JPH0728038B2 - 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 nitride oxide 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.

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 is applicable to a gate insulating film of a submicron MOS that is more stable with less flat band voltage shift and interface state density increase due to hot carrier injection. It is an object of the present invention to provide a method for manufacturing a simple insulating film.

Means for Solving the Problems In order to achieve the above object, in the method for manufacturing a semiconductor device of the present invention, a first step of forming an oxide film on a semiconductor substrate to be thinner than a final film thickness of a fourth oxynitride film. A second step of nitriding the oxide film to form a first oxynitride film; and an oxidization treatment of the first oxynitride film in the second step. A third step of forming a second oxynitride film thickened to a predetermined thickness while reducing the amount of hydrogen introduced therein, and nitriding the second oxynitride film to form a third oxynitride film. A fourth step of forming a film; and a step of oxidizing the third oxynitride film to reduce the hydrogen introduced into the third oxynitride film in the fourth step, and the final film thickness. And a fifth step of forming a fourth oxynitride film thickened up to this point.

Further, it is desirable that the second and fourth steps be performed by nitriding treatment in an ammonia atmosphere. Further, it is desirable that the third step be an oxidation treatment in an oxygen atmosphere.

Effect The present invention, due to the above-mentioned treatment, has a low hydrogen concentration and a small trapped charge density, and thus has a small flat band voltage shift,
Moreover, since the nitrogen concentration in the vicinity of the insulating film / semiconductor interface is high, a good insulating film with a small increase in interface state density can be obtained.

Embodiment FIG. 1 shows a method of manufacturing a semiconductor device according to an embodiment of the present invention. A thermal oxide film 2 thinner than the final insulating film thickness is formed on the semiconductor substrate 1. Then, the first oxynitride film 3 is formed by nitriding in an ammonia atmosphere. After that, an insulating film is formed thick to a predetermined thickness by performing an oxidation treatment in an oxygen atmosphere, and a second oxynitride film 4 is formed. Then, as a second-stage treatment, the second oxynitride film 4 is again nitrided in an ammonia atmosphere to form a third oxynitride film 5, and then reoxidized in an oxidizing atmosphere. Thus, the reoxidation film 6 is formed.

First, in an insulating film system of a nitrided oxide film that has been subjected to a nitriding treatment and a reoxidized film that has been subjected to a reoxidation treatment after that, it is essential that a flat band voltage shift and an increase in interface state density due to hot carrier injection Describe the results of investigating the cause. The thickness of the insulating film used in the experiment is
It is about 8 nm.

Fig. 2 shows the nitrogen profile in the oxynitride film evaluated by Auger spectroscopy at each temperature of 950 ℃, 1050 ℃ and 1150 ℃.
The nitriding oxide film that has been nitrided for 120 seconds is shown. 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 such a oxynitride layer 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. While the amount of nitrogen near the surface decreases as the reoxidation temperature increases, the nitrogen profile near the insulating film / semiconductor substrate interface hardly changes, and even if reoxidation is performed, the insulating film / semiconductor substrate 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 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 are shown for the reoxidized film which was reoxidized for 60 seconds at each temperature of 950 ° C, 1050 ° C and 1150 ° C. 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. As described above, reoxidizing the oxynitride film 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. I understand.

Figure 7 shows the hydrogen content in the insulating film, which was evaluated by SIMS for the increase in the interface state density when 0.1 clone / cm ² electrons were 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, these two conditions conflict with each other in the thermal nitriding treatment in a general ammonia atmosphere. This is because the amounts of nitrogen and hydrogen taken into the insulating film show the same processing temperature and processing time dependence. For example, if the nitriding oxide film that has been subjected to the nitriding treatment at a low temperature for a short time is reoxidized so that hydrogen is not taken in during the nitriding treatment of the thermal oxide film, that is, if the original hydrogen content is small, However, the reoxidation temperature and the reoxidation time are small, and better characteristics can be expected in a shorter treatment time. However, because of the shallower nitriding process,
It is lower than the nitrogen concentration in the vicinity of the semiconductor interface, and the effect of suppressing the generation of interface states becomes smaller.

The present invention has been made in view of these points, and in order to satisfy two contradictory conditions, a thermal oxide film thinner than the final film thickness formed on a semiconductor substrate is nitrided in a nitriding atmosphere and nitrided. An oxide film is formed, and then an oxidation process is performed in an oxidizing atmosphere to form a thick insulating film up to a predetermined film thickness. Then, as a second stage process, the insulating film is nitrided again in a nitriding atmosphere. Then, a reoxidation treatment is subsequently performed in an oxidizing atmosphere.

Generally, it is well known that the amount of nitrogen taken into the vicinity of the insulating film / semiconductor interface is remarkably large as the insulating film is thin, because a process of diffusing nitrogen into the insulating film / semiconductor interface is required. The present invention takes advantage of this fact. By nitriding a thermal oxide film, which is formed intentionally thinner than the final film thickness, in an ammonia atmosphere, first, the nitriding oxide having a higher nitrogen concentration at the insulating film / semiconductor interface is formed. Form a film. Then, the insulating film is thickly formed to a predetermined thickness by performing reoxidation treatment in an oxidizing atmosphere. It is clear from the experimental results that this reoxidation treatment sufficiently removes the hydrogen introduced by the immediately preceding nitriding treatment. On the other hand, it is clear from the experimental results that the nitrogen concentration at the insulating film / semiconductor interface is hardly changed by this reoxidation treatment. Thereafter, as a second-stage treatment, the insulating film is again subjected to a nitriding treatment in a nitriding atmosphere, and subsequently, the hydrogen introduced by the second-stage nitriding treatment is removed, so that the re-oxidation treatment is performed again. It is clear from the experimental results that the nitrogen concentration at the insulating film / semiconductor interface is hardly changed by the second-stage reoxidation treatment. 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 two-step treatment according to the present invention provides a condition in which the nitrogen concentration near the insulating film / semiconductor interface is higher and the hydrogen content is lower, and an insulating film having a lower trapped charge density is obtained. .

As described above, according to the present invention, an insulating film having a low trapped charge density can be obtained by an extremely simple manufacturing method, and in a fine MOS type semiconductor device, an electric field induced by hot carriers can be obtained. It is extremely useful in practical use, because the deterioration of the physical characteristics is remarkably suppressed and the number of rewritable times is remarkably improved even in the EEPROM semiconductor device.

BRIEF DESCRIPTION OF THE 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, Figure 3 is a distribution chart of nitrogen and oxygen in the oxynitride film evaluated by Auger spectroscopy.
Fig. 4 is a hydrogen distribution map in the oxide film and oxynitride film evaluated by SIMS, Fig. 5 is a hydrogen distribution map in the reoxidized film evaluated by SIMS, and Fig. 6 is various nitriding oxide films and SIMS-evaluated flat band voltage shift when 0.1 coulomb / cm ² of electrons in the oxide film is injected into the insulating film is plotted against hydrogen content in the insulating film. FIG. 3 is a characteristic diagram in which the increase amount of the interface state density when 0.1 coulomb / cm ² of electrons in the oxide film and the re-oxidized film is injected into the insulating film is plotted against the hydrogen content in the insulating film evaluated by SIMS. . 1 ... Semiconductor substrate, 2 ... Thermal oxide film, 3 ... First nitrided oxide film, 4 ... Second nitrided oxide film, 5 ... Third nitrided oxide film, 6 ... Re-oxidized film.

Claims (5)

[Claims] 1. A first step of forming an oxide film on a semiconductor substrate to be thinner than a final film thickness of a fourth nitrided oxide film, and a step of nitriding the oxide film to form a first nitrided oxide film. And a second step of oxidizing the first oxynitride film to reduce the hydrogen introduced into the first oxynitride film in the second step and increase the thickness to a predetermined film thickness. And a fourth step of forming the third nitrided oxide film by nitriding the second nitrided oxide film, and an oxidation treatment of the third nitrided oxide film. And a fifth step of forming a fourth oxynitride film thickened to the final film thickness while reducing the amount of hydrogen introduced into the third oxynitride film in the fourth step. Manufacturing method of semiconductor device. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the second and fourth steps are nitriding treatments in an ammonia atmosphere. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the third step is an oxidation treatment in an oxygen atmosphere. 4. The method of manufacturing a semiconductor device according to claim 1, wherein the fourth oxynitride film is used as a gate insulating film of a MOS type semiconductor device. 5. The method of manufacturing a semiconductor device according to claim 1, wherein the fourth oxynitride film is used as a tunnel insulating film of a nonvolatile memory.