Evaporation apparatus and evaporation method

Abstract

To generate a convection in a molten vapor deposition material in a container in an evaporation apparatus according to an indirect heating method.SOLUTION: A vapor deposition material together with a convection induction member 42 are placed in a container 24. The convection induction member 42 interacts with the molten vapor deposition material 26, resulting in generating a convection (Marangoni convection) in the molten vapor deposition material. The vapor deposition material, for example, is MgF2, and the convection induction member 42, for example, is a Ta foil. Another material for constituting the convection induction member 42 includes Fe, Cr, and Ti. Any of these materials has an electronegativity close to that of Mg.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an evaporation device and an evaporation method, and more particularly to a technique for melting and evaporating an evaporation material. [Background technology]

[0002] A deposition apparatus is an apparatus that forms a deposition film on the surface of a target object by vaporizing a deposition material. The deposition apparatus is equipped with an evaporation device that melts and vaporizes the deposition material. Known deposition materials include metals, oxides, and fluorides. For example, when forming an optical thin film, fluorides (fluoride compounds) are used as deposition materials. A typical example of a fluoride is MgF2.

[0003] Known vacuum deposition methods include resistance heating, direct heating, and indirect heating. For example, the indirect heating method is used to form a high-quality deposition film made of fluoride. In the indirect heating method, an electron beam is irradiated onto the bottom wall of a container (liner) containing the deposition material, and the container is heated. This indirectly heats the deposition material inside the container. As an evaporation device that uses the indirect heating method, a non-scanning evaporation device that irradiates the center of the bottom wall with an electron beam is known, and a scanning evaporation device that has a function of scanning the electron beam irradiated onto the bottom wall is also known. An evaporation device that uses the indirect heating method is also called a bombardment deposition source.

[0004] Patent Document 1 discloses an evaporation apparatus according to a direct heating method. In the evaporation apparatus, a material that adsorbs oxygen in a molten metal material is provided in a crucible. Tantalum is described as an example of such a material. Patent Document 2 also discloses a deposition apparatus according to a direct heating method. In the evaporation apparatus, a convection suppression plate is provided in the crucible. Patent Document 3 discloses an evaporation apparatus according to a resistance heating method. In the evaporation apparatus, a member that forcibly changes the direction of convection is provided in the crucible. None of Patent Documents 1, 2, and 3 disclose a technology that uses a chemical action to generate convection in a molten deposition material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 3-191291 [Patent Document 2] Japanese Patent Application Publication No. 64-21072 [Patent Document 3] JP 2005-89835 A Summary of the Invention [Problem to be solved by the invention]

[0006] In an evaporation device according to the indirect heating method, an electron beam is irradiated onto the bottom wall of a container that contains an evaporation material, and the entire container is heated. Therefore, in general, natural convection due to a temperature gradient is difficult to occur in the molten evaporation material in the container. Under such circumstances, irradiation of the bottom wall with an electron beam, particularly local irradiation of a strong electron beam at a specific position on the bottom wall, makes it easier for the molten evaporation material to vaporize near the inner surface of the bottom wall. When bubbles generated near the inner surface rise to the surface and burst on the liquid surface of the molten evaporation material, the quality of the evaporation layer is reduced. This bursting phenomenon is also called splashing. In order to suppress the bursting phenomenon, it is desirable to cause temperature diffusion, i.e., convection, in the molten evaporation material in the container.

[0007] An object of the present invention is to generate convection in the molten deposition material in a container in an indirect heating type evaporation device, or to suppress the generation of bubbles near the inner surface of the bottom wall of the container in an indirect heating type evaporation device. [Means for solving the problem]

[0008] The evaporation device according to the present invention is characterized in that it includes a container for containing an evaporation material, a heating device for indirectly heating the evaporation material by irradiating an electron beam to a bottom of the container to heat the container, thereby producing a molten evaporation material, and a convection inducing member that is provided in the container at a location in contact with the molten evaporation material, has a melting point higher than that of the evaporation material, and interacts with the molten evaporation material within the container to produce convection in the molten evaporation material.

[0009] The evaporation method of the present invention includes the steps of placing a convection inducing member and a deposition material in a container, and indirectly heating the deposition material by irradiating an electron beam against a bottom wall of the container, thereby generating a molten deposition material, and is characterized in that the convection inducing member includes a metal that has a higher melting point than the deposition material and interacts with the molten deposition material in the container to generate convection in the molten deposition material. Effect of the Invention

[0010] According to the present invention, in an evaporation device using an indirect heating method, it is possible to generate convection in the molten deposition material in the container. Alternatively, according to the present invention, in an evaporation device using an indirect heating method, it is possible to suppress the generation of bubbles near the inner surface of the bottom wall of the container. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a configuration example of an evaporation device according to an embodiment; [Diagram 2] FIG. 1 illustrates several convection inducing material candidates and their properties. [Diagram 3]4 is a flowchart showing an example of the operation of the evaporation device. [Figure 4] FIG. 13 shows an evaporation device according to another embodiment. [Diagram 5] FIG. 1 illustrates several forms for deposition materials. [Figure 6] FIG. 13 is a diagram showing a modified example of the container. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment will be described with reference to the drawings.

[0013] (1) Overview of the embodiment The evaporation device according to the embodiment includes a container, a heating device, and a convection inducing member. The container contains an evaporation material. The heating device irradiates an electron beam to a bottom of the container to heat the container, thereby indirectly heating the evaporation material, thereby generating a molten evaporation material. The convection inducing member is provided at a location in the container where it contacts the molten evaporation material, has a melting point higher than that of the evaporation material, and interacts with the molten evaporation material in the container to generate convection in the molten evaporation material.

[0014] According to the above configuration, since the convection inducing member is provided in the container, a chemical interaction occurs between the convection inducing member and the molten deposition material, and as a result, convection occurs in the molten deposition material. This convection diffuses the temperature and prevents or reduces the generation of bubbles near the bottom of the container. This suppresses splashing, improving the quality of the deposition layer. The above convection is considered to be Marangoni convection caused by a concentration difference, i.e., a surface tension difference. The conditions under which Marangoni convection occurs will be described later.

[0015] In an embodiment, the deposition material is a compound having fluorine and a first metal. The convection inducing member includes a second metal that can be chemically bonded to fluorine. In an embodiment, the first metal has a first electronegativity, and the second metal has a second electronegativity. The second electronegativity is greater than the first electronegativity. For example, the difference between the first electronegativity and the second electronegativity is less than 0.85. The difference may be less than 0.8, or may be less than 0.52.

[0016] In an embodiment, the first metal is Mg and the second metal is one or more metals selected from Fe, Cr, Ti and Ta. In a specific example described below, the deposition material is MgF2 and the convection inducer is Ta.

[0017] In one embodiment, the convection inducing member is a member dropped into the container, i.e., the convection inducing member is a separate member from the container and is introduced into the container prior to the introduction of the deposition material. In another embodiment, the convection inducing member constitutes a coating layer provided on the inner surface of the container, i.e., the convection inducing member is integrated with the container. In either case, the convection inducing member is provided so as to be in contact with the molten deposition material.

[0018] In the embodiment, the mass per unit volume of the convection inducing member is greater than the mass per unit volume of the molten deposition material. Therefore, if the convection inducing member is a member independent of the container, i.e., if it is a member that is not fixed to the container, the convection inducing member will sink to the bottom in the molten deposition material. It has been confirmed by experiments that convection occurs even if the convection inducing member is quite small compared to the molten deposition material. It has also been confirmed by experiments that the convection inducing member can be used repeatedly to a certain extent (for example, up to about 4 or 5 times). No deterioration in the quality of the deposition layer due to the use of the convection inducing member has been confirmed in experiments so far.

[0019] The evaporation method according to the embodiment includes a charging step and a heating step. In the charging step, a convection inducing member and a deposition material are charged into a container. In the heating step, the deposition material is indirectly heated by irradiating an electron beam onto a bottom wall of the container, thereby generating a molten deposition material. The convection inducing member includes a metal that has a higher melting point than the deposition material and interacts with the molten deposition material in the container to generate convection in the molten deposition material.

[0020] According to the above-mentioned configuration, convection occurs in the molten deposition material due to the action of the molten deposition material, which reduces the variation in temperature of the entire molten deposition material, and therefore prevents only the bottom wall from becoming hot, thereby suppressing the generation of bubbles near the inner surface of the bottom.

[0021] In the embodiment, the heating step includes a first irradiation step and a second irradiation step. In the first irradiation step, a first electron beam having a first energy is irradiated onto the bottom wall. This causes the lower part of the deposition material in the container to be in a molten state. In the second irradiation step, a second electron beam having a second energy higher than the first energy is irradiated onto the bottom wall. This causes the entire deposition material in the container to be in a molten state. After the second irradiation step, a third electron beam having a third energy lower than the second energy is irradiated onto the bottom wall to form a deposition layer on the target object.

[0022] If the bottom wall is irradiated with an electron beam having high energy from the beginning, the melting of the deposition material is promoted, but the temperature of the bottom wall becomes very high, and bubbles are likely to be generated near the inner surface of the bottom wall. When bubbles are generated, the bubbles rise along the inner surface of the container. As a result, the peripheral part of the liquid surface (interface) of the molten deposition material tends to creep up along the inner surface of the container, and the peripheral part tends to remain unmelted.

[0023] By carrying out the first and second irradiation steps in a stepwise manner, the above problems do not occur or are less likely to occur. In the first irradiation step, the effect of the convection inducing member is limited or small, but bubbles generated near the inner surface of the bottom wall pass through the gaps present above the deposition material and are released upward. In the subsequent second irradiation step, the deposition material melts in its entirety, and thereafter, the generation of bubbles near the inner surface of the bottom wall is suppressed by convection caused by the convection inducing member. When forming the deposition layer, the energy of the electron beam is switched to an energy corresponding to a desired deposition rate. The energy of the electron beam is generally changed by varying the emission current.

[0024] (2) Details of the embodiment 1 shows a main part of a deposition apparatus 10 according to an embodiment. The deposition apparatus 10 has a vacuum chamber 12, an evaporator 14, and a turntable 16. The evaporator 14 and the turntable 16 are disposed in the vacuum chamber 12. A plurality of objects 18 are fixed to the turntable 16. Each object 18 is, for example, a substrate. In the embodiment, an optical thin film is formed on each substrate by deposition. A deposited film may also be formed on other objects.

[0025] The evaporation device 14 has a holder 22 supported by a number of supports 20. A container (liner) 24 is held by the holder 22. The container 24 consists of a body and a rim. The rim has a circular shape, and the body has a cup-like or dish-like shape.

[0026] The container 24 is made of, for example, molybdenum. Other materials that can be used to make the container 24 include high-melting point materials such as tungsten and carbon. In many cases, molybdenum is selected as the container material from the standpoint of cost and ease of processing. An alloy may also be selected as the container material. In any case, a high-melting point material is selected as the container material.

[0027] An electron beam irradiation facility serving as a heating facility is provided below the vessel 24. Specifically, an electron beam source 28 is disposed below the vessel 24, and a cooling block 30 having a scanning coil 32 is also disposed therebelow. Reference numeral 36 denotes an anode. A high voltage for extracting thermoelectrons is applied between the anode 36 and a cathode in the electron beam source 28.

[0028] A cathode current and the like are supplied from a power supply 38 to the electron beam source 28, and a scan current is supplied from the power supply 38 to the scan coil 32. The power supply 38 has, for example, an emission current control unit, a cathode current driver, a scan current driver, an acceleration power supply, etc. The operation of the power supply is controlled by a control unit 40.

[0029] The deposition material is placed in the container 24. The deposition material is heated to melt it, generating a molten deposition material 26. In this embodiment, the deposition material is a fluoride, specifically MgF2. Other deposition materials include LiF, NdF3, YbF3, YF3, and the like. A shutter 27 is provided on the upper side of the container 24.

[0030] In the embodiment, a small piece of tantalum is placed in the container 24 as the convection inducing member 42. For example, it is a tantalum foil having a size of 1×1 (mm). The thickness of the piece is 0.1 mm. From the viewpoint of handling, a tantalum foil having a larger size may be used. Other convection inducing members will be described in detail later. In any case, a material that interacts with the molten deposition material and thereby generates a convection in the molten deposition material is selected as the convection inducing member 42.

[0031] It has been confirmed that even with such a small convection inducer 42 as described above, convection occurs in the molten deposition material. The convection inducer 42 is located at the center of the inner surface of the bottom wall of the container, but is not fixed. Since the center of the inner surface is usually the hottest, that is, bubbles are likely to occur there, it is desirable to place the convection inducer 42 at the center of the inner surface. However, even if the convection inducer 42 is located at the periphery of the inner surface, convection occurs. In any case, the convection inducer 42 is provided in the container 24 so that the convection inducer 42 contacts the molten deposition material. Note that the flow lines 43 shown in FIG. 1 are expressed diagrammatically and do not necessarily represent actual flows. The same applies to FIG. 4, which will be described later.

[0032] Other forms of the convection inducing member 42 include plates, cylinders, and particles. Experiments have shown that the larger the surface area of ​​the convection inducing member 42, the greater the amount of convection. Considering cost and ease of handling, it is preferable to select foil. Multiple convection inducing members may be placed in the container 24.

[0033] After the convection inducing member 42 and the deposition material are put into the container 24, the deposition material is melted by continuously irradiating the bottom wall of the container 24 with the electron beam 34. Then, after the molten deposition material 26 starts to evaporate, the shutter 27 opens at a predetermined timing. As a result, a deposition film made of the deposition material is formed on the surface of the target object 18.

[0034] In the molten deposition material 26, convection occurs due to the convection inducing member 42. This convection agitates the molten deposition material 26, reducing the temperature variation in the molten deposition material 26. This suppresses the generation of bubbles near the bottom surface, making it difficult for bubbles to burst on the liquid surface of the molten deposition material 26.

[0035] FIG. 2 shows the experimental results. MgF2 is the deposition material. Each of the materials in the box 51 is the subject of the experiment. FIG. 2 shows the electronegativity of each material. The electronegativity of Mg (1.31) is the reference electronegativity. FIG. 2 shows the difference in electronegativity from the reference electronegativity. FIG. 2 also shows the melting point of each material. The portion indicated by the reference numeral 52 corresponds to the experimental results. The convection promotion effect 54 and the bubble generation suppression effect 56 were evaluated by visual observation.

[0036] When C and W were used, no convection was observed. When Mo was used, only slight convection was observed, and no significant bubble generation suppression effect was observed. When Fe was used, convection was observed, but only a small bubble generation suppression effect was observed. When Cr, Ti, and Ta were used, significant convection was observed, and a bubble generation suppression effect was also observed.

[0037] Therefore, when the deposition material is MgF2, Fe, Cr, Ti, and Ta can be used as the convection inducer as indicated by reference numeral 58, and it is particularly desirable to use Cr, Ti, and Ta as the convection inducer as indicated by reference numeral 60. Among them, the melting points of Cr and Ti are significantly lower than that of Ta. Therefore, in the embodiment, Ta is selected as the convection inducer. An alloy containing the above-mentioned metals may be used as the convection inducer. When the deposition film formed by the technology according to the embodiment was measured with an X-ray spectrometer, it was confirmed that the deposition film did not contain Ta.

[0038] The conditions under which convection occurs will be considered below.

[0039] Considering the experimental results shown in Figure 2, it can be said that electronegativity is related to the induction of convection. All of the materials that caused the convection have an electronegativity close to that of Mg. These materials are denoted as X. It is believed that the interaction between MgF2 and X resulted in a variation in the concentration of MgF2 in the container, which in turn caused the Marangoni convection. Marangoni convection is a flow that occurs due to non-uniform surface tension. Once Marangoni convection occurs, it usually continues.

[0040] In general, when the difference in electronegativity between two atoms that make up a molecule is large, the ionic bond becomes stronger and the covalent bond becomes weaker. Conversely, when the difference in electronegativity between two atoms that make up a molecule is small, the ionic bond becomes weaker and the covalent bond becomes stronger. In general, covalent bonds are stronger than ionic bonds. To transition to a bond that is stronger than the current bond, that is, to transition from an ionic bond to a covalent bond, external energy is required.

[0041] Taking the above into consideration, let us consider the relationship between MgF2 and X. In this consideration, we will assume that the electronegativity of X is greater than that of Mg.

[0042] In the case of MgF2, the electronegativity of F is much larger than that of Mg. In other words, the difference between the two electronegativities is large. Therefore, the ionic bond between Mg and F is strong. On the other hand, the difference between the electronegativity of X and that of Mg is small. Therefore, if X and F were to bond, the covalent bond would be relatively strong. The bond between Mg and F is more stable than the bond between X and F. In other words, in a steady state, MgF2 remains stable.

[0043] On the other hand, under heating by an electron beam, the energy for excitation is given from the outside, so it is possible for F to leave Mg and bond to X, from a probabilistic point of view. In particular, since the difference between the electronegativity of X and that of Mg is small, the energy required for a new bond may be small. In other words, the probability of F bonding to X increases.

[0044] When F transfers between Mg and X, the concentration of MgF2 in the container becomes non-uniform. This is thought to cause Marangoni convection. The transfer of F between Mg and X is understood to be a two-way transfer that occurs stochastically. In other words, the adsorption of F to X and the desorption of F from X occur simultaneously.

[0045] In addition, if the electronegativity of X is smaller than that of Mg, the bond between X and F will be more stable than the bond between Mg and F. In other words, this will affect the composition of MgF2. Therefore, such a combination cannot be adopted.

[0046] To summarize the above, X must be selected to satisfy the first condition that the electronegativity of X is greater than that of Mg, and the second condition that the difference between the electronegativity of X and that of Mg is small. Regarding the second condition, X may be determined so that the difference between the two electronegativities is smaller than 0.85, and preferably, X is determined so that the difference is 0.52 or less.

[0047] The above reasoning is believed to be valid for fluorides other than the deposition material MgF2, which was the subject of the experiment. This is because the electronegativity of F is very large. The above reasoning is also believed to be generally applicable to deposition materials other than fluoride compounds. A convection inducing member can be clearly defined in terms of inducing convection or in terms of placing such a member in a container.

[0048] 3 is a flow chart showing a vapor deposition method according to an embodiment. In S10, a convection inducing member is placed, for example, at the center on the inner surface of a bottom wall of a container. In S12, a powder or granular vapor deposition material is placed in the container.

[0049] S14 is a process for partially melting the deposition material. Specifically, a first electron beam energy (first emission current value) is set, and then an electron beam is irradiated onto the bottom wall of the container. The first electron beam energy is smaller than a second electron beam energy described below. In S14, the lower part of the deposition material in the container is partially melted. At that time, the upper part is in a non-melted state. When bubbles are generated near the inner surface of the bottom of the container, the bubbles rise to the bottom and are released to the outside world through a gap included in the upper part.

[0050] S16 is a process for melting the entire deposition material. Specifically, a second electron beam energy (second emission current value) is set. That is, an electron beam with a larger energy is irradiated onto the bottom wall of the container. This causes the entire deposition material in the container to be in a melted state.

[0051] The convection inducing member functions continuously during the transition process from when the deposition material is partially melted to when the deposition material is entirely melted, and during the subsequent deposition process. At either stage, temperature variation is suppressed by generating convection in the melted portion. In the absence of convection, the amount of bubbles rising along the inner surface, which has a high temperature, increases, but with convection, the amount of bubbles rising along the inner surface can be reduced. Therefore, creeping up and solidification of the deposition material around the liquid surface (interface) is suppressed.

[0052] S18 is a deposition step. Specifically, a third electron beam energy (third emission current value) is set. The third electron beam energy is appropriately determined according to the deposition rate, and is usually smaller than the second electron beam energy. In S18, the shutter is opened and deposition starts. In the deposition process, the thickness of the deposited film is measured by a film thickness meter, and the deposition rate is controlled based on the measurement result.

[0053] 4 shows an evaporation device according to another embodiment. The container 62 is composed of a main body and a coating layer 64. The coating layer 64 covers the inner surface 62A of the bottom wall and the inner surface 62B of the side wall. The coating layer 64 is composed of a convection inducing member, for example, Ta.

[0054] The container 62 contains a molten deposition material. The coating layer 64 causes convection in the molten deposition material. This prevents localized temperature rises that tend to occur in the molten deposition material under indirect heating, and prevents or reduces splashing. The coating layer 64 has a large surface area (contact area), which increases the amount of convection.

[0055] 5 shows several examples of the form of the convection inducing member. Examples of the form include a foil 72, a plate 74, a rod 76, and a grain 78. When Ta is selected as the convection inducing member, it is desirable to select the foil 72 because Ta is a relatively expensive material.

[0056] A modified example of the container is shown in Fig. 6. A recess 84 is formed in the center of a bottom wall 82 of the container 80. A Ta foil 86, which is a convection inducing member, is disposed in the recess 84. This configuration makes it possible to position the convection inducing member. The container may be provided with another structure for holding the convection inducing member. The convection inducing member may be used in a manner other than the indirect heating method. [Explanation of symbols]

[0057] 10 deposition apparatus, 12 vacuum chamber, 14 evaporation apparatus, 18 substrate, 24 vessel, 26 molten deposition material, 28 electron beam source, 42 convection inducing member.

Claims

1. A container for containing a deposition material; a heating device for irradiating an electron beam onto a bottom portion of the container to heat the container and thereby indirectly heat the deposition material, thereby producing a molten deposition material; a convection inducing member provided in the container at a location in contact with the molten deposition material, the convection inducing member having a melting point higher than that of the deposition material, and interacting with the molten deposition material in the container to generate convection in the molten deposition material; An evaporation device comprising:

2. 2. The evaporation device according to claim 1, the deposition material is a compound containing fluorine and a first metal, The convection inducing member includes a second metal capable of chemically bonding with the fluorine. An evaporation device characterized in that

3. The evaporation device according to claim 2, the first metal has a first electronegativity; the second metal has a second electronegativity; the second electronegativity is greater than the first electronegativity; An evaporation device characterized in that

4. The evaporation device according to claim 3, the difference between the first electronegativity and the second electronegativity is less than 0.85; An evaporation device characterized in that

5. The evaporation device according to claim 4, the first metal is Mg; The second metal is a metal selected from Fe, Cr, Ti and Ta; An evaporation device characterized in that

6. 6. The evaporation device according to claim 5, The deposition material is MgF2, The convection inducing member is Ta. An evaporation device characterized in that

7. 2. The evaporation device according to claim 1, The convection inducing member is a member dropped into the container. An evaporation device characterized in that

8. 2. The evaporation device according to claim 1, The convection inducing member constitutes a coating layer provided on the inner surface of the container. An evaporation device characterized in that

9. placing a convection inducing member and a deposition material in a container; indirectly heating the deposition material by irradiating a bottom wall of the container with an electron beam, thereby producing a molten deposition material; Including, the convection inducing member includes a metal having a melting point higher than that of the deposition material and interacting with the molten deposition material in the container to induce convection in the molten deposition material; The evaporation method according to claim 1,

10. The evaporation method according to claim 9, The step of forming the molten deposition material comprises: a first irradiation step of irradiating the bottom wall with a first electron beam having a first energy, thereby melting a lower portion of the deposition material in the container; a second irradiation step of irradiating the bottom wall with a second electron beam having a second energy higher than the first energy, thereby melting the entire deposition material in the container; Including, After the step of producing the molten deposition material, a third electron beam having a third energy lower than the second energy is irradiated onto the bottom wall to form a deposition layer on the target. The evaporation method according to claim 1,

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