semiconductor wafer or a polycrystalline silicon film doped with impurities, The step of cleaning the wafer, the step of thermally nitriding the natural oxide film on the wafer cleaned by this step to convert it into a nitride, the step of forming a CVD silicon nitride film on the nitride, the CVD And a step of growing the silicon oxide film by oxidizing the surface of the silicon nitride film. 2. The method of manufacturing a semiconductor device according to claim 1, wherein when the thermal nitriding is performed, the wafer is almost 1
A method of manufacturing a semiconductor device, which comprises rapidly heating to 200 ° C. to react ammonia gas with the natural oxide film. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the composite insulating film is used for insulating between electrodes of a capacitor of a memory cell.