Yttrium ingot and sputtering target using the same

Abstract

To provide an yttrium ingot and a sputtering target using the same capable of depositing an yttrium-based film with a high plasma resistance at a high-speed.SOLUTION: An yttrium ingot contains a fluorine atom of 0.05wt% or more and 10wt% or less, and a relative density of 96% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a yttrium ingot for film formation and a sputtering target using the same. [Background technology]

[0002] In semiconductor device manufacturing, microfabrication using dry etching with highly corrosive halogen-based gases, such as fluorine-based and chlorine-based gases, and their plasmas is an important process. These corrosive gases and plasmas corrode and damage the components of semiconductor manufacturing equipment, and the resulting particles are known to cause degradation of device quality. Many of the components in semiconductor manufacturing equipment are consumables, and they are replaced periodically to prevent yield and quality degradation due to the damage. Equipment downtime for component replacement and equipment maintenance reduces equipment utilization and productivity, creating problems. Therefore, the development of components with excellent plasma and gas corrosion resistance is required in the semiconductor manufacturing process.

[0003] As semiconductor elements become more miniaturized, the plasma used in dry etching processes is becoming denser, and yttrium oxide has attracted attention as a material that can withstand such high-density plasma. Regarding the manufacturing method of components containing yttrium oxide, a method of forming an yttrium oxide film on a substrate by thermal spraying, as described in Patent Document 1, is the mainstream industrial process due to the considerations of manufacturing costs and size. However, because the thermal spraying method involves melting ceramic powder and rapidly solidifying it to form a film, surface defects and voids exist on the film surface. The presence of such defects not only deteriorates plasma resistance but also causes particle generation, so a method for forming a dense yttrium oxide film with high efficiency is desired.

[0004] Sputtering is one of the film formation methods other than thermal spraying. Sputtering physically bombards a target placed on a cathode with positive ions such as Ar ions, releasing the target's constituent materials with the collision energy and depositing a film on a substrate placed opposite. Examples of sputtering include direct current (DC) sputtering, radio frequency (RF) sputtering, and alternating current (AC) sputtering. Generally, sputtering allows for lower-temperature film formation compared to thermal spraying, suppresses the generation of defects such as voids, and is believed to produce denser films. Furthermore, sputtering can also be used for reactive sputtering, in which gases such as oxygen and nitrogen are introduced into the sputtering chamber, to form oxide or nitride films. For example, as described in Non-Patent Document 1, reactive DC sputtering, in which a yttrium target is subjected to DC discharge and oxygen is introduced during sputtering, can form an yttrium oxide film on a substrate. However, the quality of the resulting film varies significantly depending on the sputtering conditions. Incidentally, in Non-Patent Document 1, a film is formed using a 99.5% pure yttrium target, but sufficient research has not been conducted on the correlation between the physical properties of the sputtering target, such as density and purity, and the sputtering characteristics, and the relationship with the quality of the film formed by sputtering. Therefore, further research was needed on the physical properties of the yttrium target, the sputtering characteristics, and the characteristics of the film formed.

[0005] Yttrium is typically produced by precipitating chlorides by molten salt electrolysis, as described in Patent Document 2. However, this method focuses only on high purity and does not describe additives or structure. Furthermore, chlorides are typically used to achieve high purity, and using fluorides as raw materials has been considered difficult for achieving high purity. Furthermore, separating rare earth elements is difficult, and it has not been possible to achieve both. Furthermore, sputtering targets containing fluorine and oxygen have never been used due to the need for high purity. Furthermore, yttrium oxyfluoride has high resistance and cannot be subjected to DC discharge, so it can only be produced by a thermal spraying method, as described in Patent Document 3. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-307311 [Patent Document 2] WO2013-005349 publication [Patent Document 3] Japanese Patent Application Publication No. 2018-185657 [Non-patent literature]

[0007] [Non-Patent Document 1] P.Lei et al. Surface & Coatings Technology 276(2015)39-46 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an yttrium ingot for a low-resistivity yttrium sputtering target that has high plasma resistance and is capable of realizing a high film formation rate, and a sputtering target using the same. [Means for solving the problem]

[0009] The present inventors have conducted extensive research into yttrium ingots suitable for yttrium sputtering targets, and as a result have found an yttrium ingot for use in yttrium sputtering targets that can produce yttrium oxide-based films with high plasma resistance, thereby completing the present invention.

[0010] That is, the aspects of the present invention are as follows. (1) A yttrium ingot characterized by having a fluorine atom content of 0.05 wt% or more and 10 wt% or less and a relative density of 96% or more. (2) A yttrium ingot according to (1), containing yttrium oxyfluoride. (3) A yttrium ingot according to (1) or (2), wherein the content of rare earth elements is 98≦100−RE<99.999, where RE is the wt% content of rare earth elements. (4) The yttrium ingot according to any one of (1) to (3), having an average particle size (D50) of 100 μm or less. (5) The yttrium ingot according to any one of (1) to (4), having a volume resistivity of 1 Ω·cm or less. (6) A yttrium sputtering target comprising the yttrium ingot according to any one of (1) to (5). (7) The sputtering target according to (6), which comprises a backing plate and an yttrium ingot. (8) The yttrium sputtering target according to (7), wherein the adhesion rate between the backing plate and the yttrium ingot is 90% or more. (9) A method for producing an yttrium oxide film, comprising sputtering using the yttrium sputtering target according to any one of (6) to (8).

[0011] The present invention will be described in detail below.

[0012] The yttrium ingot of the present invention is characterized by a fluorine atom content of 0.05 wt% to 10 wt%. By incorporating fluorine atoms, it becomes possible to form a yttrium-based film with high plasma resistance. The fluorine atom content is more preferably 0.05 wt% to 8 wt%, 0.05 wt% to 5 wt%, 0.1 wt% to 4 wt%, and even more preferably 0.2 wt% to 3 wt%. If the fluorine atom content exceeds 10 wt%, the resistivity of the ingot increases, making it impossible to achieve highly productive DC discharge. Furthermore, if the fluorine content is less than 0.05 wt%, the plasma resistance is not improved by the addition of fluorine.

[0013] Here, the content of fluorine atoms refers to the weight ratio of fluorine atoms to the entire yttrium ingot, and can be measured using GDMS (glow discharge mass spectrometry) or ICP (inductively coupled plasma (ICP)).

[0014] The relative density is 96% or more, preferably 98% or more, more preferably 99% or more, and even more preferably 99.8% or more. If the relative density is less than 96%, particularly large ingots, are prone to cracking, making it impossible to produce ingots with a high yield. Furthermore, when high power is applied during sputtering using such ingots, cracks are likely to occur during discharge, which is undesirable as it reduces the productivity of the film formation process.

[0015] The yttrium ingot of the present invention preferably contains yttrium oxyfluoride. By including yttrium oxyfluoride, it is possible to prevent the inability to generate yttrium oxyfluoride due to compositional deviation during sputtering. Many compounds exist as yttrium oxyfluoride (YOF), but it is preferable that it exists primarily as trigonal YOF. Trigonal YOF has high stability and therefore exhibits excellent final mechanical properties. Furthermore, its abundance ratio is preferably 0.1% to 35% in terms of area ratio, more preferably 0.1% to 20%, and even more preferably 0.1% to 10%. Setting the abundance ratio within this range enables stable discharge and enables the production of a film containing yttrium oxyfluoride.

[0016] The yttrium ingot of the present invention contains a specific amount of fluorine, and the content of impurities other than fluorine, when the content of rare earth elements is RE wt%, is preferably 98≦100−RE<99.999, more preferably 99≦100−RE<99.999, and even more preferably 99.9≦100−RE<99.999. By reducing the amount of rare earth impurities and increasing the purity of the yttrium target, abnormal discharge and particle generation can be suppressed. Increasing the purity is undesirable because the purification process becomes more complicated and the production cost increases. The inventors investigated the correlation between the impurity amount and discharge characteristics within the above range and determined a purity suitable for use in sputtering film formation. The rare earth elements herein are Ce, Pr, Nd, Sn, Eu, Gd, Tb, Py, Ho, and Er.

[0017] The average particle size (D50) of the yttrium ingot is preferably 100 μm or less, more preferably 0.1 μm to 100 μm, more preferably 0.1 μm to 75 μm, and particularly preferably 0.1 μm to 20 μm. By uniformly dispersing a yttrium fluoride compound in the yttrium ingot, the average particle size is refined, resulting in an yttrium ingot that maintains high strength even when containing yttrium oxyfluoride. A sputtering target using such an ingot enables high-speed film formation using high power. Furthermore, because the fluorine is uniformly dispersed, it is also possible to reduce compositional variations in the film.

[0018] Next, the volume resistivity of the yttrium ingot in the present invention is preferably 1 Ω·cm or less, more preferably 0.00001 Ω·cm or more and 1 Ω·cm or less, and even more preferably 0.00001 Ω·cm or more and 0.001 Ω·cm or less. Yttrium is very susceptible to oxidation and oxidizes naturally in the atmosphere. Yttrium oxide formed by oxidation is an insulator, and therefore can cause abnormal discharge during sputtering discharge, especially when forming a film using DC discharge. By keeping the volume resistivity within the above range, stable discharge characteristics can be obtained in DC sputtering, RF sputtering, and AC sputtering.

[0019] The yttrium ingot of the present invention has a pore count of 0.1 / cm with a diameter of 100 μm or more. 2 It is preferable that the number of particles is less than 0.01 particles / cm. 2 or less, and more preferably 0.005 particles / cm 2 The number of pores with a diameter of 100 μm or more is 0.1 / cm 2 If it is greater than this, it may cause abnormal discharge or particles during sputtering.

[0020] The surface roughness of the yttrium ingot of the present invention is important in terms of the surface roughness of the sputtering surface when used as a sputtering target, and the surface roughness of the sputtering surface when used as a sputtering target is preferably 10 nm to 2 μm, more preferably 10 nm to 1 μm, and even more preferably 10 nm to 0.3 μm. The sputtering surface refers to the area from which sputter particles are actually emitted (erosion area).

[0021] The yttrium ingot of the present invention can be ground into a plate shape using a machining machine such as a surface grinder, a cylindrical grinder, a lathe, a cutting machine, or a machining center.

[0022] The method for producing the yttrium ingot of the present invention is not particularly limited, but in order to mix a certain amount of fluorine, it is preferable to use a production method that involves reduction treatment using yttrium fluoride, followed by melting and solidifying, such as vacuum melting or EB melting.

[0023] Yttrium fluoride is a relatively stable substance, and can be further reduced to produce yttrium oxyfluoride. By controlling the reduction state at that time, it is possible to leave behind the necessary amount of fluorine, and synthesize an yttrium ingot containing a specific amount of fluorine, in which the fluorine is uniformly dispersed. Using chloride as the starting material is not preferable because it is not possible to uniformly contain fluorine.

[0024] In melt solidification processes such as vacuum melting and EB melting, coarse pores of 100 μm or larger tend to occur due to vaporization during melting, making it difficult to obtain an ingot with few pores. Therefore, it is preferable to compress the ingot produced by the melting method using hot isostatic pressing (HIP) to eliminate the pores. However, since yttrium is a material that is easily oxidized, it is preferable to seal the outer periphery with metal. The HIP temperature is preferably 1000°C or less. Furthermore, since yttrium is relatively brittle, the pressure is preferably 100 MPa or less. This makes it possible to obtain a yttrium ingot with few pores of 100 μm or larger.

[0025] The yttrium ingot of the present invention can be used as a sputtering target made of the yttrium ingot. As a method for producing a sputtering target, a sputtering target can be obtained by bonding a backing plate or a backing tube made of oxygen-free copper, titanium, or the like using indium solder, etc., as needed, and among these, a sputtering target made of a backing plate and an yttrium ingot is preferred.

[0026] The surface roughness of the yttrium ingot side of the bonding surface between the yttrium ingot and the backing plate (bonding surface roughness) is preferably 10 nm or more and 2 μm or less, more preferably 10 nm or more and 1 μm or less, and even more preferably 10 nm or more and 0.3 μm or less. By making it 2 μm or less, the specific surface area of ​​the surface layer is reduced, and by reducing the surface oxygen of the easily oxidized yttrium, peeling at the oxidized portion during bonding can be prevented. Furthermore, treating the bonding surface in an oxidized state makes treatment impossible due to peeling of the oxide layer, ultimately reducing the bonding rate. By making it 10 nm or more, the surface and the treated surface are better interlocked, improving adhesion and enabling high-power discharge. However, since surface oxidation progresses, it is preferable to polish the surface after target formation.

[0027] The backing plate is used to efficiently attach the ingot, which is the film material part of the sputtering target, to the sputtering device, and to prevent the ingot part from overheating during sputtering, the backing plate part is cooled with water, etc. The adhesive material used is indium or indium alloy, which has high thermal conductivity and is easy to use as solder.

[0028] The material of the backing plate is not particularly limited, and copper, stainless steel, titanium, etc. can be used.

[0029] In a sputtering target consisting of a backing plate and an yttrium ingot, the adhesion rate between the yttrium ingot and the backing plate is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. By achieving the above adhesion rate, it is possible to quickly diffuse the heat generated in the target during sputtering and prevent the sputtering target from being excessively heated and the solder material from melting.

[0030] The adhesion rate between the yttrium ingot and the backing plate can be determined, for example, by ultrasonic flaw detection measurement. When determining the bonding rate by ultrasonic flaw detection measurement, it is preferable to adjust the measurement conditions using a pseudo-defect sample in which a pseudo-void hole is provided in the center of a plate material of a predetermined size. The measurement sensitivity is adjusted so that the area of ​​the detected defect matches the area of ​​the predetermined void hole. The material of the pseudo-defect sample is preferably the same as the material of the sputtering target. It is preferable that the distance from the ultrasonic incident surface of the pseudo-defect sample to the bottom surface of the void hole is the same as the distance from the ultrasonic incident surface of the sputtering target to the bonding layer.

[0031] When bonding, it is preferable to polish the bonding surface of the yttrium ingot and quickly perform surface treatment. The surface of the yttrium ingot oxidizes over time, and the resulting oxide film makes it difficult to bond with the solder material. Therefore, before bonding, the oxide layer on the yttrium surface is removed and surface treatment is quickly performed. Although the treatment method is not particularly limited, it is preferable to perform vapor deposition of a metal that adheres well to the solder material, plating treatment, treatment with an ultrasonic soldering iron, etc. This makes it possible to bond the solder and yttrium without peeling them off. It is preferable to perform the surface treatment after the oxidation treatment within 3 hours.

[0032] Furthermore, an yttrium oxide film can be produced by sputtering using the obtained yttrium sputtering target. [Effects of the Invention]

[0033] The yttrium sputtering target using the yttrium ingot of the present invention makes it possible to produce a highly plasma-resistant yttrium-based film with high productivity. [Example]

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Measurements in the examples were carried out as follows. (1) Relative density The relative density of the yttrium ingot was measured by the Archimedes method in accordance with JIS R 1634, and the true density of metallic yttrium (4.47 g / cm 3 ) to obtain the relative density. (2) Pore ratio measurement The entire image is measured using an X-ray transmission image, and pores of 100 μm or larger are extracted from the image and their number and size are measured. The number of pores / cm is calculated from the measured area. 2 was converted to. (3) Volume resistivity The value was obtained by measuring three or more points using the four-probe method and averaging the results. (4) Average particle size The particles were polished to a mirror finish and observed using a scanning electron microscope with electron backscatter diffraction (SEM-EBSD) (SEM: manufactured by JEOL Ltd., EBSD: manufactured by Oxford University Press), and the arithmetic mean particle size was measured from the images obtained. At least three randomly selected points were observed. Particles with a crystal orientation tilt of 5° or more were counted as one particle, and the diameter was calculated after spherical approximation. The mean value here refers to the 50% particle size. (5) Contained crystal phase, abundance ratio The specimen was polished to a mirror finish and observed using a scanning electron microscope with electron backscatter diffraction (SEM-EBSD). From the identified crystalline phases, the contained crystalline phases were identified and their abundance ratio was calculated as an area ratio. (6) Method for measuring adhesion ratio Measurement was carried out using an ultrasonic flaw detector, and the adhesion rate was calculated. (7) Measurement of surface roughness (Ra) The surface roughness Ra was measured using a Mitutoyo surface roughness measuring device. (8) Metal content analysis After sintering, the surface of the yttrium ingot was ground to a depth of 1 mm or more, and the analytical values ​​of a sample cut out from an arbitrary portion were used as measurement data.

[0035] Measurement method: Glow discharge mass spectrometry (GDMS) Example 1 Yttrium oxyfluoride-containing yttrium ingots were obtained by reducing yttrium fluoride using Li-Mg. Further pore reduction treatment was performed on the yttrium ingots, and measurements yielded favorable results. The properties of the yttrium ingots are shown in Table 1. Furthermore, the results for the metal impurities contained are shown in Table 2.

[0036] Relative density: 100.3% Fluorine atom content: 0.6 wt% Before bonding, the bonding surface was polished to the specified roughness, and then indium solder was quickly applied using an ultrasonic soldering iron. After surface treatment, the target was attached to a backing plate using indium solder. The yttrium target characteristics are shown in Table 1.

[0037] (Examples 2 and 3) Except for changing the amount of yttrium fluoride added in Example 1, yttrium ingots and sputtering targets of Examples 2 and 3 containing yttrium oxyfluoride were produced in the same manner as in Example 1. The characteristics of the yttrium ingots and targets are shown in Table 1.

[0038] Example 4 Yttrium powder (3N bulk product, manufactured by Nippon Yttrium Co., Ltd.) and yttrium oxyfluoride powder (Grade: 5LW230, manufactured by Nippon Yttrium Co., Ltd.) were charged into a Cu crucible in a weight ratio of 90:10. The mixture was heated and melted in an arc melting furnace, and then cooled to obtain a yttrium ingot containing yttrium oxyfluoride. The obtained yttrium ingot was processed into a predetermined shape and then attached to a backing plate in the same manner as in Example 1 to produce a sputtering target. The characteristics of the yttrium ingot and the target are shown in Table 1.

[0039] Example 5 To the yttrium ingot containing yttrium oxyfluoride prepared in Example 4, yttrium oxyfluoride was added so that the final yttrium:yttrium oxyfluoride ratio was 50:50, and the mixture was placed in a Cu crucible. The mixture was heated and melted in an arc melting furnace, and then cooled to obtain an yttrium ingot containing yttrium oxyfluoride. A sputtering target was prepared by mounting the ingot on a backing plate in the same manner as in Example 1. The characteristics of the yttrium ingot and the target are shown in Table 1.

[0040] Example 6 To the yttrium ingot containing yttrium oxyfluoride prepared in Example 4, yttrium oxyfluoride was added so that the final yttrium:yttrium oxyfluoride ratio was 40:60, and the mixture was placed in a Cu crucible. The mixture was heated and melted in an arc melting furnace, and then cooled to obtain an yttrium ingot containing yttrium oxyfluoride. A sputtering target was prepared by mounting the ingot on a backing plate in the same manner as in Example 1. The characteristics of the yttrium ingot and the target are shown in Table 1.

[0041] (Comparative Example 1) A fluorine-free yttrium ingot synthesized using chloride molten salt electrolysis was prepared and attached to a backing plate to produce a sputtering target in the same manner as in Example 1. The characteristics of the yttrium ingot and the target are shown in Table 1.

[0042] (Comparative Example 2) An yttrium ingot and a sputtering target of Comparative Example 2 containing yttrium oxyfluoride were obtained in the same manner as in Example 4, except that the mixing ratio of yttrium powder and yttrium oxyfluoride powder in Example 4 was set to 30:70. The characteristics of the yttrium ingot and the target are shown in Table 1.

[0043] The adhesion rates of the sputtering targets of Examples 1 to 6 and Comparative Examples 1 and 2 were measured. The adhesion rates were measured using an ultrasonic imaging inspection device (model: AT LINE, manufactured by Hitachi Construction Machinery Finetech Co., Ltd.) equipped with an ultrasonic flaw detector (model: I3-0508-T). Prior to the measurement, a pseudo sample made of the same material as the sputtering target was used, and the sensitivity was adjusted so that the area of ​​the detected defects matched the area of ​​the pseudo hole in the pseudo sample. The measurement conditions were as follows:

[0044] Gain (sound wave strength): 15dB Measurement pitch: 0.61 mm Echo level: ≥ 3.1V Ultrasonic wave incidence: target side The adhesion rate of the sputtering target was measured using the analysis program attached to the device. The measurement results are shown in Table 1.

[0045] The sputtering targets of Examples 1 to 4 were mounted in a DC sputtering apparatus and films were formed on quartz substrates. After that, annealing treatment was carried out in an oxygen atmosphere to obtain yttrium oxide films. The sputtering conditions were as follows:

[0046] Target size: Φ101.6×6mmt Power: 200W Sputtering gas: Ar Gas pressure: 0.5 Pa Film thickness: 5 μm When the sputtering target of Comparative Example 1 was sputtered, oxidation of the sputtering surface of the yttrium target progressed, and the adhesion rate was low, so DC discharge was not possible.

[0047] When the sputtering target of Comparative Example 2 was used for sputtering, DC discharge was not possible due to the high bulk resistivity of the target.

[0048] The samples obtained in Examples 1 to 4 were set in an etching chamber capable of evaluating plasma resistance, and the etching rate was calculated from the change in film thickness before and after plasma irradiation. The plasma resistance evaluation conditions were as follows.

[0049] Sample size: 20mm x 20mm Power: 300W Etching gas: Ar+CF4+O2 Processing time: 4 hours The results of the plasma resistance evaluation are shown in Table 3.

[0050] In the yttrium films of Examples 1 to 4, the etching rate was extremely small compared to that of the quartz substrate, and good plasma resistance characteristics were obtained.

[0051] [Table 1]

[0052] [Table 2]

[0053] [Table 3]

Claims

1. The yttrium ingot has a fluorine atom content of 0.05 wt % or more and 10 wt % or less, a relative density of 96% or more, and a pore count of 100 μm or more in diameter of 0.1 / cm ２ A yttrium ingot characterized by:

2. 2. The yttrium ingot of claim 1, comprising yttrium oxyfluoride.

3. 3. The yttrium ingot according to claim 1, wherein the content of rare earth elements is 98≦100−RE<99.999, where RE wt% is the rare earth element content.

4. The yttrium ingot according to any one of claims 1 to 3, wherein the average particle diameter (D50) is 100 µm or less.

5. The yttrium ingot according to any one of claims 1 to 4, having a volume resistivity of 1 Ω cm or less.

6. A yttrium sputtering target comprising the yttrium ingot according to any one of claims 1 to 5.

7. The sputtering target according to claim 6, comprising a backing plate and an yttrium ingot.

8. 8. The yttrium sputtering target according to claim 7, wherein the surface roughness of the sputtering surface is 10 nm or more and 2 μm or less.

9. A method for producing an yttrium oxide film, comprising sputtering using the sputtering target according to any one of claims 6 to 8.

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