JP2008294319A - Method for manufacturing thin-film capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the heating step in a vacuum apparatus unnecessary in a step of forming projections and recesses in the lower electrode of a thin-film capacitor. <P>SOLUTION: On a base material 101, a lower electrode 102 including an adhesive layer 102a and a titanium nitride film 102b is formed äfigure (b)}. An oxide thin film forming agent 103a is coated on the lower electrode 102 äfigure (c)}. The coated oxide thin film forming agent 103a is fired to form an oxide thin film 103 äfigure (d)}. At this time, projections and recesses are formed on the surface of the lower electrode 102. An upper electrode 106 is formed on the oxide thin film 103 äfigure (e)}. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a thin film capacitor formed on a semiconductor device or a multilayer wiring board, and relates to a method of manufacturing a thin film capacitor having a small size and a high capacity.

Thin film capacitors are widely used not only for semiconductor devices but also for mounting substrates and electronic circuits. In general, by increasing the capacity per unit area, it is possible to reduce the size and increase the performance of capacitor components.
There are three means for increasing the capacitance: thinning the capacitor dielectric, increasing the dielectric constant of the dielectric material, and expanding the electrode area.
It is possible to enlarge the electrode area by forming a groove in the substrate. However, forming a trench with a high aspect ratio and forming a capacitor electrode and dielectric in the trench to form a highly insulating capacitor requires a complicated manufacturing process, and the manufacturing equipment is special and expensive. Is a problem. On the other hand, since the method of providing unevenness on the electrode surface can increase the electrode area by a relatively simple method, various methods have been devised and some have been put into practical use (for example, Patent Documents 1 to 3). reference).

In Patent Document 1, an amorphous silicon layer is formed on a substrate in a vacuum, and then heated in vacuum to be polycrystallized to form hemispherical grains on the surface of the polycrystalline silicon layer. It is disclosed that a polycrystalline silicon layer having grains is used as a capacitor electrode.
Patent Document 2 discloses a capacitor electrode having a larger surface area by growing germanium or silicon germanium in an island shape on the surface of a polycrystalline silicon layer having a hemispherical protrusion proposed in Patent Document 1. Is disclosed.
Patent Document 3 discloses that a tungsten (W) film having unevenness on the surface of the TiN film and a TiN film having an uneven tungsten film on the surface are used as capacitor electrodes.
Japanese Patent Laid-Open No. 04-127519 JP 05-013677 A Japanese Patent Application Laid-Open No. 08-250665

Each of the conventional examples described in Patent Documents 1 to 3 requires a high-temperature heating process in a vacuum apparatus in the manufacturing process, resulting in poor throughput.
An object of the present invention is to solve the above-mentioned problems of the prior art, and the object is to make it possible to form irregularities on the surface of the capacitor electrode by a heating method that does not use a vacuum device, and to achieve a small size and high capacity. It is to be able to manufacture a thin film capacitor having high productivity with low cost.

  In order to achieve the above object, according to the present invention, there is provided a method of manufacturing a thin film capacitor having a lower electrode, a dielectric film, and an upper electrode, the step of forming an unevenness forming material layer on a substrate, A step of applying an oxide thin film forming agent on the unevenness forming material layer; and firing the oxide thin film forming agent to form an oxide thin film on the unevenness forming material layer, and the unevenness forming material layer and the oxide A step of forming irregularities at the interface with the thin film, and the irregularities formed at the interface between the irregularity forming material layer and the oxide thin film are reflected on the surface of the lower electrode. A manufacturing method is provided.

  In the present invention, a metal oxide thin film is formed on a concavo-convex forming material layer by a film forming technique called sol-gel processing, thereby forming concavo-convex on the surface of the concavo-convex forming material layer. Is reflected in the surface shape of the lower electrode of the thin film capacitor, so that a heating step in the vacuum apparatus is not required to form irregularities on the electrode. Therefore, according to the present invention, the surface area of the capacitor lower electrode can be increased by a simple method with good workability.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. 1A to 1D are cross-sectional views in order of steps showing an embodiment of a method for manufacturing a thin film capacitor of the present invention. First, the base material 11 is prepared [FIG. 1 (a)]. The substrate 11 may be a substrate including a semiconductor such as Si, GaAs, or SOI, or an inorganic material substrate made of ceramic, heat resistant glass, or the like. And the uneven | corrugated formation material layer 12 which consists of an electroconductive material is formed on the base material 11 using a sputtering method or a vapor deposition method [FIG.1 (b)]. The concavo-convex forming material layer 12 can be used as it is as a lower electrode of a capacitor, but a conductive material film can be further formed thereon to constitute a lower electrode. Moreover, in order to improve the adhesion between the substrate 11 and the concavo-convex forming material layer 12 by forming the concavo-convex forming material layer 12 with a multilayer film, an adhesive layer can be formed in the lowest layer of the concavo-convex forming material layer 12. The material of the unevenness forming material layer 12 is not particularly limited, but a material that easily forms unevenness on the surface thereof is selected in the heat treatment step that is the subsequent oxide film forming step. For example, titanium, titanium nitride, aluminum, platinum, etc. are mentioned. Next, an oxide thin film forming agent 13a is applied onto the concavo-convex forming material layer 12 by using a dipping method or a spin coating method [FIG. 1 (c)]. In the present invention, the oxide thin film forming agent is a colloidal solution of metal (including silicon in this case) alkoxide, and a commercially available material for forming an oxide thin film by a sol-gel method is used. it can. For example, a solution containing one or a plurality of compounds of silicon, aluminum, titanium, zirconium, hafnium, tantalum, niobium, lanthanum, and yttrium can be used. The applied oxide thin film forming agent 13a is dried and then baked to form the oxide thin film 13. At this time, since hillocks are generated in the unevenness forming material layer 12, unevenness is formed on the surface thereof (FIG. 1 (d)). In order to form the unevenness more reliably, it is desirable to select a material so that the thermal expansion coefficient of the oxide thin film is larger than that of the unevenness forming material layer. As the baking apparatus, any of a diffusion furnace, a hot plate, and a rapid thermal annealer (RTA) can be used, but a diffusion furnace is preferable from the viewpoint of ease of heating process and throughput.

At least a part of the formed unevenness forming material layer 12 can be used as a lower electrode. Further, the formed oxide thin film 13 can be used as a dielectric of a capacitor. In such a case, an upper electrode is formed on the oxide thin film 13. And the uneven | corrugated material layer 12 comprises a lower electrode as it is. Alternatively, the oxide thin film 13 may be removed to newly form a thin film serving as a capacitor dielectric. In this case, a conductive thin film that becomes a part of the lower electrode can be formed on the unevenness forming material layer 12 before the formation of the dielectric thin film. In particular, when the newly formed dielectric thin film is a high-permittivity dielectric with a perovskite structure, it is resistant to oxidation when formed at high temperatures in order to increase the dielectric constant of the high-permittivity dielectric. It is desirable to form a conductive thin film as a conductive material on the unevenness forming material layer 12.
Without using the unevenness forming material layer 12 as an electrode material, a material layer for simply forming unevenness on the lower electrode may be used. In that case, the lower electrode, the dielectric thin film, and the upper electrode are formed on the formed concavo-convex shape with or without removing the oxide thin film 13.
When aluminum or platinum is used as the material for the concavo-convex forming material layer 12, the concavo-convex tip tends to be sharp. Is done. Therefore, when these are used as the lower electrode or a part thereof, the tip of the concavo-convex is etched, or a conductive thin film layer that becomes a part of the lower electrode is deposited on the concavo-convex forming material layer 12 to form a point. It is desirable to relax the shape. Further, when titanium or aluminum is used as the material of the unevenness forming material layer 12, titanium oxide or aluminum oxide is easily formed on the surface of these material layers. Therefore, when these are used as the lower electrode, it is desirable to form a highly conductive conductive thin film on the concavo-convex forming material layer 12 in order to improve the conductivity of the lower electrode.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  2A to 2E are cross-sectional views in order of steps showing Example 1 of the present invention. First, a 500 μm-thick silicon substrate having a 0.2 μm-thick silicon oxide film on the surface was used as the substrate 101 [FIG. 2A]. After the base material 101 is put into a sputter deposition apparatus and a desired degree of vacuum is reached, Ti as an adhesion layer 102a is formed by DC sputtering, and a titanium nitride film 102b is continuously formed. An electrode 102 was obtained [FIG. 2 (b)]. The respective film thicknesses were 50 nm and 100 nm. On the lower electrode 102 having the titanium nitride film 102b as a surface, an aluminum oxide thin film forming agent having an aluminum compound of 3 wt% was applied as an oxide thin film forming agent 103a by a spin coating method [FIG. 2 (c)]. . After the aluminum oxide thin film forming agent (103a) was applied, it was temporarily fired on a hot plate heated to 300 ° C., and then fired in a diffusion furnace under a nitrogen atmosphere heated to 600 ° C. Cracks did not occur in the aluminum oxide thin film of the oxide thin film 103 after firing. When the surface morphology was observed with an electron microscope, irregularities having a protruding structure 104 were formed on the surface [FIG. 2 (d)]. A titanium nitride film to be the upper electrode 106 was deposited to a film thickness of 100 nm by DC sputtering [FIG. 2 (e)]. The titanium nitride film to be the upper electrode 106 and the aluminum oxide film to be the oxide thin film 103 were processed into desired patterns by a photolithography process and an etching process, respectively. When the capacitance of the capacitor using the oxide thin film 103 as a capacitive insulating film was measured using an impedance analyzer, the capacitance was about 1.6 times higher than the capacitance calculated from the electrode area of the parallel plate. Electric capacity was obtained. On the other hand, the current-voltage characteristics were measured using an electrometer, but no deterioration was observed in the insulating properties. A small thin film capacitor having a high capacitance could be manufactured without deteriorating the insulation.

[Comparative example]
As a comparative example, a case where a thin film capacitor is manufactured outside the scope of the present invention will be described. The manufacturing process of Comparative Example 1 was the same up to the process of spin-coating the oxide thin film forming agent 103a in Example 1 and pre-baking with a hot plate heated to 300 ° C. After the preliminary firing, firing was performed in a diffusion furnace heated to 450 ° C., but the morphology of the surface having unevenness due to the formation of the protruding structure 104 on the lower electrode 102 was not observed. After a titanium nitride film having a thickness of 100 nm is formed as the upper electrode 106, the upper electrode and the capacitive insulating film are processed into a desired pattern, and the capacitance is measured by an impedance analyzer. It was in good agreement with the capacitance, and no increase in capacitance was observed. For this reason, a small-sized thin film capacitor having a high capacitance could not be manufactured.

3A to 3H are cross-sectional views in order of steps showing Example 2 of the present invention. Up to the step of firing the aluminum oxide thin film, it was manufactured in the same steps as in Example 1 (FIGS. 3A to 3D). After forming an aluminum oxide thin film as the oxide thin film 103, the aluminum oxide was etched away using phosphoric acid to expose the surface of the titanium nitride film 102b [FIG. 3 (e)]. The surface morphology of the exposed titanium nitride film 102b was a morphology having irregularities due to the protruding structure 104 on the same surface as the aluminum oxide thin film surface. Next, after putting in a DC sputtering apparatus and reaching a desired degree of vacuum, Ti serving as an adhesion layer and then Pt serving as an oxidation-resistant conductive material layer are continuously formed on the titanium nitride film 102b by DC sputtering. A laminated conductive film 102c was formed to obtain a lower electrode 102 [FIG. 3 (f)]. Next, it was introduced into an RF sputtering apparatus in order to form a high dielectric constant thin film 105. A high dielectric constant thin film 105 was obtained by depositing SrTiO ₃ having a perovskite structure to a film thickness of 100 nm by RF sputtering at a substrate temperature of 600 ° C. [FIG. The sample was again introduced into the DC sputtering apparatus, and a Pt film having a thickness of 100 nm was formed as the upper electrode 106 by DC sputtering [FIG. 3 (h)]. Next, Pt of the upper electrode 106 and SrTiO ₃ of the high dielectric constant thin film 105 were respectively processed into desired patterns by photolithography and etching. When the capacitance was measured with an impedance analyzer, a capacitance of about 1.6 times the capacitance calculated from the electrode area was obtained. When SrTiO ₃ having a perovskite structure was formed under the same conditions on a flat lower electrode having no protruding electrode, and Pt serving as the upper electrode was formed to form a thin film capacitor, the relative dielectric constant was about 200. On the other hand, the thin film capacitor formed by the manufacturing method of the present invention has an effective relative dielectric constant of about 320, and a small thin film capacitor having a higher capacity than that of Example 1 can be manufactured. It was.

  4 (a) to 4 (h) are cross-sectional views in order of steps showing Example 3 of the present invention. As the oxide thin film forming agent 103a, a hafnium oxide thin film forming agent having a 7% by weight hafnium compound is used, and the steps up to the step of forming a hafnium oxide thin film (oxide thin film 103) by baking in a diffusion furnace are as in Example 1. The same process as that of FIG. 4 (FIGS. 4A to 4D). In the case of hafnium oxide, no crack was observed in the thin film itself, but a crack 107 that was considered to be caused by the tip of the titanium nitride protrusion structure 104 was observed. When the cracked hafnium oxide thin film was immersed in dilute hydrofluoric acid, which was the etchant, and the hafnium oxide thin film was removed, the dilute hydrofluoric acid etchant that penetrated from the crack etched the protruding structure of titanium nitride, and the tip was A gentle protrusion structure 104 was obtained [FIG. 4 (e)]. Thereafter, in Example 2, the same process as the process of forming the capacitive insulating film was performed [FIGS. 4F to 4H]. When the capacitance as a capacitor was measured, a capacitance of about 1.8 times the capacitance calculated from the electrode area was obtained. On the other hand, there was no deterioration in the current-voltage characteristics, and a thin film capacitor having a small size and a high capacity could be manufactured.

As mentioned above, although the preferable Example of this invention was described, this invention is not limited to said Example. For example, as an example of a conductive thin film, a laminated film of Ti and Pt is given as an example. However, the present invention is not limited to this, and a conductive oxide thin film such as Ru, Ir, oxides thereof, or SrRuO ₃ having a perovskite structure. It may be. Further, although SrTiO ₃ has been described as a high dielectric constant dielectric, an oxide having a perovskite structure such as (Ba, Sr) TiO ₃ or (Pb, Zr) TiO ₃ may be used. Further, the firing atmosphere in the diffusion furnace is not limited to the nitrogen atmosphere of the embodiment.

Sectional drawing of the order of a process which shows the manufacturing method of the thin film capacitor of embodiment of this invention. Sectional drawing of the process order which shows the manufacturing method of the thin film capacitor of Example 1 of this invention. Sectional drawing of the order of a process which shows the manufacturing method of the thin film capacitor of Example 2 of this invention. Sectional drawing of the order of a process which shows the manufacturing method of the thin film capacitor of Example 3 of this invention.

Explanation of symbols

11 Substrate 12 Concavity and convexity forming material layer 13a Oxide thin film forming agent 13 Oxide thin film 101 Base material 102a Adhesion layer 102b Titanium nitride film 102c Conductive thin film 102 Lower electrode 103a Oxide thin film forming agent 103 Oxide thin film 104 Protrusion structure 105 High Dielectric constant thin film 106 Upper electrode 107 Crack

Claims (14)

A method of manufacturing a thin film capacitor having a lower electrode, a dielectric film, and an upper electrode, the step of forming an unevenness forming material layer on a substrate, and applying an oxide thin film forming agent on the unevenness forming material layer And a step of firing the oxide thin film forming agent to form an oxide thin film on the unevenness forming material layer and forming unevenness at an interface between the unevenness forming material layer and the oxide thin film. A method of manufacturing a thin film capacitor, wherein the unevenness formed at the interface between the unevenness forming material layer and the oxide thin film is reflected on the surface of the lower electrode. 2. The method of manufacturing a thin film capacitor according to claim 1, further comprising a step of forming an upper electrode on the oxide thin film, wherein the unevenness forming material layer is used as a lower electrode. Removing the oxide thin film; removing the oxide thin film; forming a dielectric thin film on the concavo-convex forming material layer exposed; and forming an upper electrode on the dielectric thin film; 2. The method of manufacturing a thin film capacitor according to claim 1, wherein at least part of the unevenness forming material layer is used as a lower electrode. 4. The method of manufacturing a thin film capacitor according to claim 3, wherein when the oxide thin film is removed by etching, a part of the surface of the unevenness forming material layer is also removed by etching. 5. The method of manufacturing a thin film capacitor according to claim 3, wherein a conductive thin film is formed on the unevenness forming material layer prior to the step of forming the dielectric thin film. A step of forming a conductive thin film, a step of forming a dielectric thin film, and an upper electrode are formed on the unevenness forming material layer or on the oxide thin film without removing the oxide thin film. The method for manufacturing a thin film capacitor according to claim 1, further comprising: using a conductive thin film as a lower electrode. The method for manufacturing a thin film capacitor according to claim 3, wherein the dielectric thin film is formed of an oxide material having a perovskite structure. The method for manufacturing a thin film capacitor according to claim 1, wherein at least the uppermost portion of the unevenness forming material layer is formed of titanium nitride. The method for manufacturing a thin film capacitor according to claim 8, wherein the unevenness forming material layer is formed with a titanium layer serving as an adhesion layer in a lowermost layer portion. The method for manufacturing a thin film capacitor according to claim 1, wherein the oxide thin film forming agent contains a metal alkoxide. The method for producing a thin film capacitor according to any one of claims 1 to 10, wherein a firing temperature for firing the oxide thin film forming agent is in a range of 500 ° C to 700 ° C. The method of manufacturing a thin film capacitor according to claim 1, wherein the base material is silicon, glass, or ceramic. The oxide thin film is an oxide having at least one element selected from silicon, aluminum, titanium, zirconium, hafnium, tantalum, niobium, lanthanum, and yttrium. A method of manufacturing a thin film capacitor. 14. The method of manufacturing a thin film capacitor according to claim 1, wherein the oxide thin film has a thermal expansion coefficient larger than that of the uppermost material of the unevenness forming material layer.

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