JPH01146332A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a manufacturing method of an insulating film wherein the shift of flat band voltage and the increase of boundary surface level density caused by hot carrier implantation are little, and application to the stable gate insulating film and the like of a submicron MOS is capable, by a method wherein a thermal oxide film is subjected to, in order, nitriding treatment, oxidizing treatment, nitriding treatment, and oxidizing treatment. CONSTITUTION:A thermal oxide film 2 formed on a semiconductor substrate 1, which film is thinner than the final thickness, is subjected to nitriding treatment in a nitriding atmosphere, and a nitride oxide film 3 is formed, which is sequentially subjected to oxidizing treatment in an oxidizing atmosphere, so that an insulating film 4 is formed in thickness up to a specified value. After that, as a second stage treatment, the insulating film 4 is again subjected to nitriding treatment 5 in a nitriding atmosphere, and sequentially is again subjected to oxidizing treatment 6 in an oxidizing atmosphere. Thereby obtaining an insulating film having low captured charge density by a simple manufacturing method. In a fine MOS type semiconductor device, the deterioration of electric characteristics caused by hot carrier is restrained. In an EEPROM, too, available frequency of rewriting is improved.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to a fine field effect type (hereinafter abbreviated as MOS type)
The present invention relates to a method for forming a high quality insulating film in a semiconductor device.

BACKGROUND ART Conventionally, a thermal oxide film and a nitrided oxide film formed on a semiconductor substrate are used as a gate oxide film of an MO3 type semiconductor device and an E E P
It was used as a tunnel oxide film for ROM semiconductor devices.

Problems to be Solved by the Invention In fine MO3 type semiconductor devices, deterioration of electrical characteristics due to a flat band voltage shift induced by hot carriers and an increase in interface state density is a major problem. Further, in the EEFROM semiconductor device, there is also a problem in that the flat band voltage shift and the interface state density increase greatly due to the rewriting operation of injecting electrons or diodes into the insulating film. Conventional thermal oxide films have a particular problem in that the interface state density increases significantly, which is induced by injecting hot carriers into the insulating film. Some researchers are considering using a nitrided oxide film instead of a thermal oxide film in order to suppress the increase in interface state density, but this is not fully practical at present. It's not something I can bear.

Therefore, the present invention has been made in view of such problems, and is applicable to stable submicron MO3 gate insulating films, etc., which have less flat band voltage shift and less increase in interface state density due to injection of hot carriers. The purpose of the present invention is to provide a method for manufacturing an insulating film that is possible.

Means for Solving the Problems In order to achieve the above object, the present invention forms a nitrided oxide film by nitriding a thermal oxide film thinner than the final film thickness formed on a semiconductor substrate in a nitriding atmosphere, Subsequently, the insulating film is formed to a predetermined thickness by oxidation treatment in an oxidizing atmosphere, and then, as a second stage treatment, this insulating film is again nitrided in a nitriding atmosphere, and then oxidized. This is a method for manufacturing a semiconductor device characterized by performing reoxidation treatment in an atmosphere.

Effect of the present invention Due to the above-described processing, the hydrogen concentration is close and the trapped charge density is small, so the flat band voltage shift is small.
In addition, since the nitrogen concentration near 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 for 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 a semiconductor substrate 1. Thereafter, a first nitrided oxide film 3 is formed by nitriding in an ammonia atmosphere. Thereafter, the insulating film is thickened to a predetermined thickness by oxidation treatment in an oxygen atmosphere, and the second nitrided oxide film 4 is formed. Thereafter, as a second step, the second nitrided oxide film 4 is again nitrided in an ammonia atmosphere to form a third nitrided oxide film 5, and then reoxidized in an oxidizing atmosphere. A re-oxidized film 6 is formed by this.

First, in general, in an insulating film system of a nitrided oxide film that has been subjected to nitriding treatment, and a reoxidized film that has been subsequently reoxidized, the essence of FLA 7) band voltage shift and increase in interface state density due to injection of hot carriers. We will describe the results of our investigation into the causes of this problem. The thickness of the insulating film used in the experiment was
It is approximately 8 nm.

Figure 2 shows nitridation oxidation evaluated by Augor spectroscopy.

Nitrogen profiles in the film are shown for nitrided oxide films that were nitrided at temperatures of 950° C., 1050 tE, and 1150° C. for 120 seconds. In the nitrided oxide film, a nitrided oxide layer is formed near the surface and near the insulating film/semiconductor substrate interface, and the nitrogen concentration increases as the nitriding temperature increases. It is thought that such a nitride oxide layer formed near the semiconductor substrate interface is effective in reducing the interface state induced when electrons are injected into the insulating film.

Figure 3 shows the nitrogen and oxygen profiles in the insulating film evaluated by Auger spectroscopy for a nitrided oxide film (No) that was nitrided for a short time of 60 seconds at 950°C, and for various reoxidation films of the nitrided oxide film (No). A reoxidized film that has been subjected to a short-term reoxidation treatment at a temperature of 60 seconds is shown.

In the nitrided oxide film (No), a nitrided oxide layer of about Sat% 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, whereas the nitrogen profile near the insulating film/semiconductor substrate interface hardly changes, and even after reoxidation treatment, the amount of nitrogen near the surface decreases. It can be seen that nitrogen near the interface is stable.

On the other hand, from the oxygen profile, it can be seen that a new oxide layer is formed near the insulating film/semiconductor substrate interface, and the insulating film/semiconductor substrate interface is moving toward the semiconductor substrate, especially due to the reoxidation treatment at 1160°C.

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 after 60 seconds at each temperature of 9 sotl: and 1150° C. It can be seen that as the nitriding temperature increases, the hydrogen concentration in the nitrided oxide film increases significantly. As described above, a problem arises in that a large amount of hydrogen enters the insulating film due to the nitriding process, which increases the electron trapping charge density.

Figure 6 shows the hydrogen profile in the insulating film evaluated by SIMS for a nitrided oxide film (No) that was nitrided at 950°C for 60 seconds, and its NO at 950°C.

A reoxidized film subjected to reoxidation treatment at each temperature of 1060° C. and 1150° C. for 60 seconds is shown. It can be seen that as the reoxidation process progresses, the hydrogen concentration in the insulating film decreases significantly, and eventually becomes as low as or lower than that of the thermally oxidized film. In this way, 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 increase in interface state density due to injection of hot carriers, a constant current Streno method was used in which a tunnel current of 10 rnA/d was applied to the insulating film. Evaluation using this constant current stress method involves applying constant current stress to the insulating film for a certain period of time, and evaluating the induced increase in interface state density and flat band voltage shift from the C-V characteristics of the MOS capacitor. It is something.

Figure 6 shows the flat band voltage shift in the oxide film, nitrided oxide film, and re-oxidized film when 0.1 coulomb/d electrons are injected into the insulating film, evaluated by SIMS. Hydrogen content in the insulating film Plotted against quantity. In the case of an oxide film, a flat band voltage shift in the negative direction is observed due to the significant generation of interface states. In addition, the hydrogen content in the nitrided oxide film is quite large, and therefore the flat band voltage shift in the positive direction is large due to the increased trapping charge density of electrons. On the other hand, it can be seen that as reoxidation progresses, the flat band voltage shift becomes smaller. In other words, a large amount of hydrogen taken in during the nitriding process is reduced as the reoxidation process is performed, and the flat band voltage shift becomes proportionally smaller.9 Furthermore, the nitrided oxide film shown in FIG. / The formation of a nitrided oxide layer near the semiconductor substrate interface has the added effect of suppressing the generation of interface states, and compared to a thermal oxide film, the amount of increase in interface state density and flat band voltage of the re-oxidized film It is thought that the shift will be reduced. As described above, reoxidizing the nitrided oxide film is extremely effective in removing hydrogen introduced into the nitrided oxide film and reducing the amount of increase in interface state density and flat band voltage shift. I understand.

Figure 7 shows the amount of increase in interface state density in various oxide films, nitrided oxide films, and re-oxidized films when 0.1 coulomb/i electrons are injected into the insulating film, evaluated by SIMS. Hydrogen in the insulating film Plotted against content. In the case of oxide films, significant interfacial state generation is observed. Further, the hydrogen content in the nitrided oxide film is quite large, so the increase in interface state density is large.

On the other hand, it can be seen that as the reoxidation progresses, the amount of increase in the interface state density becomes smaller. In other words, a large amount of hydrogen taken in during the nitriding process is reduced as the reoxidation process is performed, and the amount of increase in the interface state density becomes smaller in proportion to this.

In this way, it is clear that the presence of hydrogen in the insulating film significantly affects the generation of interface states, and reoxidizing the nitrided oxide film removes the hydrogen introduced into the nitrided oxide film and improves the interface state. It can be seen that this is very effective in reducing the amount of increase in potential density. Furthermore, it can be seen that the correlation between the amount of increase in the interface state density and the hydrogen content largely depends on the nitriding conditions, that is, the nitrogen concentration near the insulating film/semiconductor interface. Insulating film/
The nitrogen concentration near the semiconductor interface is 98i01:: and 1
For the nitride film subjected to nitriding treatment at 000° C. for 60 seconds, the concentrations are 5 at% and 11.5 at%, respectively. That is, it can be seen that the higher the nitrogen concentration near the insulating film/semiconductor interface, the more effective it is to suppress the generation of interface states. Thus, it can be seen that the generation of interface states has two effects: the promoting effect due to the presence of hydrogen in the insulating film and the suppressing effect due to the nitrided oxide layer at the insulating film/semiconductor interface.

To summarize the above, in order to obtain a good insulating film with a small increase in interface state density and a small flat band voltage shift, the nitrogen concentration near the insulating film/semiconductor interface should be as high as possible, and the hydrogen content should be as high as possible. It can be seen that it is sufficient to form an insulating film that satisfies the two conditions of a small amount.

However, these two conditions conflict with each other in thermal nitriding treatment in a general ammonia atmosphere. This is because the amounts of nitrogen and hydrogen incorporated into the insulating film exhibit the same processing temperature and processing time dependence. For example, in order to avoid incorporating hydrogen when nitriding a thermal oxide film, if a nitrided oxide film that has been nitrided as shallowly as possible, that is, at a low temperature for a short time, is re-oxidized, the original hydrogen content will be reduced. Therefore, the reoxidation temperature and reoxidation time can be reduced, and better properties can be expected with shorter processing times. However, due to the shallower nitriding process, the insulation film/
This is lower than the nitrogen concentration near the semiconductor interface, and the effect of suppressing the generation of interface states is also smaller.

The present invention was made in view of the above, and in order to satisfy the two contradictory conditions, a thermal oxide film thinner than the final film thickness formed on a semiconductor substrate is nitrided in a nitriding atmosphere. After forming an oxide film and then performing oxidation treatment in an oxidizing atmosphere to form an insulating film thick to a predetermined thickness, the insulating film is again nitrided in a nitriding atmosphere as a second step. , followed by re-oxidation treatment in an oxidizing atmosphere.

Generally, a process for nitrogen to diffuse into the insulating film/semiconductor interface is required, and it is well known that the thinner the insulating film, the greater the amount of nitrogen taken into the vicinity of the insulating film/semiconductor interface. The present invention makes use of this fact, and by first nitriding a thermal oxide film that is intentionally formed thinner than the final film thickness in an ammonia atmosphere, the nitrogen concentration at the insulating film/semiconductor interface is nitrided. Form an oxide film. Subsequently, the insulating film is formed thick 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 nitridation treatment. On the other hand, the experimental results show that the insulating film/
It is clear that the nitrogen concentration at the semiconductor interface hardly changes. Thereafter, as a second stage process, this insulating film is again nitrided in a nitriding atmosphere, and then, in order to remove the hydrogen introduced by this second stage nitriding process, it is again subjected to a reoxidation process. The nitrogen concentration at the insulating film/semiconductor interface hardly changes due to this second-stage reoxidation treatment.
This is clear from the experimental results.

The insulating film obtained by the above treatment has two conditions: high nitrogen concentration near the insulating film/semiconductor interface and low hydrogen content, and has a higher interface state density and a flat band. Good characteristics with small voltage shift can be expected.

As described above, the two-step process according to the present invention satisfies the conditions of a very high nitrogen concentration near the insulating film/semiconductor interface and a very low hydrogen content, resulting in an insulating film having a very low trapped charge density. is obtained.

Effects of the Invention 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 electricity induced by hot carriers can be obtained in a fine MO8 type semiconductor device. The deterioration of physical characteristics is significantly suppressed, and the number of rewrites can be significantly improved in EEFROM semiconductor devices, which is extremely useful in practice.

[Brief explanation of the drawing]

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 nitrided oxide film evaluated by Augor spectroscopy, and FIG. 3 is a diagram of the distribution of nitrogen in a nitride oxide film evaluated by Augor spectroscopy.
Figure 4 shows the distribution of nitrogen and oxygen in the nitrided oxide film evaluated by spectroscopy, Figure 4 shows the distribution of hydrogen in the oxide film and nitrided oxide film evaluated by SIMS, and Figure 5 shows the distribution of hydrogen in the nitrided oxide film evaluated by SIMS. Hydrogen distribution diagram in re-oxidized film, Figure 6 shows 0 and 1 coulomb/crA in various nitrided oxide films and re-oxidized films.
Figure 7 is a characteristic diagram in which the flat band voltage shift when electrons are injected into the insulating film is plotted against the hydrogen content in the insulating film evaluated by SIMS. , '1 Coulomb 7- electrons are injected into the insulating film, and the amount of increase in the interface state density 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.
...Reoxidation film. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Mouth 0 2 Rossbazutawank゛°Time (yn'tn) Takashi 3 Figure Suba・ltaling Time Newshao, Klingsaki I! Figure 4 Rinse (A) Figure 6 Figure 71< System 471 (x 10"cm-') Figure 7r71

Claims (1)

[Claims] A thermal oxide film thinner than the final film thickness formed on a semiconductor substrate is nitrided in a nitriding atmosphere to form a nitrided oxide film,
Next, the insulating film is formed to a predetermined thickness by oxidation treatment in an oxidizing atmosphere, and then, as a second step, the insulating film is nitrided again in a nitriding atmosphere, and then oxidized. A method for manufacturing a semiconductor device, the method comprising the step of performing reoxidation treatment in an atmosphere.