Patent ID: 12230527

DETAILED DESCRIPTION OF EMBODIMENT

A mode for carrying out the disclosure will be described below with reference to the drawings. Incidentally, in each of the drawings, the same reference signs will be given to the same constituent portions, and redundant explanations thereof may be omitted.

Structure of Substrate Fixing Device

FIG.1is a sectional view illustrating a substrate fixing device according to a first embodiment in a simplified manner. With reference toFIG.1, the substrate fixing device1has a base plate10, an adhesive layer20, and an electrostatic chuck30as major constituent elements.

The base plate10is a member for mounting the electrostatic chuck30thereon. Thickness of the base plate10can be, for example, set in a range of about 20 mm to 50 mm. The base plate10is, for example, formed of aluminum, and can be also used as an electrode or the like for controlling plasma. Predetermined high-frequency electric power is fed to the base plate10to control energy for making generated ions or the like in a plasma state collide against a wafer adsorbed on the electrostatic chuck30so that an etching process can be effectively performed on the wafer.

A water channel15is provided inside the base plate10. The water channel15has one end where a cooling water introduction portion15ais provided, and the other end where a cooling water discharge portion15bis provided. The water channel15is connected to a cooling water control device (not shown) provided outside the substrate fixing device1. The cooling water control device (not shown) introduces cooling water into the water channel15from the cooling water introduction portion15aand discharges the cooling water from the cooling water discharge portion15b. When the base plate10is cooled by the cooling water circulated in the water channel15, the wafer adsorbed on the electrostatic chuck30can be cooled. In addition to the water channel15, a gas channel or the like for introducing inert gas to cool the wafer adsorbed on the electrostatic chuck30may be provided in the base plate10.

The electrostatic chuck30is configured to adsorb and hold the wafer, which is an object to be adsorbed. The electrostatic chuck30can be, for example, shaped like a circle in plan view. The diameter of the wafer, which is the object to be adsorbed by the electrostatic chuck30, can be, for example, set at about 8, 12, or 18 inches.

The electrostatic chuck30is mounted on one face of the base plate10through the adhesive layer20. For example, a silicone-based adhesive agent can be used as the adhesive layer20. Thickness of the adhesive layer20can be, for example, set at about 2 mm. Thermal conductivity of the adhesive layer20is preferably set at 2 W/m·K or higher. The adhesive layer20may be formed into a laminate structure in which adhesive layers are disposed on one another. For example, the adhesive layer20is formed into a two-layer structure in which an adhesive agent with high thermal conductivity and an adhesive agent with a low elastic modulus are combined, so that it is possible to obtain an effect of reducing stress caused by a difference in thermal expansion between the base plate made of aluminum and the adhesive layer20.

The electrostatic chuck30has a base body31, an electrostatic electrode32, at least one thermal diffusion layer33, an insulating layer34, and a heating element35. The electrostatic chuck30is, for example, a Johnsen-Rahbek type electrostatic chuck. However, the electrostatic chuck30may be a Coulomb force type electrostatic chuck.

The base body31that is a dielectric substance has a mounting face31aon which the object to be adsorbed can be mounted. For example, ceramics such as aluminum oxide (Al2O3) and aluminum nitride (AlN) can be used as the base body31. Thickness T of the base body31can be, for example, set in a range of about 4 mm to 10 mm, and a relative dielectric constant (at 1 kHz) of the base body31can be, for example, set in a range of about 9 to 10.

The electrostatic electrode32that is a thin-film electrode is built into the base body31. The electrostatic electrode32is electrically connected to a vertical wiring built into the base body31. The vertical wiring includes pads36and vias37that are disposed on each other alternately. The vertical wiring is provided so as to extend along the thickness direction of the base body31. One of the pads36positioned at a lowermost layer is exposed in a recess31xthat is opened on a back face side of the base body31. The pad36positioned at the lowermost layer is connected to a power supply provided outside the substrate fixing device1. When a predetermined voltage is applied to the pad36in the lowermost layer from the power supply, an adsorption force caused by static electricity is generated between the water and the electrostatic electrode32. As a result, the wafer can be adsorbed and held on the mounting face31aof the base body31of the electrostatic chuck30. As the voltage applied to the electrostatic electrode32is higher, the adsorption and holding force is stronger. The electrostatic electrode32may be a unipolar shape or a bipolar shape. For example, tungsten, molybdenum, etc. can be used as each of materials of the electrostatic electrode32, the pads36, and the vias37.

The thermal diffusion layer33is built into the base body31. The thermal diffusion layer33is a layer by which heat generated by the heating element35can be made uniform and diffused. The thermal diffusion layer33is formed of a material higher in thermal conductivity than the base body31. The thermal conductivity of the thermal diffusion layer33is preferably 400 W/m·K or higher. Examples of the material that can achieve such thermal conductivity include metals such as copper (Cu), a copper alloy, silver (Ag), a silver alloy, tungsten, and molybdenum, carbon nanotube, and the like. Thickness of the thermal diffusion layer33can be, for example, set in a range of about 5 μm to 20 μm.

When at least one thermal diffusion layer33is provided in the base body31, it is possible to obtain an effect of uniformly diffusing the heat generated by the heating element35into the entire base body31. When a plurality of thermal diffusion layers33are disposed in the thickness direction of the base body31, the effect of uniformly diffusing the heat generated by the heating element35into the entire base body31is greater. From a viewpoint of improving the effect of diffusing the heat, each of the thermal diffusion layers33is preferably arranged all over the inside of the base body31in a horizontal direction (parallel direction to the mounting face31a).

In the first embodiment, by way of example, the thermal diffusion layers33are respectively arranged in all the layers where the pads36are arranged. That is, in the thickness direction of the base body31, the position of each of the pads36is the same as the position of a corresponding one of the thermal diffusion layers33. In the example ofFIG.1, seven thermal diffusion layers33are disposed at predetermined intervals. Each of the intervals between the thermal diffusion layers33vertically adjacent to one another is, for example, 0.45 mm. The vertical wiring is built into the base body31so as to be spaced from the thermal diffusion layers33. Specifically, each of the thermal diffusion layers33is arranged to be spaced from a corresponding one of the pads36so as not to electrically continue to the corresponding pad36. Assume that the pad36is shaped like a circle in plan view. In this case, for example, a circular opening with a larger diameter than the pad36is formed in the thermal diffusion layer33, and the pad36is positioned in the opening. In addition, the thermal diffusion layers33surround the vertical wiring in plan view.

In the first embodiment, by way of example, each of the thermal diffusion layers33is formed all over the inside of the base body31in the horizontal direction except for a pad arrangement area where the pad36is formed, and an entire outer circumferential face of the thermal diffusion layer33is exposed in an outer circumferential face of the base body31. That is, the thermal diffusion layer33is formed to extend to the outermost circumference of the base body31. Here, the pad arrangement area means an area from an outer edge of the pad36to 100 μm outside the outer edge.

Incidentally, in the background-art electrostatic chuck, the metal layer or the like which functions as a thermal diffusion layer is fixed to a base body through an adhesive layer or the metal layer is patterned into a predetermined shape, so that satisfactory heat uniformity cannot be achieved.

The insulating layer34is formed directly on the back face31b(face located on an opposite side to the mounting face31a) of the base body31. The insulating layer34is a layer that insulates the base body31and the heating element35from each other. For example, an epoxy resin, a bismaleimide-triazine resin, or the like, having high thermal conductivity and high heat resistance can be used as the insulating layer34. The thermal conductivity of the insulating layer34is preferably set at 3 W/m·K or higher. Since a filler of alumina, aluminum nitride, etc. is contained in the insulating layer34, the thermal conductivity of the insulating layer34can be improved. Moreover, glass transition temperature (Tg) of the insulating layer34is preferably set at 250° C. or higher. Moreover, thickness of the insulating layer34is preferably set in a range of about 100 μm to 150 μm, and a variation in the thickness of the insulating layer34is preferably set in a range of ±10% or less.

The heating element35is built into the insulating layer34. The circumference of the heating element35is covered with the insulating layer34to be protected from the outside. The heating element35to which a voltage is applied from the outside of the substrate fixing device1generates heat to heat the mounting face31aof the base body31to a predetermined temperature. The heating element35can, for example, heat the temperature of the mounting face31aof the base body31to about 250° C. to 300° C. For example, copper (Cu), tungsten (W), nickel (Ni), constantan (an alloy of Cu/Ni/Mn/Fe), etc. can be used as the material of the heating element35. Thickness of the heating element35can be, for example, set in a range of about 20 μm to 100 μm. The heating element35can be, for example, set to have a concentric pattern.

Incidentally, in order to improve tight adhesiveness between the heating element35and the insulating layer34under high temperature, at least one face (one or each of upper and lower faces) of the heating element35is preferably roughened. Both the upper and lower faces of the heating element35may be roughened. In this case, different roughening methods may be used on the upper and lower faces of the heating element35. The roughening methods are not limited particularly, but may include a method based on etching, a method using coupling agent-based surface modification technology, a method using dot processing by a UV-YAG laser with a wavelength of 355 nm or less, etc.

Method for Manufacturing Substrate Fixing Device

FIGS.2A to4Bare views illustrating a process of manufacturing the substrate fixing device according to the first embodiment. The process of manufacturing the substrate fixing device1will be centered around a process of forming the electrostatic chuck and described with reference toFIGS.2A to4B. Incidentally,FIGS.2A to4Aare drawn in a vertically inverted state toFIG.1.

First, in a step shown inFIG.2A, a green sheet311is prepared. In a case where, for example, ceramics forming a base body31is aluminum oxide, a material forming the green sheet311includes particles of aluminum oxide. The material forming the green sheet311may include a binder, a solvent etc. The green sheet311is, for example, 0.58 mm to 0.62 mm thick (changes to be about 0.45 mm thick after firing). Next, a metal paste321is printed with a predetermined pattern on one face of the green sheet311. The metal paste321is a material that will be turned to an electrostatic electrode32by firing. The metal paste321is, for example, a tungsten paste or a molybdenum paste.

Next, in a step shown inFIG.2B, a green sheet312covering the metal paste321is provided on the face of the green sheet311. The size and the material of the green sheet312are similar to or the same as those of the green sheet311. Next, via processing is performed on the green sheet312, and a via obtained thus is filled with a metal paste371. The metal paste371is a material that will be turned to a via37by firing. The metal paste371is, for example, a tungsten paste or a molybdenum paste.

Next, in a step shown inFIG.2C, metal pastes331and361are printed on one face of the green sheet312with predetermined patterns. The metal paste331is a material that will be turned to a thermal diffusion layer33by firing. The metal paste361is a material that will be turned to a pad36by firing. The metal pastes331and361are, for example, a tungsten paste or a molybdenum paste. The metal pastes331and361may be different materials.

Next, in a step shown inFIG.2D, the steps ofFIG.2BandFIG.2Care repeated a required number of times so that the required number of green sheets can be then further provided. For example, assume that each of the green sheets is 0.58 mm to 0.62 mm thick. In this case, one layer of the metal paste331, that will be turned to a thermal diffusion layer33, can be formed every increase of 0.58 mm to 0.62 mm in thickness. Next, after surface polishing etc. performed if occasions demand, the green sheets are integrated by firing so as to form a base body31. Moreover, by firing, the electrostatic electrode32, the thermal diffusion layers33, the pads36, and the vias37are formed from the respective metal pastes. After the firing, a recess31xis formed. The recess31xcan be formed, for example, by blasting, drilling, or the like. Incidentally, in a case where there is another groove or hole such as a gas introduction portion, processing is also performed in a similar manner or the same manner.

Next, in a step shown inFIG.3A, an insulating resin film341is directly arranged on an opposite face (upper face inFIG.3A) of the base body31to a mounting face31a. Lamination of the insulating resin film341in a vacuum is suitable for making it possible to prevent entrapment of voids. The insulating resin film341is not cured but is left in a semi-cured state (B-stage) in advance. The insulating resin film341is temporarily fixed on the base body31by adhesive force of the insulating resin film341that is in the semi-cured state.

For example, an epoxy resin, a bismaleimide-triazine resin, or the like, which has high thermal conductivity and high heat resistance, can be used as the insulating resin film341. The thermal conductivity of the insulating resin film341is preferably set at 3 W/m·K or higher. Due to a filler of alumina, aluminum nitride, etc. contained in the insulating resin film341, the thermal conductivity of the insulating resin film341can be improved. Moreover, glass transition temperature of the insulating resin film341is preferably set at 250° C. or higher. Moreover, from a viewpoint of enhancing thermal conduction performance (increasing thermal conduction speed), thickness of the insulating resin film341is preferably set at 60 μm or less. A variation in the thickness of the insulating resin film341is preferably set in a range of ±10% or less.

Next, in a step shown inFIG.3B, a metal foil is arranged on the insulating resin film341, and the metal foil is patterned to form a heating element35. The heating element35can be, for example, set to have a concentric circular pattern. Specifically, for example, a resist is formed on the entire metal foil, and the resist is exposed to light and developed so that a resist pattern that covers only a portion that will be left as the heating element35is formed. Next, a portion of the metal foil that is not covered with the resist pattern is removed by etching. Assume that, for example, the material of the metal foil is copper. In this case, a cupric chloride etching solution, a ferric chloride etching solution, or the like, can be used as an etching solution for removing the metal foil.

Then, the resist pattern is stripped by a stripping solution so that the heating element35is formed at a predetermined position on the insulating resin film341(photolithography method). Due to the formation of the heating element35by the photolithography method, a variation in a widthwise dimension of the heating element35can be reduced so that a heat generation distribution can be improved. Incidentally, the heating element35formed by etching can be, for example, formed into an approximately trapezoidal shape in section. In this case, a difference in wiring width between a face contacting the insulating resin film341and an opposite face thereto can be, for example, set in a range of about 10 μm to 50 μm. The heating element35is formed into the simple approximately trapezoidal shape in section, so that the heat generation distribution can be improved.

Next, in a step shown inFIG.3C, an insulating resin film342covering the heating element35is arranged on the insulating resin film341. Lamination of the insulating resin film342in a vacuum is suitable for making it possible to prevent entrapment of voids. The material of the insulating resin film342can be, for example, set to be similar to or the same as that of the insulating resin film341. However, thickness of the insulating resin film342can be appropriately determined as long as the insulating resin film342can cover the heating element35. The insulating resin film342does not have to be the same in thickness as the insulating resin film341.

Next, in a step shown inFIG.4A, the insulating resin films341and342are cured by heating at a curing temperature or higher while being pressed against the base body31. Thus, the insulating resin films341and342are integrated into an insulating layer34. As a result, the insulating layer34directly bonded to the thermal diffusion layers33is formed. In addition, the circumference of the heating element35is covered with the insulating layer34. Next, a through hole is formed in the insulating layer34to communicate with the recess31x. Incidentally, the heating temperature of the insulating resin films341and342is preferably set at 200° C. or lower in consideration of stress that is generated when the temperature returns to normal temperature. In the aforementioned manner, the electrostatic chuck30is completed.

Incidentally, the insulating resin films341and342are cured by heating while being pressed against the base body31, so that roughness of an upper face (face not contacting the electrostatic chuck30) of the insulating layer34affected by the presence/absence of the heating element35can be reduced so as to be made flat. The roughness of the upper face of the insulating layer34is preferably set at 7 μm or less. When the roughness of the upper face of the insulating layer34is set at 7 μm or less, voids can be prevented from being entrapped between the insulating layer34and an adhesive layer20in a next step. That is, adhesiveness between the insulating layer34and the adhesive layer20can be prevented from deteriorating.

Next, in a step shown inFIG.4B, a base plate10where a water channel15etc. has been formed is prepared, and the adhesive layer20(uncured) is formed on the base plate10. The electrostatic chuck30shown inFIG.4Ais vertically inverted and arranged on the base plate10through the adhesive layer20, and the adhesive layer20is cured. Thus, the substrate fixing device1in which the electrostatic chuck30is disposed on the base plate10through the adhesive layer20is completed.

Thus, in the electrostatic chuck30, the thermal diffusion layers33are built in the base body31. Accordingly, heat generated by the heating element35can be easily and uniformly transferred to the base body31. That is, heat uniformity can be further improved by the electrostatic chuck30in comparison with a background-art structure in which a thermal diffusion layer is provided outside a base body.

In addition, since each of the thermal diffusion layers33is formed all over the inside of the base body31in the horizontal direction, the heat generated by the heating element35can be diffused uniformly into the entire base body31. In addition, since the thermal conductivity of each of the thermal diffusion layers33is set at 400 W/m·K or higher, the heat can be quickly diffused in the base body31in the horizontal direction. The heat uniformly diffused by the thermal diffusion layers33can heat the base body31uniformly.

Incidentally, when a thermal diffusion distance between the heating element35and the mounting face31ais short, i.e., when the thickness T of the base body31is small, a dimensional variation etc. of the heating element35easily affects the mounting face31a. In other words, as the thickness T of the base body31increases, the thermal diffusion distance between the heating element35and the mounting face31aincreases. Therefore, a temperature distribution of the mounting face31ais easily blurred so that the temperature distribution can be improved. With the combination of the provision of the thermal diffusion layers33inside the base body31and the increase in the thickness T of the base body31, the temperature distribution can be improved more effectively. In the background art, the thickness T of the base body31is often about 4.5 mm. In order to improve the temperature distribution, the thickness T of the base body31is preferably set to be not smaller than 4.95 mm and not larger than about 9 mm.

Modification 1 of First Embodiment

An example in which the number of thermal diffusion layers disposed on one another is further increased will be shown in Modification 1 of the first embodiment. Incidentally, in the Modification 1 of the first embodiment, description about constituent portions which are the same as those in the aforementioned embodiment may be omitted.

FIG.5is a sectional view illustrating a substrate fixing device according the Modification 1 of the first embodiment in a simplified manner. With reference toFIG.5, the substrate fixing device1A differs from the substrate fixing device1in that some of thermal diffusion layers33are provided to be lower than layers where pads36are formed.

That is, in the substrate fixing device1A, ones of the thermal diffusion layers33are arranged on a nearer side to a back face31bof a base body31than one of the pads36that is arranged on a nearest side to the back face31bof the base body31. Further in other words, a distance between the pad36positioned at a lowermost layer and the back face31bis longer than a distance between a lowermost thermal diffusion layer33and the back face31bin a thickness direction of the base body31. On the other hand, in the substrate fixing device1shown inFIG.1, a distance between the pad36positioned at the lowermost layer and the back face31bis equal to a distance between a lowermost thermal diffusion layer33and the back face31bin the thickness direction of the base body31. In addition, in the substrate fixing device1A shown inFIG.5, the number of the layers of the pads36is smaller than the number of the thermal diffusion layers33. To provide each of the thermal diffusion layers33lower than the layers where the pads36are formed, a layer of a metal paste331that will be turned to the thermal diffusion layer33may be formed whenever a green sheet where the recess31xis formed is additionally provided in the step ofFIG.2D.

In this manner, an area lower than the layers where the pads36are formed is effectively used, and the thermal diffusion layers33are also provided in this area. Accordingly, the number of the thermal diffusion layers33is further increased. Consequently, heat uniformity can be further improved.

In addition, in the substrate fixing device1A shown inFIG.5, a distance between an uppermost thermal diffusion layer33and the mounting face31ais longer than a distance between the lowermost thermal diffusion layer33and the back face31bin the thickness direction of the base body31. On the other hand, in the substrate fixing device1shown inFIG.1, a distance between an uppermost thermal diffusion layer33and the mounting face31ais shorter than a distance between the lowermost thermal diffusion layer33and the back face31b.

Simulation

Four types of samples shown in the following Table 1 were used to simulate a temperature distribution (heat uniformity) in a mounting face of a base body when average temperature of the mounting face of the base body was controlled to be 60° C. In Table 1, a sample Ref is a sample that includes a base body 4.5 mm thick but does not include any thermal diffusion layers, and that corresponds to a background-art electrostatic chuck. In addition, a sample A is a sample that includes a base body 6.8 mm thick but does not include any thermal diffusion layers, and that differs from the sample Ref only in the thickness of the base body. In addition, a sample B is a sample that includes a base body 6.8 mm thick and five thermal diffusion layers, and that differs from the sample A only in the presence/absence of the thermal diffusion layers. In addition, a sample C is a sample that includes a base body 6.8 mm thick and fourteen thermal diffusion layers, and that differs from the sample B only in the number of the thermal diffusion layers.

TABLE 1Base BodyThermal Diffusion LayerThick-OuterThick-NumberLayerSamplenessDiameterMaterialnessof LayersIntervalRef4.5 mm295.8 mm————A6.8 mm295.8 mm————B6.8 mm295.8 mmTungsten0.01 mm50.45 mmC6.8 mm295.8 mmTungsten0.01 mm140.45 mm

Table 2 shows simulation results. In Table 2, an average value is an average value of temperature of the mounting face of the base body, Range is a difference between lowest and highest temperatures, and Sigma is a standard deviation.

TABLE 2TemperatureAverageSampleValueSigmaRangeRef60.0080.2752.145A60.0020.7261.437B60.0410.2241.402C60.0410.2231.359

FIG.6Ashows Range values shown in Table 2 with the value for the sample Ref as a reference (100%).FIG.6Bshows Sigma values shown in Table 2 with the value for the sample Ref as a reference (100%).

Based on comparison between the sample Ref and the sample A inFIG.6Ait is understood that the Range value was reduced by about 33% when the base body was made thicker. In addition, based on comparison between the sample Ref with the sample A inFIG.6B, it is understood that the Sigma value was reduced by about a little less than 20% when the base body was made thicker.

In addition, based on comparison between the sample A and the sample B inFIG.6A, it is understood that the Range value was slightly improved when the thermal diffusion layers were built in the base body. In addition, based on comparison between the sample A and the sample B inFIG.6B, it is understood that the Sigma value was slightly improved when the thermal diffusion layers were built in the base body.

In addition, based on comparison between the sample B and the sample C inFIG.6A, it is understood that the Range value was further improved when the number of the thermal diffusion layers built in the base body was increased. In addition, based on comparison between the sample B and the sample C inFIG.6B, it is understood that the Sigma value was further improved when the number of the thermal diffusion layers built in the base body was increased.

Thus, it was confirmed that due to an increase in the thickness of the base body, the variation in the temperature distribution in the mounting face of the base body was greatly improved, and due to the thermal diffusion layers built in the base body, the variation in the temperature distribution in the mounting face of the base body was further improved, to thereby improve heat uniformity. Moreover, it was also confirmed that due to an increase in the number of the thermal diffusion layers built in the base body, the variation in the temperature distribution in the mounting face of the base body was further improved, to thereby further improve the heat uniformity.

The preferred embodiment or the like has been described above in detail. However, the present disclosure is not limited to the aforementioned embodiment or the like. Various modifications and substitutions can be made on the aforementioned embodiment or the like without departing from the scope of Claims.

For example, in addition to the semiconductor wafer (such as a silicon wafer), a glass substrate etc. used in a process of manufacturing a liquid crystal panel etc. can be exemplified as the object to be adsorbed by the substrate fixing device according to the present disclosure.

Although the preferred embodiments etc. have been described above in detail, the present disclosure is not limited to the aforementioned embodiments etc., and various modifications and substitutions can be added to the aforementioned embodiments etc. without departing from the scope described in Claims.