JP4908089B2 - Electrostatic chuck and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electrostatic chuck for attracting and holding a silicon wafer and a photomask, and in particular, in a reduction exposure (EUVL) process using extreme ultraviolet rays for which high-precision pattern formation is required. The present invention relates to an electrostatic chuck suitable for holding a mask and a manufacturing method thereof.

  In recent years, in the manufacturing process of semiconductor devices, in order to improve the degree of integration of integrated circuits, pattern miniaturization is rapidly progressing. Therefore, an electrostatic chuck for fixing a wafer or a photomask needs to use a material having a small dimensional variation with respect to a temperature change and a smooth surface as a member constituting the electrostatic chuck.

As low thermal expansion materials used in conventional electrostatic chucks, cordierite, LAS (Li ₂ 0-A1 ₂ 0 ₃ —Si0 ₂ ) -based ceramics, and the like are known (see, for example, Patent Document 1). .

However, the linear thermal expansion coefficient of these materials is on the order of 1 × 10 ⁻⁶ / K, and the linear thermal expansion coefficient is too large for use in, for example, the EUVL process, which is an exposure process smaller than the 45 nm technology node.

  In addition, since these are crystalline materials, unevenness caused by crystal grain boundaries occurs when the surface is polished. Therefore, it is not suitable for applications where a smooth surface is required for the adsorption surface. In addition, in order to produce such materials, it is necessary to strictly control the mixing ratio of raw materials and synthesis conditions. This is because if the mixing ratio of raw materials is deviated, or if the firing temperature and atmosphere are not appropriate, bubbles may remain inside the sintered body or composition deviation may occur, resulting in a sintered body with uniform physical properties. This is because it cannot be obtained.

  As an electrode forming method in an electrostatic chuck using such a low thermal expansion ceramic, there is a method in which a metal foil or a metal mesh is embedded in a ceramic powder and then molded and fired. However, in such a manufacturing method, distortion and undulation are likely to occur on the metal surface, which makes it difficult to reduce the distance between the adsorption surface and the electrode surface, and also causes in-plane variation in the adsorption force. Occurs.

Another method for forming electrodes in electrostatic chucks using low thermal expansion ceramics is to bond disk-shaped low thermal expansion ceramics with conductive paste applied to the surface so that their application areas overlap and sinter. Thus, there is a method of bonding these low thermal expansion ceramics simultaneously with forming the electrode. This method requires steps of paste application, drying, degreasing, and firing, but it is difficult to degrease the central portion, especially when the paste application area is large, and it is difficult to form an electrode film with uniform properties. .
JP 2004-335742 A (paragraph [0010] etc.)

  The present invention has been made in view of such circumstances, and provides an electrostatic chuck using a material that has a low linear thermal expansion coefficient and can increase the smoothness of the attracting surface, and a method for manufacturing the electrostatic chuck. An object of the present invention is to provide an electrostatic chuck in which the flatness of a metal to be contained is good and a method for manufacturing the same.

The electrostatic chuck according to the present invention is an electrostatic chuck in which a metal is embedded in a low thermal expansion material having an absolute value of an average linear thermal expansion coefficient at 18 ° C. to 30 ° C. of 5 × 10 ⁻⁸ / K or less. The low thermal expansion material contains 1% by weight to 15% by weight of TiO ₂ provided on the suction surface side of the electrostatic chuck , and the balance is an amorphous material of SiO ₂ or 1% by weight to 15% by weight. A base portion having an adsorption surface portion that includes the following TiO ₂ and 1% by weight to 6% by weight of F ₂ , and the balance being an amorphous material of SiO ₂ , and an interface bonded to the adsorption surface portion by heat fusion bonding And the metal is provided between the adsorption surface portion and the base portion, and a metal thin film or metal foil having a thickness of 0.5 μm or more and 250 μm or less, or a metal constituted by a wire having a diameter of φ0.5 μm or more and φ250 μm or less Featuring a mesh .

For manufacturing an electrostatic chuck in which a metal is embedded in such a low thermal expansion material, a low thermal expansion material having an absolute value of an average linear thermal expansion coefficient at 18 ° C. to 30 ° C. of 5 × 10 ⁻⁸ / K or less is used. Consists of 1% by weight to 15% by weight of TiO ₂ , the balance being an amorphous material of SiO ₂ , or 1% by weight to 15% by weight of TiO ₂ and 1% by weight to 6% by weight of F comprises _2, the balance of the first plate member is an amorphous material of SiO _2, the second plate, subjected to mirror polishing on each major surface, the main surface and the second of the first plate Between the main surfaces of the plate material, a metal thin film or metal foil having a thickness of 0.5 μm or more and 250 μm or less, or a metal comprising a metal mesh composed of a wire having a diameter of φ0.5 μm or more and φ250 μm or less is sandwiched, 1150 to 1300 ° C. in the same time perpendicular to the main surface when heated By applying a predetermined pressure in the direction, a method is used in which the first plate and the second plate are bonded by heat fusion via a metal .

  Since the electrostatic chuck of the present invention is made of a material whose absolute value of linear thermal expansion coefficient is lower than that of conventional ceramics, deformation due to temperature change is extremely small, so that performance in exposure processing with short wavelength light can be improved. it can. Further, by using an amorphous material for the attracting surface, an electrostatic chuck with extremely high smoothness can be realized. Furthermore, since the flatness of the metal (electrode) is high, the thickness from the metal surface to the adsorption surface can be made thin and uniform, and thereby a uniform and large adsorption force can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 is a schematic sectional view of the electrostatic chuck. The electrostatic chuck 10 has a structure in which a metal 14 is embedded in a low thermal expansion material 12, and the low thermal expansion material 12 is opposite to a thin plate-like portion (adsorption surface portion) 12 a on the adsorption surface side and the metal 14. It consists of a base 12b on the side. The surface of the thin plate-like portion 12a becomes an adsorption surface for adsorbing and holding a wafer and a photomask.

The absolute value of the average linear thermal expansion coefficient at 18 ° C. to 30 ° C. of the low thermal expansion material 12 is 5 × 10 ⁻⁸ / K or less. By satisfying such characteristics, for example, when the electrostatic chuck 10 is used for holding a photomask in a photolithography process, the performance of the exposure process is improved. This effect is particularly remarkable in a photolithography process using short-wavelength light as in the EUVL process.

  The average linear thermal expansion coefficient when the materials of the thin plate-like part 12a and the base part 12b are different is [volume ratio of the thin plate-like part 12a] × [linear thermal expansion coefficient of the thin plate-like part 12a] + [of the base part 12b. The volume ratio] × [linear thermal expansion coefficient of the base portion 12b] is indicated.

  The thin plate-like portion 12a on the suction surface side is made of an amorphous material. Thus, when the surface of the thin plate-like portion 12a is polished, since there is no crystal grain boundary on the surface, unevenness due to the grain boundary does not occur, and an extremely good smooth surface can be obtained.

Specifically, an amorphous material containing 1% by weight to 15% by weight of TiO ₂ and the balance being SiO ₂ is suitably used for the thin plate-like part 12a. When TiO ₂ is less than 1% by weight, the absolute value of the linear thermal expansion coefficient exceeds 5 × 10 ⁻⁸ / K, so that the adsorbent is easily affected by thermal expansion. On the other hand, if TiO ₂ exceeds 15% by weight, it will crystallize, making it impossible to obtain a smooth adsorption surface.

It is also preferable to include F ₂ in this TiO ₂ —SiO ₂ based material. That is, for the thin plate-like portion 12a, an amorphous material containing 1% by weight to 15% by weight of TiO ₂ and 1% by weight to 6% by weight of F ₂ with the balance being SiO ₂ is also preferably used. It is done. By including F ₂ , the thermal fusion temperature when manufacturing the electrostatic chuck 10 (the temperature at which at least one of the two plates can be joined to the other by thermal fusion, as will be described later) is reduced. Can be made. When the F ₂ content is less than 1% by weight, the effect of lowering the heat fusion temperature is small. On the other hand, if a material having a high F ₂ content is produced, bubbles are likely to enter, and if the F ₂ content exceeds 6% by weight, this problem is likely to occur.

As long as the absolute value of the average linear thermal expansion coefficient at 18 ° C. to 30 ° C. of the low thermal expansion material 12 is 5 × 10 ⁻⁸ / K or less, in the case of a material mainly composed of SiO ₂ TiO _2. A component different from that may be added.

The base part 12b may be comprised with the same material as the thin plate-shaped part 12a, and may be comprised with a different material. The base part 12b may be amorphous or crystalline. For example, when the TiO ₂ —SiO ₂ material is used for the thin plate portion 12a and the base portion 12b, the thin plate portion 12a contains F ₂ but the base portion 12b contains F _2. It may be configured that the TiO ₂ content is different between the thin plate-like portion 12a and the base portion 12b. Further, the thin plate portion 12a may be amorphous and the base portion 12b may be crystalline.

In the electrostatic chuck 10, since the base portion 12 b usually occupies most of the low thermal expansion material 12, the absolute value of the average linear thermal expansion coefficient of the low thermal expansion material 12 at 18 ° C. to 30 ° C. is 5 × 10 ^−8. In order to satisfy the condition that it is equal to or less than / K, the base part 12b substantially needs to satisfy this condition.

  The metal 14 generally has a planar shape parallel to the suction surface, and a metal foil, punching metal, mesh, wire, or the like is used. In addition, the metal 14 has a predetermined pattern by a method such as vapor deposition or plating on a plate material made of a low thermal expansion material (a plate material that becomes the thin plate-like portion 12a and the base portion 12b after joining), which is used when the electrostatic chuck 10 is manufactured. It may be formed.

  In addition, when forming a vapor deposition film on the board | plate material which consists of a low thermal expansion material, even if the board | plate material used as the thin plate-shaped part 12a and the base part 12b is the same material, respectively, even if a vapor deposition film is formed in which board | plate material However, when the heat fusion temperatures of these plate materials are different, the flatness of the vapor deposition film can be increased by forming a vapor deposition film on the plate material having a higher heat fusion temperature.

  The material of the metal 14 can be appropriately selected in consideration of the temperature at which the electrostatic chuck 10 is manufactured, but Ni, Mo, W, and Pt are preferably used from the viewpoint of versatility and reactivity. It is done.

The thickness of the metal 14 (thickness in a direction perpendicular to suction surface) shall be the 0.5μm or 250μm or less. When a mesh and a wire are used for the metal 14, a metal wire having a diameter of 0.5 μm or more and 250 μm or less is used. When the thickness of the metal 14 is less than 0.5 μm, cracks (cracks) or the like are likely to occur in the metal 14 when the electrostatic chuck 10 is manufactured, and when the thickness is more than 250 μm, the low thermal expansion material 12. The probability of occurrence of cracks (cracks) increases.

  Although the manufacturing method of the electrostatic chuck 10 will be described in detail later, the flatness of the metal 14 can be reduced to 50 μm or less by the manufacturing method. The flatness refers to distortion from a virtual plane, and is represented by, for example, the difference between the longest distance and the shortest distance from the adsorption surface to the surface of the metal 14. Thereby, since the thickness of the thin plate-like part 12a can be made thin and uniform, a uniform and large adsorption force can be obtained.

  Next, a method for manufacturing the electrostatic chuck 10 will be described. A plate material that becomes the thin plate portion 12 a, a plate material that becomes the base portion 12 b, and a metal member that becomes the metal 14 are prepared. At least one main surface of each plate material is mirror-polished, and the plate material that forms the thin plate portion 12a is made of an amorphous material. In addition, when using a vapor deposition film as the metal 14, the metal vapor deposition film should just be formed in the mirror surface of one board | plate material.

  The mirror surfaces of these two plate materials face each other, and a metal member is sandwiched between them and installed in the furnace. By using the mirror surfaces of the two plate materials as the joining surfaces, the flatness of the metal member can be increased.

  The furnace atmosphere is set to a vacuum atmosphere and heated to a predetermined temperature, and at the same time, a predetermined pressure is applied to these plate members in a direction perpendicular to the main surface. The heating temperature (= joining temperature) is set to be equal to or higher than the temperature at which at least one of the two plate members can be joined to the other by thermal fusion (= thermal fusion temperature). The pressure is set to a value that does not increase the amount of deformation of the two plates in consideration of the bonding temperature. By making the treatment atmosphere a vacuum atmosphere, it is possible to prevent entrainment of bubbles on the bonding surface.

Thereafter, the joined body is taken out from the furnace, the joined body is ground, and the suction surface side is polished. Thereby, the electrostatic chuck 10 is obtained.

  In such a manufacturing method of the electrostatic chuck 10, when there is a difference in the heat fusion temperature between the two plate materials, from the viewpoint of keeping the metal flatness good, the plate material to be the thin plate-like portion 12 a The material of these two plate materials is selected so that the heat fusion temperature is higher than the heat fusion temperature of the plate material used as the base portion 12b. On the other hand, if importance is attached to the ease of manufacturing, the thermal fusion temperature of the plate material that becomes the base portion 12b is higher than the thermal fusion temperature of the plate material that becomes the thin plate portion 12a. The material for these two sheets is selected.

  When there is a difference in the heat fusion temperature between the two plate materials, it is preferable to match the bonding temperature to the lower one of the heat fusion temperatures, thereby suppressing the deformation at the joining interface between the two plate materials. The flatness of the metal can be kept high. On the other hand, as long as the deformation of the bonding interface is allowed, that is, as long as the flatness of the buried metal is maintained at a constant value, the bonding temperature may be higher, and the upper limit is higher It can be set as the heat fusing temperature. By increasing the bonding temperature in this way, the bonding strength can be increased.

Examples and comparative examples will be described. Using the plate-like amorphous glass material or powder containing TiO ₂ and F ₂ in weight percent shown in Table 1 and the balance being SiO ₂ , and the metal member shown in Table 1, the static electricity is produced according to the manufacturing method described above. A chuck was produced. The amorphous glass material was joined in a vacuum atmosphere at a joining temperature of 1150 ° C. to 1300 ° C. for 1 hour and a pressing pressure at that time of 10 MPa to 20 MPa. The front and back surfaces of the structural material obtained by this joining treatment were ground with a surface grinder, and then the suction surface side was finished into a mirror surface with a grinder.

  The presence or absence of grain boundaries on the mirror surface was observed with a scanning electron microscope (SEM). In addition, the presence or absence of bubbles and the presence or absence of cracks in the metal were observed with an optical microscope to evaluate the state of the bonding interface. Furthermore, the flatness of the buried metal was measured at 9 points or more from the suction surface side with an ultrasonic displacement meter, and the flatness of the metal (difference in plane distortion) was determined by the least square method. The results are also shown in Table 1.

As shown in Table 1, in Comparative Example 1 in which the low thermal expansion material was made of a glass material made only of SiO ₂ , the absolute value of the average linear thermal expansion coefficient exceeded 5 × 10 ⁻⁸ / K. Further, when a TiO ₂ —SiO ₂ material was used, a grain boundary was observed on the mirror surface in Comparative Example 2 having a TiO ₂ content of 17% by weight, and the smoothness decreased. In Comparative Example 3 in which the metal thickness was 280 μm, cracks and cracks occurred in the low thermal expansion material. In Comparative Example 4 in which the metal thickness was 0.3 μm, the metal part was disconnected and could not be used as an electrostatic chuck because voltage could not be applied. Other examples were confirmed to be good electrostatic chucks. When the powder was used to form the base portion as in Comparative Example 5, the flatness of the metal decreased.

  The electrostatic chuck according to the present invention is suitable for holding a wafer or a photomask in a short wavelength exposure process. Further, the member having the configuration of the electrostatic chuck of the present invention can be applied to an XY stage with little dimensional deformation due to temperature. Further, if attention is paid to the configuration of a low thermal expansion material in which a metal is buried, it can be used as a shielding material for shielding electromagnetic waves or the like, and further, a heater can be realized by using a resistance material for the metal.

Sectional drawing which shows schematic structure of an electrostatic chuck.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electrostatic chuck, 12 ... Low thermal expansion material, 12a ... Thin plate part (adsorption surface part), 12b ... Base part, 14 ... Metal.

Claims (5)

An electrostatic chuck in which a metal is embedded in a low thermal expansion material having an average linear thermal expansion coefficient at 18 ° C. to 30 ° C. of 5 × 10 ⁻⁸ / K or less,
The low thermal expansion material contains 1% by weight to 15% by weight of TiO ₂ provided on the suction surface side of the electrostatic chuck , and the balance is an amorphous material of SiO ₂ or 1% by weight to 15% by weight. Comprising a sorbent surface part made of an amorphous material of SiO ₂ and the balance of the TiO ₂ and 1% by weight or more and 6% by weight or less of F ₂ , and a base part having an interface bonded to the suction surface part by heat fusion bonding ,
The metal is provided between the adsorption surface portion and the base portion, and a metal mesh composed of a metal thin film or metal foil having a thickness of 0.5 μm or more and 250 μm or less, or a wire having a diameter of φ0.5 μm or more and φ250 μm or less. An electrostatic chuck comprising the electrostatic chuck.   The electrostatic chuck according to claim 1, wherein the metal has a flatness of 50 μm or less. 1% to 15% by weight of TiO ₂ constituting a low thermal expansion material having an absolute value of an average linear thermal expansion coefficient at 18 ° C. to 30 ° C. of 5 × 10 ⁻⁸ / K or less , with the balance being SiO ₂ An amorphous material, or 1% by weight to 15% by weight of TiO ₂ and 1% by weight to 6% by weight of F ₂ with the balance being a SiO ₂ amorphous material , For the second plate, after mirror polishing each main surface,
Between the main surface of the first plate and the main surface of the second plate, a metal thin film or metal foil having a thickness of 0.5 μm to 250 μm, or a wire having a diameter of φ0.5 μm to φ250 μm Sandwiching a metal with a metal mesh,
By heating at 1150 to 1300 ° C. and simultaneously applying a predetermined pressure in a direction perpendicular to the main surface, the first plate member and the second plate member are bonded by heat fusion via the metal, and the low heat An electrostatic chuck manufacturing method comprising forming an electrostatic chuck in which the metal is embedded in an expansion material. The method of manufacturing an electrostatic chuck according to claim 3, wherein the predetermined pressure is 10 to 20 MPa. The first plate member and the second plate member having a difference in heat fusion temperature are used, and the first plate member and the second plate member are bonded by heat fusion at the lower heat fusion temperature. The method for manufacturing an electrostatic chuck according to claim 3 or 4 , wherein:

Images