Patent Application
20110259270
This application claims priority from Japanese Patent Application No. 2010-098080, filed on Apr. 21, 2010, the entire subject matter of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a carbon component and a method for manufacturing the carbon component.
2. Description of the Related Art
In a CVD system for epitaxially growing silicon or a compound semiconductor wafer, a susceptor has been used for mounting thereon a wafer. A conductive graphite base material has generally been used in the susceptor for generating heat by means of induction heating. Since graphite exhibits low electrical resistance, high heat resistance and chemical stability, it can be preferably used in such a field of CVD system. However, since a process rate is important for epitaxial growth, wafers are exchanged even at a relatively high temperature before an interior of the CVD system is sufficiently cooled, so that the susceptor is exposed to the atmosphere while still remaining heated. Therefore, if the graphite is used for a base material as it is, there will arise a problem of the base material reacting with air, to thus become heavily deteriorated. In a system of using a CVD susceptor for epitaxial growth of gallium nitride, and the like, ammonium is used as a source gas. When decomposed by heat, ammonium produces hydrogen and nitrogen. Although nitrogen is used as a source gas for a gallium nitride film, hydrogen reacts with the graphite at a high temperature, to thus produce a hydrocarbon gas, like methane. Therefore, the graphite is eroded. For this reason, in order to prevent reaction of the atmosphere or hydrogen with graphite, the susceptor made of graphite is coated with ceramic, like SiC (see, for instance, JP-B-4071919 or JP-A-2004-200436). The contents of JP-B-4071919 and JP-A-2004-200436 are incorporated herein by reference.
An illustrative embodiment of the present invention has been made in view of the above circumstances. According to an illustrative embodiment, there is provided a carbon component that can be used with less deterioration even in an atmosphere including an oxidizing gas or a decomposable gas, and in particular, that is likely to prevent generation of particles from the inside of an elongated hole, by forming a coating on an inner surface of the elongated hole of the carbon component.
According to an illustrative embodiment of the present invention, there is provided a carbon component having a hole therein and an outer surface covered with a ceramic coating comprises two carbon plate members joined together, wherein the hole is defined by a groove formed on a mating surface of at least one of the carbon plate members and a mating portion of the other of the carbon plate members, which opposes the groove, and wherein an inner surface of the hole including a surface of the groove is entirely covered with a ceramic coating.
According to another illustrative embodiment of the present invention, there is provided a method for manufacturing a carbon component having a hole therein and an outer surface covered with a ceramic coating comprises: preparing two carbon plate members, each having a mating surface to be joined together; forming a groove on the mating surface of at least one of the carbon plate members; purifying the carbon plate members to remove impurity from the carbon plate members; forming a ceramic coating on the groove of the at least one of the carbon plate members, a mating portion of the other of the carbon plate members, which opposes the groove, and an outer surface of the carbon plate members at least except for the mating surface; and joining the carbon plate members together while the mating surfaces oppose each other.
The above and other aspects of the present invention will become more apparent and more readily appreciated from the following description of illustrative embodiments of the present invention taken in conjunction with the attached drawings, in which:
The susceptor of a CVD system is structured to be able to mount thereon a plurality of wafers. Although some simple susceptor has a structure for mounting thereon a plurality of wafers directly on the susceptors. Another susceptor has a structure, in order to enhance uniformity of film thickness of the wafer, for making a film uniform by rotating a wafer or a wafer carrier on the susceptor by utilization of a gas flow in addition to rotation of (revolution) of the entire susceptor. In such a susceptor, a gas is introduced into an inside of the susceptor from the outside, the gas is discharged from a vertical hole (an outlet nozzle) formed substantially at a center of a mount surface of the wafer or the wafer carrier, to thus exit while generating a vortex in a space between the wafer or the wafer carrier and the susceptor. On this occasion, the vortex of gas imparts rotational energy to the wafer, whereby the wafer can rotate on the susceptor. In order to enable passage of the gas, gas inlet hole is formed in the susceptor from a gas inlet part formed in a side surface of the susceptor to a neighborhood of a center of the wafer mount surface (or wafer carrier). The gas inlet hole is formed in the side surface of the susceptor by boring, with a drill, an elongated hole that passes through a position located immediately below the neighborhood of the center of the wafer mount surface (or the wafer carriers), boring a vertical hole for establishing a connection of the center of the wafer mount surface (or the wafer carrier) with the elongated hole, and sealing an end of the elongated hole.
In addition to boring of the elongated hole, a base material used as a susceptor (referred to as a susceptor base material) is subjected to another shape machining. Further, a ceramic coating, like a SiC-CVD film, a TaC-CVD film, and a pyrolytic carbon film, is formed on a surface of the susceptor base material, thereby completing a susceptor that can be used in a CVD system for epitaxial growth.
In a carbon component having the elongated hole, it tends to be difficult to form the ceramic coating deep into the hole. Specifically, in order to form a ceramic coating on the surface of the carbon component, the susceptor base material is loaded into a CVD furnace for forming a coating. After heating of the base material, for instance, for a SiC coating, a silane-based source gas and a hydrocarbon-based source gas are introduced into the furnace. It is noted that the CVD furnace used at this time is for forming a ceramic coating on a base material of graphite and is totally different from the CVD furnace for epitaxial growth. The source gas introduced into the CVD furnace becomes decomposed upon contacting with the hot base material, to thus build up on the base material and form a ceramic coating. A ceramic coating is formed at high speed on a front surface of the base material to be supplied with a source gas. However, the ceramic coating is formed at low speed on a back surface, a deep interior of a recess (hole), and the like, where the source gas is difficult to reach and a coating generally tends to become thinner. Further, the source gas for a ceramic coating enters the gas inlet hole of the susceptor from a small hole, to thus proceed to a deep side while contacting and building up on the wall surface of the elongated hole. For this reason, the concentration of the supplied source gas becomes low at a deep position in the elongated hole, and the source gas becomes hard to reach the deep position, so that the ceramic coating might not be formed.
When the carbon component is used in an atmosphere including an oxidizing gas and a decomposable gas, the outer surface of the carbon component having such an elongated hole is protected by a ceramic coating. However, the inner surface of the elongated hole that is not protected by the ceramic coating is likely to undergo oxidation and decomposition, and thickness reduction starts from the inner surface of the elongated hole, which is likely to cause damage that extends over the entire component with time.
If the carbon component is a susceptor having an elongated hole for epitaxial growth and if a coating is not formed over the elongated hole, the susceptor contacts the outside air at replacement of wafers, and when hydrogen is used for rotating the wafer or the wafer carrier by means of a gas vortex, an inner wall of the elongated hole is likely to become oxidized, decomposed, and deteriorated. Since the graphite base material is a porous material, the material does not become uniformly deteriorated from its surface, so that the deterioration tends to be accompanied by separation of particles. For this reason, the thus-separated particles spread as graphite particles over the interior of the CVD furnace for epitaxial growth, and the particles adhere to the wafer. If an epitaxial film is formed over the wafer with the particles, the particles are likely to cause defects. If the particles float within a hot zone, the particles are like to act in the air as nuclei for depositing the source gas. Then, the nuclei are likely to be deposited on the wafer, to thus cause crystal defects.
Next, illustrative embodiments of the present invention will be described by reference to the drawings.
A carbon component 100 according to an illustrative embodiment of the present invention may be preferably used as a wafer holding member (a susceptor for epitaxial growth) that is heated by means of high frequency induction, a heater, and the like, in order to hold and heat a semiconductor wafer. The carbon component 100 is herein also referred to as a susceptor 100. As shown in
In order to enable the passage of the gas, holes 11 for introducing a gas are formed within the susceptor 100 so as to extend from an unillustrated gas introduction device to the wafer mount surfaces 31. Each of the holes 11 is connected to vertical holes 41 at two substantially center positions of each of the wafer mount surfaces 31, and an end of each of the holes 11 is sealed, whereby the holes are formed.
As shown in
The susceptor 100 has the holes 11 therein, and an outer surface 13 thereof (see
A cross sectional shape of the hole 11 that is orthogonal to an axial (extending) line of the hole may be a substantially square shape shown in
As shown in
The hole 11 may have opening at both ends; namely, an inlet and an outlet, or only on one side. A preferred ratio (L/D) of a depth (length: L) of the hole with respect to a diameter (D) of the hole 11 may be about 20 or more. When the ratio (L/D) of the depth (L) with respect to the diameter (D) is about 20 or more, the source gas of CVD becomes difficult to reach a deep position (a deep interior) of the hole 11. However, by adopting the configuration of the present invention, it is likely to form a ceramic coating substantially uniformly over the substantially entire inner surface of the hole.
The internal diameter of the hole 11 is not limited to a substantially uniform diameter. The hole 11 may have a shape that has an opening of small internal diameter and an interior space of large internal diameter or a gourd shape having a narrowed midsection. When the hole 11 has a gourd shape, consideration should be given to a depth from the narrow midsection. A preferred ratio (L/D) of a depth (length: L) from the narrow midsection with respect to the diameter (D) of the narrowed midsection may be about 20 or more.
A coating formed on the outer surface 13 and on the surface of the holes 11 of the carbon members 19 is a ceramic coating 15 and includes at least one of, for instance, a SiC coating, a pyrolytic carbon coating, a BN coating, a TaN coating, and a TaC coating. In particular, the SiC coating, the BN coating, the TaN coating, and the TaC coating are superior to carbon of a base material 37 in terms of corrosion resistance to hydrogen or nitrogen, and therefore, can be preferably utilized. Although pyrolytic carbon is inferior to the ceramic coating 15 of the other types in terms of corrosion resistance but tends to be superior to the same in terms of heat resistance. The pyrolytic carbon is a dense material, and therefore, superior to the graphite base material in terms of corrosion resistance. Additionally, since the pyrolytic carbon is made of carbon, the pyrolytic carbon can be preferably utilized in the case of high temperature. The coating may be configured as a single layer or a plurality of layers. In the case of a plurality of layers, the layers may be a substantially single type or a plurality of different types.
The coating formed on the surface of the hole 11 may be formed by use of any method. However, a coating formed by the CVD method is preferable. Since a dense coating is likely to be formed with the CVD method, carbon of the base material 37 is likely to be blocked from an oxidizing gas or a reactive gas. In the case of the coating including a plurality of layers, all of the layers or only one of the layers may be a CVD coating. In the case of the coating including only one layer of CVD coating, a layer reactively transformed by a CVR (chemical vapor reaction) method may be on a base material side of the coating. In the case where the coating including a CVD layer and a CVR layer is formed from a substantially single element, the CVR layer can act as a buffer layer between the CVD layer and the base material 37, so that the ceramic coating 15 less susceptible to separation is likely to be formed. Since the CVR layer is resultant from reactive transformation of graphite, the CVR layer is likely to be joined strongly to the graphite base material. Additionally, the graphite base material is substantially identical with a CVR layer formed on a front surface layer of the coating in terms of thermal expansion coefficient, and therefore, the coating can be less likely to be separated.
The susceptor 100 has the mating surface 23 substantially parallel to the axis of the hole 11. Since the susceptor has the mating surface 23 substantially parallel to the axis of the hole 11, the elongated hole can be made by shallowly grooving the mating surface side of the carbon member and joining the thus-grooved carbon members together. Therefore, the elongated hole is likely to be readily formed without causing the holes to bent, or a cutting tool to be broken when compared with a case where the hole is bored with a drill.
The ceramic coating 15 can be omitted from the mating surfaces as shown in
The carbon members 19 are joined together by means of a heat resistant adhesive. As a result of the mating surfaces 23 of the respective carbon members 19 being joined together by means of a heat resistant adhesive, the joined portion is sandwiched between the carbon members coated with the ceramic coating so as not to come out on the outer surface or the inner surface. The joined portion and the base material hardly contact the oxidizing gas or the decomposable gas, so that a possibility of occurrence of thickness reduction is likely to become small. A carbon-based adhesive layer, a SiC-based adhesive layer, or the like, may be preferably utilized for the adhesive. The heat resistant adhesive can be cured when subjected to heat treatment at about 200 to about 300° C. Impurities, like organic components, are removed by subjecting the adhesive to heat treatment of about 1000 to about 1500° C. without inflicting damage to the ceramic coating.
An amount of impurity content in the base material 37 of the carbon members is preferably about 20 ppm or less. When the impurity content is about 20 ppm or less, the carbon base material is hardly oxidized and decomposed by catalytic action of impurities and is hardly dissipated. In a case where the carbon members are used for a susceptor, when the impurity content is about 20 ppm or less, the impurities is less likely to spread in the CVD furnace and separated particles by exhaustion is less likely to spread to thereby less adversely affect the wafers during epitaxial growth.
The susceptor 100 is not limited to a specific application but may be preferably utilized for a CVD system for manufacturing semiconductors. According to an illustrative embodiment of the present invention, the coating film is formed even in the hole, and therefore, the inner surface of the hole is less likely to be subjected to thickness reduction by wastage, and there becomes little possibility of scattering of particles in the system.
The susceptor 100 may preferably be utilized for a CVD system for epitaxial growth of silicon, a compound semiconductor, and an SiC semiconductor. Hydrogen is often used as a carrier gas for epitaxial growth and spreads at high speed. For these reasons, hydrogen easily enters the interior of the elongated hole, and the base material 37 has to be blocked from hydrogen. However, according to an illustrative embodiment of the present invention, the ceramic coating is formed on the surface of the hole. In particular, the carbon base material becomes easily deteriorated during epitaxial growth of a compound semiconductor and a SiC semiconductor. Therefore, the susceptor 100 according to an illustrative embodiment of the present invention can preferably be utilized for those systems.
Thus, the carbon component according to an illustrative embodiment of the present invention is preferably the susceptor 100 since the susceptor 100 directly contacts the wafer, and further, a gas supplying port for levitating the wafer carrier is provided in the component. Therefore, there is a high possibility of the wafer being adversely affected by wearing of the interior of the hole.
The susceptor 100 according to an illustrative embodiment of the present invention may be manufactured as follows.
A set of carbon members 19 each having the mating surface 23 is manufactured (prepared) from a graphite material. The respective separated carbon members 19 may have a sandwich structure in which the carbon members have the substantially same size. Alternatively, the carbon members may have a fitting structure in which one of the carbon members is larger, and the other one is smaller and fit into the larger carbon member.
As shown in
It is desirable to supply a purifying gas (chlorine, a halogen gas, a halogen-based gas, or the like) to an inside of a purifying furnace 43 shown in
As shown in
When the groove 25 and the area of the mating surface 23 adjacent to the groove 25 or the area of the mating surfaces adjacent to the outer surface of the susceptor 100 are coated, it may be better to machine the mating surfaces 23 to be coated by previously reducing the thickness of the mating surfaces 23 by an amount equal to a thickness A of the coating layer as shown in
As shown in
In order to smooth the mating surfaces 23 after joining of the carbon members 19, the mating surfaces may be again coated. In a second coating step, a coating is formed over the mating surfaces 23, and therefore, the mating surfaces 23 can be sealed, to thus be likely to be protected from intrusion of a reactive gas from the outer surface of the susceptor 100.
Accordingly, in the above manufacturing method, it is possible to reliably form the ceramic coating 15 on the groove 25 of one carbon member 19 and the mating portion 27 of the other carbon member 19, which opposes the groove 25 while the carbon members 19 are separated from each other. Specifically, since the entire interior of the hole 11 is opened, the concentration of the source gas supplied is less likely to be reduced, and therefore, even when the elongated hole has a large depth (length), the ceramic coating 15 is likely to be substantially uniformly and reliably formed.
Moreover, in the susceptor 100, the ceramic coating is likely to be surely formed on the interior of the elongated hole. Therefore, the carbon members can be used without being deteriorated even in the oxidizing gas or the decomposable gas. Since carbon particles are less likely to be produced within the CVD system, wafers including no or few defects can be obtained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-098080 | Apr 2010 | JP | national |
