Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1998-12-22
2001-04-03
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S421000
Reexamination Certificate
active
06210502
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the processing methods for the high-pure titanium, and more specifically, to the working methods for the high-pure titanium suitable for a titanium target for sputtering. In more detail, the invention relates to the methods of a cold plastic working for the titanium material (raw material) having a purity higher than 4N so as to obtain the titanium material having a fine grain size.
In manufacturing semiconductor devices, sputtering, vacuum deposition or ion plating is employed for forming a circuit material or a barrier metal in the form of a film on a semiconductor element. Of those methods, sputtering is generally used in practice. In sputtering, ions such as argon ions impact on a metallic target, thereby ejecting the metal ions, and which are piled on a base plate, resulting in forming a film. Many kinds of metallic targets are known, and among these, titanium targets are widely used for the semiconductor devices.
In order to produce a uniform thickness of the film on the semiconductor element, and to control the occurrence of so-called “particles” (which means a phenomenon that some large particles adhere on the film surface in spattering), the grain size of titanium targets must be about 20 &mgr;m or smaller. After preparing the titanium material by forging and rolling, the grain size is controlled by recrystallization and annealing to satisfy the requirements for the titanium target mentioned above. For example, Japanese Patent Unexamined Publication (Kokai) No. 8-232061 discloses a method that the matrix of a titanium ingot was broken by drawing and upsetting in the temperature higher than the transformation temperature (882° C.), and performing the same forging as mentioned above in the temperature lower than that of the transformation. The disclosed method allows the matrix to accumulate working strain so as to reduce the grain size in the matrix. In addition, Japanese Patent Unexamined Publication (Kokai) No. 8-269698 and No. 8-333676 discloses a method that the grain size in the titanium targets are reduced by rolling or forging in the temperature lower than that of the transformation.
The conventional methods disclosed in the publications for reducing the grain size require at least a heating equipment in forging and/or rolling at a temperature from 400 to 800° C., leading to the high operation cost regarding such as an electric consumption, thereby having disadvantages in view of the cost. In addition, the methods mentioned above accompany the scale growth on the surface of the titanium material, and the additional descaling process, which complicates the subsequent process.
An object of the invention is to provide a method for processing the high-pure titanium having an average grain size of 50 &mgr;m or smaller, preferably of 40 &mgr;m or smaller, and more preferably of 35 &mgr;m or smaller, in which the scale growth is prevented and at comparatively low cost.
DISCLOSURE OF THE INVENTION
The inventors forged the high-pure titanium having a purity of 4N (99.99%, except for gas inclusions) and an amount of other gas impurities of O, N and C less than 600 ppm in the temperature lower than that of the transformation, and studied the matrix structure of the resultant material. As a result, they have found that;
(a) the cracks are not found through cold forging;
(b) the grain size distribution of the titanium material obtained by annealing the forged material is uniform;
(c) the grain size is reduced in the range smaller than 35 &mgr;m or further 20 &mgr;m;
(d) the scale growth is prevented on the surface of the titanium material.
The invention is completed based on the above-mentioned studies. The invention provides a processing method for the high-pure titanium wherein the cold plastic working are performed for the titanium raw material, having a purity of 4N or higher (hereinafter referred to as “titanium raw material”). It should be noted that the term “cold” refers to the temperature of the titanium raw material before forging, and the temperature moves in the range from room temperature to 300° C. The temperature elevation of the titanium material itself does not affect the effects of the invention.
The details of the invention are explained hereinafter. The titanium raw material employed for the plastic working is a high-pure titanium having a purity of 4N or higher. The resulting material obtained by the plastic working is referred to as “titanium worked material”, specifically the material obtained by the forging is referred to as “titanium forged material”. The essential reason the plastic working can be easily performed on the titanium raw material at room temperature or near the room temperature before forging is that the titanium raw material has a workability sufficient for the cold working when the impurity content thereof is in the above-mentioned range.
Therefore, the invention offers better effects or advantages as the purity of the titanium raw material increases. The titanium raw material can be used for the ductile materials, wire rods and targets. When further uniformity of grain size distribution are required for the titanium worked material used for the targets, warm forging may be preferable after cold forging so as to obtain titanium raw materials having a more uniform grain size distribution. It should be noted that the term “warm” refers to the temperature before the forging of the titanium raw material and the temperature ranges from 300 to 600° C., in which a suitable temperature depends on the condition of the titanium raw material.
The processing method for the high-pure titanium of the invention will be explained in detail hereinafter.
The invention uses the high-pure titanium having a purity of 4N or higher (99.99%, except for gas inclusions) as a raw material. That is, when the oxygen content is high, the titanium raw material cannot offer the sufficient workability, so that the worked titanium materials having the uniform grain size cannot be obtained even if the titanium raw material has a high purity. Therefore, the total amount of the gas impurities such as O, N and C is preferably less than 600 ppm, and the amount of oxygen is preferably less than 500 ppm.
The titanium raw material accumulates the working strain by the plastic working in the low temperature, namely in the range from room temperature to 300° C., and simultaneously is formed into a titanium material having a suitable shape (for example a plate) corresponding to the various applications. The plastic working according to the invention includes working methods such as forging, plate milling, rod milling, wire drawing, drawing, upsetting and the like. The forging is the most suitable for producing the titanium worked materials used for targets.
When titanium ingots or billets are used as a titanium raw material, the raw material is generally heated up to the temperatures of 400° C. or higher in forging. The titanium raw material of the invention has a good workability since it has a purity of 4N or higher, so that the forging is easily applicable at the temperature of 300° C. or lower.
When the titanium raw material at room temperature is forged, the material itself may be heated up to the temperature of 300° C. or higher in some situations. When the titanium material is heated up to the temperature of 300° C. or higher in forging, the working strain accumulated in the titanium raw material is liberated, so that the grain size is not reduced by the subsequent annealing. Therefore, the temperature elevation of the titanium raw material should be restricted and the temperature should be maintained in the temperature of 300° C. or lower to reduce the grain size through the subsequent annealing. In order to restrict the temperature elevation, the titanium raw material in forging may be cooled, or the forging die may be cooled by air.
The titanium forged material obtained by the forging is annealed in the temperature range from 400 to 600° C., so that the titanium forged material of the invention is produced. The obt
Oliff & Berridg,e PLC
Oltmans Andrew L.
Sheehan John
Toho Titanium Co., Ltd.
LandOfFree
Processing method for high-pure titanium does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Processing method for high-pure titanium, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Processing method for high-pure titanium will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2498999