Method for producing an sic epitaxial layer on a first monocrystalline sic layer and device having an sic epitaxial layer on a first monocrystalline sic layer

Abstract

The invention relates to a method (100) for producing an SiC epitaxial layer on a first monocrystalline SiC layer, comprising the steps of: changing (110) a crystal lattice of the first monocrystalline SiC layer at a specific depth by implanting hydrogen; applying (120) the first monocrystalline SiC layer to a carrier substrate by means of bonding; and producing (140) an SiC epitaxial layer above the first monocrystalline SiC layer.

Description

[0001] Description

[0002] title

[0003] Method for producing a SiC epitaxial layer on a first monocrystalline SiC layer and device with a SiC epitaxial layer on a first monocrystalline SiC layer

[0004] The invention relates to a method for producing a SiC epitaxial layer on a first monocrystalline SiC layer and device with a SiC epitaxial layer on a first monocrystalline SiC layer.

[0005] State of the art

[0006] SiC power components feature epitaxially deposited layers of varying doping. These serve as buffer layers, drift zones, and current distribution zones. The doping and layer thicknesses are selected depending on the current class and current-carrying capacity of the respective power component.

[0007] In the operating mode of the power device with a high proportion of negative and positive charge carriers, the positive charge carriers can lead to damage at the interface between the SiC substrate and the epitaxial layer. The disadvantage of this is that existing substrate defects can propagate into the epitaxial layer, also known as bipolar degradation.

[0008] To prevent this, buffer layers with layer thicknesses of at least 1 to 5 pm are arranged on the SiC substrate to achieve increased recombination of the charge carriers in the buffer layer and prevent bipolar degradation. The dopant used can be nitrogen, for example. The transition from a lightly doped drift zone to a highly doped buffer zone causes the power components to exhibit hard diode breakdown in diode operation. The disadvantage is that with high doping and greater buffer layer thickness, the operating modes are limited in terms of permissible switching edges at high currents. Therefore, complex and expensive process steps are incorporated into the production of the epitaxial layer before, in, or behind the buffer layer.

[0009] The object of the invention is to overcome these disadvantages.

[0010] Disclosure of the invention

[0011] The method according to the invention for producing a SiC epitaxial layer on a first monocrystalline SiC layer comprises changing a crystal lattice of the first monocrystalline SiC layer at a specific depth by implanting hydrogen, applying the first monocrystalline SiC layer to a carrier substrate by bonding, and producing a SiC epitaxial layer above the first monocrystalline SiC layer.

[0012] The advantage here is that the production costs are low.

[0013] In a further development, the first monocrystalline SiC layer has a nitrogen doping greater than 1 e19 1 / cm 3 on.

[0014] The advantage here is that the SiC epitaxial layer acts as a buffer layer.

[0015] In a further embodiment, a second monocrystalline SiC layer is bonded to the first monocrystalline SiC layer, wherein the second monocrystalline SiC layer has a nitrogen doping of less than 1 e16 1 / cm 3 has.

[0016] The advantage here is that two bonded layers of low-defect monocrystalline SiC with different doping levels are arranged on a substrate material, eliminating the need for matching layers for the buffer layer with comparable doping levels, and allowing additional SiC epitaxial layers to be grown with minimal matching effort. Furthermore, process times are short.

[0017] The device according to the invention comprises a carrier substrate and a first monocrystalline SiC layer bonded to the carrier substrate, wherein the first monocrystalline SiC layer has been treated by hydrogen implantation. According to the invention, an SiC epitaxial layer is arranged above the first monocrystalline SiC layer.

[0018] The advantage here is that no bipolar degradation occurs within the epitaxial layer, which acts as a buffer layer.

[0019] In a further development, the first monocrystalline SiC layer comprises a nitrogen doping greater than 1 e19 1 / cm 3 , where the SiC epitaxial layer has a doping between 1 e18 1 / cm 3 and 1e19 1 / cm 3 has.

[0020] The advantage here is that the defects created by hydrogen implantation, especially voids, diffuse into the SiC epitaxial layer due to the high temperature during deposition, thus forming additional recombination centers. This allows the dopant concentration to be kept lower, making the epitaxial process less demanding on adjustments and thus more cost-effective.

[0021] In a further embodiment, the first monocrystalline SiC layer has a layer thickness of 600 nm - 1200 nm.

[0022] The advantage here is that the layer thickness can be adjusted cost-effectively during the manufacturing process via the implantation depth of the hydrogen ions and final polishing processes.

[0023] In a further development, the SiC epitaxial layer has a layer thickness between

[0024] 1 pm and 3 pm, in particular a layer thickness of 1 pm. The advantage here is that conventional processes can be used optionally, and at the same time, the improvement through the beneficial effect of the defects created during hydrogen implantation via diffusion into the SiC epitaxial layer changes the diode behavior in such a way that higher switching edges can be realized, or the processes can be manufactured more cost-effectively with larger process windows regarding layer thickness, adaptation gradients, and dopant concentration.

[0025] In a further embodiment, the first monocrystalline SiC layer has a nitrogen doping greater than 1 e19 1 / cm 3 where the SiC epitaxial layer has a doping of less than 1 e18 1 / cm 3 and has a layer thickness of less than 1 pm, in particular between 100 nm and 500 nm.

[0026] The advantage here is that the manufacturing costs are reduced by lower layer thicknesses, but at the same time the bipolar degradation is avoided by the effect described above and the switching behavior of the diode becomes smoother.

[0027] In a further development, the first monocrystalline SiC layer has a nitrogen doping greater than 1 e19 1 / cm 3 and a layer thickness of 600 nm - 1200 nm, with the SiC epitaxial layer having a doping of less than 1 e16 1 / cm 3 and has a layer thickness greater than 5 pm.

[0028] The advantage here is that manufacturing costs can be significantly reduced. The function of the buffer layer is assumed by recombination centers, which diffuse from the first monocrystalline SiC layer into the SiC epitaxial layer during the inventive growth of the SiC epitaxial layer. This further improves the diode behavior.

[0029] In a further embodiment, the first monocrystalline SiC layer has a nitrogen doping of less than 1 e19 1 / cm 3 , especially between 1 e18 1 / cm 3 and 1 e19 1 / cm 3 , and a layer thickness of 600 nm - 1200 nm, wherein a second monocrystalline SiC layer is arranged on the first monocrystalline layer, and the second monocrystalline layer has a nitrogen doping of less than 1 e16 1 / cm 3 and has a layer thickness of 600 nm - 1200 nm, wherein the SiC epitaxial layer is arranged on the second monocrystalline SiC layer.

[0030] The advantage here is that the effort required for an adaptation layer can be reduced, and the drift zone is grown on the second monocrystalline layer. This can be particularly cost-effective if the second monocrystalline layer was also produced using an epitaxial process with the same or a similar dopant concentration as the drift zone before being applied to the first monocrystalline layer. Another advantage is that the second monocrystalline layer has also undergone a hydrogen implantation, which can contribute to preventing bipolar degradation via the mechanisms described above.

[0031] Further advantages arise from the following description of embodiments and the dependent patent claims.

[0032] Short description of the drawings

[0033] The present invention is explained below with reference to preferred embodiments and the accompanying drawings. They show:

[0034] Figure 1 shows a method according to the invention for producing a SiC epitaxial layer on a first monocrystalline SiC layer,

[0035] Figure 2 shows a first embodiment of a device according to the invention with a SiC epitaxial layer on a first monocrystalline SiC layer, and

[0036] Figure 3 shows a second embodiment of a device according to the invention with a SiC epitaxial layer on a first monocrystalline SiC layer. Figure 1 shows a method 100 according to the invention for producing a SiC epitaxial layer on a first monocrystalline SiC layer. The method 100 starts with a step 110 in which a crystal lattice of the first monocrystalline SiC layer is modified at a specific depth by implanting hydrogen. The modification leads, for example, to a destruction of the crystal lattice. The first monocrystalline SiC layer has, for example, a nitrogen doping greater than 1 e19 1 / cm 3In a subsequent step 120, the first monocrystalline layer is applied to a carrier substrate by means of bonding. The bonding takes place by means of covalent bonding or by applying an intermediate material that supports the bonding. In a subsequent step 140, an SiC epitaxial layer is created above the first monocrystalline SiC layer. In other words, monocrystalline SiC is treated with a hydrogen ion implantation, preferably as part of the chipping off of thin layers of monocrystalline SiC, i.e., up to 1 pm, wherein the thin monocrystalline SiC layer is bonded to a carrier material, wherein the carrier material comprises another monocrystalline SiC or polycrystalline SiC. The specific depth, starting from a surface of the first monocrystalline SiC layer, at which the change in the crystal lattice takes place corresponds to the layer thickness of the thin monocrystalline SiC layer that is bonded to the carrier material.An optimized buffer layer is arranged on the thin monocrystalline SiC layer depending on the targeted voltage class of the power semiconductor component to be produced.

[0037] Optionally, in a step 130 following step 120, a second monocrystalline SiC layer is bonded to the first monocrystalline SiC layer, wherein the second monocrystalline SiC layer has a nitrogen doping of less than 1 e16 1 / cm 3 has.

[0038] The method 100 can, for example, be combined with a method for cleaving monocrystalline SiC substrates. In step 110, a predetermined breaking point is created in the first monocrystalline SiC substrate by means of hydrogen ion implantation, wherein the predetermined breaking point is arranged, for example, at a distance of up to 1 pm below a surface of the first monocrystalline SiC substrate. Subsequently, the surface of the first monocrystalline SiC substrate is applied to the carrier substrate by means of bonding. In order to create the first monocrystalline layer on the carrier substrate, the predetermined breaking point must subsequently be activated by means of thermal or mechanical treatment. In step 140, the SiC epitaxial layer is then created above the first monocrystalline SiC layer.

[0039] Figure 2 shows a first embodiment of a device 200 according to the invention with a SiC epitaxial layer 203 on a first monocrystalline SiC layer 202, wherein the monocrystalline SiC layer 202 is arranged on a carrier substrate 201. The first monocrystalline SiC layer 202 has been treated by means of hydrogen implantation, in which the hydrogen is not incorporated into the crystal lattice, but merely has the task of changing the crystal lattice of the monocrystalline grown material, be it for the production of defects, such as carbon defects, or for the production of a predetermined breaking point for a subsequent bonding process in which defects are also produced in various areas.The dose and energy of the hydrogen implantation are selected such that, for example, a carbon vacancy concentration of at least 1 e15 1 / cm3 is achieved near the interface between the first monocrystalline SiC layer 202 and the SiC epitaxial layer 203.

[0040] In a first embodiment, the first monocrystalline SiC layer 202 has a nitrogen doping greater than 1 e19 1 / cm 3 , wherein the SiC epitaxial layer 203 has a doping between 1 e18 1 / cm 3 and 1 e19 1 / cm 3The first monocrystalline SiC layer 202 has a layer thickness between 600 nm and 1200 nm. The SiC epitaxial layer 203 has a layer thickness between 1 pm and 3 pm, preferably a layer thickness of 1 pm. Transition layers with a layer thickness of up to 200 nm can be arranged between the SiC epitaxial layer 203 of the first monocrystalline SiC layer 202. The transition layer has a different doping than the SiC epitaxial layer 203 and the first monocrystalline SiC layer 202. In this embodiment, the SiC epitaxial layer 203 functions as a buffer layer. In a second embodiment, the first monocrystalline SiC layer 202 has a nitrogen doping greater than 1 e19 1 / cm 3 , wherein the SiC epitaxial layer 203 has a doping between 1 e18 1 / cm 3 and 1 e19 1 / cm 3wherein the SiC epitaxial layer may have a doping gradient. The first monocrystalline SiC layer 202 has a layer thickness between 600 nm and 1200 nm. The layer thickness of the SiC epitaxial layer 203 is less than 1 pm, in particular it has a value between 100 nm and 500 nm, preferably 200 nm. Transition layers with doping gradients may be arranged between the SiC epitaxial layer 203 and the monocrystalline SiC layer 202. The SiC epitaxial layer 203 functions as a buffer layer in this embodiment.

[0041] In a third embodiment, the first monocrystalline SiC layer 202 has a nitrogen doping greater than 1 e19 1 / cm 3 The layer thickness of the first SiC layer 202 is 600 nm - 1200 nm. The SiC epitaxial layer 203 has a doping of less than 1e18 1 / cm 3and a layer thickness of less than 1 pm, in particular a value between 100 nm and 500 nm. The SiC epitaxial layer 203 functions as a buffer layer in this embodiment.

[0042] In a fourth embodiment, the first monocrystalline SiC layer 202 has a nitrogen doping greater than 1 e19 1 / cm 3 The layer thickness of the first SiC layer 202 is 600 nm - 1200 nm. The SiC epitaxial layer 203 has a doping of less than 1e16 1 / cm 3and a layer thickness greater than 5 pm. In this embodiment, the SiC epitaxial layer 203 functions as a drift layer. Optionally, an adjustment layer of a few tens of nm to a few hundred nm is arranged between the drift layer and the monocrystalline SiC layer 202 to adjust the growth parameters of the SiC epitaxial layer 203. The doping of the adjustment layer is equal to the doping of the monocrystalline SiC layer 202 or lies between the doping of the monocrystalline SiC layer 202 and the drift layer, i.e., the SiC epitaxial layer 203.

[0043] Figure 3 shows a second embodiment of the inventive

[0044] Device comprising a first monocrystalline SiC layer 302, wherein the monocrystalline SiC layer 302 is arranged on a carrier substrate 301. The first monocrystalline SiC layer 302 has a hydrogen implantation. The first monocrystalline SiC layer 302 has a nitrogen doping of less than 1 e19 1 / cm 3 , especially between 1 e18 1 / cm 3 and 1 e19 1 / cm 3 , and a layer thickness of 600 nm - 1200 nm. A second monocrystalline SiC layer 303 is arranged on the first monocrystalline SiC layer 302. The second monocrystalline layer 303 has a nitrogen doping of less than 1 e16 1 / cm 3 , preferably between 1 e15 and 1e16 1 / cm 3 , especially 5e15 1 / cm 3and a layer thickness of 600 nm - 1200 nm. A SiC epitaxial layer 304 is arranged on the second monocrystalline SiC layer 303. The first monocrystalline SiC layer 302 is bonded to the carrier substrate 301, and the second monocrystalline SiC layer 303 is bonded to the first monocrystalline SiC layer 302. In other words, this is a substrate with two thin layers of low-defect monocrystalline SiC of different doping bonded to one another on a carrier material, wherein the carrier material is highly conductive and / or particularly favorable. A SiC epitaxial layer 304 with a doping comparable to that of the second monocrystalline layer 303 is applied to the second monocrystalline SiC layer 303.

[0045] The device 300 shown in Figure 3, i.e., a substrate, is manufactured, for example, using a method in which hydrogen implantation is carried out in the second monocrystalline SiC substrate with low nitrogen doping. This creates a predetermined breaking point within the second monocrystalline SiC substrate at a distance of between 600 nm and 1200 nm from the surface of the second monocrystalline SiC substrate. The surface of the second monocrystalline SiC substrate is bonded to a first monocrystalline layer arranged on a carrier substrate. The predetermined breaking point is then thermally or mechanically activated, and a second monocrystalline layer is detached from the second monocrystalline SiC substrate. A SiC epitaxial layer is then applied to the second monocrystalline SiC layer.In all these embodiments, the first monocrystalline SiC layer can be produced in a variety of ways, such as by means of PVT (physical vapor transport) processes, HT-CVD (high temperature chemical vapor deposition) processes, growth from the liquid phase, SiC epitaxy on otherwise produced substrates or the like.

[0046] On the devices according to the invention, ie, the substrates, a SiC power semiconductor component can be advantageously produced in a voltage class up to 1700 V breakdown voltage. In principle, the method can also be applied to higher voltage classes. The SiC power semiconductor component exhibits advantageous diode behavior. If the SiC epitaxial layer functions as a buffer layer, the first manufacturing step of the SiC power semiconductor component comprises the growth of a drift layer.

[0047] The invention finds application, for example, in SiC power transistors, particularly MOSFETs, used in electric drivetrains of electric or hybrid vehicles, for example, in DC / DC converters and inverters, as well as in vehicle chargers. The power transistors can also be used in inverters for household appliances such as washing machines.

[0048] The process described here for nitrogen-doped n-type silicon carbide can in principle also be applied to p-type material with other dopants in the future.

Claims

Claims 1 . Method (100) for producing a SiC epitaxial layer on a first monocrystalline SiC layer, comprising the steps: • Changing (110) a crystal lattice of the first monocrystalline SiC layer at a certain depth by implanting hydrogen, • Applying (120) the first monocrystalline SiC layer to a carrier substrate by means of bonding, • Creating (140) a SiC epitaxial layer above the first monocrystalline SiC layer.

2. Method (100) according to claim 1, characterized in that the first monocrystalline SiC layer has a nitrogen doping greater than 1e19 1 / cm 3 has.

3. Method (100) according to one of claims 1 or 2, characterized in that a second monocrystalline SiC layer is bonded to the first monocrystalline SiC layer, wherein the second monocrystalline SiC layer has a nitrogen doping of less than 1e16 1 / cm3 has.

4. Device (200) with a carrier substrate (201) and a first monocrystalline SiC layer (202) bonded to the carrier substrate (201), wherein the first monocrystalline SiC layer (202) has been treated by means of hydrogen implantation, characterized in that a SiC epitaxial layer (203) is arranged above the first monocrystalline SiC layer (202).

5. Device (200) according to claim 4, characterized in that the first monocrystalline SiC layer (202) has a nitrogen doping greater than 1e19 1 / cm 3 wherein the SiC epitaxial layer (203) has a doping between 1 e18 1 / cm 3 and 1 e19 1 / cm 3 has.

6. Device (200) according to claim 5, characterized in that the first monocrystalline SiC layer (202) has a layer thickness of 600 nm - 1200 nm.

7. Device (200) according to claim 5, characterized in that the SiC epitaxial layer (203) has a layer thickness between 1 pm and 3 pm, in particular a layer thickness of 1 pm.

8. Device (200) according to claim 4, characterized in that the first monocrystalline SiC layer (202) has a nitrogen doping greater than 1 e19 1 / cm 3 , wherein the SiC epitaxial layer (203) has a doping of less than 1 e18 1 / cm 3 and has a layer thickness of less than 1 pm, in particular between 100 nm and 500 nm.

9. Device (200) according to claim 4, characterized in that the first monocrystalline SiC layer (202) has a nitrogen doping greater than 1 e19 1 / cm 3 and a layer thickness of 600 nm - 1200 nm, wherein the SiC epitaxial layer (203) has a doping of less than 1 e16 1 / cm 3 and has a layer thickness greater than 5 pm.

10. Device (200, 300) according to claim 4, characterized in that the first monocrystalline SiC layer (202, 302) has a nitrogen doping of less than 1 e19 1 / cm 3 , especially between 1 e18 1 / cm 3 and 1 e19 1 / cm 3 and a layer thickness of 600 nm - 1200 nm, wherein a second monocrystalline SiC layer (303) is arranged on the first monocrystalline layer (202, 302), wherein the second monocrystalline layer (303) has a nitrogen doping of less than 1 e16 1 / cm 3 and has a layer thickness of 600 nm - 1200 nm, wherein the SiC epitaxial layer (203, 304) is arranged on the second monocrystalline SiC layer (303).

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