JP4502632B2 - Thin film capacitor - Google Patents

Description

  The present invention relates to a thin-film capacitor comprising a metal oxide formed on a substrate, wherein a dielectric layer to which a voltage is applied is hermetically covered with a protective film mainly composed of silicon dioxide, and is particularly effective. The present invention relates to a thin film capacitor provided with a protective film having excellent moisture resistance.

  The basic configuration of the thin film electronic component is usually a base (hereinafter referred to as a generic name including a so-called substrate) that is sufficiently thicker than the thin film that constitutes the functional element region, and individual elements that constitute the element on the surface thereof. An element manufactured by forming and processing a thin film layer, a protective film for protecting the element from the external environment, and a terminal portion for connecting to the outside can be roughly classified. Of these, the substrate has a relatively high durability against external impacts and dirt, high temperature, high humidity environment, etc., but the functional element region of the thin film has a very poor durability against these factors. There are many things.

For this reason, conventionally, by forming a protective film for protecting the functional element region from the external environment, the functional element region has been protected and the resistance to the environment as a thin film electronic component has been improved. In addition to protecting from external mechanical shocks, the protective film has a role of preventing deterioration due to humidity, chemical contamination, oxidation, and the like. For this reason, the material used for the protective film is a material resistant to chemicals and oxidation. For example, the inorganic material includes silicon dioxide (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ) including glass and the like, and the organic material includes polyimide, BCB (benzocyclobutene), and the like. These materials do not deteriorate the properties of the device and the protective film by reacting with the metal and dielectric materials that make up the device, and are excellent in moisture resistance and airtightness. It is used as a film material. Among these materials, SiO ₂ is widely used because it is resistant to heat, does not have a reducing action that causes element deterioration, and has a common part with the silicon device.

  The functional element region of the thin film is usually weak to external environmental factors such as humidity, oxidizing atmosphere, and reducing atmosphere, and these elements often deteriorate characteristics or lead to destruction. For this reason, a protective film is formed so as to cover the functional element region, and the function of the protective film is to isolate the thin film element from these external factors and to prevent characteristic deterioration and destruction.

  Therefore, the protective film must be able to completely prevent the entry of external factors such as water molecules, or at least reduce the functional element region so as not to be affected. In order to realize such a function, the protective film is made of a material having a small transmission coefficient of an external factor to be shielded such as water molecules, and in particular, the step between the layers of the element and the covering of the end portions are sufficient. It is required to be. Under normal conditions of use, water molecules are the biggest problem as an external factor, and therefore, a material with little water molecule permeation is often used for the protective film. Further, regarding the covering of the element, since it is most difficult to sufficiently cover the stepped portion and the end portion, a thin film having a film thickness that completely fills the concave portion on the element surface is formed as a protective film.

The above-mentioned SiO ₂ is widely used as a protective film at present, and for silicon devices, it has a permeability coefficient of an external factor that should be shielded, such as water molecules, that is small enough to function as a moisture-resistant protective film. Have. This means that the moisture shielding resistance is sufficient with respect to external factor concentrations such as water molecules at a level at which the silicon device deteriorates. Therefore, in general, whether or not to function as a moisture-resistant protective film is determined by the moisture-shielding resistance against the concentration of external factors such as water molecules at a level at which the thin-film element deteriorates, that is, the relationship of the transmission coefficient. .

In general, a silicon device has Si or SiO ₂ as a main component, and has higher resistance to redox action than a general metal material excluding noble metals. Even when several dopant components are contained, many have high oxidation-reduction resistance. Deterioration caused by the penetration of external factors such as water molecules into the thin film element is caused by the progress of the redox reaction due to the action of both external factors such as water molecules and the applied electric field. Therefore, the progress of deterioration depends on both the amount of external factors such as water molecules that have entered and the activation energy of the oxidation-reduction reaction using the external factors such as water molecules as a catalyst.

  Silicon is a covalently bonded element, and the activation energy required for chemical reaction with other elements is relatively high. On the other hand, general metal elements excluding noble metals are metal-bonding elements, and the activation energy of chemical reaction is relatively small, and it is relatively easy to form a compound with other elements. This means that a thin film device having a metal element has a lower activation energy for a chemical reaction, that is, a redox reaction, and a higher reaction rate than a silicon device. In the rapid progress of the oxidation-reduction reaction that causes deterioration of the thin film element, this activation energy is supplied by an applied electric field or the like, but this activation energy is small, and the oxidation-reduction reaction proceeds even with a relatively small electric field strength. Furthermore, it means that the reaction rate is increased even with the same electric field strength. Therefore, a device having a structure in which an electric field is applied to a metal oxide film or the like, for example, a high-capacity compound dielectric capacitor or a piezoelectric thin film element, Deterioration is faster than. In particular, in a thin film capacitor having a dielectric layer covered with a protective film manufactured by a conventional technique, a load life in a moisture is shorter than that of a silicon device. Regarding the electric field strength, the value necessary for the operation of the element is determined regardless of the moisture resistant load life, and therefore it is basically impossible to secure the moisture resistant load life by reducing this value. Therefore, a measure that can be taken for ensuring the moisture resistant load life is to reduce the transmittance of external factors such as water molecules of the protective film.

  As a method of reducing the transmittance of the protective film, a method of closing a bond defect site in which a bond between oxygen and silicon in the film, which is a passage route of external factors such as water molecules, is blocked is common. is there. In many cases, impurities are mixed in as a method for closing the bonding defect site. For example, the silicon dioxide film produced by MOCVD (metal organic chemical vapor deposition), which uses a source gas containing carbon and hydrogen, is often used to produce a protective film for silicon devices. It is because it is doing. In the MOCVD method, it is considered that hydrogen and carbon are mixed in the film and play a role of closing bonding defects.

In addition, a method of adding various additives has been devised to intentionally achieve this effect. For example, there is a method for solving the problem by using a fluorine-added silicon oxide film in which fluorine is added to SiO ₂ as a protective film (see, for example, Patent Document 1). This solution is characterized in that a SiOF (silicon oxyfluoride) film is formed and the transmittance can be made smaller than that of a silicon dioxide film to which no fluorine is added.
JP-A-11-233513

  However, in this method, since the source gas is not an organometallic compound, there is a problem that the hydrogen and carbon concentrations in the formed silicon dioxide film are significantly smaller than those of the silicon dioxide film produced by the MOCVD method. This is because, when the hydrogen and carbon concentrations are low, the transmittance of external factors such as water molecules increases.

  Further, in this film forming method, it is expected that a fluorine atom replaces an oxygen atom, and there is a high possibility that a new bond defect is generated. In addition, it is not preferable to put many fluorine atoms in the film in consideration of the risk of forming a fluoride of the material used in the device. Further, since hydrogen tends to be desorbed from the film by forming hydrogen fluoride in the presence of fluorine, the hydrogen concentration in the film may further decrease. Therefore, it is impossible to increase the effect by further increasing fluorine. In other words, this solution is not optimal for the purpose of reducing the transmittance of external factors such as water molecules, and it must be said that the transmittance is not sufficiently reduced.

  The present invention has been devised in view of the above-described problems, and its main purpose is to reduce the transmittance of external factors such as water molecules by modifying the protective film. For this purpose, there is a demand for a new method that has the advantages of the silicon dioxide film formed by the MOCVD method, which is the prior art, and that can achieve the same effect as the fluorine addition disclosed in Patent Document 1. In other words, the effect of fluorine addition disclosed in Patent Document 1 is exhibited at the same time without significantly impairing the effect of impurities filling the bond defects and blocking the permeation path of external factors such as water molecules. . For this purpose, impurities that do not greatly decrease from the film even when the additive is introduced are required. From this point of view, since hydrogen tends to be desorbed from the film by introducing fluorine, a silicon dioxide film having only hydrogen as an impurity is not suitable as a thin film material serving as a base material into which fluorine is introduced. A silicon dioxide film having suitable impurities is required. There is a need for a film formation method that can introduce fluorine into the film without reducing the impurity concentration.

  An object of the present invention is to further reduce the transmittance of external factors such as water molecules by intentionally adding an additive while maintaining the advantages of a silicon dioxide film produced by MOCVD. In addition, by using the silicon dioxide film thus produced as a moisture-resistant protective film, it is possible to reduce external factors such as water molecules reaching the device, and to apply an applied voltage to the dielectric layer necessary for the operation of the thin film capacitor. The purpose is to extend the moisture resistance life without lowering. Furthermore, it aims to ensure the same moisture-resistant reliability life as a silicon device having a moisture-resistant protective film according to the prior art, even in a thin film capacitor having a functional oxide region in which a metal oxide that is more rapidly deteriorated in moisture than a silicon device. To do.

In order to achieve the above object, a thin film capacitor of the present invention comprises a substrate , a metal oxide formed on the substrate, a dielectric layer to which a voltage is applied, and the dielectric layer covered hermetically. and that has a protective film composed mainly of silicon dioxide, the silicon dioxide is a composition ratio of oxygen element against the elemental silicon stoichiometric, elemental fluorine and carbon element as a minor component wherein 2.0 × 10 ²⁰ atoms / cm ³ or more, fluorine element contained in the silicon dioxide, are increasingly content than that of the carbon element. Here, the constant ratio is an O / Si ratio in the range of 2.0 ± 0.1.

Furthermore, carbon is contained as a trace component in an amount of 2.0 × 10 ²⁰ atoms / cm ³ or more.

  In the specific production of the protective film, an organic metal compound is used as a source gas, thereby taking advantage of the advantages of the MOCVD method. Thereby, hydrogen and carbon are introduced into the silicon dioxide film. Furthermore, fluorine is introduced into the silicon dioxide film by adding a fluorine-containing gas to the source gas.

  Conventionally, fluorine has a high risk of substituting part of oxygen to form a SiOF film and generate a new bond defect, whereas in the fluorine introduction method according to the present invention, the ratio of oxygen to silicon is high. Can be kept at a constant ratio = 2. Furthermore, in the present invention, carbon is present in the silicon dioxide film. Carbon is relatively less desorbed in the presence of fluorine than hydrogen, and its concentration decrease is small. On the other hand, hydrogen has a risk of reducing the metal oxide and degrading the characteristics of the capacitor. Therefore, it is preferable for the capacitor containing the metal oxide to have a low hydrogen concentration. For these reasons, it is necessary to maintain a state where carbon is contained in a certain amount or more. In order not to reduce the advantage of the MOCVD method, it is necessary that the carbon concentration is not reduced with respect to the silicon dioxide film manufactured by the MOCVD method without adding fluorine. Then, fluorine is introduced into the silicon dioxide film containing carbon using a fluorine-containing gas to fill bond defects that are not filled with carbon.

  The present invention is a moisture-resistant protective film composed of a thin film mainly composed of silicon dioxide as described above, wherein fluorine and carbon are present at a constant concentration as impurities contained. Preferably, the film thickness is 1.0 to 3.0 μm.

  Further, the present invention is a thin film capacitor formed by laminating a thin film layer on a substrate, and the thin film capacitor using the moisture-resistant protective film as a protective film. Furthermore, the thin film element includes a metal oxide film layer, and has a structure in which an electric field is applied to the metal oxide film. Further, the thin film capacitor is characterized in that the main component metal of the metal oxide layer contains one or more elements of Pb, Ti, Zr, Ba, Sr, Mg, and Nb. Furthermore, the moisture-resistant protective film and the substrate are in close contact with each other at the outer edge portion of the thin film element to completely seal the thin film element. More preferably, the thin film element has a structure in which irregularities on the surface of the thin film element are equal to or less than the film thickness of the moisture resistant protective film, and a pattern side surface of the thin film layer constituting the thin film element is completely buried in the moisture resistant protective film layer. It is a thin film capacitor.

  In the present invention, in order to improve the moisture shielding property of the moisture-resistant protective film mainly composed of silicon dioxide according to the prior art, by introducing fluorine into silicon dioxide, the transmittance of external factors such as water molecules can be reduced. Has the effect of reducing. As a result, even a thin film capacitor having a metal oxide film with a high electric field achieves a sufficient moisture resistance load life equivalent to that of a silicon device.

  In the moisture-resistant protective film mainly composed of silicon dioxide, a bond defect or the like in the film forms a path that allows external factors such as water molecules to pass through. Even in the prior art, this bonding defect is terminated and eliminated to some extent by an impurity element mixed during film formation, and the transmittance of external factors such as water molecules is lowered. As mentioned earlier, the silicon dioxide film made by MOCVD has excellent moisture resistance because it is already mixed with hydrogen, carbon, etc. in the film-forming source gas used during film formation. is there.

  In the present invention, the effect of mixing impurities is actively used, and specific elements are intentionally mixed to promote termination and elimination of bond defects and reduce the transmittance of external factors such as water molecules. It is about to try. The element to be introduced must have high reactivity with silicon, easily form a bond, and do not adversely affect the characteristics of the thin film element covered by the moisture-resistant protective film. Elements present in the thin film element or in the thin film element fabrication process are preferred. For these reasons, fluorine is used in the thin film processing process, and fluorine having high reactivity with silicon is used as the introduced element. Since fluorine has a higher reactivity with silicon than oxygen, it can also bond to sites that are not capable of reacting with oxygen and become bond defects, and the bond defects can be terminated and eliminated. Although the risk of reacting with the elements used in the device cannot be denied, there is no problem as long as the concentration is at the level used in the thin film processing process according to the prior art. Further, hydrogen and carbon existing as impurities are also responsible for terminating and eliminating bond defects, and therefore must be present in silicon dioxide at a constant concentration. In particular, carbon is a stable element in the film even in the presence of fluorine, and has a relatively high concentration. Therefore, carbon is an important element for terminating and eliminating bond defects. Therefore, it must be avoided that the concentration decreases.

  In this way, the transmittance of external factors such as water molecules of the silicon dioxide film into which fluorine has been introduced is lowered, and the amount of external factors such as water molecules reaching the coated thin film element is reduced. Therefore, in the metal oxide film layer, it takes a long time for the concentration of external factors such as water molecules that have passed through the moisture-resistant protective film to reach the concentration necessary for the oxidation-reduction reaction to proceed rapidly by the applied electric field. . As a result, the time until breakdown starts to occur becomes longer, and the life in the moisture resistance load test can be extended.

According to the thin film capacitor of the present invention, the thin film capacitor is made of a metal oxide formed on a substrate, and a dielectric layer to which a voltage is applied is hermetically covered with a protective film mainly composed of silicon dioxide. The composition ratio of O (oxygen) to silicon (Si) in the silicon dioxide is a constant ratio, and fluorine is contained as a trace component in an amount of 2.0 × 10 ²⁰ atoms / cm ³ or more. As a result, the transmittance of external factors such as water molecules can be reduced, excellent shielding properties can be exhibited, and the dielectric layer can be actually protected by the protective film, so that a highly reliable thin film capacitor can be provided.

Furthermore, by containing a predetermined amount (2.0 × 10 ²⁰ atoms / cm ³ ) or more of carbon that seems to exhibit the same behavior as fluorine, the oxygen ratio is lowered and the carbon concentration in the film is deteriorated. Reduction can be prevented as much as possible. Thereby, it is possible to greatly improve the moisture resistance of the functional element region including the dielectric layer and further increase the moisture resistance load life. Here, the above-described excellent moisture-proof shielding property can be further exhibited particularly by increasing the film thickness of the protective film rather than the unevenness on the surface of the functional element region.

  In addition, the thin film capacitor of the present invention is characterized in that the functional element region includes a dielectric layer, so that external factors such as water molecules are more effectively applied than when a conventional moisture-resistant protective film is used. A thin film capacitor that can be shielded and has excellent long-term reliability can be provided.

The thin film capacitor of the present invention will be described in detail below with reference to the drawings. First, the moisture resistant protective film will be described in detail. The introduction of fluorine into the silicon dioxide film according to the present invention is realized by introducing tetrafluorocarbon (CF ₄ ) gas into the raw material gas when forming the silicon dioxide film. The silicon dioxide film is formed by MOCVD using tetraethoxysilane (TEOS) and oxygen as source gases, and CF ₄ gas is introduced into this source gas. A sample is placed on an electrode plate having a diameter of 20 cm, and film formation is performed in parallel plate plasma. Secondary ion mass spectrometry or Rutherford backscattering is used for composition analysis of the produced silicon dioxide film sample.

In the moisture resistance load test, barium strontium titanate ((Ba, Sr) TiO ₃ ; hereinafter referred to as BST), lead zirconate titanate (Pb (Zr, Ti) O ₃ ; hereinafter referred to as PZT), niobic acid. This is performed by using a thin film capacitor in which lead magnesium acid (Pb (Mg _1/3 , Nb _2/3 ) O ₃ ; hereinafter referred to as PMN) is used as a dielectric layer.

FIG. 4 shows a sectional view of this thin film capacitor. In this thin film capacitor, a capacitor element, which is a functional element region, is formed on a sapphire substrate 41 whose main component is Al ₂ O ₃ . This capacitor element is completely covered with the protective film 46 according to the present invention, and is configured by forming electrode layers on the upper and lower surfaces of the dielectric layer 42. A through hole is formed in the protective film so that a part of the terminal electrode layer (45a, 45b) connected to the upper electrode layer 44 and the lower electrode layer 42 of the capacitor element covered by the protective film is exposed. Yes. For example, a solder barrier layer made of Ni is formed on the terminal electrode layer 45a exposed in these through holes. On the solder barrier layer, for example, external terminals made of solder bumps are formed. As described above, the thin film capacitor of the present invention is a thin film in which the dielectric layer 42 formed of the metal oxide formed on the substrate 41 and applied with a voltage is hermetically covered with the protective film 46 mainly composed of silicon dioxide. The capacitor is a thin film capacitor in which the composition ratio of O (oxygen) to silicon (Si) in silicon dioxide is a constant ratio, and fluorine is contained as a minor component in an amount of 2.0 × 10 ²⁰ atoms / cm ³ or more.

  Hereinafter, each layer of the thin film capacitor will be described. First, as the material of the capacitor electrode layer, gold (Au), platinum (Pt), palladium (Pd), copper (Cu), silver (Ag), titanium (Ti), chromium (Cr), nickel (Ni) Although there are thin films and the like, among these, a gold (Au) or platinum (Pt) thin film that has low reactivity and is difficult to be oxidized is optimal. The film forming method is a PVD method. The solder barrier layer is also produced by the same material and film formation method. The dielectric layer uses any of BST, PZT, and PMN described above. The film thickness is 0.3 to 0.5 μm, and it is produced by a known method such as a PVD method, a CVD method, or a sol-gel method. Using these materials, a capacitor element is fabricated by forming a lower electrode layer 42, a dielectric layer 43, an upper electrode layer 44, and terminal electrode layers (45a, 45b) in this order on a base 41. For pattern formation of each layer, thin film processing is performed by a known method such as a wet etching method using chemical dissolution or a RIE (reactive ion etching) method using plasma of a reactive gas.

A silicon dioxide moisture-resistant protective film according to the present invention is formed on the capacitor element thus produced. The silicon dioxide protective film according to the prior art is manufactured by a known method such as a sol-gel method, an RF sputtering method, a CVD method, an ECR sputtering method, etc., but the film formation process in the present invention uses CF ₄ gas first. The described MOCVD method is used. The protective film 46 of silicon dioxide is produced so as to completely cover the capacitor element. Then, through holes for connecting external terminals were formed in the protective film 46 of silicon dioxide by a photolithography process and an RIE process. Terminal electrode layers for the upper and lower electrodes are exposed at the bottom of the through hole. Except for this through hole, the capacitor element is completely covered with a protective film 46 of silicon dioxide. Since the dielectric layer 43 does not exist immediately below the through hole, the dielectric layer 43 is completely covered with the silicon dioxide protective film 46.

  Finally, an external terminal electrode made of a solder bump is formed on this terminal electrode layer, and then wafer dicing is performed to cut out individual elements, which are mounted on a moisture resistance load resistance evaluation board. The moisture resistance load test employs a method of examining a change in the insulation resistance value after applying a DC bias voltage for a certain time under humidification conditions under high temperature and pressure.

Thus, according to the thin film capacitor of the present invention, the thin film capacitor is made of a metal oxide formed on the substrate, and the dielectric layer to which a voltage is applied is hermetically covered with the protective film mainly composed of silicon dioxide. In this case, the composition ratio of O (oxygen) to Si (silicon) of silicon dioxide is a constant ratio, and fluorine is contained as a trace component in an amount of 2.0 × 10 ²⁰ atoms / cm ³ or more as will be described in detail later. The transmittance of external factors such as water molecules can be reduced, excellent shielding properties can be exhibited, the dielectric layer can be actually protected by a protective film, and a highly reliable thin film capacitor can be provided.

Furthermore, by containing more than a predetermined amount (2.0 × 10 ²⁰ atoms / cm ³ ) of carbon, which is considered to exhibit the same behavior as fluorine, a reduction in the oxygen ratio that deteriorates such shielding properties, A decrease in carbon concentration in the film can be prevented as much as possible. Thereby, it is possible to greatly improve the moisture resistance of the functional element region including the dielectric layer and further increase the moisture resistance load life. Here, the above-described excellent moisture-proof shielding property can be further exhibited particularly by increasing the film thickness of the protective film rather than the unevenness on the surface of the functional element region.

  In addition, the thin film capacitor of the present invention is characterized in that the functional element region includes a dielectric layer, so that external factors such as water molecules are more effectively shielded than when a conventional moisture-resistant protective film is used. Thus, a thin film capacitor with excellent long-term reliability can be provided.

  Examples in which the present invention is further embodied will be described below.

First, a silicon dioxide film according to the prior art and a silicon dioxide film according to the present invention were formed on a 4-inch φ substrate of silicon. The film formation conditions were those according to the prior art. The substrate temperature was 380 ° C., the flow rate of the source gas was TEOS: 20 sccm, oxygen: 234 sccm, the pressure during film formation was 80 Pa, and the RF power was 200 W. In addition to this condition, the sample according to the present invention introduces CF ₄ gas into the raw material gas. The flow rate of CF ₄ gas was varied from 2 to 6 sccm. In either case, a sample having a thickness of 2 μm was prepared.

  Next, composition analysis of the silicon dioxide film thus produced was performed. First, the ratio of oxygen and silicon, which are main components, was measured by Rutherford backscattering (RBS) spectrum analysis. The measurement results were O / Si ratios of 2.00 to 2.01, indicating that the silicon dioxide film had a constant ratio. However, since a measurement error of about ± 5% is expected, the possibility of the composition ratio is in the range of 2.0 ± 0.1. Next, an impurity concentration analysis in the silicon dioxide film was performed. The elements to be measured are hydrogen, carbon, and fluorine. This is because contamination from the raw material gas is expected. Dynamic SIMS (secondary ion mass spectrum analysis) was used for the compositional analysis of the impurity elements.

FIG. 1 shows the result of concentration analysis of fluorine and carbon in the protective film of silicon dioxide produced in the present invention. Data when the flow rate of CF ₄ gas is 4 sccm is shown. FIG. 2 shows the concentrations of fluorine and carbon in the silicon dioxide protective film according to the prior art. The horizontal axis is the distance from the surface of the protective film toward the film thickness direction, and it can be seen that in any case, no concentration fluctuation is observed in the film thickness direction. Comparing the two, the fluorine concentration in the protective film according to the present invention is an average of 4.8 × 10 ²⁰ atoms / cm ³ , whereas the fluorine concentration in the silicon dioxide protective film according to the prior art is an average of 0.9 × 10 ²⁰ atoms. / cm ^3, and it can be seen that significant difference in fluorine concentration has occurred. It can be seen that the introduction of CF ₄ gas introduces a high concentration of fluorine into the film as intended.

FIG. 3 shows the relationship between the flow rate of the introduced CF ₄ gas and the fluorine concentration in the film. Obviously, the concentration in the film increases in proportion to the flow rate. From this, the fluorine concentration in the protective film can be controlled by the method used in the present invention. On the other hand, the carbon concentration has not been greatly reduced compared to the prior art. Even in the case of the present invention, the carbon concentration is 2.5 ± 0.5 × 10 ²⁰ atoms / cm ³ , and the carbon concentration in the case of the prior art is 4.0 ± 0.5 × 10 ²⁰ atoms / cm ^3. unacceptable. In the SiOF film disclosed in Patent Document 1, carbon is not included in the source gas, and even if the hydrogen concentration is described as being considerably smaller than 1 × 10 ²¹ atoms / cm ³ , the protection according to the present invention is achieved. In the film, the carbon concentration seems to be much higher than that of the SiOF film disclosed in Patent Document 1. Of course, it is needless to say that the decrease in the carbon concentration is smaller and it is preferable to include more carbon.

  Next, a thin film capacitor was manufactured using the protective film whose impurity concentration was found. FIG. 4 shows a cross-sectional view of the manufactured capacitor element. First, sapphire is used for the substrate 41, and it is in the form of a 4-inch φ wafer having a thickness of 0.25 mm. As the material constituting the capacitor element formed on the base body 41, Pt is used for the lower electrode layer 42, Au is used for the upper electrode layer 44, Ni is used for the terminal electrode layer 45, and BST, PZT and PMN are used. A method for forming each layer will be described step by step.

  First, the lower electrode layer 42 was formed on the substrate 41. The film forming method is a direct current sputtering method, and in order to improve the adhesion between the base body 41 and the lower electrode layer 42, a Pt film is formed after an extremely thin titanium oxide film having a thickness of 20 to 30 nm is formed. Ar gas was introduced into the process chamber as a sputtering gas, and sputtering film formation was performed. The film thickness is 200 nm. Subsequently, a lower electrode layer was formed by forming a lower electrode pattern by a photolithographic process and ion beam processing using Ar ions.

Next, dielectric layers 43 made of BST, PZT, and PMN were formed on the lower electrode layer 42, respectively. The dielectric layer 43 was formed by using a high frequency magnetron sputtering method. Ar gas was introduced into the process chamber as a sputtering gas, the film forming pressure was maintained at 6.7 Pa by evacuation, and the substrate-target distance was fixed at 60 mm. The substrate holder has a heating mechanism using a heater. A high-frequency voltage of 13.56 MHz is applied between the substrate holder and the target by an external high-frequency power source, and a high-density plasma is generated in the vicinity of the target by a magnetron magnetic field formed by a permanent magnet installed on the back surface of the target. Was sputtered to form a film on the opposing sample. Under the conditions of a substrate temperature of 650 ° C. and a high frequency power of 200 W, the film thickness is 300 nm. A wet etching method was used to form the dielectric layer pattern. After forming a mask pattern by a photolithographic process, etching with an HF + HNO ₃ mixed solution was performed to form a dielectric layer 43.

The upper electrode layer 44 was produced using a direct current sputtering method in the same manner as the lower electrode layer 42. An Au film having a thickness of 300 nm was formed by sputtering of an Au target. The upper electrode pattern was formed by the photolithography process and the wet etching process using KI + I ₃ solution, and the upper electrode layer 44 was produced. Subsequently, a Ni film and an Au film were formed by the same DC sputtering method, and a terminal electrode layer 45 was formed. The film thickness is 1 μm for the Ni layer 45a and 0.1 μm for the Au layer 45b. A wet etching method was also used for patterning the Ni layer 45a, and after forming a mask pattern by a photolithographic process, etching with an HNO ₃ solution was performed. The patterning method for the Au layer 45b is the same as the method for forming the upper electrode layer 44.

Subsequently, a protective film 46 of silicon dioxide was formed so as to completely cover the capacitor element thus manufactured. The film formation conditions were as described above, and the film thicknesses were all 2 μm. The silicon dioxide moisture-resistant protective film according to the present invention was prepared by adding CF ₄ as a raw material gas to 2, _4, and 6 sccm. After forming a mask pattern by a photolithographic process, terminal electrode through holes were formed by RIE processing using CF ₄ gas. Therefore, the capacitor element was completely covered with the silicon dioxide protective film 46 except for the terminal electrode 45 portion.

  Finally, external terminal electrodes made of solder bumps were formed on the terminal electrode layers (45a, 46b), and then the wafer was diced to cut out individual elements and mounted on a board for evaluating moisture resistance load resistance.

The thin film capacitor thus manufactured was subjected to a moisture resistance load test as follows. The content of the test is a moisture resistance acceleration test under the conditions of 121 ° C., 1.7 atm, and 85% RH (USPCBT). The target moisture-resistant life was set to 96 hours under this accelerated test condition. The number of samples to be measured was 24, and those having an insulation resistance of less than 1 MΩ after 96 hours were judged as deteriorated products (NG products).

As a result of the test, in the sample according to the conventional technique, the insulation deterioration occurred between 48 hours and 96 hours after the start of the test, and the deterioration was 50% or more. The representative results are shown in Table 1. This was the same for all of BST, PZT, and PMN. On the other hand, in the sample according to the present invention, in the sample having a fluorine concentration of 2 × 10 ²⁰ atoms / cm ³ or more (CF _{4 4} sccm or more), the deteriorated sample was zero even after 96 hours. Here, the same results were obtained with BST, PZT, and PMN, and basically no difference depending on the type of dielectric was recognized. 5 is a thin film capacitor using BST, FIG. 6 PZT, and FIG. 7 PMN as the dielectric layer 43. The fluorine concentration in the silicon dioxide moisture-resistant protective film 46 and the deterioration rate after 96 hours (= deteriorated sample) Number / total number). The fluorine concentration in the silicon dioxide film according to the prior art is about 1 × 10 ²⁰ atoms / cm ³ , and the deterioration rate at that time exceeds 80%. In contrast, the silicon dioxide film according to the present invention shows a fluorine concentration in the film of 1 × 10 ²⁰ atoms / cm ³ or more, and it can be seen that the deterioration rate is greatly reduced. When the fluorine concentration in the film is equal to or higher than the threshold value (= 2 × 10 ²⁰ atoms / cm ³ ), the deterioration rate is zero, and it is understood that the moisture-proof shielding property of the silicon dioxide moisture-resistant protective film according to the present invention is sufficiently exhibited. .

In this example, the effect of the present invention was verified using a sample having a large surface irregularity. The sample used was a silicon dioxide moisture-resistant protective film according to the present invention into which 4 sccm of CF ₄ gas was introduced. Samples having Ni film thicknesses of 1.5, 2.0, 2.5, and 3.0 μm were prepared as terminal electrode layers. The same moisture resistance load test as in Example 1 was performed, and the deterioration rates were compared. FIG. 8 shows the result. The sample with a Ni layer thickness of 2.0 μm or less has a degradation rate of 0, which is the same as the result of Example 1, but about half of the sample with a thickness of 2.5 μm and about 80% for the sample with a thickness of 3.0 μm. It can be seen that the sample of this sample is deteriorated in insulation, and the height of the step on the capacitor element surface affects the moisture resistance. From this result, it is understood that the maximum height difference on the capacitor element surface is equal to or less than the thickness of the silicon dioxide moisture-resistant protective film, which is a condition for ensuring moisture resistance.

  Thus, the silicon dioxide film according to the present invention exhibited excellent shielding properties by reducing the transmittance of external factors such as water molecules by introducing fluorine into the film. Furthermore, the oxygen ratio and the carbon concentration in the film were not reduced, which deteriorates the shielding property. By using the silicon dioxide film according to the present invention as a moisture-resistant protective film, it becomes possible to greatly improve the moisture resistance of the functional element region and increase the moisture-resistant load life. Furthermore, by making the film thickness of the moisture-resistant protective film larger than the irregularities on the surface of the functional element region, the above-described excellent moisture-shielding property could be sufficiently exhibited.

  Furthermore, the thin film capacitor using the silicon dioxide film having excellent moisture resistance shielding properties according to the present invention as the moisture resistant protective film is more effective for external factors such as water molecules than when the moisture resistant protective film according to the prior art is used. I was able to shield. Therefore, the thin film capacitor having the moisture-resistant protective film of silicon dioxide according to the present invention has a feature with excellent long-term reliability.

It is a graph which shows the trace element composition contained in the silicon dioxide film which concerns on this invention. It is a graph which shows the trace element composition contained in the silicon dioxide film which concerns on a prior art. It is a graph which shows the result regarding the fluorine introduction | transduction technique in this invention. It is sectional drawing which shows typically an example of embodiment of the thin film capacitor of this invention. It is a graph which shows the relationship between the moisture-resistant reliability of the thin film capacitor (dielectric layer is BST) of this invention, and the fluorine concentration in the silicon dioxide used for it. It is a graph which shows the relationship between the moisture-resistant reliability of the thin film capacitor (dielectric layer is PZT) of this invention, and the fluorine concentration in the silicon dioxide used for it. It is a graph which shows the relationship between the moisture-proof reliability of the thin film capacitor (dielectric layer is PMN) of this invention, and the fluorine concentration in the silicon dioxide used for it. It is a graph which shows the relationship between the magnitude | size of the level | step difference which exists on the surface of the thin film capacitor of this invention, and moisture resistance reliability.

Explanation of symbols

41: Base
42: Lower electrode layer
43: Dielectric layer
44: Upper electrode layer
45a: Terminal electrode layer (Ni layer)
45b: Terminal electrode layer (Au layer)
46: Protective film

Claims (1)

A substrate ;
A metal oxide formed on the base body, and a dielectric layer to which a voltage is applied,
The dielectric material layer covering airtightly has a protective film composed mainly of silicon dioxide,
The silicon dioxide is a composition ratio of oxygen element against the elemental silicon stoichiometric comprises elemental fluorine and carbon element 2.0 × ^{10 20} atoms / cm ³ or more as a minor component,
The thin film capacitor in which the fluorine element contained in the silicon dioxide is higher in content than the carbon element .

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