Patent Application
20120015499
The present invention relates to a method for manufacturing a semiconductor substrate, in particular, a method for manufacturing a semiconductor substrate including a portion made of silicon carbide (SiC) having a single-crystal structure.
In recent years, SiC substrates have been adopted as semiconductor substrates for use in manufacturing semiconductor devices. SiC has a band gap larger than that of Si (silicon), which has been used more commonly. Hence, a semiconductor device employing a SiC substrate advantageously has a large reverse breakdown voltage, low on-resistance, or has properties less likely to decrease in a high temperature environment.
In order to efficiently manufacture such semiconductor devices, the substrates need to be large in size to some extent. According to U.S. Pat. No. 7,314,520 (Patent Document 1), a SiC substrate of 76 mm (3 inches) or greater can be manufactured.
Industrially, the size of a SiC substrate is still limited to approximately 100 mm (4 inches). Accordingly, semiconductor devices cannot be efficiently manufactured using large substrates, disadvantageously. This disadvantage becomes particularly serious in the case of using a property of a plane other than the (0001) plane in SiC of hexagonal system. Hereinafter, this will be described.
A SiC substrate small in defect is usually manufactured by slicing a SiC ingot obtained by growth in the (0001) plane, which is less likely to cause stacking fault. Hence, a SiC substrate having a plane orientation other than the (0001) plane is obtained by slicing the ingot not in parallel with its grown surface. This makes it difficult to sufficiently secure the size of the substrate, or many portions in the ingot cannot be used effectively. For this reason, it is particularly difficult to effectively manufacture a semiconductor device that employs a plane other than the (0001) plane of SiC.
Instead of increasing the size of such a SiC substrate with difficulty, it is considered to use a semiconductor substrate having a supporting portion and a plurality of small SiC substrates disposed thereon. The size of this semiconductor substrate can be increased by increasing the number of SiC substrates as required.
However, in this semiconductor substrate, gaps are formed between adjacent SiC substrates. In the gaps, foreign matters are likely to be accumulated during a process of manufacturing a semiconductor device using the semiconductor substrate. An exemplary foreign matter is: a cleaning liquid or polishing agent used in the process of manufacturing a semiconductor device; or dust in the atmosphere. Such foreign matters result in decreased manufacturing yield, which leads to decreased efficiency of manufacturing semiconductor devices, disadvantageously.
The present invention is made in view of the foregoing problems and its object is to provide a method for manufacturing a large semiconductor substrate allowing for manufacturing of semiconductor devices with a high yield.
A method according to the present invention for manufacturing a semiconductor substrate includes the following steps.
First, there is prepared a combined substrate having a supporting portion, a first silicon carbide substrate having a single-crystal structure, and a second silicon carbide substrate having a single-crystal structure. The first silicon carbide substrate has a first backside surface connected to the supporting portion, a first front-side surface opposite to the first backside surface, and a first side surface connecting the first backside surface and the first front-side surface. The second silicon carbide substrate has a second backside surface connected to the supporting portion, a second front-side surface opposite to the second backside surface, and a second side surface connecting the second backside surface and the second front-side surface. The second side surface is disposed such that a gap having an opening between the first and second front-side surfaces is formed between the first side surface and the second side surface. Then, a closing layer is formed to close the gap over the opening. The closing layer includes at least a silicon layer. Then, the silicon layer is carbonized to form a cover made of silicon carbide and closing the gap over the opening. Then, a connecting portion for connecting the first and second side surfaces is formed so as to close the opening by depositing a sublimate from the first and second side surfaces onto the cover. The cover is removed after the step of forming the connecting portion.
According to this manufacturing method, the opening of the gap between the first and second silicon carbide substrates is closed. Hence, upon manufacturing a semiconductor device using the semiconductor substrate, foreign matters are not accumulated in the gap. This prevents yield from being decreased by the foreign matters, thus obtaining a semiconductor substrate allowing for manufacturing of semiconductor devices with a high yield.
Further, the cover on which the sublimate is deposited to close the opening is made of silicon carbide. Namely, the cover and the first and second silicon carbide substrates are all made of silicon carbide. Accordingly, the cover can be provided with a crystal structure close to that of each of the first and second silicon carbide substrates. Hence, the connecting portion formed on the cover can be also provided with a crystal structure close to that of each of the first and second single-crystal substrates. As a result, the crystal structure of each of the first and second silicon carbide substrates and the crystal structure of the connecting portion are close to each other. Accordingly, the connecting portion provides firm connection between the first and second silicon carbide substrates.
Further, the cover made of silicon carbide is formed using the silicon layer, which can be readily formed as compared with formation of a silicon carbide layer. Accordingly, the semiconductor substrate can be manufactured more readily as compared with a case of directly forming a cover made of silicon carbide.
In the above-described method for manufacturing the semiconductor substrate, preferably, the step of carbonizing the silicon layer includes the step of supplying the silicon layer with a gas containing carbon element. Accordingly, the cover made of silicon carbide can be readily formed.
In the above-described method for manufacturing the semiconductor substrate, preferably, the step of forming the closing layer includes the step of providing a carbon layer. The step of carbonizing the silicon layer includes the step of chemically combining silicon contained in the silicon layer with carbon contained in the carbon layer. Accordingly, the cover made of silicon carbide can be readily formed.
In the above-described method for manufacturing the semiconductor substrate, preferably, the step of providing the carbon layer includes the step of depositing a layer made of carbon. Accordingly, the carbon layer can be formed securely.
In the above-described method for manufacturing the semiconductor substrate, preferably, the step of providing the carbon layer includes steps of: applying a fluid (
In the above-described method for manufacturing the semiconductor substrate, preferably, the fluid is a liquid containing an organic substance. Accordingly, the fluid can be applied uniformly.
In the above-described method for manufacturing the semiconductor substrate, preferably, the fluid is a suspension containing a carbon powder. Accordingly, by removing liquid component of the suspension, the fluid can be readily carbonized.
In the above-described method for manufacturing the semiconductor substrate, preferably, the supporting portion is made of silicon carbide, as with the first and second silicon carbide substrates. Accordingly, the supporting portion can be provided with properties close to those of the first and second silicon carbide substrates.
The above-described method for manufacturing the semiconductor substrate preferably further includes the step of depositing the sublimate from the supporting portion onto the connecting portion in the gap having the opening closed by the connecting portion. Accordingly, the connecting portion can be thicker.
In the method for manufacturing the semiconductor substrate, preferably, the step of depositing the sublimate from the supporting portion onto the connecting portion is performed to bring, into the supporting portion, the whole of the gap having the opening closed by the connecting portion. Accordingly, the connecting portion can be thicker.
The method for manufacturing the semiconductor substrate preferably further includes the step of polishing each of the first and second front-side surfaces. Accordingly, the first and second front-side surfaces, which serve as the surface of the semiconductor substrate, can be flat. Hence, a high-quality film can be formed on this flat surface of the semiconductor substrate.
In the method for manufacturing the semiconductor substrate, preferably, each of the first and second backside surfaces is a surface formed through slicing. Namely, each of the first and second backside surfaces is a surface formed through slicing and not polished after the slicing. Thus, undulations are provided on each of the first and second backside surfaces. Hence, a space in a recess of the undulations can be used as a space in which the sublimation gas is spread in the case where the sublimation method is employed to provide the supporting portion on the first and second backside surfaces.
In the method for manufacturing the semiconductor substrate, preferably, the step of forming the connecting portion is performed in an atmosphere having a pressure higher than 10−1 Pa and lower than 104 Pa.
As apparent from the description above, the present invention can provide a method for manufacturing a large semiconductor substrate allowing for manufacturing of semiconductor devices with a high yield.
The following describes an embodiment of the present invention with reference to figures.
Referring to
Supporting portion 30 connects the backside surfaces of SiC substrates 11-19 (surfaces opposite to the surfaces shown in
Further, supporting portion 30 is made of a material having a high heat resistance, is preferably made of a material capable of enduring a temperature of not less than 1800° C. As such a material, silicon carbide, carbon, or a refractory metal can be used, for example. An exemplary refractory metal usable is molybdenum, tantalum, tungsten, niobium, iridium, ruthenium, or zirconium. When silicon carbide is employed as the material of supporting portion 30 from among the materials exemplified above, supporting portion 30 has properties closer to those of SiC substrates 11-19.
In supported portion 10a, gaps VDa exist between SiC substrates 11-19. These gaps VDa are closed at their front-side surface sides (upper sides in
Next, a method for manufacturing semiconductor substrate 80a of the present embodiment will be described. For ease of description, only SiC substrates 11 and 12 of SiC substrates 11-19 may be explained, but the same explanation also applies to SiC substrates 13-19.
Referring to
SiC substrate group 10 includes SiC substrate 11 (first silicon carbide substrate) and SiC substrate 12 (second silicon carbide substrate). SiC substrate 11 has first backside surface B1 connected to supporting portion 30, first front-side surface F1 opposite to first backside surface B1, and a first side surface S1 connecting first backside surface B1 and first front-side surface F1. SiC substrate 12 has second backside surface B2 connected to supporting portion 30, second front-side surface F2 opposite to second backside surface B2, and a second side surface S2 connecting second backside surface B2 and second front-side surface F2. Second side surface S2 is disposed such that a gap GP having an opening CR between first and second front-side surfaces F1, F2 is formed between first side surface S1 and second side surface S2.
Referring to
Next, silicon layer 70S is heated to have a temperature equal to or higher than the melting point of silicon. This temperature is preferably 2200° C. or smaller. Further, the atmosphere includes a gas containing carbon. Thus, the gas containing carbon is supplied to silicon layer 70S. An exemplary usable gas containing carbon is propane or acetylene. As such, the gas containing carbon is supplied to silicon layer 70S having the high temperature, thereby reacting the silicon element of silicon layer 70S with the carbon element of the atmosphere.
Referring to
Next, combined substrate 80P (
Referring to
Further, referring to
Preferably, atmosphere in the processing chamber upon the formation of connecting portion BDa is obtained by reducing pressure of atmospheric air. The pressure of the atmosphere is preferably set to be higher than 10−1 Pa and lower than 104 Pa.
The atmosphere described above may be an inert gas atmosphere. An exemplary inert gas usable is a noble gas such as He or Ar; a nitrogen gas; or a mixed gas of the noble gas and nitrogen gas. When using the mixed gas, a ratio of the nitrogen gas is, for example, 60%. Further, the pressure in the processing chamber is preferably 50 kPa or smaller, and is more preferably 10 kPa or smaller.
It should be noted that an experiment was conducted to review heating temperatures. It was found that at 1600° C., connecting portion BDa was not sufficiently formed, and at 3000° C., SiC substrates 11, 12 were damaged, disadvantageously. However, these disadvantages were not found at 1800° C., 2000° C., and 2500° C.
In addition, with the heating temperature being fixed to 2000° C., pressures upon the heating were reviewed. As a result, at 100 kPa, connecting portion BDa was not formed, and at 50 kPa, connecting portion BDa was less likely to be formed, disadvantageously. However, these disadvantages were not found at 10 kPa, 100 Pa, 1 Pa, 0.1 Pa, and 0.0001 Pa.
Referring to
The following describes a comparative example (
It should be noted that as a variation of the method for forming the closing layer (
Further, as a variation of the method for forming cover 70, there may be used a method in which formation of a silicon layer and carbonization thereof is repeated a plurality of times. Accordingly, the silicon layer carbonized in one carbonizing step is small in thickness, thus achieving more secure carbonization of the silicon layer.
In addition, it is preferable to adjust the thickness of silicon layer 70S such that cover 70 will have a thickness of more than 0.1 μm and less than 1 mm. If the thickness thereof is 0.1 μm or smaller, cover 70 may be discontinuous over opening CR. On the other hand, if the thickness of cover 70 is 1 mm or greater, it takes a long time to remove cover 70.
According to the present embodiment, as shown in
Further, since opening CR (
Further, cover 70, on which the sublimates (
Further, cover 70 made of silicon carbide is formed using silicon layer 70S, which can be formed more readily as compared with formation of a silicon carbide layer. Accordingly, semiconductor substrate 80a can be manufactured more readily as compared with a case of directly forming a cover formed of silicon carbide.
Further, since cover 70 is formed of silicon carbide, cover 70 is provided with a heat resistance enough to endure a high temperature upon the formation of connecting portion BDa (
Further, cover 70 made of silicon carbide can be formed readily by carbonizing silicon layer 70S with the gas containing carbon element and supplied to silicon layer 70S.
As a method for manufacturing a semiconductor substrate in the present embodiment, a structure similar to that of
Referring to
Next, closing layer 70K is heated to have a temperature equal to or higher than the melting point of silicon. This temperature is preferably 2200° C. or smaller. Accordingly, silicon contained in silicon layer 70S and carbon contained in carbon layer 70C are chemically combined. As a result, silicon layer 70S is carbonized, thereby forming cover 70 (
According to the present embodiment, cover 70 made of silicon carbide can be formed using silicon layer 70S and carbon layer 70C.
The following describes a first variation of the method for forming carbon layer 70C.
Referring to
Now, referring to
First, the resist liquid applied (
Then, this resist layer is thermally treated to be carbonized, thereby forming carbon layer 70C (
According to the present variation, the formation of carbon layer 70C can be accomplished by the readily implementable steps such as the application of the resist liquid serving as fluid 70L, and the carbonization thereof. Furthermore, the resist liquid is a liquid and is therefore uniformly applied readily.
The following describes a second variation of the method for forming carbon layer 70C. In the present variation, instead of the resist liquid (the above-described first variation), an adhesive agent is used as fluid 70L (
The carbon adhesive agent applied is calcined at 50° C.-400° C. for 10 seconds to 12 hours. Accordingly, the carbon adhesive agent is hardened to form an adhesive layer.
Then, this adhesive layer is thermally treated to be carbonized, thereby forming carbon layer 70C. The thermal treatment is performed under conditions that the atmosphere is an inert gas or nitrogen gas with a pressure not more than the atmospheric pressure, the temperature is more than 300° C. and less than 1400° C., and the treatment time is more than one minute and less than 12 hours. If the temperature is equal to or smaller than 300° C., the carbonization is likely to be insufficient. On the other hand, if the temperature is equal to or greater than 1400° C., the front-side surfaces of SiC substrates 11 and 12 are likely to be deteriorated. Further, if the treatment time is equal to or shorter than one minute, the carbonization of the adhesive layer is likely to be insufficient. Hence, a longer treatment time is preferable. However, a sufficient treatment time is of less than 12 hours at maximum. Thereafter, steps similar to the above-described steps in the present embodiment are performed.
According to the present variation, by removing liquid component of the suspension containing carbon powders, fluid 70L can be carbonized readily. In other words, the material of carbon layer 70C is surely carbon.
It should be noted that as a variation of closing layer 70K (
Further, as a variation of the method for forming closing layer 70K (
Further, as a variation of the method for forming cover 70, there may be used a closing layer including three or more layers, instead of closing layer 70K including one silicon layer 70S and one carbon layer 70C, i.e., closing layer 70K including two layers. Accordingly, each layer in the closing layer has a small thickness, thus allowing silicon and carbon to be chemically combined with each other in the closing layer more securely.
In the present embodiment, the following fully describes a particular case where supporting portion 30 is made of silicon carbide in the method for manufacturing combined substrate 80P (
Referring to
Next, SiC substrates 11 and 12 are placed on a first heating member 81 in the processing chamber with each of backside surfaces B1 and B2 being exposed in one direction (upward in
Preferably, this arrangement is accomplished by disposing backside surfaces B1 and B2 on the same flat plane or by disposing first and second front-side surfaces F1, F2 on the same flat plane.
Further, a minimum space between SiC substrates 11 and 12 (minimum space in a lateral direction in
Next, supporting portion 30 (
First, each of backside surfaces B1 and B2 exposed in the one direction (upward in
Solid source material 20 is made of SiC, and is preferably a piece of solid matter of silicon carbide, specifically, a SiC wafer, for example. Solid source material 20 is not particularly limited in crystal structure of SiC. Further, surface SS of solid source material 20 preferably has a roughness Ra of 1 mm or smaller.
In order to provide space D1 (
Next, SiC substrates 11 and 12 are heated by first heating member 81 to a predetermined substrate temperature. On the other hand, solid source material 20 is heated by a second heating member 82 to a predetermined source material temperature. When solid source material 20 is thus heated to the source material temperature, SiC is sublimated at surface SS of the solid source material to generate a sublimate, i.e., gas. The gas thus generated is supplied onto backside surfaces B1 and B2 in the one direction (from upward in
Preferably, the substrate temperature is set to be lower than the source material temperature. More preferably, a difference between the substrate temperature and the source material temperature is set to cause a temperature gradient of not less than 0.1° C./mm and not more than 100° C./mm in a direction of thickness of each of SiC substrates 11, 12 and solid source material 20 (vertical direction in
Referring to
Referring to
Upon the formation of supporting layer 30, the atmosphere in the processing chamber is preferably obtained by reducing the pressure of the atmospheric air. The pressure of the atmosphere is preferably higher than 10−1 Pa and lower than 104 Pa.
The atmosphere described above may be an inert gas atmosphere. An exemplary inert gas usable is a noble gas such as He or Ar; a nitrogen gas; or a mixed gas of the noble gas and nitrogen gas. When using the mixed gas, a ratio of the nitrogen gas is, for example, 60%. Further, the pressure in the processing chamber is preferably 50 kPa or smaller, and is more preferably 10 kPa or smaller.
Further, supporting portion 30 preferably has a single-crystal structure. More preferably, supporting portion 30 on backside surface B1 has a crystal plane inclined by 10° or smaller relative to the crystal plane of backside surface B1, and supporting portion 30 on backside surface B2 has a crystal plane inclined by 10° relative to the crystal plane of backside surface B2. These angular relations can be readily realized by expitaxially growing supporting portion 30 on backside surfaces B1 and B2.
The crystal structure of each of SiC substrates 11, 12 is preferably of hexagonal system, and is more preferably 4H—SiC or 6H—SiC. Moreover, it is preferable that SiC substrates 11, 12 and supporting portion 30 be made of SiC single crystal having the same crystal structure.
Further, the concentration in each of SiC substrates 11 and 12 is preferably different from the impurity concentration of supporting portion 30. More preferably, supporting portion 30 has an impurity concentration higher than that of each of SiC substrates 11 and 12. It should be noted that each of SiC substrates 11, 12 has an impurity concentration of, for example, not less than 5×1016 cm−3 and not more than 5×1019 cm−3. Moreover, supporting portion 30 has an impurity concentration of, for example, not less than 5×1016 cm−3 and not more than 5×1021 cm−3. As the impurity, nitrogen or phosphorus can be used, for example.
Further, preferably, first front-side surface F1 has an off angle of 50° or greater and 65° or smaller relative to the {0001} plane of SiC substrate 11 and second front-side surface F2 has an off angle of 50° or greater and 65° or smaller relative to the {0001} plane of the SiC substrate.
More preferably, the off orientation of first front-side surface F1 forms an angle of 5° or smaller relative to the <1-100> direction of SiC substrate 11, and the off orientation of second front-side surface F2 forms an angle of 5° or smaller with the <1-100> direction of substrate 12.
Further, first front-side surface F1 preferably has an off angle of not less than −3° and not more than 5° relative to the {03-38} plane in the <1-100> direction of SiC substrate 11, and second front-side surface F2 preferably has an off angle of not less than −3° and not more than 5° relative to the {03-38} plane in the <1-100> direction of SiC substrate 12.
It should be noted that the “off angle of first front-side surface F1 relative to the {03-38} plane in the <1-100> direction” refers to an angle formed by an orthogonal projection of a normal line of first front-side surface F1 to a projection plane defined by the <1-100> direction and the <0001> direction, and a normal line of the {03-38} plane. The sign of positive value corresponds to a case where the orthogonal projection approaches in parallel with the <1-100> direction whereas the sign of negative value corresponds to a case where the orthogonal projection approaches in parallel with the <0001> direction. This is similar in the “off angle of second front-side surface F2 relative to the {03-38} plane in the <1-100> direction”.
Further, the off orientation of first front-side surface F1 forms an angle of 5° or smaller with the <11-20> direction of substrate 11. The off orientation of second front-side surface F2 forms an angle of 5° or smaller with the <11-20> direction of substrate 12.
According to the present embodiment, since supporting portion 30 formed on backside surfaces B1 and B2 is also made of SiC as with SiC substrates 11 and 12, physical properties of the SiC substrates and supporting portion 30 are close to one another. Accordingly, warpage or cracks of combined substrate 80P (
Further, utilization of the sublimation method allows supporting portion 30 to be formed fast with high quality. When the sublimation method thus utilized is a close-spaced sublimation method, supporting portion 30 can be formed more uniformly.
Further, when the average value of space D1 (
Meanwhile, in the step of forming supporting portion 30, the temperatures of SiC substrates 11 and 12 are set lower than that of solid source material 20 (
Further, the step of placing SiC substrates 11 and 12 is preferably performed to allow the minimum space between SiC substrates 11 and 12 to be 1 mm or smaller. Accordingly, supporting portion 30 can be formed to connect backside surface B1 of SiC substrate 11 and backside surface B2 of SiC substrate 12 to each other more securely.
Further, supporting portion 30 preferably has a single-crystal structure. Accordingly, supporting portion 30 has physical properties close to the physical properties of SiC substrates 11 and 12 each having a single-crystal structure.
More preferably, supporting portion 30 on backside surface B1 has a crystal plane inclined by 10° or smaller relative to that of backside surface B1. Further, supporting portion 30 on backside surface B2 has a crystal plane inclined by 10° or smaller relative to that of backside surface B2. Accordingly, supporting portion 30 has anisotropy close to that of each of SiC substrates 11 and 12.
Further, preferably, each of SiC substrates 11 and 12 has an impurity concentration different from that of supporting portion 30. Accordingly, there can be obtained semiconductor substrate 80a (
Furthermore, the impurity concentration in supporting portion 30 is preferably higher than the impurity concentration in each of SiC substrates 11 and 12. This allows the resistivity of supporting portion 30 to be smaller than those of SiC substrates 11 and 12. Accordingly, there can be obtained semiconductor substrate 80a suitable for manufacturing of a semiconductor device in which a current flows in the thickness direction of supporting portion 30, i.e., a semiconductor device of vertical type.
Meanwhile, preferably, first front-side surface F1 has an off angle of not less than 50° and not more than 65° relative to the {0001} plane of SiC substrate 11 and second front-side surface F2 has an off angle of not less than 50° and not more than 65° relative to the {0001} plane of SiC substrate 12. This achieves further improved channel mobility in each of first and second front-side surfaces F1, F2, as compared with a case where each of first and second front-side surfaces F1, F2 corresponds to the {0001} plane.
More preferably, the off orientation of first front-side surface F1 forms an angle of not more than 5° with the <1-100> direction of SiC substrate 11, and the off orientation of second front-side surface F2 forms an angle of not more than 5° with the <1-100> direction of SiC substrate 12. This achieves further improved channel mobility in each of first and second front-side surfaces F1, F2.
Further, first front-side surface F1 preferably has an off angle of not less than −3° and not more than 5° relative to the {03-38} plane in the <1-100> direction of SiC substrate 11, and second front-side surface F2 preferably has an off angle of not less than −3° and not more than 5° relative to the {03-38} plane in the <1-100> direction of SiC substrate 12. This achieves further improved channel mobility in each of first and second front-side surfaces F1, F2.
Further, preferably, the off orientation of first front-side surface F1 forms an angle of not more than 5° with the <11-20> direction of SiC substrate 11, and the off orientation of second front-side surface F2 forms an angle of not more than 5° with the <11-20> direction of SiC substrate 12. This achieves further improved channel mobility in each of first and second front-side surfaces F1, F2, as compared with a case where each of first and second front-side surfaces F1, F2 corresponds to the {0001} plane.
In the description above, the SiC wafer is exemplified as solid source material 20, but solid source material 20 is not limited to this and may be a SiC powder or a SiC sintered compact, for example.
Further, as first and second heating members 81, 82, any heating members can be used as long as they are capable of heating a target object. For example, the heating members can be of resistive heating type employing a graphite heater, or of inductive heating type.
Meanwhile, in
Referring to
Referring to
In addition, the space may be secured by combination of the respective methods shown in
Each of the above-described methods shown in
Referring to
The following describes a method for manufacturing semiconductor substrate 80b.
First, for example, by the method described in the third embodiment, combined substrate 80P (
In the present embodiment, supporting portion 30 is made of SiC, and even after each connecting portion BDa is formed as shown in
According to semiconductor substrate 80b (
Referring to
According to the present embodiment, there can be formed each connecting portion BDc thicker than each connecting portion BDb of the fourth embodiment.
It should be noted that gap VDc may be brought to reach the side of the backside surfaces (lower side in
Referring to
In the present embodiment, semiconductor substrate 80a has n type conductivity, and has supporting portion 30 and SiC substrate 11 as described in the first embodiment. Drain electrode 112 is provided on supporting portion 30 to interpose supporting portion 30 between drain electrode 112 and SiC substrate 11. Buffer layer 121 is provided on SiC substrate 11 to interpose SiC substrate 11 between buffer layer 121 and supporting portion 30.
Buffer layer 121 has n type conductivity, and has a thickness of, for example, 0.5 μm. Further, impurity with n type conductivity in buffer layer 121 has a concentration of, for example, 5×1017 cm−3.
Reverse breakdown voltage holding layer 122 is formed on buffer layer 121, and is made of silicon carbide with n type conductivity. For example, reverse breakdown voltage holding layer 122 has a thickness of 10 μm, and includes a conductive impurity of n type at a concentration of 5×1015 cm−3.
Reverse breakdown voltage holding layer 122 has a surface in which the plurality of p regions 123 of p type conductivity are formed with spaces therebetween. In each of p regions 123, an n+ region 124 is formed at the surface layer of p region 123. Further, at a location adjacent to n+ region 124, a p+ region 125 is formed. An oxide film 126 is formed to extend on n+ region 124 in one p region 123, p region 123, an exposed portion of reverse breakdown voltage holding layer 122 between the two p regions 123, the other p region 123, and n+ region 124 in the other p region 123. On oxide film 126, gate electrode 110 is formed. Further, source electrodes 111 are formed on n+ regions 124 and p+ regions 125. On source electrodes 111, upper source electrodes 127 are formed.
The maximum value of the nitrogen atom concentration is 1×1021 cm−3 or greater in a region distant away by not more than 10 nm from an interface between oxide film 126 and each of n+ regions 124, p+ regions 125, p regions 123 and reverse breakdown voltage holding layer 122, which serve as semiconductor layers. This achieves improved mobility particularly in a channel region below oxide film 126 (a contact portion of each p region 123 with oxide film 126 between each of n+ regions 124 and reverse breakdown voltage holding layer 122).
The following describes a method for manufacturing a semiconductor device 100. It should be noted that
First, in a substrate preparing step (step S110:
Referring to
First, buffer layer 121 is formed on SiC substrate 11 of semiconductor substrate 80a. Buffer layer 121 is made of silicon carbide of n type conductivity, and is an epitaxial layer having a thickness of 0.5 μm, for example. Buffer layer 121 has a conductive impurity at a concentration of, for example, 5×1017 cm−3.
Next, reverse breakdown voltage holding layer 122 is formed on buffer layer 121. Specifically, a layer made of silicon carbide of n type conductivity is formed using an epitaxial growth method. Reverse breakdown voltage holding layer 122 has a thickness of, for example, 10 μm. Further, reverse breakdown voltage holding layer 122 includes an impurity of n type conductivity at a concentration of, for example, 5×1015 cm−3.
Referring to
First, an impurity of p type conductivity is selectively implanted into portions of reverse breakdown voltage holding layer 122, thereby forming p regions 123. Then, a conductive impurity of n type is selectively implanted to predetermined regions to form n+ regions 124, and a conductive impurity of p type is selectively implanted into predetermined regions to form p+ regions 125. It should be noted that such selective implantation of the impurities is performed using a mask formed of, for example, an oxide film.
After such an implantation step, an activation annealing process is performed. For example, the annealing is performed in argon atmosphere at a heating temperature of 1700° C. for 30 minutes.
Referring to
Thereafter, a nitrogen annealing step (step S150) is performed. Specifically, annealing process is performed in nitrogen monoxide (NO) atmosphere. Conditions for this process are, for example, as follows: the heating temperature is 1100° C. and the heating time is 120 minutes. As a result, nitrogen atoms are introduced into a vicinity of the interface between oxide film 126 and each of reverse breakdown voltage holding layer 122, p regions 123, n+ regions 124, and p+ regions 125.
It should be noted that after the annealing step using nitrogen monoxide, additional annealing process may be performed using argon (Ar) gas, which is an inert gas. Conditions for this process are, for example, as follows: the heating temperature is 1100° C. and the heating time is 60 minutes.
Referring to
First, a resist film having a pattern is formed on oxide film 126, using a photolithography method. Using the resist film as a mask, portions above n+ regions 124 and p+ regions 125 in oxide film 126 are removed by etching. In this way, openings are formed in oxide film 126. Next, in each of the openings, a conductive film is formed in contact with each of n+ regions 124 and p+ regions 125. Then, the resist film is removed, thus removing the conductive film's portions located on the resist film (lift-off). This conductive film may be a metal film, for example, may be made of nickel (Ni). As a result of the lift-off, source electrodes 111 are formed.
It should be noted that on this occasion, heat treatment for alloying is preferably performed. For example, the heat treatment is performed in atmosphere of argon (Ar) gas, which is an inert gas, at a heating temperature of 950° C. for two minutes.
Referring to
It should be noted that a configuration may be employed in which conductive types are opposite to those in the present embodiment. Namely, a configuration may be employed in which p type and n type are replaced with each other.
Further, the semiconductor substrate for use in fabricating semiconductor device 100 is not limited to semiconductor substrate 80a of the first embodiment, and may be, for example, each of the semiconductor substrates obtained according to the second to fifth embodiments and their variations.
Further, the DiMOSFET of vertical type has been exemplified, but another semiconductor device may be manufactured using the semiconductor substrate of the present invention. For example, a RESURF-JFET (Reduced Surface Field-Junction Field Effect Transistor) or a Schottky diode may be manufactured.
The semiconductor substrate of the present invention is manufactured in the following method for manufacturing.
First, a combined substrate (80P) is prepared which has a supporting portion (
The semiconductor device of the present invention is fabricated using a semiconductor substrate fabricated using the following method for manufacturing.
First, a combined substrate (80P) is prepared which has a supporting portion (
The embodiments disclosed herein are illustrative and non-restrictive in any respect. The scope of the present invention is defined by the terms of the claims, rather than the embodiments described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
A method for manufacturing a semiconductor substrate in the present invention is advantageously applicable particularly to a method for manufacturing a semiconductor substrate including a portion made of silicon carbide having a single-crystal structure.
10: SiC substrate group; 10a: supported portion; 11: SiC substrate (first silicon carbide substrate); 12: SiC substrate (second silicon carbide substrate); 13-19: SiC substrate; 20, 20p: solid source material; 30, 30p: supporting portion; 70C: carbon layer; 70K: closing layer; 70L: fluid; 70S: silicon layer (closing layer); 80a-80c: semiconductor substrate; 80P: combined substrate; 81: first heating member; 82: second heating member; 100: semiconductor device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-259674 | Nov 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/066831 | 9/28/2010 | WO | 00 | 9/13/2011 |
