KR100373819B1 - Thin film capacitors and process for making them - Google Patents

Abstract

The present invention discloses a thin film capacitor for use in a semiconductor integrated circuit device such as analog circuits, high frequency circuits and dynamic random access memory (DRAM) and a manufacturing method thereof. The capacitor has a dielectric thickness of less than about 50 nm, a capacitance density of at least about 15 fF / μm ² , and a breakdown field of at least about 1 dB / cm. The dielectric material is a metal oxide of titanium, niobium or tantalum, the metal oxide also comprising nitrogen or silicon. By depositing a metal on the substrate or on the first electrode on the substrate, a dielectric material is formed on the first electrode. The metal is then anodized to form a dielectric material of the desired thickness. Thereafter, a top electrode is formed on the dielectric layer. The upper electrode is formed of a metal that does not lower the electrical properties of the dielectric layer (eg, leakage current or breakdown voltage).

Description

Capacitors and thin film capacitors manufacturing method {THIN FILM CAPACITORS AND PROCESS FOR MAKING THEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thin film capacitors and methods of manufacturing the same, and more particularly, to thin film capacitors in integrated circuits and multichip modules.

Thin film capacitors are used in a variety of semiconductor integrated circuit devices such as analog circuits, high frequency circuits and dynamic random access memory (DRAM).

U.S. Patent No. 5,177,670 to Shinohara et al. Discloses that the dielectric layer of such capacitors should be as thin as possible, and also discloses that a good capacitor cannot be obtained when the thickness of the dielectric layer is 100 nm or less. have. One reason for limiting the lower limit of the dielectric film thickness is that the breakdown field (ie, the voltage at which the leakage current becomes very large) of a capacitor with a thin layer of dielectric material is typically very low.

J. Electrochem. Soc. (Vol. 143, No. 3 (1996. 3)) Aoyama, T. entitled "Leakage Current Mechanism of Amorphous and Polycrystalline Ta ₂ O ₅ Films Grown by Chemical Vapor Deposition" on pages 977-993. In the paper, the thin film capacitor (that is, the thickness of the Ta ₂ O ₅ film is 85 nm) is disclosed, and the breakdown voltage of the thin film capacitor is less than 2V when the gate is subjected to a positive bias, and the capacitor When the negative bias (negative bias) is applied to about 3V. According to Aoyama et al., The capacitor is formed by depositing a Ta ₂ O ₅ film and oxidizing the film to reduce leakage current flowing through the film. However, the silicon electrode under Ta ₂ O ₅ is nitrided to prevent the underlying silicon from being oxidized while oxidizing the Ta ₂ O ₅ film. As a result, the dielectric layer is formed of a double layer of a Ta ₂ O ₅ and the silicon nitride _{(silicon nitride) (Si 3 N} 4) having a Ta ₂ O single layer is less effective dielectric constant (effective dielectric constant) than _five.

In a paper by Aoyama, et al., The lower silicon was nitridated when the film was oxidized to reduce leakage current flowing through the Ta ₂ O ₅ film, thereby preventing its oxidation. "Microstructure and Electrical Properties of Tantalum Oxide Thin Film Prepared by Electron Cyclotron Resonance Plasma-Enhanced Chemical Vapor Deposition" on pages 6691-6698 of Jpn. J. Appl. Phys. , (Vol. 33: 1: 12A (1994)). It is as shown in the literature, such as the Long eye showing the expulsion _{(Kim, I), Ta 2} O 5 / SiO effective dielectric constant of the _second layer is smaller than the dielectric constant of Ta ₂ O _5. The capacitance density of the capacitor is determined by the following equation.

Where C / A is the capacitance density, ε ₀ is the permittivity constant, ε _r is the relative dielectric constant of the capacitor dielectric layer, and t is the thickness of the dielectric layer. Thus, given the thickness of the dielectric layer, the capacitor of the dielectric material having a low dielectric constant has a capacity density of the smaller capacitor as compared to the capacitor of the dielectric material having a high dielectric constant. In addition, the capacity density and the thickness of the dielectric layer have an inverse relationship, and the thinner the dielectric material for the capacitor, the higher the capacity density.

Therefore, there is a need for a capacitor having a thickness of less than 100 nm and having a high dielectric constant and having a desired degree of leakage current and breakdown voltage.

The present invention is a capacitor having a titanium oxide, tantalum oxide or niobium oxide dielectric layer having a thickness of at least about 7 nm or more but less than about 50 nm, and having a similar thickness in a conventional capacitor having a similar thickness. It relates to a capacitor having better current-voltage characteristics (ie, the capacitor according to the present invention has a capacity density of at least about 15 fF / μm ² and a breakdown field of 1 megavolt / cm). The present invention also relates to a process for manufacturing a capacitor having a thin (ie less than 50 nm thick) metal oxide dielectric layer. In certain embodiments, these metal oxides (eg, titanium oxide, tantalum oxide, or niobium oxide) also include nitrogen or silicon.

In a process, a metal-containing layer may be used for insulating or semi-insulating substrates (i.e., conventional substrates such as silicon substrates, glass, ceramics, Kapton). or oxidized surface of a suitable substrate well known to those skilled in the art) or on a first electrode formed on such a substrate, followed by anodization. In anodic oxidation, a material (eg metal) is placed in a solution and the electrode is brought into contact with the solution. A voltage is applied to the solution, where the metal in the solution acts as an anode so that the metal is oxidized. Conditions and materials for the anodic oxidation process are well known to those skilled in the art.

Since the anodic oxidation process is carried out at low temperatures (ie typically below about 200 ° C.), the process according to the invention is suitable for low temperature processes for device fabrication. Thus, in embodiments of the present invention in which the dielectric material is formed on a silicon-containing electrode (the lower electrode is a doped silicon electrode in any DRAM device), an anodizing process is performed on the upper metal layer. While the underlying silicon is not substantially oxidized. When the dielectric material is formed on a metal electrode such as aluminum (Al) (the lower electrode is typically a metal in integrated circuit devices and multichip modules), the anodic oxidation process is performed at low temperatures, so that aluminum is the anode It is not affected by the oxidation process. In prior art processes, aluminum melts or otherwise deforms when subjected to high temperature conditions that anneal the dielectric material to improve the leakage characteristics of the dielectric material.

In one embodiment of the present invention, the first electrode is formed on an oxidized surface of an insulating substrate or semi-insulating substrate, for example a silicon substrate. As a material for forming the first electrode, a conventional material of appropriate conductivity such as metal is used. In the embodiment of the present invention in which a capacitor is used in a DRAM device, a doped silicon electrode or a metal electrode is used as the first electrode.

A dielectric layer is formed on the first electrode as follows. First, a metal, for example titanium (Ti), titanium nitride (TiN _x ), titanium silicide (TiSi _x ), tantalum (Ta), tantalum nitride (TaN) is deposited on the first electrode of the capacitor using conventional deposition techniques. _x ), tantalum silicide (TaSi _x ), niobium (Nb) or niobium nitride (NbN _x ). The thickness of the metal layer is at least equal to the thickness of the desired dielectric layer. Then, the titanium containing layer, the tantalum containing layer or the niobium containing layer are anodized to make titanium dioxide (TiO ₂ ) or titanium oxynitride, niobium pentoxide (Nb ₂ O ₅ ) or niobium oxynitride, tantalum pentoxide. (Ta ₂ O ₅ ), tantalum silicon oxide or tantalum pentoxide (Ta ₂ O ₅ N _y ) layer doped with nitrogen is formed. It is also contemplated that dielectric materials (eg hafnium) that are easy to anodize and have a high dielectric constant are also suitable. The thickness of the part to be anodized is less than approximately 50 nm, preferably at least about 7 nm. The non-oxidized portion (if present) of the layer acts as part of the first electrode of the capacitor and the thickness of the metal layer is at least equal to the thickness of the resulting dielectric layer.

A second (counter) electrode of the capacitor is then formed on the dielectric layer. As the material for the counter electrode, conventional metals (for example, tungsten, titanium nitride, tantalum nitride and chromium) are suitable. In processes, high temperature annealing is performed on the device after forming the counter electrode on the dielectric layer. In these processes, the metal (such as aluminum) that will react with the adjacent dielectric layer under thermal annealing conditions is unsuitable as the material of the second electrode. However, if a barrier metal is first formed on the dielectric layer and then a reactive metal layer is formed on the barrier metal layer, a metal such as aluminum is useful for devices formed by such a process. . Capacitors with two metal layers formed on the dielectric layer are beneficial for certain applications. For example, a capacitor having an aluminum layer formed on a tungsten (W) layer has better high frequency performance than a capacitor having no aluminum layer formed on a counter electrode.

The resulting capacitor has a capacity density of at least about 15 fF / μm ² and a breakdown field of at least about 1 dB / cm. At this time, the yield electric field is preferably at least about 3 dB / cm.

In one embodiment of the present invention, the capacitor of the present invention is formed by sputter deposition of aluminum on an oxidized silicon substrate to form a first electrode. Then, about 100 nm to about 600 nm thick tantalum nitride (TaN _x ) is deposited on aluminum using conventional techniques (such as high frequency sputtering). The TaN _{x is} then anodized to form a dielectric region of Ta ₂ O ₅ N _y having a thickness of about 50 nm or less. A metal layer is then deposited on this dielectric material to form the counter electrode of the capacitor.

The capacitor according to the present invention has substantially the same characteristics when subjected to forward bias or reverse bias. In addition, since the capacitor according to the present invention has a low leakage current density (i.e., a low defect density), it is possible to form a capacitor having a larger area than a conventional capacitor. In addition, because the anodic oxidation process of the metal is performed at a relatively low temperature, the process of the present invention provides a capacitor on the substrate which cannot apply the high temperature annealing process conventionally used in the prior art to reduce the leakage current density of the dielectric material. It is useful when forming on.

1 is a flow chart showing the steps of manufacturing a thin film capacitor in accordance with the present invention;

2 is a cross-sectional view showing an embodiment of a thin film capacitor manufactured according to the method shown in FIG.

3 is a cross-sectional view of a capacitor in accordance with the present invention suitable for use in a DRAM device;

4 is a direct current-voltage (DC IV) characteristic diagram of two capacitors having 9 nm thick Ta ₂ O ₅ N _y dielectric layers having different areas.

Explanation of symbols for the main parts of the drawings

105, 205: silicon substrate 110, 210: oxide surface

120, 220: first electrode 130, 230: metal layer

140, 240: dielectric layer 150, 250: second electrode

100, 200: capacitor

Referring to the drawings, FIG. 1 is a flow chart for manufacturing an exemplary thin film capacitor of the present invention, an exemplary thin film capacitor being shown in FIG. The first step 10 oxidizes a portion of the silicon substrate 105 shown in FIG. ₂ to form an insulating layer 110 of SiO ₂ on the silicon substrate 105. Silicon is oxidized using conventional methods well known to those skilled in the art (eg, by heating the silicon substrate to a temperature of at least about 1000 ° C. in an oxygen containing atmosphere). At this time, it is preferable to adjust the conditions so that the thickness of SiO ₂ is about 0.1 μm to about 5 μm.

In another embodiment, an insulating material layer, such as silicon nitride, is formed on the silicon substrate. Methods of depositing silicon nitride on silicon substrates are well known to those skilled in the art. For example, silicon nitride films are sometimes deposited by chemical vapor deposition (CVD).

Next, in step 20, a metal layer 120, which is the first electrode of the capacitor 100, is formed on the SiO ₂ layer. At this time, examples of suitable metals include Al, Ta, Ti, TaN _x , TiN _x , TiS _x , Ta ₂ Si, and Nb. The thickness of the first electrode 120 is about 0.1 μm to about 1 μm. It is preferable to form the first electrode 120 by sputter deposition. Conditions for sputter deposition are well known to those skilled in the art. An example sputtering condition for aluminum is 10 kW of power and 20 sccm of Argon. And an exemplary thickness for the aluminum layer is from about 0.1 μm to about 1 μm.

In certain embodiments of the present invention, the first electrode is only anodized over some thickness thereof to form the dielectric layer. In these embodiments, the unanodized metal acts as part of the first electrode (in which case a metal precursor of the dielectric layer is formed on the first electrode) or as a whole of the first electrode (in this case Metal precursors are formed directly on the substrate). In the embodiment shown in FIG. 1 and described herein, the metal precursor of the dielectric layer is formed on the first electrode 120.

Next, in step 30, a niobium-containing layer, a titanium-containing layer, or a tantalum-containing layer 130 is formed on the first electrode 120 of the capacitor 100. At this time, the layer is formed by sputter deposition of Nb, NbN _x , Ti, TiN _x , TiS _x , Ta, TaN _x or Ta ₂ Si on the first electrode of the capacitor. For example, the TaN _x layer is formed by magnetron reactive sputtering using a gas flow of 20 sccm argon and about 2 sccm to about 10 sccm nitrogen (N ₂ ) and 4 kW of power. At this time, the nitrogen concentration in the TaN _x film is about 8 to about 33 atomic percent, which can be obtained by changing the flow rate of argon and nitrogen gas during the deposition process. Similar conditions are used to deposit other materials (nitrogen is not supplied when forming a nitrogen-free dielectric film). The thickness of the deposited niobium containing material, titanium containing material or tantalum containing material in the process of the present invention is sufficient to provide a dielectric layer of a desired thickness (approximately less than 50 nm). At this time, the thickness of the dielectric layer is preferably at least about 7 nm. If the thickness of the deposited metal layer is thicker than the desired dielectric layer, only a portion of the metal layer is subsequently oxidized to form the dielectric layer to a desired thickness. In the embodiment shown in FIG. 2, the non-oxidized portion of layer 130 together with the bottom metal layer 120 forms a composite first capacitor electrode.

Next, in step 40, the niobium-containing layer, titanium-containing layer, or tantalum-containing layer 130 is anodized to form dielectric material 140. Anodization is a technique well known to those skilled in the art, and conventional materials and conditions for the anodization process are considered suitable. For example, the metal polarization process is carried out in 0.01 weight percent citric acid solution using a platinum electrode. With a soak time of about 1 hour, exemplary polarization voltages for tantalum containing metals are 3V to 30V. At this time, the thickness of the dielectric film formed by the anodization treatment is about 1.6 to about 2 nm per volt. Those skilled in the art will be able to easily determine the voltage and thickness for other dielectric materials. As mentioned above, it is not necessary to fully oxidize layer 130. However, the layer 130 must be oxidized enough to form a dielectric layer of a desired thickness.

By depositing a metal and converting the deposited metal into a dielectric material through an anodic oxidation process, the side effect of making the dielectric material uniform in thickness can be obtained. When the dielectric material is deposited using a conventional deposition technique such as CVD, the resulting dielectric layer has a variation in thickness variation of about 5%, whereas the dielectric layer according to the present invention has a uniform thickness with a thickness variation of approximately 1%. .

Next, in step 50, the second electrode 150 of the capacitor 100 is formed on the anodized layer. The second electrode is formed of a conventional material such as tungsten, titanium nitride, tantalum nitride or chromium using conventional techniques such as sputter deposition. At this time, the sputtering condition used to form the first electrode of the capacitor is also useful for forming the second electrode of the capacitor.

In a second embodiment of the present invention, a capacitor is included in a DRAM device. As mentioned above, in DRAM devices, in addition to the conventional metal electrodes, an optionally doped silicon electrode is used as the first electrode. One example of such a device is shown in FIG. 3, and capacitor 200 is formed on the oxidized surface 210 of a conventional silicon substrate 205. That is, the doped silicon electrode 220 is formed on the oxidized surface 210 of the silicon substrate 205, and the metal layer 230 is formed on the doped silicon electrode 220. At least a portion of the metal layer 230 is anodized to form the dielectric layer 240. Next, the capacitor 200 is completed by forming the second metal electrode 250 on the dielectric layer 240. In this embodiment, the process according to the present invention provides the additional advantage that the silicon electrode 220 is not oxidized. As mentioned above, if the silicon electrode is oxidized, the capacitance density of the finally formed capacitor is reduced.

As described above, the capacitance density of the capacitor is equal to the value obtained by multiplying the dielectric constant and the dielectric constant of the capacitor by the thickness of the dielectric layer. Since there is a practical lower limit of the thickness of the dielectric material where the leakage property of the dielectric material becomes undesirably higher than that limit, there is a need for a dielectric material of a moderately large dielectric constant that provides a desired large capacity density.

For example, for a capacitor with a Ta ₂ O ₅ N _x dielectric layer to have a specified capacity density of at least 15 fF / μm ² , the thickness of the dielectric layer must be less than about 12 nm at most. Table 1 below lists the thickness of the dielectric layer needed to obtain a capacitor of the desired capacity density. As can be seen in Table 1, the capacity density is a function of the thickness and dielectric constant of the dielectric layer.

Dielectric layer thickness ranges for capacitors with TiO ₂ layers and Nb ₂ O ₅ layers are based on the possible range of dielectric constants (about 40-100) for these materials. For example, when the dielectric constant of Nb ₂ O ₅ is about 40, the maximum thickness of the Nb ₂ O ₅ layer to provide a capacitor with a capacity density of 15 fF / μm ² is 23.6 nm. In addition, when the dielectric constant of Nb ₂ O ₅ is about 100, the maximum thickness of the Nb ₂ O ₅ layer for providing a capacitor with a capacity density of 15 fF / μm ² is about 59 nm. The dielectric constants of TiO ₂ and Nb ₂ O ₅ depend on the process conditions used to sputter deposit metals and on subsequent conditions used to anodize the metals. Those skilled in the art will be able to easily determine the dielectric constant of a particular material.

4 shows the performance of two capacitors with a 9 nm thick Ta ₂ O ₅ N _x layer. Each capacitor is formed on an SiO ₂ insulating region on a silicon substrate, the SiO ₂ insulating region having a thickness of 1 μm. On the other hand, the first electrode of the capacitor is made of an aluminum layer of 0.25 μm thick, a TaN _x layer of 0.4 μm thick is formed on the aluminum layer. This TaN _x layer is anodized to form a 9 nm thick Ta ₂ O ₅ N _x layer. On the other hand, the second electrode of the capacitor is composed of a tungsten layer having a thickness of about 100 nm, and an aluminum layer having a thickness of about 1 μm is formed on the tungsten layer. One capacitor has an area of 0.04 mm 2 and the other has an area of 0.4 mm 2.

Measurements of the capacitance density and the breakdown field of the capacitors are made by measuring the current flowing through those capacitors at various voltages. 4 shows the currents flowing through those capacitors at various voltages in the range of -5V to 5V. Accordingly, the capacitor is biased in the forward direction (positive voltage is applied) and in the reverse direction (negative voltage is applied). First, in the case of a capacitor having an area of 0.04 mm 2, when a voltage in the range of about −4 V to about 3 V is applied, the current flowing in the capacitor is measured to be less than 10 ⁻⁷ A / cm. On the other hand, for a capacitor having an area of 0.4 mm 2, when a voltage in the range of about −4 V to about 2.9 V is applied, the current flowing through the capacitor is measured to be less than 10 ⁻⁷ A / cm. However, when a voltage of less than -4V (ie, more negative) is applied to the device, a leakage current flows through the capacitor. In addition, when a voltage greater than about 3 V (ie, greater than 2.9 V for a large area capacitor) is applied to the capacitor, a leakage current flows through the capacitor.

Thus, as shown in FIG. 4, the capacitors according to the invention have a very high threshold voltage at which leakage current flows through the dielectric material when above. In addition, as shown in FIG. 4, the capacitors have the same breakdown electric field of 4.4 mA / cm regardless of their area. As can be seen from this, the defect density of the dielectric material according to the present invention is low enough to enable the production of large area capacitors.

According to the manufacturing process of the capacitor and the thin film capacitor according to the present invention, the leakage current density of the capacitor which affects the defect density can be lowered, so that a capacitor having a larger area than that of the conventional capacitor can be formed. In addition, in the present invention, since the anodic oxidation process of the metal is performed at a relatively low temperature, a capacitor which cannot be used in the high temperature annealing process conditions can be formed on the substrate. In addition, a capacitor having almost the same characteristics as the forward bias or the reverse bias condition can be formed.

Claims (17)

Depositing a metal layer selected from the group consisting of a first electrode, a titanium, titanium nitride, niobium, niobium nitride, tantalum, tantalum silicide, and tantalum nitride on the first electrode, and anodically oxidizing the metal. Thereby comprising a dielectric material layer formed on the first electrode with a thickness of about 50 nm or less and a second electrode formed on the dielectric material layer, wherein at least about 15 fF / μm A capacitor formed on a substrate having a capacitance density of ² and a breakdown field of at least about 1 dB / cm. The method of claim 1, The dielectric material is titanium dioxide, nitrogen-containing titanium dioxide, titanium silicide, niobium pentoxide, nitrogen-containing niobium pentoxide, tantalum pentoxide And a capacitor selected from the group consisting of nitrogen-containing tantalum pentoxide, tantalum silicon oxide and nitrogen-containing tantalum silicate. The method of claim 1, Wherein the first electrode comprises silicon, and basically no silicon oxide is inserted between the first electrode and the dielectric material layer. The method of claim 1, And the first electrode is a metal electrode, and an insulating layer of silicon dioxide is formed between the first electrode and the substrate. The method of claim 2, The dielectric material is tantalum pentoxide or tantalum pentoxide doped with nitrogen, and the dielectric material has a thickness of about 7 nm to about 12 nm. The method of claim 1, And the yield electric field is at least 3 dB / cm. The method of claim 1, And said second electrode comprises at least a first metal layer, said metal selected from the group consisting of tungsten and chromium. The method of claim 7, wherein The second electrode further includes a second metal layer formed on the first metal layer, wherein the second metal layer is aluminum. In the method of manufacturing a thin film capacitor, Forming a metal layer on the insulating or semi-insulating substrate, Anodizing the metal layer over at least a portion of its thickness to form a dielectric material layer having a thickness of less than about 50 nm, and Forming an upper electrode on the dielectric material layer Thin film capacitor manufacturing method comprising a. The method of claim 9, And said metal is selected from the group consisting of titanium, titanium nitride, titanium silicide, niobium, niobium nitride, tantalum, tantalum silicide and tantalum nitride. The method of claim 10, The dielectric material is a thin film capacitor manufacturing method selected from the group consisting of titanium dioxide, titanium nitride, titanium silicate, niobium pentoxide, niobium nitride, tantalum pentoxide, tantalum silicate and tantalum pentoxide doped with nitrogen. The method of claim 11, Wherein the thickness of the dielectric material is selected to provide a capacity density of at least about 15 fF / μm ² . The method of claim 11, Forming a lower electrode on the substrate, and forming a metal layer on the lower electrode, wherein the lower electrode comprises silicon thin film that remains substantially unoxidized when the dielectric layer is formed thereon; Capacitor Manufacturing Method. The method of claim 13, Forming an insulating layer of silicon dioxide on the substrate, and forming a lower electrode thereon, wherein the lower electrode is a metal electrode. The method of claim 13, The dielectric material is tantalum pentoxide or tantalum pentoxide doped with nitrogen and has a thickness of about 7 nm to about 12 nm. The method of claim 9, Wherein said upper electrode comprises at least a first metal layer, said metal is selected from the group consisting of tungsten and chromium, and said first metal layer is in contact with said dielectric layer. The method of claim 16, The upper electrode further comprises a second metal layer formed on the first metal layer, wherein the second metal layer is aluminum thin film capacitor manufacturing method.