JP4070305B2 - Method for forming silicon carbide crystal film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a silicon carbide (SiC) crystal, and more particularly to a method capable of forming a large-diameter crystal.
[0002]
[Prior art]
Silicon carbide, which is a wide gap semiconductor, has attracted attention as a semiconductor material for environmental devices and power devices. However, it is very difficult to form a silicon carbide single crystal, and it is particularly difficult to form a large-diameter crystal.
[0003]
FIG. 5 shows a conventional silicon carbide single crystal growth apparatus. In the figure, 1 is a high-frequency coil, 2 is a quartz tube, 3 is a graphite crucible, 4 is silicon carbide powder, 5 is a seed crystal made of a silicon carbide single crystal, and 6 is a grown silicon carbide crystal.
[0004]
In the growth, a graphite crucible 3 having silicon carbide powder 4 and a seed crystal 5 placed thereon is placed in the quartz tube 2, and the inside of the quartz tube 2 is heated by high frequency induction heating by the high frequency coil 1. The inside of the quartz tube 2 is preliminarily set to a high vacuum and then replaced with argon gas, and set to a pressure suitable for growth.
[0005]
As an example, the temperature of the silicon carbide powder 4 side of the graphite crucible 3 is set to 2100 ° C. to 2400 ° C., a temperature gradient is applied so that the seed crystal 5 side is lower than this, and the total pressure in the quartz tube 2 is reduced from several Torr to several tens of Torr. When kept, the sublimated silicon carbide powder 4 is deposited on the seed crystal 5, and a silicon carbide single crystal 6 is obtained at a growth rate of 0.5 to 1.5 mm / h. This is a so-called sublimation method.
[0006]
[Problems to be solved by the invention]
However, the conventional sublimation method has a problem that the size of the single crystal 6 grown on the seed crystal plane is slightly larger than that of the seed crystal 5 and the crystal diameter does not increase. On the other hand, since the seed crystal 5 is a single crystal formed by a sublimation method or the like, it is impossible to obtain a large-diameter seed crystal, and it is impossible to increase the diameter of the single crystal obtained from this point. There was a problem.
[0007]
An object of the present invention is to provide a method for forming a silicon carbide crystal film that solves the above problems and is capable of producing a large-diameter crystal.
[0008]
[Means for Solving the Problems]
Substitution according invention in claim 1, on a substrate, a first step of forming a first film containing a compound of the replaceable metal element and silicon and carbon, the metal element constituting the compound with carbon A second step of reacting to form a silicon carbide crystal; a third step of exposing the silicon carbide crystal on the substrate; and a first step of growing a silicon carbide crystal film using the exposed silicon carbide crystal as a seed crystal. 4 and step, characterized in that it comprises a.
According to a second aspect of the present invention, there is provided a fifth step of forming a second film containing a compound of carbon and a metal element replaceable with silicon on the substrate, and replacing the metal element constituting the compound with silicon. A sixth step of reacting to form a silicon carbide crystal; a seventh step of exposing the silicon carbide crystal on the substrate; and a step of growing a silicon carbide crystal film using the exposed silicon carbide crystal as a seed crystal. And 8 steps.
According to a third aspect of the invention, a ninth step of forming a thin film of a metal element replaceable with silicon is formed on a substrate, and a third film containing a compound with carbon is formed by supplying carbon to the thin film. A tenth step, an eleventh step in which the metal element constituting the compound is substituted with silicon to form a silicon carbide crystal, and the silicon carbide crystal film is alternately repeated a plurality of times in the tenth and eleventh steps. A twelfth step of increasing the thickness; and a thirteenth step of exposing the silicon carbide crystal on the substrate.
According to a fourth aspect of the present invention, in the formation method according to the first aspect, the first film is formed by forming a thin film of the metal element on the upper surface of a silicon substrate, or the metal element is formed on the upper surface of a predetermined substrate. The thin film and the silicon thin film are formed in a predetermined order, and then heat-treated.
According to a fifth aspect of the present invention, in the forming method according to the first aspect, the first film is formed by a sputtering method using a solid solution of the metal element and the silicon as a target.
The invention according to claim 6 is the formation method according to claim 2, wherein the second film is heat-treated after forming the metal element thin film on the upper surface of the graphite substrate, or the upper surface of the predetermined substrate. And forming a thin film of the metal element by supplying carbon while heating.
The invention according to claim 7 is the formation method according to claim 2, wherein the second film is formed by sputtering using the solid solution of the metal element and the carbon as a target.
The invention according to claim 8 is the formation method according to any one of claims 1 to 7, wherein the metal element is any one of titanium, chromium, manganese, iron, cobalt, nickel, molybdenum, or tungsten. It is characterized by being.
According to a ninth aspect of the present invention, in the forming method according to the third aspect, instead of the tenth, eleventh and twelfth steps, silicon and carbon are simultaneously supplied onto the substrate under a predetermined temperature condition. The fourteenth step of forming a silicon carbide crystal is used.
According to a tenth aspect of the present invention, in the formation method according to the third aspect, instead of the tenth, eleventh and twelfth steps, an organic silicon compound is supplied onto a substrate under a predetermined temperature condition to form silicon. A fifteenth step of forming a carbide crystal is used, and the metal element according to claim 8, gold, or aluminum is used as the metal element.
The invention according to claim 11 is the forming method according to any one of claims 1 to 3, wherein the step of exposing the silicon carbide crystal removes the remaining film or metal element by etching. It is characterized by being a treatment or a treatment of washing and removing with an acid.
According to a twelfth aspect of the present invention, in the formation method according to any one of the first to second aspects, the step of exposing the silicon carbide crystal includes forming a silicon film on the metal element deposited on the surface. It is characterized in that it is a process of forming and heating to dissolve the metal element in the silicon film and then removing the silicon film.
According to a thirteenth aspect of the present invention, in the forming method according to any one of the first to third aspects, the step of forming the film includes impurities that are N-type or P-type with respect to the silicon carbide crystal. It includes a step of solid solution.
The invention according to claim 14 is the formation method according to any one of claims 1 to 3, wherein the silicon carbide crystal has a crystal structure of 6H or 4H.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
FIG. 1 is a process explanatory diagram of a first embodiment of a method for forming a silicon carbide crystal film. First, a silicon single crystal substrate or a silicon substrate 11 having an epitaxial growth film formed on the surface thereof is prepared ((a) of FIG. 1). Then, after the surface of the silicon substrate 11 is sufficiently cleaned and necessary processing is performed to reduce defects, a metal thin film 12 made of iron is applied to the surface by a PVD (Physical Vapor) such as vacuum deposition or sputtering. A stacked layer is formed by Deposition) or CVD (Chemical Vapor Deposition) ((b) of FIG. 1).
[0024]
Next, heat treatment is performed under conditions (for example, about 1200 ° C.) in which silicon and iron react at the interface between the silicon substrate 11 and the metal thin film 12 to form a compound of both. Here, it is not necessary for all iron of the metal thin film 12 to react with silicon, and a solid solution layer 13 of a compound of silicon and iron may be formed at least at the interface ((c) of FIG. 1).
[0025]
Next, the metal thin film 12 containing unreacted iron is removed by etching to expose the solid solution layer 13 formed on the upper surface of the silicon substrate 11 ((d) in FIG. 1).
[0026]
Next, a heat treatment (for example, a CVD method at about 1150 ° C.) is performed on the exposed solid solution layer 13 while supplying carbon atoms generated by thermal decomposition or plasma decomposition of a gas containing carbon (methane, butane, etc.). Then, iron constituting a part of the solid solution layer 13 undergoes a substitution reaction with carbon supplied from the atmosphere, and a silicon carbide crystal 14 is formed ((e) of FIG. 1). Here, the silicon carbide crystal 14 is not necessarily formed on the entire surface of the substrate 11.
[0027]
Next, the silicon carbide crystal 14 is exposed by removing the iron precipitated by the formation of the solid solution layer 13 and the silicon carbide crystal 14 that have not reacted with carbon ((f) in FIG. 1). For this removal treatment, a normal etching solution can be used for the solid solution layer 13. Iron can be removed with an acid. Further, the removal of iron may be performed by forming a silicon film on the entire surface where the iron is deposited, heating the solid solution in the silicon film by heat treatment, and then removing the silicon film. it can.
[0028]
Next, the silicon carbide crystal 14 exposed on the silicon substrate 11 is used as a seed crystal, and heat treatment (CVD method) is performed while introducing a hydrocarbon such as butane and a silane-based gas diluted with hydrogen. As a result, the silicon carbide single crystal film 15 is epitaxially grown on the entire surface of the silicon substrate 11 ((g) in FIG. 1).
[0029]
As described above, according to this embodiment, since the silicon carbide crystal film 15 is formed on the entire upper surface of the silicon substrate 11, the silicon carbide single crystal film 15 having a large diameter corresponding to the size of the substrate 11 can be easily obtained. Can be formed.
[0030]
The formation conditions of the above-described silicon carbide single crystal film 15 vary depending on the crystal structure of the seed crystal, but the seed is formed under the condition that a 6H (hexagonal crystal) type single crystal {0001} plane having a hexagonal close-packed structure is mainly formed. By growing the silicon carbide crystal 14 which is a crystal and then forming the silicon carbide single crystal film 15, it is possible to form a 6H type single crystal with high probability. In addition, for example, there is a report that the probability that a 4H-type crystal grows by controlling the degree of supersaturation among the growth conditions of silicon carbide. By appropriately setting the growth conditions, silicon having a desired crystal structure is reported. A carbide single crystal film 15 can be obtained.
[0031]
In particular, since the 6H type and 4H type single crystals have few crystal defects and the growth rate in the direction parallel to the substrate is faster than the film thickness direction, the silicon carbide single crystal film 15 covering the substrate can be easily obtained. There is an advantage that you can. In addition, when a device such as a Schottky barrier diode is formed on a 6H-type or 4H-type single crystal, it is confirmed that the breakdown voltage is about 10 times larger than that of silicon, and that it has high capability as a power device. Therefore, obtaining a 6H-type or 4H-type single crystal has a great advantage.
[0032]
In the case where iron remains in the growing silicon carbide single crystal film 15 and a defect occurs, a P-type or N-type impurity (phosphorus) is formed after the formation of the iron metal thin film 12 (FIG. 1B). , Arsenic, boron, etc.) are dissolved in the metal thin film 2 and the process after (c) in FIG. 1 is performed, a silicon carbide single crystal film of a desired conductivity type is obtained, and the remaining iron The concentration can be reduced by three orders of magnitude or more compared to the P-type or N-type impurity concentration, and the adverse effect can be mitigated.
[0033]
As described above, iron has been described as an example of the element constituting the metal thin film 12, but it is not limited to iron, and any element that can be substituted with a carbon element may be used. For example, any of titanium, chromium, molybdenum, manganese, cobalt, nickel, or tungsten can be substituted with a carbon element in the same manner as iron described above to obtain a silicon carbide single crystal film.
[0034]
The solid solution layer 13 of iron and silicon may be formed by sputtering using a target in which iron and silicon are in solid solution. According to this, the process of forming the metal thin film 12 (FIG. 1B) and the process of forming the solid solution layer 13 (FIG. 1C) can be omitted, and a substrate other than silicon can be used.
[0035]
[Second Embodiment]
FIG. 2 is a process explanatory diagram of a second embodiment of a method for forming a silicon carbide crystal film. In this embodiment, aluminum nitride (AlN) or aluminum oxide (Al ₂ O ₃ ) having a crystal structure, lattice constant, and thermal expansion coefficient close to those of silicon carbide is prepared as the substrate 21 ((( a)). Then, a silicon thin film 22 is formed on the surface of the substrate 21 by PVD or CVD to a thickness of about 200 angstroms or slightly less (FIG. 2 (b)). Lamination is performed ((c) of FIG. 2).
[0036]
Next, heat treatment is performed under conditions (for example, about 1200 ° C.) in which silicon and iron react at the interface between the silicon thin film 22 and the metal thin film 23 to form a compound of both. Again, it is not necessary for all the iron of the metal thin film 23 to react with silicon, and it is sufficient that a solid solution layer 24 of a compound of silicon and iron is formed at least at the interface, but all of the solid solution is shown in FIG. The case where it is the layer 24 is shown.
[0037]
Next, if a metal thin film 23 containing unreacted iron remains, this is removed by etching or the like to expose the solid solution layer 24, and then a gas containing carbon (methane, butane, etc.) is formed on the upper surface thereof. Heat treatment (CVD method) at about 1150 ° C. while supplying carbon atoms generated by thermal decomposition or plasma decomposition, and the iron constituting the solid solution layer 24 undergoes a substitution reaction with the carbon supplied from the atmosphere, A silicon carbide crystal 25 is formed ((e) of FIG. 2). At this time, the silicon carbide crystal 25 reflects the crystal structure of the aluminum nitride or aluminum oxide of the substrate and grows as a hexagonal crystal. Again, the silicon carbide crystal 25 is not necessarily formed on the entire surface of the substrate 21.
[0038]
Next, the iron precipitated by the formation of the solid solution layer 24 and the silicon carbide crystal 25 that did not react with carbon is removed to expose the silicon carbide crystal 25 ((f) in FIG. 2). At this time, the removal of the solid solution layer 24 and iron uses the same technique as that described in FIG.
[0039]
Next, using the silicon carbide crystal 25 exposed on the substrate 21 as a seed crystal, a heat treatment is performed while introducing a hydrocarbon such as butane and a silane-based gas diluted with hydrogen (CVD method). The silicon carbide single crystal film 26 is epitaxially grown on the whole ((g) of FIG. 2).
[0040]
It is to be noted that the countermeasure processing when iron remains in the growing silicon carbide single crystal film 25 or a defect can be used, or that a metal other than iron can be used is the same as described in FIG. In this embodiment, the stacking order of the metal thin film 23 and the silicon thin film 22 may be reversed. Furthermore, the solid solution layer 24 of iron and silicon formed on the substrate 21 may be formed by a sputtering method using a target in which iron and silicon are dissolved.
[0041]
[Third Embodiment]
FIG. 3 is a process explanatory diagram of a third embodiment of a method for forming a silicon carbide crystal film. Here, a graphite substrate 31 is prepared ((a) of FIG. 3). After the surface of the graphite substrate 31 is sufficiently cleaned and necessary treatments are performed to reduce defects, a metal thin film 32 made of iron is applied to the surface by PVD or CVD, about 500 angstroms or more. A few layers are formed (FIG. 3B).
[0042]
Next, heat treatment is performed under conditions (for example, about 1500 ° C.) in which graphite and iron react at the interface between the graphite substrate 31 and the metal thin film 32 to form a compound of both. Here, it is not necessary for all the iron of the metal thin film 32 to react with graphite, and it is sufficient that a solid solution layer 33 of a compound of graphite and iron is formed at least at the interface, but all of the solid solution is shown in FIG. The case where the layer 33 is formed is shown.
[0043]
Next, if a metal thin film 32 containing unreacted iron remains, this is removed by etching to expose the solid solution layer 33 formed on the upper surface of the graphite substrate 31, and a gas containing silicon (such as silane) is exposed. When heat treatment (for example, a CVD method at 1500 ° C.) is performed while supplying silicon atoms generated by thermal decomposition or plasma decomposition, iron constituting the solid solution layer 33 causes a substitution reaction with silicon supplied from the atmosphere, A silicon carbide crystal 34 is formed ((d) in FIG. 1). Here, the silicon carbide crystal 34 is not necessarily formed on the entire surface of the substrate 31.
[0044]
Next, the iron precipitated by the formation of the solid solution layer 33 and the silicon carbide crystal 34 that did not react with silicon is removed to expose the silicon carbide crystal 34 ((e) in FIG. 3). At this time, the solid solution layer 33 and iron are removed by a method similar to the method described in FIG.
[0045]
Next, when the silicon carbide crystal 34 exposed on the graphite substrate 31 is used as a seed crystal and a hydrocarbon such as butane and a silane-based gas are diluted with hydrogen and introduced, a heat treatment (CVD method) is performed. A silicon carbide single crystal film 35 is epitaxially grown on the entire surface of 31 ((f) in FIG. 3).
[0046]
It is to be noted that the countermeasure processing when iron remains in the growing silicon carbide single crystal film 35 or a defect can be used, or that a metal other than iron can be used is the same as described in FIG. Further, the solid solution layer 33 of iron and graphite is formed by using aluminum nitride or aluminum oxide for the substrate as in the second embodiment, forming the metal thin film 32 on the upper surface, and then supplying carbon. The solid solution layer 33 may be formed by heat treatment, or may be formed by sputtering using a target in which iron and graphite are dissolved.
[0047]
[Fourth Embodiment]
FIG. 4 is a process explanatory diagram of a fourth embodiment of a method for forming a silicon carbide crystal film. In the present embodiment, as in the second embodiment shown in FIG. 2, aluminum nitride or aluminum oxide is prepared as the substrate 41 ((a) of FIG. 4). Then, an iron metal thin film 42 is laminated on the surface of the substrate 41 by PVD or CVD to a thickness of about 500 angstroms or slightly less (FIG. 4B).
[0048]
Next, when methane or butane is supplied while the substrate 41 is heated to about 1000 ° C. (CVD method), a solid solution layer 43 of iron and carbon is formed ((c) of FIG. 4).
[0049]
Next, when the supply of methane or butane is stopped while the substrate temperature is maintained, and silane is supplied instead, iron constituting the solid solution layer 43 undergoes a substitution reaction with silicon, and a silicon carbide thin film 44 is formed ( (D) of FIG. At this time, the silicon carbide thin film 44 grows with a hexagonal crystal reflecting the crystal structure of the aluminum nitride or aluminum oxide of the substrate.
[0050]
By repeating the process of FIG. 4C and the process of FIG. 4D a plurality of times alternately, the thickness of the silicon carbide thin film 44 is increased, and a desired film thickness can be obtained (FIG. 4). 4 (e)).
[0051]
Finally, the silicon carbide thin film 44 epitaxially grown appears on the surface by etching away the iron appearing on the outermost surface.
[0052]
In the above, instead of alternately supplying methane, butane, and silane, a gas containing silicon and a gas containing carbon may be supplied at the same time, or by supplying an organic silicon compound (for example, dimethylsilane). Even if carbon is supplied simultaneously, the silicon carbide thin film 44 can be obtained similarly.
[0053]
Further, the countermeasure processing in the case where iron remains in the growing silicon carbide thin film 44, or a metal other than iron can be used, is the same as the case described in FIG. When the silicon carbide thin film 44 is formed by supplying the organic silicon compound, gold or aluminum can be used as a usable metal element in addition to the various elements described in the case of FIG. .
[0054]
【The invention's effect】
As described above, according to the present invention, a silicon carbide single crystal film can be obtained according to the size of the substrate used, and the diameter can be easily increased. In addition, since a normal manufacturing process of a semiconductor device is followed, there is an advantage that a silicon carbide single crystal can be obtained with good controllability, good yield, and low cost. Furthermore, the obtained silicon carbide single crystal film has few crystal defects, and has an advantage of having a high capability as a power device when a device is formed.
[Brief description of the drawings]
FIG. 1 is a process diagram of a first embodiment of the present invention.
FIG. 2 is a process diagram of a second embodiment of the present invention.
FIG. 3 is a process diagram of a third embodiment of the present invention.
FIG. 4 is a process diagram of a fourth embodiment of the present invention.
FIG. 5 is an explanatory diagram of a conventional method for forming silicon carbide.
[Explanation of symbols]
1: high frequency coil, 2: quartz tube, 3: graphite crucible, 4: silicon carbide powder, 5: seed crystal, 6: silicon carbide crystal,
11: Silicon substrate, 12: Metal thin film, 13: Solid solution layer of silicon and metal, 14: Silicon carbide crystal (seed crystal), 15: Silicon carbide crystal film,
21: Aluminum nitride or aluminum oxide substrate, 22: Silicon thin film, 23: Metal thin film, 24: Solid solution layer of silicon and metal, 25: Silicon carbide crystal (seed crystal), 26: Silicon carbide crystal film,
31: Graphite substrate, 32: Metal thin film, 33: Solid solution layer of metal and graphite, 34: Silicon carbide crystal (seed crystal), 35: Silicon carbide crystal film,
41: aluminum nitride or aluminum oxide substrate, 42: metal thin film, 43: solid solution layer of carbon and metal, 44: silicon carbide crystal film.

Claims (14)

Forming a first film containing a compound of silicon and a metal element capable of substituting carbon on a substrate;
A second step in which the metal element constituting the compound is subjected to a substitution reaction with carbon to form a silicon carbide crystal;
A third step of exposing the silicon carbide crystal on the substrate;
A fourth step of growing a silicon carbide crystal film using the exposed silicon carbide crystal as a seed crystal;
A method for forming a silicon carbide crystal film, comprising: A fifth step of forming a second film containing a compound of a metal element replaceable with silicon and carbon on the substrate;
A sixth step in which the metal element constituting the compound is substituted with silicon to form a silicon carbide crystal;
A seventh step of exposing the silicon carbide crystal on the substrate;
An eighth step of growing a silicon carbide crystal film using the exposed silicon carbide crystal as a seed crystal;
A method for forming a silicon carbide crystal film, comprising: A ninth step of forming a thin film of a metal element replaceable with silicon on the substrate;
A tenth step of supplying carbon to the thin film to form a third film containing a compound with carbon;
An eleventh step of replacing the metal element constituting the compound with silicon to form a silicon carbide crystal;
A twelfth step in which the tenth and eleventh steps are alternately repeated a plurality of times to increase the thickness of the silicon carbide crystal;
A thirteenth step of exposing the silicon carbide crystal on the substrate;
A method for forming a silicon carbide crystal film, comprising: The first element is formed by forming the metal element thin film on the upper surface of the silicon substrate, or forming the metal element thin film and the silicon thin film in a predetermined order on the upper surface of the predetermined substrate, followed by heat treatment. The forming method according to claim 1, wherein the forming method is performed as follows. The formation method according to claim 1, wherein the first film is formed by a sputtering method using the solid solution of the metal element and the silicon as a target. The second film is heat-treated after forming the metal element thin film on the upper surface of the graphite substrate, or carbon is supplied while heating after forming the metal element thin film on the upper surface of the predetermined substrate. The forming method according to claim 2, wherein the forming method is performed. The formation method according to claim 2, wherein the second film is formed by sputtering using the solid solution of the metal element and the carbon as a target. The metal element is titanium, chromium, manganese, iron, cobalt, nickel, molybdenum, or forming method according to any one of claims 1 to 7, characterized in that any one of tungsten. The 14th step of forming silicon carbide crystals by simultaneously supplying silicon and carbon on a substrate under a predetermined temperature condition is used instead of the 10th, 11th and 12th steps. Item 4. The forming method according to Item 3. Instead of the tenth, eleventh and twelfth steps, the fifteenth step of supplying an organosilicon compound on a substrate under a predetermined temperature condition to form a silicon carbide crystal is used, and the metal element is claimed. The formation method according to claim 3, wherein any one of the metal elements according to item 8, gold, or aluminum is used. Said step of exposing the silicon carbide crystals, residual the membrane, or a metal element, the process of removing by etching, or any one of claims 1 to 3, wherein the processing der Rukoto removed by washing with an acid forming method according to one. The step of exposing the silicon carbide crystal forms a silicon film on the metal element deposited on the surface and heats to dissolve the metal element in the silicon film, and then removes the silicon film forming method according to any one of claims 1 to 2 as a processing der characterized Rukoto to. 4. The formation according to any one of claims 1 to 3, wherein the step of forming the film includes a step of dissolving an N-type or P-type impurity in the silicon carbide crystal. Method. Forming method according to any one of claims 1 to 3, wherein the silicon carbide crystal is a crystal structure of the 6H or 4H.

Images