Method of manufacturing capacitor of semiconductor device

[0002] 1. Field of the Invention

[0003] This invention relates to a method of manufacturing a capacitor of a semiconductor device. The present invention relates particularly to a method of annealing a Ta₂O₅film having a high relative dielectric constant, which is formed on a metal or metal oxide electrode.

[0004] 2. Description of the Related Art

[0005] A relative dielectric constant of a Ta₂O₅film formed on polycrystal silicon ranges from 20 to 28. This relative dielectric constant is three times or more than that of a silicon nitride film. Therefore, the introduction of the Ta₂O₅film into a process has been studied with the Ta₂O₅film as a DRAM (Dynamic Random Access Memory) capacitor dielectric of 256 Mbit or later.

[0006] It has recently been reported and noted that a Ta₂O₅film formed on an electrode composed of a metal such as Pt, Ru or the like has indicated a relative dielectric constant close to 50.

[0007] A Ta₂O₅film immediately after its deposition, which has been formed by CVD (Chemical Vapor Deposition), produces a large leakage current. A problem on such a leakage current characteristic can be improved by post anneal subsequent to the above formation.

[0008] This point of view will be described in detail. Many impurities caused by a raw gas are contained in the Ta₂O₅film obtained immediately after its formation. Oxygen is also often deficient in the Ta₂O₅film. These impurities and oxygen deficiencies are considered to serve as current paths and thereby result in a large leakage current flow.

[0009] Therefore, the Ta₂O₅film is heat-treated at a high temperature near 800° C. in an atmosphere of oxygen or at a comparatively low temperature of 400° C. or less in an atmosphere of ozone or nitrogen oxide to reduce the impurities and oxygen deficiencies in the Ta₂O₅film, whereby the leakage current can be greatly reduced.

[0010] However, if the Ta₂O₅film deposited on the metal electrode is post-annealed at a temperature of 600° C. or less, it is then kept in an amorphous state. Thus, the relative dielectric constant thereof results in about 25 similar to the value of a Ta₂O₅film on a silicon electrode and the leakage current is less than or equal to 10⁻⁸(A/cm⁻²).

[0011] On the other hand, when the Ta₂O₅film on the metal electrode is heat-treated at a high temperature of 700° C. or more, the Ta₂O₅film is crystallized so that its relative dielectric constant is increased to about 50. However, the leakage current is increased by one digit or more as compared with the Ta₂O₅film kept in the amorphous state.

[0012] Therefore, the implementation of the Ta₂O₅film on the metal electrode, which is indicative of the large relative dielectric constant of 50 or more, needs to decrease the leakage current in the crystallized Ta₂O₅film.

[0013] With the foregoing in view, it is therefore an object of the present invention to provide a method of manufacturing a capacitor of a semiconductor device, which improves a method of annealing a Ta₂O₅film formed on a metal or metal oxide electrode, thereby making it possible to crystallize a Ta₂O₅film and limit a leakage current flow as low as possible.

[0014] According to one aspect of the present invention, for achieving the above object, there is provided a method of manufacturing a capacitor of a semiconductor device, comprising the following steps of:

[0015] a step for forming a metal or metal oxide electrode over a semiconductor substrate;

[0016] a step for forming a Ta₂O₅film on the metal or metal oxide electrode;

[0017] a step for heat-treating the Ta₂O₅film at a temperature lower than a crystallizing temperature of the Ta₂O₅film to compensate for oxygen deficiencies and remove impurities; and

[0018] a step for heat-treating the Ta₂O₅film at a temperature higher than or equal to the crystallizing temperature of the Ta₂O₅film after said heat-treating step to crystallize the Ta₂O₅film.

[0019] Typical ones of various inventions of the present application have been shown in brief. However, the various inventions of the present application and specific configurations of these inventions will be understood from the following description.

[0020] While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

[0021] FIG. 1 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which shows a first embodiment of the present invention;

[0022] FIG. 2 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which shows a second embodiment of the present invention;

[0023] FIG. 3 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which shows a third embodiment of the present invention; and

[0024] FIG. 4 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which shows a fourth embodiment of the present invention.

[0025] Preferred embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

[0026] FIG. 1 is a cross-sectional view for explaining a method of manufacturing a capacitor of a semiconductor device, which illustrates a first embodiment of the present invention.

[0027] As shown in FIG. 1(a), a contact hole is first defined in an interlayer insulator (SiO₂film) 12 formed on a substrate 11. Polycrystal silicon 13 for contact is then embedded into the contact hole. A lower electrode 14 composed of a metal or metal oxide (such as Pt, Ru or RuO2, IrO2) is formed on the polycrystal silicon 13 and the interlayer insulator 12.

[0028] Next, a Ta₂O₅film 15 is formed as shown in FIG. 1(b). Thereafter, the Ta₂O₅film 15 is heat-treated at a temperature of about 600° C. lower than a crystallizing temperature of the Ta₂O₅film for about an hour in an atmosphere of oxygen.

[0029] The Ta₂O₅film 15 is then subjected to RTA (Rapid Thermal Annealing) at a temperature higher than or equal to the crystallizing temperature of the Ta₂O₅film as shown in FIG. 1(c), so that a crystallized and high relative dielectric Ta₂O₅film 15′ is formed. In the present embodiment, the reaction other than the crystallization of the Ta₂O₅film can be restrained by rapidly increasing the temperature for the Ta₂O₅film to an intended temperature at 100° C./sec or above, using a lamp annealer, for example.

[0030] Finally, an upper electrode 16 is deposited on the crystallized Ta₂O₅film 15′ to form a capacitor cell as shown in FIG. 1(d).

[0031] In the first embodiment, the initial heat treatment of the Ta₂O₅film is done at the temperature (of about 600° C.) lower than the crystallizing temperature of Ta₂O₅film for about one hour in the atmosphere of oxygen. It is thus possible to sufficiently compensate for a oxygen deficiencies in the Ta₂O₅film and remove impurities in the Ta₂O₅film. Thereafter, the resultant product is subjected to RTA at a high temperature above 700° C. for about one minute so as to crystallize the Ta₂O₅film. As a result, a large relative dielectric constant of the Ta₂O₅film is obtained.

[0032] Thus, the Ta₂O₅film having the high relative dielectric constant, which is able to restrict a leakage current flow, is formed on the metal or metal oxide electrode by crystallizing the Ta₂O₅film after the cause of the leakage current has sufficiently been decreased by the initial low-temperature anneal.

[0033] FIG. 2 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which illustrates a second embodiment of the present invention.

[0034] An interlayer insulator (SiO₂film) 22 is first formed on a semiconductor substrate 21 as shown in FIG. 2(a). A contact hole is then defined in the interlayer insulator 22. Polycrystal silicon 23 for contact is embedded into the contact hole. A lower electrode 24 composed of a metal or metal oxide (such as Pt, Ru or RuO2, IrO2) is formed on the polycrystal silicon 23 and the interlayer insulator 22.

[0035] Next, a Ta₂O₅film 25 is formed on the metal or metal oxide electrode as shown in FIG. 2(b). Thereafter, the Ta₂O₅film 25 is heat-treated at a temperature of about 600° C. lower than a crystallizing temperature of the Ta₂O₅film for about one hour in an atmosphere of oxygen.

[0036] Next, the Ta₂O₅film is subjected to heat treatment at a high temperature (700° C. or above) for crystallizing the Ta₂O₅film, using a diffusion furnace as shown in FIG. 2(c). Described specifically, the temperature to be applied to the Ta₂O₅film is increased to a target temperature at about 100° C./sec and the Ta₂O₅film is subjected to heat treatment for about one hour. Thereafter, the so heat-treated Ta₂O₅film is reduced in temperature at about 10° C./sec. As a result, a crystallized and high relative dielectric Ta₂O₅film 25′ is formed.

[0037] Finally, an upper electrode 26 is deposited on the crystallized Ta₂O₅film 25′ to form a capacitor cell as shown in FIG. 2(d).

[0038] In the second embodiment, the initial heat treatment of the Ta₂O₅film is carried out at the temperature (about 600° C.) lower than the crystallizing temperature of Ta₂O₅film for about one hour in the atmosphere of oxygen. It is thus possible to sufficiently compensate for oxygen deficiencies in the Ta₂O₅film and remove impurities in the Ta₂O₅film. Thereafter, a large crystal is grown by high-temperature heat treatment in the diffusion furnace, so that the Ta₂O₅film with less crystal grain boundary is obtained in the Ta₂O₅film.

[0039] Thus, the initial low-temperature anneal compensates for oxygen deficiencies in the Ta₂O₅film and allows the removal of the impurities in the Ta₂O₅film. A Ta₂O₅film having a high relative dielectric constant, which further restricts a leakage current, can be formed on the metal or metal oxide electrode by reducing the crystal grain boundary at the crystallization of the Ta₂O₅film with the subsequent anneal.

[0040] A third embodiment will next be described.

[0041] FIG. 3 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which shows the third embodiment of the present invention.

[0042] The present embodiment is a two-step anneal method using a gas stronger than oxygen in oxidizing force.

[0043] An interlayer insulator (SiO₂film) 32 is first formed on a semiconductor substrate 31 as shown in FIG. 3(a). A contact hole is defined in the interlayer insulator 32. Polycrystal silicon 33 for contact is embedded into the contact hole. A lower electrode 34 composed of a metal or metal oxide (such as Pt, Ru or RuO2, IrO2) is formed on the polycrystal silicon 33 and the interlayer insutator 32.

[0044] Next, a Ta₂O₅film 35 is formed on the metal or metal oxide electrode as shown in FIG. 3(b). Thereafter, the Ta₂O₅film 35 is heat-treated at a temperature of about 300° C. using O₃or at a temperature of about 600° C. lower than a crystallizing temperature of the Ta₂O₅film for about one hour in the atmosphere using N₂O or the like, which is strong in oxidizing force.

[0045] Next, the Ta₂O₅film 35 is heat-treated at a high temperature (700° C. or more) for crystallizing the Ta₂O₅film as shown in FIG. 3(c). As a result, a crystallized and high relative dielectric Ta₂O₅film 35′ is formed.

[0046] Finally, an upper electrode 36 is deposited on the Ta₂O₅film 35′ to form a capacitor cell as shown in FIG. 3(d).

[0047] Since the initial heat treatment of the Ta₂O₅film is conducted in the atmosphere of O₃strong in oxidizing force or the atmosphere of N₂O or the like in the third embodiment, the compensation for the oxygen deficiencies in the Ta₂O₅film is effectively carried out as compared with the first embodiment. Thereafter, the high-temperature heat treatment for crystallizing the Ta₂O₅film is carried out. As a result, a Ta₂O₅film having a high dielectric constant, which further limits a leakage current, can be formed on the metal or metal oxide electrode.

[0048] A fourth embodiment will next be described.

[0049] FIG. 4 is a cross-sectional view for describing a method of manufacturing a capacitor of a semiconductor device, which shows the fourth embodiment of the present invention.

[0050] The present embodiment is a two-step anneal method using an atmosphere under which the oxidizing force of oxygen is enhanced by light or plasma excitation.

[0051] An interlayer insulator (SiO₂film) 42 is first formed on a semiconductor substrate 41 as shown in FIG. 4(a). A contact hole is defined in the interlayer insulator 42. Polycrystal silicon 43 for contact is embedded into the contact hole. A lower electrode 44 composed of a metal or metal oxide (Pt, RU or RuO2, IrO2) is formed on the polycrystal silicon 43 and the interlayer insutator 42.

[0052] Next, a Ta₂O₅film 45 is formed on the lower electrode 44 as shown in FIG. 4(b). Thereafter, the Ta₂O₅film 45 is subjected to UV light 47 having a wavelength of about 200 nm for about one hour at a temperature below 670° C. lower than a temperature at which the Ta₂O₅film is crystallized. Further, the so-processed Ta₂O₅film 45 is heat-treated in an activated atmosphere of oxygen.

[0053] Next, the Ta₂O₅film 45 is heat-treated at a high temperature (700° C. or more) for crystallizing the Ta₂O₅film. As a result, a crystallized and high relative dielectric Ta₂O₅film 45′ is formed.

[0054] Finally, an upper electrode 46 is deposited on the crystallized Ta₂O₅film 45′ to form a capacitor cell as shown in FIG. 4(d).

[0055] In the fourth embodiment, since the initial heat treatment of the Ta₂O₅film is performed in the oxygen atmosphere activated by the UV light or the like, the compensation for the oxygen deficiencies in the Ta₂O₅film and the removal of impurities in the Ta₂O₅film are effectively done as compared with the first embodiment. Thereafter, since the high-temperature heat treatment for crystallizing the Ta₂O₅film is carried out, a Ta₂O₅film having a high dielectric constant, which is capable of further limiting the flow of a leakage current, can be formed on the metal or metal oxide electrode.

[0056] According to the present invention, if a Ta₂O₅film is of a lower electrode indicative of a larger relative dielectric constant due to its crystallization, then the same anneal method as described above is applicable to all metals or metal oxides as a method of reducing a leakage current developed in the Ta₂O₅film.

[0057] While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.