Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
1999-04-22
2001-10-09
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C252S079100, C252S079200, C051S306000, C051S308000, C051S309000
Reexamination Certificate
active
06300249
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
This invention relates to a polishing compound used for the surface polishing of the semiconductor substrate composed by a silicon wafer or a wafer of compound semiconductor, a method for preparation of said polishing compound and a polishing method by use of said polishing compound. More in detail relates to the polishing compound having buffer action and large electrical conductivity.
2. Description of the Prior Art
Usually, as the polishing compound which processes the surface of work-piece of semiconductor substrate such as a silicon wafer or a wafer of compound semiconductor (hereinafter shortened to wafers), a suspension in which fine particles of silicon oxide or hydrate of it are dispersed by colloidal state, so-called colloidal silica, is commonly used. At the actual polishing use, a work-piece is placed on the surface of a platen whose surface is tightly covered with a polishing pad composed of a foamed plastic or a suede type synthetic leather, and press the work-piece against the platen which is rotated by the constant speed and by the constant supply of the polishing compound. The term of polishing of this invention indicates a pre-polishing or a polishing process of wafers which are processed by a lapping process and then by an etching process to obtain a mirror finished surface, and a CMP (chemical-mechanical polishing) process of a device substrate.
For the pre-polishing process, a double sided polishing machine having an upper and a lower platen whose surface are covered by a thin layer of non-woven cloth is commonly used, meanwhile for the polishing process, a double sided polishing machine or a single sided polishing machine whose surfaces are covered by a thin layer of polishing pad composed of a foamed plastic or a suede type synthetic leather is commonly used. And, for the CMP process, a single sided polishing machine whose surface is covered by a thin layer of polishing pad composed by a slightly hard type foamed plastic is commonly used. At the actual use, the polishing is carried out by pressing the work-piece against the platen which rotates by constant speed, and providing the aqueous dispersion of polishing compound containing fine particles of silicon oxide.
As the polishing compound, the aqueous dispersion prepared by dispersing the fine particles of colloidal silica in an alkaline solution as disclosed in U.S. Pat. No. 3,328,141 is commonly used. The pre-polishing and polishing process are different from the previous process based on so-called mechanical processing which uses for instance a diamond grinding stone or hard abrasives of aluminum oxide. The feature of the pre-polishing and polishing process is to utilize the chemical effect of alkali to a silicon wafer, concretely utilize a corroding effect of alkali to a silicon wafer. That is, by the corroding effect of alkali, a thin soft corrosion layer is formed on the surface of a silicon wafer. The formed corrosion layer is removed by a mechanical action of fine particles of colloidal silica, thus the polishing is progressed. As mentioned above, since the polishing is progressed by the chemical action of alkaline component contained in the solution, it is necessary to maintain pH of the solution of polishing compound within the region bigger than 7. That is, when pH of the solution becomes closer to 7 which indicates the neutral region, the chemical action becomes weak and the removing rate falls down. Further, when pH of the solution becomes closed to 14 which indicates strong alkali region, the chemical action becomes strong and the removing rate is improved.
Therefore, in a case of this kind of polishing, the chemical and physical feature of the solution of polishing compound is very important. That is, the surface of the silicon wafer is corroded by an alkaline component and a thin corrosion layer is formed. The thickness and the hardness of the thin corrosion layer is largely effected by features of the solution of polishing compound. Since the electro chemical feature of the solution of polishing compound have strong influence to the thickness and the hardness, it is very important to keep pH of the solution in a stabilized region. If pH of the solution is easily affected by a change of external conditions such as heat, contact with outside air or contamination from outside, thickness of the layer, speed for corroding, consistency of the layer and removing speed of the layer fluctuate delicately, and it is difficult to expect a precise and a homogeneous polishing results, because. Further, since said corrosion layer is removed by the mechanical action of the particles of colloidal silicon oxide abrasives contained in polishing compound, it is necessary that these particleshave adequate diameter and not be easily broken or not to cohere and form gel. That is, particles of silicon oxide remove the corrosion layer formed by an alkaline component effectively by a mechanical action. Therefore, the polishing compound must not a compound which gives bad influence to the mirror finished surface after the corrosion layer is removed.
Up to the present, many kinds of compound are proposed as a polishing compounde of a silicone wafer. For instance, silica sol and silica gel are proposed as a polishing compound in U.S. Pat. No. 3,170,273. Further, the technique that the removing speed can be improved by adjusting pH of the colloidal solution within the range from 10.5 to 12.5 is disclosed in U.S. Pat. No. 3,328,141. In U.S. Pat. No. 4,169,337, the technique to add amines in a polishing compound is disclosed. In Japanese Patent Laid-Open Publication 2-158684, a polishing compound composed by water, colloidal silica, water soluble polymer of bibber than 100,000 molecular weight and water soluble salts is disclosed. Further, in Japanese Patent Laid-Open Publication 5-154760, a method for polishing by the use of a polishing compound containing 10~80 wt. % of piperazine which is a kind of water soluble amines to silica of silica gel or silica sol is disclosed. The important point of these disclosed methods is to improve the dispersing ability of a polishing compound and to improve the stability of polishing force by adding many kinds of additives to an alkaline base solution in which fine abrasives of colloidal silica or silica sol are dispersed, and is not to improve the removal speed of the conventional polishing compound.
Since a pre-polishing or a polishing process basically uses above mentioned polishing compound, the polishing speed is slow and productivity is not sufficient, further, since pH is changeable because it is easily affected by external conditions, polishing force lacks of stability. Namely, these pre-polishing or polishing processes can be said as a process which takes long time and as a troublesome process, and can not be said as a complete method. However, with advancement of integrated circuit and improvement of wafer diameter, a higher precise accuracy requirement for surface flatness of a silicon wafer or a substrate of semiconductor device is becoming important. Further, to improve the productivity, a polishing compound and a polishing method which accomplishes the higher removal speed are earnestly expected.
BRIEF SUMMARY OF THE INVENTION
The inventors of this invention have carried out an intensive study to overcome the above mentioned problems which conventional polishing compound has, and have found that the use of alkaline aqueous solution of colloidal silica containing fine particles of silicon oxide which has pH buffer action and have high electric conductivity as the solution of polishing compound, can accomplish the stabilized polishing of higher removal rate and have accomplished the present invention. The object of this invention is to provide a polishing compound having constant and stabilized pH value, higher removal speed and a feature which is stabilized at the recycling use, further to provide a method to prepare said polishing compound. And, the another object of this invention is to provide a polish
Ogawa Yoshihisa
Tanaka Hiroaki
Yoshida Akitoshi
Deo Duy-Vu
SpeedFam Co Ltd
Utech Benjamin L.
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