KR20030085822A - Method of fabricating capacitor for use in semiconductor device - Google Patents

Abstract

PURPOSE: A method for manufacturing a capacitor of a semiconductor device is provided to be capable of reducing leakage current by forming an alumina dielectric film between a lower electrode and a tantalum oxide layer. CONSTITUTION: A lower electrode(200) is formed on a semiconductor substrate. An alumina dielectric film(205) is formed on the lower electrode(200) so as to reduce the leakage current by using ALD(Atomic Layer Deposition). A tantalum oxide layer(210) is then formed on the alumina dielectric film(205). Then, an upper electrode(220) is formed on the tantalum oxide layer(210).

Description

Method of fabricating capacitor for semiconductor device {Method of fabricating capacitor for use in semiconductor device}

The present invention relates to a method for manufacturing a capacitor for a semiconductor device, and more particularly, to a method for manufacturing a capacitor for a semiconductor device exhibiting excellent characteristics without reducing leakage current and without subsequent heat treatment at a relatively high temperature.

BACKGROUND OF THE INVENTION In the manufacture of semiconductor devices, studies have continued to use materials having high dielectric constants to realize capacitors having a large capacitance in a limited area, and as a result of these efforts, dielectric constants of conventional silicon oxide films, silicon nitride films, and silicon oxide films have been studied. A tantalum oxide film or a hafnium oxide film larger than the composite film of has come to be used as a material of a capacitor.

However, such a tantalum oxide film has a disadvantage in that the leakage current is large, and efforts to reduce it have continued.

An example of a representative prior art among these efforts is shown in the cross-sectional view of FIG. 1 is a cross-sectional view illustrating a method for manufacturing a capacitor for a semiconductor device according to the prior art. Referring to FIG. 1, the lower electrode, the capacitor, and the upper electrode are sequentially formed. The first polysilicon layer 100 is used as the lower electrode, the tantalum oxide film 110 is used as the capacitor, and the TiN film 120a and the second polysilicon layer 120b which are sequentially formed as the upper electrode are used, respectively. In order to make such a structure, first, a lower electrode made of a first polysilicon layer 100 is formed on a predetermined portion of a semiconductor substrate (not shown), and then a tantalum oxide film 110 is deposited thereon by LPCVD or PECVD. . Subsequently, the tantalum oxide film 110 is subjected to high temperature heat treatment in an oxygen atmosphere, and the TiN film 120a and the second polysilicon layer 120b are sequentially formed thereon to form an upper electrode. Here, although the upper electrode is formed as a composite film of the TiN film and the polysilicon layer, the TiN film may be formed alone. In this method, including the TiN film 120a in the upper electrode replaces the titanium (Ti) element with tantalum (Ta) in the tantalum oxide film 110 during the deposition process of the TiN film so that the tantalum oxide film 110 is unstable stoichiometric ratio. This is because leakage current can be reduced by preventing the occurrence of stoichiometry. That is, if there is no TiN film 120a and the tantalum oxide film 110 is in direct contact with the second polysilicon layer 120b, the second polysilicon layer 120b may be formed at a relatively high temperature of about 600 ° C. Since the tantalum oxide film 110 and the second polysilicon layer 120b react with each other to form tantalum silicide and thereby consume tantalum, the tantalum oxide film 110 has an unstable stoichiometric ratio. Therefore, the TiN film 120a is used as a protective film for protecting it.

However, when the TiN film is used as described above, the TiN film is vulnerable to the subsequent thermal process, which causes a problem in that the heat treatment temperature of the later process is limited.

Therefore, in order to overcome this, in Korean Patent Application No. 2000-41370 published on July 15, 2000, both the upper and lower electrodes are formed of a polysilicon layer, and a tantalum oxide film (Ta ₂ O ₅₎ is formed on the lower electrode. ) And a capacitor structure in which an aluminum oxide film (Al ₂ O ₃ ) is sequentially formed. Here, the aluminum oxide film serves to make the finished capacitor have a high dielectric breakdown voltage, and unlike the TiN film, it does not impose any restrictions on subsequent thermal processes. However, the aluminum oxide film introduced in this technique is only for replacing the existing TiN film. Even if this technique is followed, the reduction of leakage current, which is a big problem of the prior art using a tantalum oxide film as a material of a capacitor, is not solved. This is because the leakage current characteristics of the capacitor are observed to occur as the interface characteristics between the lower electrode and the tantalum oxide film deteriorate as will be described later.

2A to 2D are graphs measuring characteristics of a tantalum oxide capacitor according to an example of the related art. The test wafer to obtain the graphs was made through the following process.

[Prior Example 1]

The TiN film formed by sputtering was used as a lower electrode, and this TiN film was processed for 60 second in 380 degreeC and ammonia atmosphere. Next, a 500 kPa tantalum oxide film was formed on the TiN film at 415 ° C by a chemical vapor deposition method using Ta (OC ₂ H ₅ ) ₅ (pentaethoxy tantalum: PET) as a source gas. Subsequently, the tantalum oxide film was post-processed for 180 seconds in an ozone atmosphere at 380 ° C., and a ruthenium (Ru) film having a thickness of 1000 Å was formed thereon as an upper electrode.

[Prior Example 2]

A TiN film formed by CVD was used as the lower electrode, and the TiN film was treated at 380 ° C. for 60 seconds in an ammonia atmosphere. Next, a 500 kPa tantalum oxide film was formed on the TiN film at 415 ° C by a chemical vapor deposition method using Ta (OC ₂ H ₅ ) ₅ (pentaethoxy tantalum: PET) as a source gas. Subsequently, the tantalum oxide film was post-processed for 180 seconds in an ozone atmosphere at 380 ° C, and a ruthenium (Ru) film having a thickness of 1000 Å was formed thereon as an upper electrode.

[Prior Example 3]

A TiN film formed by ALD (Atomic Layer Deposition) was used as the lower electrode, and the TiN film was treated at 380 ° C. for 60 seconds in an ammonia atmosphere. Next, a 500 kPa tantalum oxide film was formed on the TiN film at 415 ° C by a chemical vapor deposition method using Ta (OC ₂ H ₅ ) ₅ (pentaethoxy tantalum: PET) as a source gas. Subsequently, the tantalum oxide film was post-processed for 180 seconds in an 380 degreeC ozone atmosphere, and the ruthenium (Ru) film of 1000 micrometers thickness was formed on it as an upper electrode.

FIG. 2A shows the capacitor capacity measured for the samples of the conventional examples 1 to 3 per unit area, and FIG. 2C shows the leakage current measured for the samples of the conventional examples 1 to 3 per unit area.

On the other hand, Figure 2b shows the capacitor capacity measured per unit area after the heat treatment (furnace anneal) in a nitrogen atmosphere for 30 minutes at 400 ℃ for the samples of the prior art Examples 1 to 3, Figure 2d is a conventional example The leakage current measured after the heat treatment by a heating furnace in a nitrogen atmosphere for 30 minutes at 400 ° C. for the samples of 1 to 3 is shown per unit area.

2A to 2D, when the bias of the voltage applied between the lower electrode and the upper electrode of the capacitor is changed, the capacitor capacity does not change, but it can be seen that the leakage current changes greatly according to the bias. The change of the leakage current according to the bias can be confirmed by the asymmetry of the curve shape when the positive voltage is applied and the curve shape when the negative voltage is applied in FIGS. 2B and 2D. Comparing FIG. 2B and FIG. 2D, it can be seen that such asymmetry is somewhat relaxed by heat treatment in a heating furnace. However, even when considering this, it can be seen that the asymmetry of leakage current is large.

Such a phenomenon can be explained as follows.

3 is a view for explaining the asymmetry of the leakage current according to the bias. Referring to FIG. 3, the case where the positive voltage is applied to the upper electrode and the negative voltage to the lower electrode is worse than that of the reverse case. This is mainly due to the deterioration of the interfacial properties between the lower electrode and the tantalum oxide film, which generates many interface states (S) that can trap charges. This is because the tantalum oxide film having a barrier can be easily moved from the lower electrode to the upper electrode. This problem is more serious in the metal / insulator / metal (MIM) structure than in the metal / insulator / semiconductor (MIS) structure because of the tantalum oxide film in the MIM structure. This is because they cannot be heat-treated at a high temperature, so most of them exist in an amorphous form, and thus the interface state becomes more serious.

However, if the technique disclosed in Korean Patent Application No. 2000-41370 is used to overcome this problem, since the aluminum oxide film is formed between the upper electrode and the tantalum oxide film, the leakage current characteristics appearing asymmetrically due to the bias as described above are improved. Difficult to do

This problem similarly occurs when a hafnium oxide film is used as the dielectric film for the capacitor.

Therefore, the technical problem of the present invention can improve the bad leakage current characteristics caused by the interface state between the lower electrode and the tantalum oxide film or the hafnium oxide film when the positive voltage is applied to the upper electrode and the negative voltage is applied to the lower electrode, respectively. The present invention provides a method of manufacturing a capacitor for a semiconductor device.

1 is a cross-sectional view illustrating a method for manufacturing a capacitor for a semiconductor device according to the prior art;

2A to 2D are graphs measuring characteristics of a tantalum oxide capacitor according to an example of the prior art;

3 is a view for explaining the asymmetry of the leakage current according to the bias;

4 is a cross-sectional view illustrating a method of manufacturing a capacitor for a semiconductor device according to a preferred embodiment of the present invention; And

5A to 5D are graphs measuring characteristics of a capacitor for a semiconductor device according to an exemplary embodiment of the present invention.

The semiconductor device capacitor manufacturing method of the present invention for solving the above technical problem comprises the steps of: (a) forming a lower electrode on a predetermined portion of the semiconductor substrate; (b) forming an alumina (Al ₂ O ₃ ) dielectric film for reducing leakage current formed by an atomic layer deposition process on the lower electrode; (c) forming a tantalum oxide film or a hafnium oxide film on the dielectric film; (d) forming an upper electrode on the tantalum oxide film or the hafnium oxide film.

The atomic layer deposition process is performed at a relatively low temperature in the range of 250 ~ 380 ℃, it is preferable that the thickness of the deposited alumina dielectric film is within the range of 10 ~ 80Å.

In addition, the tantalum oxide film is preferably formed to a thickness of 50 to 600 kPa by a chemical vapor deposition method using Ta (OC ₂ H ₅ ) ₅ as a source gas and proceeding at a temperature within 350 to 450 ° C.

In the present invention, after the forming of the tantalum oxide film, it may not be subjected to a heat treatment step for the tantalum oxide film, and after the forming step of the upper electrode, in a heating furnace at a temperature within 350 ~ 450 ℃ and nitrogen atmosphere You can also go through a 30-minute heat treatment.

The lower electrode and the upper electrode may both be made of metal. In this case, the lower electrode may be made of TiN, and the upper electrode may be made of TiN or Ru.

In addition, the steps (a) to (d) is preferably performed in a complex cluster tool having multiple chambers, and the movement of the semiconductor substrate between the multiple chambers is performed in a vacuum or low oxygen atmosphere. It is preferred to be made from.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention.

The same reference numerals in the drawings represent the same components, duplicate description thereof will be omitted.

4 is a cross-sectional view for describing a method of manufacturing a capacitor for a semiconductor device according to an exemplary embodiment of the present invention.

Example 1

First, a lower electrode was made using a TiN film 200 formed by CVD on a predetermined portion of a semiconductor substrate. Unlike the conventional example, the TiN film 200 was not subjected to heat treatment in an ammonia atmosphere. Subsequently, an atomic layer deposition process of alternately supplying TMA (TriMethyl Aluminum; Al (CH ₃ ) ₃ ), which is an aluminum source, and H ₂ O, which is an oxygen source, is applied on the TiN film 200 to reduce leakage current. An Al ₂ O ₃ film 205, which is a dielectric film for forming, was formed to a thickness of 60 microseconds. Subsequently, a tantalum oxide film 210 of 290 Pa was formed on the Al ₂ O ₃ film 205 at 415 ° C. by a chemical vapor deposition method using Ta (OC ₂ H ₅ ) ₅ (pentaethoxy tantalum: PET) as the source gas. . Then, the tantalum oxide film 210 was post-processed for 180 seconds in an ozone atmosphere at 380 ° C, and a 1000 µm thick Ru film 220 was formed thereon as an upper electrode.

All of the above unit processes were carried out in one cluster tool with multi-chambers. The movement of semiconductor substrates between these multiple chambers was carried out in a vacuum or low oxygen atmosphere, resulting in contamination of the substrate surface. Alternatively, it was possible to prevent the occurrence of natural oxide film.

Example 2

But the same for all of the conditions as in Example 1, Al ₂ O ₃ film 205 and the different processing time in the formation of the tantalum oxide layer 210 as in Example 1, Al ₂ O ₃ film of 45Å 205 and 340Å Tantalum oxide films 210 were formed, respectively.

Example 3

But the same for all of the conditions as in Example 1, Al ₂ O ₃ film 205 and the different processing time in the formation of the tantalum oxide layer 210 as in Example 1, Al ₂ O ₃ film of 30Å 205 and 390Å Tantalum oxide films 210 were formed, respectively.

FIG. 5A shows the capacitor capacity measured for the samples of Examples 1 to 3 per unit area, and FIG. 5C shows the leakage current measured for the samples of Examples 1 to 3 per unit area.

On the other hand, Figure 5b shows the capacitor capacity measured per unit area after the heat treatment (furnace anneal) in a nitrogen atmosphere for 30 minutes at 400 ℃ for the samples of Examples 1 to 3, Figure 5d The leakage current measured after the heat treatment by a heating furnace in a nitrogen atmosphere for 30 minutes at 400 ° C. for the samples of 1 to 3 is shown per unit area.

5A to 5D, in the capacitor according to the exemplary embodiment of the present invention, the capacitor capacitance does not change even when the bias of the voltage applied between the lower electrode and the upper electrode of the capacitor is changed, and the leakage current is dependent on the bias. It can be seen that the asymmetry, which varies greatly, is also much reduced. Referring to FIG. 5D, it is confirmed that the asymmetry of the leakage current changes almost symmetrically by the heat treatment by the heating furnace. However, it can be seen from FIG. 5B that the leakage current is asymmetrical than that of FIG. 5D, but is much lower than the leakage current in FIGS. 2B and 2D. For example, when a voltage of +5 V is applied to the upper electrode, a leakage current of approximately 5 × 10 ^-4 A / cm 2 is generated in the case of FIG. 2B using only a tantalum oxide film as a capacitor and not performing heat treatment, and a tantalum oxide film as a capacitor. In the case of FIG. 2D using only heat treatment, a leakage current of approximately 5x10 ^-8 A / cm 2 is generated. On the contrary, according to the first embodiment of the present invention, in which the Al ₂ O ₃ film has a thickness of 60 mA and no heat treatment, the leakage current is approximately 1 × 10 ⁻⁹ A / cm 2 through FIG. 5B. Can be. When the method of Example of the present invention was applied and the heat treatment was performed, it was confirmed that a leakage current of approximately 1 × 10 ^-9 A / cm 2 was generated almost irrespective of the thickness of the Al ₂ O ₃ film. Therefore, it can be seen that the Al ₂ O ₃ film formed between the lower electrode and the tantalum oxide film contributes greatly to reducing the leakage current.

For this reason, it may be considered to use only the Al ₂ O ₃ film as the capacitor dielectric film. However, in order to form a film having a sufficient thickness using only the Al ₂ O ₃ film, the deposition time is too long, resulting in a problem of low productivity, and there is a concern that the Al ₂ O ₃ film is less than the tantalum oxide film in terms of reliability of the device.

In addition, as already disclosed in the prior art, it may be considered to form an Al ₂ O ₃ film between the tantalum oxide film and the upper electrode, but the current leakage characteristic of the capacitor appears mainly due to problems at the interface between the lower electrode and the tantalum oxide film. It is not efficient.

In addition, it may be considered to form an Al ₂ O ₃ film on both the upper and lower portions of the tantalum oxide film, but it is not preferable in terms of productivity since the number of steps must be added.

As described above, when the Al ₂ O ₃ film is formed between the lower electrode and the tantalum oxide film, since the band gap energy of the Al ₂ O ₃ film reaching approximately 8 eV is larger than 4.5 eV, which is the band gap energy of the tantalum oxide film, the positive voltage Even when caught by the upper electrode, electrons are not easily attracted to the upper electrode. Therefore, the leakage current level can be significantly lowered.

In the above embodiment, only the tantalum oxide film is referred to as the dielectric film for the capacitor, but the present invention is not limited thereto, and a hafnium oxide film (HfO ₂ film) may also be used.

According to the present invention as described above, it is possible to provide a semiconductor device capacitor capable of improving the bad leakage current characteristics exhibited by the interface state between the lower electrode and the tantalum oxide film or hafnium oxide film, thereby creating a semiconductor device with high reliability. Can be.

Claims (8)

In the method of manufacturing a capacitor for a semiconductor device, (a) forming a lower electrode on a predetermined portion of the semiconductor substrate; (b) forming an alumina dielectric film for reducing leakage current on the lower electrode by an atomic layer deposition process; (c) forming a tantalum oxide film or a hafnium oxide film on the alumina dielectric film; (d) forming an upper electrode on the tantalum oxide film or hafnium oxide film; Capacitor manufacturing method for a semiconductor device comprising a. The semiconductor device capacitor as claimed in claim 1, wherein the atomic layer deposition process is performed at a relatively low temperature within a range of 250 to 380 ° C., and the thickness of the deposited alumina dielectric film for reducing leakage current is within a range of about 10 to about 80 μs. Manufacturing method. The tantalum oxide film of claim 1, wherein when the tantalum oxide film is formed on the leakage current reducing alumina dielectric film, the tantalum oxide film is formed at a temperature within 350 to 450 ° C. using Ta (OC ₂ H ₅ ) ₅ as a source gas. A method for producing a capacitor for a semiconductor device, characterized in that formed by a chemical vapor deposition method 50 ~ 600Å thickness. The method of claim 3, wherein after the forming of the tantalum oxide film, the tantalum oxide film is not subjected to a heat treatment step. The method of claim 3, further comprising, after the forming of the upper electrode, further performing a heat treatment process performed in a heating furnace at a temperature within 350 to 450 ° C. for 30 minutes in a nitrogen atmosphere. The method of claim 1, wherein both the lower electrode and the upper electrode are made of metal. The method of claim 6, wherein the lower electrode is made of TiN, and the upper electrode is made of TiN or Ru. The method of claim 1, wherein the steps (a) to (d) are performed in a complex process equipment having multiple chambers, and the movement of the semiconductor substrate between the multiple chambers is performed in a vacuum or low oxygen atmosphere. Capacitor manufacturing method for a semiconductor device characterized in that.