Yttrium oxide film and film-forming method therefor

Abstract

Provided are: a yttrium oxide film resistant to reductions in plasma resistance due to abnormal growth originating from foreign matter; and a method for forming this film. In a yttrium oxide film formed on a base material, the major axis / minor axis ratio has an average of greater than 1.5 when each of a plurality of particles mainly composed of metallic yttrium and present in the film in a cross section that includes the thickness direction of the film is approximated as an ellipse.

Description

Yttrium oxide coating and method for forming same

[0001] The present invention relates to an yttrium oxide coating having excellent plasma resistance and a method for forming the same.

[0002] Conventionally, there has been a demand for materials with excellent plasma resistance for components used in environments exposed to plasma, such as semiconductor manufacturing equipment. Patent Document 1 discloses a method for obtaining such a material by using yttrium oxide (Y ２ O ３ Patent Document 2 discloses a technique for forming an yttrium oxide film on the surface of a substrate by an ion plating method using yttrium oxide as a raw material. Patent Document 2 also discloses a technique for forming an yttrium oxide film by a reactive sputtering method.

[0003] JP 2007-290933 A International Publication No. 2019 / 26818

[0004] In the techniques described in Patent Documents 1 and 2, if particles such as foreign matter are present in the yttrium oxide film during its formation, abnormal growth (nodules) will occur starting from the particles, creating voids in the film and impairing its density, i.e., plasma resistance.

[0005] An object of the present invention is to provide an yttrium oxide coating in which a decrease in plasma resistance due to abnormal growth originating from particles such as foreign matter is suppressed, and a method for forming the same.

[0006] The present invention provides an yttrium oxide coating formed on a substrate, in which a plurality of particles mainly composed of metallic yttrium present in the coating in a cross section including the thickness direction of the coating have an average major axis / minor axis ratio of greater than 1.5 when each particle is approximated as an ellipse.

[0007] This configuration prevents abnormal growth (nodule growth) from occurring in the coating starting from particles, thereby preventing the formation of voids, and thus preventing a decrease in plasma resistance.

[0008] FIG. 1 is a schematic diagram showing the general configuration of a film forming apparatus for forming an yttrium oxide film according to one embodiment of the present invention. FIG. 2A is an enlarged cross-sectional photograph showing particles in an yttrium oxide film. FIG. 2B is an enlarged cross-sectional photograph showing particles in an yttrium oxide film. FIG. 3A is a cross-sectional photograph of a substrate and an yttrium oxide film. FIG. 3B is a cross-sectional photograph of a substrate and an yttrium oxide film. FIG. 4A is a diagram showing the results of image analysis of the yttrium oxide film region in FIG. 3A. FIG. 4B is a diagram showing the results of image analysis of the yttrium oxide film region in FIG. 3B. FIG. 5 is a graph showing the relationship between particle oblateness and film porosity. FIG. 6 is a graph showing the relationship between TS distance and particle oblateness. FIG. 7 is a graph showing the relationship between film thickness and film porosity.

[0009] An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 is a schematic diagram showing the general configuration of a film formation apparatus 10 for forming an yttrium oxide film according to this embodiment. The method for forming an yttrium oxide film according to this embodiment is a method for forming a film having excellent plasma resistance on the surface of a substrate. The formed yttrium oxide film can be applied to components exposed to plasma in, for example, semiconductor manufacturing equipment.

[0010] 1 is an example of a film formation apparatus for carrying out the film formation method according to the present embodiment, and the film formation apparatus for carrying out the film formation method is not limited to that shown in Fig. 1. This film formation apparatus 10 is an apparatus that uses a physical vapor deposition (PVD) method to form a film on the surface of a workpiece W (substrate) placed in a vacuum chamber 12. Examples of this film formation apparatus 10 include an AIP (Arc Ion Plating) apparatus that forms a film using an arc ion plating method and a sputtering apparatus that forms a film using a sputtering method.

[0011] The film formation apparatus 10 is an arc ion plating apparatus and includes a vacuum chamber 12, a rotary table 14, a plurality of substrate holders 16, a bias power supply 18, a target 20 as an evaporation source, an arc power supply 22, a heater 24, an argon tank 30, an oxygen tank 32, a vacuum pump P, and a controller 50.

[0012] The vacuum chamber 12 accommodates a turntable 14 and a plurality of substrate holders 16 arranged on the turntable 14. The interior of the vacuum chamber 12 (i.e., the space accommodating the turntable 14 and the plurality of substrate holders 16) is maintained in a vacuum or near-vacuum state by a vacuum pump P during various processes including the film formation process. The vacuum chamber 12 is provided with a gas inlet 12A and an exhaust outlet 12B.

[0013] The turntable 14 has a disk shape with a centerline extending in the vertical direction in Fig. 1 . The turntable 14 is disposed within the vacuum chamber 12. During the film formation process, the turntable 14 rotates around its centerline while supporting a plurality of substrate holders 16. The turntable 14 may further include a turntable on which each of the plurality of substrate holders 16 is individually disposed so that each of the plurality of substrate holders 16 can rotate on its own axis. The number of substrate holders 16 is not limited to two as shown in Fig. 1 .

[0014] Each of the plurality of substrate holders 16 supports a workpiece W (substrate) on which a film is to be formed. In this embodiment, the workpiece W is disposed on the outer circumferential surface of the substrate holder 16. Note that only some of the workpieces W are shown in FIG. 1 .

[0015] In this embodiment, the workpiece W is made of an A6061 alloy (Al alloy) (also referred to as an Al base material) and is a square plate piece measuring 20 mm x 20 mm. The thickness of the workpiece W is 5 mm. However, the material and shape of the workpiece W are not limited to this.

[0016] Each of the substrate holders 16 is made of a conductive material, such as stainless steel.

[0017] The plurality of substrate holders 16 are arranged at equal intervals in the circumferential direction of the rotary table 14. In this state, the center line of each of the plurality of substrate holders 16 is parallel to the center line of the rotary table 14.

[0018] The bias power supply 18 applies a negative bias voltage to each of the plurality of substrate holders 16 via the rotary table 14. In this embodiment, the bias power supply 18 intermittently applies the negative bias voltage to each of the plurality of substrate holders 16. In other words, the bias power supply 18 is a pulse power supply. When the resistance of the coating formed on the workpiece W is relatively high, applying a DC bias as the bias voltage may cause a problem of charge accumulation (charge-up) due to incident ions. On the other hand, by applying a pulse voltage as the bias voltage as in this embodiment, this problem can be prevented even when the resistance of the coating formed on the workpiece W is relatively high. More specifically, the charge-up problem can be prevented by switching the bias between the negative side and 0 V or the positive side as the pulse voltage on the order of μS or mS.

[0019] Note that the bias power supply 18 does not apply a bias when it is not applying a negative bias voltage during the film formation process. Alternatively, the bias power supply 18 can alternately apply a negative bias voltage and a positive bias voltage to each of the plurality of substrate holders 16. The absolute value of the negative bias voltage is greater than the absolute value of the positive bias voltage.

[0020] If a negative bias voltage and a positive bias voltage are applied alternately, the bias power supply 18 may be, for example, an alternating current power supply (AC power supply) or a high frequency power supply (RF power supply).

[0021] The target 20 is a disk-shaped member made of yttrium. As an example, the target 20 is a disk having a diameter of 100 mm.

[0022] The arc power supply 22 is a DC power supply that functions as a discharge power supply that generates a vacuum arc discharge in the target 20 placed in the vacuum chamber 12. In this case, the target 20 functions as a cathode in the discharge. Meanwhile, as shown in FIG. 1, the vacuum chamber 12 functions as an anode in the discharge. The target 20 receives the discharge generated by the arc power supply 22 and emits ions of evaporated (melted) yttrium from its surface. The arc power supply 22, together with the target 20, constitutes an arc evaporation source.

[0023] The heater 24 is provided in the vacuum chamber 12 and generates heat when supplied with current from a heater power supply (not shown). As a result, the environment in the vacuum chamber 12 and the workpiece W are heated.

[0024] The argon tank 30 contains argon and supplies argon gas to the vacuum chamber 12. Similarly, the oxygen tank 32 contains oxygen and supplies oxygen to the vacuum chamber 12. The amount of gas supplied from these tanks is controlled by adjusting the opening of a regulator (not shown) in response to a command from the controller 50. In another embodiment, the amount of gas supplied may be manually adjusted by an operator.

[0025] The vacuum pump P creates a vacuum in the internal space of the vacuum chamber 12 through the exhaust port 12B (evacuation).

[0026] In addition to the regulators, the controller 50 controls the vacuum pump P, the bias power supply 18, the arc power supply 22, and various voltages or currents of the heater 24, as well as the rotation of the rotary table 14, etc.

[0027] Next, an example of the film formation method according to this embodiment will be described. In the following description, oxygen may be represented as O and yttrium as Y. The present invention is not limited to the scope of the following example. To carry out the film formation method, as shown in FIG. 1, a target 20 and a workpiece W are installed in a film formation apparatus 10, and a vacuum chamber 12 is evacuated to a vacuum state by a vacuum pump P.

[0028] Next, after preheating inside the vacuum chamber 12 by the heater 24, argon gas is introduced from the argon tank 30 into the vacuum chamber 12 through the gas inlet 12A, and as a pretreatment, the surface of the workpiece W is bombarded with argon gas ions. Here, bombardment means generating heavy inert gas ions such as argon ions by plasma discharge, and irradiating the workpiece W with these ions to heat and sputter the surface of the workpiece W, thereby cleaning moisture and contaminants from the surface.

[0029] After the above bombardment, an Ar-O2 mixed gas (for example, Ar 450 sccm, oxygen 50 sccm) is introduced so that the pressure inside the chamber becomes about 2 Pa. In order to maintain a stable discharge, it is desirable to set the total pressure inside the chamber in the range of 0.6 Pa to 4 Pa.

[0030] Next, a target 20 made of metallic yttrium is discharged in the vacuum chamber 12 while functioning as a cathode, and an yttrium oxide film is formed on the workpiece W. During this process, the temperature of the workpiece W during film formation is approximately 300°C (200°C to 400°C). For example, the arc current is 100 A (preferably in the range of 100 A to 125 A). The voltage applied to the workpiece W is a unipolar pulse with a frequency of 200 kHz and a duty of 56%, with the average voltage varying between 10 and 100 V. The thickness of the yttrium oxide film formed on the workpiece W is approximately 50 to 100 μm. As mentioned above, for example, A6061Al (20 mm x 20 mm square piece, 5 mm thick) is used as the workpiece W. In this experiment, the workpiece W (Al substrate) was positioned at various distances from the target 20, approximately 155 to 400 mm.

[0031] In this example, an experiment was also conducted using an AIP deposition apparatus different from the one described above. ２A gas mixture (Ar 900 sccm, oxygen flow rate approximately 50 sccm) was introduced into the chamber to approximately 1 Pa, and a metal Y cathode was discharged to form an yttrium oxide film on the substrate. In this case, the substrate temperature during film formation was approximately 200°C, the arc current was 100 A, and the voltage applied to the workpiece W was a unipolar pulse with a frequency of 30 kHz and a duty of 50%, with the average voltage varied between 40 and 60 V.

[0032] Next, a method for evaluating the yttrium oxide film formed on the workpiece W will be described together with its indicators.

[0033] (1) Evaluation of particle (particle, foreign matter) shape: A test piece (workpiece W made of an Al substrate) on which a coating was formed was cut along the film thickness direction and embedded in a resin for evaluation. The cross section was observed from the cross-sectional direction using a scanning electron microscope (SEM). Specifically, the coating portion of a backscattered electron image at 500x magnification was image-processed, and the binarized image was analyzed to determine the shape of particles in the coating with a perimeter of approximately 2.7 μm, i.e., a circle-equivalent diameter of approximately 0.86 μm or more. These particles correspond to foreign matter compared to the main component of the yttrium oxide coating, and many of them are parts with a lower oxygen content than the yttrium oxide matrix. The area of ​​the SEM image to be analyzed was approximately 100 μm (film thickness) × 250 μm (width). In other words, the term "particle" in the following description refers to particulate foreign matter made of a material other than yttrium oxide within the yttrium oxide coating.

[0034] 2A and 2B are enlarged cross-sectional photographs showing particles in a yttrium oxide coating. In either case, when a particle has a nearly circular shape as shown in FIG. 2A or a long elliptical shape as shown in FIG. 2B, the major axis (long diameter) and minor axis (minor diameter) can be identified through image analysis. The ellipse that best fits the particle shape is determined, and its major axis and perpendicular minor axis are determined to calculate the oblateness. Here, the ratio of the major axis to the minor axis for each particle is defined as the oblateness. Note that particles that arrive in a molten state flatten along the substrate surface of the workpiece W, so they rarely extend obliquely relative to the substrate surface. However, even for particles that extend obliquely, the same method for calculating the oblateness is used. Under each condition, the average oblateness of multiple particles in the SEM images described above is calculated. Here, the particle shape is defined by observing it from the cross-sectional direction. If the particle shape is circular when observed from the cross-sectional direction, the actual particle shape is spherical, and if the particle shape is elliptical or flat, the actual shape is close to an ellipsoid or a thick disk.

[0035] (2) Evaluation of Porosity For samples prepared in the same manner as in (1), the cross section was observed using an SEM image at 500x magnification, and the voids in the coating observable in the cross section were calculated by image analysis. The image analysis procedure was as follows: (Step 1) The analysis portion was cut out from the image. In this case, a region approximately 20 μm deep from the surface of the coating was cut out. (Step 2) The image was binarized. (Step 3) The defect (void) area was calculated. The proportion of the void area contained in the image was evaluated as the void ratio. Note that voids are formed by nodules generated from particles. If the particle shape becomes spherical, it is presumed that this is due to the action of surface tension in space after being released in a molten state. If the spherical particle solidifies and adheres to the workpiece W (substrate), a void will form between the spherical particle and the substrate at the bottom, and the void will not be filled by the film-forming particles entering from a perpendicular direction.

[0036] Figures 3A and 3B are cross-sectional photographs of a substrate and an yttrium oxide coating. In both cross-sectional photographs, the lower side is the substrate portion and the upper side is the coating portion. Figure 3A shows particles mainly having the shape shown in Figure 2A scattered throughout, while Figure 3B shows particles mainly having the shape shown in Figure 2B scattered throughout. Figure 4A is a diagram showing the results of image analysis of the yttrium oxide coating region of Figure 3A. Figure 4B is a diagram showing the results of image analysis of the yttrium oxide coating region of Figure 3B.

[0037] The images in Figures 3A and 4A were obtained under the condition that the shortest distance between the target and the substrate was 400 mm, while the images in Figures 3B and 4B were obtained under the condition that the shortest distance between the target and the substrate was 155 mm. Under the conditions of Figures 3A and 4A, the average flatness of the particles in the images was 1.2, and the porosity was 1.7%. On the other hand, under the conditions of Figures 3B and 4B, the average flatness of the particles in the images was 3.7, and the porosity was 0.15%. From these results, it was newly discovered that in coatings in which the particle shapes are close to flat and many particles have a large flatness, the generation of nodules is suppressed and voids are reduced. Note that the black areas visible around the white particles in Figure 3A are voids. In Figure 3B, these voids are not very visible.

[0038] 5 is a graph showing the relationship between particle oblateness and coating porosity. As described above, the graph shows the relationship between the particle oblateness (average value) in the coating and the porosity, which was determined by image analysis from cross-sectional SEM observation. As shown in FIG. 5, when the average particle oblateness is small, i.e., when the particle shape is close to a sphere, the porosity is large. However, when the particle oblateness exceeds 1.5 (see the dashed line in FIG. 5), the porosity is 0.2% or less, and it has been found that a dense coating can be formed.

[0039] FIG. 6 is a graph showing the relationship between the TS distance and the particle flatness. The TS distance is defined as the linear distance between the substrate and the target. FIG. 6 shows the relationship between the shortest TS distance and the flatness (average value) of particles contained in the coating when the TS distance is varied in various ways during film formation using the AIP method. Note that the shortest distance is defined as the distance between the substrate and the target at the closest point when the substrate is mounted on a rotary table as shown in FIG. 1 . Strictly speaking, the TS distance changes during film formation because the target is consumed by discharge. However, here, it is defined as the distance from the target surface at the start of film formation. Even when the substrate moves on a trajectory other than rotation, the shortest distance is defined as the distance between the substrate and the target at the closest point. During the experiment, the target surface gradually wears away, so the distance gradually increases. When the TS distance from the target to the substrate is 300 mm or less, the flatness of the particles contained in the coating is greater than 1.5. In this case, it was found that a dense yttrium oxide film with a small porosity could be formed, as can be seen from the relationship in the graph of FIG.

[0040] FIG. 7 is a graph showing the relationship between the film thickness and porosity of a coating. FIG. 7 shows the relationship between the film thickness and porosity of an yttrium oxide film formed when the TS distance was 400 mm. The porosity was calculated for a thick yttrium oxide film of about 100 μm, with the porosity calculated for each region 25, 50, and 75 μm from the interface and the entire film thickness, and the value was used for each film thickness. As a result, it was found that, although there was some variation, the porosity exceeded 0.2% when the film thickness exceeded 30 μm. On the other hand, as shown in FIGS. 3B and 4B, when the TS distance was short, the particle flatness exceeded 2, and the porosity was 0.2% or less. This confirmed that the present invention is effective for film thicknesses of 30 μm or more.

[0041] In this embodiment, in the yttrium oxide coating formed on the workpiece W, when a cross section including the thickness direction of the coating is taken, and each of the particles mainly (mainly) composed of metallic yttrium present in the coating is approximated by an ellipse, the average ratio of the major axis to the minor axis (flatness) is greater than 1.5. It is more preferable that the average flatness is greater than 2.0. Furthermore, it is more preferable that the average flatness is 3.0 or greater.

[0042] This configuration prevents abnormal growth (nodule growth) from occurring in the coating starting from particles, thereby preventing the formation of voids, and as a result, prevents a decrease in plasma resistance.

[0043] In the above configuration, the coating may have a thickness of 30 μm or more.

[0044] Nodule growth and void formation due to particles become significant when the film thickness is 30 μm or greater, or even 40 μm or greater. With this configuration, by focusing on the flatness of the particles, even in this thickness range, it is possible to prevent abnormal growth from occurring in the film starting from foreign matter, forming voids, and resulting in a decrease in plasma resistance.

[0045] The present invention provides a method for forming the above-described yttrium oxide coating, which comprises setting an appropriate distance between a target and the substrate, and then melting and evaporating the surface of the target by an arc ion plating method to form the coating on the substrate. Note that the appropriate distance is a predetermined distance such that the shape of the particles in cross section becomes flat with a major axis / minor axis ratio of more than 1.5, as described above.

[0046] Particle contamination is particularly prevalent in the AIP process, where melting and scattering of the target due to arc discharge are unavoidable. Even in such cases, this method prevents the formation of voids in the coating due to abnormal growth originating from particles such as foreign matter, thereby preventing a decrease in plasma resistance. That is, this method allows the particles to have a flat shape with a long axis / short axis ratio of greater than 1.5 by appropriately setting the distance (TS distance) between the target 20 and the workpiece W. In the AIP process, particles (molten metal) scattered from the target 20 are cooled by radiation as they travel from the target 20 to the workpiece W. If the distance from the target 20 to the workpiece W is long, the particles cool and solidify before reaching the workpiece W, becoming spherical and adhering to the workpiece W. In this case, voids form between the workpiece W (substrate) and the particles, and nodules are formed starting from these voids. On the other hand, if the distance from the target 20 to the workpiece W is short, the particles are likely to reach the workpiece W in a molten state, and are deformed to conform to the shape of the workpiece W, becoming flat. In this case, voids like those in the spherical particles are unlikely to occur, and nodule growth is unlikely to occur.

[0047] The above method may further comprise setting the distance between the target and the substrate during film formation so that the porosity of the film is 0.2% or less.

[0048] According to this method, the porosity of the coating is set to 0.2% or less, so that a dense yttrium oxide coating can be formed.

[0049] The above method may further comprise setting the shortest distance between the target and the substrate during film formation to 300 mm or less, more preferably 200 mm or less.

[0050] As described above, according to the present embodiment, it is possible to provide an yttrium oxide coating and a method for forming the same in which a decrease in plasma resistance due to abnormal growth originating from foreign matter is suppressed.

[0051] To explain one example of the film formation method according to this embodiment in more detail, the method is a method for forming an yttrium oxide film on a substrate by arc ion plating. The method includes placing a target made of yttrium and the substrate in a chamber, introducing at least oxygen into the chamber, applying a predetermined bias voltage to the substrate, and evaporating the surface of the target in the oxygen to form an yttrium oxide film on the substrate. The film formed by this film formation method has the above-mentioned characteristics of flatness.

[0052] To achieve a practical film formation rate, it is desirable to form the film using an arc ion plating method rather than a conventional ion plating method or reactive sputtering method. For example, conventional etching equipment typically uses a film with a thickness of 100 μm or more, and the slow film formation rate of ion plating or sputtering methods is an issue. On the other hand, the inventors have discovered a significant problem with the arc ion plating method, which is expected to achieve a high film formation rate: abnormal growth (nodule growth) originating from particles (foreign matter) can increase the porosity, resulting in a decrease in plasma resistance. The inventors have newly discovered that this problem can be solved by controlling the oblateness of the particles in the film. In the above-mentioned thickness range, it is difficult to achieve a practical film formation rate while reducing the porosity using conventional sputtering methods.

[0053] In the present invention, the yttrium oxide film is a film containing Y ２ O ３ and Y are mixed together, and Y ２ O ３ As a result of changing the ratio of Y to O in the film, the ratio of Y to O in the film changes. ２ O ３ Films in which Y and O are mixed together are collectively referred to as "yttrium oxide films." Note that the ratio of Y to O in this case is an atomic ratio.

[0054] The yttrium oxide film obtained by the film forming method according to the present invention has excellent plasma resistance and can therefore be widely applied to members exposed to plasma, such as semiconductor manufacturing equipment.

[0055] It should be noted that these are merely examples, and the present invention should not be construed as being limited in any way by the description of the above-mentioned embodiments. In the present invention, the substrate is not limited to one made of an insulating material, and may be made of a conductive material. The method for forming the coating is not limited to the AIP method, and other PVD methods may also be used. In this case, nodule growth may occur, and the present invention can be effectively used. However, the AIP method, which is prone to generating a large number of particles, is particularly effective.

[0056] The present invention provides an yttrium oxide coating formed on a substrate, in which a plurality of particles mainly composed of metallic yttrium present in the coating in a cross section including the thickness direction of the coating have an average major axis / minor axis ratio of greater than 1.5 when each particle is approximated as an ellipse.

[0057] This configuration prevents abnormal growth (nodule growth) from occurring in the coating starting from particles, thereby preventing the formation of voids, and thus preventing a decrease in plasma resistance.

[0058] In the above configuration, the coating may have a thickness of 30 μm or more.

[0059] The above-described particle-based nodule growth and void formation become significant when the film thickness is increased to 30 μm or greater. According to this configuration, by focusing on the particle oblateness, even in this thickness range, abnormal growth originating from particles in the film and the formation of voids can be suppressed, and a decrease in plasma resistance can be suppressed.

[0060] The present invention provides a method for forming the above-described yttrium oxide coating, which comprises appropriately setting the distance between a target and the substrate, and then melting and evaporating the surface of the target by an arc ion plating method to form the coating on the substrate.

[0061] Particle contamination is particularly prevalent in arc ion plating, where arc discharge inevitably melts and scatters the target. Even in such cases, this method prevents the formation of voids in the coating due to abnormal growth originating from particles such as foreign matter, thereby preventing a decrease in plasma resistance. Specifically, this method allows particles to have a flat shape with a long / short axis ratio of greater than 1.5 by appropriately setting the distance between the target and the workpiece. In arc ion plating, particles (molten metal) scattered from the target are cooled by radiation as they travel from the target to the substrate. If the distance from the target to the substrate is long, the particles cool and solidify before reaching the substrate, becoming spherical and adhering to the substrate. In this case, voids form between the substrate and the particles, and nodules form from these voids. On the other hand, if the distance from the target to the substrate is short, the particles are more likely to reach the substrate in a molten state, deforming to conform to the shape of the substrate and becoming flat. In this case, voids like those in spherical particles are less likely to form, making nodule growth less likely.

[0062] The above method may further comprise setting the distance between the target and the substrate during film formation so that the porosity of the film is 0.2% or less.

[0063] According to this method, the porosity of the coating is set to 0.2% or less, so that a dense yttrium oxide coating can be formed.

[0064] The above method may further comprise setting the shortest distance between the target and the substrate during film formation to 300 mm or less.

[0065] According to the present invention, it is possible to provide an yttrium oxide coating in which a decrease in plasma resistance due to abnormal growth originating from particles such as foreign matter is prevented, and a method for forming the coating.

Claims

1. A yttrium oxide coating formed on a substrate, wherein a plurality of particles primarily composed of metallic yttrium present in the coating have an average major axis / minor axis ratio of greater than 1.5 when each particle is approximated as an ellipse in a cross section including the thickness direction of the coating.

2. The yttrium oxide coating according to claim 1, wherein said coating has a thickness of 30 μm or more.

3. A method for forming the yttrium oxide coating described in claim 1, comprising: setting an appropriate distance between a target and the substrate; and then melting and evaporating the surface of the target by arc ion plating to form the coating on the substrate.

4. A film forming method according to claim 3, further comprising setting the distance between the target and the substrate during film formation so that the porosity of the film is 0.2% or less.

5. A film formation method according to claim 4, further comprising setting the shortest distance between the target and the substrate during film formation to 300 mm or less.

Images