JP2005101531A - Manufacturing method for dielectric thin film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric thin film capacitor that is a dielectric capacitor composed of a substrate, a contact layer, a dielectric layer, and an upper electrode, which does not exert an adverse influence on the capacitor characteristic and has a contact layer whose manufacturing cost is low. <P>SOLUTION: The manufacturing method includes the steps of applying a liquid raw material onto a substrate 10 to do a first heat treatment and form a contact layer 20, forming a lower electrode 30 on the contact layer 20, applying the liquid raw material onto the lower electrode 30 to do a second heat treatment for crystallization and form a dielectric layer 40, forming upper electrodes 51 and 52 on the dielectric layer 40, and doing a third heat treatment at a temperature higher than the first and second heat treatments. The contact layer 20 and the dielectric layer 40 are composed of the same compositional materials or the same materials. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a dielectric thin film capacitor.

  A dielectric thin film capacitor used in a semiconductor device such as a DRAM or a noise filter has a structure in which a substrate, a lower electrode, a dielectric thin film, and an upper electrode are sequentially laminated. The dielectric thin film can be formed by sputtering, CVD method (chemical vapor deposition method), MBE method (molecular beam epitaxy method), sol-gel method, MOD method (organometallic decomposition method), etc. In this respect, the sol-gel method and the MOD method are advantageous.

  When forming a dielectric thin film by a sol-gel method or a MOD method, a raw material solution in which an organic compound as a dielectric raw material is dissolved in an organic solvent is applied and heat-treated in an oxidizing atmosphere. Therefore, a noble metal that is difficult to oxidize is used for the lower electrode, and specifically, Pt is often used.

  By the way, a Si substrate is generally used as the substrate of the dielectric thin film capacitor. However, since Si oxidizes when left in the air, a Si oxide layer is formed on the surface of the Si substrate.

Since the Si oxide on the surface of the substrate and the noble metal as the lower electrode have poor adhesion, if a process such as dicing cut is included after the formation of the dielectric thin film capacitor, the substrate and the lower electrode may be increased in order to improve the adhesion. It is necessary to form an adhesion layer between them. Ti is often used as the adhesion layer (see Patent Document 1).
JP-A-8-78636 (particularly paragraph numbers “0018” to “0020”, FIG. 2)

  As described in Patent Document 1, when Ti is used as the adhesion layer, the substrate is warped due to oxidation of the Ti layer, and there is a problem that the dielectric layer is cracked. Patent Document 1 discloses that the warpage of a substrate is suppressed by limiting the thickness of a Ti layer that is an adhesion layer.

  However, even if the thickness of the Ti layer is limited, another problem occurs. That is, even if the thickness of the adhesion layer is limited, Ti is still oxidized in a process such as annealing. When Ti is oxidized and diffused to the interface between the lower electrode and the dielectric layer, the following two problems occur.

First, when a dielectric layer uses barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), strontium barium titanate ((Ba, Sr) TiO ₃ , hereinafter abbreviated as BST), etc. Ti oxide diffused at the interface between the layer and the lower electrode may cause a crystal structure shift at the interface between the lower electrode and the dielectric layer, and may cause disorder in the crystallinity of the dielectric layer. When the crystallinity of the dielectric layer is disturbed, a sufficient dielectric constant cannot be obtained.

  Second, since Ti oxide is a substance having a high resistance and a low dielectric constant, a layer having a high resistance and a low dielectric constant exists at the interface between the lower electrode and the dielectric layer, resulting in significant deterioration of capacitor characteristics. Sometimes.

  Further, in Patent Document 1, an upper electrode is formed after provisional firing at a temperature lower than the crystallization temperature in order to flatten the surface of the dielectric layer, and main firing is performed at a temperature higher than the crystallization temperature after the upper electrode is formed. Has been described. However, as shown in FIG. 2 of Patent Document 1, the dielectric constant of the dielectric layer obtained by this manufacturing method is about 220, and the relative dielectric constant of BST is a relatively low value. In the present situation where there is a strong demand for circuit integration, a capacitor capable of obtaining a large capacitance with a small area is required, and it is necessary to obtain a dielectric layer having a high relative dielectric constant.

  That is, with the technique described in Patent Document 1, although the occurrence of cracks that cause leakage current can be suppressed to some extent, there are problems such as deterioration of capacitor characteristics and difficulty in obtaining a large relative dielectric constant.

  Therefore, the present invention has an adhesion layer that does not cause cracks that cause leakage current and deterioration of capacitor characteristics, and has a flat surface and sufficient dielectric constant so that leakage current does not occur. An object of the present invention is to provide a method for manufacturing a dielectric thin film capacitor having a dielectric layer.

  In order to solve the above problems, a method of manufacturing a dielectric thin film capacitor according to the present invention includes a step of forming an adhesion layer precursor film on a substrate and performing a first heat treatment to form the adhesion layer, Forming a lower electrode on the adhesion layer; forming a dielectric layer precursor film made of the same material as the adhesion layer precursor film on the lower electrode; and Performing a second heat treatment at a temperature higher than the crystallization start temperature to form a dielectric layer; forming an upper electrode on the dielectric layer; and a first heat treatment and a second heat treatment And performing a third heat treatment at a temperature higher than the temperature.

  By using a material having the same composition as that of the dielectric layer for the adhesion layer, warpage of the substrate due to expansion of the adhesion layer can be eliminated, and cracks can be prevented from occurring in the dielectric layer. Further, even if the adhesion layer diffuses to the interface between the lower electrode and the dielectric layer, the capacitor characteristics are not deteriorated.

  Here, the material having the same composition system means a material in which main constituent elements are the same, and includes materials having different ratios of main constituent elements and materials containing different trace elements.

  In addition, a dielectric layer having a sufficient dielectric constant can be obtained by setting the second heat treatment temperature to a temperature higher than the crystallization start temperature of the dielectric layer precursor film. When the second heat treatment temperature is lower than the crystallization start temperature, the dielectric layer does not have a sufficient dielectric constant even if the third heat treatment is performed at a sufficiently high temperature.

  Furthermore, even when the temperature of the first heat treatment and the second heat treatment is relatively lowered by performing the third heat treatment at a temperature higher than that of the first heat treatment and the second heat treatment after forming the upper electrode. A dielectric layer having a sufficient relative dielectric constant can be obtained. The treatment temperature in the first heat treatment and the second heat treatment is preferably lower from the viewpoint of planarization of the surface.

  Furthermore, the dielectric thin film capacitor manufacturing method of the present invention is characterized in that the adhesion layer precursor film and the dielectric layer precursor film are made of the same material. As a result, the physical properties of the adhesion layer and the dielectric layer are substantially the same, so that the change in the capacitor characteristics when the adhesion layer diffuses to the interface between the lower electrode and the dielectric layer becomes smaller. In addition, since the adhesion layer and the dielectric layer can be formed using the same material and equipment, the manufacturing cost is reduced.

  Furthermore, in the method for manufacturing a dielectric thin film capacitor of the present invention, it is preferable that the processing temperature in the first heat treatment is higher than the crystallization start temperature of the adhesion layer precursor film.

  Patent Document 1 describes that a dielectric layer having a flat surface is formed by heat-treating the dielectric layer at a temperature lower than the crystallization start temperature. It was found that the surface is not flattened even when the heat treatment temperature is too low. The first heat treatment temperature is preferably higher than the crystallization start temperature of the precursor film and lower than the temperature at which large crystal grains that reduce the flatness of the surface grow.

  In the method for manufacturing a dielectric thin film capacitor of the present invention, ferroelectric materials such as barium titanate, strontium titanate, and strontium barium titanate can be used as the material of the dielectric layer.

  Furthermore, the dielectric thin film capacitor manufacturing method of the present invention is characterized in that the lower electrode is made of platinum. The upper electrode is made of platinum. Since platinum is a noble metal, it is not oxidized even after the heat treatment step, and is suitable as a lower electrode or an upper electrode.

  As described above, in the method for manufacturing a dielectric thin film capacitor according to the present invention, since the adhesion layer is formed of a material having the same composition system as the dielectric layer, the substrate does not warp due to the oxidative expansion of the dielectric layer, and the dielectric It is possible to prevent cracks from occurring in the layer. Further, even if the adhesion layer diffuses to the interface between the lower electrode and the dielectric layer, the capacitor characteristics are not deteriorated.

  Furthermore, in the method for manufacturing a dielectric thin film capacitor according to the present invention, the first and second heat treatments are performed at a temperature higher than the crystallization start temperature of the dielectric layer, and the third heat treatment is performed at a higher temperature after forming the upper electrode. By performing the above, it is possible to obtain a dielectric layer having a sufficiently high relative dielectric constant and free from cracks.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a manufacturing process of a dielectric thin film capacitor according to the present invention.

  First, the substrate 10 is prepared as shown in FIG. When a Si substrate is used as the substrate 10, since the surface is usually a Si oxide layer 12, the substrate has a two-layer structure of a Si layer 11 and a Si oxide layer 12.

  Next, a sol-gel raw material solution or an MOD raw material solution in which an organic compound is dissolved is applied by spin coating and dried to form an adhesion layer precursor film. Drying may be performed by an appropriate method such as using a hot plate or leaving it at room temperature.

  The raw material solution used here has the same composition as that of the raw material solution used for forming the dielectric layer described later. It is more preferable to use materials having the same composition. The coating and drying processes may be repeated a plurality of times until a desired film thickness is obtained. When the adhesion layer precursor film having a desired thickness is obtained, the first heat treatment is performed to crystallize the adhesion layer precursor film, thereby forming the adhesion layer 20 as shown in FIG.

  At this time, the heat treatment temperature is preferably higher than the crystallization temperature of the precursor film. When the heat treatment temperature is lower than the crystallization temperature, the adhesion layer 20 may be formed in an agglomerated state and the surface flatness may be impaired. On the other hand, even when the heat treatment temperature is too high, large crystal grains grow and impair the surface flatness. Therefore, it is preferable to perform the heat treatment at a temperature at which crystal grains having a relatively small grain size grow. An RTA (rapid thermal annealing) apparatus or an electric furnace can be used for the heat treatment.

  Next, the lower electrode 30 is formed on the adhesion layer 20 as shown in FIG. The lower electrode 30 is preferably formed of a material that is difficult to oxidize in processes such as the second and third heat treatments described later, and a noble metal such as Au, Pd, or Rh can be used, but Pt is preferred. . The lower electrode 30 can be formed by sputtering or the like.

  Next, a sol-gel raw material solution or an MOD raw material solution in which an organic compound is dissolved is applied onto the lower electrode 30 by spin coating and dried to form a dielectric layer precursor film. The coating and drying processes may be repeated a plurality of times until a desired film thickness is obtained. When a dielectric layer precursor film having a desired thickness is obtained, a second heat treatment is performed to crystallize the dielectric layer precursor film, thereby forming a dielectric layer 40 as shown in FIG. . As the dielectric layer 40, ferroelectric materials such as barium titanate, strontium titanate, and barium strontium titanate (BST) can be used.

  Here, as described above, the adhesion layer 20 and the dielectric layer 40 are formed of the same composition material or the same material. Examples of the material having the same composition system include a material in which both the adhesion layer 20 and the dielectric layer 40 are made of BST, and the composition ratio of Ba: Sr: Ti is different, and a small amount of constituent elements other than these main constituent elements. Different materials.

  At this time, the heat treatment temperature is preferably higher than the crystallization temperature of the precursor film. When the heat treatment temperature is lower than the crystallization temperature, the dielectric layer 40 may be formed in an agglomerated state and the surface flatness may be impaired. In addition, when heat treatment is performed at a temperature lower than the crystallization temperature, it is known that the dielectric layer 40 cannot obtain a sufficient dielectric constant even if heat treatment is performed at a temperature higher than the crystallization temperature after the formation of the upper electrode described later. .

  On the other hand, even when the heat treatment temperature is too high, large crystal grains grow and impair the surface flatness. Therefore, it is preferable to perform the heat treatment at a temperature at which crystal grains having a relatively small grain size grow.

  Next, upper electrodes 51 and 52 are formed on the dielectric layer. After the formation of the upper electrodes 51 and 52, a third heat treatment is performed at a temperature sufficiently higher than the crystallization temperature of the dielectric layer 40, thereby completing the dielectric thin film capacitor shown in FIG.

  The upper electrodes 51 and 52 are preferably made of Pt and made of a noble metal such as Au, Pd, or Rh so that they are not easily oxidized even in the third heat treatment.

  In FIG. 1E, the upper electrodes 51 and 52 are formed on part of the dielectric layer 40, but may be formed on the entire surface of the dielectric layer 40.

  In the present invention, the second heat treatment temperature is set higher than the crystallization start temperature, and the third heat treatment is performed at a temperature higher than the second heat treatment temperature after the upper electrodes 51 and 52 are formed. The dielectric constant of the body layer 40 is sufficiently increased.

  Further, in the present invention, since the adhesion layer 20 is formed of the same material as the dielectric layer 40, warpage of the substrate 10 is not caused by oxidative expansion of the adhesion layer 20, and cracks are prevented from occurring in the dielectric layer 40. it can. Furthermore, even if the adhesion layer 20 diffuses between the lower electrode 30 and the dielectric layer 40, the adhesion layer 20 is made of the same material as that of the dielectric layer 40, that is, a ferroelectric material, and thus adversely affects the capacitor characteristics. There is no.

  In the following, more specific examples of the present invention will be described. FIG. 1A shows the substrate 10. Here, a (100) plane Si substrate having a diameter of 3 inches and a thickness of 0.38 mm is used. Since the Si oxide 12 layer having a thickness of 1 μm is formed on the surface of the substrate 10 by heat treatment, the substrate has a two-layer structure of the Si layer 11 and the Si oxide layer 12.

  Next, a sol-gel raw material solution in which an organic compound as a raw material of BST (strontium barium titanate) was dissolved was applied onto the substrate 10 by spin coating, and dried on a hot plate heated to 300 ° C. for 5 minutes. By repeating this coating and drying twice, an adhesion layer precursor film was formed. Then, as the first heat treatment, RTA heat treatment was performed in oxygen at 650 ° C. for 10 minutes. By this heat treatment, the adhesion layer precursor film is crystallized to become an adhesion layer 20 made of BST as shown in FIG. The composition of the raw material solution used here is Ba: Sr: Ti = 70: 30: 100.

  Next, as shown in FIG. 1C, a lower electrode 30 made of Pt having a thickness of about 200 nm was formed on the adhesion layer 20 by sputtering.

  Next, application and drying of the sol-gel raw material solution of BST was repeated twice in the same manner as described above, and RTA heat treatment was performed in oxygen at 650 ° C. for 10 minutes (second heat treatment). As a result, a dielectric layer 40 is formed as shown in FIG. When the state of the dielectric layer after the second heat treatment was examined by XRD (X-ray diffraction analysis), it was confirmed that the dielectric layer 40 was crystallized. However, since the crystal grain size is small, microcracks due to thermal stress during cooling hardly occur.

  Next, as shown in FIG. 1E, upper electrodes 51 and 52 made of Pt having a diameter of 1 mm and a thickness of about 200 nm were formed at intervals of 2 mm using a stainless steel metal mask. In this state, the capacitance was measured by applying a probe to two adjacent upper electrodes 51 and 52, and the capacitance was 7.0 nF and the relative dielectric constant was about 320. Further, as the third heat treatment, an RTA heat treatment was performed at 750 ° C. for 60 minutes in an oxygen atmosphere. In this state, the capacitance and the leakage current when 2.0 V was applied were measured by the same method as described above. The capacitance was 9.5 nF, the relative dielectric constant was about 440, and the leakage current was 98 pA. The short-circuit rate was 2%. The dielectric constant increased by the third heat treatment, and the dielectric layer 40 having a high relative dielectric constant could be obtained. In addition, since cracks are difficult to occur, the leakage current is small and the short-circuit rate is low.

  After measuring the capacitance and leakage current, a cut test was performed with a dicing saw. However, it was found that each layer did not peel and each layer had sufficient adhesion strength.

  (Comparative Example 1) A dielectric thin film capacitor was manufactured by the same method as described above except that the second heat treatment was performed at 500 ° C for 10 minutes. When the state of the dielectric layer after the second heat treatment was examined by XRD (X-ray diffraction analysis), it was not crystallized. The capacitance after the second heat treatment was 1.1 nF and the relative dielectric constant was about 50. Since the dielectric layer 40 is not yet crystallized, the relative dielectric constant is low. The capacitance after the third heat treatment was 5.2 nF, and the relative dielectric constant was about 240. Since the temperature of the second heat treatment was equal to or lower than the crystallization start temperature, the relative dielectric constant did not sufficiently increase even when the third heat treatment was performed at a temperature higher than the crystallization temperature. This seems to be due to the restriction of Pt, which is the upper electrodes 51 and 52, when the dielectric layer 40 is crystallized.

  Further, the leakage current is 160 pA and the short-circuit rate is 33%, which is particularly inferior to the embodiment. This is because when the dielectric layer 40 is crystallized by the third heat treatment, crystallization of BST is regulated by Pt in the portion where the upper electrodes 51 and 52 are formed, whereas the upper electrodes 51 and 52 Since it is not restricted in the portion where there is no upper electrode 51, 52, it is considered that crystallization and grain growth are relatively easy to proceed in the portion where the upper electrode 51, 52 is not present, and stress is concentrated on the dielectric layer 40 near the outer periphery of the upper electrode 51, 52. .

  (Comparative Example 2) A second heat treatment was performed at 750 ° C. for 60 minutes, and a dielectric thin film capacitor was manufactured without performing the third heat treatment. When the state of the dielectric layer 40 after the second heat treatment was examined by XRD (X-ray diffraction analysis), it was confirmed that it was crystallized. The capacitance after the second heat treatment was 8.1 nF, the relative dielectric constant was about 370, the leakage current was 230 pA, and the short rate was 12%.

  Since the second heat treatment is performed at a temperature sufficiently higher than the crystallization start temperature, the relative dielectric constant is relatively high. However, since the temperature of the second heat treatment is higher than that of the example, the dielectric layer 40 receives a strong tensile stress over the entire surface due to the difference in the linear expansion coefficient between the substrate 10 and the dielectric layer 40 due to the cooling after the second heat treatment. Thus, many micro cracks are generated in the dielectric layer 40, and the leakage current is increased.

  From the results of Examples and Comparative Examples 1 and 2, the first and second heat treatments are performed at a temperature higher than the crystallization temperature and at a level at which large crystal grains do not grow, and after the upper electrodes 51 and 52 are formed, It can be seen that by performing the third heat treatment at a temperature higher than the second heat treatment temperature, it is possible to obtain the dielectric layer 40 having a sufficient relative dielectric constant and free from cracks. Note that the heat treatment temperature described in the examples and comparative examples has a suitable temperature range depending on the composition of the raw material solution of the adhesion layer 20 and the dielectric layer 40.

It is sectional drawing which shows the manufacturing process of the dielectric thin film capacitor which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11 Si layer 12 Si oxide layer 20 Adhesion layer 30 Lower electrode 40 Dielectric layer 51, 52 Upper electrode

Claims (6)

Forming an adhesion layer precursor film on a substrate and performing a first heat treatment to crystallize and form an adhesion layer;
Forming a lower electrode on the adhesion layer;
A dielectric layer precursor film made of a material having the same composition as that of the adhesion layer precursor film is formed on the lower electrode, and a second time at a temperature higher than the crystallization temperature of the dielectric layer precursor film. Performing a heat treatment to form a dielectric layer;
Forming an upper electrode on the dielectric layer;
And a step of performing a third heat treatment at a temperature higher than a heat treatment temperature of the first heat treatment and the second heat treatment.   2. The method of manufacturing a dielectric thin film capacitor according to claim 1, wherein the adhesion layer precursor film and the dielectric layer precursor film are made of the same material. .   The dielectric thin film capacitor manufacturing method according to claim 1 or 2, wherein a processing temperature in the first heat treatment is higher than a crystallization start temperature of the adhesion layer precursor film. Manufacturing method of thin film capacitor.   4. The dielectric thin film capacitor according to claim 1, wherein the dielectric layer is made of any one of barium titanate, strontium titanate, and barium strontium titanate. 5. Method.   The method for manufacturing a dielectric thin film capacitor according to claim 1, wherein the lower electrode is made of platinum.   6. The method for manufacturing a dielectric thin film capacitor according to claim 1, wherein the upper electrode is made of platinum.

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