Wafer support member, wafer-holding tool and wafer- holding device

[0001] [Technical field to which the invention belongs] The present invention relates to a wafer holding member, a wafer holder, and a wafer holding device suitable for heat treatment of silicon wafers, particularly high temperature heat treatment such as fabrication of SIMOX (Separation by encapsulated oxygen) wafers and annealed wafers. [0002] [Conventional technology] In recent years, as the diameter of silicon wafers has increased, vertical heat treatment furnaces have come to be used as heat treatment devices for silicon wafers. A vertical boat is installed in this vertical heat treatment furnace, and the vertical boat is provided with a plurality of vertically extending struts, and wafers are mounted in a plurality of support grooves provided on the inner side surfaces of the struts. Heat treatment is performed. However, in such a support method, a wafer support portion is provided on the outermost periphery of the wafer, and the weight of the wafer is concentrated near the support portion. Therefore, high-temperature heat treatment such as fabrication of a SIMOX wafer or an annealed wafer is performed. In the case of, a large bending stress is generated near the wafer support, and if this stress exceeds the yield stress of the silicon wafer at the heat treatment temperature, a defect called slip inside the wafer during the heat treatment is performed. There was a problem that occurred. [0003] In order to avoid this problem, as shown in FIG. 5, the wafer support plate 6 is placed in the support grooves 3 of the plurality of columns 2 of the boat 1, the wafer is placed on the wafer support plate 6, and the support area is increased by performing heat treatment. A method of increasing and suppressing the occurrence of slip has been used. Furthermore, by forming a concave notch 7 in this support plate, it is possible to apply a wafer transfer device that sucks and conveys the back surface of the wafer with a vacuum chuck, and high productivity is realized by high-speed loading and unloading. Has been done. [0004] However, even with this technique, slip is not sufficiently suppressed. In the above technique, the shape of the wafer support plate is not symmetrical with respect to the center thereof, and the support plate itself is asymmetrically supported by the support columns 2, so that the wafer support plate is deformed during the heat treatment. On the other hand, as the contact area between the wafer support plate and the silicon wafer increases, the frictional force between the wafer support plate and the silicon wafer increases. Therefore, the stress due to thermal deformation of the wafer support plate is easily transmitted to the silicon wafer, and slip is easily generated. [0005] In order to avoid this problem, in Japanese Patent Application Laid-Open No. 2000-91406, as shown in FIG. 6, three silicon balls 12 serving as wafer receiving members are placed on a wafer support plate 11 having no notch. A support for supporting the silicon wafer 10 at three points by a silicon ball has been proposed. In this method, since the wafer support plate has no notch, the thermal deformation of the wafer support plate is relatively small. Further, in the non-oxidizing atmosphere heat treatment in which the silicon sphere and the silicon wafer are not welded, the frictional force between the wafer support plate and the wafer can be relaxed by the point support. Therefore, slip caused by thermal deformation of the wafer support plate can be suppressed. [0006] However, even with this technique, in the heat treatment in an oxidizing atmosphere used in SIMOX annealing, the silicon spheres are welded to the silicon wafer, so that slip due to thermal deformation of the wafer support plate has not been sufficiently suppressed. Further, since the wafer support plate has no notch, the wafer transfer device becomes large, and the space required for the transfer operation expands above and below the wafer support plate. Further, since the transport operation is complicated, the transport time becomes longer than before. Therefore, the productivity of the heat treatment furnace per batch is reduced. An even bigger problem is that in this technique, a load of 1/3 of the wafer's own weight is concentrated and applied to the support, so that the stress due to the wafer's own weight causes slip in the wafer support. In this way, in the above method of distributing the weight of the wafer to the wafer support portions at only three locations, the weight of the wafer continues to increase as the diameter of the silicon wafer increases, and the problem of slip occurrence will occur in the future. It is clear that it will become more and more serious. [0007] On the other hand, a method of preventing slip occurrence without using a wafer support plate has also been proposed. For example, as in JP-A-11-40569, this is a method in which a boat is provided with four wafer support portions per wafer. In this case, since there are four wafer support parts, it is clear that the stress generated by the weight of the silicon wafer at each wafer support part is smaller than when the wafer is supported by three similarly shaped wafer support parts. Is. However, in this method, it is necessary that the heights of the wafer support portions are aligned with an accuracy of 30 μm or less at all four locations, so that it becomes extremely difficult and expensive to manufacture a boat having this dimensional accuracy. I have a problem to say. Further, if the boat is provided with five or more wafer support parts per wafer, it becomes more difficult to manufacture a boat having this dimensional accuracy, and therefore the number of wafer support parts cannot be easily increased. I have a problem to say. Needless to say, the same problem also occurs when the number of silicon balls mounted on the wafer support plate is set to 4 or more in the method of JP-A-2000-91406. [0008] [Problems to be Solved by the Invention] In heat treatment of silicon wafers, especially high-temperature heat treatment such as fabrication of SIMOX wafers and annealed wafers, it is possible to sufficiently suppress the occurrence of slips by using an inexpensive wafer holder without impairing productivity. From the viewpoint of improving the manufacturing yield, it is an important issue that must be solved, and in order to realize it, a wafer holder that satisfies the following requirements is required. That is, (1) a holder structure that can tolerate a dimensional error exceeding 30 μm in order to enable the manufacture of an industrially feasible and inexpensive holder, and (2) generation of stress due to the weight of the wafer itself. The structure is such that the wafer can be supported by four or more wafer support parts in order to suppress the above, and (3) the structure is such that the wafer is point-supported in order to alleviate the stress due to thermal deformation of the wafer support plate. 4) In order to maintain high productivity, the wafer holder has a concave notch, and it is possible to apply a wafer transfer device that sucks and conveys the back surface of the wafer with a vacuum chuck. 5) The holder must meet the requirements that it is composed of a silicon wafer and a material that does not weld during heat treatment. Further, a wafer holding device and a heat treatment furnace incorporating a wafer holder satisfying the above requirements are required. [0009] However, as already described, the prior art has not yet solved the above problems. [0010] An object of the present invention is to solve the above-mentioned problems and to provide a wafer support member, a wafer holder, and a wafer holding device suitable for high-temperature heat treatment of a silicon wafer. [0011] [Means for solving problems] As described above, the present inventor has created a silicon wafer that satisfies the requirements (1) to (5) above, which is suitable for heat treatment of silicon wafers, particularly high-temperature heat treatment for manufacturing SIMOX wafers and annealed wafers. We have been diligently studying the holding method. Among them, it was thought that a holder capable of satisfying the above five requirements could be manufactured by imparting a height adjusting function to the support member supporting the wafer, and an experiment was conducted to complete the invention. [0012] That is, the present invention (1) A support member that is placed on a wafer holder and on which a wafer is placed. The support member is composed of three structures, an upper part, an intermediate part, and a lower part, and at least the material of the intermediate part structure is A wafer support member characterized by being made of a material that softens at a wafer heat treatment temperature. (2) The wafer support member according to (1) above, wherein the upper and lower structures of the support member have a convex shape such that they make point contact with the wafer or the wafer holder. (3) The materials of the upper and lower structures of the support member are SiC and Si.₃N₄Or, SiC and / or Si on the surface₃N₄The wafer support member according to (1) or (2) above, which is one kind selected from Si coated with the above, or a combination thereof. (4) The wafer support member according to any one of (1) to (3) above, wherein the material of the intermediate structure is quartz glass. (5) A plate-shaped holder on which a wafer is placed on the upper surface, in which n or more wafer receiving members are arranged on the holder, and at least (n-2) of the wafer receiving members (however). , N is an integer of 4 or more) is the wafer support member according to any one of (1) to (4) above. (6) The material of the plate-shaped holder is SiC, Si.₃N₄, SiO₂, Si, or SiC on the surface and / or Si₃N₄The wafer holder according to (5) above, which is one selected from Si coated with. (7) A wafer holding device for supporting and placing a plurality of wafers, and the above (5) or the above-mentioned (5) or in a plurality of holding tool recesses formed in a plurality of columns arranged substantially in parallel of the holding device. (6) A wafer holding device characterized in that the wafer holder described above is inserted and held horizontally. [0013] BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described. [0014] The support member of the present invention is arranged on the wafer holder to support the wafer. The support member of the present invention is composed of three main structures, an upper structure, an intermediate part structure, and a lower structure. Among them, the upper structure and the lower structure are composed of members made of a material that does not lose the rigidity to withstand the load from the Si wafer during the annealing process. Further, it is desirable that these structures are not welded to the Si wafer and the wafer support plate. Specifically, SiC, Si₃N₄Or, SiC and / or Si on the surface₃N₄One selected from Si coated with or a combination thereof. On the other hand, the material of the intermediate structure is a substance that has rigidity to withstand the weight of the wafer at room temperature, but softens at a high temperature during annealing. However, it is necessary that it does not melt. Specifically, quartz glass is preferable. [0015] Further, it is desirable that the upper and lower structures have protrusions so as to make point contact with the wafer and the wafer holder. By supporting by point contact, the possibility of welding with the wafer and the wafer holding member can be reduced. Specifically, it is desirable that the shape has a spherical surface with a radius of curvature of 100 mm or less. Further, it is necessary to prevent the intermediate structure from causing non-uniform deformation at the time of deformation. From the viewpoint of ease of manufacturing the support member, it is desirable that the lower surface of the upper structure and the upper surface of the lower structure, and the upper surface and the lower surface of the intermediate structure are parallel planes. However, the shape is not limited as long as the intermediate structure is not deformed non-uniformly. Further, in order to avoid buckling of the intermediate structure, it is preferable to make the width direction larger than the height. In the case of the simplest structure, as shown in FIG. 1, the upper and lower structures have a hemispherical shape, and the intermediate structure has a cylindrical shape. The upper structure and the lower structure are usually the same, but if the conditions of the present invention are satisfied, there is no problem even if the shapes and sizes are different as shown in FIG. [0016] The wafer holder of the present invention is a plate-shaped holder on which a wafer is placed on the upper surface, and n or more wafer receiving members are arranged on the holder. Where n is an integer greater than or equal to 4. That is, the wafer holder of the present invention has four or more wafer support points. When the number of support points is 3 or less, the stress due to the weight of the wafer tends to cause slip in the wafer support portion, which is not preferable. Further, at least (n-2) of the wafer receiving members must be the above-mentioned wafer holding members of the present invention. Normally, when a wafer is supported by four or more support points, all the support points must be aligned on almost the same plane, so the heights of the support points must be aligned with high accuracy, for example, within 30 μm. is there. However, since the support member of the present invention has an intermediate structure made of a material that deforms at high temperature in the structure, the intermediate structure softens as annealing progresses, so that the support point is supported by the weight of the wafer itself. The heights of the wafers are uniform, and the weight of the wafer is evenly distributed at the support points. Further, even when the wafer holder is deformed by thermal stress, uniform loading at each support point can be realized by the same mechanism. In addition, even if the number of support members is further increased to 5 or more, uniform weighting at each support point can be realized by the same mechanism. By using the support member of the present invention, it is possible to easily cope with the future increase in the diameter of the wafer, that is, the increase in the weight of the wafer. [0017] Further, if one or two of the support points are used, a conventional support member having no intermediate structure, for example, a support member having a sphere or a pin shape, may be used instead of the support member of the present invention. good. When the support members of the present invention are used to support other than these support points, the height of the support members of the present invention can be adjusted to achieve uniform loading. Therefore, when the support members of the present invention are used for all the support points. It is possible to obtain almost the same effect as. A fixed support member integrated with the wafer holder may be used instead of the conventional support member. [0018] In the wafer holding plate of the present invention, for example, as shown in FIG. 3, a wafer supporting member is mounted on a disk-shaped wafer holding plate. The material of this wafer holding plate is usually SiC or Si.₃N₄, SiO₂, Si, or SiC on the surface and / or Si₃N₄It is one kind selected from Si coated with. If you have a fixed support member, the fixed support member is SiC, Si₃N₄Or, SiC and / or Si on the surface₃N₄It is desirable to make it with Si coated with. An example is shown in Fig. 4. It is desirable that the wafer holder has a notch formed at the insertion position of the vacuum chuck so that a wafer transfer device of a method of sucking and transporting the back surface of the wafer by the vacuum chuck can be applied. [0019] Such a wafer holder is inserted into a wafer holding device for supporting and placing a plurality of wafers provided in a semiconductor heat treatment furnace, and is held horizontally. This wafer holding device is a vertical boat 1 having three or four columns 2 in the vertical direction, as shown in FIG. 5, in which case the wafer holding device is inserted into the holding tool groove 3. .. Vertical boats are usually SiC, SiO₂Or formed by Si. [0020] After the wafer holder is held horizontally by the wafer holding device, the wafer 10 is attracted to the back surface of the wafer 10 by a wafer transfer device having a vacuum chuck, and is horizontally carried onto the upper part of the wafer holder from the opening direction of the notch 22. Will be done.When the wafer 10 is carried horizontally to a position where the center of the wafer 10 and the substantially center of the wafer holder 21 are aligned in the vertical direction, the vacuum chuck is lowered in the vertical direction. Along with this, the wafer 10 also descends in the vertical direction, and the wafer adsorption by the vacuum chuck is released here, so that the wafer 10 is supported on the wafer holder via the receiving member. [0021] [0021] The vacuum chuck is then pulled out from the opening of the notch 22 and moves on to the next transfer operation. Such a transfer operation is also a method adopted in the conventional technique of directly supporting a silicon wafer by a boat. In this method, the distance between the grooves 3 for the holder can be made smaller than the method in which the lifting pin and the automatic transfer chuck are used for transportation as described in Japanese Patent Application Laid-Open No. 2000-91406. It does not impair productivity. Further, since the transport mechanism is simple, high-speed transport is possible, and at the same time, the transport device is difficult to increase in size. [0022] After the wafer 10 is held on the wafer holder via the plurality of receiving members according to the above procedure, the wafer holding device, for example, the vertical boat 1, is placed in a heat treatment tube installed in the heat treatment furnace. After being introduced, a predetermined heat treatment is subsequently carried out. The conditions of heat treatment vary depending on the purpose of treatment, but most of them have a standby furnace temperature in the range of 600 to 1000 ° C when the vertical boat 1 is introduced into the furnace, and 0.1 to 20 ° C / from there. A process in which the temperature inside the furnace is raised at a heating rate of about min, heat-treated in the range of 600 to 1400 ° C for a predetermined time, and then returned to the standby furnace temperature at a temperature lowering rate of about 0.1 to 20 ° C / min. It becomes. At this time, the atmosphere in the furnace is generally argon, hydrogen, oxygen, HCl or the like or a mixture thereof. [0023] For heat treatment of wafers, in addition to the treatment in a vertical heat treatment furnace, rapid thermal annealing / oxidation (RTA / RTO) treatment, in which the wafer is rapidly raised and lowered after being introduced into the furnace, is performed. It goes without saying that the wafer holder described in the present invention can also be used for this RTA / RTO treatment. [0024] The heat-treated wafer is discharged from the heat treatment tube together with the vertical boat 1. After that, the wafer transfer device having the vacuum chuck performs the reverse operation of the wafer loading procedure described above, so that the wafer 10 is directed from the upper portion of the wafer holder 21 to the notch 22 formed in the wafer holder 21. Is discharged horizontally. [0025] [Example] Examples of the present invention will be described below. [0026] (Experimental example) It was confirmed from experiments whether the wafer support member and the holder of the present invention exert a desired effect. The manufactured support member is of the type shown in Fig. 1. Specifically, the material of the upper structure and the lower structure is SiC, and the shape is 10 mm in diameter, 5 mm in height, and 5 mm in radius of curvature. The material of the hemispherical, intermediate structure is quartz glass, and its shape is a cylinder with a diameter of 10 mm and a height of 5 mm. These were piled up and integrated. In addition, a SiC support member having almost the same size as the integrated support member was manufactured and used. As the wafer holder, a disk as shown in FIG. 3 was used. The material used was SiC. In addition, a holder with a fixed support member as shown in FIG. 5 was also used. The size of the holder is 220 m in diameter for 8 inches (200 mm) and 320 mm in diameter for 12 inches (300 mm). The support member was arranged at a position 70% of the wafer radius away from the center of the holder and at a position where the polygon formed by the support point becomes a regular polygon. [0027] The wafers used in the experiment are an 8-inch silicon wafer (diameter 200 mm) and a 12-inch wafer (diameter 300 mm). The heat treatment pattern was dry oxidation treatment at 1390 ° C for 12 hours, and the slip occurrence situation at that time was investigated using X-ray topography. [0028] The results are shown in Table 1. In the table, indicates that no slip has occurred, Δ indicates that there is a slight slip, and × indicates that there is a severe slip. As shown in Table 1, in the comparative example, there are many Δ or ×, whereas in the example of the present invention, all of them are , indicating that the present invention is extremely effective in preventing slippage. [0029] [table 1]<img file="JP4589545B2_D0001.tif" />[0030] [Effect of the invention] As described above, according to the present invention, an industrially feasible and inexpensive wafer support member and wafer holder suitable for heat treatment of silicon wafers, particularly high temperature heat treatment such as fabrication of SIMOX wafers and annealed wafers. Therefore, it is possible to provide a wafer support member and a wafer holder capable of preventing the occurrence of slipping of a silicon wafer. Further, according to the present invention, it is possible to provide a wafer holding device capable of preventing the silicon wafer from slipping while maintaining high productivity by mounting the wafer holder. [Simple explanation of drawings] FIG. 1 is a diagram showing an embodiment of a support member of the present invention. FIG. 2 is a diagram showing another embodiment of the support member of the present invention. FIG. 3 is a diagram showing an embodiment of the holder of the present invention. FIG. 4 is a diagram showing another embodiment of the holder of the present invention. FIG. 5 shows a vertical boat equipped with a wafer holder. FIG. 6 is a diagram showing a wafer holder of the prior art. [Explanation of symbols] 1 ... boat 2 ... Boat prop 3 ... Support groove 6 ... Wafer holding plate 7 ... notch 10 ... Silicon wafer 11 ... Wafer holding plate 12 ... Silicon sphere 21 ... Superstructure of support member 22 ... Intermediate structure of support member 23 ... Substructure of support member 31 ... Wafer support member 32 ... Wafer fixing support member