WO2011024854A1 - SiCエピタキシャルウェハ及びその製造方法 - Google Patents
SiCエピタキシャルウェハ及びその製造方法 Download PDFInfo
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- WO2011024854A1 WO2011024854A1 PCT/JP2010/064375 JP2010064375W WO2011024854A1 WO 2011024854 A1 WO2011024854 A1 WO 2011024854A1 JP 2010064375 W JP2010064375 W JP 2010064375W WO 2011024854 A1 WO2011024854 A1 WO 2011024854A1
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- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 167
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 154
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 19
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- 229910052710 silicon Inorganic materials 0.000 abstract description 6
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
- C30B25/18—Epitaxial-layer growth characterised by the substrate
- C30B25/20—Epitaxial-layer growth characterised by the substrate the substrate being of the same materials as the epitaxial layer
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/20—Deposition of semiconductor materials on a substrate, e.g. epitaxial growth solid phase epitaxy
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/0684—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions characterised by the shape, relative sizes or dispositions of the semiconductor regions or junctions between the regions
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/36—Carbides
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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- H01L21/02365—Forming inorganic semiconducting materials on a substrate
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02518—Deposited layers
- H01L21/02587—Structure
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02612—Formation types
- H01L21/02617—Deposition types
- H01L21/0262—Reduction or decomposition of gaseous compounds, e.g. CVD
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/16—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only elements of Group IV of the Periodic Table
- H01L29/1608—Silicon carbide
Definitions
- the present invention relates to a SiC epitaxial wafer and a manufacturing method thereof, and more particularly to a step bunching-free SiC epitaxial wafer and a manufacturing method thereof.
- SiC has many polytypes, but 4H-SiC is mainly used to fabricate practical SiC devices.
- a SiC single crystal wafer processed from a bulk crystal produced by a sublimation method or the like is used as the substrate of the SiC device, and an SiC epitaxial film that becomes an active region of the SiC device is usually formed thereon by chemical vapor deposition (CVD). Form.
- a polytype different from the polytype used for the substrate is likely to be mixed in the epitaxial film. For example, when 4H—SiC is used for the substrate, 3C—SiC or 8H—SiC is mixed.
- Epitaxial growth is generally performed by performing a step flow growth (a lateral growth from an atomic step) with a slight inclination of the SiC single crystal substrate in order to suppress these contaminations.
- the fine tilt angle (off angle) has been mainly 8 °.
- the terrace width on the wafer surface is small, and step flow growth can be easily obtained.
- an SiC substrate having an off angle of about 4 ° is mainly used for a SiC substrate of 3 inches or more from the viewpoint of cost reduction.
- the terrace width of the wafer surface is twice as large as that at an off angle of 8 °.
- step bunching refers to a phenomenon in which atomic steps (usually about 2 to 10 atomic layers) gather on the surface and coalesce, and sometimes refers to the step on the surface itself.
- Non-Patent Document 1 shows a typical step bunching.
- Non-Patent Documents 1 and 2 Conventionally, observation and evaluation of step bunching has often been performed by a combination of an optical microscope such as a differential interference microscope and an atomic force microscope (AFM) having atomic resolution (for example, Non-Patent Documents 1 and 2).
- an optical microscope such as a differential interference microscope and an atomic force microscope (AFM) having atomic resolution
- etching and supply of source gas Conventionally, when a SiC epitaxial film is formed on a SiC single crystal substrate, after mechanical polishing, chemical mechanical polishing (CMP) and gas etching are sequentially performed to perform surface treatment of the SiC single crystal substrate. Thereafter, an SiC epitaxial film was formed by chemical vapor deposition.
- CMP chemical mechanical polishing
- gas etching etching is mainly performed using hydrogen gas at a high temperature of about 1500 ° C. as a pretreatment in order to remove damage caused by the polishing process, polishing marks (scratches), and planarize the surface.
- Non-Patent Document 3 Gas etching was performed while adding propane (C 3 H 8 ) gas, which is a raw material gas for the SiC epitaxial film, to a hydrogen atmosphere (Patent Document 1, Paragraph [0002] of Patent Document 2, and Non-Patent Document). 3).
- propane (C 3 H 8 ) gas which is a raw material gas for the SiC epitaxial film
- hydrogen gas etching is essential to obtain a good epitaxial surface, but it is shown that Si droplets are generated only by hydrogen, It is said that the addition of C 3 H 8 has an effect of suppressing the generation.
- damage or scratches (scratches) due to polishing remain on the substrate surface after the gas etching, then there are different polytypes, dislocations, stacking faults, etc. in the epitaxial film formed on the substrate surface.
- gas etching is performed by adding C 3 H 8 gas or SiH 4 gas, which is a raw material gas of the SiC epitaxial film, and after the gas etching, the added gas is exhausted. Without continuing, the other gas is introduced and the SiC epitaxial film is formed (FIG. 2 of Patent Document 1 and FIG. 4 of Patent Document 2). That is, propane (C 3 H 8 ) gas or silane (SiH 4 ) gas already exists on the surface of the SiC substrate before starting the growth of the SiC epitaxial film.
- Patent Documents 1 and 2 when starting the growth of the SiC epitaxial film, the supply of the C 3 H 8 gas and the SiH 4 gas as the source gases are simultaneously performed. Did not do.
- AFM with atomic resolution (hereinafter also referred to as “normal AFM”) can directly observe the atomic arrangement on the surface, the maximum observation range is about 10 to 20 ⁇ m ⁇ , and it is difficult to measure over a wide range beyond that. .
- normal AFM AFM with atomic resolution
- step bunching on the surface of the SiC epitaxial film was recognized as being continuous from end to end of the wafer, the mechanical defects of the AFM were not particularly inconvenient when combined with an optical microscope. .
- Non-Patent Document 2 a differential interference microscope is used to observe a range of about 200 ⁇ m to 1 mm ⁇ , which is wider than AFM.
- the step height cannot be quantified, and there is a disadvantage that a step having a height of several nm cannot be detected particularly when the magnification is large.
- step bunching hinders flattening of the surface of the SiC epitaxial film, it is necessary to suppress its generation in order to improve the performance of the SiC device. Since step bunching is a step on the surface, an oxide film is formed on the surface of the SiC epitaxial film, and in the MOSFET (Metal-Oxide-Semiconductor-Field-Effect-Transistor) in which the interface is energized, its presence is considered to improve the operating performance and reliability May have a fatal effect. Therefore, research on the suppression of step bunching has been energetically performed.
- MOSFET Metal-Oxide-Semiconductor-Field-Effect-Transistor
- the active region of the SiC power device including this MOSFET is larger than the normal AFM measurement range. For this reason, in order to obtain an epitaxially grown surface capable of producing a device having excellent characteristics, evaluation with a normal AFM or differential interference microscope is not sufficient.
- C 3 H 6 gas or SiH 4 gas which is a raw material gas
- SiH 4 gas which is a raw material gas
- the other gas was introduced to perform the SiC epitaxial film forming process.
- these source gases have not been supplied to the substrate surface at the same time.
- etching may be performed using only hydrogen gas, the importance of simultaneous supply of source gas to the substrate surface has not been recognized.
- the present inventors have developed an optical surface inspection apparatus capable of observing a wider range than a differential interference microscope, using a laser beam and having a sensitivity in the height direction similar to that of an AFM, and a wide-range observation type.
- AFM broad-range observation type AFM
- the SiC epitaxial wafer which has been considered to suppress step bunching by the conventional method, is observed and evaluated, and captured by a normal AFM or differential interference microscope
- step bunching which is difficult to do, exists as a standard state of the surface.
- Step bunchings that were newly clarified were present at an average interval of about 100 ⁇ m and had a length of 100 to 500 ⁇ m in the [1-100] direction. As will be described later, this step bunching is caused by shallow pits formed by screw dislocations appearing on the growth surface and forming steps on the surface, and screw dislocations are originally formed in the epitaxially grown film. Since it is contained in the SiC single crystal substrate used as a substrate, it can be said that it originates in the substrate.
- conventionally known step bunching exists at an average interval of about 1.5 ⁇ m and has a length of 5 mm or more in the [1-100] direction (note that In the present specification, in the Miller index notation, “ ⁇ ” means a bar attached to the index immediately after that).
- ⁇ means a bar attached to the index immediately after that.
- the occurrence occurs by the following mechanism. Originally, since the surface of the SiC single crystal substrate has an off angle, the surface has corresponding atomic steps. This atomic step moves during the process of epitaxial growth or gas etching. When the movement speed varies between steps, these steps merge with each other, and conventional step bunching occurs regardless of dislocations in the substrate.
- step bunching that has been newly clarified is distinguished from conventional step bunching and is also referred to as “short step bunching”.
- FIG. 1 shows an AFM image (stereoscopic surface perspective image) of 10 ⁇ m ⁇ on the surface of an SiC epitaxial wafer observed by a normal AFM (Dimension V manufactured by Veeco Instruments).
- FIG. 1A is an AFM image showing conventional step bunching
- FIG. 1B is an AFM image showing short step bunching.
- FIG. 2 shows an AFM image of 200 ⁇ m ⁇ on the surface of the SiC epitaxial film observed by the wide-range observation type AFM (Nanoscale Hybrid Microscope VN-8000 manufactured by Keyence) used in the present invention.
- 2A is an AFM image showing conventional step bunching
- FIG. 2B is an AFM image showing short step bunching.
- FIG. 2 (a) it can be observed that the conventional step bunching exists at an average interval of about 1.5 ⁇ m as in the case of a normal AFM image.
- FIG. 2B shows that two lines (arrows B and C) are observed stably at equal intervals.
- the fact that the step can be stably observed in such a wide range of 200 ⁇ m ⁇ does not indicate mere noise or a peculiar surface area, and confirms the existence of step bunching having different properties from the conventional step bunching.
- optical surface inspection apparatus In order to confirm the presence of short step bunching with another surface inspection apparatus, observation was performed with an optical surface inspection apparatus using a laser beam (Candela CS20 manufactured by KLA-Tencor).
- This optical surface inspection apparatus is suitable for measuring the density of short step bunching because the measuring range is larger than the entire surface of a wafer of several ⁇ m ⁇ to 4 inches or more and the wide-area observation type AFM.
- the optical surface inspection apparatus used in the present invention is a method in which laser light is incident on a wafer obliquely and scattered light from the wafer surface is reflected. It has the system which detects intensity
- the surface of the wafer is spiral scanned. Since the reflection position changes so as to trace the unevenness of the wafer surface, roughness (surface roughness) can be calculated from this position information.
- a 100 ⁇ m filter is used in the calculation, and long-period waviness information on the wafer surface is removed.
- step bunching is parallel to the [1-100] direction, a step is not detected in a region where the laser beam and the scanning direction are parallel during spiral scanning. Therefore, for the calculation of roughness information, a range of 70 ° between 55 ° to 125 ° and 235 ° to 305 ° in general polar coordinates is selected. Further, since the center of the spiral scan is a singular point where the laser beam hardly moves, the position information of the reflected light in the vicinity does not reflect the roughness. Therefore, the central ⁇ 10 mm range was excluded from the calculation area. The calculation range set in this way is about 35% of the entire wafer surface. However, with respect to step bunching, the morphology in this range almost reflects the entire wafer surface. Since the roughness calculated in this way has a correlation with the roughness measured using the AFM, it can be seen that the roughness is in accordance with the actual surface morphology.
- FIG. 3 shows the observation result of the SiC epitaxial wafer in which short step bunching is observed with the optical surface inspection apparatus, using a differential interference microscope. As shown by the arrows, a noticeable shallow pit and accompanying short step bunching can be confirmed. The depth of the shallow pits on the epilayer surface was 6.3 nm.
- FIG. 4 shows an observation result by a differential interference microscope after performing KOH etching to confirm the origin of the shallow pit.
- the presence of screw dislocations and the accompanying short step bunching can be confirmed. From this, it can be inferred that the short step bunching occurred as a result of step follow growth being hindered by the step of the shallow pit generated on the surface.
- the origin of the short step bunching is the shallow pit caused by the screw dislocation in the epi layer inherited from the substrate.
- the present inventors have observed this short step bunching on the surface by observing and evaluating the surface of the SiC epitaxial film by combining an optical surface inspection device and a surface inspection device different from the conventional one called a wide-range observation type AFM. It was found that it exists as a standard state, not a unique state. As a result of intensive studies, the present inventors have clarified the origin of short step bunching and suppressed the occurrence of the step bunching, thereby reaching a method for manufacturing a step bunching-free SiC epitaxial wafer.
- the present inventor considers the importance of simultaneously supplying SiH 4 gas and C 3 H 8 gas in amounts necessary for epitaxial growth of silicon carbide on the surface of the SiC single crystal substrate in the formation of the SiC epitaxial film. I found it.
- the present invention has been made in view of the above circumstances, and an object thereof is to provide a step bunching-free SiC epitaxial wafer having no step bunching on the entire surface of the wafer and a method for manufacturing the same.
- the inventors of the present invention differed from the origin of conventional step bunching and started by discovering step bunching caused by the SiC substrate.
- Step bunching-free SiC is formed by simultaneously supplying H 8 gas to the substrate surface at a predetermined concentration ratio, performing film formation, holding the substrate temperature simultaneously until the gas is removed, and then lowering the temperature. It has been found that an epitaxial wafer can be obtained.
- Epitaxial growth is performed by performing a step flow growth (a lateral growth from an atomic step) with a slight inclination of the SiC single crystal substrate in order to suppress mixing of a polytype different from the polytype used for the substrate.
- a step flow growth a lateral growth from an atomic step
- the step end is brought out on the growth surface and the step flow growth is performed.
- the inclination angle is 0.4 ° or more.
- the present invention is effective in the case of 5 ° or less, which is a low off-angle substrate where step bunching is likely to occur.
- the effect of the present invention is effective in the range of an inclination angle of 0.4 ° to 5 °.
- the inclination angle is 2 ° or more
- the terrace width on the substrate is narrow, and step flow growth is promoted to obtain a mirror surface. It is particularly effective because it is easily handled.
- the 4 ° off substrate that is generally sold has a standard tilt angle range of 3.5 ° to 4.5 °, but the present invention is particularly effective for a 4 ° off substrate having this tilt angle range. It is.
- the 4 ° off substrate is inexpensive because it has less loss when it is cut out from a single crystal than the 8 ° off substrate, which is a standard product that has been used in the past, because a mirror surface is easily obtained. Therefore, by applying the technique of the present application to a 4 ° off substrate, an epitaxial wafer with good quality and low cost can be obtained.
- the present invention provides the following means.
- a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a 4H—SiC single crystal substrate tilted at an off angle of 0.4 ° to 5 °, and the above-described optical surface inspection apparatus using laser light is used.
- “optical surface inspection apparatus using laser light” refers to an apparatus that performs surface inspection based on the same principle as Candela CS20 manufactured by KLA-Tencor.
- Rq root mean square roughness
- Ry 3.0 nm or less.
- a method for producing an SiC epitaxial wafer comprising:
- “amount required for epitaxial growth of silicon carbide” means that desorption (sublimation) and adsorption (growth) of Si and C from the substrate occur simultaneously on the surface of the substrate at an elevated temperature.
- the cleaning step is performed by adding SiH 4 gas and / or C 3 H 8 gas to the hydrogen atmosphere, and the epitaxial growth step is started after exhausting the added gas.
- the method for producing an SiC epitaxial wafer according to item (5) which is characterized in that
- a step bunching-free SiC epitaxial wafer can be provided.
- (A) It is the image which observed the cross section of the conventional SiC single crystal substrate surface with the transmission electron microscope, (b) is an enlarged image of (a). It is the image which observed the SiC epitaxial wafer surface of the comparative example 2 with the optical surface test
- FIGS. 5 and 6 show a SiC epitaxial wafer according to an embodiment of the present invention in which a SiC epitaxial layer is formed on a 4H—SiC single crystal substrate tilted at an off-angle of 4 °.
- the result of observation with an optical surface inspection apparatus using laser light (Candela CS20 manufactured by KLA-Tencor) is shown.
- FIG. 5 (a) is a 200 ⁇ m ⁇ wide observation type AFM image of the surface of the SiC epitaxial wafer of the present invention.
- FIG. 5 (b) shows a 200 ⁇ m ⁇ wide-range observation type AFM image of the surface of a conventional SiC epitaxial wafer.
- step linear density 0 / mm ⁇ 1 the linear density of the step is 5 mm ⁇ 1 or less.
- the root mean square roughness Rq was 0.4 nm, and the maximum height difference Ry was 0.7 nm.
- the average Rq of three regions randomly selected from the same sample was 0.52 nm, and the average Ry was 0.75 nm. Therefore, it can be seen that the observed root mean square roughness Rq is 1.0 nm or less and the maximum height difference Ry is 3.0 nm or less.
- step bunching in which a large number of steps were combined at a linear density of 340 lines / mm ⁇ 1 was observed.
- the average step line density of the other three regions of this sample was 362 lines / mm ⁇ 1 . It can also be seen that the steps extend beyond the observation range.
- the root mean square roughness Rq was 2.4 nm
- the maximum height difference Ry was 3.6 nm.
- the average Rq of three regions randomly selected from the same sample was 3.2 nm, and the average Ry was 4.5 nm.
- FIGS. 6 (a) and 6 (b) show images (hereinafter referred to as “candela images”) observed by an optical surface inspection apparatus using laser light for the 1 mm ⁇ range of the same sample in FIGS. 5 (a) and 5 (b), respectively.
- the observed surface root mean square roughness Rq was 1.2 nm in the SiC epitaxial wafer of the present invention. Therefore, it can be seen that the thickness is 1.3 nm or less. On the other hand, it is 1.7 nm in the conventional SiC epitaxial wafer, and it can be seen that there is a clear difference in surface flatness between the present invention and the conventional SiC epitaxial wafer.
- the 4H—SiC single crystal substrate is polished until the lattice disorder layer on the surface becomes 3 nm or less.
- the “lattice disordered layer” is a TEM lattice image (image in which the lattice can be confirmed), and a striped structure corresponding to the atomic layer (lattice) of the SiC single crystal or a part of the stripe is clear. A layer that is not.
- FIGS. 7 and 8 show transmission electron microscope (TEM) images near the surface of the SiC single crystal substrate after the polishing step.
- FIG. 7A and 7B are TEM images showing examples of the SiC single crystal substrate of the present invention.
- the surface flatness disorder cannot be observed.
- the lattice image FIG. 7B
- disorder is observed only in the uppermost atomic layer (lattice), and a clear striped structure is observed from the lower atomic layer (lattice). it can.
- a layer sandwiched by arrows is a “lattice disorder layer”. From this TEM image, it can be confirmed that the “lattice disordered layer” on the surface is 3 nm or less.
- FIGS. 8A and 8B are TEM images showing an example of a SiC single crystal substrate having a lattice disorder layer of 3 nm or more on the surface.
- a clear disturbance of surface flatness is observed, and a lattice image (FIG. 8B) which is an enlarged image of a portion which appears flat in FIG. 8A.
- FIG. 5 the disturbance of the stripe structure can be observed over 6 nm from the surface.
- a “lattice disorder layer” of about 7 nm (a layer sandwiched between arrows on the right side in the image) can be observed, and it can be seen that the surface “lattice disorder layer” cannot achieve 3 nm or less in this sample. .
- the polishing process includes a plurality of polishing processes such as rough polishing, usually called lapping, precision polishing called polishing, and chemical mechanical polishing (hereinafter also referred to as CMP) which is ultra-precision polishing.
- the polishing process is often performed in a wet manner, but the common process in this process is to apply a polishing head to which a silicon carbide substrate is bonded while supplying polishing slurry to a rotating surface plate to which a polishing cloth is attached. Is to be done.
- the polishing slurry used in the present invention is basically used in such a form, but the form is not limited as long as it is wet polishing using the polishing slurry.
- the particles used as the abrasive grains may be particles that do not dissolve and disperse in this pH range.
- the pH of the polishing liquid is preferably less than 2.
- diamond, silicon carbide, aluminum oxide, titanium oxide, silicon oxide, or the like can be used as the abrasive particles.
- abrasive particles having an average diameter of 1 to 400 nm, preferably 10 to 200 nm, more preferably 10 to 150 nm are used as abrasive grains.
- silica is preferred in that small particles are commercially available at low cost. More preferred is colloidal silica.
- the particle size of an abrasive such as colloidal silica can be appropriately selected depending on processing characteristics such as processing speed and surface roughness. When a higher polishing rate is required, an abrasive having a large particle size can be used. When the surface roughness is small, that is, when a highly smooth surface is required, an abrasive having a small particle diameter can be used. Those having an average particle diameter exceeding 400 nm are expensive because they are expensive and the polishing rate is not high. When the particle diameter is extremely small such as less than 1 nm, the polishing rate is remarkably reduced.
- the addition amount of abrasive particles is 1% by mass to 30% by mass, preferably 1.5% by mass to 15% by mass. If it exceeds 30% by mass, the drying speed of the abrasive particles becomes high, which increases the risk of causing scratches, and is uneconomical. Further, if the abrasive particles are less than 1% by mass, the processing speed becomes too low, which is not preferable.
- the polishing slurry in the present invention is a water-based polishing slurry, and the pH at 20 ° C. is less than 2.0, desirably less than 1.5, and more desirably less than 1.2. In the region where the pH is 2.0 or more, a sufficient polishing rate cannot be obtained.
- the slurry less than pH 2 the chemical reactivity with respect to silicon carbide is remarkably increased even under a normal indoor environment, and ultraprecision polishing becomes possible.
- the silicon carbide is not directly removed by the mechanical action of the oxide particles in the polishing slurry, but the polishing liquid causes the silicon carbide single crystal surface to chemically react with the silicon oxide, and the silicon oxide is mechanically treated by the abrasive grains.
- polishing composition liquid so that silicon carbide can easily react, that is, setting the pH to less than 2, and selecting oxide particles having an appropriate hardness as abrasive grains can cause scratching and processing. It is very important to obtain a smooth surface without an altered layer.
- the polishing slurry is adjusted to have a pH of less than 2 using at least one acid, preferably two or more acids.
- an inorganic acid is preferable, and as the inorganic acid, hydrochloric acid, nitric acid, phosphoric acid, and sulfuric acid are preferable.
- the reason why it is effective to use a plurality of acids is unknown, but it has been confirmed by experiments, and there is a possibility that a plurality of acids interact with each other and enhance the effect.
- the amount of acid added is, for example, within the range of 0.5 to 5% by mass of sulfuric acid, 0.5 to 5% by mass of phosphoric acid, 0.5 to 5% by mass of nitric acid, and 0.5 to 5% by mass of hydrochloric acid.
- the type and amount are selected so that the pH is less than 2.
- the inorganic acid is effective because it is a stronger acid than the organic acid and is extremely convenient for adjusting to a predetermined strongly acidic polishing liquid. If an organic acid is used, it is difficult to adjust the strongly acidic polishing liquid.
- the polishing of silicon carbide is performed by removing the oxide layer with oxide particles due to the reactivity to the oxide film generated on the surface of silicon carbide by the strongly acidic polishing liquid. In order to accelerate this surface oxidation, polishing is performed.
- an oxidizing agent is added to the slurry, a further excellent effect is recognized.
- the oxidizing agent include hydrogen peroxide, perchloric acid, potassium dichromate, ammonium persulfate sulfate, and the like.
- the polishing rate is improved by adding 0.5 to 5% by mass, preferably 1.5 to 4% by mass, but the oxidizing agent is not limited to hydrogen peroxide solution. .
- an anti-gelling agent can be added to suppress gelation of the abrasive.
- phosphate ester type chelating agents such as 1-hydroxyethylidene-1,1-diphosphonic acid and aminotriethylenephosphonic acid are preferably used.
- the anti-gelling agent is added in the range of 0.01 to 6% by mass, preferably 0.05 to 2% by mass.
- the damage pressure is reduced to 50 nm by using a polishing pressure of 350 g / cm 2 or less and using abrasive grains having a diameter of 5 ⁇ m or less in mechanical polishing before CMP.
- the polishing slurry contains abrasive particles having an average particle diameter of 10 nm to 150 nm and an inorganic acid, and preferably has a pH of less than 2 at 20 ° C.
- Silica more preferably 1 to 30% by mass, and more preferably at least one of inorganic acid, hydrochloric acid, nitric acid, phosphoric acid and sulfuric acid.
- the gas etching is performed for 5 to 30 minutes with the SiC single crystal substrate held at 1400 to 1600 ° C., the hydrogen gas flow rate of 40 to 120 slm, and the pressure of 100 to 250 mbar.
- the substrate After cleaning the polished SiC single crystal substrate, the substrate is set in an epitaxial growth apparatus, for example, a mass production type multiple planetary CVD apparatus. After introducing hydrogen gas into the apparatus, the pressure is adjusted to 100 to 250 mbar. Thereafter, the temperature of the apparatus is raised, the substrate temperature is set to 1400 to 1600 ° C., preferably 1480 ° C. or higher, and gas etching of the substrate surface is performed with hydrogen gas for 1 to 30 minutes. When gas etching with hydrogen gas is performed under such conditions, the etching amount is about 0.05 to 0.4 ⁇ m.
- an epitaxial growth apparatus for example, a mass production type multiple planetary CVD apparatus.
- the pressure is adjusted to 100 to 250 mbar.
- the temperature of the apparatus is raised, the substrate temperature is set to 1400 to 1600 ° C., preferably 1480 ° C. or higher, and gas etching of the substrate surface is performed with hydrogen gas for 1 to 30 minutes.
- the etching amount is about 0.05 to 0.4
- the substrate surface is damaged by the polishing process, and it is considered that not only damage that can be detected as a “lattice disorder layer” in the TEM but also distortion of the lattice that cannot be detected by the TEM exists.
- the purpose of gas etching is to remove the layer damaged in this way (hereinafter also referred to as “damage layer”).
- the gas etching is not sufficient and the damaged layer remains, dissimilar polytypes are present in the epitaxial growth layer. Or dislocations, stacking faults, and the like are introduced, and if etching is performed too much, surface reconstruction occurs on the substrate surface, and step bunching occurs before the start of epitaxial growth. For this reason, it is important to optimize the damaged layer and the amount of gas etching.
- the present inventors have found that as a sufficient condition in the production of a step bunching-free SiC epitaxial wafer, They found a combination of the damage layer when the layer was thinned to 3 nm or less and the gas etching conditions described above.
- the root mean square roughness Rq of the outermost surface of the epitaxial layer obtained by analyzing an area of 35% or more of the entire wafer surface using an optical surface inspection apparatus is 1.3 nm or less. I can confirm that.
- the step bunching is 1.0 nm or less at 10 ⁇ m ⁇ , 1.0 nm or less at 200 ⁇ m ⁇ , and a length of 100 to 500 ⁇ m observed at 200 ⁇ m ⁇ . It can be confirmed that the maximum height difference Ry in (short step bunching) is 3.0 nm or less. It can also be confirmed that the linear density of this step is 5 mm ⁇ 1 or less. It is important to maintain the flatness of the substrate surface in the subsequent film forming process and temperature lowering process.
- SiH 4 gas and / or C 3 H 8 gas may be added to the hydrogen gas.
- SiH 4 gas having a concentration of less than 0.009 mol% is added to hydrogen gas to make the environment in the reactor Si-rich.
- the concentration ratio C / Si of the amount of SiH 4 gas and C 3 H 8 gas required for the epitaxial growth of silicon carbide is 0.7 to 0.8 on the surface of the cleaned substrate.
- silicon carbide is epitaxially grown.
- “simultaneous supply” means that supply is not required until the time is completely the same, but is supplied with a difference within several seconds.
- “simultaneous supply” means that supply is not required until the time is completely the same, but is supplied with a difference within several seconds.
- the difference in supply time between the SiH 4 gas and the C 3 H 8 gas is within 5 seconds, a step-bunching-free SiC epitaxial wafer can be manufactured. It was.
- Each flow rate, pressure, and substrate temperature of SiH 4 gas and C 3 H 8 gas are 15 to 150 sccm, 3.5 to 60 sccm, 80 to 250 mbar, and 1400 to 1600 ° C., respectively. Determine while controlling the growth rate.
- the carrier concentration in the epitaxial layer can be controlled.
- As a method for suppressing step bunching during growth in order to increase the migration of Si atoms on the growth surface, it is known to lower the concentration ratio C / Si of the source gas to be supplied. 0.7 to 1.2.
- the growth rate is about 3 to 20 ⁇ m per hour.
- the epitaxial layer to be grown usually has a film thickness of about 5 to 20 ⁇ m and a carrier concentration of about 2 to 15 ⁇ 10 15 cm ⁇ 3 .
- SiH 4 gas and C 3 H 8 gas are used as source gases
- N 2 gas is used as a doping gas
- H 2 gas or HCl gas is used as a carrier gas and an etching gas
- mass production type multiple planetary CVD is used.
- An SiC epitaxial film was grown on a Si surface inclined by 4 ° in the ⁇ 11-20> axial direction with respect to the (0001) plane of 4H—SiC crystal by Hot Wall SiC CVD manufactured by Ixtron, which is an apparatus.
- the roughness of the obtained epitaxial wafer surface was examined using an optical surface inspection apparatus (Candela CS20 manufactured by KLA-Tencor), a normal AFM, and a wide-area observation type AFM.
- the wide-area observation type AFM is an AFM having an observation region of about 200 ⁇ m ⁇ while the resolution in the vertical direction is lower than that of a normal AFM.
- Example 1 In the polishing step, mechanical polishing before CMP was performed at a processing pressure of 350 g / cm 2 using abrasive grains having a diameter of 5 ⁇ m or less. Further, CMP was performed for 30 minutes using silica particles having an average particle diameter of 10 to 150 nm as abrasive particles, a slurry containing sulfuric acid as an inorganic acid and a pH of 1.9 at 20 ° C.
- the polished substrate was introduced into the growth apparatus after RCA cleaning.
- the RCA cleaning is a wet cleaning method generally used for Si wafers, and a substrate is prepared by using a mixed solution of sulfuric acid / ammonia / hydrochloric acid and hydrogen peroxide solution and a hydrofluoric acid aqueous solution.
- the cleaning (gas etching) step was carried out at a hydrogen gas flow rate of 90 slm, a reactor pressure of 200 mbar, and a substrate temperature of 1550 ° C. for 10 minutes.
- SiH 4 gas is supplied after 3 seconds. did.
- a growth process was carried out for 2 hours at a reactor internal pressure of 200 mbar and a substrate temperature of 1550 ° C. to form a SiC epitaxial layer having a thickness of 10 ⁇ m.
- the SiC epitaxial wafer thus fabricated was measured with a wide-area observation type AFM and an optical surface inspection apparatus, as shown in FIGS. 5A and 6A, and measured with an optical surface inspection apparatus.
- the Rq measured was 1.2 nm
- the Rq measured by the wide-range observation type AFM was 0.4 nm
- the maximum height difference Ry was 0.7 nm
- no step bunching was observed.
- Example 2 A SiC epitaxial wafer was manufactured under the same conditions as in Example 1 except for the gas etching conditions.
- the gas etching process is different from that in Example 1 in that SiH 4 gas having a concentration of 0.008 mol% is added to hydrogen gas.
- the SiC epitaxial wafer thus produced was measured with an optical surface inspection apparatus and a wide-area observation type AFM.
- FIGS. 6B and 5B Images of the manufactured SiC epitaxial wafer measured by an optical surface inspection apparatus and a wide-area observation type AFM are as shown in FIGS. 6B and 5B, respectively.
- the root mean square roughness Rq measured by the optical surface inspection apparatus was 1.7 nm
- the root mean square roughness Rq measured by the wide-range observation type AFM was 2.4 nm
- the maximum height difference Ry was 3.6 nm. .
- Comparative Example 2 In the SiC epitaxial growth step, a SiC epitaxial wafer was produced under the same conditions as in Example 1 except that the C 3 H 8 gas was introduced and the SiH 4 gas was introduced 30 seconds later. Therefore, the comparison with Comparative Example 1 is that SiH 4 gas and C 3 H 8 gas are introduced at a concentration ratio C / Si of 1.1.
- FIGS. 9A and 9B show a candela image and a wide-range observation type AFM image of the manufactured SiC epitaxial wafer.
- the root mean square roughness Rq measured by the optical surface inspection apparatus was 1.4 nm
- the root mean square roughness Rq measured by the wide range observation type AFM was 1.4 nm
- the maximum height difference Ry was 2.8 nm.
- the linear density of the step was 10 pieces / mm ⁇ 1 .
- the SiC epitaxial wafer of the present invention is a step bunching-free SiC epitaxial wafer and can be used for manufacturing various silicon carbide semiconductor devices such as power devices, high-frequency devices, and high-temperature operation devices.
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Abstract
Description
本願は、2009年8月28日に、日本に出願された特願2009-198872号に基づき優先権を主張し、その内容をここに援用する。
SiC基板が2インチ程度までのサイズの場合、この微傾斜角度(オフ角)は主に8°が用いられてきた。このオフ角においてはウェハ表面のテラス幅が小さく、容易にステップフロー成長が得られる。しかし、オフ角が大きいほど、SiCインゴットから得られるウェハ枚数が少なくなる。そのため、3インチ以上のSiC基板においてはコスト削減の観点から、主に4°程度のオフ角のものが用いられている。4°程度のオフ角では、ウェハ表面のテラス幅が8°のオフ角の場合に比べて2倍になるため、ステップ端に取り込まれるマイグレーション原子の取り込まれ速度、すなわちステップ端の成長速度にバラツキが生じやすくなる。その結果、遅い成長速度を持つステップに速い成長速度を持つステップが追いついて合体し、ステップバンチングが発生する。特にエピタキシャル表面がSi面の場合、C面よりも表面原子のマイグレーションが抑えられるため、容易にステップバンチングを生じる。ここで、ステップバンチングとは、表面において原子ステップ(通常2~10原子層程度)が集まって合体する現象をいい、この表面の段差自体を指すこともある。非特許文献1に典型的なステップバンチングが示されている。
SiC単結晶基板上にSiCエピタキシャル膜を成膜する際には、従来、機械研磨を行った後、化学的機械研磨(CMP)及びガスエッチングを順に行ってSiC単結晶基板の表面処理を行った後、化学的気相成長法によりSiCエピタキシャル膜を成膜していた。ガスエッチングは、研磨工程に起因するダメージや研磨痕(スクラッチ)の除去や表面平坦化のために、前処理として1500℃程度の高温で主に水素ガスを用いてエッチングを行うものである。
しかしながら、研磨によるダメージや研磨痕(スクラッチ)が、ガスエッチング後の基板表面にも残留していると、その後、その基板表面に形成されたエピタキシャル膜中に異種ポリタイプや転位、積層欠陥などが導入されてしまうという問題があった。一方これを回避するために、ガスエッチング時間を延長してエッチング量を増加させすぎてしまうと、今度は基板表面で表面再構成が生じて、エピタキシャル成長開始前に基板表面にステップバンチングを生じさせてしまうという問題があった。
本発明者らは、高さ方向の感度がAFMと同程度であって、かつ、レーザー光を用い、微分干渉顕微鏡よりも広範囲を観察することができる光学式表面検査装置と、広範囲観察型のAFM(以下「広範囲観察型AFM」ともいう)とを組み合わせて用いて、従来の方法でステップバンチングを抑制したとされたSiCエピタキシャルウェハの観察・評価を行い、通常のAFMや微分干渉顕微鏡では捉えることが困難なステップバンチングが表面の標準的な状態として存在することを見出した。
図2(a)は従来のステップバンチングを示すAFM像であり、図2(b)は短いステップバンチングを示すAFM像である。
図3に、光学式表面検査装置で短いステップバンチングが観察されたSiCエピタキシャルウェハの微分干渉顕微鏡による観察結果を示す。矢印で示すように、顕著なシャローピットとそれに付随した短いステップバンチングを確認することができる。エピ層表面におけるシャローピットの深さは6.3nmであった。
本発明は、ステップバンチングが生じやすい低オフ角度の基板である5°以下の場合に有効である。本発明の効果は、傾斜角度0.4°~5°の範囲で有効であるが、傾斜角度2°以上の場合には基板上のテラス幅が狭く、ステップフロー成長が促進されて鏡面が得られやすいため、特に有効である。
さらに一般に販売されている4°オフの基板は、傾斜角度の規格範囲は3.5°~4.5°であるが、この傾斜角範囲を持つ4°オフ基板に対して本発明は特に有効である。4°オフ基板は、鏡面が得られやすいということで従来用いられていた規格品である8°オフ基板に比べて単結晶から切り出す場合のロスが少ないため低価格である。そのため、4°オフ基板に本出願の技術を適用することにより、品質が良好でコストの低いエピタキシャルウエハを得ることができる。
(1)0.4°~5°のオフ角で傾斜させた4H-SiC単結晶基板上にSiCのエピタキシャル層を形成したSiCエピタキシャルウェハであって、レーザー光を用いる光学式表面検査装置により前記SiCエピタキシャルウェハ層の表面を測定した場合に、前記表面の二乗平均粗さRqが1.3nm以下であることを特徴とするSiCエピタキシャルウェハ。
本発明において、「レーザー光を用いる光学式表面検査装置」とは、KLA-Tencor社製Candela CS20と同じ原理で表面検査する装置をいう。
(2)0.4°~5°のオフ角で傾斜させた4H-SiC単結晶基板上にSiCのエピタキシャル層を形成したSiCエピタキシャルウェハであって、原子間力顕微鏡により前記SiCエピタキシャルウェハ層の表面を測定した場合に、前記表面の二乗平均粗さRqが1.0nm以下であり、かつ、最大高低差Ryが3.0nm以下であることを特徴とするSiCエピタキシャルウェハ。
(3)前記ウェハのエピタキシャル層表面のステップの線密度が5mm-1以下であることを特徴とする前項(1)又は(2)のいずれかに記載のSiCエピタキシャルウェハ。
(4)前記ステップが前記SiCエピタキシャル層中のらせん転位に起因したシャローピットに連結していることを特徴とする前項(3)に記載のSiCエピタキシャルウェハ。
(5)0.4°~5°のオフ角で傾斜させた4H-SiC単結晶基板を、その表面の格子乱れ層が3nm以下となるまで研磨する工程と、水素雰囲気下で、前記研磨後の基板の表面を1400~1600℃にしてその表面を清浄化する工程と、前記清浄化後の基板の表面に、炭化珪素のエピタキシャル成長に必要とされる量のSiH4ガスとC3H8ガスとを濃度比C/Siが0.7~1.2で同時に供給して炭化珪素をエピタキシャル成長させる工程と、前記SiH4ガスとC3H8ガスの供給を同時に停止し、SiH4ガスとC3H8ガスとを排気するまで基板温度を保持し、その後降温する工程と、を備えたことを特徴とするSiCエピタキシャルウェハの製造方法。
本発明において、「炭化珪素のエピタキシャル成長に必要とされる量」とは、温度を上げた基板の表面では、基板からのSiとCの脱離(昇華)と、吸着(成長)とが同時に生じており、脱離>吸着の場合にはガスエッチング、脱離<吸着の場合には成長という形になるが、ガスエッチング(清浄化工程)の際にSiH4及び/又はC3H8を添加する場合(次項(6))にこれら原料ガスの量は少ないので、仮に原料ガスを添加していても優勢なガスエッチングが生じるだけであるので、ガスエッチング時のSiH4ガス及び/又はC3H8の供給量との差異を明確にする意で用いられている表現である。
また、本発明において、「同時に供給」とは、完全に同一時刻であることまでは要しないが、数秒以内の差で供給されることを意味する。後述する実施例で示した装置ではSiH4ガス及びC3H6ガス供給の時間差を5秒以内にすると、ステップバンチングの発生を抑制できた。同時供給がステップバンチングの発生にどのように関わるのかそのメカニズムは不明ではあるが、成膜開始初期における2種類の原料ガスの空間濃度分布に関係するものと推測される。この原料ガスの空間濃度分布は装置の形状・構成にも依存するので、許容される供給時間差の具体的な数値を述べることはできないが、当業者であれば、数秒単位の時間差でステップバンチングの発生を調べることで、本発明の同時供給が許容する時間差を見つけることができる。
(6)前記清浄化する工程を、前記水素雰囲気に、SiH4ガス及び/又はC3H8ガスを添加して行い、前記エピタキシャル成長させる工程は、前記添加したガスを排気した後に開始することを特徴とする前項(5)に記載のSiCエピタキシャルウェハの製造方法。
図5及び図6に、4°のオフ角で傾斜させた4H-SiC単結晶基板上にSiCのエピタキシャル層を成膜した、本発明の実施形態であるSiCエピタキシャルウェハを、広範囲観察型AFM及びレーザー光を用いる光学式表面検査装置(KLA-Tencor社製Candela CS20)で観察した結果を示す。
また、表面の二乗平均粗さRqは2.4nmであり、最大高低差Ryは3.6nmであった。同じサンプルでランダムに選んだ3個の領域の平均のRqは3.2nmであり、また、平均のRyは4.5nmであった。
観察した表面の二乗平均粗さRqは、本発明のSiCエピタキシャルウェハでは1.2nmであった。従って、1.3nm以下であることがわかる。
これに対して、従来のSiCエピタキシャルウェハでは1.7nmであり、本発明と従来のSiCエピタキシャルウェハの表面平坦性に明らかな差異を有することがわかる。
以下、本発明を適用した一実施形態であるSiCエピタキシャルウェハの製造方法について詳細に説明する。
研磨工程では、4H-SiC単結晶基板をその表面の格子乱れ層が3nm以下となるまで研磨する。
本明細書中で、「格子乱れ層」とは、TEMの格子像(格子が確認できる像)において、SiC単結晶の原子層(格子)に対応する縞状構造又はその縞の一部が明瞭になっていない層をいう。
図7(a)で示したTEM像において表面の平坦性の乱れは観察できない。また、その拡大像である格子像(図7(b))において、最上層の原子層(格子)だけに乱れが観察され、その下の原子層(格子)からは明瞭な縞状構造が観察できる。矢印で挟まれた層が「格子乱れ層」である。
このTEM像から、表面の「格子乱れ層」が3nm以下であることが確認できる。
図8(a)で示したTEM像において明らかな表面平坦性の乱れが観察され、また、図8(a)で平坦に見える部分でも、その拡大像である格子像(図8(b))において、表面から6nm以上にわたって縞状構造の乱れが観察できる。
このTEM像において7nm程度の「格子乱れ層」(像中の右側の矢印で挟まれた層)が観察でき、このサンプルでは表面の「格子乱れ層」が3nm以下を達成できていないことがわかる。
研磨工程は、通常ラップと呼ばれる粗研磨、ポリッシュとよばれる精密研磨、さらに超精密研磨である化学的機械研磨(以下、CMPともいう)など複数の研磨工程が含まれる。研磨工程は湿式で行われることが多いが、この工程で共通するのは、研磨布を貼付した回転する定盤に、研磨スラリーを供給しつつ、炭化珪素基板を接着した研磨ヘッドを押しあてて行われることである。本発明で用いる研磨スラリーは、基本的にはそれらの形態で用いられるが、研磨スラリーを用いる湿式研磨であれば形態は問わない。
炭化珪素の研磨は、強酸性研磨液によって炭化珪素の表面に生成した酸化膜に対する反応性により、酸化層を酸化物粒子により除去することで行われるが、この表面酸化を加速するために、研磨スラリーに酸化剤を添加すると更に優れた効果が認められる。酸化剤としては過酸化水素、過塩素酸、重クロム酸カリウム、過硫酸アンモニウムサルフェートなどが挙げられる。たとえば、過酸化水素水であれば0.5~5質量%、望ましくは1.5~4質量%加えることにより研磨速度が向上するが、酸化剤は過酸化水素水に限定されるものではない。
清浄化工程では、水素雰囲気下で、前記研磨後の基板を1400~1600℃にしてその表面を清浄化(ガスエッチング)する。
ガスエッチングは、SiC単結晶基板を1400~1600℃に保持し、水素ガスの流量を40~120slm、圧力を100~250mbarとして、5~30分間行う。
この後の成膜工程及び降温工程において、この基板表面の平坦性を維持することが重要となる。
成膜(エピタキシャル成長)工程では、前記清浄化後の基板の表面に、炭化珪素のエピタキシャル成長に必要とされる量のSiH4ガスとC3H8ガスとを濃度比C/Siが0.7~1.2で同時に供給して炭化珪素をエピタキシャル成長させる。
降温工程では、SiH4ガスとC3H8ガスの供給を同時に停止し、SiH4ガスとC3H8ガスとを排気するまで基板温度を保持し、その後降温する。
[実施例]
本実施例では、原料ガスとしてSiH4ガスおよびC3H8ガス、ドーピングガスとしてN2ガス、キャリアガスおよびエッチングガスとしてH2ガスあるいはHClガスを使用し、量産型の複数枚プラネタリー型CVD装置であるアイクストロン社製Hot Wall SiC CVDによって、4H-SiC単結晶の(0001)面に対して<11-20>軸方向へ4°傾けたSi面にSiCエピタキシャル膜を成長させた。得られたエピタキシャルウェハ表面のラフネスについて、光学式表面検査装置(KLA-Tencor社製Candela CS20)と、通常のAFM及び広範囲観察型AFMを用いて調べた。広範囲観察型AFMとは、通常のAFMに比べて縦方向の分解能が低下している一方で、200μm□程度の観察領域を持つAFMのことである。
研磨工程において、CMP前の機械研磨は直径5μm以下の砥粒を用いて、加工圧力を350g/cm2で行った。また、CMPは、研磨材粒子として平均粒子径が10~150nmのシリカ粒子を用い、無機酸として硫酸を含み、20℃におけるpHが1.9の研磨スラリーを用いて、30分間行った。
研磨後の基板をRCA洗浄後、成長装置内に導入した。尚、RCA洗浄とは、Siウェハに対して一般的に用いられている湿式洗浄方法であり、硫酸・アンモニア・塩酸と過酸化水素水を混合した溶液ならびにフッ化水素酸水溶液を用いて、基板表面の有機物や重金属、パーティクルを除去することができる。
清浄化(ガスエッチング)工程は、水素ガスの流量90slm、リアクタ内圧力を200mbar、基板温度を1550℃で、10分間行った。
SiCエピタキシャル成長工程は、SiH4ガス及びC3H8ガスの流量を48sccm、17.6sccmで基板面に同時に供給されるようにC3H8ガスを供給後、3秒後、SiH4ガスを供給した。C/Siは1.1を選択した。リアクタ内圧力を200mbar、基板温度を1550℃として2時間成長工程を実施して、厚さ10μmのSiCエピタキシャル層を成膜した。
実施例1とガスエッチングの条件を除いて同じ条件でSiCエピタキシャルウェハを製造した。ガスエッチング工程において、水素ガスに0.008mol%の濃度のSiH4ガスを添加して行った点が実施例1と異なる。
SiCエピタキシャル成長工程において、SiH4ガスとC3H8ガスとを濃度比C/Siを1.9として導入したこと、及び、C3H8ガスを導入して30秒後にSiH4ガスを導入したことを除いて、実施例1と同じ条件でSiCエピタキシャルウェハを作製した。
カンデラ像及びAFM像において、ウェハ表面全体に従来のステップバンチングが観察された。光学式表面検査装置で測定した二乗平均粗さRqは1.7nmであり、広範囲観察型AFMで測定した二乗平均粗さRqは2.4nmであり、最大高低差Ryは3.6nmであった。
SiCエピタキシャル成長工程において、C3H8ガスを導入して30秒後にSiH4ガスを導入したことを除いて、実施例1と同じ条件でSiCエピタキシャルウェハを作製した。従って、比較例1との比較では、SiH4ガスとC3H8ガスとを濃度比C/Siを1.1として導入した点が異なる。
光学式表面検査装置で測定した二乗平均粗さRqは1.4nmであり、広範囲観察型AFMで測定した二乗平均粗さRqは1.4nmであり、最大高低差Ryは2.8nmであった。ステップの線密度は10本/mm-1であった。
Claims (6)
- 0.4°~5°のオフ角で傾斜させた4H-SiC単結晶基板上にSiCのエピタキシャル層を形成したSiCエピタキシャルウェハであって、レーザー光を用いる光学式表面検査装置により前記SiCエピタキシャルウェハ層の表面を測定した場合に、前記表面の二乗平均粗さRqが1.3nm以下であることを特徴とするSiCエピタキシャルウェハ。
- 0.4°~5°のオフ角で傾斜させた4H-SiC単結晶基板上にSiCのエピタキシャル層を形成したSiCエピタキシャルウェハであって、原子間力顕微鏡により前記SiCエピタキシャルウェハ層の表面を測定した場合に、前記表面の二乗平均粗さRqが1.0nm以下であり、かつ、最大高低差Ryが3.0nm以下であることを特徴とするSiCエピタキシャルウェハ。
- 前記ウェハのエピタキシャル層表面のステップの線密度が5mm-1以下であることを特徴とする請求項1又は2のいずれかに記載のSiCエピタキシャルウェハ。
- 前記ステップが前記SiCエピタキシャル層中のらせん転位に起因したシャローピットに連結していることを特徴とする請求項3に記載のSiCエピタキシャルウェハ。
- 0.4°~5°のオフ角で傾斜させた4H-SiC単結晶基板を、その表面の格子乱れ層が3nm以下となるまで研磨する工程と、
水素雰囲気下で、前記研磨後の基板を1400~1600℃にしてその表面を清浄化する工程と、
前記清浄化後の基板の表面に、炭化珪素のエピタキシャル成長に必要とされる量のSiH4ガスとC3H8ガスとを濃度比C/Siが0.7~1.2で同時に供給して炭化珪素をエピタキシャル成長させる工程と、
前記SiH4ガスとC3H8ガスの供給を同時に停止し、SiH4ガスとC3H8ガスとを排気するまで基板温度を保持し、その後降温する工程と、を備えたことを特徴とするSiCエピタキシャルウェハの製造方法。 - 前記清浄化する工程を、前記水素雰囲気に、SiH4ガス及び/又はC3H8ガスを添加して行い、
前記エピタキシャル成長させる工程は、前記添加したガスを排気した後に開始することを特徴とする請求項5に記載のSiCエピタキシャルウェハの製造方法。
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JP4959763B2 (ja) | 2012-06-27 |
CN102576666A (zh) | 2012-07-11 |
EP2472568A4 (en) | 2017-08-02 |
CN102576666B (zh) | 2015-10-21 |
EP2472568B1 (en) | 2022-01-12 |
KR101369577B1 (ko) | 2014-03-04 |
US20140339571A1 (en) | 2014-11-20 |
US8823015B2 (en) | 2014-09-02 |
JP2011049496A (ja) | 2011-03-10 |
EP2472568A1 (en) | 2012-07-04 |
US20120146056A1 (en) | 2012-06-14 |
KR20120046282A (ko) | 2012-05-09 |
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