JP4911659B2 - Method for manufacturing dielectric thin film capacitor - Google Patents

Description

  The present invention relates to a method for manufacturing a dielectric thin film capacitor using a dielectric thin film such as barium strontium titanate.

  There is a dielectric thin film capacitor as a capacitor used for decoupling an integrated circuit or a DRAM. With the miniaturization of electronic devices, dielectric thin film capacitors are also required to have a large capacitance with a small area, and a technique for forming a thin dielectric film with a thin film thickness and a high dielectric constant is required.

  As a conventionally known method for manufacturing a dielectric thin film capacitor, there is an invention described in Patent Document 1.

  The invention described in Patent Document 1 includes (a) a step of forming a lower electrode on a substrate, (b) a step of forming a dielectric film by applying a raw material solution of a dielectric thin film on the lower electrode, (C) a preliminary firing step at a temperature lower than the temperature at which the dielectric crystallizes; (d) a step of forming an upper electrode on the dielectric film; and (e) a temperature equal to or higher than the temperature at which the dielectric crystallizes. And a main baking step.

In this invention, calcination is performed at a temperature lower than the crystallization temperature, and after the upper electrode is formed and then main baking is performed at a temperature higher than the crystallization temperature, the crystallization of the dielectric in the main baking is regulated by the upper electrode, and the surface is smooth. A dielectric thin film can be obtained. As a result, a dielectric film having a uniform thickness can be obtained, and leakage current is reduced.
JP-A-8-78636

  According to FIG. 2B of Patent Document 1, when a dielectric thin film capacitor is manufactured by the above-described method using barium strontium titanate as a dielectric film, the dielectric film has a relative dielectric constant of about 220 at the highest. It is.

  This relative dielectric constant is a relatively low value for barium strontium titanate, which is disadvantageous in promoting the miniaturization of dielectric thin film capacitors.

  The present invention has been made in view of this problem, and an object of the present invention is to provide a dielectric thin film capacitor having a sufficiently high dielectric constant while being smooth.

In order to achieve the above object, a dielectric thin film capacitor manufacturing method according to the present invention includes: (a) a step of forming a lower conductor on a substrate; and (b) a precursor by applying a raw material solution on the lower conductor. A step of forming a film, and (c) a step of performing a first heat treatment at a temperature 50 ° C. to 150 ° C. higher than the crystallization temperature of the precursor film to crystallize the precursor film to obtain a dielectric thin film And (d) forming an upper conductor on the dielectric thin film; and (e) performing a second heat treatment at a temperature 100 ° C. higher than the first heat treatment temperature. This makes it possible to obtain a dielectric thin film capacitor having a sufficiently smooth surface, few cracks and the like, and a sufficiently high dielectric constant.

  When the first heat treatment temperature is not higher than the crystallization temperature by 50 ° C. or more, tan δ is large even if the second heat treatment is performed, and sufficient insulation cannot be obtained. On the other hand, if the temperature of the first heat treatment is too high, dielectric crystal grains grow too much and the surface of the dielectric thin film is difficult to flatten, causing cracks and an increase in leakage current. Therefore, it is preferable that the first heat treatment temperature is 50 ° C. to 150 ° C. higher than the crystallization temperature of the precursor film.

  In addition, when the temperature of the second heat treatment is not higher than the temperature of the first heat treatment by 100 ° C. or more, the crystal growth of the dielectric does not proceed sufficiently, and the dielectric constant of the dielectric thin film does not sufficiently increase, Furthermore, short-circuit defects are likely to occur. Therefore, it is preferable that the second heat treatment temperature is 100 ° C. higher than the first heat treatment temperature.

  Furthermore, in the present invention, as the dielectric thin film, a metal compound having a perovskite structure such as barium titanate, strontium titanate, barium strontium titanate or the like can be suitably used.

  Since the metal compound having a perovskite structure has a high dielectric constant, a small dielectric thin film capacitor having a large capacity can be obtained.

  As described above, according to the present invention, the first heat treatment is performed at a temperature 50 to 150 ° C. higher than the crystallization temperature, and the second heat treatment is performed at a temperature higher by 100 ° C. than the first heat treatment. Thus, a dielectric thin film capacitor having a sufficiently smooth surface and few cracks and a sufficiently high dielectric constant can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing a manufacturing process of a dielectric thin film capacitor according to the present invention, and FIG. 2 is a flowchart showing a main part of the manufacturing process.

First, as shown in FIG. 1A, a substrate 10 made of single crystal Si is prepared. Since the SiO ₂ film 12 is formed on the surface of the substrate 10, the substrate 10 has a two-layer structure of the Si layer 11 and the SiO ₂ film 12.

Next, as shown in FIG. 1B, a raw material solution containing an organic compound of Ba, Sr, Ti is applied by spin coating, dried and heat-treated in an oxidizing atmosphere, and barium strontium titanate (BaSrTiO _3). , Hereinafter referred to as BST).

  The adhesion layer 20 is not limited to BST, and Ti, Ta, or the like may be used, or the adhesion layer 20 may not be formed.

Next, as shown in FIG. 1C, the lower conductor 30 is formed on the adhesion layer 20 by any film forming method such as sputtering or vapor deposition. The lower conductor 30 is preferably a noble metal or a conductive oxide that is difficult to increase in resistance even when heated in an oxidizing atmosphere, and specifically, Pt, RuO ₂ , IrO _2, or the like can be used.

  Next, a raw material solution of BST containing an organic compound of Ba, Sr, Ti and prepared to have Ba: Sr: Ti = 7: 3: 10 is applied onto the lower conductor 30 by spin coating, and then on a hot plate. To form a precursor film. Application and drying of the raw material solution may be repeated until an arbitrary film thickness is obtained. Then, the precursor film is crystallized by performing a heat treatment (first heat treatment) at a temperature 50 ° C. to 150 ° C. higher than the crystallization temperature of the dielectric (here, BST) in an oxidizing atmosphere. As a result, a dielectric thin film 40 is obtained as shown in FIG.

  The dielectric thin film 40 is preferably a metal compound having a perovskite structure having a high dielectric constant, and barium strontium titanate, barium titanate, strontium titanate, or the like can be used.

Next, as shown in FIG. 1E, upper conductors 51 and 52 are formed on the dielectric thin film 40 by an arbitrary film forming method such as sputtering or vapor deposition. As the upper conductors 51 and 52, a noble metal or a conductive oxide that is difficult to increase in resistance even when heated in an oxidizing atmosphere is preferable, and specifically, Pt, RuO ₂ , IrO _2, or the like can be used.

  Although the upper conductors 51 and 52 are partially formed on the dielectric thin film 40 in the figure, the upper conductor may be formed on the entire surface of the dielectric thin film 40.

  Next, the dielectric constant of the dielectric thin film 40 is increased by performing a heat treatment (second heat treatment) at a temperature higher by 100 ° C. than the first heat treatment in an oxidizing atmosphere. At this time, unless the temperature is higher by 100 ° C. or more than the first heat treatment, the crystallization of the dielectric thin film 40 does not proceed sufficiently, and the dielectric constant does not increase or the insulating property decreases.

  As a result, a dielectric thin film capacitor having a sufficiently high dielectric constant with a flat surface and few cracks is completed.

  Hereinafter, a more specific embodiment of the present invention will be described with reference to FIG. 1 again.

As shown in FIG. 1A, a substrate 10 made of single crystal Si and having a diameter of 4 inches is prepared. The substrate 10 has a two-layer structure of an Si layer 11 and an SiO ₂ film 12.

  Next, a raw material solution in which an organic compound as a BST raw material was dissolved was applied by spin coating and dried on a hot plate. After applying spin coating and drying several times, heat treatment was performed at 650 ° C. for 10 minutes in an oxidizing atmosphere using an RTA (rapid thermal annealing) apparatus, and from BST as shown in FIG. The resulting adhesion layer 20 was formed.

  Next, as shown in FIG. 1C, a lower conductor 30 made of Pt is formed on the adhesion layer 20 by RF sputtering. Increasing the film thickness of the lower conductor 30 reduces the equivalent series resistance of the dielectric thin film capacitor, but increases the manufacturing cost. Therefore, the film thickness may be set appropriately according to the desired equivalent series resistance and the manufacturing cost.

  Next, a raw material solution of BST containing an organic compound of Ba, Sr, Ti and prepared to have Ba: Sr: Ti = 7: 3: 10 is applied onto the lower conductor 30 by spin coating, and then on a hot plate. To form a precursor film. Here, in order to obtain a desired film thickness, application and drying of the raw material solution were repeated twice. Then, using an RTA apparatus, heat treatment is performed in an oxidizing atmosphere at a temperature 50 ° C. to 150 ° C. higher than the crystallization temperature of the dielectric (first heat treatment). As a result, the precursor film is crystallized to obtain a dielectric thin film 40 as shown in FIG. The film thickness of the dielectric thin film 40 was 125 to 130 nm as a result of measurement with an ellipsometer (an ellipsometer).

  Here, since it has been confirmed in advance that the crystallization temperature of the dielectric is between 500 and 550 ° C., heat treatment is performed at 600 ° C. or higher in order to obtain a temperature at least 50 ° C. higher than the crystallization temperature. Just do it. In order to prevent the temperature from being higher than 150 ° C. above the crystallization temperature, heat treatment may be performed at 650 ° C. or lower.

  The crystallization temperature of the dielectric varies depending on the type and composition of the dielectric, and also varies depending on the composition of the raw material solution even if it is the same composition. Here, an analysis was performed by an X-ray diffraction method after the heat treatment, and a peak derived from the perovskite phase of BST was confirmed to confirm whether or not it was crystallized.

  Next, as shown in FIG. 1E, upper conductors 51 and 52 made of Pt and having a diameter of 1 mm were formed by RF sputtering using a stainless steel metal mask.

Next, the dielectric constant of the dielectric thin film 40 is increased by performing a heat treatment for a predetermined time (second heat treatment) at a temperature higher by 100 ° C. than the first heat treatment temperature in an oxidizing atmosphere using an RTA apparatus. Thus, the dielectric thin film capacitor according to the present invention is completed.
(Experiment 1)
In the above process, the first heat treatment was performed at a predetermined temperature from 550 ° C. to 700 ° C. for 30 minutes to produce a dielectric thin film capacitor, and the dielectric constant and tan δ of the dielectric thin film 40 were measured. The measurement results are shown in Table 1. In Table 1, sample numbers # 1 and # 4 are comparative examples outside the scope of the present invention. The values of relative permittivity and tan δ are measured values at a measurement frequency of 1 kHz.

  As is apparent from Table 1, in the case of # 1 in which the first heat treatment temperature is 550 ° C., the first heat treatment temperature is not higher than the crystallization temperature by 50 ° C. or more. This is not preferable.

  In # 4, since the temperature of the first heat treatment was too high, cracks occurred in the dielectric thin film 40 to cause a short circuit, and the relative dielectric constant and tan δ could not be measured.

On the other hand, # 2 and # 3, which are within the scope of the present invention, have relative dielectric constants of 390 and 385, respectively, and can obtain a large dielectric constant as compared with the dielectric thin film capacitor described in Patent Document 1. In addition, the value of tan δ is as low as 2.1, which is low loss.
(Experiment 2)
In the above process, the second heat treatment was performed at a predetermined temperature from 700 ° C. to 850 ° C. for 30 minutes to produce a dielectric thin film capacitor, and the relative dielectric constant, tan δ and defect rate of the dielectric thin film 40 were measured. The measurement results are shown in Table 2. In Table 2, sample number # 5 is a comparative example outside the scope of the present invention. The value of tan δ is a measurement value at a measurement frequency of 1 kHz. The defect rate indicates the ratio of defects due to initial short circuit.

  As is apparent from Table 2, when the second heat treatment temperature is not higher than the first heat treatment temperature by 100 ° C. or more, # 5, the relative dielectric constant of the dielectric thin film 40 remains at a relatively low value of 250. The defect rate is 46% and the yield is remarkably lowered. This is considered to be because the crystallization of the dielectric thin film 40 did not proceed sufficiently because the second heat treatment temperature was not sufficiently high.

  On the other hand, in # 6 to # 8, which is within the scope of the present invention, the relative dielectric constant is 325 to 420, and a large dielectric constant can be obtained as compared with the dielectric thin film capacitor described in Patent Document 1. In addition, the value of tan δ is as low as 1.7 to 2.2, which is low loss. Moreover, the defect rate is also suppressed to 4% or less, and the effect of improving the yield is also seen.

In addition, when the leakage current at room temperature was measured in order to investigate the insulation of the sample # 8, the leakage current density with respect to the electric field strength of 10 kV / cm was very low as 3.1 × 10 ⁻¹⁰ A / cm ^2, which was good. It was confirmed that it has a good insulating property.

  As described above, according to the method for manufacturing a dielectric thin film capacitor of the present invention, it is possible to obtain a dielectric thin film capacitor having a smooth surface, few cracks and the like, and a sufficiently high dielectric constant.

  In addition, this invention is not limited to said Example, You may add a various change within the range which can obtain the effect of this invention. For example, the shapes and film thicknesses of the lower conductor, the upper conductor, and the dielectric thin film may be arbitrarily changed, and another configuration may be added.

It is sectional drawing which shows the manufacturing process of this invention. It is a flowchart explaining the principal part of the manufacturing process of this invention.

Explanation of symbols

10 Substrate 20 Adhesion layer 30 Lower conductor 40 Dielectric thin film 51, 52 Upper conductor

Claims (1)

Forming a lower conductor on the substrate;
Applying a raw material solution on the lower conductor to form a precursor film;
Performing a first heat treatment at a temperature 50 ° C. to 150 ° C. higher than the crystallization temperature of the precursor film to crystallize the precursor film to obtain a dielectric thin film;
Forming an upper conductor on the dielectric thin film;
Performing a second heat treatment at a temperature 100 ° C. higher than the first heat treatment temperature, and the dielectric thin film is any one of barium strontium titanate, barium titanate, and strontium titanate. A method for manufacturing a dielectric thin film capacitor.

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