Patent ID: 12211725

DESCRIPTION OF EMBODIMENT

Electrostatic Chuck Assembly

FIGS.1A and1Billustrate schematic cross-sectional views of an electrostatic chuck assembly10according to an aspect of the present invention. The electrostatic chuck assembly10includes an electrode-embedded ceramic plate12, a disc-shaped cooling plate14, an annular or arcuate internal fixation member16, female threads18,18′,18″,18′″, and insertion holes20. The electrode-embedded ceramic plate12is a disk-shaped plate having a configuration as an electrostatic chuck. The cooling plate14is a disk-shaped plate with an annular or arcuate internal space14aand supports the bottom surface of the electrode-embedded ceramic plate12. The internal fixation member16is an annular or arcuate member that is accommodated in the internal space14aso as to be rotatable about the central axis of the cooling plate14. The female threads18,18′,18″,18′″ are spaced apart from each other in the internal fixation member16. The number of female threads18,18′,18″,18′″ is a multiple of n (where n is an integer of 2 or more). The insertion holes20are holes for insertion of bolts22for being fixed to a chamber and are provided at the bottom of the cooling plate14such that one set of n female threads18is exposed, as illustrated inFIG.2A, and hence the number of insertion holes20is n. Each of the female threads18,18′,18″,18′″ is disposed such that another set of n female threads18′,18″, or18″ is exposed in the insertion holes when the internal fixation member16is rotated at a predetermined angle or at an angle being a multiple of the predetermined angle. As thus described, by employing the disk-shaped cooling plate14with the annular or arcuate internal space14aand the annular or arcuate internal fixation member16rotatably accommodated in the internal space14aand by providing the female threads18,18′,18″,18′″ in a multiple of n in the internal fixation member16such that the n female threads18are exposed from the insertion holes20on the back surface of the cooling plate14, when at least one of the n female threads18deteriorates, another set of n female thread18′,18″, or18′″ having not deteriorated can be exposed from the insertion holes by simply rotating the internal fixation member16, and as a result, the service life of the electrostatic chuck assembly can be increased multiplicatively.

That is, as described above, there has been a risk that the female thread118or118′ may deteriorate as the electrostatic chuck assembly110or110′ is assembled to or detached from the vacuum chamber130, making the assembling impossible. However, even in such a case, the electrostatic chuck assembly10according to the present invention can sequentially expose the female thread18′,18″, or18′″ having not deteriorated in the insertion holes20by simply rotating the internal fixation member16, so that the bolts22are re-screwed thereinto, and the electrostatic chuck assembly10can thereby continue to be used without being discarded. As a result, the service life of the electrostatic chuck assembly10can be increased multiplicatively (i.e., [(total number of female threads)/n] times, four times in the illustrated example).

The fact that the service life of the electrostatic chuck assembly10can be increased multiplicatively is extremely advantageous in view of the following circumstances in the vacuum chamber of the plasma etching apparatus. That is, in each of the conventional structures illustrated inFIGS.7and8, torque applied to the bolt122for the assembling of the electrostatic chuck assembly110or110′ is desirably a value that ensures an axial force necessary for crushing the O-ring132between the back surface of the cooling plate114and the vacuum chamber130by a predetermined amount under an environment where atmospheric pressure is applied to the upper side in the vertical direction (in the direction of arrow A in each of the drawings). This value depends on the nominal diameters of the bolts122used for fixing and the number thereof, but in the case of, for example, 12 bolts of M6 (outer diameter 6 mm) made of a material of 2.4T series (e.g., carbon steel), as high as 1 Nm of torque can be applied. With the electrostatic chuck assembly110or110′ being subjected to repeated temperature rise and fall in use, not only the stress and reaction force generated at the time of the fixing of the bolt122but also the thermal stress caused by the temperature rise and fall is applied to a screw fixation part. For this reason, coupled with the conventional fixing methods as illustrated inFIGS.7and8, it is easily assumed that biting and thread crushing (i.e., deterioration in the female thread118or118′) due to the interference between the screw threads will occur. In particular, even though the function of the electrostatic chuck assembly110or110′ as a susceptor itself has no problem after use, the service life as the susceptor may be limited due to the deterioration in the female thread118or118′, and hence there is an urgent need to improve the portion related to the female thread118. It can thus be said that the problems associated with the deterioration in the female thread118or118′ as described above are particularly remarkable in the use in the vacuum chamber of the plasma etching apparatus, and the present invention can solve these problems successfully.

The electrostatic chuck assembly10of the present invention is also advantageous in being able to cope with the following problem in addition to the problems associated with the deterioration in the female thread118or118′.

In each of the conventional structures illustrated inFIGS.7and8, the portion fixed with the bolt122has a strong pulling force vertically downward as compared with the portion not fixed with the bolt122, and hence there is also a problem that a surface112aof the electrode-embedded ceramic plate112is likely to be uneven. In this regard, according to the present invention, clamping load due to the fixing of the bolt122is dispersed by the annular or arcuate internal fixation member16, so that the unevenness of the surface112aof the electrode-embedded ceramic plate112due to the assembling of the electrostatic chuck assembly10becomes less than in the conventional cases.

In the conventional structure illustrated inFIG.8, a shape (e.g., hexagon like a nut, double chamfers, etc.) that restrains the rotation of the independent part119at the time of the fixing of the bolt122is required. However, when the independent part119is small, it is not possible to ensure large dimensions of the rotation restraining shape, and the rotation restraining effect becomes insufficient. Besides, when the rotation restraining shape is deformed, the fixing with the bolt122becomes impossible. In this regard, according to the present invention, with the internal fixation member16being annular or arcuate, the side surface of the internal fixation member16is restricted over a sufficient length by the inner wall of the annular or arcuate internal space14ain the cooling plate14, so that the rotation associated with the fixing of the bolt122can be restrained effectively.

The electrostatic chuck assembly10is used as a stand, on which a wafer is mounted, to perform chemical vapor deposition (CVD), etching, or the like on the wafer by using plasma and is fixed to a vacuum chamber30(particularly a lower part of the chamber) for manufacturing semiconductor devices.

The electrostatic chuck assembly10includes the electrode-embedded ceramic plate12and the cooling plate14. The cooling plate14can be caused to adhere to a back surface12bof the electrode-embedded ceramic plate12on the side opposite to a front surface12a, which is the wafer mounting surface, via a bonding layer13.

The electrode-embedded ceramic plate12may have a structure generally used as an electrostatic chuck. A typical electrode-embedded ceramic plate12includes a disk-shaped ceramic substrate12c, and an electrostatic electrode12dand a heater electrode12ethat are buried in the ceramic substrate12capart from each other in the thickness direction. In the ceramic substrate12c, the electrostatic electrode12dis provided near the front surface12a, while the heater electrode12eis provided near the back surface12b. Examples of ceramic material constituting the ceramic substrate12cinclude aluminum nitride, silicon carbide, silicon nitride, and aluminum oxide.

The electrostatic electrode12dcan be a conductive layer (e.g., a conductive mesh or plate) and is provided parallel to the front surface12a. The back surface of the electrostatic electrode12dpasses through the vacuum chamber30, the cooling plate14, and the bonding layer13, and is connected to a power supply rod34inserted into the ceramic substrate12c. A DC voltage is applied to the electrostatic electrode12dvia the power supply rod34.

The heater electrode12eis made of a conductive coil or a printed pattern and is formed so as to be connected from one end to the other end in a manner of a single stroke across the entire electrode-embedded ceramic plate12in a plan view. One end and the other end of the heater electrode12epass through the vacuum chamber30, the cooling plate14, and the bonding layer13and are connected to a pair of power supply rods (not illustrated) inserted into the ceramic substrate12c. A voltage is applied to the heater electrode12evia the power supply rod.

However, the electrodes embedded in the ceramic substrate12care not limited to the electrostatic electrode12dand the heater electrode12ebut may be other types of electrodes, and the number of layers of the electrodes embedded is not limited to two but may be three or more. For example, four layers of electrodes, which are an electrostatic electrode for a wafer, a bias electrode for a wafer, an electrostatic electrode for the focus ring, and a bias electrode for the focus ring, may be buried in the ceramic substrate12cfrom the front surface12ato the back surface12b, the electrodes being spaced apart from each other in order.

The cooling plate14is a disk-shaped plate for supporting the bottom surface of the electrode-embedded ceramic plate12and has the annular or arcuate internal space14afor accommodating the internal fixation member16. The internal space14ais formed in such a structure that the internal fixation member16can be accommodated so as to be rotatable about the central axis of the cooling plate14. The cooling plate14may have a configuration of a cooling plate generally used for an electrostatic chuck, except that the cooling plate14has the internal space14a. The cooling plate14may be made of a metal, such as aluminum or aluminum alloy, or a metal matrix composite (MMC) such as SiSiCTi (a composite material containing Si, SiC, and Ti). A typical cooling plate14is disk-shaped and has on its inside a flow path14bthrough which a refrigerant can be circulated. The flow path14bis connected to a refrigerant supply path and a refrigerant discharge path (not illustrated) that pass through the vacuum chamber30, and the refrigerant discharged from the refrigerant discharge path is returned again to the refrigerant supply path after temperature adjustment. In the cooling plate14, a lower portion of the cooling plate14(a portion on the side closer to the vacuum chamber30) extends in a radially expanding direction to form a flange14c.

The cooling plate14can be caused to adhere to the back surface12bof the electrode-embedded ceramic plate12via the bonding layer13. The bonding layer13may be a bonding sheet or a metal layer such as aluminum alloy layer. In particular, when the cooling plate14is made of a metal matrix composite (MMC) such as SiSiCTi, the cooling plate14is preferably bonded to the back surface12bof the electrode-embedded ceramic plate12by thermal compression bonding (TCB). TCB refers to a known method in which a metal bonding material is sandwiched between two members to be bonded and the two members are pressure-bonded while being heated to a temperature equal to or lower than the solidus temperature of the metal bonding material. Examples of the metal bonding material include aluminum alloy.

The internal fixation member16is an annular or arcuate member that is accommodated in the internal space14aso as to be rotatable about the central axis of the cooling plate14. Thus, the internal fixation member16is formed in a shape suitable for the internal space14a. The internal fixation member16may be annular as illustrated inFIGS.2A,3A, and3B, or may be one of arcuate members16′,16″, and16′″ with various central angles as illustrated inFIGS.3C to3E. The central angles of the arcuate internal fixation member16illustrated inFIGS.3C,3D, and3Eare about 45°, about 90°, and about 135°, respectively. In the case where the internal fixation member16is formed into an arcuate shape, the internal space14aof the cooling plate14may be annular or arcuate. When the internal space14aof the cooling plate14is arcuate, it is desirable to make the arcuate central angle of the internal space14alarger than the central angle of the arcuate internal fixation member16because the arcuate internal fixation member16needs to be accommodated in the internal space14aso as to be rotatable about the central axis.

The internal fixation member16only needs to be made of a material capable of forming the female thread18. Examples of such a material include metals such as titanium and stainless steel.

The female threads18,18′,18″,18″ are spaced apart from each other in the internal fixation member16. The total number of female threads18,18′,18″,18″ is a multiple of n (where n is an integer of 2 or more). In this regard, in the aspect illustrated inFIGS.2A and3A, the number of female threads18, the number of female threads18′, the number of female threads18″, and the number of female threads18″ are each 12, that is, n=12, and the number of types of female threads18,18′,18″,18′″ is four, so that the total number of female threads18,18′,18″,18′″ is n×4=12×4=48. Note that the female threads18,18′,18″,18″ are preferably of the same shape and size as each other, and reference numerals18,18′,18″, and18′″, which are different from each other, are merely provided for convenience of distinguishable description. However, the number of types and the total number of female threads18,18′,18″,18′″ illustrated inFIGS.2A and3Aare merely examples, and the present invention is not limited thereto.

The value of n is not particularly limited as long as being an integer of 2 or more, but the value of n is preferably 2 to 24, typically 3 to 20, and more typically 5 to 15. The total number of female threads18,18′,18″,18″ is preferably 2-5 times n. Most preferably, as illustrated inFIGS.2A and3A, the value of n is 12, and the total number of female threads18,18′,18″,18′″ is four times n (i.e.,48). Preferably, the n female threads18,18′,18″,18″ are equally spaced apart from each other.

The insertion holes20are holes for insertion of the bolts22for being fixed to the chamber, and n insertion holes20are provided at the bottom of the cooling plate14such that one set of n female threads18is exposed. The insertion hole20is preferably formed to have a size slightly larger than the outer diameter of each of the female threads18,18′,18″,18′″, so that the bolt22can be inserted into the female thread18without difficulty, except for a case where the insertion hole20has an excess opening20ato be described later.

Each of the female threads18,18′,18″,18′″ is disposed such that another set of n female threads18′,18″, or18″ is exposed in the insertion holes20when the internal fixation member16is rotated at a predetermined angle or at an angle being a multiple of the predetermined angle. Another set of n female threads18′,18″, or18″ refers to a set of female threads (in the illustrated example, a combination of n female threads18′, a combination of n female threads18″, or a combination of n female threads18′″) that can be simultaneously exposed in n insertion holes20, in addition to the female threads (in the illustrated example, the female thread18) already exposed in the insertion holes20. In this manner, when the female thread18already exposed in the insertion hole20deteriorates due to use, an unused set of female threads18′,18″, or18′″ can be exposed in the insertion holes20and newly used by simply rotating the internal fixation member16at a predetermined angle or at an angle being a multiple of the predetermined angle. That is, the bolt22can be screwed into a set of unused female threads18′,18″, or18″. As a result, it is possible to multiplicatively increase the service life of the electrostatic chuck assembly10in use in the vacuum chamber.

It is preferable that identification symbols (1, 2, 3, and 4 in the illustrated example) be visibly provided next to the female threads18,18′,18″,18″ of the internal fixation member16and that at least one of the n insertion holes20have an excess opening20athat makes the identification symbol visible externally. In this manner, the used set of female threads18and the unused set of female threads18′,18″, or18″ can be distinguished from the excess opening20aby the identification symbols, and the unused set of female threads18′,18″, or18″ to be exposed next to the insertion hole20can be selected in an easy and appropriate manner. It is thus preferable that the same identification symbol be assigned to each of one set of n female threads18,18′,18″, or18′″, which can be simultaneously exposed in the insertion holes20, and that the identification symbol be different from an identification symbol assigned to each of another set of n female threads18,18′,18″, or18″. For example, as illustrated inFIGS.2A and3A, it is preferable that the identification symbols be numbers and that the numbers be assigned to the respective female threads18,18′,18″,18′″ such that the female threads18,18′,18″,18″ are arranged in sequential order from 1 to m (where m is an integer of 2 or more and is a value obtained by dividing the total number of female threads by n). In this case, the female thread to be exposed in the insertion hole20may be determined in order according to the identification numbers. Preferably, the identification symbol is visibly provided in the internal fixation member16by engraving. The engraving is advantageous in that the identification symbol is hard to fade away even after a long period of use.

The insertion hole20with the excess opening20ais preferably an arcuate insertion hole. There are preferably two insertion holes20with excess openings20a, and these two insertion holes20with excess openings20aare more preferably disposed diagonally.

When the internal fixation member16is an annular member, as illustrated inFIG.2B, a central angle θ of an arc formed by the arcuate insertion hole20(the insertion hole20with the excess opening20a) is preferably [(360/N)+θ1] degrees or more (where N is the total number of female threads18,18′,18″,18″, and81is an angle formed by two tangent lines drawn from the center of the cooling plate14to the female thread18,18′,18″, or18′″ in a plan view). With this configuration, after the use of the female thread18is finished and the bolt22is removed, by simply inserting a rod or a finger into the female thread18and rotating the internal fixation member16about the central axis, the unused female thread18′,18″, or18″ to be used next can be easily exposed in the arcuate insertion hole20as illustrated inFIG.2B. That is, not only the used female thread18but also the unused female thread18′,18″, or18′″ can be exposed in the same arcuate insertion hole20. In particular, since the internal fixation member16is accommodated in the internal space14aof the cooling plate14, and the portion where the internal fixation member16is exposed to the outside is only the portion corresponding to the insertion hole20, ingenuity is required to rotate the internal fixation member16, but according to the above aspect, the internal fixation member16can be rotated easily.

A similar approach can be applied to the arcuate member16′,16″, or16″. In this case, the internal fixation member16includes two or more arcuate members16′,16″, and/or16′″ with a central angle of 360/n degrees or more. In each of the arcuate members16′,16″, and16′″, the central angle θ of the arc formed by the arcuate insertion hole20(the insertion hole20with the excess opening20a) is preferably [(360/n)/N′)+θ1] degrees or more (where N′ is the number of female threads in the arcuate member16′,16″, or16′″, and θ1is an angle formed by two tangent lines drawn from the center of the cooling plate to the female thread18,18′,18″, or18′″ in a plan view).

Manufacturing Method

The electrostatic chuck assembly of the present invention may be manufactured according to a known method, and the manufacturing method for the electrostatic chuck assembly is not particularly limited. For example, each of the electrode-embedded ceramic plate12, the parts for the cooling plate14, and the internal fixation member16is prepared, and these members are bonded by TCB, whereby the electrostatic chuck assembly10can be produced. Each step will be described below with reference toFIGS.4to6.

(1) Preparation of Electrode-Embedded Ceramic Plate

First, a slurry containing ceramic raw material particles, a binder, a dispersant, and the like is prepared. Examples of the ceramic raw material particles include aluminum nitride particles, silicon carbide particles, silicon nitride particles, and aluminum oxide particles. The slurry is filtered, and a curing agent is added and mixed. The resulting slurry is poured into a mold and dried. A green sheet obtained by the drying is subjected to degreasing, calcination, and processing to obtain a disk-shaped green sheet42. InFIG.4, three green sheets42are prepared, but the number of green sheets42is not limited thereto, and four or more green sheets42may be used. Here, for convenience of description, it is assumed that three green sheets42are used.

As illustrated inFIG.4(a), electrodes12dor12eare printed on two green sheets42. Then, the three green sheets42are laminated such that the electrodes12d,12eare sandwiched between the green sheets42. As illustrated inFIG.4(b), the resulting laminate is fired by hot pressing. As illustrated inFIG.4(c), the fired laminate is machined to form a hole connectable to the electrodes12d,12e. Thus, the electrode-embedded ceramic plate12is obtained.

(2) Preparation of Cooling Plate Parts

As illustrated inFIG.5(a), MMC raw material particles are press-molded to obtain a green compact44, and thereafter, as illustrated inFIG.5(b), the green compact44is fired by hot pressing. Thus, three MMC sintered bodies46are prepared. As illustrated inFIG.5(c), each of the three MMC sintered bodies46is machined to form an internal space14aand/or a flow path14b. Thus, cooling plate parts48a,48b,48care obtained. Although three cooling plate parts48a,48b,48care prepared inFIG.5, the number of cooling plate parts is not limited thereto, and four or more cooling plate parts may be used.

(3) Preparation of Internal Fixation Member

A material made of titanium is machined to obtain an annular internal fixation member16with equally spaced female threads18,18′,18″, or18′″ as illustrated inFIGS.3A and3B.

(4) Putting Together and Assembling of Electrostatic Chuck Assembly

As illustrated inFIG.6(a), the electrode-embedded ceramic plate12, the three cooling plate parts48a,48b,48c, and the internal fixation member16are put together such that the internal fixation member16is accommodated in an internal space14a. At this time, an aluminum alloy sheet43is interposed between the electrode-embedded ceramic plate12and the cooling plate part48and between the cooling plate parts48. As illustrated inFIG.6(b), TCB is performed to bond the electrode-embedded ceramic plate12and the cooling plate part48c, and the cooling plate parts48a,48b,48cto each other. As illustrated inFIG.6(c), the resulting bonded body is subjected to additional machining, terminal bonding, thermal spraying, sleeve adhesion, and the like to obtain the electrostatic chuck assembly10. Finally, as illustrated inFIG.6(d), the electrostatic chuck assembly10is disposed in a vacuum chamber30with an O-ring32interposed therebetween, and a bolt22is penetrated through a hole in the vacuum chamber30(particularly its support plate) and inserted into the female thread18exposed in the insertion hole20for screwing. Thus, the electrostatic chuck assembly10is fixed to the vacuum chamber30.