Patent Grant
11830724
The present disclosure is directed to an apparatus and method for fabricating semiconductor wafers.
Semiconductor devices are typically fabricated in silicon wafers. However, silicon carbide (SiC) wafers have become increasing popular due, at least in part, to the chemical-physical properties of SiC. For example, SiC generally has a higher band gap than silicon. As a result, SiC, even at relatively small thicknesses, has a higher breaking voltage compared to silicon. Accordingly, SiC is desirable for applications that have high voltages, such as power applications.
SiC may occur in a number of different crystallographic structures or polytypes. The most common polytypes are the cubic polytype (3C polytype), the hexagonal polytype (4H and 6H polytypes), and the rhombohedric polytype (15R polytype). 3C SiC wafers possess unique properties in comparison other wafer polytypes. For example, 3C SiC wafers generally have lower density of traps and/or higher channel electron mobility than 4H SiC wafers.
The present disclosure is directed to an apparatus and method for fabricating a semiconductor wafer, such as a silicon carbide (SiC) wafer.
According to one embodiment, the apparatus includes a body, a heater, an input duct, an output duct, a support, and a receptacle. The support is positioned on the receptacle and in the reaction chamber. The support includes a plurality of arms for supporting a substrate or a wafer, such as a silicon substrate. The arms allows for physical contact between the support and the substrate to be minimized. As a result, when the substrate is melted, surface tension between the arms and molten material is reduced, and the molten material will be less likely to cling to the support, itself.
According to one embodiment, a method is used to fabricate a SiC wafer. The method includes positioning a silicon substrate on the support, and forming a first layer of silicon carbide on the silicon substrate by exposing the silicon substrate to a flow of precursors (i.e., hetero-epitaxy). The silicon substrate has a first melting temperature and the silicon carbide has a second melting temperature that is higher than the first melting temperature. The method further includes heating the reaction chamber to a temperature that is higher than the first melting temperature and lower than the second melting temperature such that the silicon substrate begins to melt. The melted silicon substrate drains through an opening in the support and into the receptacle. The temperature of the reaction chamber is maintained until the first layer of silicon carbide is substantially separated from the silicon substrate. Simultaneously with or subsequent to the melting of the silicon substrate, the first layer of silicon carbide is exposed to a flow of precursors to form a second layer of silicon carbide (i.e., homo-epitaxy). Once the second layer of silicon carbide reaches a desired thickness, any remaining portions of the silicon substrate coupled to the first layer of silicon carbide is removed by an etching process.
In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the disclosure. However, one skilled in the art will understand that the disclosure may be practiced without these specific details. In some instances, well-known details associated with, for example, reaction chambers, fabrication processes, and/or semiconductor wafers have not been described to avoid obscuring the descriptions of the embodiments of the present disclosure.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
In the drawings, identical reference numbers identify similar features or elements. The size and relative positions of features in the drawings are not necessarily drawn to scale.
One solution for fabricating a silicon carbide (SiC) wafer is disclosed in U.S. patent application Ser. No. 15/715,940, entitled “APPARATUS FOR MANUFACTURING A SILICON CARBIDE WAFER”. The fabrication of the SiC wafer disclosed in U.S. patent application Ser. No. 15/715,940 includes, for example, placing a silicon substrate on a support having a plurality of bars and openings, growing a 3C—SiC epitaxial layer on the silicon substrate, and then separating the silicon substrate from the 3C—SiC epitaxial layer by melting the silicon substrate. The melted silicon is drained through the plurality of openings in the support and into a receptacle. The inventors have since discovered that the support disclosed in U.S. patent application Ser. No. 15/715,940 may not always properly drain the melted silicon into the receptacle. Rather, the inventors have discovered that the melted silicon may sometimes stick or cling to the support, itself, due to surface tension between the melted silicon and the support.
An improved apparatus and method for fabricating a wafer, such as a SiC wafer, are described herein. The apparatus may address one or more of the problems associated with the fabrication of a SiC wafer as described in U.S. patent application Ser. No. 15/715,940.
The body 12 forms a reaction chamber 24. The reaction chamber 24 provides an enclosed space for various reactions to occur. The support 20 and the receptacle 22 are positioned within the reaction chamber 24. In one embodiment, the body 12 is made of an insulating material that thermally insulates the reaction chamber 24 from an external environment.
The heater 14 is coupled to the body 12. The heater 14 heats the reaction chamber 24 and any contents within the reaction chamber 24 (e.g., the support 20, the receptacle 22, gases, substrates, wafers, or other various objects). The heating device 14 may be any type of heating device. For example, the heater 14 may be an inductive heater including, for example, a plurality of coils; a resistive heater including, for example, carbide covered resistors; etc.
The input duct 16 provides a fluidic path from an environment external to the apparatus 10 and into the reaction chamber 24. In one embodiment, as will be discussed in further detail below with respect to
The output duct 18 provides a fluidic path from the reaction chamber 24 and out to an environment external to the reaction chamber 24. In one embodiment, as will be discussed in further detail below with respect to
In one embodiment, the apparatus 10 is a horizontal flux reaction chamber. In this embodiment, as shown in
The support 20 is positioned on the receptacle 22 and in the reaction chamber 24. The support 20 provides a platform to receive and hold various objects, such as a substrate or a wafer, within the reaction chamber 24. For example, as will be discussed in further detail below with respect to
As will be discussed in further detail below with respect to
The receptacle 22 is positioned in the reaction chamber 24 and directly underlies the support 20. The support 20 rests upon the receptacle 22. The receptacle 22 collects any material that is drained through the opening 28 of the support 20. The receptacle 22 includes a base 32 and sidewalls 34. The base 32 directly underlies the opening 28 and the arms 30 of the support 20. The sidewalls 34 directly underlie the frame 26 of the support 20. In one embodiment, the sidewalls 34 are in direct physical contact with the frame 26 of the support 20.
The frame 26 physically couples the plurality of arms 30 together. As previously discussed with respect to
The opening 28 is formed in the frame 26. Stated differently, the opening 28 is surrounded and enclosed by the frame 26. The opening 28 provides a drain through which material may flow. For example, as will be discuss in further detail below with respect to
The arms 30 are physically coupled to each other by the frame 26, and are cantilevered from the frame 26. In particular, as best shown in
In one embodiment, all of the arms 30 may also have the same length. In another embodiment, the arms 30 have varying lengths. For example, in one embodiment, the arms 30 include multiple sets of arms with each set of arms having a different length. For example, as best shown in
In one embodiment, all of the arms 30 are positioned within the same plane. For example, as shown in
In one embodiment, the arms of the multiple sets of arms are positioned in an alternating fashion. For example, as best shown in
Although the first set of arms 36 and the second set of arms 38 each include four arms, each of the multiple sets of arms may include any number of arms. For example, the first set of arms 36 may include 3, 5, 6 or 8 arms.
In one embodiment, the arms 30 are spaced from each other. For example, as best shown in
In one embodiment, the arms 30 are spaced from each other by substantially equal distances along the frame 26. For example, referring to
As previously discussed, in one embodiment, the arms 30 include multiple sets of arms with each set of arms having a different length. In one embodiment, the arms of each set of arms are spaced from each other by substantially equal distances along the frame 26. For example, referring to
As previously discussed, the support disclosed in U.S. patent application Ser. No. 15/715,940 may not always properly drain the melted silicon into the receptacle. Rather, the inventors have discovered that the melted silicon may sometimes stick or cling to the support, itself, due to surface tension between the melted silicon and the support. To address this problem, in one or more embodiments, the arms 30 are configured to minimize physical contact between the arms 30 and the substrate (e.g., a silicon substrate) placed on the arms 30. By minimizing physical contact between the arms 30 and the substrate placed on the arms 30, when the substrate is melted, surface tension between the arms 30 and molten material (e.g., melted silicon) is reduced. As a result, the molten material will be less likely to stick or cling to the arms 30 and will instead flow off of the arms 30 and in to the receptacle 22.
The body portion 44 includes a first end physically coupled to the frame 26, and a second end physically coupled to the raised portion 46. In one embodiment, as best shown in
The upper surface 48 of the body portion 44 is a planar surface. In one embodiment, the upper surface 48 is substantially coplanar with an upper surface 52 of the frame 26.
The side surfaces 50 of the body portion 44 are slanted or tilted surfaces. The side surfaces 50 are slanted or tiled downward so that melted material may readily slide off of the body portion 33, through the opening 28, and in to the receptacle 22.
The raised portion 46 is physically coupled to the body portion 44. The raised portion 46 is used to support a substrate within the reaction chamber 24. The raised portion 46 includes an upper surface 54 and side surfaces 56.
The upper surface 54 of the raised portion 46 provides a planar surface for substrates to rest upon. For example, as will be discussed in further detail below with respect to
The upper surface 54 allows physical contact between the support 20 and a substrate (e.g., a silicon substrate) placed on the support 20, specifically the arms 30, to be minimized. Namely, when a substrate is placed on the upper surface 54, the substrate will physically contact the upper surface 54 but will not physically contact the remaining portions of the support 20 (e.g., the frame 26, the body portion 44 of the arms 30, and the side surfaces 56 of the raised portion 46, etc.). Thus, when the substrate is melted, surface tension between the support 20 and molten material (e.g., melted silicon) is reduced. As a result, the molten material is less likely to stick or cling to the arms 30 and will instead flow off of the arms 30 and in to the receptacle 22.
The side surfaces 56 of the raised portion 46, similar to the side surfaces 50 of the body portion 44, are slanted or tilted downward so that melted material may readily slide off of the raised portion 46, through the opening 28, and in to the receptacle 22. The raised portion 46 may include any number of side surfaces 56 (e.g., one, three, four, five side surfaces). For example, in the embodiment shown in
The raised portion 46 lifts or raises the substrate placed on its upper surface 54 to be above the body portion 44 and/or the frame 26. For example, as shown in
The support 20 may be made from a wide variety of materials. For example, the support 20 may be made of graphite, iron, copper, aluminium, nickel etc. In one embodiment, the support 20 is made of a material having a high melting temperature such that the support 20 does not melt when the heater 14 is on. In one embodiment, the support 20 has a melting temperature that is greater than a melting temperature of a substrate intended to be melted in the reaction chamber 24.
In one embodiment, the support 20, including the frame 26 and the arms 30, are a single contiguous piece. For example, the support 20 may be formed from a single piece of material.
The support 20 may be fabricated using various fabrication techniques. For example, the support 20 may be fabricated by stamping a flat sheet of material using a forming press.
As shown in
Once the silicon substrate 58 is positioned on the support 20, the reaction chamber 24 is sealed and heated by the heater 14 to a first temperature. In one embodiment, the first temperature is between 450 and 550 degrees Celsius. The reaction chamber 24 is also set to have a first pressure level. In one embodiment, the first pressure level is between 8E-5 and 12E-5 bar.
Subsequent to the reaction chamber 24 being heated to the first temperature, the reaction chamber 24 is heated by the heater 14 to a second temperature that is greater than the first temperature. In one embodiment, the second temperature is between 1050 to 1150 degrees Celsius. The reaction chamber 24 is also set to have a second pressure level that is greater than the first pressure level. In one embodiment, the second pressure level is between 75-125 mbar.
The reaction chamber 24 is maintained at the second pressure level for the remainder of the process.
Subsequent to the reaction chamber 24 being heated to the second temperature, the silicon substrate 58 is immersed in hydrogen (H2). The H2 is introduced into reaction chamber 24 through the input duct 16. In addition, the silicon substrate 58 is subjected to activation operations by introducing hydrogen chloride (HCl) into the reaction chamber 24 through the input duct 16.
The reaction chamber 10 is then heated by the heater 14 to a third temperature that is greater than the second temperature. In one embodiment, the third temperature is between 1340 and 1400 degrees Celsius.
While or subsequent to the reaction chamber 24 being heated to the third temperature, a carbon precursor is introduced into the reaction chamber 24 through the input duct 16. The carbon precursor carbonizes the superficial silicon atoms of the silicon substrate 26 to form a thin layer (e.g., in the order of a few nanometers) of SiC, such as 3C SiC. This is often referred to as ramp carbonization. As will be discussed below, the thin layer of SiC acts as a seed for SiC growth.
Once the reaction chamber 24 is at the third temperature, a silicon precursor is added to the carbon precursor in the reaction chamber 24. By introducing the silicon precursor into the reaction chamber 24, a layer of a second material begins to grow. In particular, a first SiC layer 60 begins to epitaxially grow from the thin layer of SiC as shown in
While maintaining a flow of H2 into the reaction chamber 24 through the input duct 16, a melting process is performed. In particular, the reaction chamber 24 is heated by the heater 14 to a fourth temperature. The fourth temperature is greater than a melting temperature of the silicon substrate 58 and less than a melting temperature of the first SiC layer 60. In one embodiment, the fourth temperature is between 1550 to 1650 degrees Celsius. As a result, as shown in
As previously discussed, the upper surface 54 allows physical contact between the support 20 and a substrate placed on the support 20 to be minimized. In this case, as the silicon substrate 58 is placed upon the upper surface 54 of the raised portion 46 of the arms 30, the silicon substrate 58 will physically contact the upper surface 54 but will not physically contact the remaining portions of the support 20 (e.g., the frame 26, the body portion 44 of the arms 30, and the side surfaces 56 of the raised portion 46, etc.). Thus, when the silicon substrate 58 is melted, surface tension between the support 20 and the melted silicon material 66 is reduced. As a result, the melted silicon material 66 is less likely to stick or cling to the arms 30 and will instead flow off of the arms 30 and in to the receptacle 22.
Further, as previously discussed, the body portion 44 and the raised portions 46 of the arms 30 have side surfaces 50 and side surfaces 56, respectively, that are slanted or tilted downward. As a result, the melted silicon material 66 may easily slide off of the arms 30, through the opening 28, and in to the receptacle 22.
In one embodiment, the fourth temperature of the reaction chamber 24 is maintained until all of the silicon substrate 58 is removed from the first SiC layer 60.
In one embodiment, the fourth temperature of the reaction chamber 24 is maintained until the silicon substrate 58 is substantially melted and separated from the first SiC layer 60. For example, as shown in
As shown in
When the second SiC layer 68 reaches a desired thickness, the flow of silicon and carbon precursor is stopped. Further, any reaction gases in the reaction chamber 24 are removed from the reaction chamber 24 through the output duct 18.
As previously discussed, in one embodiment, the fourth temperature of the reaction chamber 24 is maintained until all of the silicon substrate 58 is removed from the first SiC layer 60. In this embodiment, after the second SiC layer 68 reaches a desired thickness, the reaction chamber 10 is shut down, vented, and returned to a lower temperature (e.g., room temperature). In one embodiment, the resulting SiC wafer 72 is subsequently immersed in H2 or Ar.
As previously discussed, in one embodiment, the fourth temperature of the reaction chamber 24 is maintained until the silicon substrate 58 is substantially melted and separated from the first SiC layer 60. In this embodiment, after the second SiC layer 68 reaches a desired thickness, the residual portions 70 of the silicon substrate 58 is removed by a subsequent etching process. As shown in
It is noted that it is possible to remove the residual portions 70 of the silicon substrate 58 by a subsequent etching process because the raised portion 46 of the arms 30 lifts or raises the first SiC layer 60, the second SiC layer 68, and the residual portions 70 to be above the body portion 44 and/or the frame 26. By raising the first SiC layer 60, the second SiC layer 68, and the residual portions 70, the etching gas is able to flow to contact the residual portions 70, which are positioned below the first SiC layer 60.
Although the apparatus 10 has been largely discussed with respect to fabricating a SiC wafer, the apparatus 10 may be used for any process in which a first layer of material is melted and separated from a second layer of material.
The various embodiments provide an apparatus and method for fabricating a wafer, such as a SiC wafer. The apparatus includes a support having a plurality of arms for supporting a substrate, such as a silicon substrate. The arms are configured to minimize physical contact between the support and the substrate. As a result, when the substrate is melted, surface tension between the arms and molten material is reduced, and the molten material will be less likely to stick or cling to the support.
The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
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| Number | Date | Country | |
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| Number | Date | Country | |
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| Parent | 16182050 | Nov 2018 | US |
| Child | 17695400 | US |
