Method for depositing gallium nitride GAN on silicon si

Abstract

The invention relates to a method for depositing a layer consisting of elements of main groups III and V on a SiC surface of a substrate made of silicon in a process chamber (2) of a CVD reactor, in which method the SiC surface is generated by means of a first chemical reaction of a first gaseous starting material containing carbon with the surface of the Si substrate at a first increased temperature of the substrate (6), and the layer is generated by means of a second chemical reaction of a second gaseous starting material containing the element of main group III with a third gaseous starting material containing the element of main group V at a second increased temperature.

Description

METHOD FOR DEPOSITING GALLIUM NITRIDE GAN ON SILICON SI field of technology

[0001] The invention relates to a method for depositing a layer consisting of elements of main groups III and V on a SiC surface of a silicon substrate in a process chamber of a CVD reactor, wherein the SiC surface is produced by a first chemical reaction of a carbon-containing gaseous first starting material with the surface of the Si substrate at a first elevated temperature of the substrate and the layer is produced by a second chemical reaction of a second gaseous starting material containing the element of main group III and a third gaseous starting material containing the element of main group V at a second elevated temperature. State of the art

[0002] US 2005 / 0263754 A1 discloses a method for depositing AlN or GaN on a Si substrate, wherein the substrate has an upwardly open opening that imparts a high degree of roughness to the substrate. At temperatures between 800°C and 1400°C, propane, methane, or butane is fed into a process chamber containing the substrate to be coated to carbonize the surface. This is intended to form a SiC layer with a thickness of at least 0.1 nanometers and a maximum of 100 nanometers, onto which the III-V layer is subsequently deposited.

[0003] US 2004 / 0029365 A1 discloses a method for depositing Gallium nitride on a silicon substrate, where the surface is first converted to SiC by introducing a hydrocarbon, such as ethylene. SiC is then epitaxially deposited on top. The III-V layer is then deposited onto this SiC layer.

[0004] EP 1 842941 B1 or EP 1 842940 A1 describe a process in which a Si substrate is placed in a reactor and heated to an elevated temperature. The substrate is first treated with hydrogen at a temperature of 1100°C to create an H-terminated surface. At the same temperature, a small mass flow of TMA1 is fed into the process chamber. On the substrate, the TMA1 decomposes into Al(III)C, leaving a methyl residue. The methyl residue decomposes into carbon and hydrogen. The carbon bonds with silicon atoms of the substrate to form a monomolecular layer of SiC on the surface. The remaining aluminum can diffuse into the substrate, where it can create an AlSi alloy. However, it can also remain on the surface and act catalytically during the deposition of a subsequent III-V layer.As a III-V layer, GaN is deposited with an increased TMAl flux and simultaneous injection of ammonia.

[0005] US 2010 / 0273291 Al describes an MOCVD process for depositing GaN layers, wherein the process chamber is cleaned with HCl in the absence of substrates prior to the deposition process.

[0006] EP 3503 163 A1 describes a method for depositing indium-containing layers on a Si substrate, wherein the substrate, previously heated to an elevated temperature between 1000°C and 1100°C, is exposed to a low flow of an indium-containing organic compound so that a SiC layer is formed on the surface of the substrate.

[0007] The processes described in the aforementioned US 2005 / 0263754 A1 and US 2004 / 0029365 A1 produce layers with insufficient surface quality. The variants described in the aforementioned EP 1 842941 B1 and EP 3 503 163 A1, in which a By using a metal-containing precursor to form the SiC layer, the layer quality can be improved. However, these variants carry the risk that the metal atoms remaining on the surface or diffusing into the substrate may have a negative effect on the electronic properties of the III-V layer, especially if it is a nitrogen-containing layer.

[0008] The problem with all of the previously described processes is that if the deposition process is repeated, especially multiple times, metal atoms can be incorporated into the silicon substrate.

[0009] It is also known in the art to pretreat the silicon substrate at a relatively low temperature of <150° Celsius by introducing an organometallic compound of an element of the III main group, for example, aluminum. Summary of the invention

[0010] The invention is based on the object of improving the method mentioned at the outset in such a way that the disadvantages described above are eliminated.

[0011] The problem is solved by the technical teaching specified in the claims, wherein the subclaims are not only further developments of the method specified in claim 1, but independent solutions to the problem.

[0012] The task is solved by a procedure with the following Process steps: a. Providing a CVD reactor with a gas inlet device for feeding reactive gases into a process chamber of the CVD reactor, which has a heating device with which a susceptor can be brought to an elevated temperature, and which has a gas outlet device with which decomposition products of the process gas can be removed from the process chamber; b. Providing a cleaning gas which has the property of chemically reacting with metallic residues on surfaces of the process chamber at a cleaning temperature to form a gas containing the metallic residues; c. Providing a carbon-containing reactive gas which does not contain any metal; d. Providing a first gaseous starting material which contains an element of main group III and a second gaseous starting material which contains an element of main group V; e. Tempering the surfaces of the process chamber to a cleaning temperature; f.Feeding the cleaning gas into the process chamber and removing the metallic residues by forming the gas containing the metallic residues and removing this gas through the gas outlet element; g. Flushing the process chamber with an inert gas; h. Loading the susceptor with at least one silicon substrate; i. Tempering the substrate to a first elevated temperature; j. Producing a SiC surface that is as closed as possible by feeding the carbon-containing reactive gas into the process chamber and carrying out a chemical reaction of the carbon-containing gas with the Si surface of the substrate; k. Tempering the substrate to a second elevated temperature;. 1. Depositing a III-V layer on the SiC surface by feeding the first and second gaseous precursors into the process chamber.

[0013] Essential here are process steps b, e, and f, which are carried out without the presence of a substrate. These steps ensure that no metallic residues from previous processes remain on the surfaces by feeding a cleaning gas into the process chamber. It is also essential that process steps j to 1 are carried out immediately one after the other. For this purpose, it is particularly advantageous if the first elevated temperature corresponds to the second temperature. The III-V layer is then deposited (step 1) immediately after the SiC surface has been created (step j). All steps are carried out in the same process chamber.

[0014] Before the actual coating of the substrate with a III-V layer, parasitic coatings that were created during a previous coating process are removed from the surfaces of the process chamber in a cleaning process. These layers contain gallium. Only when these surfaces have been made metal-free, i.e. no longer contain gallium, can the silicon substrate be introduced into the process chamber. This can be a pretreated silicon substrate in which the native oxides have been removed by pretreatment at an elevated temperature in a hydrogen atmosphere. This pretreatment of the substrate can take place in a different process chamber. But it can also take place in the same process chamber. For example, after the cleaning step and before the SiC surface is produced, hydrogen can be fed into the process chamber at an elevated temperature.This occurs preferably in the presence of the substrate, so that a reaction with the hydrogen. Oxides can be removed from the surface of the substrate. The at least one silicon substrate can have a diameter of at least 150 mm. The thickness of the substrate is less than 1.2 mm. A substrate with a diameter of 300 mm can have a thickness of 1.5 mm. The thickness of the substrate can thus be between 1 mm and 2 mm. Polished silicon substrates can be used as substrates, which have smooth surfaces on which a layer structure comprising a plurality of layers can be deposited. The carbon-containing reactive gas can be a hydrocarbon. It can be methane, ethane, prothane, butane, ethylene, etc. It can be alkanes, alkenes, or alkynes. The gaseous starting materials of main groups III and V can be organometallic compounds of main group III and hydrides of main group V. Preferably, the element of main group III is aluminum or gallium, and the element of main group VMain group nitrogen. The method enables, in particular, the deposition of AIN layers or GaN layers on a silicon substrate, wherein the silicon surface of the substrate is previously carbonized. The carbonization takes place in such a way that no reaction takes place between the organometallic starting material and the silicon surface during deposition of the III-V layer. The SiC layer can be polycrystalline. The cleaning step and the deposition of the III-V layer can take place at a temperature between 950°C and 1100°C, at a temperature between 1000°C and 1060°C or at a temperature between 970°C and 1000°C. The temperature at which the silicon surface is carbonized is preferably identical to that at which the III-V layer is deposited. It can also be provided that the carbon-containing reactive gas is introduced for a transition period simultaneously with the reactive gases of the III-V and V groups.Main group is present in the process chamber. The molar flow of the carbon-containing gas into the process chamber can be in the range between 0.1% and 0.3% of the total molar flow.

[0015] After deposition of the III-V layer or after deposition of further layers on this first III-V layer, the process chamber can be brought into a discharge-capable state. After discharging the substrate, the process chamber is closed, and steps e and f are performed. The surfaces of the process chamber that contain parasitic coatings, particularly Al or Ga, i.e., metals, during the initial deposition of the III-V layer are cleaned. These metals are removed during this cleaning process. The process chamber can then be reloaded with one or more substrates, and the coating process described above can be repeated. This process begins by annealing the substrate to remove the natural oxides from the silicon substrate, producing a SiC monolayer, and then depositing at least one III-V layer.

[0016] The cleaning process preceding loading the susceptor with the substrate can be carried out using the cleaning steps described in DE 102013 104 105 A1. In a first cleaning step, which is carried out at a high cleaning temperature in the range between 1000°C and 1300°C, essentially only hydrogen is introduced into the process chamber. At a total pressure that can be between 50 mbar and 900 mbar, preferably around 100 mbar, 10 to 100 slm of H2 are introduced into the process chamber for approximately 10 to 60 minutes. In this process, GaN deposited on the process chamber walls is converted into NH3. Any silicon oxide layers present are reduced. In a possible second cleaning step, additional metal components are removed from the surface. This step takes place at low pressures, particularly below 100 mbar. The susceptor temperature here is in a range between 800°C and 900°C.During this time, Cl2 and N2 can be fed into the process chamber. During this decomposition step, metals react to form volatile chlorides, which can be removed through the gas outlet device.

[0017] The method according to the invention is also advantageous over the method mentioned above, in which the silicon substrate is pretreated with an organometallic compound, for example, an organometallic aluminum compound, at a reduced temperature. This is because it is not necessary to cool the process chamber to a temperature below 750°C after removing the oxide layer from the surface of the silicon substrate at temperatures above 1000°C, which is time-consuming. The method according to the invention thus also allows for reduced cycle times. Short description of the drawings

[0018] An embodiment of the invention is explained below with reference to the accompanying drawings. Figure 1 shows a schematic diagram of a CVD reactor. Description of the embodiments

[0019] The CVD reactor 7 has a gas-tight housing. Located within the housing is a gas inlet device 1, through which process gas 9, 10, which contains various reactive gases and is provided by a gas supply system 15, can be fed into a process chamber 2.

[0020] The process chamber 2 contains a susceptor 4, which can be heated from below to a process temperature by a heating device 3. Decomposition products can be removed from the process chamber via a gas outlet device 5. The decomposition products can be fed to a gas purification system 16.

[0021] A control device 17 is provided with which the valves and mass flow controllers (not shown) via which the gases from the gas sources 8, 9, 10, 11, 13 are fed into the process chamber 2 can be controlled.

[0022] To deposit a III-V layer on a silicon substrate, the process chamber 2 is first brought into a process-ready state by removing metal residues remaining on the surface of the walls of the process chamber 2 from previous processes in a first cleaning step. This occurs without the presence of a substrate 6 in the process chamber 2. Chlorine or ammonia, or ammonia and chlorine in succession, can be fed into the process chamber 2.

[0023] After purging the process chamber 2 with an inert gas and cooling it, the process chamber 2 is loaded with the silicon substrate. The process chamber 2 is purged and heated. The silicon substrate 6 preferably has a polished surface, although it may still contain oxides.

[0024] Hydrogen is injected into the process chamber to remove oxides from the substrate surface. This pretreatment process, i.e., the removal of oxides from the surface of the silicon substrate, can also be performed in another process chamber, from which the substrate is removed and placed in the cleaned process chamber.

[0025] Thereafter, a carbon-containing gas, for example an alkane, is fed into the process chamber through the gas inlet element 5. The carbon of the carbon-containing gas reacts at a temperature which above 970°C, and preferably in the range between 970°C and 1000°C, with the surface of the substrate to form a monolayer of SiC. The reaction lasts 4 to 10 seconds. The flow rate of the carbon-containing gas is more than 66 sccm. This saturates the substrate surface. With a total hydrogen flow of 180 slm (approximately 8 mol / min), the ethene flow should be between 0.5 and 50 mmol / min. The C Hi concentration in H2 should be 0.006-0.6% (60-6000 ppm) at a process chamber pressure of 35-300 mbar.

[0026] Immediately thereafter, or while the carbon-containing gas is still being fed into the process chamber, a process gas consisting of an organometallic aluminum compound and ammonia, as well as an inert gas such as hydrogen, nitrogen, or a noble gas, is fed into the process chamber 2 through the gas inlet element 5, forming an AlN layer on the SiC monolayer. This can occur at the same temperature.

[0027] Subsequently, the process chamber 2 is purged with an inert gas or further layers are deposited. It is particularly intended that one layer of a subsequently deposited layer sequence contains gallium and is, in particular, a GaN layer.

[0028] After completion of the coating step, the process chamber 2 is cooled and the substrate 6 is removed from the process chamber 2.

[0029] It is considered essential that before feeding in a gas containing a metal, especially a metal of the III main group, a transformation of the silicon surface of the substrate takes place by feeding a metal-free reactive gas into the process chamber, which contains carbon which reacts with the silicon surface of the substrate. It is further considered essential that the heating of the substrate takes place in a metal-free environment, for which it is necessary to first clean the environment of the substrate using a suitable process. The gas supply system 15 can have a cleaning gas source 8, which stores, for example, a chlorine-containing gas, a process gas source 9, which stores, for example, a gallium-containing gas, a further process gas source 10, which contains a nitrogen-containing gas, and a gas source 11 in which the carbon-containing gas is present. The gases are fed via a feed line into the process chamber 2, in which the gases react chemically. Reaction products 12 are formed, which are transported via a gas discharge line to a gas cleaning system 16.

[0030] It is particularly advantageous if the same layer sequences are deposited in the process chamber 2 several times in succession in an industrial manufacturing process, wherein at least one of the layer sequences contains gallium, and gallium is deposited on surfaces of the process chamber 2 during deposition. By cleaning the process chamber prior to each deposition process, the gallium remaining in the process chamber 2 is removed. This prevents the formation of gaseous gallium when the process chamber 2 is heated in the presence of the substrate 6, which could have an etching effect on the silicon surface of the substrate.

[0031] The above statements serve to explain the inventions covered by the application as a whole, which each independently develop the state of the art by at least the following combinations of features, whereby two, several or all of these combinations of features can also be combined, namely:

[0032] A method for depositing a layer consisting of elements of main groups III and V on a silicon substrate, comprising the following steps: a. Providing a CVD reactor R with a gas inlet element 1 for feeding reactive gases into a process chamber 2 of the CVD reactor, which process chamber has a heating device 3 with which a susceptor 4 can be brought to an elevated temperature, and which has a gas outlet element 5 with which decomposition products of the process gas can be led out of the process chamber 2; b. Providing a cleaning gas 8 which has the property of chemically reacting with metallic residues on surfaces of the process chamber 2 at a cleaning temperature to form a gas containing the metallic residues; c. Providing a carbon-containing reactive gas 11 which contains no metal; d. Providing a first gaseous starting material 9 which contains an element of main groups III and V.Main group and a second gaseous starting material 10 which contains an element of main group V; e. Tempering the process chamber 2, which has metallic residues on its surfaces and does not contain a substrate, to a cleaning temperature TR; f. Feeding the cleaning gas 8 into the process chamber 2 and removing the metallic residues by forming the gas 12 containing the metallic residues and removing this gas through the gas outlet element 4; g. Flushing the process chamber 2 with an inert gas 13; h. Loading the susceptor 4 with at least one substrate 6 made of silicon; i. Tempering the substrate to a first elevated temperature TI;. j. Producing a SiC surface by feeding the carbon-containing reactive gas 11 into the process chamber 2 and carrying out a chemical reaction of the carbon-containing gas 11 with the Si surface of the substrate 6; k. Tempering the substrate to a second elevated temperature T2; l. Depositing a III-V layer onto the SiC surface by feeding the first and second gaseous starting materials 9, 10 into the process chamber 2; wherein all steps are carried out consecutively in the same process chamber 2 and steps j, k, 1 are carried out immediately one after the other.

[0033] A method which is characterized in that, before producing the SiC surface (step j), hydrogen is fed into another or the same process chamber 2 in which the substrate 6 is located, and this process chamber 2 then containing hydrogen is heated to a third elevated temperature T3.

[0034] A process characterized in that the first reactive starting material 9 is an organometallic compound or an organometallic gallium compound or aluminum compound and that the second reactive starting material 10 is a hydride or NH?.

[0035] A process characterized in that the carbon-containing reactive gas 11 is a hydrocarbon or is C2H4.

[0036] A process characterized in that the cleaning gas 8 contains ammonia or a halogen and the cleaning temperature is between 1000°C and 1300°C.

[0037] A method characterized in that the SiC surface is produced at the first temperature TI between 950°C and 1050°C or between 970°C and 1000°C and the injection of the carbon-containing reactive gas continues until the Si surface of the substrate is completely saturated with SiC, or wherein the duration of the injection is at least 2 seconds or 4 to 10 seconds.

[0038] A process characterized in that the deposition of the III-V layer takes place at a temperature between 1000°C and 1060°C.

[0039] A method characterized in that the second elevated temperature T2 corresponds to the first elevated temperature TI and steps j, 1 are carried out in immediate succession.

[0040] A method which is characterized in that the feeding of the first and second gaseous starting material 9, 10 immediately follows the feeding of the carbon-containing reactive gas 11 into the process chamber 2, so that at the beginning of the deposition of the layer the carbon-containing reactive gas 11 is in the process chamber 2.

[0041] A method characterized in that the carbon-containing reactive gas (11) is introduced at a total flow of less than 15 gmol / min and / or that the molar partial flow of the carbon-containing reactive gas (11) corresponds to less than 0.3% of the total molar flow.

[0042] A method characterized in that steps j, k, 1 of claim 1 are carried out with a process chamber pressure of at least 25 mbar and maximum 800 mbar, at least 35 mbar and a maximum of 75 mbar or at least 35 mbar and a maximum of 145 mbar.

[0043] All disclosed features are essential to the invention (individually, but also in combination with one another). The disclosure of the application hereby fully incorporates the disclosure content of the associated / attached priority documents (copy of the prior application), also for the purpose of incorporating features of these documents into claims of the present application. The subclaims characterize, even without the features of a referenced claim, independent inventive developments of the prior art with their features, in particular for filing divisional applications based on these claims. The invention specified in each claim may additionally comprise one or more of the features provided in the above description, in particular with reference numbers, and / or specified in the list of reference numbers.The invention also relates to designs in which individual features mentioned in the above description are not implemented, in particular insofar as they are clearly unnecessary for the respective intended use or can be replaced by other technically equivalent means. List of reference symbols 1 gas inlet organ R CVD reactor 2 Process chamber TR cleaning temperature 3 Heating device TI first temperature 4 Susceptor T2 second temperature 5 Gas outlet T3 third temperature 6 Substrat 7 CVD reactor 8 Cleaning gas source 9 Process gas source III 10 Process gas source V 11 Gas source for C-containing gas 12 Gas containing residues 13 Inert gas source 15 Gas supply system 16 Gas cleaning system 17 Control device

Claims

Claims 1. A method for depositing a layer consisting of elements of main groups III and V on a silicon substrate, comprising the following steps: a. Providing a CVD reactor (R) with a gas inlet element (1) for feeding reactive gases into a process chamber (2) of the CVD reactor, which has a heating device (3) with which a susceptor (4) can be brought to an elevated temperature, and which has a gas outlet element (5) with which decomposition products of the process gas can be removed from the process chamber (2); b. Providing a cleaning gas (8) which has the property of chemically reacting, at a cleaning temperature, with residues containing a metal, and in particular compounds of main groups III and V such as GaN or AIN, on surfaces of the process chamber (2) to form a gas (12) containing the residues; c. Providing a carbon-containing reactive gas (11) which does not contain any metal; d.Providing a first gaseous starting material (9) containing an element of main group III and a second gaseous starting material (10) containing an element of main group V; e. Tempering the surfaces of the process chamber (2) to a cleaning temperature (TR); f. Feeding the cleaning gas (8) into the process chamber (2) and removing the residues by forming the gas (12) containing the residues and removing this gas (12) through the gas outlet element (4); g. Flushing the process chamber (2) with an inert gas (13);. h. Loading the susceptor (4) with at least one substrate (6) made of silicon; i. Tempering the substrate to a first elevated temperature (T1); j. Producing a SiC surface by feeding the carbon-containing reactive gas (11) into the process chamber (2) and carrying out a chemical reaction of the carbon-containing gas (11) with the Si surface of the substrate (6); k. Tempering the substrate to a second elevated temperature (T2); l. Deposition of a III-V layer on the SiC surface by feeding the first and second gaseous starting materials (9, 10) into the process chamber (2); wherein all steps are carried out consecutively in the same process chamber (2) and steps j, k, 1 are carried out directly one after the other.

2. Method according to claim 1, characterized in that before producing the SiC surface (step j), hydrogen is fed into another or the same process chamber (2) in which the substrate (6) is located, and this process chamber (2) containing hydrogen is then heated to a third temperature (T3).

3. Method according to one of the preceding claims, characterized in that the first reactive starting material (9) is an organometallic compound or an organometallic gallium compound or aluminum compound and that the second reactive starting material (10) is a hydride or NH?.

4. Method according to one of the preceding claims, characterized in that the carbon-containing reactive gas (11) is a hydrocarbon or C2H4.

5. Method according to one of the preceding claims, characterized in that the cleaning gas (8) contains ammonia or a halogen and the cleaning temperature is between 1000°C and 1300°C.

6. Method according to one of the preceding claims, characterized in that the SiC surface is produced at the first temperature (TI) between 950°C and 1050°C or between 970°C and 1000°C and the feeding of the carbon-containing reactive gas continues until the Si surface of the substrate is completely saturated with SiC, or wherein the duration of the feeding is at least 2 seconds or 4 to 10 seconds.

7. Method according to one of the preceding claims, characterized in that the deposition of the III-V layer takes place at a temperature between 1000°C and 1100°C or 1000°C and 1060°C.

8. Method according to one of the preceding claims, characterized in that the second elevated temperature (T2) corresponds to the first elevated temperature (TI) and steps j, 1 are carried out in immediate succession.

9. Method according to one of the preceding claims, characterized in that the feeding of the first and second gaseous starting material (9, 10) immediately follows the feeding of the carbon-containing reactive gas (11) into the process chamber (2), so- that at the beginning of the deposition of the layer, the carbon-containing reactive gas (11) is in the process chamber (2).

10. Method according to one of the preceding claims, characterized in that the carbon-containing reactive gas (11) is introduced with a total flow of less than 15 mmol / min.

11. The method according to any one of the preceding claims, characterized in that the molar partial flow of the carbon-containing reactive gas (11) corresponds to less than 0.3% of the total molar flow.

12. The method according to any one of the preceding claims, characterized in that steps j, k, 1 of claim 1 are carried out with a process chamber pressure of at least 25 mbar and a maximum of 800 mbar, of at least 35 mbar and a maximum of 75 mbar, or of at least 35 mbar and a maximum of 145 mbar.

13. The method characterized by one or more of the characterizing features of any one of the preceding claims.

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