JPH0728039B2 - Method for manufacturing semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a high-quality insulating film in a fine field effect (hereinafter abbreviated as MOS) semiconductor device.

2. Description of the Related Art Conventionally, a thermal oxide film and a oxynitride film formed on a semiconductor substrate have been used as a gate oxide film of a MOS semiconductor device and a tunnel oxide film of an EEPROM semiconductor device.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In a fine MOS semiconductor device, deterioration of electrical characteristics due to a flat band voltage shift induced by hot carriers and an increase in interface state density is a serious problem.
Further, also in the EEPROM semiconductor device, there is a problem that the flat band voltage shift and the increase amount of the interface state density are large due to the rewriting operation of injecting electrons or holes into the insulating film. The conventional thermal oxide film has a problem that the amount of increase in the interface state density induced by injecting hot carriers into the insulating film is large. Although some researchers have considered using a oxynitride film instead of a thermal oxide film for the purpose of suppressing the increase in the interface state density, at present, it is sufficiently practical. Not a thing.

Therefore, the present invention has been made in view of the above problems, and explores the essential causes of the flat band voltage shift and the increase of the interface state density due to the injection of hot carriers, and a new approach makes it more stable. Submicron
It is an object of the present invention to provide a method for manufacturing an insulating film that can be applied to a MOS gate insulating film and the like.

Means for Solving the Problems A method of manufacturing a semiconductor device according to the present invention comprises a first step of forming an oxide film on a semiconductor substrate and a nitriding treatment of the oxide film to form a first nitrided oxide film. 2), the first nitrided oxide film is heat-treated in an inert gas atmosphere, and hydrogen introduced into the first nitrided oxide film in the second step is added to the amount of hydrogen contained in the oxide film. And a third step of forming a second oxynitride film so as to be reduced to at least the same degree.

In addition, it is desirable that the second step be a nitriding treatment in a nitriding atmosphere containing ammonia. Further, in the second step, it is desirable to perform nitriding treatment using a short-time heating furnace in a nitriding atmosphere.

Further, it is desirable that the third step is heat-treated in an inert gas atmosphere using a short-time heating furnace.

Effect The present invention has the above-mentioned structure, and the first nitriding treatment is performed on the oxide film
Forming a oxynitride film, and heat-treating the first oxynitride film in an inert gas atmosphere so that the hydrogen introduced into the first oxynitride film is at least about the same as the amount of hydrogen contained in the oxide film. Since the second oxynitride film is formed so as to be reduced, the second oxynitride film having a low hydrogen content and a low trapped charge density can be formed.

Embodiment FIG. 1 shows a method of manufacturing a semiconductor device according to an embodiment of the present invention. A thermal oxide film 2 is formed on the semiconductor substrate 1. Then, the nitrided oxide film 3 is formed by rapid heating by radiant heating in an ammonia atmosphere using a short-time heating furnace. Then, the reheated oxynitride film 4 is formed by heating for a short time in an oxygen atmosphere using a short-time heating furnace.

First, in general, a flat band voltage shift and an interface state density due to hot carrier injection in an insulating film system of a nitrided oxide film that has been subjected to a nitriding treatment and a re-oxidized nitrided oxide film that has been heated for a short time in a nitrogen atmosphere. The results of an investigation into the essential causes of the increase in The thickness of the insulating film used in the experiment is about 8 nm.

FIG. 2 shows the nitrogen profile in the nitrided oxide film evaluated by Auger spectroscopy for the nitrided oxide film that has been nitrided for 120 seconds at each temperature of 950 ° C., 1050 ° C., and 1150 ° C. In the oxynitride film, a oxynitride layer is formed near the surface and near the insulating film / semiconductor substrate interface, and the nitrogen concentration thereof increases as the nitriding temperature increases. It is considered that the nitrided oxide film formed near the interface of the semiconductor substrate is effective in reducing the interface state induced when electrons are injected into the insulating film.

Fig. 3 shows the nitrogen and oxygen profiles in the insulating film evaluated by Auger spectroscopy, which were obtained by nitriding oxide film (NO) which was nitrided for a short time at 950 ° C for 60 seconds, and at various reoxidation temperatures. The following shows a reoxidized film that has been subjected to a short-time reoxidation treatment of 60 seconds. In the nitric oxide film (NO), a nitric oxide layer of about 5 at% is formed near the surface and near the insulating film / semiconductor substrate interface. As the reoxidation temperature increases, the amount of nitrogen near the surface decreases, while the nitrogen profile near the interface between the insulating film and the semiconductor substrate hardly changes. It can be seen that nitrogen near the interface is stable. On the other hand, from the oxygen profile,
In particular, it can be seen that a new oxide layer is formed near the insulating film / semiconductor substrate interface by the reoxidation treatment at 1150 ° C., and the insulating film / semiconductor substrate interface moves to the semiconductor substrate side.

On the other hand, FIG. 4 shows the hydrogen profile in the nitrided oxide film evaluated by SIMS for the nitrided oxide film and the thermal oxide film which were nitrided for 60 seconds at each temperature of 950 ° C. and 1150 ° C. It can be seen that the hydrogen concentration in the nitrided oxide film significantly increases as the nitriding temperature increases. As described above, the nitriding process causes a large amount of hydrogen to enter the insulating film, which causes a problem that the trapped charge density of electrons increases.

Fig. 5 shows the hydrogen profile in the insulating film evaluated by SIMS.
And its NO at 6 at temperatures of 950 ° C, 1050 ° C, and 1150 ° C.
A reoxidized film that has been reoxidized for 0 seconds is shown. It can be seen that the hydrogen concentration in the insulating film decreases remarkably as the reoxidation process progresses, and eventually becomes as low as or lower than that of the thermal oxide film. As described above, the reoxidation treatment is very effective in reducing the hydrogen concentration in the insulating film.

Next, in order to investigate the flat band voltage shift and the increase in interface state density due to the injection of hot carriers, the insulating film was
The constant current stress method in which a tunnel current of 10 mA / cm ² is applied was used. The evaluation by the constant current stress method is that the increase amount of the interface state density and the flat band voltage shift induced by applying the constant current stress to the insulating film for a certain period of time
It is evaluated from the CV characteristics of the S capacitor.

Fig. 6 shows the flat band voltage shift when 0.1 Coulomb / cm ² electrons are injected into the insulating film in various oxide films, oxynitride films and re-oxidized films by SIMS with respect to the hydrogen content in the insulating film. I plotted it. In the case of an oxide film, a flat band voltage shift in the negative direction is observed due to the remarkable generation of interface states. Further, the hydrogen content in the oxynitride film is considerably large, and therefore, the positive flat band voltage shift is large due to the increased trapped charge density of electrons. On the other hand, it can be seen that the flat band voltage shift becomes smaller as the reoxidation progresses. In other words, a large amount of hydrogen taken in during the nitriding process decreases as the reoxidation process is performed, and the flat band voltage shift decreases in proportion to this, and further, the oxynitride film shown in FIG.
When the nitrided oxide layer is formed near the interface of the semiconductor substrate, the effect of suppressing the generation of the interface states is added, and the increase in the interface state density and the flat band voltage shift of the reoxidized film are reduced as compared with the thermal oxide film. Conceivable. Re-oxidizing the oxynitride film in this manner is very effective in removing hydrogen introduced into the oxynitride film and reducing the increase amount of the interface state density and the flat band voltage shift. Recognize.

Fig. 7 shows the hydrogen content in the insulating film evaluated by SIMS for the increase in the interface state density when 0.1 Coulomb / cm ² electrons are injected into the insulating film in various oxide films, oxynitride films, and reoxidized films. Plotted against quantity. In the case of an oxide film, remarkable interface state generation is observed. Further, the hydrogen content in the oxynitride film is considerably large, and therefore, the increase amount of the interface state density is large. On the other hand, as the reoxidation progresses, the increase amount of the interface state density becomes smaller. In other words, a large amount of hydrogen taken in during the nitriding treatment decreases as the reoxidation treatment is performed, and in proportion to this, the increase amount of the interface state density decreases. Thus, it was found that the presence of hydrogen in the insulating film significantly affects the generation of interface states, and reoxidation of the oxynitride film removes hydrogen introduced into the oxynitride film, It can be seen that it is very effective in reducing the increase in density. Furthermore, it can be seen that the correlation between the increase in the interface state density and the hydrogen content largely depends on the nitriding condition, that is, the nitrogen concentration near the insulating film / semiconductor interface. Nitrogen concentration near the insulating film / semiconductor interface is 950 ℃ and 1150
5at for each nitride film that has been nitrided for 60 seconds at ℃
% And 11.5 at%. That is, it can be seen that the higher the nitrogen concentration near the insulating film / semiconductor interface, the more effectively the interface state generation is suppressed. As described above, it can be seen that the generation of the interface state has two effects: the promotion effect due to the presence of hydrogen in the insulating film and the suppressing effect due to the oxynitride layer at the insulating film / semiconductor interface.

In summary, in order to obtain a good insulating film with a smaller interface state density increase and a flat band voltage shift, the nitrogen concentration near the insulating film / semiconductor interface is as high as possible and the hydrogen content is as high as possible. It can be seen that it is only necessary to form an insulating film that meets the two conditions that have less.

However, the reoxidation treatment in a general oxidizing atmosphere is
As can be seen from FIG. 3, the nitrogen concentration in the vicinity of the insulating film / semiconductor interface is also reduced by this, and there is a drawback in that the effect of suppressing the interface state generation of nitrogen introduced by the nitriding treatment cannot be fully utilized. It was

The present invention has been made in view of the above points, and in order to solve the above-mentioned drawbacks, a thermal oxide film formed on a semiconductor substrate is nitrided in a nitriding atmosphere to form a nitrided oxide film, Re-heat treatment in an inert atmosphere.

Fig. 8 shows the nitrogen and silicon profiles in the insulating film evaluated by Auger spectroscopy. The nitrided oxide film (NO) was subjected to a short-time nitriding treatment at 950 ° C for 60 seconds.
A reheated oxynitride film which has been subjected to a short time reheat treatment at 50 ° C. for 60 seconds is shown. Insulating film of reoxidized oxynitride film shown in FIG.
It can be seen that the nitrogen concentration near the interface of the semiconductor substrate is considerably lower than that of the nitrided oxide film (NO), whereas the reheated nitrided oxide film shows almost no decrease in the nitrogen concentration. Further, it can be seen that the increase in the insulating film thickness caused by the reoxidation treatment is hardly observed in the case of the reheated oxynitride film.
On the other hand, it was found from SIMS evaluation that the hydrogen concentration in the insulating film was remarkably reduced by the reheat treatment in the inert atmosphere to the same level as or higher than the reoxidation treatment. The present invention utilizes these facts. The thermal oxide film formed on the semiconductor substrate is nitrided in a nitriding atmosphere to form a nitrided oxide film, and then reheated in an inert atmosphere. As a result, the nitrogen concentration in the insulating film / semiconductor interface is hardly decreased and the insulating film thickness is hardly increased as compared with the case of the reoxidation treatment, and the hydrogen concentration in the insulating film is reduced to the same level or higher. To form. The insulating film obtained by the above treatment has two conditions: a high nitrogen concentration and a low hydrogen content in the vicinity of the insulating film / semiconductor interface. Good characteristics with small shift can be expected.

As described above, the re-heat treatment in the inert atmosphere according to the present invention provides a condition that the nitrogen concentration near the insulating film / semiconductor interface is higher and the hydrogen content is lower, and the insulating film having a lower trapped charge density is obtained. Is obtained. Moreover, since the number of insulating films does not increase, an extremely thin insulating film can be formed more stably.

EFFECTS OF THE INVENTION As described above, according to the present invention, the oxide film is nitrided to form the first nitrided oxide film, and the first nitrided oxide film is heat-treated in an inert gas atmosphere, Since the second oxynitride film is formed so that the amount of hydrogen introduced into the first oxynitride film is reduced to at least about the same as the amount of hydrogen contained in the oxide film, trapping with a low hydrogen content A second oxynitride film having a low charge density can be obtained. Also, fine
In MOS type semiconductor devices, deterioration of electrical characteristics induced by hot carriers is significantly suppressed, and the EEPR
Even in the OM semiconductor device, the number of rewritable times is remarkably improved, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a schematic process diagram of a method for manufacturing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a distribution diagram of nitrogen in a oxynitride film evaluated by Auger spectroscopy, and FIG. 3 is Auger spectroscopy. Distribution chart of nitrogen and oxygen in the nitrided oxide film and re-oxidized nitrided oxide film evaluated by the method, FIG. 4, hydrogen distribution in the oxide film and nitrided oxide film evaluated by SIMS, and FIG.
Distribution of hydrogen in oxynitride oxide film and reoxynitriding oxynitride film evaluated by SIMS, Fig. 6 shows the electron injection film of 0.1 coulomb / cm ² in various oxynitride oxide film and reoxynitriding oxynitride film. Fig. 7 is a characteristic diagram in which the flat band voltage shift of the is plotted against the hydrogen content in the insulating film evaluated by SIMS, and Fig. 7 shows 0.1 coulomb / cm ² electrons in various nitrided oxide films and reoxidized nitrided oxide films. FIG. 8 is a characteristic diagram in which the increase amount of the interface state density when injected into the insulating film is plotted against the hydrogen content in the insulating film evaluated by SIMS.
FIG. 3 is a distribution diagram of nitrogen and silicon in a nitrided oxide film and a reheated nitrided oxide film evaluated by Auger spectroscopy. 1 ... semiconductor substrate, 2 ... thermal oxide film, 3 ... nitride oxide film, 4 ... reheated oxynitride film.

Claims (7)

[Claims] 1. A first step of forming an oxide film on a semiconductor substrate, a second step of nitriding the oxide film to form a first nitrided oxide film, and the first nitrided oxide film. Is heat treated in an inert gas atmosphere to reduce the hydrogen introduced into the first oxynitride film in the second step to at least about the same as the amount of hydrogen contained in the oxide film. And a third step of forming a oxynitride film. 2. The nitriding treatment in the nitriding atmosphere containing ammonia in the second step.
A method for manufacturing a semiconductor device as described above. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the second step is a nitriding treatment using a short-time heating furnace in a nitriding atmosphere. 4. The method of manufacturing a semiconductor device according to claim 1, wherein the third step is a heat treatment in a nitrogen atmosphere. 5. The method of manufacturing a semiconductor device according to claim 1, wherein the third step is a heat treatment using a short-time heating furnace in an inert gas atmosphere. 6. The first nitride oxide film is used as a gate insulating film of a MOS type semiconductor device.
A method for manufacturing a semiconductor device as described above. 7. The first nitride oxide film is used as a tunnel insulating film of a non-volatile memory.
A method for manufacturing a semiconductor device as described above.