JP2007180398A - Method for manufacturing capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a capacitor having a dielectric layer having a high dielectric constant, and preventing leakage current from deteriorating by a large amount. <P>SOLUTION: The capacitor manufacturing method comprises an application process for forming an application film, by applying a dielectric precursor solution containing titanium, barium, strontium, and a group IA element to the surface of a base material; and a heat treatment process for performing heat treatment on the application film at 700 to 900°C to obtain a high dielectric film. The high dielectric film contains the group IA element of 1.5 to 5 pts.wt. with respect to the dielectric substance of 100 pts.wt. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a capacitor, and more particularly to a method for manufacturing a capacitor that can be suitably used for a method for manufacturing a decoupling capacitor used for power supply of a semiconductor.

  Due to the recent increase in calculation speed, the operating power supply voltage of semiconductor elements tends to become unstable when the impedance changes rapidly. In order to stabilize the power supply voltage and reduce high frequency noise, a decoupling capacitor is disposed between the voltage power supply line and the ground line. A conventional decoupling capacitor is mounted on a circuit board, which is a motherboard, by providing a chip capacitor near the semiconductor chip. In this case, wiring must be routed between the chip capacitor and the semiconductor chip, and a relatively large inductance exists between these leads. Therefore, even if a chip capacitor is provided, the effects of suppressing fluctuations in power supply voltage and reducing high-frequency noise are reduced with respect to a semiconductor operating at high speed. What is required of the decoupling capacitor is to reduce the equivalent series resistance and equivalent series inductance of the substrate circuit. In particular, the increase in inductance due to the wiring between the decoupling capacitor and the semiconductor hinders the high frequency characteristics of the decoupling capacitor. In view of this, it has been proposed to reduce the inductance by arranging a capacitor immediately below the semiconductor to minimize the wiring distance between the semiconductor and the decoupling capacitor (Patent Document 1).

  A decoupling capacitor directly under such a semiconductor is required to have a large capacity and a thin capacitor. Therefore, a counter electrode type thin film capacitor in which a dielectric thin film with a high dielectric constant is sandwiched between electrodes rather than a multilayer ceramic capacitor. Is preferred.

  It is known that the use of barium strontium titanate (hereinafter referred to as “BST”) having a perovskite structure as a thin-film dielectric layer is preferable as an environment-adaptive capacitor because it does not contain a high dielectric constant and Pb. (Patent Document 2).

On the other hand, although the structure uses the same dielectric layer, a dielectric film for a semiconductor memory can be crystallized at a low temperature of 250 to 500 ° C. by adding Li, Na, and K as a group Ia element to BST. It has been proposed that this can be realized (Patent Document 3).
Japanese Patent Laid-Open No. 04-225594 Japanese Patent Application Laid-Open No. 09-078249 JP 2000-77616 A

However, BST suitable for a thin film decoupling capacitor has a composition of (Ba _1-x Sr _x ) _y TiO ₃ (x is 0 to 1, y is 1.0 to 1.10.), But the composition is the same. However, if the manufacturing method is different, the structure is different, so that the dielectric constant, leakage characteristics, and the like change greatly. In the conventional manufacturing method, it is difficult to achieve both a sufficiently high dielectric constant and low leakage characteristics.

  The dielectric element described in Patent Document 3 is an element using the same BST. However, since it is for a semiconductor memory, a higher temperature (500 ° C.) heat treatment is performed even at a low temperature heat treatment of 250 to 500 ° C. The purpose is to “maintain a high remanent polarization Pr value”, which is equivalent to the case where is used. In addition, since the BST film is formed by sputtering, the film formation cost is high, and it is difficult to apply to a decoupling capacitor that is a general-purpose electronic component. It should be noted that the decoupling capacitor is not required to have good remanent polarization characteristics, and is not particularly problematic at all.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a capacitor manufacturing method that can manufacture a high-capacity capacitor that has a high dielectric constant and does not significantly deteriorate a leakage current at low cost.

  The present invention includes a coating step of coating a dielectric precursor solution containing titanium, barium, strontium, and a group IA element on a substrate to form a coating film, and heat-treating the coating film at 700 to 900 ° C. A heat treatment step for obtaining a high dielectric film, wherein the high dielectric film is a method for manufacturing a capacitor containing 1.5 to 5 parts by weight of an IA group element with respect to 100 parts by weight of a dielectric.

  According to these dielectric film manufacturing methods, it is possible to suppress an increase in leakage current even if the dielectric constant is improved. When the dielectric film does not contain a group IA element, the dielectric constant increases slightly when the firing temperature is increased, but carriers due to defects in the lattice are likely to be generated, which is a cause of significant deterioration of the leakage current. It becomes. In contrast, the present invention includes a specific amount of the group IA element and sets the firing temperature in a specific range, so that the generation of carriers as described above is sufficiently suppressed, resulting in a significant increase in dielectric constant. Nevertheless, the leakage current is suppressed. Moreover, since the dielectric precursor solution is applied onto a substrate to form a coating film, a large-area coating film can be formed with an inexpensive apparatus.

  In the present invention, the Group IA element is preferably Li. Li is more easily dissolved in BST than other group IA elements such as Na and K. Therefore, when Li is used, there is an advantage that the dielectric constant of the dielectric film can be improved more easily.

  The capacitor of the present invention is particularly preferably used as a decoupling capacitor. This is because a dielectric thin film having a high dielectric constant and low leakage characteristics can be formed on a large area at a low cost, and the entire capacitor can be made thin.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the capacitor | condenser which has a dielectric layer with a high dielectric constant, a leak current does not deteriorate greatly, and can be formed in a large area cheaply is provided.

  Hereinafter, embodiments of the present invention will be described in detail.

  The method for producing a capacitor of the present invention includes a step of forming a lower electrode on a substrate, a coating step of coating a dielectric precursor solution to form a coating film, and a baking process for heat-treating the coating film to obtain a high dielectric film. It is manufactured from a process and a process of forming an upper electrode on the dielectric film. Of these, the step of forming the lower electrode on the substrate and the step of forming the upper electrode on the dielectric film are the same general-purpose steps as conventionally known steps.

As a step of forming the lower electrode on the substrate, for example, a TiO ₂ layer is formed as a bonding layer on a Si wafer with a thermal oxide film by a sputtering method, and then a conductive material such as Pt is formed by a sputtering method. . Alternatively, it is possible to use a metal foil having the functions of both the base and the lower electrode, for example, a nickel metal foil.

  In the coating process in which the dielectric precursor solution is applied to form a coating film, examples of the dielectric precursor solution include a sol-gel raw material solution in which an organic compound is dissolved and a MOD (organic metal decomposition method) raw material solution. For example, a solution obtained by dissolving a metal alkoxide or an organic acid salt in an organic solvent such as toluene or xylene.

  Note that the sol-gel method and the MOD method are not completely separate methods and are generally used in combination with each other. For example, a solution can be prepared using Ba acetate as the Ba source and using the metal alkoxide as the Ti and Sr sources. Alternatively, the two methods of the sol-gel method and the MOD method may be collectively referred to as the sol-gel method, and in either case, the dielectric layer can be formed by applying the precursor solution and baking.

That is, an organometallic salt such as a metal alkoxide, a metal complex, or a metal carboxylate can be used as the source of the Ba, Sr, Ti, and Group IA elements of the dielectric precursor solution. As the metal alkoxide, it can be used, for example _{OCH 3, OC 2 H 5,} OC 3 H 7, OC 4 H 9, alkoxide consisting of alkoxyl groups such as _OC 2 H 4 OCH _3. Examples of the metal complex compound include complexes of the above metal acetylacetone, benzoylacetone, benzoyltrifluoroacetone, benzoyldifluoroacetone, benzoylfluoroacetone, and the like. Moreover, as a metal carboxylate, metal carboxylates, such as an acetic acid and an oxalic acid, can be used, for example. The solvent to be used is not particularly limited as long as it can dissolve the dielectric precursor as the metal source. For example, toluene, xylene, alcohols such as methanol, ethanol, isopropyl alcohol, and butanol can be used. .

  In the present invention, the precursor of the group IA element is added to the dielectric precursor solution so that 1.5 to 5 parts by weight of the group IA elements such as Li, Na, and K are included with respect to 100 parts by weight of the fired dielectric. Add. If the addition amount is less than the above range, the effect is not remarkable, and if it exceeds the above range, the dielectric constant decreases. Depending on the firing conditions, some elements are likely to escape from the film due to volatilization or the like in the firing stage, so the amount added to the precursor solution may be taken into account.

  Next, a dielectric precursor solution is apply | coated on a lower electrode, and a coating film is formed (application | coating process). The coating can be performed by a known method such as a spin coating method, a spin casting method, a blade method, a spray coating method, a bar coating method, or a dip method. Thereafter, the coating film is dried to substantially remove the solvent in the coating film.

  And the heat processing (baking) process which heat-processes a coating film and obtains a high dielectric material film is performed. Usually, when baking a coating film by a dielectric precursor solution method, baking is performed in two steps. That is, first, the coating film is temporarily baked and then the main baking is performed. Temporary firing is usually performed by setting the firing temperature to 300 to 500 ° C., the rate of temperature rise to 1 to 1000 ° C./minute, and the holding time to 1 to 30 minutes. These can be performed on a hot plate.

  In the main baking, the temporarily fired coating film is fired at 700 to 900 ° C. (baking step). Below this range, the leakage current is low, but the dielectric constant is also low. When the above range is exceeded, the leakage current increases rapidly, making it difficult to evaluate the dielectric constant.

  As long as firing is performed within the above temperature range, the rate of temperature rise and the holding time are not particularly limited and can be set as appropriate. Usually, the cycle of coating film formation-temporary baking-main baking is repeated until the coating film reaches a target film thickness. At this time, a cycle of coating film formation-temporary baking may be repeated, and final baking may be performed to form a dielectric film having a target film thickness. Thus, the production of the dielectric film is completed.

  Next, as a step of forming the upper electrode on the dielectric film, a conductive material, for example, Cu is formed by sputtering. When a film thickness of 5 to 30 μm is required, it can be further thickened by copper plating or the like. The manufacture of the capacitor is completed as described above.

  According to the method for manufacturing a capacitor, it is possible to obtain a capacitor having a dielectric layer that has a high dielectric constant, does not significantly deteriorate leakage current, and can be formed on a large area at a low cost. Although the reason why the dielectric constant is high and the leakage current is not greatly deteriorated is not clear, a specific amount of Group IA element is added, and the main firing is performed in a specific temperature range, so that carriers due to lattice defects can be obtained. I think that it is because generation | occurrence | production is fully suppressed.

  Next, the content of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

A TiO ₂ layer having a thickness of 5 nm was formed on a Si wafer with a thermal oxide film having a thickness of 0.5 mm by a sputtering method. Subsequently, Pt was sputtered on the TiO ₂ film to form a lower electrode layer made of Pt and having a thickness of 100 nm.

Next, a dielectric precursor solution was prepared as follows. Octyl containing titanium, barium and strontium in a mixed solvent consisting of toluene and butanol so that BST represented by the composition formula: (Ba _0.7 Sr _0.3 ) _1.03 TiO ₃ is obtained after firing. Li was added as lithium octylate to the MOD precursor solution for BST using an acid as a raw material with respect to 100 parts by weight of BST after firing.

  Next, the dielectric precursor solution prepared as described above was applied onto the lower electrode layer by a spin coating method to form a coating film. Thereafter, the coating film was dried at 150 ° C. for 10 minutes to remove the solvent in the coating film.

  Next, the coating film was baked. Firing is temporary firing (firing temperature: 300 ° C., heating rate: 10 ° C./min, holding time: 10 minutes) and main baking (baking temperature: 300 to 1000 ° C., heating rate: 100 ° C./min, holding time: 30 minutes).

  Then, the dielectric precursor solution was applied again, and the above-described two-stage firing was performed. Thus, the coating and the two-stage baking were repeated five times as one cycle to form a dielectric thin film having a thickness of 130 nm.

  Finally, an upper electrode layer made of Pt and having a thickness of 200 nm was obtained on the dielectric film by sputtering of Pt. A capacitor was obtained as described above.

  With respect to the capacitor thus obtained, the relative permittivity, the leakage current density, and the dielectric loss were measured. The probe needle was pressed against the upper electrode and the lower electrode, and the dielectric constant and dielectric loss at 100 kHz were measured with an impedance analyzer. Similarly, the leakage current density was measured at room temperature with a semiconductor parameter analyzer. As for the leakage current density, a current generated when an electric field of 100 kV / cm was applied between the upper electrode layer and the lower electrode layer at room temperature was measured. The results are shown in FIG. 1 and FIG. In FIG. 1 and FIG. 2, “◯” indicates that the Li content is 0 parts by weight, “●” indicates 1.0 part by weight, “Δ” indicates 1.5 parts by weight, and “▲” indicates 3.0 parts by weight. Part by weight, “▽” indicates 5.0 parts by weight, and “▼” indicates 8.0 parts by weight.

  In other words, when the Li content is 1 part by weight, there is no significant difference compared to the case where no Li is added. However, in the case of 1.5, 3 and 5 parts by weight, a clear increase in the dielectric constant is seen at 700 to 900 ° C. as compared with no addition, but the leakage current is rather lowered as compared with no addition. is doing. In the case of 8 parts by weight, the dielectric constant decreased in any temperature range. In the heat treatment at 1000 ° C., a large leak current flows, so that it is difficult to measure the dielectric constant.

  In addition, the dielectric loss was 5% or less at a heat treatment temperature of 900 ° C. or less, but exceeded 20% at 1000 ° C.

  From the above results, when a BST film containing Li was formed using a dielectric precursor solution and baked at 700 to 900 ° C., the dielectric constant was obtained when the Li content was 1.5 to 5 parts by weight. It was confirmed that an increase in leakage current could be suppressed while improving.

  The dielectric film composition was confirmed by ICP, and the film composition almost corresponding to the added amount ratio of the dielectric precursor solution was confirmed.

  Further, the capacitor of this example showed a high capacity of 2 μF or more even when the counter electrode area was 2 cm square, and could be used as a decoupling capacitor installed directly under the CPU. Furthermore, it has a higher capacity than a capacitor having a BST thin film formed by sputtering, and the manufacturing cost is approximately 50%. The effects of the present invention are clear from the above results.

FIG. 1 is a diagram showing a change in dielectric constant depending on a firing temperature, with a Li content as a parameter. FIG. 2 is a diagram showing the change in leakage current according to the firing temperature and the Li content as parameters.

Claims (3)

An application step of applying a dielectric precursor solution containing titanium, barium, strontium, and a group IA element on a substrate to form a coating film;
A heat treatment step of heat-treating the coating film at 700 to 900 ° C. to obtain a high dielectric film,
The high dielectric film is a method of manufacturing a capacitor containing 1.5 to 5 parts by weight of a group IA element with respect to 100 parts by weight of a dielectric.   The method for manufacturing a capacitor according to claim 1, wherein the Group IA element is Li.   The method for manufacturing a capacitor according to claim 1, wherein the capacitor is a decoupling capacitor.

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