Patent Application
20250162950
The present disclosure relates to a bonded body.
Circuit formation in production of semiconductor devices is generally carried out by plasma etching. Plasma etching is carried out by introducing an inert gas into a vacuum chamber in a plasma etching system and converting it into plasma. A plasma etching system has an electrostatic chuck assembly provided therein that functions as a susceptor for mounting a wafer to be etched. A typical electrostatic chuck assembly includes an electrode embedded-ceramic plate functioning as an electrostatic chuck and a cooling plate supporting the bottom surface of the electrode embedded-ceramic plate. The wafer is electrostatically adsorbed to the ceramic plate with a built-in electrode to thereby be fixed on the electrostatic chuck assembly, and in that state, the wafer is plasma-etched. On the other hand, the cooling plate is provided on the bottom surface of the ceramic plate having a built-in electrode, and is thus configured to conduct away heat generated in the wafer by plasma etching. The electrode embedded-ceramic plate generally has a structure including: a ceramic base material made of aluminum oxide or aluminum nitride, which is excellent in heat resistance and corrosion resistance; and an inner electrode embedded therein, such as an electrostatic chuck (ESC) electrode, an RF electrode and a heater electrode.
Patent Literature 1 (JP2009-141204A) discloses a supporter for a substrate, as an example of an electrostatic chuck assembly, the supporter including a first ceramic sintered body as a first base material and a second ceramic sintered body as a second base material, wherein the first base material and the second base material are bonded to each other via a bonding metal film containing Al. In this literature, it is disclosed that the first base material and the second base material with the bonding metal film containing Al interposed therebetween are subjected to thermal compression bonding at a pressure of 4 to 20 MPa while the metal is being heated, so that the first base material and the second base material are bonded to each other via the bonding film. It is purported that the Al-containing metal is desirably an Al alloy containing Ma in a range from 0.5 to 5% by weight.
Recently, metal matrix composites (MMC) have attracted attention. The metal matrix composites are materials obtained by combining a metal matrix made of a metal such as Al or metallic Si with a reinforcing ceramic material such as SiC or TiC, and it is known that the metal matrix composites have advantages including light weight, high rigidity, high thermal conductivity, and small thermal expansion. Methods for bonding a metal matrix composite (MMC) and a ceramic material have been proposed, and in Patent Literature 2 (JP4373538B) discloses a bonded body including an MMC containing an aluminum alloy as a matrix and a ceramic material, wherein the MMC and the ceramic material is bonded to each other via a wax material made of an Al alloy containing Mg.
It is desirable to use an MMC plate as a cooling plate of an electrostatic chuck assembly, in light of advantages including high thermal conductivity and small thermal expansion. Thus, there is a need for improvement in bond strength between an MMC plate and a ceramic plate of a bonded body.
The inventors have found that a bonded body including a ceramic plate and an MMC plate and having a large bond strength can be provided by (1) interposing a predetermined bonding layer between the MMC plate and the ceramic plate and (2a) allowing the bonding interface between the ceramic plate and the bonding layer to include a Mg-containing layer and/or (2b) allowing the MMC plate to have an Al-diffused layer over a predetermined depth (thickness) from the bonding interface between the bonding layer and the MMC plate.
Thus, an object of the present invention is to provide a bonded body including a ceramic plate and an MMC plate and having a large bond strength.
The present disclosure provides the following aspects.
A bonded body comprising:
The bonded body according to aspect 1, wherein the Mg-containing layer further comprises Al and O.
The bonded body according to aspect 2, wherein the Mg-containing layer has a weight ratio Al:Mg:O of 1:0.1 to 0.50:0.001 to 0.100.
The bonded body according to any one of aspects 1 to 3, wherein the Mg-containing layer has a thickness of 1 to 10 μm.
The bonded body according to any one of aspects 1 to 4, wherein the bonding of the ceramic plate, the bonding layer and the MMC plate is thermal compression bonding.
The bonded body according to any one of aspects 1 to 5, wherein the MMC comprises Si, C, and Ti.
The bonded body according to any one of aspects 1 to 6, wherein the MMC plate includes an Al-diffused layer in which Al derived from the bonding layer is diffused over a predetermined depth DAl from a bonding interface between the bonding layer and the MCC plate.
The bonded body according to aspect 7, wherein the MMC plate includes a Mg-diffused layer in which Mg derived from the bonding layer is diffused over a predetermined depth DMg from a bonding interface between the bonding layer and the MMC plate.
The bonded body according to aspect 8, wherein the depth DAl of the Al-diffused layer is larger than the depth DMg of the Mg-diffused layer to satisfy DAl>DMg.
The bonded body according to any one of aspects 1 to 9, wherein a surface of the MMC plate, on the bonding interface side, has an arithmetic mean roughness Ra of 0.01 to 1.0 μm.
The bonded body according to any one of aspects 1 to 10, having a bond strength of 200 MPa or more in four point bending test.
The bonded body according to any one of aspects 1 to 11, wherein the ceramic plate comprises aluminum oxide and/or aluminum nitride, and comprises an embedded inner electrode.
A bonded body comprising:
The bonded body according to aspect 13, wherein the MMC plate includes a Mg-diffused layer in which Mg derived from the bonding layer is diffused over a predetermined depth DMg from a bonding interface between the bonding layer and the MMC plate.
The bonded body according to aspect 14, wherein the depth DAl of the Al-diffused layer is larger than the depth DMg of the Mg-diffused layer to satisfy DAl>DMg.
The bonded body according to any one of aspects 13 to 15, wherein the ceramic plate comprises aluminum oxide and/or aluminum nitride, and comprises an embedded inner electrode.
The bonded body according to any one of aspects 13 to 16, wherein the bonding of the ceramic plate, the bonding layer, and the MMC plate is thermal compression bonding.
The bonded body according to any one of aspects 13 to 17, wherein a surface of the MMC plate, on the bonding interface side, has an arithmetic mean roughness Ra of 0.01 to 1.0 μm.
The bonded body according to any one of aspects 13 to 18, having a bond strength of 200 MPa or more in four point bending test.
The ceramic plate 12 is a plate-shaped member including a ceramic sintered body, and may have the same configuration as that of a ceramic plate employed for a known ceramic susceptor (e.g., an electrostatic chuck assembly or a ceramic heater). Typically, an inner electrode 18 is embedded in the ceramic plate 12. The ceramic sintered body serving as the main body (i.e., the ceramic base material) of the ceramic plate 12, excluding the inner electrode 18, preferably includes aluminum oxide and/or aluminum nitride, in terms of, for example, the excellent thermal conductivity, the high electrical insulation property, and the thermal expansion characteristic similar to that of silicon, and more preferably includes aluminum nitride. In addition to the aluminum oxide and/or aluminum nitride, the ceramic sintered body included in the ceramic plate 12 may include an additive such as MgO. In this case, the content of the aluminum oxide and/or aluminum nitride in the ceramic sintered body included in the ceramic plate 12 is typically 50 to 100 mass %, and the remainder may include the additive such as MgO. The thickness of the ceramic plate 12 may be a thickness of a general ceramic plate and is not particularly limited. The thickness is typically 2 to 10 mm, and may be more typically 2 to 5 mm.
Examples of the inner electrode 18 embedded in the ceramic plate 12 include an ESC electrode, a heater electrode, and an RF electrode. Two types of inner electrodes 18 may be provided in the ceramic plate 12. The ESC electrode is the abbreviation of an electrostatic chuck (ESC) electrode and also referred to as an electrostatic electrode. The ESC electrode is preferably a circular thin-layer electrode having a slightly smaller diameter than that of the ceramic plate 12, and may be, for example, a mesh electrode in a sheet form obtained by weaving a thin metal wire into a net. The ESC electrode may be used as a plasma electrode. Specifically, a high-frequency wave can be applied to the ESC electrode to thereby use the ESC electrode as a plasma electrode, so that film formation can be carried out by the plasma CVD process. When a voltage is applied to the ESC electrode by an external power supply, the ESC electrode chucks a wafer mounted on the surface of the ceramic plate 12 by the Johnson-Rahbek effect. The heater electrode is not particularly limited, and may be, for example, a conductive coil that is wired throughout the whole area of the ceramic plate 12 in a unicursal manner. When a power is supplied to the heater electrode by a heater power supply, the heater electrode generates heat to heat a wafer mounted on the surface of the ceramic plate 12. The heater electrode is not limited to the coil, and may be ribbon (long and narrow, thin plate) or mesh. The heater electrode having the shape of ribbon may be formed by a printing method.
The MMC plate 14 is made of a metal matrix composite (MMC). The MMC is not particularly limited, and may be a known material obtained by combining a metal matrix with a reinforcing ceramic material. Examples of the metal matrix include aluminum and metallic silicon. Examples of the reinforcing ceramic material include SiC and TiC. A preferable MMC contains Si, C, and Ti. Examples of the MMC containing Si, C, and Ti include a composite material that contains 37 to 60 mass % of silicon carbide and also contains titanium silicon carbide and titanium carbide in respective amounts smaller than the content (mass %) of the silicon carbide. The thickness of the MMC plate 14 is not particularly limited, and typically 5 to 35 mm.
The surface of the MMC plate 14, on the bonding interface 22 side, preferably has an arithmetic mean roughness Ra of 0.01 to 1.0 μm, and more preferably 0.05 to 0.70 μm. An arithmetic mean roughness Ra within the above range can more effectively enhance the bond strength. It is considered that the reason for this is that not too large an Ra enhances the adhesion of the MMC plate 14 to the bonding layer 16, and additionally that not too small an Ra brings about the anchor effect due to the surface roughness or unevenness of the MMC plate 14.
The bonding layer 16 is a metal layer including Al as a main component and Si and Mg as subcomponents. Here, the “main component” means a component that accounts for 80% by weight or more of the bonding layer 16. The “subcomponent” is a component the content of which is smaller than that of the main component (but excluding inevitable impurities). Accordingly, the bonding material forming the bonding layer 16 is preferably an Al alloy containing Si and Mg. The Si content of the Al alloy is preferably 5 to 15% by weight. The Mg content of the aluminum alloy is preferably 0.1 to 5.0% by weight. In other words, the bonding layer 16 is preferably made of an Al alloy containing 5 to 15% by weight of Si and 0.5 to 5.0% by weight of Mg and also containing Al and inevitable impurities as the remainder.
The bonding interface 20 between the ceramic plate 12 and the bonding layer 16 preferably includes a Mg-containing layer 24. It is considered that the Mg-containing layer 24 present in the bonding interface 20 improves the bond strength between the ceramic plate 12 and the bonding layer 16, and that as a result, a large bond strength can be achieved between the ceramic plate 12 and the MMC plate 14. The Mg-containing layer 24 is identified as a layer containing Mg at a higher concentration than its periphery in the bonding interface 20, in an elemental mapping image acquired by an EPMA (electron probe micro analyzer). The Mg-containing layer 24 preferably further contains Al and O. In this case, the weight ratio Al:Mg:O in the Mg-containing layer 24 is preferably with in the range of 1:0.01 to 0.50:0.001 to 0.100, and more preferably 1:0.05 to 0.30:0.005 to 0.050. The weight ratio Al:Mg:O can be determine by an EPMA. The thickness of the Mg-containing layer 24 is preferably 1 to 10 μm and more preferably 1 to 7 μm, in view of improvement in the bond strength.
The bonding of the ceramic plate 12, the bonding layer 16, and the MMC plate 14 is preferably thermal compression bonding. Thermal compression bonding is a method including sandwiching a metal bonding film (corresponding to the bonding layer 16) between two members to be bonded to each other and bonding the two members by pressing them while heating at a temperature less than the liquidus temperature of the metal bonding film (see Patent Literature 1).
The MMC plate 14 preferably includes an Al-diffused layer 26 in which Al derived from the bonding layer 16 is diffused over a predetermined depth DAl from the bonding interface 22 between the bonding layer 16 and the MMC plate 14, as shown in
In addition to the Al-diffused layer 26, the MMC plate 14 preferably also includes a Mg-diffused layer 28 in which Mg derived from the bonding layer 16 is diffused over a predetermined depth DMg from the bonding interface 22 between the bonding layer 16 and the MMC plate 14, as shown in
The MMC plate 14 may have an inner space that may be, for example, a flow channel through which a coolant is allowed to pass through. This allow the MMC plate 14 to have a configuration suitable as a cooling plate of an electrostatic chuck assembly.
The bonded body 10 preferably has a bond strength of 200 MPa or more, more preferably 250 MPa or more, and even more preferably 300 MPa or more, in four point bending test. The four point bending test is carried out in the procedure and conditions disclosed in Examples, which will be described later, and the maximum bending stress to be thus obtained is used as the bond strength. Since a larger bond strength is desirable, the upper limit thereof is not particularly limited, and the bond strength is typically 500 MPa or less, and more typically 450 MPa or less.
The bonded body of the present invention may be produced any method as long as the resultant bonded body has the specific layer structure. A preferable production method will be described below.
First, a ceramic plate having an embedded inner electrode, an MMC plate, and a bonding layer are provided. Details of each member are as described hereinabove. All of the ceramic plate, the MMC plate, and the bonding layer to be used may be known ones, or may be appropriately produced by known methods.
Next, the ceramic plate, the MMC plate, and the bonding layer are ultrasonically washed with an organic solvent. Soil adhered to the surface of each member can be removed by the ultrasonically washing, so that the adhesiveness of each member to the bonding layer can be improved to result in large bond strength. Preferable examples of the organic solvent include acetone and isopropyl alcohol (IPA). More soil can be removed by the ultrasonically washing for a longer duration, so that migration and diffusion of elements such as Mg and Al during the thermal compression bonding can be facilitated. Thus, control of the duration of the ultrasonically washing can regulate formation/non-formation of the Mg-containing layer and can change the depth (thickness) of the Al-diffused layer and the depth (thickness) of the Mg-containing layer, in the following thermal compression bonding. For example, when the ultrasonically washing is carried out for a longer duration, a Mg-containing layer can be formed and, at the same time, the depth of the Al-diffused layer and the depth of the Mg-containing layer can become large. In view of effectively removing the soil adhered to the surface of each member, it is desirable to carry out both of ultrasonically washing with acetone and that with isopropyl alcohol (IPA). The ceramic plate and the MMC plate that have been ultrasonically washed are preferably further cleaned by washing with running pure water, blowing with N2 gas, wiping with a wipe sheet impregnated with an organic solvent (such as IPA), and drying. The bonding layer that has been ultrasonically washed is preferably further cleaned by blowing with N2 gas.
The ceramic plate, the MMC plate, and the bonding layer each thus cleaned are used for thermal compression bonding to prepare a bonded body. For example, the ceramic plate and the MMC plate may be bonded to each other via the bonding layer by sandwiching the bonding layer between the ceramic plate and the MMC plate, and thermal compression bonding the resultant at a pressure of 4 MPa to 30 MPa while heating at a temperature less than the liquidus temperature of the film of the bonding material. The temperature of the thermal compression bonding is desirably less than the liquidus temperature of the bonding layer, and more than a temperature less than the solidus temperature of the bonding layer by about 30° C. For example, an aluminum alloy containing 10 weight % of Si and 1 weight % of Mg has a liquidus temperature of about 590° C. and a solidus temperature of about 560° C. Accordingly, it can be said that in this case, the temperature of the thermal compression bonding is desirably about 520° C. or more and less than about 540° C. In this manner, the bonded body of the present invention including a ceramic plate and an MMC plate bonded to each other via a bonding layer can be obtained.
The present invention will further be described specifically by way of Examples below. However, the present invention is not limited to Examples below.
A disk-shaped sintered body (thickness: 5 mm, diameter 300 mm) of aluminum oxide having an embedded ESC electrode was prepared as a ceramic plate in the following manner. First, provided were the first and second disk-shaped green sheets made of alumina. An ESC electrode was formed on one side of the first green sheet by screen printing, and on the other hand, a heater electrode was formed on one side of the second green sheet by screen printing. Next, another green sheet made of alumina (hereinafter also referred to as the third green sheet) was laid on the side of the first green sheet on which the ESC electrode was formed, and the second green sheet was laid thereon such that the heater electrode was in contact with the third green sheet. The resulting layered body was fired by hot pressing, to thereby obtain a ceramic sintered body having the embedded ESC electrode and heater electrode. Working, such as grinding and blasting, was carried out on the both sides of the resulting ceramic sintered body to adjust the shape and the thickness, to obtain a ceramic plate as a plate-shaped electrostatic chuck. The specific conditions for producing the electrostatic chuck were set with reference to the conditions described in JP2006-196864A.
A plate containing Si, C, and Ti (SiSiCTi plate) as an MMC plate was prepared in the following manner. First, provided as starting materials were an SiC material (commercially available product having a purity of 97% or more and an average particle size of 15.5 μm), a metallic Si material (commercially available product having a purity of 97% or more and an average particle size of 9.0 μm), and a metallic Ti material (commercially available product having a purity of 99.5% or more and an average particle size of 31.1 μm). The SiC material, the metallic Si material, and the metallic Ti material were weighted such that the blending percentages were SiC: 49.5 mass %, Si: 20.0 mass %, and Ti: 30.5 mass %, and these materials together with isopropyl alcohol as a solvent were placed in a nylon-made pot and wet-mixed for 4 hours with iron core-containing nylon balls having a diameter of 10 mm. The resulting slurry was taken out, dried in nitrogen flow at 110° C., and allowed to pass through a 30-mesh sieve to obtain a formulated powder. The formulated powder was subjected to uniaxial press-molding at a pressure of 200 kgf/cm2 to prepare a disk-shaped body having a diameter of about 50 mm and a thickness of about 17 mm, which was placed in a graphite mold for firing.
The disk-shaped body was fired while hot pressing, to thereby obtain an MMC plate. The firing while hot pressing was carried out by keeping at a firing temperature (highest temperature) of 1400° C. for 4 hours in evacuated environment while pressing at a pressure of 200 kgf/cm2.
For the MMC plate thus prepared, the arithmetic mean roughness Ra was measured on its surface to which the bonding layer was to be bonded, using a stylus-type surface roughness meter in accordance with JIS B 0601-2001. The result was as shown in Table 1.
An Al alloy sheet containing Si and Mg and having a thickness of 0.12 mm (alloy composition: Si: 10% by weight, Mg: 1% by weight, balance: Al and inevitable impurities) was provided to use as a bonding layer.
The following cleaning steps (i) to (v) were carried out in this order on each of the ceramic plate and the MMC plate, and on the other hand, only the following cleaning steps (i), (ii), and (vi) were carried out in this order on the Al alloy sheet containing Si and Mg.
In these steps, the total washing time of (i) ultrasonically washing with acetone and (ii) ultrasonically washing with isopropyl alcohol (IPA), that is, the duration of ultrasonically washing with organic solvents was varied in Experimental Examples as shown in Table 1. Thus, the ultrasonically washing (i) and (ii) were not carried out in Example 9 as described above.
The ceramic plate, the MMC plate, and the bonding sheet each cleaned were subjected to thermal compression bonding in the following manner. Specifically, the bonding sheet as a bonding layer was sandwiched between the ceramic plate and the MMC plate, and these were subjected to thermal compression bonding by heating in vacuo at 530° C. (temperature less than the liquidus temperature of the Al alloy containing Si and Mg, and more than a temperature less than the solidus temperature of the alloy by about 30° C.) at a pressure of 20 MPa, to thereby bond the ceramic plate, the bonding sheet (bonding layer), and the MMC plate to each other. Thus, a bonded body was obtained that had a ceramic plate and an MMC plate bonded to each other via a bonding layer.
The following evaluation was made on the bonded body prepared.
The bonded body obtained was cut to obtain its cross section, and the cross section was mirror-polished. Flat ion milling with Ar ions was carried out on the cross section, to obtain a cross section for observation. Observation was made using a SEM (scanning electron microscope) on an area of 75 μm×75 μm including the ceramic plate 12, the bonding interface 20, and the bonding layer 16 in the resulting cross section for observation. On that area, elemental analysis was carried out using an EPMA (manufactured by JEOL Ltd.) in a measurement condition of an acceleration voltage of 15 kV, to acquire an elemental mapping image for Si, C, Ti, O, Mg, and Al.
Observation using a SEM and elemental analysis using an EPMA were also made in the same manner as above on an area of 75 μm×75 μm including the bonding layer 16, the bonding interface 22, and the bonding interface 22 in the resulting cross section for observation.
Furthermore, observation using a SEM and element analysis using an EPMA was also made on a larger area of 300 μm×300 μm including the bonding layer 16, the bonding interface 22, and the bonding interface 22 in the cross section in the same manner as above, except that the magnification was decreased and the concentration scale was reduced.
From the determination results by the EPMA, a semi-quantitative amount of each element was calculated in every pixel, which corresponded to 0.24 μm×0.24 μm, and the weight ratio was calculated from the average from 300 pixels to obtain the weight ratio Al:Mg:O.
From the bonded body obtained, a long sample was cut out such that the bonding layer was positioned at the longitudinal center, and the surface of the sample was polished to prepare a specimen having dimensions of 1.5 mm×2.0 mm×20 mm. On this specimen, four point bending test was carried out such that the bonding interface was positioned at the center under the conditions of a lower span of 15 mm, an upper span of 5 mm, and a cross head speed of 0.5 mm/min, and the found maximum bending stress (MPa) was used as the bond strength. The results were as shown in Table 1.
This application is a continuation application of PCT/JP2023/041672 filed Nov. 20, 2023, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2023/041672 | Nov 2023 | WO |
| Child | 18760081 | US |
