WO2020090977A1 - Yttrium sputtering target and film-forming method using same - Google Patents

Abstract

Provided is a yttrium sputtering target characterized by having a maximum pore radius of 1 mm or less. Additionally, the number of pores existing on a cross-section of the yttrium sputtering target is preferably 0-2. Additionally, the maximum length of cracks is preferably 3 mm or less. Additionally, the tensile strength of the yttrium sputtering target is preferably 100 MPa or higher.

Description

Yttrium sputtering target and film forming method using the same

One aspect of the present invention relates to a yttrium sputtering target and a film forming method using the same.

Application of yttrium metal to electronic materials such as metal gate materials and high dielectric constant materials is under study. Further, yttrium oxide has good durability against plasma and chemicals. Therefore, it has been attempted to use the yttrium oxide film as a protective film of parts for plasma processing apparatuses.
Japanese Patent No. 6084464 (Patent Document 1) discloses a component for a plasma etching processing apparatus having a yttrium oxide coating. Patent Document 1 discloses an yttrium oxide coating film having a controlled crystal structure and the like. As a result, in Patent Document 1, the plasma resistance is improved. In Patent Document 1, a film is formed by injecting yttrium oxide powder at high speed using a plasma combustion flame. The plasma combustion flame requires a high temperature of about 10,000 ° C. Therefore, the equipment is expensive and safety measures are required.
A sputtering method is mentioned as a film forming method that does not use a plasma combustion flame. The sputtering method is a method in which a sputtering target is placed in a vacuum chamber and ionized particles are made to collide with the sputtering target. As a result, atoms or molecules on the surface (sputtering surface) of the sputtering target are repelled and a film is formed. A rare gas element or nitrogen is used for the ionized particles. Since the sputtering method does not use a plasma combustion flame, the equipment is relatively inexpensive. Further, since the film forming process is performed in the vacuum chamber, it is a relatively safe film forming method.
Japanese Patent No. 5738993 (Patent Document 2) discloses a high-purity yttrium sputtering target. In Patent Document 2, high purity was achieved by combining molten salt electrolysis and electron beam melting.

Japanese Patent No. 6084464 Japanese Patent No. 5738993

In the conventional sputtering target, defects such as cracking of the target occurred during the sputtering process. When the cause was investigated, it was found that the target had large pores and cracks. In Patent Document 2, electron beam melting is repeated 2 to 4 times to manufacture an yttrium ingot. High purity can be obtained by performing electron beam melting about four times. On the other hand, large pores remained in the ingot. Moreover, since yttrium metal is a material having low fracture toughness, cracks are likely to occur during processing into a target.
The sputtering method is a film forming method in which an ionized rare gas element is caused to collide with a sputtering target. The target with large pores and cracks could not stand the collision and was damaged.

The yttrium sputtering target according to the embodiment is characterized in that the maximum diameter of the pore is 1 mm or less.

The figure which shows an example of the yttrium sputtering target concerning embodiment. The figure which shows an example of the structure of a yttrium crystal in the yttrium sputtering target concerning embodiment. The figure which shows an example of a pore in the yttrium sputtering target concerning embodiment. The figure which shows an example of a crack in the yttrium sputtering target concerning embodiment. The figure which shows the other example of the structure of a yttrium crystal in the yttrium sputtering target concerning embodiment.

Embodiment

The yttrium sputtering target according to the embodiment is characterized in that the maximum diameter of the pore is 1 mm or less.
FIG. 1 shows an example of the yttrium sputtering target according to the embodiment. In the figure, 1 is a yttrium sputtering target (hereinafter may be simply referred to as “target”), 2 is a sputtering surface, and 3 is a side surface. In FIG. 1, the case where the yttrium sputtering target 1 is a cylindrical target is illustrated, but the shape is not particularly limited, such as a quadrangular prism type. In addition, a backing plate shall be provided if necessary when installing in a sputtering device.
In addition, FIGS. 2 and 5 show an example of the texture structure of the yttrium sputtering target 1 according to the embodiment. 2 and 5, 4 is a yttrium crystal. The gap surrounded by yttrium crystals is called a pore or crack.
The yttrium sputtering target 1 according to the embodiment is a polycrystalline body. The pore is a gap formed between two particles of yttrium crystal particles or between three particles (triple point). A crack is a gap formed between four or more yttrium crystal particles.

An example of the pore is shown in FIG. 3 and an example of the crack is shown in FIG. In FIG. 3, the gap surrounded by the yttrium crystals 4-1, 4-2 and 4-3 is the pore 5. FIG. 3 shows an example of pores formed at triple points between three crystal grains. Further, in FIG. 4, cracks 6 are formed in the gaps surrounded by the yttrium crystals 4-1, 4-2, 4-3, 4-4, 4-5 and 4-6.
For the measurement of pores or cracks, an arbitrary cross section of the target 1 is observed with an optical microscope. The arbitrary cross section means a cross section orthogonal to the central axis of the cylindrical target 1, a vertical cross section orthogonal to the cross section, or any other cut section. It is possible to distinguish between yttrium crystals and pores (or cracks) by the difference in the contrast of the optical micrograph. The optical micrograph has a magnification of 10 times or more. If necessary, the cross section is polished so that the surface roughness Ra is 2 μm or less. Further, when the unit area described later cannot be measured in one visual field, it may be measured in a plurality of divided areas. In addition, when the measurement is performed in a plurality of divisions, the adjacent visual fields are measured.
Further, the presence or absence of pores and cracks can be inspected by ultrasonic flaw detection or X-ray X-ray inspection. These tests are non-destructive tests. The pores and cracks inside the entire target 1 can be measured by ultrasonic flaw detection or X-ray radiography. A method of cutting out a cross section after performing a nondestructive inspection is effective.

The yttrium sputtering target 1 according to the embodiment is characterized in that the maximum diameter of the pore is 1 mm or less. Further, it is preferable that the number of pores present in any cross section of the yttrium sputtering target 1 is 0 or more and 2 or less. In addition, not only when the whole arbitrary cross section of the yttrium sputtering target 1 is used as the visual field of the arbitrary cross section, but also in the arbitrary cross section, for example, a unit area of 10 mm × 10 mm is connected to form a visual field of the arbitrary cross section. May be
The longest diagonal line of the pores in the optical micrograph having a unit area of 10 mm × 10 mm is the maximum diameter. Here, the diagonal line refers to the length from each point on the outer circumference of the pore to other points. The length from each point to the other plural points may be a linear distance from each point to the other plural points. A unit area of 10 mm × 10 mm is performed at three positions, and the largest value among them is set as the maximum diameter of the pore. If the maximum diameter of the pores exceeds 1 mm and is large, the strength of the target 1 decreases. The sputtering method is a film forming method in which ionized particles collide with the target 1. Ion particles collide with the sputtering surface of the target. As the sputtering progresses, the sputtered surface is cut away. If there is a pore having a maximum diameter of more than 1 mm, the target will be cracked from the pore due to collision of ion particles. For this reason, in the conventional target, the replacement time had to be advanced.
In addition, the sputter rate tends to change at the location where the pores are formed. When the sputter rate changes, the deposited film tends to become non-uniform. Therefore, the maximum diameter of the pores of the target 1 is preferably 1 mm or less, more preferably 0.5 mm or less. Further, it is most preferable that there are no pores (= the maximum diameter of pores is 0 mm).
Further, it is preferable that the number of pores existing in a unit area of 10 mm × 10 mm is 0 or more and 2 or less. Even if the maximum diameter of the pores is 1 mm or less, if the pores are gathered close to each other, cracking of the target and non-uniformity of the sputter rate are likely to occur. Therefore, in the target 1, if the number of pores having a maximum diameter of 1 mm or less is 2 or less in a unit area of 10 mm × 10 mm, it is possible to suppress cracking of the target and unevenness of the sputtering rate.

Further, it is preferable that the maximum crack length of the target 1 is 3 mm or less. A crack is a gap formed between four or more yttrium crystal particles. The pores connected between four or more yttrium crystal particles become cracks. The maximum diameter of cracks shall also be measured using optical micrographs. As with pores, cracks can be identified by the difference in contrast. Further, a crack is a space formed by four or more crystal grains, and is therefore not limited to a linear shape, but a undulating shape or the like. The maximum length of the crack means the length from the first end to the second end on the opposite side in the longitudinal direction of the crack shown in the optical microscope. The length from the first end to the second end may be a linear distance from the first end to the second end, or from the first end through the axis of the crack to The curve distance to the end of 2 may be sufficient. The former is effective in the case of a crack having a linear shape or a relatively small waviness, and the latter is effective in the case of a crack having a relatively large waviness. If the crack length exceeds 3 mm and is large, it is likely to cause cracking of the target or uneven sputtering rate. Therefore, the maximum length of the crack is preferably 3 mm or less, and more preferably 2 mm or less. Moreover, it is most preferable that there is no crack (= the maximum length of the crack is 0 mm). Further, pores and cracks can be distinguished from each other in the optical micrograph by the difference in contrast with the yttrium crystal.
The maximum length of the crack is measured by observing an optical microscope photograph of an arbitrary cross section of the target 1. The longest crack observed in a unit area of 30 mm × 30 mm is the maximum crack length. A unit area of 30 mm × 30 mm may be connected to form a cross-sectional field of view. Also, cracks can be measured inside the entire target 1 by ultrasonic flaw detection or X-ray X-ray inspection. A method of cutting out a cross section after performing a nondestructive inspection is effective.
Further, it is preferable that the number of cracks is 0 or more and 2 or less in a unit area of 30 mm × 30 mm. Even if the cracks are 3 mm or less, if three or more cracks exist in a unit area of 30 mm × 30 mm, the cracks of the target and the nonuniformity of the sputter rate are likely to occur.

Further, it is preferable that the yttrium has a purity of 4 N or more excluding the rare earth element and the gas component.
The rare earth element is a rare earth element other than yttrium (Y). Therefore, the rare earth elements other than yttrium are lanthanoid elements and actinoid elements. The total amount of rare earth elements other than yttrium is preferably 500 wtppm or less. The lanthanoid elements are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. Compared with the lanthanoid element, the actinide element is contained in a very small amount as an unavoidable impurity. Among the lanthanoid elements, La (lanthanum), Ce (cerium), Ho (fornium), Er (erbium), and Nd (neodymium) are the main inevitable impurities. The content of the impurity metal component is determined by GDMS analysis (glow discharge mass spectrometry). The GDMS analysis is suitable for quantitative analysis of metal components. Also, many elements can be analyzed at one time. Therefore, the contents of rare earth elements and other metal impurity elements can be analyzed.

The gas components are O (oxygen), N (nitrogen), C (carbon), S (sulfur) and H (hydrogen). The gas component includes a simple substance of these elements and a compound of other components. Examples of compounds with other components include carbon monoxide (CO), carbon dioxide (CO ₂ ), yttrium oxide (Y ₂ O ₃ ), and oxides of impurity rare earth elements. In addition, what is made into a compound shall be converted into a gas component simple substance. For _example, those detected by the Y 2 _{O 3 is} the oxygen in the Y 2 _{O 3} counts and gas components.
The total amount of gas components is preferably 1% by mass or less. Of the gas components, oxygen is the most abundant element. This is because yttrium is an element that is easily oxidized. The oxygen content is preferably 0.6% by mass or less. In addition, the analysis of the content of the gas component is performed by the IGA (Interstitial Gas Analysis) method. According to the IGA method, the contents of O (oxygen), N (nitrogen), C (carbon), S (sulfur) and H (hydrogen) can be measured.

Further, as impurity elements excluding rare earth elements and gas components, Al (aluminum), Mg (magnesium), Na (sodium), Fe (iron), Zn (zinc), Ca (calcium), K (potassium), Examples include Ni (nickel), Cu (copper), W (tungsten), Mo (molybdenum), and Ta (tantalum).
A film obtained by sputtering an yttrium sputtering target 1 as described later is suitable for a plasma processing apparatus component. The plasma processing apparatus is used for manufacturing a semiconductor device.
Mixing Na, K, Ca, and Mg into the semiconductor film adversely affects semiconductor performance. Therefore, from the stage 1 of the target and the stage of the ingot, it is better that these elements are less.
Further, Al, Mg, Fe, Zn, Ni, Cu, W, Mo, and Ta have high reactivity with plasma. If these elements are mixed in the obtained film, the plasma resistance of the film deteriorates.
The content of Al (aluminum) in the target 1 is preferably 300 mass ppm or less. The content of Mg (magnesium) is preferably 50 mass ppm or less. The content of Na (sodium) is preferably 100 mass ppm or less. The content of Fe (iron) is preferably 800 mass ppm or less. The content of Zn (zinc) is preferably 100 mass ppm or less. The content of Ca (calcium) is preferably 4000 mass ppm or less. The content of K (potassium) is preferably 10 mass ppm or less. The content of Ni (nickel) is preferably 300 mass ppm or less. The content of Cu (copper) is preferably 200 mass ppm or less. The content of W (tungsten) is preferably 6000 mass ppm or less. The content of Mo (molybdenum) is preferably 3000 mass ppm or less. The content of Ta (tantalum) is preferably 8000 mass ppm or less.

The average grain size of the yttrium crystal is preferably 0.3 mm or more and 25 mm or less. If the average grain size is less than 0.3 mm, grain boundaries increase. As the number of grain boundaries increases, cracks are more likely to be formed. On the other hand, when the average crystal grain size is larger than 25 mm, the triple point between yttrium crystals becomes large. When the triple point becomes large, large pores are easily formed. Therefore, the average crystal grain size is preferably 0.3 to 25 mm, more preferably 1 to 20 mm.
The average crystal grain size is measured by observing the sputtering surface 2 with an optical microscope. The sputtered surface 2 is photographed with an optical microscope photograph (magnification 10 times or more). When the sputter surface 2 cannot be photographed in one field of view, it may be photographed separately. Further, the sputtering surface 2 may be subjected to etching processing to the extent that grain boundaries can be confirmed.
First, the number of yttrium crystals shown in the optical micrograph is counted. By this operation, the number of yttrium crystals observed on the sputter surface 2 is obtained. If the sputter surface 2 cannot be photographed in one visual field, it may be photographed several times. The number of yttrium crystals can be calculated by connecting the photographs.
Next, the area of one crystal is calculated by "the area of the sputter surface / the number of yttrium crystals observed on the sputter surface". It is assumed that one crystal is a perfect circle and the diameter is obtained. This diameter shall be the average crystal grain size. The yttrium crystal preferably has a wavy shape with a random contour. Since the contour has a corrugated shape, the bonds between the crystals are strengthened.

The tensile strength of the yttrium sputtering target 1 is preferably 100 MPa or more. The tensile strength is a value obtained by dividing the maximum load when a tensile load is applied to the sample to break the sample by the cross-sectional area (cross-sectional area of the sample). It can be said that the higher the tensile strength, the less likely it is to break.
The tensile strength of the target 1 is measured according to JIS-Z-2241. The sample size shall be 6 mm ± 0.1 mm in diameter. The cross-sectional area of the sample having a diameter of 6 mm is 28.26 mm ² . The measuring device shall be a 5567 type precision universal testing machine manufactured by Instron or has performance equivalent thereto. The measurement conditions are room temperature, air, and a pulling speed of 12.6 mm / min.
Since the target 1 according to the embodiment has small pores or cracks, the tensile strength can be improved. Yttrium metal is a brittle material. On the other hand, the target 1 needs to have a flat sputtering surface 2. This is because the sputter rate is not stable on a sputtered surface having large irregularities. In order to obtain a flat surface, surface processing such as polishing is required for the sputter surface 2. If the tensile strength is less than 100 MPa, cracks are likely to occur during surface processing. Therefore, the tensile strength is preferably 100 MPa or more, more preferably 135 MPa or more.
Further, the breaking elongation of the target 1 is preferably 5 to 30%. Elongation at break refers to the elongation of a sample up to the breaking point when a tensile test is performed. The larger the elongation at break, the greater the amount of deformation until failure. If the elongation at break is less than 5%, the amount of deformation before breaking is too small, and the durability against the stress of processing is low. If the elongation at break exceeds 30% and is large, the amount of deformation is too large and it becomes difficult for the target 1 to obtain a flat surface. Therefore, the elongation at break is preferably 5 to 30%, more preferably 10 to 20%.
The elongation at break shall be measured according to JIS-Z-2241. The sample size is similar to that of tensile strength. Further, it is preferable that the measuring device is also the same. In addition, the measurement condition of the elongation at break is set to a gauge length of 30 mm.

The diameter of the sputter surface 2 is preferably 100 mm or more. The larger the sputtering surface 2, the larger the amount of film that can be formed in one sputtering step. Considering the time and effort required to replace the target 1, mass productivity is improved. Since the target 1 according to the embodiment has a small pore, the sputter rate can be made uniform even if the target 1 is made large. Further, it is possible to suppress the occurrence of cracks in the target 1 during the sputtering process.
Therefore, the diameter of the sputtering surface 2 can be 100 mm or more, and further 160 mm or more. Moreover, the thickness of the target 1 can be 10 mm or more, further 16 mm or more. The upper limit of the diameter of the sputtering surface 2 is not particularly limited, but a diameter of 400 mm or less is preferable. The upper limit of the thickness of the target 1 is not particularly limited, but is preferably 30 mm or less. If the diameter or thickness of the target 1 is too large, it may be difficult to control the average crystal grain size. Therefore, the diameter of the sputtering surface 2 of the target 1 is preferably 100 to 400 mm, more preferably 160 to 350 mm. The thickness of the target 1 is preferably 10 to 30 mm, more preferably 16 to 25 mm.

The surface roughness Ra of the sputter surface 2 is preferably 2.0 μm or less. The sputter surface 2 is a surface on which the ionized particles collide. If the surface of the sputter surface 2 is rough, the manner of collision of ionized particles becomes non-uniform. As a result, the sputter rate becomes non-uniform. The surface roughness Ra of the sputter surface 2 is preferably 2.0 μm or less, more preferably 1.2 μm or less. Since the target 1 according to the embodiment has improved tensile strength, it is possible to suppress the occurrence of cracks even if polishing is performed.
The surface roughness of the sputter surface 2 means the surface roughness of the sputter surface of a new target before performing the sputtering step.

The yttrium sputtering target 1 as described above is used in a film forming method for forming a film by sputtering.
Examples of the film to be formed include a metal yttrium film and a yttrium compound film.
Examples of the yttrium compound include oxides, nitrides, fluorides, and composite compounds thereof. Specifically, it is one selected from yttrium oxide (Y ₂ O ₃ ), yttrium nitride (YN), yttrium fluoride (YF ₃ ), and yttrium oxyfluoride (YOF).
When forming the yttrium oxide film, a method of sputtering in an oxygen-containing atmosphere can be mentioned. A method of sputtering using an oxygen-containing atmosphere while performing an oxidation reaction is called reactive sputtering. Further, a method of forming a metal yttrium film and then subjecting it to an oxidation treatment may be mentioned. The method using reactive sputtering or the method of reacting the metal yttrium film with the compound film can be applied to the nitride film, the fluoride film, and the composite compound film.
Further, examples of the sputtering device include DC sputtering, magnetron sputtering, and ion beam sputtering. DC sputtering is a method of applying a DC voltage between electrodes. The magnetron sputtering is a method in which a magnet is arranged on the target 1 side and a DC voltage is applied between the electrodes. Magnetron sputter is a type of DC sputter. By arranging the magnet, a magnetic field can be generated around the target 1 and the electron moving direction can be controlled. Thereby, the sputtering speed can be increased. The ion beam sputtering is a method of irradiating the sputtering surface 2 of the target 1 with the ions emitted from the ion gun. Since the ion beam sputtering uses only the ions desired to be used for sputtering, it is possible to suppress the mixing of impurities.
Further, in the sputtering process, the degree of vacuum is preferably 0.5 Pa or less. Further, it is preferable that the power supply output of the sputtering device is 800 W (0.8 kW) or more. The power output of the sputtering apparatus is the voltage applied between the electrodes.
By increasing the power output of the sputtering apparatus, the film formation speed can be increased. This improves mass productivity. With the target 1 according to the embodiment, cracking of the target 1 does not occur even if the power output of the sputtering apparatus is 800 W or higher. Therefore, the power output of the sputtering apparatus can be set to 1000 W (1 kW) or more. Further, when the power output of the sputtering apparatus is increased, the collision energy of ions or electrons on the sputtering surface 2 becomes stronger. The target 1 according to the embodiment can suppress the cracking of the target 1 even when the collision energy increases. Therefore, the life of the target 1 can be extended. Along with the increase in the size of the sputtering surface 2, a film forming method having excellent mass productivity can be obtained. The upper limit of the power output of the sputtering device is not particularly limited, but is preferably 50 kW or less. When the power output exceeds 50 kW, the possibility that the target 1 will crack increases. In other words, it is suitable for a power source output of the sputtering device of 0.8 kW or more and 50 kW or less, and further 1 kW or more and 40 kW or less.

Next, a method for manufacturing the yttrium sputtering target 1 according to the embodiment will be described. The yttrium sputtering target 1 according to the embodiment is not particularly limited in its manufacturing method as long as it has the above-mentioned configuration, but the method for obtaining a high yield is as follows.
The first manufacturing method is a method using electron beam melting (EB melting). Commercially available metal yttrium has a purity of about 2N to 3N excluding rare earth elements other than Y and gas components. EB melting is performed using commercially available metal yttrium as a raw material. The EB melting is a method of irradiating a raw material with an electron beam, melting the material, and then solidifying the material. This EB melting is repeated twice or more to produce an yttrium ingot. Impurity elements are reduced by performing EB melting. Moreover, by repeating the process three times or more, it becomes difficult to form pores in the ingot. That is, the pores can be eliminated by repeatedly EB-melting the ingot after EB melting. For this reason, the number of EB dissolutions is preferably 2 or more, more preferably 3 or more. The upper limit of the number of EB dissolutions is not particularly limited, but is preferably 10 times or less. Even if the number is increased over 10 times, it is difficult to obtain a further effect, which causes a cost increase. The output of the electron beam is preferably in the range of 1 to 1000 kW. If the output of the electron beam is less than 1 kW, it takes time to melt. If it exceeds 1000 kW, the laser output is too strong and the variation in crystal grain size is likely to occur. Therefore, the electron beam output is preferably 1 to 1000 kW, more preferably 5 to 300 kW.
It is also effective to slow down the pulling speed. EB melting is a method in which a melted material that is melted by an electron beam is pulled up and solidified. When the pulling speed is increased, pores are more likely to occur due to insufficient solidification. Therefore, the pulling rate is preferably less than 1 mm / min. Further, it is preferable that the pulling-up step is continuously performed without being stopped halfway. When the pulling rate is changed, the average crystal grain size tends to vary.
Further, the diameter of the ingot is to be taken out after the diameter of the target 1 is increased by 20 mm or more. Yttrium metal is a material that is easily oxidized. The surface of the ingot is easily oxidized and pores are easily formed on the surface of the ingot. Therefore, a method of making an ingot larger than the target size of the target 1 by 20 mm or more is effective. As a result, a portion having a small pore from the ingot can be used as the target 1.

The second manufacturing method is a method using a high frequency melting method. The high frequency melting method is a method of melting a metal using an induction coil. When a high frequency current is applied to the coil, an eddy current is generated in the metal and heat is generated. This is a method of melting the metal by this heat. The high frequency current is preferably 500 Hz or higher. The generated heat energy is proportional to the radius of the metal and inversely proportional to the height. Further, the generated heat energy is proportional to the square of the frequency of the current. Therefore, the thermal energy can be adjusted by controlling the size of the metal to be melted and the frequency of the current.
Induction skull melting is preferable as the high-frequency melting method. Induction skull melting is a melting method that combines a water-cooled metal crucible and an induction coil. Examples of the water-cooled metal crucible include a water-cooled copper crucible. A metallic material is placed in the crucible. When a high frequency current is applied to the induction coil, the metal material in the crucible melts. The molten metal material is condensed at the bottom of the crucible to form a skull. Further, when a high frequency current is applied to the induction coil, a magnetic field is generated. The magnetic field stirs the molten metal in the crucible. A strong stirring force allows homogeneous dissolution. In addition, a degassing effect and an effect of volatilizing impurities can be obtained by creating a vacuum inside the crucible.
Moreover, an ingot can be produced by casting a molten metal. By using a mold that matches the target size of the target 1 that is the target, an ingot close to the target size can be manufactured. That is, the amount to be deleted from the ingot can be reduced to 10 mm or less. With such an ingot, the target 1 can be finished without performing forging or rolling.

In addition, the target 1 is finished by subjecting the ingot obtained by the first manufacturing method or the second manufacturing method to cutting processing, polishing processing, or the like. The sputtered surface is polished so that the surface roughness Ra is 2.0 μm or less.
Moreover, forging, rolling, etc. shall be performed as needed. It is easy to adjust the target size by performing forging or rolling. In addition, the pores existing in the ingot can be crushed and made smaller. On the other hand, if the stress during processing is too large, cracks are likely to be formed in the ingot.
Since the ingot obtained by the method for producing an ingot described above has generation of pores suppressed, it can be processed into the target 1 without forging or rolling.
In addition, a backing plate shall be joined if necessary.

(Example)
(Examples 1 to 8 and Comparative Example 1)
Commercially available yttrium was prepared as a raw material. The purity of commercially available yttrium excluding rare earth elements other than Y and gas components is 3N.
Next, EB dissolution was performed on commercially available yttrium under the conditions according to Examples 1 to 5 and the condition according to Comparative Example 1, respectively. The electron beam output for EB melting was unified at 20 kW. A target was cut out from the obtained ingot. In addition, the sputtered surface was polished. The number of EB meltings, the pulling rate, the ingot size, the target size, and the surface roughness Ra of the sputter surface were as shown in Table 1.

In addition, induction skull melting was performed on commercially available yttrium under the conditions according to Examples 6 to 8. The high frequency current applied was 500 Hz or higher. Moreover, it melt | dissolved in a vacuum. The diameter, target size, and surface roughness Ra of the sputter surface of the obtained ingot were as shown in Table 2.

All of the plurality of targets obtained from commercially available yttrium under a plurality of conditions had a purity of 4N or more excluding rare earth elements other than Y and gas components. The content of the impurity metal component was determined by GDMS analysis. The content of the gas component was determined by the IGA method.
Next, the maximum diameter of the pores, the maximum length of the cracks, the average crystal grain diameter, and the tensile strength of the plurality of targets obtained from commercially available yttrium were measured under a plurality of conditions.
The maximum diameter of the pore is measured by taking an optical micrograph (50 times) of a unit area of 10 mm × 10 mm in an arbitrary cross section of the target. Measure the longest diagonal of the pores in the picture. This work was carried out for three places of a unit area (10 mm × 10 mm), and the largest diagonal line among them was taken as the maximum diameter. In addition, the unit area (10 mm × 10 mm) for three locations shows the largest number of pores.
For the maximum diameter of the maximum crack length, an optical microscope photograph (50 times) of a unit area of 30 mm × 30 mm is taken. The length of cracks (pores connected to four crystal grains) shown in the photograph was determined. The unit area (30 mm × 30 mm) was performed for three places, and the longest one was taken as the maximum crack length. In addition, the unit area (30 mm × 30 mm) for three locations shows the number of cracks that was the largest.
The average crystal grain size is measured by photographing the sputtering surface of the target with an optical microscope photograph (50 times). Count the number of yttrium crystals in the photo. The area of one crystal is calculated by "area of sputter surface / number of yttrium crystals observed on sputter surface". The diameter is calculated assuming that one crystal is a perfect circle.
The tensile strength was measured according to JIS-Z-2241. As the sample size, a cylinder having a diameter of 6 mm and a length of 100 mm was cut out from the target. An Instron 5567 type precision universal tester was used as a measuring device. The measurement conditions were room temperature, air, and a pulling speed of 12.6 mm / min. The breaking elongation was measured at a gauge length = 30 mm.
The results are shown in Table 3.

The plurality of targets 1 obtained under the conditions according to Examples 1 to 8 had a tensile strength of 100 MPa or more, and further 135 MPa or more. This is because the pores and cracks are small. Further, in the plurality of targets 1 obtained under the conditions according to Examples 1 to 8, the yttrium crystal had a wavy outline. As with the plurality of targets 1, the plurality of ingots obtained under the conditions according to Examples 1 to 8 also have small pores and cracks and a small number.
Next, sputtering was performed using the plurality of targets 1 obtained under the conditions according to Examples 1 to 8 and the target obtained under the conditions according to Comparative Example 1. Sputtering was performed at a vacuum degree of 0.5 Pa or less.
The power output of the sputtering apparatus was set to 800 W and 2000 W, and it was confirmed whether or not the target was cracked.
In addition, the rate of change of the sputter rate was measured. The rate of change in the sputter rate was determined by the amount of change in the cumulative amount of input power. "A" when the amount of change is 5% or less, "B" when it exceeds 5% and 10% or less, "C" when it exceeds 20% and 20% or less, and "D" when it exceeds 20%. " In other words, “A”, “B”, “C”, and “D” are listed in the descending order of the amount of change.
The results are shown in Table 4.

As can be seen from Table 4, cracks did not occur during the sputtering process with the multiple targets 1 obtained under the conditions according to Examples 1 to 8. Further, a stable sputtering rate was also obtained with the plurality of targets 1 obtained under the conditions according to Examples 1 to 8. Further, in the plurality of targets 1 obtained under the conditions according to Examples 3 to 8 in which the maximum diameter of the pores is 0.5 mm or less and the maximum length of the cracks is 1.2 mm or less, a particularly stable sputtering rate is obtained. Was given. Further, since the plurality of targets 1 obtained under the conditions according to Examples 4 to 8 had no cracks, the sputtering rate was stable even if the power output of the sputtering apparatus was increased.

Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the scope equivalent thereto. Further, the above-described respective embodiments can be implemented in combination with each other.

Claims (11)

1. ▽ A sputtering target made of yttrium characterized in that the maximum diameter of the pore is 1 mm or less.
2. The yttrium sputtering target according to claim 1, wherein the number of pores present in an arbitrary cross section of the yttrium sputtering target is 0 or more and 2 or less.
3. The yttrium sputtering target according to any one of claims 1 and 2, wherein the yttrium has a purity of 4N or more excluding rare earth elements and gas components.
4. The yttrium sputtering target according to any one of claims 1 to 3, wherein the maximum crack length is 3 mm or less.
5. The yttrium sputtering target according to any one of claims 1 to 4, wherein an average grain size of the yttrium crystal is within a range of 0.3 to 25 mm.
6. The yttrium sputtering target according to any one of claims 1 to 5, which has a tensile strength of 100 MPa or more.
7. The yttrium sputtering target according to any one of claims 1 to 6, wherein the sputtering surface has a diameter of 100 mm or more.
8. The yttrium sputtering target according to any one of claims 1 to 7, wherein the sputtering surface has a surface roughness Ra of 2.0 µm or less.
9. A film forming method for forming a film by sputtering the yttrium sputtering target according to any one of claims 1 to 8.
10. 10. The film forming method according to claim 9, wherein the formed film is a metal yttrium film, and the yttrium oxide film is formed by oxidizing the metal yttrium film.
11. 10. The film forming method according to claim 9, wherein the yttrium oxide film is formed by sputtering in an oxygen-containing atmosphere.

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