JP5572944B2 - Wiring structure manufacturing method and wiring structure - Google Patents

Description

  The present invention relates to a wiring structure using carbon nanotubes for vertical wiring and a method for manufacturing the same.

  Copper (Cu) is mainly used as a wiring material for semiconductor integrated circuit elements. As the wiring width becomes finer, deterioration of reliability and increase in electrical resistance due to electromigration have become apparent. In order to solve these problems, carbon nanotubes have attracted attention as a new wiring material that replaces copper. A wiring structure using carbon nanotubes for wiring in the vertical direction (thickness direction of the substrate) is known. A graphite structure grown on carbon nanotubes is also known.

JP 2007-220742 A JP 2008-137846 A Daiyu Kondo et al., "Self-organization of Novel Carbon Composite Structure: Graphene Multi-Layers Combined Perpendicularly with Aligned Carbon Nanotubes", Applied Physics Express 1 (2008) 074003

  It is relatively easy to grow carbon nanotubes in a direction perpendicular to the substrate surface. In order to grow carbon nanotubes in the lateral direction (direction parallel to the substrate surface), it is necessary to form a catalyst film having a flat and minute surface on the side wall. However, it is difficult to form such a catalyst film.

A method of manufacturing a wiring structure that solves the above problems is as follows.
A catalyst film for vertical wiring having a first thickness is formed in two vertical wiring regions spaced apart from each other on the substrate surface, and the horizontal wiring region continuous from one vertical wiring region to another vertical wiring region Forming a lateral wiring catalyst film having a second thickness greater than the first thickness;
Vapor-phase-growing a structure containing carbon on the vertical wiring catalyst film and the horizontal wiring catalyst film,
In the initial stage of the vapor phase growth, graphite is formed on the catalyst film for vertical wiring and the catalyst film for horizontal wiring, and then carbon nanotubes grow between the graphite and the substrate in the vertical wiring region. The first thickness and the second thickness are set so that the graphite in the horizontal wiring region is supported in a hollow manner by the carbon nanotubes grown in the vertical wiring region.

A wiring structure that solves the above problems
Vertical wiring composed of a plurality of carbon nanotubes extending from each of a plurality of conductive regions on the surface of the substrate;
And horizontal lines consisting of graphite extending laterally from at least two on one of the upper end of the vertical line to the other upper end,
A support member comprising a plurality of carbon nanotubes extending toward the substrate side from the part of the bottom surface of said horizontal lines,
An insulating film disposed between a lower end of the support member and the substrate;

  By forming both the vertical wiring and the horizontal wiring with a carbon material, the current density resistance can be increased. This facilitates miniaturization of the wiring and enhances electromigration resistance.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a perspective view of a wiring structure according to the first embodiment. A plurality of first-layer vertical wirings 11 are formed on a substrate 10 on the surface of which a plurality of semiconductor elements and wirings are formed. Each of the vertical wirings 11 in the first layer is composed of a bundle of carbon nanotubes extending in a direction perpendicular to the surface of the substrate 10.

  The upper ends of at least two first-layer vertical wirings 11 are connected to the first-layer horizontal wirings 12. The first-layer horizontal wiring 12 is made of graphite, and is supported in a hollow space by the first-layer vertical wiring 11. A second-layer vertical wiring 13 is formed on the first-layer horizontal wiring 12. The upper ends of at least two second-layer vertical wirings 13 are connected to the second-layer horizontal wirings 14. Further, a vertical wiring and a horizontal wiring of the third layer or more are formed. Also in the second and higher wiring layers, the vertical wiring 13 and the like are formed of carbon nanotubes, and the horizontal wiring 14 and the like are formed of graphite. The horizontal wirings 14 and the like in the second layer or more are supported in a hollow manner by the vertical wirings 11 and 13 and the horizontal wirings 12 below it.

  With reference to FIGS. 2A to 2O, a method for manufacturing a wiring structure according to the first embodiment will be described.

  As shown in FIG. 2A, a conductive film 20 made of TiN and having a thickness of 1 nm to 30 nm, for example, 5 nm is formed on the substrate 10. On the conductive film 20, a 2.6 nm-thickness catalyst film 21 for vertical wiring made of Co is formed. For the formation of the conductive film 20 and the vertical wiring catalyst film 21, for example, a magnetron sputtering method can be applied. In addition, a laser ablation method, an electron beam evaporation method, a molecular beam epitaxy (MBE) method, a chemical vapor deposition (CVD) method, an atomic layer deposition (ALD) method, or the like may be used.

  A resist pattern 22 is formed to cover a region (first vertical wiring region) 23 in which the first-layer vertical wiring is to be formed on the surface of the vertical wiring catalyst film 21. The planar shape of the first vertical wiring region 23 is, for example, a circle having a diameter of 100 nm or a square having a side length of 100 nm. In the region where the first-layer vertical wiring is not formed, the vertical wiring catalyst film 21 is exposed.

  As shown in FIG. 2B, the vertical wiring catalyst film 21 and the conductive film 20 in a region not covered with the resist pattern 22 are removed by ion milling or the like. As shown in FIG. 2C, the resist pattern 22 is removed. In the first vertical wiring region 23, a laminated structure including the patterned conductive film 20 and the vertical wiring catalyst film 21 remains. Note that the lift-off method or chemical etching may be used for patterning the conductive film 20 and the vertical wiring catalyst film 21. Further, in order to avoid contamination due to contact of the resist with the catalytic metal, a hard mask made of an insulating film or the like can be used as an etching mask.

  As shown in FIG. 2D, a resist pattern 30 is formed to cover the first vertical wiring region 23 and the region (first non-wiring region) 25 where the first-layer horizontal wiring is not formed. An opening 30A of the resist pattern 30 is formed in a region (first lateral wiring region) 26 where the first-layer lateral wiring is formed. The first horizontal wiring region 26 is continuous from one first vertical wiring region 23 to another first vertical wiring region 23.

An insulating film 34 made of TiO ₂ is formed on the bottom surface of the opening 30A and on the upper surface of the resist pattern 30, and a 4.5 nm thick wiring wiring catalyst film 35 made of Co is formed thereon. The thickness of the insulating film 34 is preferably equal to the thickness of the conductive film 20. For example, magnetron sputtering is applied to the formation of the insulating film 34 and the lateral wiring catalyst film 35.

The vertical wiring catalyst film 21 and the horizontal wiring catalyst film 35 may be made of a material other than Co that acts as a catalyst for forming carbon nanotubes, such as Ni, Fe, Pt, or Au. A conductive material containing any one of Ti, TiSi, TiN, Mo, W, Hf, Zr, Al, Nb, V, Ta, TaN, and TaSi may be used for the conductive film 20. An insulating material including any one of Ti, TiSi, TiN, TiO ₂ , Mo, W, Hf, Zr, Al, Al ₂ O ₃ , Nb, V, Ta, TaN, and TaO ₂ is used for the insulating film 34. May be. The conductive film 20 and the insulating film 34 have a role of supporting the metal constituting the vertical wiring catalyst film 21 and the horizontal wiring catalyst film 35.

  As shown in FIG. 2E, the resist pattern 30 is removed together with the insulating film 34 and the lateral wiring catalyst film 35 deposited thereon. In the first lateral wiring region 26, the insulating film 34 and the lateral wiring catalyst film 35 remain. In the first vertical wiring region 23, the vertical wiring catalyst film 21 is exposed. The surface of the substrate 10 is exposed in the first non-wiring region 25.

Thereafter, carbon is grown on the vertical wiring catalyst film 21 and the horizontal wiring catalyst film 35 by thermal chemical vapor deposition (thermal CVD). The growth conditions are, for example, as follows.
・ Growth temperature 450 ℃
-Source gas Acetylene diluted with argon (acetylene partial pressure ratio 10%)
・ Pressure 1kPa
As shown in FIG. 2F, graphite (lateral wiring) 12 grows on the vertical wiring catalyst film 21 and the horizontal wiring catalyst film 35 in the initial growth stage. Graphite is not formed in the first non-wiring region 25. As the growth continues, the vertical wiring catalyst film 21 absorbs carbon and becomes fine particles.

  As shown in FIG. 2G, when the thickness of the horizontal wiring 12 reaches about 20 nm, the carbon nanotube 11A grows downward from the catalyst metal in the form of fine particles. A bundle of carbon nanotubes 11 </ b> A constitutes the vertical wiring 11. The height of the vertical wiring 11 is, for example, 200 nm. Since the horizontal wiring catalyst film 35 is formed thicker than the vertical wiring catalyst film 21, it does not form fine particles, and carbon nanotubes do not grow thereunder. When the vertical wiring 11 grows, the horizontal wiring 12 is lifted upward, and a cavity is formed below the horizontal wiring 12 in the first horizontal wiring region 26.

  FIG. 2H shows a cross-sectional view of the vertical wiring 11 and the horizontal wiring 12. On the lower surface of the horizontal wiring 12, catalyst fine particles 21a in which the metal element of the vertical wiring catalyst film 21 is formed into fine particles are attached. The carbon nanotubes 11A extend downward from the catalyst fine particles 21a. Although FIG. 2H shows a case where the carbon nanotube 11A has a two-layer structure, a single-walled carbon nanotube or a multilayered carbon nanotube of three or more layers may be formed. The thickness of the carbon nanotube 11 is, for example, about 10 nm. The thickness of the carbon nanotube 11 can be controlled by the diameter of the catalyst fine particles, the catalyst, and the growth conditions, and the thickness of the carbon nanotube 11 is preferably in the range of 1 to 50 nm.

  As shown in FIG. 2I, a silicon oxide-based filling film 40 is formed on the substrate 10 and the horizontal wiring 12 by a spin coating method using spin-on-glass (SOG). The filling film 40 may be formed by CVD or other embedding methods. In the first lateral wiring region 26, the cavity between the lateral wiring 12 and the substrate 10 is filled with the filling film 40. Further, the first non-wiring region 25 is also filled with the filling film 40.

  As shown in FIG. 2J, the filling film 40 in the second vertical wiring region 50 where the second vertical wiring is to be formed is removed by etching or the like to expose the first horizontal wiring 12. At the same time, the surface layer of the filling film 40 is such that the upper surface of the filling film 40 in the second lateral wiring region 51 in which the second lateral wiring is to be formed is the same height as the upper surface of the first lateral wiring 12. Remove the part. In the second no-wiring region 52 where neither the vertical wiring nor the horizontal wiring is formed in the second layer, the filling film 40 remains above the upper surface of the first wiring 12.

  As shown in FIG. 2K, a conductive film 55 and a vertical wiring catalyst film 56 are formed in the second vertical wiring region 50. The conductive film 55 and the vertical wiring catalyst film 56 are formed by the same method as the first conductive film 20 and the vertical wiring catalyst film 21 shown in FIGS. 2A to 2C.

  As shown in FIG. 2L, an insulating film 57 and a lateral wiring catalyst film 58 are formed in the second lateral wiring region 51. The insulating film 57 and the lateral wiring catalyst film 58 are formed by the same method as the first insulating film 34 and the lateral wiring catalyst film 35 shown in FIGS. 2D to 2E.

  As shown in FIG. 2M, the second vertical wiring 13 is formed in the second vertical wiring area 50, and two layers are formed in the second horizontal wiring area 51 and the second vertical wiring area 50 continuous thereto. The horizontal wiring 14 of eyes is formed. The vertical wiring 13 and the horizontal wiring 14 in the second layer are formed by the same method as the vertical wiring 11 and the horizontal wiring 12 in the first layer shown in FIGS. 2F to 2G. When the second lateral wiring 14 is formed, a space is formed between the second lateral wiring 14 and the insulating film 57.

  A second-layer filling film 60 is formed on the first-layer filling film 40 and the second-layer lateral wiring 14. The cavity below the second-level horizontal wiring 14 is also filled with the filling film 60.

  As shown in FIG. 2N, the third-layer conductive film 65, the insulating film 66, the vertical wiring 67, and the horizontal wiring 68 are formed in the same manner as in the second layer. A fourth or higher wiring layer may be formed by the same method.

As shown in FIG. 2O, the filling films 40 and 60 are removed by wet etching using hydrofluoric acid. It is also possible to remove by dry etching using CF ₄ or the like. A space is formed between the substrate 10 and the first to third horizontal wires 12, 14, 68. This cavity is filled with a gas such as air or an inert gas or is kept in a vacuum state. Furthermore, in order to increase the strength of the entire wiring, it is possible to leave an interlayer insulating film in a part of the wiring.

  In the first embodiment, the vertical wirings 11, 13, and 67 are formed of carbon nanotubes, and the horizontal wirings 12, 14, and 68 are formed of graphite. Carbon nanotubes and graphite have a current density tolerance that is about three orders of magnitude higher than copper, and exhibit excellent electrical characteristics such as ballistic conduction. Furthermore, carbon nanotubes and graphite exhibit high thermal conductivity. For this reason, even if the wiring is miniaturized, the occurrence of electromigration can be suppressed.

  Further, in the first embodiment, the wiring is insulated by a cavity. This cavity is filled with air, an inert gas such as nitrogen or argon, and the like. Alternatively, this cavity is kept in a vacuum state. These gases and vacuum have a low dielectric constant (relative dielectric constant is about 1) compared to a general interlayer insulating film material. For this reason, parasitic capacitance can be reduced.

  In Example 1, the thickness of the vertical wiring catalyst film 21 was 2.6 nm, and the thickness of the horizontal wiring catalyst film 35 was 4.5 nm. A suitable thickness of the catalyst films 21 and 35 depends on the growth conditions of the carbon nanotubes. When the catalyst film is thick, since the catalyst does not become fine particles, graphite grows on the catalyst film, but the carbon nanotube does not grow downward. Therefore, it is preferable that the vertical wiring catalyst film is thinned to the extent that carbon nanotubes grow downward, and the horizontal wiring catalyst film is thickened to the extent that carbon nanotubes do not grow.

  FIG. 3 is a cross-sectional view of the first layer wiring of the wiring structure according to the modification of the first embodiment. In this modification, the carbon nanotubes 11 </ b> B grow downward from the lower surface of the horizontal wiring 12 in the horizontal wiring region 26. Carbon nanotubes grow faster as the catalyst film is thinner. When the growth rate of the carbon nanotubes in the horizontal wiring region 26 is sufficiently slower than the growth rate of the carbon nanotubes in the vertical wiring region 23, the length of the carbon nanotubes 11B formed in the horizontal wiring region 26 is The length is shorter than the length of the carbon nanotubes 11 </ b> A formed in the wiring region 23. Since the horizontal wiring 12 is lifted to a position higher than the length of the carbon nanotubes 11 </ b> B, a cavity is formed between the tip of the carbon nanotubes 11 </ b> B formed in the horizontal wiring region 26 and the substrate 10. For this reason, the carbon nanotube 11B does not contact an unexpected conductive region.

  Even when carbon nanotubes grow in the horizontal wiring region 26 as in the modification shown in FIG. 3, the growth rate is sufficiently slower than the growth rate of the carbon nanotubes in the vertical wiring region 23. In the same manner as in the first embodiment, the horizontal wiring 12 can be supported in a hollow state. In order to support the horizontal wiring in a hollow state, the film thickness and the growth conditions are set so that the growth rate of the carbon nanotubes in the horizontal wiring region 26 is 50% or less of the growth rate of the carbon nanotubes in the vertical wiring region 23. Is preferred.

  As an example, the growth temperature of the carbon nanotube is preferably in the range of 300 ° C to 600 ° C. As the source gas, hydrocarbons such as acetylene, ethylene and methane, and alcohols such as ethanol and methanol can be used. Argon, hydrogen, nitrogen, or helium can be used as a gas for diluting the source gas. As an example, the gas pressure during growth can be set to 0.1 kPa to 10 kPa. The length of the carbon nanotube can be controlled by the growth time. For example, the growth time is about 60 minutes. Oxygen, water vapor, and alcohol may be mixed in the growth gas as additive gases (for example, about 1% of the growth gas pressure).

  The thickness of the vertical wiring catalyst film 21 is in the range of 1 nm to 5 nm, and the thickness of the horizontal wiring catalyst film 35 is thicker than the vertical wiring catalyst film 21 and in the range of 2 nm to 50 nm.

  In the first embodiment, the filling films 40 and 60 are finally removed. However, a low dielectric constant material such as porous silica may be used for the filling films 40 and 60 and left as they are. If the filling films 40 and 60 are left, the mechanical strength of the wiring can be increased. Similarly, a filler may be used for a part of the wiring and the remaining part may be removed. Also in this case, the mechanical strength of the wiring can be increased.

  With reference to FIG. 4A-FIG. 4F, the manufacturing method of the wiring structure by Example 2 is demonstrated. In the following description, paying attention to differences from the manufacturing method of Example 1, description of the same steps as those of the manufacturing method of Example 1 may be omitted.

  As shown in FIG. 4A, the conductive film 20 and the vertical wiring catalyst film 21 are formed in a plurality of vertical wiring regions 23 spaced from each other on the surface of the substrate 10. The surface of the substrate 10 is exposed in a horizontal wiring region 26 that continues from one vertical wiring region 23 to another vertical wiring region 23.

  As shown in FIG. 4B, an insulating film 34 and a lateral wiring catalyst film 35 are formed in the lateral wiring region 26.

  As shown in FIG. 4C, the lateral wiring catalyst film 35 in the support region 27 is removed, and the insulating film 34 is exposed. The support region 27 is defined as a region separated from any of the vertical wiring regions 23 that are continuous to the horizontal wiring region 26 in the horizontal wiring region 26. For example, ion milling can be used to remove the lateral wiring catalyst film 35. Note that the lift-off method may be used to form the patterned lateral wiring catalyst film 35 as shown in FIG. 4C.

  As shown in FIG. 4D, a support catalyst film 36 is formed in the support region 27. The supporting catalyst film 36 is formed of the same material as the vertical wiring catalyst film 21, and the thickness thereof is the same as that of the vertical wiring catalyst film 21. The supporting catalyst film 36 can be patterned using, for example, a lift-off method.

  As shown in FIG. 4E, the horizontal wiring 12 and the vertical wiring 11 are formed. At this time, the support member 15 composed of a bundle of carbon nanotubes is also formed in the support region 27.

  As shown in FIG. 4F, the second conductive film 55, the insulating film 57, the vertical wiring 13, and the horizontal wiring 14 are formed on the horizontal wiring 12. One vertical wiring 13 in the second layer is arranged at a position overlapping the support member 15 in plan view.

  In the second embodiment, the horizontal wiring 12 is supported not only by the vertical wiring 11 but also by the support member 15. The position of the vertical wiring 11 is determined by the design requirements of the electronic circuit. For this reason, the position of the vertical wiring 11 cannot be set freely. When the distance between the two vertical wirings 11 to be connected by one horizontal wiring 12 is wide, the mechanical strength in the horizontal direction 12 that is supported hollowly becomes weak. By supporting the horizontal wiring 12 with the support member 15 as in the second embodiment, sufficient mechanical strength of the horizontal wiring 12 can be maintained.

  If the second-layer vertical wiring 13 is arranged in the hollow portion of the first-layer horizontal wiring 12, the first-layer horizontal wiring 12 is easily broken by the weight of the upper-layer wiring. As in the second embodiment, a sufficient mechanical strength capable of withstanding the weight of the upper layer wiring is ensured by disposing the first layer support member 15 directly below the second layer vertical wiring 13. Can do. Thereby, the freedom degree of arrangement | positioning of the vertical wiring 13 of an upper layer increases.

  Since the insulating film 34 is disposed between the support member 15 and the substrate 10, the horizontal wiring 12 is electrically connected to an unexpected conductive region on the substrate 10 via the support member 15. There is nothing.

  FIG. 5 shows a cross-sectional view of a wiring structure according to a modification of the second embodiment. A second-layer horizontal wiring 14 is supported by a support member 17. A second insulating film 57 is connected to the lower end of the support member 17. The second-layer insulating film 57 is reinforced by the first-layer support member 15 disposed immediately below the second-layer support member 17. Between the first-layer support member 15 and the second-layer insulating film 57, a dummy wiring 16 formed in the same process as the first-layer horizontal wiring 12 is disposed.

  In this manner, the second-layer horizontal wiring 14 can be reinforced by arranging the first-layer support member 15 and the second-layer support member 17 so as to overlap in plan view.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

1 is a perspective view of a wiring structure according to Example 1. FIG. (2A) to (2E) are cross-sectional views in the course of manufacturing the wiring structure according to the first embodiment. (2F) to (2H) are cross-sectional views in the course of manufacturing the wiring structure according to the first embodiment. (2I) to (2K) are cross-sectional views in the course of manufacturing the wiring structure according to the first embodiment. (2L) to (2M) are cross-sectional views in the course of manufacturing the wiring structure according to the first embodiment. (2N) is a cross-sectional view in the process of manufacturing the wiring structure according to the first embodiment, and (2O) is a cross-sectional view of the wiring structure according to the first embodiment. 7 is a cross-sectional view of a wiring structure according to a modification of Example 1. FIG. (4A) to (4D) are cross-sectional views in the course of manufacturing the wiring structure according to the second embodiment. (4E)-(4F) are sectional views in the course of manufacturing the wiring structure according to the second embodiment. 10 is a cross-sectional view of a wiring structure according to a modification of Example 2. FIG.

Explanation of symbols

10 substrate 11 first layer vertical wiring 12 first layer horizontal wiring 13 second layer vertical wiring 14 second layer horizontal wiring 15 support member 20 conductive film 21 vertical wiring catalyst film 22 resist pattern 23 first vertical wiring Wiring area 25 First non-wiring area 26 First horizontal wiring area 27 Support area 30 Resist pattern 34 Insulating film 35 Lateral wiring catalyst film 40 Filling film 50 Second vertical wiring area 51 Second horizontal wiring area 52 2 non-wiring region 55 conductive film 56 vertical wiring catalyst film 57 insulating film 58 horizontal wiring catalyst film 60 filling film 65 conductive film 66 insulating film 67 third layer vertical wiring 68 third layer horizontal wiring

Claims (4)

A catalyst film for vertical wiring having a first thickness is formed in two vertical wiring regions spaced apart from each other on the substrate surface, and the horizontal wiring region continuous from one vertical wiring region to another vertical wiring region Forming a lateral wiring catalyst film having a second thickness greater than the first thickness;
Vapor-phase-growing a structure containing carbon on the vertical wiring catalyst film and the horizontal wiring catalyst film,
In the initial stage of the vapor phase growth, graphite is formed on the catalyst film for vertical wiring and the catalyst film for horizontal wiring, and then carbon nanotubes grow between the graphite and the substrate in the vertical wiring region. And manufacturing the wiring structure in which the first thickness and the second thickness are set so that the graphite in the horizontal wiring region is supported in a hollow manner by the carbon nanotubes grown in the vertical wiring region. Method.   2. The method for manufacturing a wiring structure according to claim 1, wherein the first thickness is in a range from 1 nm to 5 nm, and the second thickness is in a range from 2 nm to 50 nm. Vertical wiring composed of a plurality of carbon nanotubes extending from each of a plurality of conductive regions on the surface of the substrate;
And horizontal lines consisting of graphite extending laterally from at least two on one of the upper end of the vertical line to the other upper end,
A support member comprising a plurality of carbon nanotubes extending toward the substrate side from the part of the bottom surface of said horizontal lines,
A wiring structure having an insulating film disposed between a lower end of the support member and the substrate.   The wiring structure according to claim 3, wherein a vacuum is formed between the horizontal wiring and the substrate, or a gas is filled between the horizontal wiring and the substrate.

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