JP3590776B2 - Circuit board and its manufacturing method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a circuit board for a semiconductor integrated circuit which can operate at high speed with a high degree of integration, and a method for manufacturing the same. In particular, the present invention relates to a circuit board having a low dielectric constant by a film having a porous structure in which diamond fine particles are bonded. It relates to the manufacturing method.
[0002]
[Prior art]
In semiconductor VLSI devices, with the miniaturization and high integration of wiring, delay of signals passing through wiring formed in a circuit board has become a serious problem. In particular, in high-speed devices such as logic, RC delay due to wiring resistance and distributed capacitance is the biggest issue. In particular, use a material with a low dielectric constant as an insulating material between wirings in order to reduce distributed capacitance. Is needed.
[0003]
Conventionally, as an insulating material between multilayer wirings in a semiconductor integrated circuit, a silica film (SiO ₂ ) to which fluorine or an organic substance is added has been used as a low dielectric constant film. Further, as a method of lowering the density of the insulating film for further lowering the dielectric constant, a method in which an organic silica material having a foaming property is heat-treated, a porous silica film formed by laminating silica fine particles, and silica are included. The use of non-existing organic polymer materials is being studied.
[0004]
However, since the silica-based material is composed of two or more types of atoms and contains oxygen atoms having high electronegativity as a main component, large orientation polarization remains as one of the factors for increasing the dielectric constant. Therefore, there is a limit in reducing the dielectric constant. In the case of organic polymer materials, even though it is possible to lower the dielectric constant by reducing the orientation polarization, since the thermal decomposition temperature of the organic polymer is essentially low, the heat-resistant temperature required for the circuit board is required. There is a problem that it is difficult to raise.
[0005]
Further, in the case of a porous silica film formed by laminating silica fine particles, since the particles used are amorphous, it has a variety of particle shapes, and it is difficult to reduce the dispersion of the particle size. However, there is a problem in that the pores having approximately the same diameter are easily continuous with each other over a wide range, and the pores are connected to each other, thereby reducing the mechanical strength required for the circuit board.
[0006]
On the other hand, recently, a technique for producing diamond fine particles having a small particle shape dispersion and a substantially uniform particle size at a low cost has been developed, so that the application of a diamond film to a circuit board is specifically examined. It has become. Diamond has excellent thermal conductivity (2,000 W / mK) and mechanical strength in each step more than other materials, so it is an effective material for circuit boards with high integration and large heat generation. is there.
An example of a technique using such a diamond film for a circuit board is described in Patent Document [Japanese Unexamined Patent Publication No. 6-97671 (applicant: Toshiba Corporation)]. In this technique, a diamond film having a thickness of 5 μm constituting an insulating layer is formed by a film forming method such as a sputtering method, a CVD method, an ion plating method, and a cluster ion beam method, and heat generated by circuit elements is used as a substrate. The heat conductivity for heat dissipation is increased. Further, in order to prevent signal propagation delay in the wiring portion, the periphery of the wiring is covered with a low dielectric constant film of borosilicate glass. However, the CVD method for forming a diamond film used in this technique has a problem in safety because it uses harmful gas and flammable gas.
[0007]
[Problems to be solved by the invention]
Conventional attempts to use diamond films for circuit boards with high integration and fine wiring such as VLSI have focused on the high thermal conductivity and mechanical strength of diamond films. However, the CVD method used for forming a diamond film has a problem in safety, such as the use of a harmful gas. In addition, the relative dielectric constant of diamond is 5.68 and the distribution capacity of the wiring is large. Since propagation delay becomes a problem, it has been necessary to cover the periphery of the wiring with another film of a low dielectric constant material. As a result, the manufacturing process of the integrated circuit is complicated, and the production efficiency cannot be increased much.
[0008]
An object of the present invention is to manufacture a low-dielectric-constant film for eliminating the problematic wiring signal delay with high efficiency by a relatively simple process and to increase the mechanical strength of the low-dielectric-constant film. It is in.
[0009]
[Means for Solving the Problems]
The present invention applies a colloid solution containing diamond fine particles of nanometer size to a substrate such as a semiconductor integrated circuit, and by drying, a fine particle of diamond is uniformly dispersed with nanometer sized voids, thereby obtaining a low dielectric constant. This is for forming an insulating layer of a porous diamond film. In addition, the number of chemical bonds between the fine particles is increased by the crosslinking treatment between the fine diamond particles, thereby increasing the strength of the diamond film.
[0010]
FIG. 1A shows a porous structure of a diamond film according to the present invention. A film is formed in a state where the diamond fine particles 10 are bonded to each other, and minute voids 11 are substantially uniformly dispersed between the diamond fine particles to form a porous structure. By adjusting the degree of porosity of the diamond film, that is, the porosity, the relative dielectric constant can be easily reduced.
[0011]
FIG. 1B shows the relationship between the porosity p of the porous diamond film and the relative dielectric constant ε. When the porosity p is changed from 0% to 100%, the relative dielectric constant ε of the diamond film linearly changes between the relative dielectric constant of diamond alone (bulk) 5.68 and the relative dielectric constant 1 of air. Change.
[0012]
The diamond film having a porous structure can be formed by preparing a solution in which diamond fine particles are dispersed in a solvent at an appropriate concentration, applying the solution to a substrate surface (the surface of an underlayer on the substrate), and drying the solution. The diamond film is irradiated with ultraviolet light after drying to promote a dehydration reaction between hydroxyl groups on the surface of the diamond fine particles, thereby forming a bridge between the diamond fine particles, and exposing the diamond film to a cross-linking molecular material vapor to form a diamond film. The mechanical strength of the diamond film can be increased by performing one or both of the processes for forming a chemical multi-point cross-linking structure using cross-linking molecules.
[0013]
FIG. 2 shows a chemical multipoint crosslinked structure by the crosslinking molecule of the present invention.
[0014]
The mechanism of strengthening the film structure by the crosslinking step will be described with reference to FIGS.
[0015]
In FIG. 2A, a large number of hydroxyl groups (—OH) exist on the surface of the diamond fine particles 10. Crosslinked molecules having two or more functional groups capable of reacting with hydroxyl groups are caused to penetrate into the voids 11 of the diamond fine particles. The cross-linking molecule forms a chemical bond 12 between adjacent diamond fine particles as shown in FIG. Whereas cross-linking (-O-) by dehydration reaction between hydroxyl groups is almost one-point bonding, this cross-linking step involves three-dimensional chemical bonding between diamond fine particles at many points corresponding to the length of the cross-linking molecule. Therefore, the number of bonding points is increased, and the mechanical strength can be further increased.
[0016]
The porous diamond film and the method of manufacturing the same according to the present invention are configured according to the following items.
(1) A circuit board having a diamond film in which diamond fine particles are bonded to each other with minute gaps uniformly dispersed therein,
A configuration of a circuit board, characterized in that a crosslinked structure of a crosslinked molecular material having two or more functional groups capable of binding to a hydroxyl group on the surface of diamond fine particles is present at a bonding portion between the diamond fine particles.
(2) The circuit board according to the above (1), wherein the crosslinked molecular material is hexachlorodisiloxane.
(3) a step of forming a solution in which diamond fine particles are uniformly dispersed in a solvent, a step of applying the solution to a substrate, and a step of dispersing the solvent in the applied solution to form a diamond film. A method for manufacturing a circuit board having at least:
A method of manufacturing a circuit board, comprising: a film structure strengthening step of connecting diamond fine particles of a diamond film with bridging molecules after the step of forming a diamond film by dispersing the solvent.
(4) The configuration of the method for manufacturing a circuit board according to the above (3), wherein the cross-linking molecule is a molecule having two or more functional groups capable of binding to a hydroxyl group.
(5) The method for manufacturing a circuit board according to the above (4), wherein the cross-linking molecule is hexachlorodisiloxane.
[0017]
[Action]
Diamond is characterized by the absence of orientational polarization and ionic polarization among the dielectric polarizations that determine the dielectric constant of a material, and of small electronic polarization. Also, the decomposition temperature is high. However, a simple substance of diamond has a higher relative dielectric constant of 5.68 than other low dielectric constant materials, and therefore is not suitable as a low dielectric constant material for a circuit board as it is. Therefore, the dielectric constant was reduced by forming a diamond film having a porous structure having minute gaps.
[0018]
By forming diamond particles having a small particle size dispersion by a coating method, the particles are bonded to each other, and the formed diamond film increases the mechanical strength and thermal conductivity required for forming a circuit board. be able to.
[0019]
If the porosity of the diamond fine particles is 57% or more, a relative dielectric constant of 3.0 or less can be obtained, which is comparable to the relative dielectric constant of other low dielectric materials.
[0020]
Further, by setting the particle size of the diamond fine particles to 20 nm or less, the size of the voids can be reduced to about 20 nm or less, and even in a super LSI having a fine groove structure of about 100 nm, the inside and outside of the grooves are densely formed by the diamond fine particles. It is possible to fill.
[0021]
Further, a layer having an arbitrary thickness can be obtained by repeating the coating step and the radiation step a plurality of times.
[0022]
Further, when ultraviolet irradiation is performed after the radiation step, the bonding of the particles is further strengthened.
[0023]
Further, if a crosslinked structure is formed between the diamond fine particles with a crosslinked molecular material after the radiation step, the bonding of the particles becomes stronger.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the present invention will be described below. The meanings of the terms used in this description are as follows.
"Diamond fine particles": Nano-sized solid particles having a diameter of 1 nm to 1,000 nm are carbon isotopes having a diamond crystal structure. Also, "diamond-like carbon" described in the above-mentioned patent document is not included. If the particle size exceeds 1,000 nm, the bonding strength between the particles required for the construction of the circuit board cannot be obtained even by film formation by a coating method, and fine particles of 1 nm or less are difficult to manufacture, and are excluded. Is done. Fine diamond particles having high crystallinity are synthesized by a high-pressure method or a gas-phase method, and commercially available products are easily available.
"Uniformly dispersed voids": The voids are spaces other than the diamond fine particles, and are spaces after the solvent is evaporated. The case where a part of the solution remains is included in the space. The term “uniformly dispersed” means that voids are not intentional or locally generated due to variations in the manufacturing process. This refers to a state where pores are distributed at a similar density in a certain range.
“Layer”: A part that has a certain thickness on the whole or a part of the substrate. This includes the case where the film is separated by metal wiring in the processing after film formation. Not only those that are not necessarily parallel to the base material but also cases where layers are formed in other directions are included.
[Example 1]
FIG. 3 shows an embodiment of a manufacturing process for forming a porous diamond film on a substrate according to the present invention. As shown in the figure, this production process includes (1) formation of a colloid solution, (2) spin coating, (3) drying, (4) enhancement of film structure by UV irradiation, and (5) enhancement of film structure by cross-linking molecules. It consists of five steps.
{Circle around (1)} Step of producing colloid solution In the step of producing a colloid solution, in the step of producing a colloidal solution, pure diamond or an alcoholic solvent such as ethanol, a saturated hydrocarbon solvent such as hexane, or a fluorocarbon solvent such as perfluorohexane is used. And then ultrasonically dispersed to disperse the diamond fine particles in the solution. Polyethylene glycol (PEG) is added to adjust the viscosity of the colloid solution. In addition to PEG, an organic polymer containing oxygen in the molecule and decomposable at a relatively low temperature of about 300 ° C. can be used for adjusting the viscosity. By adding PEG, the viscosity of the colloid solution can be increased, and a thicker film can be formed in the next spin coating step.
[0025]
In addition, when performing ultrasonic dispersion, the size and agglomeration of diamond fine particles can be controlled by changing the power and time of the applied ultrasonic wave, and as a result, the degree of porosity (porosity) of the diamond film is controlled. It is possible. When the power of the ultrasonic wave is large and the time is long enough, the diamond fine particles are completely separated individually, but in that case, the structure is close to the close-packed structure, and the porous degree of the diamond film is 50% or less. Become. In order to make the degree of porosity 50% or more and sufficiently lower the dielectric constant, it is necessary to form an aggregate having a size of 10 or more diamond fine particles and to form a film by networking the aggregate. desirable. When the number of particles of the aggregate exceeds 10,000, the number of aggregates having a size exceeding 200 nm increases, and it becomes difficult to form an insulating film on a fine pattern of the VLSI.
{Circle over (2)} Spin coating step The colloid solution is applied to the substrate surface by spin coating. Therefore, the solution is dropped on the substrate surface by rotating the substrate, and the dropped solution is diffused by centrifugal force,
It is applied thinly and uniformly on the substrate surface. Examples of the coating method include a spin coating method and a curtain coating method, and the spin coating method is advantageous in that the film thickness can be easily adjusted.
{Circle around (3)} Drying process The colloidal solution film thinly applied to the substrate surface is dried by heating to remove the solvent and additives, thereby forming a porous diamond film. The heating temperature is in the range of 200 to 500 ° C. at which the organic polymer decomposes. At the time of the heating and drying, some of the diamond fine particles in contact with each other in the film dehydrate and condense hydroxyl groups on the surface to form a crosslinked structure.
(4) Step of strengthening the film structure by UV irradiation The formed diamond film having a porous structure is further irradiated with ultraviolet (UV) rays to promote a dehydration reaction between hydroxyl groups on the surface of the diamond fine particles, to thereby enhance the diamond. It increases the cross-linking structure between the fine particles and increases the strength of the porous diamond film.
[0026]
By repeating the steps (2) and (3) or the steps (2) to (4) and laminating the films, a film having an arbitrary thickness can be formed. Furthermore, it is also possible to change the film quality such as the degree of crosslinking of the film in the thickness direction.
(5) Step of strengthening the film structure by cross-linking molecules After the drying step, a step of strengthening the film structure by UV irradiation is used to convert the diamond film into a functional group such as hexachlorodisiloxane capable of bonding to a hydroxyl group on the surface of diamond fine particles. Is exposed to the vapor atmosphere of a cross-linked molecular material having two or more of the above, and a multipoint chemical bond structure is formed between the diamond fine particles.
[0027]
Examples of the functional group capable of reacting with a hydroxyl group include a chlorosilyl group (-SiCl) and an alkoxysilyl group (-SiOA). As a molecule having two chlorosilyl groups in a molecule, there is hexachlorodisiloxane (SiCl ₃ OSiCl ₃ : HCDS) shown in FIG. As shown in FIG. 4, HCDS chemically bonds between hydroxyl groups by a dehydrochlorination reaction. HCDS is excellent as a cross-linking molecule because it evaporates at room temperature and easily enters the pores of the porous diamond film.
[0028]
In the chemical bonding of FIG. 4, since the bonding angles of the Si atoms are the same, the upper and lower arms of the Si atoms can bond to other hydroxyl groups of the diamond fine particles (not shown). Examples of the alkoxysilyl group (—SiOA) include methoxysilane (—SiOCH ₃ ) and ethoxysilane (—SiOC ₂ H ₅ ). A chemical bond can be similarly formed using a molecule having two or more of these groups in the molecule.
[Example 2]
FIG. 5 shows an embodiment in which the porous diamond film of the present invention is applied to a two-layer circuit board for an integrated circuit. The figure shows a partial cross section of a two-layer circuit board, in which 1 is a substrate, 2 is a barrier layer, 3 is a diamond layer having a porous structure, 4 is a metal wiring, 5 is a diamond coating layer having a porous structure. is there.
[0029]
The diamond layer 3 is an interlayer insulating film in the semiconductor integrated circuit, and has a low dielectric constant by having a porous structure. The size of the diamond fine particles used in this layer is desirably monodisperse of 20 nm or less. In order to reduce the relative dielectric constant of the diamond layer 3 to 3.0 or less by the porous structure, a porosity of 57% or more is required. In order to prevent moisture absorption of the diamond layer 3 having a porous structure and diffusion of metal of the metal wiring 4, a barrier layer 2 is provided at an interface between the diamond layer 3 and the base material 1 and the metal wiring 4. I have. As the barrier layer 2, a dense film such as a silicon oxide film, a silicon nitride film, a silicon carbide film, and an organic polymer film is used.
[0030]
The diamond coating layer 5 is a final protective film in a semiconductor integrated circuit using a porous structure diamond film. In the case of the coating layer 5, the size of the diamond fine particles having a size of 100 nm or less is used to enhance the heat conduction characteristics of the diamond, thereby enabling the heat generation of the integrated circuit to be efficiently guided to the outside.
[Example 3]
One embodiment of the manufacturing process of the porous diamond film according to the present invention will be described below.
(1) Diamond fine particles having an average particle diameter of 4.4 nm were dispersed in pure water at a concentration of 5%. Further, 1% of polyethylene glycol having a molecular weight of 600 was added to prepare a homogenized solution.
(2) The solution was applied dropwise onto the substrate rotating at 1,000 rpm by a spin coating method.
(3) The film was heated at 300 ° C. for 1 hour in the atmosphere, dried and formed into a film.
[0031]
FIG. 6 shows a scanning electron micrograph of a cross section of the manufactured porous diamond film. It can be seen that nanopores having a diameter of about 10 nm are uniformly dispersed. The refractive index was measured, and the relative dielectric constant determined by the square was 2.72, and the porosity was 63%.
[Example 4]
FIG. 7 shows one embodiment of a process in which the porous diamond film of the present invention is applied to a stopper in a metal wiring CMP (chemical polishing) process. The figure shows the detailed steps (1), (2), and (3) of forming a metal wiring by partial cross sections of a circuit board, where 1 is a substrate, 6 is an interlayer insulating layer, 7 is a diamond layer having a porous structure, 8 is a metal layer and 9 is a metal wiring.
{Circle around (1)} Step of forming groove pattern A diamond layer 7 having a porous structure is formed on the interlayer insulating layer 6, and a hole and groove pattern for embedding metal wiring are formed by lithography and dry etching. The interlayer insulating layer 6 is a low dielectric constant material such as silicon oxide, fluorine-containing silicon oxide, and an organic insulating film.
(2) Wiring process The metal layer 8 is deposited on the patterned substrate formed in the process (1). For the metal layer 8, a material such as copper and a copper alloy material, aluminum and an aluminum alloy, or tungsten formed by a sputtering method, a CVD method, or a plating method was used.
{Circle over (3)} Polishing process Polishing is performed to remove the metal layer above the hole and groove patterns. Since the porous diamond layer 7 is a material that is mechanically and chemically stable, the polishing is stopped when the polishing proceeds to the diamond layer 7, and the metal wiring 9 embedded in the interlayer insulating layer 6 is removed. Could be formed.
[0032]
At present, silicon nitride and silicon carbide are used as a stopper layer for CMP, but there is a problem that their relative dielectric constants are as high as about 7 to 10.
[0033]
The porous diamond film according to the present invention has a high mechanical strength due to being composed of diamond, is chemically stable, and has a low dielectric constant by being porous. By applying to a layer, a reduction in capacitance in a multilayer wiring can be realized.
[0034]
[Example 5]
According to the method shown in Example 3, a diamond colloid solution is spin-coated on a silicon oxide film, dried and heated to have a film thickness of about 1. A 5 μm porous diamond film was formed.
[0035]
The cross-linking step was performed by placing the sample in a glove box replaced with a nitrogen atmosphere at normal temperature and normal pressure, and maintaining the sample in an HCDS vapor atmosphere diluted with chloroform for 1 hour. The mechanical strength of the film was measured by the amount of peeling of the film (area ratio with respect to the adhered surface) when the attached tape was peeled off. Before the cross-linking step, peeling and film destruction were observed on almost the entire surface of the tape. The peel amount was about 30%, and the adhesion and the film strength of the film could be improved. At this time, almost no change in the relative dielectric constant as seen from the refractive index was observed as shown in FIG. When the HCDS concentration was increased to 1%, no delamination occurred, but the relative dielectric constant increased about twice. Since it is considered that the polymerization reaction of HCDS occurs in the void, it can be suppressed by lowering the atmospheric moisture.
[0036]
Note that dichloromethane other than chloroform may be used for dilution of HCDS.
[0037]
【The invention's effect】
The present invention provides a circuit board having a highly integrated and miniaturized wiring such as a super LSI, by using a diamond film having a porous structure as an interlayer insulating film or the like of the circuit board to reduce the dielectric constant around the wiring, It is possible to significantly reduce the signal delay in the wiring, which has been a problem in the past, and to achieve high heat resistance and high strength of the circuit board. Furthermore, such a low dielectric constant diamond film Can be easily produced with high efficiency. Further, by adding a simple film strengthening step using a crosslinked molecular material, the mechanical strength of the film can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of a porous diamond film according to the present invention.
FIG. 2 is an explanatory diagram of a crosslinked structure of a chemical bond by the crosslinked molecule of the present invention.
FIG. 3 is a flowchart showing one embodiment of a diamond film manufacturing process according to the present invention.
FIG. 4 is an explanatory diagram of a chemical bond by hexachlorodisiloxane.
FIG. 5 is a cross-sectional view of one embodiment of a two-layer circuit board using a diamond film according to the present invention.
FIG. 6 is an electron micrograph showing a porous image of a cross section of the diamond film according to the present invention.
FIG. 7 is an explanatory view showing one embodiment of a step in a case where the porous diamond film of the present invention is applied to a stopper in a metal wiring CMP step.
FIG. 8 is a graph showing a relationship between a refractive index of a diamond film and a change in relative dielectric constant when the HCDS concentration is changed in a crosslinking step using HCDS.
[Explanation of symbols]
1: base material 2: barrier layer 3: porous diamond layer 4: metal wiring 5: porous diamond coating layer 6: interlayer insulating layer not using a diamond film 7: porous diamond layer 8: metal layer 9: Metal wiring 10: diamond fine particles 11: void 12: chemical bonding

Claims (5)

A circuit board having a diamond film in which diamond fine particles are bonded to each other with minute voids dispersed uniformly,
A circuit substrate, characterized in that a cross-linked structure of a cross-linked molecular material having two or more functional groups capable of bonding to a hydroxyl group on the surface of diamond fine particles is present at a bonding portion between the fine diamond particles. The circuit board according to claim 1, wherein the cross-linking molecular material is hexachlorodisiloxane. A circuit including at least a step of forming a solution in which diamond fine particles are uniformly dispersed in a solvent, a step of applying the solution to a substrate, and a step of dispersing the solvent in the applied solution to form a diamond film A method for manufacturing a substrate, comprising:
A method of manufacturing a circuit board, comprising a step of strengthening a film structure in which diamond particles of a diamond film are connected with cross-linking molecules after the step of forming a diamond film by dispersing the solvent. The method for manufacturing a circuit board according to claim 3, wherein the cross-linking molecule is a molecule having two or more functional groups capable of binding to a hydroxyl group. The method according to claim 4, wherein the cross-linking molecule is hexachlorodisiloxane.

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