Method of producing target material of Mo alloy
Disclosed is a method of producing a target material of a Mo alloy, which includes the steps of (a) preparing a green compact by compressing a raw material powder blend consisting of a Mo powder having an average particle size of not more than 20 μm and a transition metal powder having an average particle size of not more than 500 μm; (b) pulverizing the green compact to produce a secondary powder having an average particle size of from not less than an average particle size of the raw material powder blend to not more than 10 mm; (c) filling the secondary powder into a container for pressurizing; and (d) subjecting the secondary powder with the container for pressurizing to sintering under pressure thereby obtaining a sintered body of the target material.
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The present invention relates to a method of producing a target material of a Mo alloy by a powder sintering method.
At present, a film of a refractory metal such as Mo having low electric resistance is used for a thin film electrode, thin film wiring and so on in a liquid crystal display (hereinafter referred to as LCD), which thin metal film is generally formed from a target material for sputtering. In recent years, there is a trend toward larger size LCDs which accompany a demand for a larger size of the target material, particularly, a long size article having a length of not less than 1 m or a large size article having a sputtering area of more than 1 m2.
Conventionally, in response to the trend toward a larger size of the sputtering area, there have been proposed several ways including a method of bonding a number of raw target material sections to a backing plate. However, according to such a method of using the number of bonded raw target material sections, there arises a problem of particles contained in a deposited film due to abnormal spatters of the material which are generated during sputtering process because of a clearance existing between the respective adjacent bonded raw target material sections. In order to overcome such a problem, there has been a need for using an integrated raw target material member.
Hitherto, while there has been used a powder sintering process in order to produce a target material of a refractory metal such as Mo, when producing such an integrated raw target material member having a larger size, important is how to obtain a high density and a larger size material. There are various types of the powder sintering process, which include a hot isostatic pressing method (herein below referred to as HIP). According to the HIP method, it is possible to apply a high pressing pressure three-dimensionally to a raw powder, whereby advantageously enabling it to have a high and uniform density as compared with a hot pressing method according to which the pressing pressure can be applied to the raw powder only two-dimensionally.
In the HIP method, it is necessary to fill a raw powder to be sintered into a container for pressurizing efficiently and uniformly prior to pressurizing the raw powder. Thus, there has been proposed some methods how to apply a pressurizing pressure to the packed raw material powder, which can be seen JP-A-2002-167669 and JP-A-2003-342720, for example.
However, even by the method of producing a Mo or Mo alloy target material disclosed in the above patent publications, when producing the target material of a Mo alloy containing an additive element(s), there arises a problem that a segregation of the additive element(s) is liable to occur, which problem cannot be solved by the above method. In addition, there arises also a problem of an unfavorable shape-change of a pressurized and sintered body.
SUMMARY OF THE INVENTIONAn object of the present invention is to provide a method of producing a target material of a Mo alloy, according to which method a packing density of a raw material powder in a container for pressurizing is improved, an unfavorable shape-change of a pressurized and sintered body is reduced, and a segregation of material components is decreased.
The present inventors examined various methods of producing the target material of the Mo alloy, and found that the above problems can be solved by controlling a particle size of the raw material powder blend which is filled into the container for pressurizing whereby attaining the present invention.
According to one aspect of the invention, there is provided a method of producing a target material of a Mo alloy, which comprises the steps of (a) preparing a green compact by compressing a raw material powder blend consisting of a Mo powder having an average particle size of not more than 20 μm and a transition metal powder having an average particle size of not more than 500 μm; (b) pulverizing the green compact to produce a secondary powder having an average particle size of from not less than an average particle size of the raw material powder blend to not more than 10 mm; (c) filling the secondary powder into a container for pressurizing; and (d) subjecting the secondary powder with the container for pressurizing to sintering under pressure thereby obtaining a sintered body of the target material.
According to one embodiment of the above method, the transition metal is any one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr and W.
According to another embodiment of the above method, after the process (d), the sintered body being enveloped in the container is subjected to hot plastic working.
According to still another embodiment of the above method, after the step (d), the sintered body being enveloped with the container is subjected to hot plastic working followed by recrystallization heat treatment.
The raw material powder blend is preferably compressed by cold isostatic pressing. More preferably the compression is conducted under pressure of not less than 100 MPa.
Preferably the green compact has a relative density of not less than 50%.
The sintering under pressure is preferably carried out by the HIP method. Preferable conditions of the HIP method are of a temperature of 1000 to 1500° C. and a pressure of not less than 100 MPa. Preferably the sintered body has a relative density of not less than 98%.
Preferably the container filled with the secondary powder has an inner space of which maximum length is not less than 1000 mm.
Preferably the container filled with the secondary powder is of a metal capsule having a substantially rectangular parallelepiped form one of which face is used as an inlet opening for filling the secondary powder, the face being opposite to a bottom wall of the container forming the maximum depth, and which inner space has a maximum side length of not less than 1000 mm.
Preferably the hot plastic working is of plural times of plastic working under the conditions of a reduction ratio of 2 to 50% and a temperature of 500 to 1500° C.
The recrystallization heat treatment is carried out preferably at a temperature of 1000 to 1500° C.
Preferably the sintered body is sliced to obtain a plurality of tabular targets so as to maintain a maximum side length of the sintered body.
According to the present invention, it is possible to achieve the above object that a packing density of a raw material powder blend in a container for pressurizing is improved, an unfavorable shape-change of a pressurized and sintered body is reduced, and a segregation of material components is decreased.
BRIEF DESCRIPTION OF THE DRAWING
A key aspect of the invention resides in the process of obtaining the green compact by compressing the raw material powder blend consisting of the Mo powder and the transition metal powder, subsequently pulverizing the green compact to produce the secondary powder having an average particle size of from not less than an average particle size of the raw material powder blend to not more than 10 mm, and filling the secondary powder into the container for pressurizing, whereby improving a packing ratio of the secondary powder in the container and decreasing a segregation of material components.
In the case of producing a target material of a Mo alloy by powder sintering with utilization of a container for pressurizing, usually a fine Mo powder is used. However, when the Mo powder is filled in the container, the distribution of powder components in the container is liable to vary, because the Mo powder has high liability of agglomeration and is inferior in fluidity.
In this regard, the present inventors found after full consideration that it is possible to improve the packing ratio of the raw material powder blend in the container by adjusting a particle size of the raw material powder blend so as to be large in some degree. On the other hand, in the case where the Mo powder and the other transition metal powder are mixed, a segregation of material components is liable to occur in connection with reasons of the liability of agglomeration of the powder, the fluidity of the powder and so on. Accordingly, the present inventors found also that it is effective for solving the problem by obtaining the green compact by compressing the raw material powder blend consisting of the Mo powder and the transition metal powder, subsequently pulverizing the green compact to produce the secondary powder, and filling the secondary powder into the container for pressurizing, whereby improving the segregation of the raw material powder blend in the container for pressurizing and also the other segregation of the material components of the sintered body in the container for pressurizing.
Herein below, there will be provided details of the invention method.
A common Mo powder has a fine particle size, which is of an average particle size of not more than 20 μm, because it is produced chemically. On the other hand, transition metal powders of Nb, Cr, Ti and so on have a comparatively large particle size, which is of an average particle size of not more than 500 μm, because such powders are often produced by pulverizing a cast ingot. In the present invention, the green compact is produced by compressing the fine raw material powder blend, and subsequently the green compact is subjected to pulverizing to obtain the secondary powder, having an average particle size of from not less than an average particle size of the raw material powder blend to not more than 10 mm, is produced. The secondary powder is filled into a container for pressurizing and subsequently subjected to sintering under pressure, thereby obtaining the sintered body to be used for a raw material of the target material.
The reason why the lower limit of the average particle size of the secondary powder should be not less than the average particle size of the raw material powder blend is that it will make no sense to produce and pulverize the green compact in order to obtain a secondary powder having an average particle size less than the average particle size of the raw material powder blend. The reason why the upper limit of the average particle size of the secondary powder should be not more than 10 mm is that there will be appeared clear lines of particle boundaries in the metal structure of a sintered body produced from a secondary powder having an average particle size exceeding 10 mm will have a clear boundary line, which metal structure has a kind of patterned appearance. Such a sintered body implies a risk of a locally high oxygen amount because particle boundaries are in contact with the atmosphere preferentially. Thus, the average particle size should be not more than 10 mm in order to make the particle boundaries not to be observed in appearance and also in order to make the particle size of the secondary powder as uniform as possible.
In the present invention, while the Mo and the transition metal powders are blended, important is to produce the green compact and pulverize it, so as to have the average particle size of not more than 10 mm, in order to restrain the segregation of the transition metal powder blended with the Mo powder.
Herein, there is provided a definition that, in a particle size distribution of the Mo powder, the transition metal powder, the raw material powder blend, or the secondary powder, a size (D50) of particles, of which number is 50% of a total number of the particles, is referred to as the average particle (or grain) size.
Preferably, the Mo powder to be compressed an average particle size of not more than 10 μm, and the secondary powder obtained from the green compact by pulverizing has an average particle size of not more than 5 mm.
The reason is that the smaller the particle size is, the higher a relative density of the sintered body can be obtained easily. From a viewpoint of improving the packing density of a metal powder in the container for pressurizing, it is effective to use a larger particle size of the secondary powder. However, from a viewpoint of a sintering property, preferably the raw material powder with a high density has a smaller particle size. Especially, with regard to Mo which is a main component of the sintered body produced by the invention method, since it is a refractory metal and has generally a high diffusion temperature, preferably the raw material powder blend in the container is processed at high temperature while increasing contact areas of the particles of the raw material. Thus, preferably the average particle size of the Mo powder is not more than 10 μm. The reason why the secondary powder has preferably the average particle size of not more than 5 mm is that by such a particle size, it is possible to decrease local concentration of the oxygen amount, and to enhance the dispersion of an additive element(s) in Mo alloy. More preferably, the average particle size of the secondary powder is not more than 0.5 to 3 mm.
Further, the reason why the transition metal powder blended with the Mo powder has the average particle size of not more than 500 μm is that, if the average particle size exceeds this value, the segregation of component in the target material cannot be reduced.
With regard to the green compact, preferably it is compressed so as to have a relative density of not less than 50% in order to maintain the particle size of the secondary powder to be filled into the container for pressurizing.
The raw material, of which primary component is Mo, is compressed preferably by a cold isostatic pressing method (herein below referred to as CIP) in which preferably a pressure not less than 100 MPa is applied to the raw material powder in order to enhance the green compact to have relative density of not less than 50%.
Sintering of the raw material under pressure is preferably carried out by the HIP method because it is possible to three dimensionally apply a high pressure to the raw material during sintering. Desirable conditions of the HIP method are a temperature of 1000 to 1500° C. and a pressure of not less than 100 MPa. If the HIP method is carried out under a pressure of less than 100 MPa at a temperature of less than 1000° C., it is hard to produce the sintered body having a relative density of not less than 98% which is required to the target material. On the other hand, while it is preferable to conduct the sintering at a temperature as high as possible in order to obtain the sintered body of which primary component is Mo, the processing temperature of the HIP method is restricted by a material type of the container for pressurizing and an equipment. In a usual HIP apparatus, an upper limit of the working temperature is approximately 1500° C. A higher temperature than 1500° C. will not be practical.
With regard to a size of the container for pressurizing, while there are problems that, when using a larger size container, the packing density is hardly improved and the component segregation is liable to occur, the invention method is suitable for producing a large size target material which requires to use the container for pressurizing which maximum length is not less than 1000 mm. Regarding a way of filling the powder into the container, in order to improve the packing density with utilization of a specific gravity of the powder, it is more preferable to use the container for pressurizing which has a substantially rectangular parallelepiped form one of which face is used as an inlet opening for filling the secondary powder, the face being opposite to a bottom wall of the container forming the maximum depth, and which inner space has a maximum length of not less than 1000 mm. After filling the powder into the container, it is desirable to seal the container by means of a top lid while pressing the top lid against the powder in the container. This is because an extra space can be eliminated from a top region of the powder in the container by such pressing the lid against the powder, upon which region no effect by the specific gravity of the powder is exerted, whereby attaining a uniform and dense packing state of the powder in the container from the top region to the bottom region.
According to one feature of the invention method, the sintered body being enveloped in the container is subjected to hot plastic working, since such working is suitable to make the sintered body to have a much larger size.
One reason why the hot plastic working of the sintered body is conducted together with the container is that, if the sintered body is subjected to the working with its surface as exposed, there is a risk of a surface contamination of the sintered body. From another viewpoint, according to such a working way of the sintered body with the container, it is possible to omit one process of removing the container from the sintered body thereby enabling to reduce the production cost.
Desirably the hot plastic working is conducted plural times each with a reduction ratio of 2 to 50% while maintaining the sintered body at a temperature of 500 to 1500° C.
If the temperature is lower than 500° C., a working load applied to the sintered body must be increased due to lower ductility thereof whereby arising a problem of the productivity. On the other hand, if the temperature exceeds 1500° C., there are a risk that the container is melted and a problem that crystal particles of the sintered body are coarsened. If the reduction ratio of the hot plastic working exceeds 50%, there arise problems that cracking and inner defects occur in the sintered body. If the reduction ratio of the hot plastic working is lower than 2%, the sintered body is hardly deformed thereby arising a waste production cost problem. Further, in the case where a high reduction working as a whole is required for the sintered body, plural times of working under the above conditions of the temperature and the reduction ratio are effective in order to avoid occurrence of cracking or other defects.
According to another feature of the invention method, after hot plastic working, the sintered body is subjected to recrystallization heat treatment. The work as rolled has a fiber metal structure, a degree of which structure differs every section of the work, especially at a surface portion and a central portion in the thickness direction of the work. Preferably the target material should have a uniform crystal structure, since a non-uniform crystal structure of the target material adversely affect the uniformity of a film deposited by sputtering. Thus, preferably the work as rolled is subjected to homogenization treatment with utilization of the recrystallization phenomenon in order to make its crystal structure uniform.
The recrystallization heat treatment is preferably conducted at a temperature of 1000 to 1500° C. If the temperature is not higher than 1000° C., there is a high possibility that the fiber metal structure will remain after the heat treatment because of properties of the chemical composition with a primary component of Mo. If the temperature exceeds 1500° C., there will occur partially coarsening of crystal particles at a surface region that has previously suffered high reduction working.
According to still another feature of the invention method, the sintered bodies, which include those merely sintered, subjected to hot plastic working and subjected to both of hot plastic working and recrystallization heat treatment, are sliced to obtain a plurality of tabular targets so as to maintain a maximum side length of the respective sintered body. This method is advantageous in the point that a number of target material are produced by only one time pressurizing and sintering process in accordance with a need for a large sized target material, whereby reducing the production cost.
Desirably the raw powder material in the invention method contains not less than 50 atomic % Mo. Taking into consideration that the Mo powder, having high agglomeration property, is hard to be filled uniformly into the container for pressurizing, it is very effective to use the raw powder material in the invention method in order to obtain a target material containing not less than 50 atomic % Mo.
Herein below, there will be provided a description of some Examples with regard to the invention method.
EXAMPLE 1There were prepared a Mo powder having an average particle size of 12 μm, a W (tungsten) powder having an average particle size of 12 μm, a Nb powder having an average particle size of 100 μm, a Ti powder having an average particle size of 100 μm, and a Zr powder having an average particle size of 100 μm.
Specimen Nos. 1 to 6 target materials shown in Table 1 were produced by the following process, which are of the present invention.
(1) In order to produce each of the specimens, given amounts in atomic % of the Mo powder and any one of the transition metal powder were checkweighed.
(2) The checkweighed powders were blended for 10 minutes with utilization of a V-type blender to obtain a raw material powder.
(3) The raw material powder was compressed under pressure of 265 MPa by a CIP machine to form a green compact.
(4) The green compact was pulverized with utilization of a jaw crusher and a disc mill to produce a secondary powder.
(5) The secondary powder was blended in a V-type blender for 10 minutes and subsequently filled into a container for pressurizing, which is made of low carbon soft steel and has an inner space dimension of a thickness of 100 mm, a width of 1000 mm and a height of 1300 mm. After filling the secondary powder, a top lid with a deaerating port was welded to the container in order to close an inlet opening thereof.
(6) The container filled with the secondary powder was subjected to a degassing process under vacuum at a temperature of 450° C. and subsequently the deaerating port was sealed. Thereafter, the secondary powder was sintered under pressure together with the container by means of a HIP machine. Operational conditions of the HIP machine were of a temperature of 1250° C., a pressure of 150 MPa and an operation time of 5 hours.
(7) The thus obtained sintered body was sliced and machined to produce six tabular target materials each having a rectangular parallelepiped shape of which dimension is of a thickness of 6 mm, a width of 810 mm and a length of 950 mm.
(8) A packing density of the secondary powder in the container was measured, which value is shown in Table 1.
(9) Specimens were taken from the green compact and the sintered body to examine a relative density, respectively, by an Archimedes method, which values are shown in Table 1.
Further, in order to produce Reference Specimen Nos. 7 and 8 target materials shown in Table 1, a Mo powder having an average particle size of 6 μm and a Nb powder having an average particle size of 100 μm were prepared, and processed to obtain sintered bodies by the same manner as described above. Each of the thus obtained sintered bodies was sliced and machined to produce six tabular target materials each having a rectangular parallelepiped shape of which dimension is of a thickness of 6 mm, a width of 810 mm and a length of 950 mm.
A packing density of the each secondary powder in the container was measured, which value is shown in Table 1.
Specimens were taken from the green compact and the sintered body to examine a relative density, respectively, by an Archimedes method, which values are shown in Table 1.
In order to produce Comparative Specimen Nos. 9 and 10 target materials shown in Table 1, a Mo powder and a Nb powder were prepared. Comparative Specimen Nos. 9 and 10 target materials were produced by the following process.
(1) In order to produce Comparative Specimen Nos. 9 and 10, given amounts in atomic % of the Mo powder and the Nb metal powder were checkweighed, respectively.
(2) The checkweighed powders were blended for 10 minutes with utilization of a V-type blender to obtain a raw material powder for each of Comparative Specimen Nos. 9 and 10.
(3) The raw material powder for each of Comparative Specimen Nos. 9 and 10 was filled into a container for pressurizing without subjecting to the compression treatment, which is made of low carbon steel.
(4) After filling the raw powder, a top lid with deaerating port was welded to the container in order to close an inlet opening thereof.
(5) The container filled with each of the raw powders was subjected to a deaerating process under vacuum at a temperature of 450° C. and the deaerating port was sealed. Thereafter, the respective powder was sintered under pressure together with the container by means of a HIP machine. Operational conditions of the HIP machine were of a temperature of 1250° C., a pressure of 150 MPa and an operation time of 5 hours.
(6) Each of the thus obtained sintered bodies was sliced and machined to produce three tabular target materials each having a rectangular parallelepiped shape of which dimension is of a thickness of 6 mm, a width of 610 mm and a length of 710 mm.
(7) A packing density of each of the powders for Comparative Specimen Nos. 9 and 10 in the container was measured, which value is shown in Table 1.
(8) Specimens were taken from the respective sintered body to examine a relative density by an Archimedes method, which value is shown in Table 1.
With regard to all Specimen Nos. 1 to 10 target materials, a form variation of the respective sintered body was evaluated, which variation was occurred during sintering.
As shown in Table 1, in Invention and Reference Specimen Nos. 1 to 8, since a secondary powder, having the average particle size of not more than 10 mm, was produced by pulverizing a green compact produced by compressing a raw material powder, respectively, the packing densities of the secondary powders in Specimen Nos. 1 to 8 are of not less than 52% which is significantly high. From this, it is appreciated that the target material can be produced with a satisfactory yield since degrees of a dimensional contraction and a form variation of the sintered body are reduced by virtue of a high packing density.
Seeing Invention Specimen No. 8 in Table 1, it is appreciated that with utilization of a raw material powder blend having an average particle size of not more than 10 μm, and a secondary powder having an average particle size of not more than 1 mm, the packing density and the relative density are significantly increased.
On the other hand, with regard to Comparative Specimen No. 9 in which the raw material powder blend was filled directly without compression into the container for pressurizing and subjected to sintering under pressure, an yield is inferior when producing the target material because of a low packing density of not more than 40%, and because a dimensional contraction and a form variation of the sintered body are large. Further, even if a container with the same size as the other cases is used, there is a risk that a target material with an expected size can not be produced because of a large dimensional contraction and a large form variation of the sintered body.
A sintered body, having the same chemical composition and the same size as those of Invention Specimen No. 2 shown in Example 1, was produced by the same manner as the case of Invention Specimen No. 2, and after the HIP process it is subjected to hot rolling thrice together with a container for pressurizing under conditions of a temperature of 1150° C. and a reduction ratio of not more than 50%. An expected size of a target material is of a width of 1500 mm and a length of 1800 mm. A result of rolling of the sintered body is shown in Table 2.
As will be seen from Table 2, by carrying out the rolling under conditions of a heating temperature of 500 to 1500° C. and a reduction ratio of 2 to 50%, a large size target raw material can be produced without occurrence of cracking.
It should be noted that while a sintered body was subjected to rolling at a temperature of 450° C., ductility of the sintered body cannot be maintained due to a low heating temperature, disadvantageously resulting in that rolling of a reduction ratio of a few percent had to be conducted cyclically.
EXAMPLE 3 The target material as hot-rolled in Example 2 was subjected to a recrystallization heat treatment in vacuum at temperatures of 900° C., 1150° C. and 1300° C., respectively. After the work is heated up to a heat treatment temperature, the temperature is held for one hour, and thereafter the work is cooled. Specimen Nos. 2-1-1 , 2-1-2 and 2-1-3 were taken from the three type works, respectively. Microstructures of the specimens were compared with one another with utilization an optical microscope with magnification of 100. The observation result is shown in Table 3. With regard to the specimens subjected to a recrystallization heat treatment at temperatures of 900° C. and 1300° C., respectively, there are provided photographs showing microstructures of the specimens with utilization of an optical microscope with magnification of 100 in
From Table 3,
Claims
1. A method of producing a target material of a Mo alloy, which comprises the steps of:
- (a) preparing a green compact by compressing a raw material powder blend consisting of a Mo powder having an average particle size of not more than 20 μm and a transition metal powder having an average particle size of not more than 500 μm;
- (b) pulverizing the green compact to produce a secondary powder having an average particle size of from not less than an average particle size of the raw material powder blend to not more than 10 mm;
- (c) filling the secondary powder into a container for pressurizing; and
- (d) subjecting the secondary powder with the container for pressurizing to sintering under pressure thereby obtaining a sintered body of the target material.
2. A method according to claim 1, wherein the transition metal is any one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr and W.
3. A method according to claim 1, wherein after the sintering process (d), the sintered body being enveloped in the container is subjected to hot plastic working.
4. A method according to claim 1, wherein the hot plastic working is of plural times of plastic working under the conditions of a reduction ratio of 2 to 50% and a temperature of 500 to 1500° C.
5. A method according to claim 1, wherein after the step (d), the sintered body being enveloped in the container is subjected to hot plastic working followed by recrystallization heat treatment.
6. A method according to claim 5, wherein the hot plastic working is of plural times of plastic working under the conditions of a reduction ratio of 2 to 50% and a temperature of 500 to 1500° C.
7. A method according to claim 6, wherein the recrystallization heat treatment is carried out at a temperature of 1000 to 1500° C.
8. A method according to claim 1, wherein the compression process in the step (a) is carried out by cold isostatic pressing under a pressure of not less than 100 MPa.
9. A method according to claim 1, wherein the sintering process in the sintering process (d) is carried out by hot isostatic pressing at a temperature of 1000 to 1500° C. under a pressure of not less than 100 MPa.
10. A method according to claim 1, wherein the container filled with the secondary powder is of a metal capsule having a substantially rectangular parallelepiped form one of which face is used as an inlet opening for filling the secondary powder, the face being opposite to a bottom wall of the container forming the maximum depth, and which inner space has a maximum length of not less than 1000 mm.
11. A method according to claim 10, wherein the sintered body is sliced to obtain a plurality of tabular targets so as to maintain a maximum side length of the sintered body.
Type: Application
Filed: Feb 25, 2005
Publication Date: Sep 1, 2005
Applicant:
Inventors: Katsunori Iwasaki (Yasugi), Keisuke Inoue (Yasugi), Norio Uemura (Yonago)
Application Number: 11/066,228
