Patent Application
20090208737
1. Field of the Invention
The present invention relates to lamella structured thin films having ultralow dielectric constants (K) and high hardness and a method of manufacturing the same.
2. Description of the Background Art
Recently, researches on new materials having low dielectric constant are actively performed since the low dielectric constant material is required for reducing the feature dimension of an integrated circuit to improve the degree of integration. The silicon dioxide (SiO2) film has been the material of choice for the conventional semiconductor packaging and the interlayer insulating material. However, the dielectric constant of the silicon dioxide (SiO2) film is about 4, which is too high to be used as the next generation chip-to-chip package material that particularly requires low dielectric constant.
On the other hand, several researchers have sought solutions to the problems of silicon dioxide from nanoporous silica, which can have lower dielectric constants by introducing air of dielectric constant 1 into the nanometer-sized pores. The nanoporous silica have been synthesized by spin-on glass (SOG) method or chemical deposition methods by using tetramethoxysilane (TMOS), tetraethoxylsilane (TEOS), or other similar compounds as the precursor. The nanoporous silica have many advantages: Because their pore size can be controlled, their pore density, mechanical strength and dielectric constant can be controlled. They can have low dielectric constant and thermal stability up to 900° C., and their pore dimensions are smaller than the feature dimensions of the microelectronics in the integrated circuits. They can be synthesized by using silica or TEOS that are used in the current semiconductor industry, and by using synthesis methods similar to the conventional SOG process. Therefore, the nanoporous silica thin films have been synthesized by various methods based on the conventional techniques.
However, in order to reduce the dielectric constant, the porosity has to be increased, which significantly reduces the mechanical strength of the silica thin film.
In particular, although the characteristic standards for the material is not established because the kind of the low dielectric constant material used for manufacturing a semiconductor device varies with the wiring line structure and the application field of the semiconductor device, stable electrical, chemical, mechanical, and thermal characteristics are commonly required for the dielectric materials. That is, in order to increase metallization density and to reduce signal delay, the material must have low dielectric constant and allow facile design of metallization and facile processes of manufacturing. In addition, chemical inertness and low ion transport property during the metallization process, and mechanical strength enough to withstand processes such as a chemical mechanical polishing (CMP) process are required. A dielectric material cannot be used as the interlayer material for metallization unless the dielectric material satisfies various characteristics such as low moisture absorption to prevent the mechanical failure or the increase of dielectric constant, heat resistance against the processing temperature, adhesive force capable of minimizing various stresses and lamination that can be generated by the interface between low dielectric material and metal, low stress, and low thermal expansion coefficient.
As described above, the excellent thermal, chemical, and mechanical characteristics including low dielectric constant and high mechanical strength are objects to be simultaneously pursued in the researches on low dielectric constant materials. However, since these objects conflict with each other in the conventional material design, there have been no solutions.
Therefore, the inventors of the present invention conducted researches on manufacturing lamella structured thin film that, while maintaining the characteristics of the conventional silicon dioxide film, has lower dielectric constant than the conventional dielectric materials and excellent electrical, chemical, mechanical, and thermal characteristics simultaneously.
It is an object of the present invention to provide lamella structured thin films having ultralow dielectric constants and high hardness.
It is another object of the present invention to provide a method of manufacturing lamella structured thin films having ultralow dielectric constants and high hardness through simple and economical processes.
In order to achieve the above objects, there is provided lamella structured thin film, in which silica layers and air layers are alternately and repeatedly stacked along the vertical direction of the surface of a wafer.
That is, the silica layers having thickness of 0.1 to 10 nm, preferably 1 to 8 nm, and the air layers having thickness of 0.1 to 10 nm, preferably 1 to 5 nm, are stacked on the surface of a wafer with the repeat thickness of 0.2 to 20 nm, preferably 2 to 13 nm, and more preferably 7 to 9 nm in the vertical direction. However, the repeat thickness of the lamella structured thin film is not limited. For example, the thicknesses of the silica layers and the air layers can vary with the change of the composition or the agitation time of the silica sol solution.
Also, there is provided a method of manufacturing lamella structured thin films having ultralow dielectric constant and high hardness, comprising agitating silica sol solution containing surfactant and silica precursor, spin-coating the solution on a silicon wafer to form a thin film, aging the thin film, and heat-treating the thin film to remove the surfactant and organic materials from the thin film.
According to the present invention, lamella structured thin film is formed by a method based on evaporation induced self-assembly (EISA) mechanism in which the precursor solution is evaporated so that the surfactant, the structure directing agent, forms a mesostructure depending on the volume fraction of the surfactant in the spun-cast thin film.
That is, when the size, the distribution, and the amount of silica sol particles and the amount of the surfactant are controlled, a structure in which the silica particles and the surfactant are alternatively repeated, that is, a lamella structure can be obtained. In general, when such lamella structured thin film is heat-treated at high temperature, since the surfactant as an organic material is heated to be removed so that the space occupied by the surfactant is emptied, adjacent silica layers become in contact with each other (that is, the air layers disappear). As a result, a thin film structure that contains no structure in the length scale of a range of nanometers is expected. At this time, according to the present invention, to the contrary, conditions such as the composition of the silica sol solution and treatment after spin-coating or evaporation are controlled so that the space that has been previously occupied by the surfactant is not completely removed but is converted to layers having a significantly lower density than the silica layers, that is, “the air layers”.
Therefore, it is important that the composition of the surfactant is in a specific range. That is, when the composition range of the surfactant deviates from the specific value, thin film having structures other than the lamella structure is formed. Then, the physical properties such as low dielectric constant and high surface strength represented in the lamella structure thin film according to the present invention are not obtained. For example, a cubic structure thin film has a dielectric constant of about 3 to 4 and a hardness value of about 0.3 GPa so that it is not possible to obtain physical property effect of the low dielectric constant and the high hardness represented in the lamella structure thin film. The silica sol solution preferably contains a surfactant of 0.1 to 0.8 wt % and silica of 5 to 20 wt % for the weight of the entire silica sol solution.
All kinds of surfactants used for synthesizing a mesostructured material such as cetyltrimethylammonium bromide (CTAB), block copolymers having chemical formulas of EOmPOnEOm and EOmPOn (EO is ethylene oxide, PO is propylene oxide, and n and m are integers), block copolymer (in Brij type) having a chemical formula CmH2m+1EOn (EO is an ethylene oxide and n and m are integers), tween series surfactants, triton series surfactants, and tergitol series surfactants can be used as the surfactant. In particular, a block copolymer (F-127 manufactured by Sigma-Aldrich) having chemical formula of EO106PO70EO106 can be used as the surfactant.
Triethoxysilane (TES), trimethoxysilane (TMOS), or vinyltrimethoxysilane (VTMOS) can be used as the silica precursor. In particular, tetraethoxysilane (TEOS) is preferably used as the silica precursor.
The silica sol solution can further contain solvent and/or catalyst. All kinds of solvents used for synthesizing the mesopstructured materials such as water, butanol, methanol, ethanol, propanol, and other organic solvent can be used as the solvent. Ethanol is preferred as the solvent. Acids such as HNO3, HCl, HBr, H1, H2SO4, or HClO4, can be used as the catalyst. In particular, HCl is preferred as the catalyst.
The silica sol solution contains silica of 5 to 20 wt % and surfactant of 0.1 to 0.8 wt %, preferably, silica of 8 to 15 wt % and surfactant of 0.1 to 0.6 wt % for the weight of the entire solution. The silica sol solution can also contain solvent of 70 to 87 wt % and catalyst of 5.04×105 to 1.97×10−4 wt %.
In a preferred embodiment of the present invention, silica sol solution can contain TEOS as silica precursor, F-127 as surfactant, HCl as acid catalyst, and H2O and EtOH as solvents and the molar ratio of TEOS:F-127:HCl:H2O:EtOH is preferably 1:1.65×10−3 to 6.60×10−3:2.08×103 to 7.03×103:2.31 to 4.62:22.6 to 93.90. However, the present invention is not limited to the above.
The agitating process can be performed for 10 to 60 hours, preferably, 10 to 30 hours. At this time, since the lamella structured thin film is not formed with the agitation temperature about 10° C., the silica sol solution is preferably agitated at the temperature about 20 to 30° C. The humidity during the agitating process is preferably 18 to 40%.
The aging process is preferably performed at a temperature of 50 to 100° C. for 12 to 24 hours.
The thin film generated according to the present invention has lamella structure in which the air layers and the silica layers are alternately arranged on the surface of the wafer in the vertical direction. Actually, the thin film has a structure in which the density of silica is periodically increased and reduced in the vertical direction to the surface of the wafer. The density variation between the two kinds of layers can be abrupt and/or continuous. In other words, the boundary between the silica layer and the air layer is not clearly limited.
Therefore, in the specification and claims “the silica layers” mean portions having high silica density of 50 wt % or more, preferably, 70 wt % or more, and more preferably, 90 wt % or more, and “the air layers” mean portions having low silica density and relatively high air ratio in the repeated structures, that is, layers composed of silica of 50 wt % or less, preferably, 30 wt % or less.
In the spin-coating process, the silica sol solution is dropped on the center of the wafer while rotating the wafer by a predetermined rpm. The dropped solution is coated on the surface of the wafer while uniformly spreading to the periphery by centrifugal force. According to the present invention, the spin-coating process is preferably performed at a temperature of 25 to 35° C. and with a humidity of 55 to 80%.
The lamella structured thin film according to the present invention has the following effects.
First, the high hardness of the films can be understood in an analogy to the superhard coating having similar structure characteristics. The superhard coating or superhard thin film is a multilayered structure in which a material having significantly high hardness and a material having relatively low hardness are alternately stacked to thicknesses of several nm, respectively, by a vapor deposition technique. That is, the material having significantly high hardness and the material having relatively low hardness are alternately stacked in a repeat thickness of about 10 nm. In such lamella structured thin film, resistance against external mechanical shock is significantly larger than the average of the two materials. In the film made of only the material having high hardness, the external shock is effectively transmitted to the inside of the material. However, in the lamella structured thin film, since the external shock spreads at the interface between the material with high hardness and the material with low hardness, it is possible to prevent the external shock from being transmitted to the inside of the thin film. Since the thin film according to the present invention has the structure in which silica having relatively high hardness and the air layer having significantly low hardness are alternately stacked, it has the effect of dissipating the external shock. Therefore, although the thin film of the present invention is made of silica having low hardness, its hardness is higher than pure silica.
In addition, the lamella structured thin film in which silica having relatively high dielectric constant and air having lower dielectric constant are repeated in the range of several nm provides a mechanism that effectively reduces the dielectric constant. The mechanism can be explained by the changes in the overall dielectric constant when two dielectric materials having different dielectric constants are differently arranged. The two dielectric materials can be connected to each other in parallel or in serial as illustrated in
Referring to
In the conventional silica thin film, in order to reduce the dielectric constant, the ratio of pores is to be increased, which deteriorates the mechanical strength of the thin film. On the other hand, according to the present invention, since it is possible to reduce the dielectric constant lower than that of the conventional silica thin film while reducing the ratio of the pores, the mechanical strength of the thin film does not significantly deteriorate. Also, since the lamella structured thin film itself represents the effect of increasing the hardness, the hardness of the film increases.
Therefore, it is possible to provide thin films having ultralow dielectric constants and high mechanical strength simultaneously, which the prior arts could not achieve. Therefore, the present invention provides structure that can solve the two problems and a method of manufacturing actually usable materials.
In the conventional porous low dielectric constant thin films, the pores are connected to the outside of the thin film so that moisture can easily permeate to the internal pores. The moisture increases the dielectric constant. The pores of the lamella structured thin film according to the present invention with the air layer between the dense silica layers is prevented from being connected to the outside, and accordingly moisture does not permeate. Therefore, it is possible to prevent the dielectric constant from being rapidly increased by absorbing moisture.
In summary, the lamella structured thin film manufactured by the present invention is made of silica material and has excellent mechanical strength, chemical stability, and low dielectric constant (K is preferably no more than 2.5, and more preferably, no more than 2.0).
In addition, in the method of manufacturing the lamella structured thin film, since only pure silica is used and no additional surface treatment is required, the semiconductor fabrication processes can be simple and economical.
The present invention now will be described more fully with reference to embodiments thereof. However, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Manufacture of Lamella Structured Thin Film
The amount of tetraethoxy silane (TEOS) of 99.999% manufactured by Sigma-Aldrich as the material of silica wall was fixed to 1.0 g and the amounts of surfactant F-127 manufactured by Sigma-Aldrich, solvent EtOH, and catalyst HCl as structure forming materials were controlled as illustrated in TABLE 1 to provide solutions for four lamella structured thin films. In TABLE 1, numbers represent molar ratio for one mole of TEOS.
The solutions were agitated under conditions defined as temperature of 15° C. and humidity of no more than 11% at the agitation times illustrated in TABLE 1. Then the solutions were spin-coated on a silicon wafer having the size of 1×1 cm under conditions of the temperature of 28 to 29° C. and the humidity of 60% at the speed of 4,500 rpm for 1 minute. At this time, the silicon wafer was dipped into Piranha (a 1:1 mixture of H2SO4:H2O2) for about 2 hours and then, was washed by distilled water and ethanol so that OH groups were formed on the surface of silicon wafer. Then, the spun-cast thin film on the silicon wafer was aged in an oven at a temperature of 80° C. for 12 to 24 hours. Then, the thin film was put in a furnace and, after the temperature of the furnace was increased to 450° C. at the speed of 1° C./min, was kept at 450° C. for 5 hours. Then, the temperature of the furnace was reduced to 40° C. at a speed of 10° C./min. Then, the surfactant and the organic materials were removed to manufacture porous thin films.
X-Ray Diffraction (XRD) Analysis
As illustrated in
X-Ray Diffraction (XRD) Analysis after High Temperature Treatment
The thin films obtained by performing the heat-treatment process at 450° C. for 5 hours were high temperature heat treated at 800° C. for 30 minutes and taken to X-ray diffraction (XRD) analysis (refer to
Infrared (IR) Analysis
The thin films obtained by the embodiment 1 were IR analyzed using TENSOR27 (manufactured by BRUKER) (refer to
Transmission Electron Microscope (TEM) Analysis
The TEM photographs of
Scanning Electron Microscope (SEM) Analysis
Nonointendation
The nanoindentation measurement data of
Dielectric Constant
The dielectric constants of the thin films according to the present invention were measured by an HP 4248A Precision LCR meter and were calculated by the next equation;
C
p=ε0εA/d
wherein, ε0 represents the dielectric constant under vacuum, ε represents the dielectric constant of the thin film of the present invention, A represents the area of electrode, and d represents the thickness of the low dielectric material.
As illustrated in
Test on the Resistance Against Water Vapor Treatment
In order to test the moisture absorption property of the lamella structured thin films, the following analysis experiments were performed. After leaving the manufactured thin films in the vapor environment of boiling water at 100° C., that is, in a significantly humid environment, for 30 minutes, an IR analysis was performed. The graphs in the left-hand side of
Analysis of 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) Spectrums
The NMR spectrums of the precursor silica sol solutions for the lamella structured thin films (SKUL series) were analyzed and the results were illustrated in
In order to compare the thin films of the present invention with the existing low dielectric constant materials, main results of reference documents are summarized.
SiLK as low dielectric constant material was manufactured by a spin-coating method using a polymer and an organic solvent described in the reference document (Adv. Mater. 2000, 12, 1769). However, the dielectric constant of the material is 2.65, the Young's modulus of the material is 2.45 GPa, and the hardness of the material is 0.38 GPa. Therefore, it is noticed that the material of the comparative embodiment 1 has a significantly higher dielectric constant and significantly lower Young's modulus and hardness than those of the present invention. Therefore, it was noticed that the films of the present invention have significantly higher performance than conventional low dielectric constant materials.
In accordance with the reference document (Chem. Mater. 2002, 14, 1845-1852), low dielectric constant thin film having mesopores was manufactured by a spin-coating method using a silica source based on hydrogen silsesquioxane and a solvent having low boiling point such as methylpropyl ketone.
In accordance with the reference document (Langmuir 2001, 17, 6683-6691), low dielectric constant thin film was manufactured by a spin-coating method using PMSSQ/BTMSE prepolymer, Bis(1,2-trimethoxysilyl)ethane (BTMSE), and methyltrimethoxysilane (MSSQ).
As a result of measuring the dielectric constants of the thin films generated by the comparative embodiments 1 to 3, it was noticed that the dielectric constants were about 2.5 to 3.5, which are significantly larger than the dielectric constants of the films manufactured by the method of the present invention.
As described above, the lamella structured thin film according to the present invention has excellent mechanical strength and chemical stability, in particular, have significantly low dielectric constant of no more than 2.5 and high hardness. In addition, according to the method for manufacturing the lamella structured thin film of the present invention, the semiconductor manufacturing processes can be simple and economical since only pure silica is used and no additionally surface treatment is performed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0005595 | Jan 2008 | KR | national |
