JP2011256096A - METHOD OF PRODUCING SiC BULK SINGLE CRYSTAL HAVING NO FACET, AND SINGLE CRYSTAL SiC SUBSTRATE HAVING HOMOGENEOUS RESISTANCE DISTRIBUTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a SiC bulk single crystal having improved characteristics for producing devices, and a single crystal SiC substrate.SOLUTION: In a method of producing a SiC bulk single crystal 2; a SiC-growing gas phase 9 is generated in a crystal-growing region 5 of a glowing crucible 3; the SiC bulk single crystal 2 having a central vertical axis 14 is grown by depositing it from the SiC-growing gas phase 9, when deposition is carried out on a boundary face 16 of the growing SiC bulk single crystal 2; the SiC-growing gas phase 9 is supplied at least partly from a SiC source material 6 residing in a store region 4 of the growing crucible 3 and contains at least one doping substance belonging to the group consisting of nitrogen, aluminum, vanadium, and boron; and the crystal-growing region 5 is demarcated into SiC surface sections and carbon surface sections, and selected so that the area ratio of SiC/C, which is obtained by subtracting a carbon surface section ratio from a SiC surface section ratio, always has a value smaller than 1.

Description

  The present invention relates to a method for producing a SiC bulk single crystal and a single crystal SiC substrate.

  Silicon carbide (SiC), a semiconductor material, is based on its outstanding physical, chemical, electrical and optical properties and is the starting material for power electronics semiconductor devices, high frequency devices and special semiconductor devices that produce light. It is used as. For such a device, a SiC substrate (= SiC wafer) having as wide a substrate diameter as possible, as high a quality as possible and a specific electrical resistance as uniform as possible is required.

  The base of the SiC substrate is an expensive SiC bulk single crystal, which is usually manufactured by physical vapor deposition, and in particular, sublimation described in, for example, Patent Literature 1 and Patent Literature 2. Produced by the law. A disk-shaped single crystal SiC substrate is cut out from such a SiC bulk single crystal, and then at least one epitaxial layer made of SiC in particular is provided on the substrate as part of device manufacture. The quality and reliability of the device depends in particular on how uniformly the local electrical resistance caused by doping material addition during sublimation growth is distributed. Lateral variations in doping substance concentration in the SiC substrate can lead to non-uniform device characteristics and can even lead to overall device failure depending on where the device is located on the SiC substrate. Since the SiC substrate is included in one of the active components of the device, for example by backside contact, defects and / or non-uniformities that occur in the SiC substrate, for example doping non-uniformity, ie variations in resistance distribution, affect the device characteristics. Effect. That is, the quality greatly depends on the quality of the grown SiC bulk single crystal and the quality of the SiC substrate obtained therefrom.

  During conventional sublimation growth, different partial regions are formed at the growth interface of the growing SiC bulk single crystal. In the central region or at least near the center, a substantially flat and smooth surface structure (= surface morphology) with a very high ratio of the step depth (or step width) to the step height of the crystal growth step occurs. This facet region is surrounded by a transition region, and the transition region is followed by an edge region with a curved and rough surface structure in which the ratio of the step depth to the step height of the crystal growth step is approximately balanced. There is. Each of the partial regions described above is also partly different with respect to the respective doping substance concentrations, and accordingly, also with respect to the respective local electric resistances. Since the edge region occupies the largest proportion of the growth interface, the growth conditions are currently selected so that the edge region has the desired doping material concentration. This leads to the result that the facet region is too heavily doped, resulting in poor quality devices and in the worst case not usable.

  The phenomenon of facet formation and the unavailability of facet regions for device manufacturing are described in, for example, the summary of Patent Document 3.

US Patent Application Publication No. 6,773,505B2 German Patent No. 19931332C2 Japanese Patent Laid-Open No. 2008-290895A

  Accordingly, it is an object of the present invention to provide a method for producing a SiC bulk single crystal and a single crystal SiC substrate that have been given improved suitability for device production.

The method for producing the SiC bulk single crystal of the present invention includes:
In the method for producing a SiC bulk single crystal (2),
a) An SiC growth vapor phase (7) is generated in the crystal growth region (5) of the growth crucible (3), and an SiC bulk single crystal (2) having a central central longitudinal axis (14) is converted into an SiC growth vapor phase (9 At this time, the deposition takes place at the growth interface (16) of the growing SiC bulk single crystal (2),
b) a group consisting of nitrogen, aluminum, vanadium and boron, wherein the SiC growth vapor phase (9) is at least partially supplied from the SiC source material (6) in the reserve region (4) of the growth crucible (3) In such a method comprising at least one doping substance belonging to
c) The crystal growth region (5) is divided by a SiC surface section and a carbon surface section, and these surface sections are the area of SiC / C obtained by dividing the SiC surface section ratio by the carbon surface section ratio. The method is characterized in that the ratio is always selected to have a value smaller than 1.
The method according to the present invention is a method in which an SiC growth vapor phase is generated in a crystal growth region of a growth crucible, and an SiC bulk single crystal having a central central longitudinal axis is grown by deposition from the SiC growth vapor phase. At this time, the deposition is performed at the growth interface of the growing SiC bulk single crystal. The SiC growth vapor phase is supplied at least in part from a SiC source material in the storage region of the growth crucible and includes at least one doping substance belonging to the group consisting of nitrogen, aluminum, vanadium and boron. The crystal growth region is delimited by the SiC surface section and the carbon surface section. These surface sections are selected such that the SiC / C area ratio obtained by dividing the SiC surface section ratio by the carbon surface section ratio always has a value less than one.

  In the present invention, the conventional inconvenient growth boundary surface trisection into facet, transition and edge regions, which leads to a non-uniform resistance distribution in the lateral direction, is substantially avoided. Instead, a sublimation growth method according to the invention produces a SiC bulk single crystal without facet regions or at least without significant facet regions. This is achieved by adjusting the growth conditions similar to the edge region or even the same growth conditions at the center around the central longitudinal axis. In particular, the growth interface of the growing SiC bulk single crystal has a step shape of a crystal growth step that is at least equivalent to that of the edge region at the center. This is especially true for the entire period of SiC bulk single crystal production. In the central part, it is also preferable to have a rough surface structure with crystal growth steps whose step height is similar to the step depth. In particular, the step depth is a maximum of five times the step height. That is, the ratio of the step depth to the step height is preferably in the range of 1 to 5 in the central portion, as in all the places near the other growth boundary surfaces. As a result, the same condition or at least a similar condition for the implantation of the doping substance is established at all points near the growth boundary surface. Therefore, in the growing SiC bulk single crystal, the uniform doping is performed at virtually any point. A substance concentration will result, resulting in a local specific electrical resistance of the same or similar magnitude at virtually every location. The resistance distribution in the lateral direction (and preferably in the axial direction) is very uniform, especially the jumping change that occurs at the lateral transition from the facet region to the edge region in a conventional SiC bulk single crystal. Does not have.

  In the method of the present invention, doping material addition to the SiC growth gas phase during the growth results in the desired doping material concentration at virtually any location in the growing SiC bulk single crystal, with the desired intrinsic electrical properties. It is adjusted to produce resistance. As described above, the facet area is not formed, so the traditional inefficient operation of separating the facet area (previously too strong) for high value device manufacturing and making the expensive substrate surface unusable Is also unnecessary.

  Furthermore, it has been found in the present invention that favorable elimination of the facet region can be achieved by excess carbon prepared in the SiC growth gas phase. It is particularly preferred that the excess carbon occurs over the entire period of SiC bulk single crystal formation and exists directly at the growth interface or immediately before the growth interface. According to the present invention, the proportion of carbon (C) that is higher than silicon (Si) in the SiC growth gas phase is realized by dividing the crystal growth region by a higher proportion of the carbon surface than the SiC surface. Here, these surfaces are to be universally understood and include not only surfaces that can be grasped by geometric outer dimensions, but also that SiC-grown vapor phases can also contact or interact. It also includes an “internal” surface that may be particularly important in the case of powdered or highly porous materials. Thus, the SiC surface section particularly comprises the interface of the preferably SiC powder source material with the crystal growth region and also the growth interface of the growing SiC bulk single crystal. . The carbon surface section, on the other hand, can in particular comprise the walls of the growth crucible, preferably made of graphite material, which laterally delimit the crystal growth region.

  Overall, the growth method of the present invention can produce SiC bulk single crystals that are substantially facet free, resulting in a substantially uniform lateral distribution of local electrical resistance. The large resistance fluctuation in the conventionally manufactured SiC bulk single crystal does not exist in the SiC bulk single crystal manufactured according to the present invention. That is, the SiC bulk single crystal manufactured according to the present invention is characterized by high quality, and can be efficiently used secondary particularly for manufacturing semiconductor devices.

In one preferred aspect, the SiC bulk single crystal has a circular cross section with a crystal diameter D perpendicular to the central longitudinal axis, and the crystal growth region is the growth region length in the direction of the central longitudinal axis. Extending over L, the growth region length L is selected to be longer than half of the crystal diameter D, in particular up to 250 mm. At this time, the excess carbon in the SiC growth vapor phase according to the present invention is caused to appear on the basis of a design policy that can be substantially derived from the geometrical viewpoint of the partial surface that delimits the crystal growth region. At this time, the SiC surface section is formed by two substantially circular boundaries, that is, by the surface of the SiC source material and the growth interface. The crystal diameter D of the growing SiC bulk single crystal may change during the growth process, particularly increase. In the axial direction, each crystal diameter D can vary, for example, by up to about 20%. The upper limit of the crystal diameter D is given by the cross-sectional area of the crucible internal space in the crystal growth region. That is, assuming a cylindrical crucible internal space, the internal space is a major geometric parameter for both the maximum cross-sectional area of the SiC bulk single crystal and the surface area of the SiC source material. Accordingly, the total area of both circular SiC interfaces is given by π × (D / 2) ² + π × (D / 2) ² = 2 × π × (D / 2) ² , where D Represents on the one hand the maximum crystal diameter and on the other hand the crucible internal space diameter. The carbon surface section is defined by the cylindrical inner wall of a growth crucible made from graphite material and calculated according to 2 × π × (D / 2) × L, where D also represents the crucible internal space diameter. L represents the growth region length of the crystal growth region. Considering the condition of the present invention that the carbon surface section is larger than the SiC surface section, the condition L> (D / 2) is obtained from both of these area calculation rules. That is, the growth region length L is adjusted to be longer than half of the (maximum) crystal diameter D. As the growth region length L increases, so does the excess carbon realized. However, the growth region length L is preferably not longer than 250 mm. Otherwise, material transportation from the SiC source material to the growth interface cannot be ensured on a sufficient scale, or cannot be ensured without significant additional costs.

  In another preferred aspect, a value less than 0.01 is selected for the SiC / C area ratio. In that case, the carbon surface section will be much larger than the SiC surface section, which will result in a particularly preferred very large excess of carbon in the SiC growth phase, with the central growth interface being particularly large and curved. Or a growth step with special characteristics. During growth, a very rich gas phase of Si is transported from the high temperature SiC source material to the crystal growth region. In order for silicon to react with carbon and grow as SiC, it is particularly desirable to use as wide a carbon-containing surface as possible, such as a graphite surface, at the wall of the crystal growth region. This can be embodied in particular by the use of a porous or powdered material having an “inner” surface that is wider than the original (geometric) outer surface. When using small particle size powders, the “inner” surface can be made several orders of magnitude wider than the outer surface in particular, so that an area ratio of SiC / C smaller than 0.01 can be easily achieved. it can.

  In another preferred aspect, the side wall of the growth crucible delimiting the crystal growth region consists of three layers, the first graphite material for the outer layer, carbon powder for the intermediate layer, and the inner layer. A second graphite material is used that is more porous than the first graphite material. Thereby, a particularly high carbon surface compartment ratio is achieved. The reason is in particular the wide “inside” surface of the inside, in particular the intermediate layer. The second graphite material of the inner layer is more porous and less dense than the first graphite material of the outer layer, but nevertheless the inner layer is mechanically stable and has a discrete carbon in the middle layer. Fix the powder to the wall. Furthermore, the inner layer, based on its porosity, allows the Si-rich gas phase to access the intermediate layer carbon powder. Carbon powder is based on its wide “inside” surface and saturates the Si-rich gas phase with carbon.

In another preferred aspect, a density lower than 60% of the theoretical maximum density of 2.3 g / cm ³ of graphite is employed for the second graphite material of the inner layer. The second graphite material employed for the inner layer, on the one hand, provides sufficient mechanical stability to fix the intermediate layer carbon powder, and on the other hand, the material from and to the intermediate layer. Provide sufficient porosity for transport.

  In another preferred aspect, particles having an average particle size of at least 90% of the intermediate layer carbon powder of at most 250 μm, preferably at most 50 μm are used. Thereby, the carbon powder of the intermediate layer has a particularly preferred small particle size. The smaller the particle size, the wider the “inside” surface of the interlayer material that is reachable for the gas phase gas rich in Si.

In another preferred aspect, the SiC source material is coated with a layer consisting of carbon powder, which is further on the opposite side of the SiC source material, in particular the theoretical maximum density of 2.3 g / cm of graphite. ³ is coated with a porous graphite material having a density lower than 60%. That is, the SiC source material is coated with a double layer made of a carbon-containing material, and the lower layer made of discrete carbon powder is fixed by a layer made of a porous graphite material disposed thereon. Such a strategy further increases the carbon surface compartment ratio.

  In another preferred aspect, between 20% and 40% excess carbon is supplied to the initially implanted SiC source material. Thus, already in the SiC source material, the carbon percentage exceeds the silicon percentage, and in particular by 20 to 40 mole%, typically only about 25 mole%, excess carbon in the SiC growth gas phase. Formation is supported.

  In another preferred aspect, the growth interface of the growing SiC bulk single crystal has a plurality of local growth steps and one growth front point that projects farthest in the direction of the central longitudinal axis. And the growth interface is also provided with a substantially curved shape in the central region around the growth front point, so that it is perpendicular to at least one of the local growth steps present in this central region An axial height difference Δh of at least 10 μm, preferably at least 100 μm, measured in the direction of the central longitudinal axis between the start point and the end point of a partial section of 1 mm in length, which is located at the growth boundary surface. Arise.

  In that case, the growth interface has a substantially uniform step shape, in particular at any location, so that the formation of the facet region is particularly effectively suppressed, and the growth to the growing SiC bulk single crystal. A substantially uniform doping material is injected.

Single crystal SiC substrate of the present invention, the single crystal SiC substrate and a main surface of the substrate (35) and the substrate thickness (t), of any first of measuring 4 mm ² square of the substrate main surface (35) The local specific electric resistance obtained with respect to the partial thickness on the basis of the substrate thickness (t) is 4 mΩcm at maximum with respect to the local specific electric resistance of an arbitrary second partial surface of a square having a width of 4 mm ^2. It is a different SiC substrate.
The single-crystal SiC substrate according to the present invention is a substrate having a substrate main surface and a substrate thickness t, and is obtained on the basis of the substrate thickness t for an arbitrary first partial surface having a width of 4 mm ² , particularly a square. The local specific electrical resistance differs by a maximum of 4 mΩcm from the local specific electrical resistance of an arbitrary second partial surface with a width of 4 mm ² , in particular square.

  In particular, the SiC substrate can have a general (= average) specific resistance value obtained with reference to the entire substrate main surface of 20 mΩcm at the maximum, for example, 15 mΩcm or 16 mΩcm. For this purpose, the SiC substrate is preferably doped with at least one doping substance, the at least one doping substance being an element belonging to the group consisting of nitrogen, aluminum, vanadium and boron.

  Overall, the SiC substrate according to the present invention is characterized by a particularly uniform distribution of local specific electrical resistance in the main area of the substrate surface, and therefore for the efficient production of particularly high-value devices with a low defect rate. Excellently suitable. In contrast, device manufacturing using conventional SiC substrates causes low yields and / or high defect rates due to the non-uniformly distributed electrical resistance of conventional SiC substrates. That is, the SiC substrate according to the present invention can be applied particularly advantageously as a substrate for manufacturing a semiconductor device, for example.

  Such a single crystal SiC substrate having a particularly low electrical resistance that is evenly distributed has not existed in the past, and is based on the SiC bulk single crystal manufactured based on the method of the present invention described here or its aspect. It can be produced for the first time, for example, by continuous disc-shaped cutting or sawing from such a SiC bulk single crystal. In particular, the main surface of the SiC substrate is substantially perpendicular to the growth direction of the SiC bulk single crystal.

  The SiC substrate according to the present invention satisfies industrial demands related to applications for manufacturing semiconductor devices. The substrate thickness of such a SiC substrate measured perpendicular to the substrate main surface is in particular in the range from about 100 μm to about 1,000 μm, preferably in the range from about 200 μm to about 500 μm, Preferably, it has a general thickness variation of 20 μm at maximum observed over the entire main surface of the substrate. Furthermore, at least one of the two main substrate surfaces facing each other preferably has a surface roughness of at most 3 nm. This SiC substrate has a certain degree of mechanical stability and is particularly self-supporting. It preferably has a substantially round disc shape, i.e. the main surface of the substrate is substantially circular. In some cases, there may be slight differences from a strictly circular shape based on at least one identification marking provided at the circumferential edge.

  In one preferred aspect, the local specific electrical resistance of any first partial surface differs from the local specific electrical resistance of any second partial surface by a maximum of 2 mΩcm. In that case, since a very uniform lateral resistance distribution is established, this SiC substrate has a requirement for manufacturing a device with a particularly low defect rate or a requirement for manufacturing a device with a particularly high value, Satisfies.

In another preferred aspect, the main substrate surface has a particularly large diameter D, which can in particular take values of at least 76.2 mm, 100 mm, 150 mm, 200 mm or 250 mm. The larger the substrate diameter, the more efficiently secondary processing of a single crystal SiC substrate, for example for the manufacture of semiconductor devices. Thereby, the manufacturing cost of the semiconductor device is reduced. Such a SiC substrate with a large diameter has the advantage that it can also be used for the production of relatively large semiconductor devices, for example having a bottom of about 1 cm ² . However, as the crystal diameter or the substrate diameter increases, it becomes difficult to embody the excess carbon intended in the production method of the present invention. The area ratio of SiC / C decreases as the crystal diameter or the substrate diameter increases. The cause is that the distance between the SiC source material and the growth interface, that is, the growth region length L of the crystal growth region should not be arbitrarily increased. In particular, this length should always be approximately the same as much as possible to ensure proper transport from the SiC source material to the growth interface, for example, regardless of the crystal diameter or substrate diameter in each case. . In that sense, the excess carbon when manufacturing a SiC bulk single crystal having a large crystal diameter is not caused by an increase in the growth area length L, but by an increase in the carbon area ratio by other methods, for example, This may be done by increasing the “internal” surface area or by additional placement. That is, in that sense, in the case of an extremely large SiC substrate that also has as uniform a resistance distribution as possible, if the above-described strategy for suppressing facet regions is implemented during the crystal growth process, a special Convenient to.

  Other structural requirements, advantages, and specific matters of the present invention will be apparent from the following description of embodiments with reference to the drawings.

It is one Example of the growth apparatus for manufacturing a SiC bulk single crystal by sublimation growth. It is sectional drawing which shows the conventional SiC bulk single crystal. It is a top view which shows the conventional SiC bulk single crystal. It is an Example of the growth apparatus for carrying out the sublimation growth of a SiC bulk single crystal provided with an additional carbon armor in a growth crucible. FIG. 5 is another example of a growth apparatus for sublimation growth of a SiC bulk single crystal with an additional carbon sheath in the growth crucible. It is the elements on larger scale of sectional drawing which shows the Example of the SiC bulk single crystal manufactured with the growth apparatus of any one of FIG.1, FIG4 and FIG.5. It is the elements on larger scale of the top view which shows the Example of the SiC bulk single crystal produced by any one growth apparatus of FIG.1, FIG4 and FIG.5. FIG. 6 is a partially enlarged view of a central portion showing an example of an SiC bulk single crystal manufactured by any one of the growth apparatuses of FIGS. 1, 4, and 5. It is sectional drawing which shows the Example of the single crystal SiC substrate manufactured from the SiC bulk volume single crystal manufactured by any one growth apparatus of FIG.1, FIG4 and FIG.5.

  In FIG. 1 to FIG. 9, the same reference numerals are used for the same parts. Each part of the embodiments described in detail below is also an invention in itself and can be a part of the subject of the invention.

  FIG. 1 shows an embodiment of a growth apparatus 1 for producing a SiC bulk single crystal 2 by sublimation growth. The growth apparatus 1 includes a growth crucible 3 including an SiC storage region 4 and a crystal growth region 5. Within the SiC reserve area 4 is a powdered SiC source material 6 which is filled into the SiC reserve area 4 of the growth crucible 3 as a prefabricated starting material, for example, before the start of the growth process.

  A seed crystal 8 is attached to the crystal growth region 5 on the inner wall of the growth crucible 3 facing the SiC storage region 4, that is, the crucible lid 7. On the seed crystal 8, the SiC bulk single crystal 2 to be grown is grown by deposition from the SiC growth vapor phase 9 formed in the crystal growth region 5. Growing SiC bulk single crystal 2 and seed crystal 8 have substantially the same diameter. When there is a difference, there is a difference of 10% at the maximum, and the seed diameter of the seed crystal 8 is correspondingly smaller than the single crystal diameter of the SiC bulk single crystal 2.

In the embodiment of FIG. 1, the growth crucible 3 including the crucible lid 7 is made of a graphite crucible material that conducts electricity and heat, for example, having a density of at least 1.75 g / cm ³ . A thermal insulation layer 10 is disposed around the periphery. The latter is made, for example, of expanded graphite insulation material, whose porosity is clearly higher than that of graphite crucible material in particular.

  The insulated growth crucible 3 is arranged inside a tubular container 11, and this tubular container is constructed as a quartz glass tube in this embodiment, and constitutes an autoclave or a reactor. In order to heat the growth crucible 3, an induction heating device is arranged around the container 11 in the form of a heating coil 12. The growth crucible 3 is heated by the heating coil 12 to a growth temperature exceeding 2,000 ° C., in particular to about 2,200 ° C. The heating coil 12 leads the current inductively to the conductive crucible wall 13 of the growth crucible 3. This current substantially flows as a circulating current in the circumferential direction inside the cylindrical or hollow cylindrical crucible wall 13 and heats the growth crucible 3 at that time. If necessary, the relative position between the heating coil 12 and the growth crucible 3 can be changed in the axial direction, ie in the direction of the central longitudinal axis 14 of the growing SiC bulk single crystal 2. In particular, this is to adjust, if necessary, change the temperature or temperature change inside the growth crucible 3. The position of the heating coil 12 that can be changed axially during the growth process is illustrated in FIG. In particular, the heating coil 12 is displaced while adjusting in accordance with the progress of the growth of the growing SiC bulk single crystal 2. This displacement is preferably carried out downward, i.e. in the direction of the SiC source material 6 and preferably by the same length as the SiC bulk single crystal 2 has grown, for example about 20 mm in total. For this purpose, the growth apparatus includes correspondingly configured management means, control means and adjustment means (details not shown).

The SiC growth vapor phase 9 in the crystal growth region 5 is supplied by the SiC source material 6. The SiC growth vapor phase 9 includes at least gas components in the form of Si, Si ₂ C, and SiC ₂ (= SiC gas species). Transport from the SiC source material 6 to the growth interface 16 of the growing SiC bulk single crystal 2 is performed along an axial temperature gradient. At the growth interface 16, an axial temperature gradient is formed, measured in particular in the direction of the central longitudinal axis 14 of at least 5 K / cm, preferably at least 10 K / cm.

  The temperature inside the growth crucible 3 decreases toward the growing SiC bulk single crystal 2. This can be achieved by various strategies. For example, axially varying heating can be performed through the division of heating coil 12 into two or more axial sub-regions (details not shown). Furthermore, in the lower area of the growth crucible 3, a stronger heating action can be generated than in the upper area of the growth crucible 3, for example by the corresponding axial positioning of the heating coil 12. Further, the heat insulating portions may be formed in different types in both axial crucible end walls. To that end, as schematically illustrated in FIG. 1, the thermal insulating layer 10 can have a greater thickness at the lower crucible end wall than at the upper crucible end wall.

  In the embodiment shown in FIG. 1, the SiC bulk single crystal 2 grows in the growth direction 18 from top to bottom, that is, from the crucible lid 7 toward the SiC storage region 4. The growth direction 18 extends parallel to the central central longitudinal axis 14. In the illustrated embodiment, the growing SiC bulk single crystal 2 is concentrically arranged inside the growth apparatus 1, so that the central central longitudinal axis 14 can be assigned to the entire growth apparatus 1.

Further, the SiC growth gas phase 9 also contains a doping substance (not shown in detail) in the drawing of FIG. 1, which is nitrogen (N ₂ ) in this embodiment. Alternative or additional doping substances are also possible, such as in particular aluminum (Al), vanadium (V) and / or boron (B). The supply of the doping substance takes place as a gas or through a correspondingly pretreated SiC source material 6. At this time, the proportion of nitrogen in the SiC growth vapor phase 9 is such that the grown SiC bulk single crystal 2 has a relatively low average (= general) specific electrical resistance of about 20 mΩcm at the maximum. The bulk single crystal 2 is adjusted so that nitrogen doping is strong.

  2 and 3 show a conventional SiC bulk single crystal 19 as a cross-sectional view and a plan view, respectively. The SiC bulk single crystal 19 has a crystal structure based on 4H modification, and its crystallographic [0001] principal axis extends parallel to the growth direction 18 in the illustrated embodiment. The central longitudinal axis 14 also extends in parallel. The SiC bulk single crystal 19 has three partial regions 20 to 22. A central facet region 20 is arranged around the central longitudinal axis 14 and is surrounded by an edge region 21, and a transition region 22 is formed between both partial regions 20 and 21. .

  The facet region 22 has a substantially flat and smooth surface structure (= surface morphology). The crystal growth step schematically depicted in FIG. 2 has a step height B measured in the growth direction 18, ie, the [0001] direction, which in stepping region 20 is It is much smaller than the step depth A measured perpendicular to the growth direction 18. That is, here, the quotient N = A / B has a very large value. The step height B is typically less than 1 μm, whereas the step depth A is typically about 100 μm.

  In contrast, the edge region 21 has a curved surface structure substantially corresponding to the temperature region, typically convex, in front of the growth interface 16. The curved surface structure leads to an approximately balanced ratio of step depth A to step height B. Here, the quotient N = A / B has a value of about 1. As a result, the surface of the edge region 21 is clearly rougher than the facet region 20. Here, the step height B and the step depth A are typically about 1 mm each.

  The doping material implantation varies greatly for crystal surfaces with different orientations, and in the facet region 20, the proportion of the plane perpendicular to the growth direction 18 (that is, the plane in the direction of step depth A) dominates. For this reason, in the facet region 20, the doping substance is injected into a crystal structure that is clearly higher than the edge region 21. As a whole, in the SiC bulk single crystal 19, the doping substance concentration and the local specific electric resistance associated therewith are unevenly distributed in the direction perpendicular to the growth direction 18. The reason why this is inconvenient is that the specific resistance of either the facet region 20 or the edge region 21 does not match the desired setting, so that the corresponding partial region can be used secondary, for example, for device manufacturing. This is because it cannot be used or only limitedly available.

  The facet region 20 is not necessarily arranged concentrically with respect to the central longitudinal axis 14. In particular, when a SiC bulk single crystal grows with a low inclination, for example 1 ° to 10 °, with respect to the crystallographic [0001] main axis, the facet region produced in that case is asymmetrical or non-concentric with respect to the central longitudinal axis 14. There is a possibility of being arranged. However, this does not cause any change with regard to the non-uniform distribution of doping concentration and specific electrical resistance.

  In order to achieve improved usability, the SiC volume crystal 2 is grown so that it has virtually no facet region 20. In order to achieve this, the growth interface 16 is also curved in the central region around the central longitudinal axis 14 where it grows in the crystal growth region 5 in particular so as to have a step shape at least similar to the edge region. Conditions are adjusted. For this purpose, excess carbon in the SiC growth vapor phase 9 appears in the region before the growth interface 16, and this is caused by the corresponding configuration of the plane separating the crystal growth region 5. These surfaces have a SiC surface section and a carbon surface section. These surface sections are dimensioned so that the SiC / C area ratio obtained by dividing the SiC surface section ratio by the carbon surface section ratio has a value that is always less than one, i.e. over the entire production time. Is done.

  In the growth apparatus 1 shown in FIG. 1, the SiC / C area ratio of less than 1 is such that the growth region length L of the crystal growth region 5 extending in the direction of the central longitudinal axis 14 is the cylindrical internal space of the growth crucible 3. This is realized by being longer than the radius (= half the inner space diameter) oriented perpendicular to the central longitudinal axis 14. In this case, the inner space diameter is in particular equal to the maximum crystal diameter of the growing SiC bulk single crystal 2 having a substantially round cross section perpendicular to the central longitudinal axis 14. As the progress of growth increases, the length of the growing SiC bulk single crystal 2 increases, so the growth region length L decreases. The above-described conditions for the area ratio of SiC / C are satisfied until the end of the growth process, that is, the minimum growth region length L that occurs in that case is also satisfied. The SiC surface section is formed by the surface of the SiC source material 6 and the growth interface 16. The carbon surface section is formed by a portion of the crucible wall 13 made of graphite crucible material that is in contact with the crystal growth region 5.

  4 and 5, respectively, have been modified to produce particularly low values for the area ratio of SiC / C, in particular less than 0.01. Each contains a structure. The growth apparatuses 23 and 24 have a configuration similar to that of the growth apparatus 1. Only the differences will be described in detail below.

In the growth apparatus 23 of FIG. 4, the crystal growth region 5 is divided laterally by a three-layer wall structure. This three-layer wall structure consists of a crucible wall 13 made of a graphite crucible material (= first graphite material) as an outer layer, a carbon powder as an intermediate layer 25, and a graphite crucible material as an inner layer 26. Is also porous, especially including a graphite fixing material (= second graphite material) having a density lower than 60% of the theoretical maximum density of graphite. This maximum density is 2.3 g / cm ³ . The carbon powder of the intermediate layer 25 is composed of relatively small powder particles. At least 90% of the powder particles have an average particle size of at most 250 μm, preferably at most 50 μm. The inner layer 26, constructed as a hollow cylinder, is mechanically stable and keeps the loose powder of the intermediate layer 25 in place with a three-layer wall structure.

  Based on the porosity of the inner layer 26 and in particular based on the small particle size of the carbon powder of the intermediate layer 25, the carbon surface section delimiting the crystal growth region 5 is dramatically increased. That is, the carbon surface compartment also includes an “internal” surface that also interacts with the SiC growth vapor phase 9 and thus contributes to the intended excess carbon. The carbon powder of the porous inner layer 26 and the intermediate layer 25 has a very wide “inside” surface of this kind, resulting in a particularly low SiC / C area ratio.

  In the growth apparatus 24 of FIG. 5, in addition to the three-layer wall structure as in the growth apparatus 23, a two-layer coating of the SiC source material 6 is also provided. Here, the SiC source material 6 is directly covered with a first source covering layer 27 made of the same carbon powder as the intermediate layer 25 having a three-layer wall structure. Furthermore, this carbon powder-containing source coating layer 27 is covered with a porous second source coating layer 28 on the side opposite to the SiC source material, which is in particular an inner layer of a three-layer wall structure. 26 is a graphite material made of a porous graphite fixing material similar to that of No. 26.

  Similarly, the second source coating layer 28 fixes the carbon powder of the first source coating layer 27. In addition, the coating of the SiC source material 6 reduces the SiC / C area ratio from a double viewpoint. First, the surface area of the carbon surface is increased by a coating made of an additional carbon material. On the other hand, at the same time, the SiC surface partition area is reduced by the coating of the SiC source material 6, at this time the two-layer carbon coating is in order to continue to ensure mass transport to the growing SiC bulk single crystal 2. The gas species sublimating from the source material 6 can pass through. In any case, the carbon coating of the SiC source material 6 additionally contributes to the formation of excess carbon in the SiC growth gas phase 9.

  Yet another optional measure useful for the formation of excess carbon in the SiC growth vapor phase 9 is to supply excess carbon to the implanted SiC source material 6 in advance, which is in particular from 20 mol% to 40 mol. It may be between mol% and typically is about 25 mol%.

  FIGS. 6 to 8 show a SiC bulk single crystal 2 manufactured according to the present invention as a cross-sectional view, a plan view, and a partially enlarged view, respectively. Unlike the conventional SiC bulk single crystal 19 shown in FIGS. 2 and 3, this bulk single crystal does not have a facet region 20. In the drawings shown in FIGS. 6 and 7, the facet region 20 that is always present in the conventional SiC bulk single crystal 19 is drawn with a broken line in order to clarify this difference. In the SiC bulk single crystal 2 manufactured according to the present invention, the growth interface 16 is not flat in the central region 29 around the central longitudinal axis 14 as in the case of the conventional SiC bulk single crystal 19 but is curved. is doing.

  Due to such a curvature, a step shape of a crystal growth step having characteristics similar to the edge region 21 is generated in the central region 29. In particular, as is apparent from FIG. 6, the step height B of the crystal growth step of the growth boundary surface 16 and the ratio of the step depth A to the step height B, ie, the quotient N = A / B, are also It is almost the same size as the region 21. The growth interface 16 has a growth front point 30 that protrudes most in the direction of the central longitudinal axis 14 and in the growth direction 18, around which a central region 29, preferably without facets, of the growth interface 16. Is arranged. Even in the central region 29 around the growth front point 30, that is, apart from the shape of the step in particular, the shape of the curved growth interface 16 is from the partially enlarged view of FIG. 6 VIII shown in FIG. it is obvious. The step shape of the central region 29 is oriented substantially perpendicular to at least one of the local growth steps in the central region 29, i.e. substantially relative to the step side that defines the step height B. In any partial section 31 of 1 mm in length, which is vertically oriented, it is measured in the direction of the central longitudinal axis 14 between the start point 32 and the end point 33 of the partial section 31 located on the growth boundary surface 16. And an axial height difference Δh of at least 10 μm, typically at least 100 μm.

  The slight curvature difference or step shape difference that may occur between the central region 29 and the edge region 21 has only secondary significance. In particular, when injecting a doping substance, this difference plays no role, which results in a very uniform distribution of the doping substance concentration and the associated electrical resistance. As described above, the SiC bulk single crystal 2 is particularly characterized by a transition of the distribution of local specific electric resistance that is substantially uniform in the lateral direction. In this embodiment, the SiC bulk single crystal 2 has n doping of nitrogen. Furthermore, this is 4H—SiC. However, other dopings and other SiC polytypes are possible in principle.

  Producing a single-crystal SiC substrate 34 that does not have facet regions and also has very favorable mechanical and electrical properties from the facetless SiC bulk single crystal 2 manufactured according to the invention Can do. A single crystal SiC substrate 34 of this kind, whose one embodiment is shown in cross-section in FIG. 9, is all continuous as a disk perpendicular to the growth direction 18 or the central longitudinal axis 14. It is obtained from the SiC bulk single crystal 2 by being cut or sawed in the axial direction. The SiC substrate 34 is large and thin. In this embodiment, the substrate main surface 35 has a large substrate diameter D of 150 mm, while the substrate thickness t is a low value of only about 500 μm.

Further, the SiC substrate 34 has a specific electric resistance distributed very uniformly like the SiC bulk single crystal 2, and the (general) average obtained with respect to the entire substrate main surface 35 and the substrate thickness t. The value is about 16 mΩcm. For any first partial surface of substrate main surface 35 with a width of 4 mm ² , the local specific electrical resistance determined with respect to the substrate thickness t is the local characteristic of any second partial surface with a width of 4 mm ^2. The electrical resistance differs by a maximum of 4 mΩcm, and in the preferred case by a maximum of 2 mΩcm. Thus, the resistance distribution is extremely uniform. In this embodiment, the SiC substrate is also n-doped like the SiC bulk single crystal 2 and is of 4H polytype.

  Because of the very uniform specific electrical resistance, the SiC substrate 34 is equally well suited everywhere for secondary processing as part of semiconductor device manufacturing. Accordingly, the yield is high and the defect rate is low.

1, 23, 24 Growth apparatus 2 SiC bulk single crystal 3 Growth crucible 4 SiC storage area 5 Crystal growth area 6 SiC source material 7 Crucible lid 8 Seed crystal 9 SiC growth gas phase 10 Thermal insulation layer 11 Tubular vessel 12 Heating coil 13 Crucible Wall, outer layer of crucible wall 14 central longitudinal axis 16 growth interface 18 growth direction 19 SiC bulk single crystal 20 facet region 21 edge region 22 transition region 25 intermediate layer of crucible wall 26 inner layer of crucible wall 27 first source Cover layer 28 Second source cover layer 29 Central region 30 Growth front point 31 Partial section 32 Partial section start point 33 Partial section end point 34 SiC substrate 35 Substrate main surface

Claims (12)

In the method for producing a SiC bulk single crystal (2),
a) An SiC growth vapor phase (7) is generated in the crystal growth region (5) of the growth crucible (3), and an SiC bulk single crystal (2) having a central central longitudinal axis (14) is converted into an SiC growth vapor phase (9 At this time, the deposition takes place at the growth interface (16) of the growing SiC bulk single crystal (2),
b) a group consisting of nitrogen, aluminum, vanadium and boron, wherein the SiC growth vapor phase (9) is at least partially supplied from the SiC source material (6) in the reserve region (4) of the growth crucible (3) In such a method comprising at least one doping substance belonging to
c) The crystal growth region (5) is divided by a SiC surface section and a carbon surface section, and these surface sections are the area of SiC / C obtained by dividing the SiC surface section ratio by the carbon surface section ratio. The method is characterized in that the ratio is always selected to have a value less than one.   The SiC bulk single crystal (2) has a circular cross section having a crystal diameter (D) perpendicular to the central longitudinal axis (14), and the crystal growth region (5) Extending over the growth region length (L) in the direction of the axis (14), the growth region length (L) being selected to be longer than half of the crystal diameter (D). Item 2. The method according to Item 1.   The method according to claim 1 or 2, wherein a value smaller than 0.01 is selected for the area ratio of SiC / C.   The side wall of the growth crucible (3) dividing the crystal growth region (5) is composed of three layers, the first graphite material for the outer layer (13) and the carbon for the intermediate layer (25). 4. A method according to any one of claims 1 to 3, wherein a second graphite material is used in which the powder is more porous than the first graphite material for the inner layer (26). 5. The method according to claim 4, wherein for the second graphite material of the inner layer (26), a density lower than 60% of the theoretical maximum density of 2.3 g / cm < ³ > of graphite is employed.   6. The method according to claim 4, wherein for the carbon powder of the intermediate layer (25), particles having an average particle size of at least 90% at most 250 μm are used. The SiC source material (6) is coated with a layer (27) of carbon powder, which is on the opposite side of the SiC source material (6) from the theoretical maximum density of 2 7. A method according to any one of the preceding claims, coated with a porous graphite material having a density of less than 60% of ³ g / cm < ³ >.   The method according to any one of the preceding claims, wherein between 20% and 40% excess carbon is provided in the SiC source material (6) initially injected.   The growth boundary surface (16) of the growing SiC bulk single crystal (2) has a plurality of local growth steps and one growth front point protruding farthest in the direction of the central longitudinal axis (14). (30), and the growth boundary surface (16) is also provided with a substantially curved shape in the central region (29) around the growth front point (30), whereby the center Between the start point and the end point of any 1 mm long subsection oriented perpendicular to at least one of the local growth steps in region (29) and located at the growth interface (16) The method according to claim 1, wherein an axial height difference (Δh) of at least 10 μm measured in the direction of the central longitudinal axis (14) occurs. In a single crystal SiC substrate having a substrate main surface (35) and a substrate thickness (t), the substrate thickness (t) for an arbitrary first partial surface of a square of 4 mm ² in width of the substrate main surface (35). The SiC substrate in which the local specific electric resistance obtained on the basis of is different from the local specific electric resistance of an arbitrary second partial surface of a square having a width of 4 mm ^{2 by} a maximum of 4 mΩcm.   The local specific electrical resistance of any of the first partial faces differs from the local specific electrical resistance of any of the second partial faces by a maximum of 2 mΩcm. SiC substrate.   The SiC substrate according to claim 10 or 11, wherein the substrate main surface (35) has a diameter (D) of at least 100 mm.

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