JP5098660B2 - Carbon nanotube sheet, method for producing the same, and electronic device - Google Patents

Description

  The present invention relates to a carbon nanotube sheet, a method for manufacturing the same, and an electronic device, and in particular, characteristics such as high heat conductivity, electrical conductivity, and allowable current density as a heat dissipation sheet such as a heat spreader used as a heat propagation member in a semiconductor package. It is related with the structure for reducing the thermal resistance of the contact interface with the to-be-heat-dissipated member at the time of using the carbon nanotube which has this.

  Since carbon nanotubes (CNT) have a high thermal conductivity, a heat-dissipating sheet containing CNTs is produced (for example, see Patent Document 1 or Patent Document 2).

As an important function required for such a carbon nanotube heat dissipation sheet,
a. High thermal conductivity,
b. Low thermal resistance and
c. Adhesion is required.

For example, in Patent Document 2, a carbon nanotube is used as a heat sink as a carbon nanotube fiber using a resin, or a carbon nanotube fiber is combined into a container shape.
JP 2005-277096 A JP 2005-116839 A

  However, in order to obtain high heat conduction characteristics, it is necessary to align the direction in which heat is desired to escape with the orientation direction of the carbon nanotubes. However, in the configuration as described in Patent Document 2, such orientation arrangement is impossible. There is a problem.

  In addition, in order to obtain low thermal resistance characteristics, it is necessary to make the thermal resistance of the heat dissipation sheet and the heating element or the contact interface between the heat dissipation sheet and the heat dissipation element as small as possible. It is necessary to improve the adhesion.

  However, when carbon nanotubes having the same orientation direction are used, the contact between the tips of the carbon nanotubes and the heating element is insufficient, and there arises a problem that the thermal resistance becomes the highest at this interface.

  Accordingly, an object of the present invention is to reduce the thermal resistance of the contact interface between a carbon nanotube sheet having a uniform alignment direction and a heat radiating member or a heat generating member.

  The carbon nanotube sheet is composed of a group of carbon nanotube bundles and a plating metal, the orientation direction of the carbon nanotube bundle is held in the vertical direction of the sheet, and at least the tip of the carbon nanotube bundle is made of the plating metal. It is a requirement that they are bonded and have a cavity on the side opposite to the tip of the carbon nanotube bundle.

  From another point of view, the carbon nanotube sheet manufacturing method includes a step of forming a plating seed metal film on a substrate, and a step of regularly arranging catalyst layers on the seed metal film at predetermined intervals. A step of growing a carbon nanotube bundle on the catalyst layer; and an electrolytic plating of a plating metal on at least a tip portion of the carbon nanotube bundle to bond at least the tip portion of the carbon nanotube bundle with the plating metal; It is a requirement to have a step of forming a cavity on the opposite side of the tip of the nanotube bundle and a step of removing the substrate.

  Furthermore, from another point of view, as an electronic device, the above-described carbon nanotube sheet is required to be disposed in close contact between the electronic device and the heat radiator.

  According to the disclosed carbon nanotube sheet, since the carbon nanotubes are oriented along the vertical direction of the heat radiating sheet, high heat dissipation in the vertical direction can be realized.

  In addition, since the metal film is formed by using plating at the tip of the carbon nanotube that becomes the interface between the carbon nanotube and the heating element, the contact thermal resistance between the heating element and the carbon nanotube can be significantly suppressed.

Here, with reference to FIG. 1 thru | or FIG. 6, embodiment of this invention is described.
FIG. 1 is a schematic cross-sectional view of a carbon nanotube sheet of the present invention. Catalysts 12 are regularly arranged at predetermined intervals on a metal film 11 for plating seeds, and carbon nanotubes are seeded by plating with the catalyst 12 as a growth nucleus. The carbon nanotube bundle 13 is formed by being oriented and grown in the vertical direction with respect to the metal film 11, and then the plated metal 14 is plated by electrolytic plating to bond the carbon nanotube bundles 13 to each other, and the cavity 15 is formed on the catalyst 12 side. Is provided.

  The catalyst layer constituting the catalyst 12 in this case depends on the material of the plating seed metal film 11, but is a single Fe film, Fe film / Al film, Fe film / Al film / Ta film, Co film / TiN film or the like. When a carbon nanotube is grown using a laminated structure such as the above, Fe or Co on the outermost surface is finely divided to become a growth nucleus.

In this case, the planar shape of the growing carbon nanotube bundle 13 is determined by the shape of the catalyst layer, and the CNT density of the carbon nanotube bundle 13 is preferably 1 × 10 ¹⁰ pieces / cm ² or more from the viewpoint of heat dissipation. .
The length of the carbon nanotube bundle 13 is not particularly limited, but is preferably in the range of 5 μm to 500 μm from a practical viewpoint.

  In addition, since the heat conduction of the carbon nanotube is performed not by electrons but by lattice vibration, the growing carbon nanotube may be a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT).

  FIG. 2 is an explanatory diagram of an example of the shape of the catalyst layer, and as shown in the figure, for example, a circle, a triangle, a quadrangle, a hexagon, or a stripe pattern can be mentioned, but the shape may be anything, especially It is not limited.

  FIG. 3 is an explanatory diagram of an arrangement example of the catalyst layer, FIG. 3 (a) is an example in which circular patterns are arranged in a matrix, and FIG. 3 (b) is an example in which circular patterns are arranged in a close-packed pattern. 3 (c) is an example in which triangular patterns are arranged in a hexagonal close-packed pattern, FIG. 3 (d) is an example in which square patterns are arranged in a matrix, and FIG. 3 (e) is a comb. FIG. 3 (f) shows an example in which circular patterns are arranged in a matrix.

  FIG. 4 is an explanatory diagram of an example of the arrangement interval of the catalyst layers, which is an example in which circular patterns having a diameter of 1 μm to 20 mm are regularly arranged in a matrix form at intervals of 1 μm to 20 μm. The thickness is set to be not more than twice the thickness of the plating metal formed on the part.

  FIG. 5 is an explanatory diagram of another example of the arrangement interval of the catalyst layers, and is an example in which square patterns with sides of 1 μm to 20 mm are regularly arranged in a matrix at intervals of 1 μm to 20 μm. It is set so as to be not more than twice the film thickness of the plating metal formed on the tip of the metal.

  FIG. 6 is an explanatory view of still another example of the arrangement interval of the catalyst layers. A stripe pattern having a short side of 1 μm to 20 mm and a long side of 1 μm to 20 mm is regularly arranged in a line and space (1 μm to 20 μm interval). In this case, the interval is set so as to be not more than twice the film thickness of the plating metal formed at the tip of the carbon nanotube bundle.

Since plating proceeds from a portion with good electrical conductivity, that is, a portion close to the tip of the carbon nanotube bundle 13, the plating metal formed on the tip of the adjacent carbon nanotube bundle 13 is also formed in the lateral direction. The plated metals finally contact each other to form an integral plated metal 14.
On the other hand, an unplated cavity 15 is formed in the vicinity of the root between adjacent carbon nanotube bundles 13, and the cavity 15 is deformed to absorb unevenness of the heating element and the heat dissipation element, thereby improving the adhesion.

  The plating metal in this case may be anything as long as electrolytic plating is possible, and examples thereof include gold, copper, silver, nickel, zinc, chromium, platinum, solder, and tin.

Based on the above, next, the manufacturing process of the carbon nanotube sheet of Example 1 of the present invention will be described with reference to FIG.
First, as shown in FIG. 7A, a plating seed layer 23 made of an Au film having a thickness of, for example, 100 nm is formed on a silicon substrate 21 on which a SiO ₂ film 22 is formed.

Next, a Ta film 25 having a thickness of, for example, 5 nm, an Al film 26 having a thickness of, for example, 10 nm, and an Fe film 27 having a thickness of, for example, 2.5 nm are sequentially formed on the plating seed layer 23. After the film formation, the catalyst pattern 24 is formed by etching into a predetermined pattern.
In this case, the catalyst pattern 24 is, for example, a square pattern having a side of 100 μm and is regularly arranged in a matrix with an interval of 2 μm.

Next, as shown in FIG. 7B, MWCNT growth is performed using, for example, a hot filament CVD method, and a carbon nanotube bundle 28 depending on the shape of the catalyst pattern 24 is formed on the catalyst pattern 26 at a height of, for example, 100 μm. Let it grow.
As the growth conditions of the hot filament CVD method, for example, acetylene: argon = 1 sccm: 9 sccm is introduced as the growth gas, the pressure is 1 kPa, and the growth temperature is 620 ° C.

Next, as shown in FIG. 7C, for example, a Ni plating film 29 is formed on the carbon nanotube bundle 28 by using an electrolytic plating method.
At this time, since the plating proceeds from the vicinity of the tips of the carbon nanotube bundles 28 having good electrical conductivity, the Ni plating films 29 grown in the vicinity of the tips of the carbon nanotube bundles 28 are in contact with each other at the end of the film formation. It becomes.
In addition, the base portion of the carbon nanotube bundle 28 having poor electrical conductivity is hardly plated, so that a cavity 30 is formed.

Next, as shown in FIG. 7 (d), in order to separate the group of plated carbon nanotube bundles 28 from the substrate and form a sheet of carbon nanotubes, for example, the entire substrate is immersed in a hydrofluoric acid aqueous solution to form SiO. The basic structure of the carbon nanotube sheet 20 of the present invention can be obtained by selectively etching the _two films 22 and separating the silicon substrate 21 and the plating seed layer 23.

  According to the carbon nanotube sheet of the present invention, since the carbon nanotubes oriented and grown on the substrate are used, high heat dissipation in the vertical direction of the substrate can be realized.

  In addition, since the metal film is formed by plating at the tip of the carbon nanotube bundle that becomes the interface between the carbon nanotube sheet and the heating element, the contact thermal resistance between the heating element and the carbon nanotube can be significantly reduced. it can.

  In addition, since a cavity is provided in the vicinity of the root between adjacent carbon nanotube bundles, deformation of the sinus can absorb the unevenness of the heat generating body and the heat radiating body, thereby improving adhesion.

Next, a semiconductor module using the carbon nanotube sheet of Example 2 of the present invention will be described with reference to FIG.
FIG. 8 is a schematic cross-sectional view of a semiconductor module using the carbon nanotube sheet of Example 2 of the present invention. After the semiconductor chip 41 is attached to the carbon nanotube sheet 20 serving as a heat spreader via the indium solder 42, the solder Flip chip bonding is performed to the circuit board 44 through the bumps 43.

  Next, the semiconductor device is mounted on the printed wiring board 46 via the solder bumps 45, and the heat sink 47 provided with heat radiation fins on the other surface of the carbon nanotube sheet 20 is attached via the indium solder 48. The semiconductor module of Example 2 of the invention is completed.

  Thus, in the semiconductor module of Example 2 of the present invention, since the carbon nanotube sheet is closely inserted between the semiconductor chip and the heat sink, the semiconductor chip can be effectively dissipated.

  In addition, when the carbon nanotube sheet is closely inserted between the semiconductor chip and the heat sink, the unevenness on the surface of the semiconductor chip or the heat sink is provided on the carbon nanotube sheet and absorbed by the deformation of the cavity, so that the adhesion is further improved. Can do.

  Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the configurations and conditions described in the embodiments and examples, and various modifications can be made. For example, in Example 1 described above, the catalyst layer is composed of a laminated structure of Fe / Al / Ta, but Fe alone, a Fe / Al laminated structure, or a Co / TiN laminated structure may be used, For example, when a Co / TiN laminated structure is used, for example, TiN: Co = 5 nm: 3.8 nm.

  Although not described in the above embodiment or examples, the present invention is similarly applied to the case where graphene grows at the tip of the carbon nanotube bundle.

  In Example 2 above, when the carbon nanotube sheet is tightly inserted between the semiconductor chip and the heat sink, the plated metal side is brought into contact with the heat sink. You may make it contact.

In the second embodiment, the carbon nanotube sheet is closely inserted between the semiconductor chip and the heat sink. However, the carbon nanotube sheet may be closely inserted between the package and the semiconductor chip.
When the semiconductor chip is face-up bonded to the package substrate, it may be inserted between the package substrate and the semiconductor chip.
Further, when flip chip bonding of the semiconductor chip to the package substrate, it may be inserted between the upper lid member of the package and the semiconductor chip.

  In the second embodiment, a semiconductor chip is used as an object to use the carbon nanotube sheet. As such a semiconductor chip, a semiconductor integrated circuit device such as a CPU, a high-power amplifier for a radio communication base station, a radio High-power amplifiers for communication terminals, high-power switches for electric vehicles, and the like.

  In addition, the object of using the carbon nanotube sheet is not limited to the semiconductor chip, but can be applied to other electronic device chips such as an optical deflecting device using a ferroelectric material. It can also be applied to heat-dissipating / conductive sheets used in products such as servers and PCs.

It is a schematic sectional drawing of the carbon nanotube sheet of the present invention. It is explanatory drawing of an example of the shape of a catalyst layer. It is explanatory drawing of the example of arrangement | positioning of a catalyst layer. It is explanatory drawing of an example of the arrangement | positioning space | interval of a catalyst layer. It is explanatory drawing of another example of the arrangement | positioning space | interval of a catalyst layer. It is explanatory drawing of another example of the arrangement | positioning space | interval of a catalyst layer. It is explanatory drawing of the manufacturing process of the carbon nanotube sheet | seat of Example 1 of this invention. It is a schematic sectional drawing of the semiconductor module using the carbon nanotube sheet | seat of Example 2 of this invention.

Explanation of symbols

11 Plating seed metal film 12 Catalyst 13 Carbon nanotube bundle 14 Plating metal 15 Cavity 20 Carbon nanotube sheet 21 Silicon substrate 22 SiO ₂ film 23 Plating seed layer 24 Catalyst pattern 25 Ta film 26 Al film 27 Fe film 28 Carbon nanotube bundle 29 Ni Plating film 30 Cavity 41 Semiconductor chip 42 Indium solder 43 Solder bump 44 Circuit board 45 Solder bump 46 Printed wiring board 47 Heat sink 48 Indium solder

Claims (6)

The carbon nanotube bundle is composed of a group of carbon nanotube bundles and a plating metal that embeds each of the carbon nanotube bundles, and the orientation direction of the carbon nanotube bundle is held in the vertical direction of the sheet, and at least the tip of the carbon nanotube bundle is the plating metal And a carbon nanotube sheet having a cavity on the side opposite to the tip of the carbon nanotube bundle. The carbon nanotube sheet according to claim 1, wherein the carbon nanotube bundles are regularly arranged at a predetermined interval. The carbon nanotube sheet according to claim 1, wherein a metal film for plating seed is provided on a side opposite to a tip portion of the carbon nanotube bundle. The carbon nanotube sheet according to any one of claims 1 to 3, wherein the plated metal is made of any one of gold, copper, silver, nickel, zinc, chromium, platinum, solder, or tin. Forming a plating seed metal film on a substrate; regularly arranging catalyst layers on the seed metal film at predetermined intervals; growing a carbon nanotube bundle on the catalyst layer; and A step of electrolytically plating a plating metal on at least the tip of the nanotube bundle to bond at least the tip of the carbon nanotube bundle with the plating metal and forming a cavity on the opposite side of the tip of the carbon nanotube bundle; A method for producing a carbon nanotube sheet, comprising a step of removing a substrate. An electronic apparatus in which the carbon nanotube sheet according to any one of claims 1 to 4 is disposed in close contact between an electronic device and a radiator.

Images