Wafer support and method for manufacturing the wafer support

Abstract

This provides a new wafer support with reduced black spots that detract from the aesthetic appearance. [Solution] The wafer support 10 comprises a base material 16 made of a ceramic sintered body and a conductive member 18 which is at least partially embedded in the base material. The base material 16 contains 96% by mass or more of aluminum oxide and contains lithium fluoride or potassium fluoride.

Description

Technical Field

[0001] The present invention relates to a support for supporting a wafer.

Background Art

[0002] Conventionally, electrostatic chucks for holding a semiconductor wafer or controlling the temperature of a semiconductor wafer have been used in various semiconductor processes. The materials used for electrostatic chucks vary depending on the environment in which they are used and the required characteristics. For example, an electrostatic chuck made of ceramics mainly composed of alumina is known from the viewpoints of plasma resistance, high breakdown voltage, high strength, and high dielectric constant (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when ceramics mainly composed of alumina are fired in an atmosphere where carbon is present (for example, using a carbon mold), black spots may be present in the fired ceramics. Such black spots not only impair the appearance of the product but may also contribute to a decrease in insulation.

[0005] The present invention has been made in view of such a situation, and an object thereof is to provide a new wafer support in which black spots that impair the appearance are reduced.

Means for Solving the Problems

[0006] To solve the above problems, a wafer support according to one aspect of the present invention comprises a substrate made of a ceramic sintered body and a conductive member that is at least partially embedded in the substrate. The substrate contains 96% by mass or more of aluminum oxide and contains lithium fluoride or potassium fluoride.

[0007] According to this embodiment, black spots that tend to occur when carbon is present in the atmosphere or equipment during firing can be reduced.

[0008] The substrate may contain 0.05 to 0.50% by mass of lithium or potassium in terms of fluoride. This allows for a reduction in black spots without the resistivity of the substrate becoming too low as a wafer support.

[0009] The substrate may further contain at least one oxide of magnesium, silicon, calcium, zirconium, and ytterbium. This enables low-temperature sintering and densification while suppressing the growth of aluminum oxide grains.

[0010] The number of black spots with a major axis of 100 μm or more may be 1 or less [spot / φ58 mm]. This makes it possible to realize a wafer support that does not impair aesthetics.

[0011] The substrate may have a relative density of 98% or higher. This makes it easier to maintain the strength and shape of the wafer support.

[0012] Another aspect of the present invention is a method for manufacturing a wafer support. This method includes the steps of: preparing a raw material powder containing 96% by mass or more of aluminum oxide and 0.05 to 0.50% by mass of lithium fluoride or potassium fluoride; placing the raw material powder in a space of a carbon mold of a predetermined shape; and firing the raw material powder by pressurizing the space in the range of 15 to 40 MPa and heating it in the range of 1350 to 1650°C.

[0013] According to this embodiment, black spots can be reduced even when a carbon mold is used during firing.

[0014] In addition, any combination of the above components, as well as those obtained by converting the expression of the present invention among methods, apparatuses, systems, etc., is also effective as an aspect of the present invention. Further, those obtained by appropriately combining the above-described elements may also be included in the scope of the invention for which patent protection is sought in this patent application.

Advantages of the Invention

[0015] According to the present invention, a new wafer support with reduced black spots that impair the aesthetics can be realized.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic cross-sectional view of an electrostatic chuck disposed in an etching chamber. [Figure 2] It is a perspective view of the electrostatic chuck according to the present embodiment. [Figure 3] It is a view showing black spots generated on a fired alumina substrate. [Figure 4] It is a view showing the measurement results of Raman spectroscopy of the black spots shown in FIG. 3. [Figure 5] It is a flowchart for explaining the manufacturing method of the wafer support according to the present embodiment.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same reference numerals are assigned to the same elements, and redundant descriptions will be omitted as appropriate.

[0018] (Wafer Support) First, the schematic configuration of the wafer support will be described. The wafer support only needs to be able to support a semiconductor substrate such as a silicon wafer, and may be provided with an adsorption mechanism and a temperature adjustment mechanism. Further, the wafer support functions as an electrostatic chuck that generates an adsorption force on the mounted wafer.

[0019] Hereinafter, a case where the wafer support is an electrostatic chuck provided with a cooling mechanism will be described as an example. FIG. 1 is a schematic cross-sectional view of an electrostatic chuck disposed in an etching chamber. FIG. 2 is a perspective view of the electrostatic chuck according to the present embodiment.

[0020] The etching apparatus 100 including the chamber 12 shown in FIG. 1 is a semiconductor manufacturing apparatus for etching the surface of a wafer W such as silicon as a semiconductor substrate with plasma P. The wafer support 10 functioning as an electrostatic chuck is used to support the wafer W in the chamber 12. Further, an upper electrode 14 for generating plasma P is provided in the chamber 12.

[0021] The wafer support 10 includes a base material 16 made of a ceramic sintered body and a conductive member 18 at least partially included in the base material 16. The wafer W is mounted on the mounting surface 16a which is the surface of the base material 16. The conductive member 18 functions as an electrostatic chuck electrode to which a voltage V for generating an adsorption force for fixing the wafer W to the mounting surface 16a is applied. In the wafer support 10 according to the present embodiment, the conductive member 18 is embedded in the base material 16 which is a sintered body. Therefore, the conductive member 18 needs to be disposed inside the raw material powder at the firing stage and is preferably a high melting point metal that does not melt at the firing temperature. For example, as the material of the conductive member, high melting point metals such as molybdenum, tungsten, tantalum, or alloys containing two or more of them are preferable.

[0022] Further, the wafer support 10 is formed with a gas supply path 20 that passes through the inside of the base material 16 from the mounting surface 16a exposed on the chamber side to an external gas supply source (not shown). The gas supply path 20 is for supplying a gas G for cooling the wafer W adsorbed on the mounting surface 16a from the back side between the mounting surface 16a and the wafer W. Thereby, the wafer W heated by plasma or the like can be cooled, and the deviation of the temperature distribution of the wafer W can be reduced. The gas G is, for example, helium which is an inert gas.

[0023] The substrate 16 is mounted on the metal plate 24 via an adhesive layer 22. The metal plate 24 is made of a metallic material such as aluminum or titanium, and has internal channels 26 through which water H, a cooling substance, flows. This allows it to be used in vacuum processes where uniform temperature across the entire wafer surface is required, such as dry etching.

[0024] (Base material components) The substrate 16 according to this embodiment contains aluminum oxide (alumina) as its main component. Alumina is used in a variety of applications due to its high strength, high resistivity, and high plasma corrosion resistance, and is also used as a component of semiconductor manufacturing equipment (for example, as a material for electrostatic chucks). Furthermore, alumina used as a component of semiconductor manufacturing equipment is required to have particularly high plasma corrosion resistance. For this reason, hot pressing, which allows for high-density, dense firing in a relatively short time, is sometimes used. In addition, since firing by hot pressing does not require the addition of impurities such as binders, it is one of the useful sintering methods when purity of the sintered body is required.

[0025] On the other hand, the equipment used for hot pressing employs carbon molds, and black spots may occur in the alumina fired within the carbon mold. Therefore, there is a concern that the aesthetic appearance of the wafer support may be impaired by firing using hot pressing. Figure 3 shows black spots that occurred on the fired alumina substrate. Figure 4 shows the results of Raman spectroscopy measurements of the black spots shown in Figure 3.

[0026] The measurement results shown in Figure 4 consist of Raman intensity data from the region containing sunspot BP in the upper panel and Raman intensity data from the normal region N without sunspots in the lower panel. The Raman peak P1 in the upper panel corresponds to the carbon D band (1360 cm²). -1 (Nearby), Raman Peak P2 is a carbon G-band (1580cm) -1This is a characteristic of the area, and it is thought that the black spots (BP) are caused by carbon. Furthermore, the mechanism by which carbon black spots occur in hot pressing using carbon molds is thought to be that when carbon monoxide (CO) gas generated by heating inside the mold is compressed, carbon dioxide (CO2) gas and carbon (C) black spots are generated as shown in equation (1) below. Equation (1) 2CO(g)→CO2(g)+C(s)

[0027] Black spots (BP) made of carbon not only impair the aesthetic appearance of products and substrates, but also cause contamination within equipment, so it is desirable to reduce them as much as possible. As a result of diligent research by the inventors of this application, they conceived the idea that black spots can be reduced by including a certain type of fluoride in the raw materials.

[0028] Specifically, the substrate of the wafer support 10 according to this embodiment contains 96% by mass or more of aluminum oxide and also contains lithium fluoride or potassium fluoride. This makes it possible to reduce black spots that tend to occur when carbon is present in the atmosphere or equipment during firing.

[0029] (Method of manufacturing wafer support) Figure 5 is a flowchart illustrating the method for manufacturing a wafer support according to this embodiment. First, a raw material powder is prepared by mixing a main raw material powder that will become a ceramic component, such as aluminum oxide, zirconium oxide, and ytterbium oxide, with a sintering aid powder such as magnesium oxide, calcium oxide, and silicon oxide, and a fluoride such as lithium fluoride and potassium fluoride, according to a predetermined blending amount (S10). The blending amount of aluminum oxide, which is the main component, is adjusted so that it is contained in the substrate at a concentration of 96% by mass or more. The aluminum oxide used in this embodiment is α-alumina with a purity of 99.99% or higher and an average particle size of about 0.4 μm.

[0030] The main component, aluminum oxide, is mixed with zirconium oxide, ytterbium oxide, magnesium oxide, calcium oxide, silicon oxide, lithium fluoride, potassium fluoride, etc., in predetermined proportions (S12). This mixing is carried out, for example, by wet mixing for 16 hours using a pot mill with a nylon pot and alumina balls. As a solvent, for example, ethanol with a concentration of about 0.75 kg / L (in the range of 0.1 to 1.0 kg / L) is used. Water or isopropyl alcohol (IPA) may be used instead of ethanol.

[0031] Next, the solvent is removed using an evaporator and the mixture is granulated. To further remove the solvent completely, the mixed raw materials are dried on a hot plate at 230°C (S14). Alternatively, the granulation may be performed using a spray dryer. The dried raw material powder is filled into a graphite mold and uniaxially pressed (S16). In this state, it is heated to 1400°C, held at a pressure of 30 MPa for 2 hours, and fired to produce a sintered body (S18).

[0032] Furthermore, a portion of the raw material powder or molded body may be replaced with a sintered body. In order to provide the electrodes of the electrostatic chuck inside the sintered body, when filling the hot press apparatus with raw material powder, molded body, or sintered body, a component or material that will become a conductor after firing (e.g., metal plate, metal foil, conductive paste, coil, mesh, etc.) should be placed (embedded) in the predetermined position. The shape of the conductor is not particularly limited. This firing can be carried out, for example, using a hot press apparatus. Hot pressing is carried out in a non-oxidizing (inert) atmosphere, such as nitrogen or argon, but it may also be carried out in pressurized nitrogen. The hot pressing temperature is, for example, in the range of 1350 to 1650°C. If the temperature is too low (e.g., below 1300°C), sintering will be insufficient and densification will not occur, and if it is too high, grain growth will occur and the withstand voltage will decrease. The applied pressure is appropriate in the range of 15 to 40 MPa. The duration of hot pressing depends on the temperature and dimensions, but is usually about 1 to 4 hours. Subsequently, the sintered body is processed into the desired shape (S20), and the wafer support is manufactured.

[0033] Various characteristics of each sample produced by the above method (Examples 1 to 8 and Comparative Examples 1 to 6, described later) are measured and evaluated.

[0034] (Relative density) Relative density was calculated using the Archimedes method with a 37mm x 4mm x 3mm flexible rod.

[0035] (Number of sunspots in the plane) Plates with a diameter of 58 mm and a thickness of 1 mm, manufactured using the method described above, were measured visually and with calipers. The black dots were counted as those with a major axis of 100 mm or more when represented as an ellipse. (brightness) A φ58mm, 1mm thick plate manufactured using the method described above was used for measurement with a color difference meter compliant with JIS Z 8722 (Konica Minolta, Inc. CM-26d). A white plate with a lightness of 90 or higher was used as the background.

[0036] (Elemental analysis of impurities and metals) The content is quantified by ICP-AES (Inductively Coupled Plasma Emission Spectroscopy). The content of constituent elements in the ceramic sintered body in terms of oxides may also be calculated as follows: First, the constituent elements of the ceramic sintered body are qualitatively analyzed using an X-ray fluorescence analyzer (XRF) or an energy dispersive analyzer (EDS) attached to a scanning electron microscope (SEM). Next, each element detected by this qualitative analysis is quantitatively analyzed using an ICP emission spectrometer. Then, the content of each element measured by this quantitative analysis is converted to oxides.

[0037] [Examples] Next, the characteristics of the wafer supports in each example and comparative example will be described. The content of ceramic components and sintering aid components in each example and comparative example is shown in Table 1. The samples in each example contain 96% by mass or more of aluminum oxide. The measurement results for each characteristic are also shown in Table 1. [Table 1]

[0038] As shown in each example, if the substrate contains 96% by mass or more of aluminum oxide and 0.05 to 0.50% by mass of lithium or potassium in terms of fluoride, the resistivity of the substrate can be reduced without becoming too low as a wafer support. Furthermore, the substrates in each example have 1 or fewer black spots [per φ58 mm] with an elliptical major axis of 100 μm or more, thus realizing a wafer support that does not impair aesthetics.

[0039] Furthermore, as shown in each example, the substrate further contains at least one of the following: (1) magnesium in the form of magnesium oxide at 0.29 to 0.49% by mass, (2) calcium in the form of calcium oxide at 0 to 0.1% by mass, (3) silicon in the form of silicon oxide at 0 to 0.15% by mass, or (4) ytterbium in the form of ytterbium oxide at 0 to 0.24% by mass. This enables low-temperature sintering and allows for densification while suppressing the grain growth of aluminum oxide.

[0040] Furthermore, the relative density of the samples in each example is 98.0% or higher according to the Archimedes method. This results in a denser ceramic sintered body, making it easier to maintain the strength and shape of the wafer support, and improving the dielectric breakdown voltage.

[0041] Furthermore, the samples in each example all had a brightness of 80 or higher. In particular, as shown in Examples 3 to 6, the samples to which 0.50% by mass or more of lithium fluoride or 0.34% by mass or more of potassium fluoride were added all had a brightness of 90 or higher, making it possible to realize a white alumina-based wafer support with almost no black spots.

[0042] On the other hand, in comparative examples 1 and 2, where neither lithium fluoride nor potassium fluoride was added, the number of black spots was higher and the brightness was lower compared to the samples in each example. Furthermore, comparative examples 3 to 6, which had manganese fluoride and zinc fluoride added, all tended to have a very large number of black spots and low brightness.

[0043] The mass percentages of each additive shown in Table 1 represent the ideal content calculated from the amount of each additive used during mixing. On the other hand, when the additives in each sample prepared as a ceramic sintered body were analyzed by ICP-AES (inductively coupled plasma atomic emission spectroscopy), the content of all additives except aluminum oxide was found to be low.

[0044] Table 2 shows the content of each additive as determined by ICP-AES analysis in Example 1 and Comparative Example 1. [Table 2]

[0045] The rate of decrease in content varies depending on the sample and amount of additive, but it was approximately 30% for lithium fluoride and up to 20% for other additives. Therefore, the lower limit of the preferred content range for each additive (excluding aluminum oxide) contained in the base material may be 20-30% lower than the aforementioned range when analyzed by ICP-AES.

[0046] Next, an example of a method for manufacturing a wafer support according to this embodiment is shown. This manufacturing method includes the steps of: preparing a raw material powder containing 96% by mass or more of aluminum oxide and 0.05 to 0.50% by mass of lithium fluoride or potassium fluoride; placing the raw material powder in the space of a carbon mold of a predetermined shape; and firing the raw material powder by pressurizing the space in the range of 15 to 40 MPa and heating it in the range of 1350 to 1650°C. This makes it possible to reduce black spots even when using a carbon mold during firing.

[0047] Although the present invention has been described above with reference to the embodiments and examples described above, the present invention is not limited to the embodiments described above, and the present invention also includes combinations and substitutions of the configurations of the embodiments as appropriate. Furthermore, it is possible to appropriately rearrange the combinations and order of processes in the embodiments or to make various design changes and other modifications to the embodiments based on the knowledge of those skilled in the art, and such modified embodiments may also be included in the scope of the present invention. [Explanation of Symbols]

[0048] 10 wafer support, 12 chamber, 14 upper electrode, 16 substrate, 16a mounting surface, 18 conductive member, 20 gas supply path, 22 adhesive layer, 24 metal plate, 26 flow path, 100 etching apparatus.

Claims

1. The device comprises a base material made of a ceramic sintered body and a conductive member in which at least a portion is embedded within the base material. The aforementioned substrate is It contains 96% or more by mass of aluminum oxide, Contains lithium fluoride or potassium fluoride, A wafer support characterized by the following features.

2. The wafer support according to claim 1, characterized in that the substrate contains 0.05 to 0.50% by mass of lithium or potassium on a fluoride basis.

3. The wafer support according to claim 2, characterized in that the substrate further contains at least one oxide of magnesium, silicon, calcium, zirconium, and ytterbium.

4. A wafer support according to any one of claims 1 to 3, characterized in that the number of black spots with a major axis of the ellipse of 100 μm or more is 1 [spot / φ58 mm] or less.

5. The wafer support according to any one of claims 1 to 3, characterized in that the substrate has a relative density of 98% or more.

6. A step of preparing a raw material powder containing 96% by mass or more of aluminum oxide and 0.05 to 0.50% by mass of lithium fluoride or potassium fluoride, A step of placing the raw material powder into a space of a carbon mold of a predetermined shape, A step of firing the raw material powder by pressurizing the space in the range of 15 to 40 MPa and heating it in the range of 1350 to 1650°C, A method for manufacturing a wafer support, characterized by including the following:

Images