Patent Application
20090324807
1. Field of the Invention
This invention relates to a pore-sealing technique, particularly to a method for forming a porous material.
2. Description of the Prior Art
Nowadays, in a semiconductor manufacturing process, the elements of integrated circuit are miniaturized gradually, but this will increase time delay in electronic signal transmission between metallic connecting lines and cause high power loss under high frequency. Therefore, for lowering time delay of signal transmission and elevating operation velocity of elements, it is necessary to employ multi-layered metal conductor connecting lines and leads of low resistivity or insulating materials of low dielectric coefficient. The low dielectric-coefficient (low-k) material commonly used is formed by mixing a low dielectric-coefficient and porous inorganic substance with an organic substance to let the inorganic substance permeate into the organic substance for lowering its dielectric coefficient and the coefficient of thermal expansion and enhancing its mechanical strength.
Although the conventional inorganic substance has its interior formed with numerous pores for containing air and lowering dielectric coefficient, yet, after the inorganic substance is mixed with the organic substance, the organic substance will be mixed to permeate into the pores of inorganic substance and produce a caulking phenomenon, thus rendering the inorganic substance impossible to lower the dielectric coefficient in its interior.
The objective of this invention is to offer a method for forming a porous material in which a porous first basic material is first mixed with a sacrificial material that is compatible with the first basic material, letting the sacrificial material permeate into the pores of the first basic material to form a first finished product. Next, the first finished product is mixed with a second basic material and then their mixture is heated over the vaporization temperature of the sacrificial material to let the ingredients of the second basic material changed to increase viscous force and impossible to get into the pores of the first basic material, and meanwhile the sacrificial material is heated and vaporized to exhaust out of pores of the first basic material to form a second finished product. Thus, the second basic material is impossible to permeate into the pores of the first basic material, able to reserve the ingredients in the pores of the first basic material. By so designing, after the second basic material is heated, its ingredients will be changed to produce high viscosity by polymerization reaction and impossible to permeate into the pores of the first basic material, and simultaneously the sacrificial material will exhaust out of the pores of the first basic material, thus able to prevent the second basic material from permeating into the pores of the first basic material and hence increase the ingredient content in the pores of the first basic material.
This invention will be better understood by referring to the accompanying drawings, wherein:
A preferred embodiment of a method for forming a porous material to be employed in a semiconductor manufacturing process and in a chip packaging process for lowering dielectric coefficient in the present invention, as shown in
(1) A first step is to select a porous first basic material 10, a second basic material 20 and a sacrificial material 30. The first basic material 10 is inorganic, and the porous and inorganic materials to be optionally used include silica, alumina oxide, silica-alumina, carbon-doped oxide (CDO), fluorinated silicate glass (FSG), calcium carbonate, alumina phosphate, alumina arsenate, alumina germanate, clay (kaolin, montmorillonite, or mica powder), glass fiber and carbon fiber. In this preferred embodiment, silica is selected for use. The second basic material 20 is organic and the organic materials to be optionally used include epoxy resin, acryl resin (acrylate), polyimide and polyurethane, and in this preferred embodiment, epoxy resin is selected for use. The sacrificial material, which is permeable and compatible with the first basic material 10 but incompatible with the second basic material 20, is siloxane, wax or the like, and in this preferred embodiment, hexamethyl cyclotrisiloxane is selected for use and its structure is:
The melting point of the sacrificial material 30 is 65° C. while its boiling point is about 134° C., and the sacrificial material could be other similar materials.
(2) A second step is to have the sacrificial material 30 of a preset proportion and the first basic material 10 heated over the melting point of the sacrificial material 30 (about 65° C.˜100° C.) and then evenly mixed for one hour, and their mixing modes can adopt closed thermal melting or solvent treatment or other heating treatments to enable the sacrificial material 30 to permeate into the pores 11 of the first basic material 10. After mixed evenly, the mixture is kept stationary until its temperature drops to room temperature to form a first finished product.
(3) A third step is to mix the first finished product with the second basic material 20 and have their mixture heated over the boiling point of the sacrificial material 30 in cooperation with the cross-linking reaction temperature condition of the second basic material 20. This reaction temperature condition is to have the temperature rising from room temperature up to 140° C.˜170° C. at a speed of 2° C. per minute and then maintain the temperature for one hour to let the molecule of the second basic material 20 polymerized and hardened and impossible to flow back and permeate into the pores 11 of the first basic material 10. When the second basic material 20 is polymerized, the sacrificial material 30 will synchronously vaporize and exhaust out of the pores 11 of the first basic material 10, and the high viscosity produced by polymerization action of the second basic material 20 disables the second basic material 20 to permeate into the pores 11 of the first basic material 10, but has the second basic material 20 covering up the outer side of the first basic material 10, thus enabling the first basic material 10 to completely reserve the original porosity of its pores 11 and forming a second finished product with low dielectric coefficient.
In order to further understand the feature of the invention, the operational technique and expected effects and how to use the invention is to be described.
The method for forming a porous material is herein applied to chip package for collating different proportions and mixing modes to put forward results for studying pore-sealing effects.
While the preferred embodiment of the invention has been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications that may fall within the spirit and scope of the invention.
