Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
1999-10-01
2001-08-07
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C450S041000, C051S304000
Reexamination Certificate
active
06270393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an abrasive slurry and a preparation process of the abrasive slurry, which is suitable for the abrasion of thin film magnetic head for use in a hard disc drive (HDD), (particularly composite thin film magnetic head), a semiconductor integrated circuit, etc.
2. Description of the Related Art
With the enhancement of the recording capacity of HDD, the recent trend is more composite thin film magnetic heads performing magnetic induction writing by “write-inductive-element” and magnetic resistance reading by “read-MR-element” in combination (so-called MR head) to be used than magnetic induction thin film magnetic heads.
Under the circumstances, the surface roughness of the substrate on which MR elements are to be formed has been noted as a property governing the characteristics of magnetic resistance element (MR element) made of thin film laminate. JP-A-9-54914 (The term “JP-A” as used herein means an “unexamined Japanese patent publication (kokai)” ) proposes that the surface of alumina as underlayer of MR be slightly abraded.
Further, JP-A-8-96237 proposes that abrasion be conducted to eliminate undulation on the surface of upper shield due to the difference of thickness of substrate layer and the final step of abrasion involve the abrasion of Al
2
O
3
and NiFe.
These conventional art techniques disclose that abrasion can be used as a method for creating surface. However, it is necessary that the composite thin film magnetic head, e.g., alumina as insulating layer and NiFe constituting the magnetic circuit be abraded at the same time. There is no specific disclosure concerning an abrasive slurry which can be used to perform abrasion satisfying the requirements that the difference in the level between the two components be kept to not more than 1,000 Å while keeping the surface roughness Max of not more than 100 Å and Ra of not more than 10 Å.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an abrasive slurry for use in the leveling abrasion in the course of the formation of a thin film magnetic head, a semiconductor integrated circuit, etc., which can satisfy the requirements for surface roughness of composite material and is adapted to keep the difference in the level between different materials.
The present invention provides a process for preparation of an abrasive slurry, comprises the steps of: preparing a solution of an inorganic salt selected from the group consisting of water-soluble inorganic aluminum salt and nickel salt and a solution of water-soluble chelating agent; mixing the two solutions; holding the mixed solution for 1 day or longer to precipitate hardly water-soluble crystal; removing the hardly water-soluble crystal from the solution; and mixing the solution with an alumina grain having an average particle diameter of from 0.05 to 1 &mgr;m, an abrasive oil and a required amount of an aqueous dispersant.
Thus, an abrasive slurry according to the present invention comprises: an alumina grain having an average particle diameter of from 0.05 to 1 &mgr;m in an amount of from 0.1 to 10% by weight; an inorganic salt selected from the group consisting of water-soluble inorganic aluminum salt and nickel salt in an amount of from 0.1 to 3% by weight; a water-soluble chelating agent in an amount of from 0.1 to 3% by weight; an abrasive oil in an amount of from 0.1 to 10% by weight; and a hardly water-soluble chelate aluminum salt or chelate nickel salt of not more than 0.1% by weight. The abrasive slurry is used for abrading an insulation layer of a semiconductor integrated circuit and a magnetic thin film head while they are produced.
The abrasive slurry according to the present invention comprises a hardly water-soluble chelate aluminum salt or chelate nickel salt causing scratch incorporated therein in a limited amount of not more than 0.1% by weight even after one month of holding after preparation. Accordingly, alumina and NiFe in composite magnetic heads abraded with the abrasive slurry according to the present invention are not found microscratched. Further, the use of an abrasive grain having an average particle diameter of from 0.05 to 1 &mgr;m makes it possible to improve the flatness of the surface of Wf.
The present invention further provides a process for abrading a thin film abraded by an abrasive slurry comprising: an alumina grain having an average particle diameter of from 0.05 to 1 &mgr;m in an amount of from 0.1 to 10% by weight; an inorganic salt selected from the group consisting of water-soluble inorganic aluminum salt and nickel salt in an amount of from 0.1 to 3% by weight; a water-soluble chelating agent in an amount of from 0.1 to 3% by weight; and an abrasive oil in an amount of from 0.1 to 10% by weight; wherein a content of said hardly water-soluble chelate aluminum salt or chelate nickel salt in said water-soluble abrasive slurry is not more than 0.1% by weight. This process can be applied to a process for abrading a semiconductor integrated circuit, a process for abrading a magnetic thin film head, and the like.
Incidentally, in the present invention, the term of “abrade” includes polish, grind, whet and the like. For example, CMP (Chemical Mechanical Polishing) is one of polishing methods.
REFERENCES:
patent: 4956015 (1990-09-01), Okajima et al.
patent: 6039775 (2000-03-01), Ho et al.
patent: 8-96237 (1996-04-01), None
patent: 9-54914 (1997-02-01), None
Kubota Toshio
Yamada Tsutomu
Eley Timothy V.
Oliff & Berridg,e PLC
TDK Corporation
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