Method for depositing gallium nitride (GaN) on silicon (Si)

Abstract

The invention relates to a method for depositing a layer of elements of main group III and V on a SiC surface of a silicon substrate in a process chamber (2) of a CVD reactor, wherein the SiC surface is formed by a first chemical reaction between a first gaseous starting material comprising carbon and the surface of the Si substrate at a first elevated temperature of the substrate (6), and the layer is formed by a second chemical reaction between a second gaseous starting material comprising an element of main group III and a third gaseous starting material comprising an element of main group V at a second elevated temperature.

Description

[Technical Field]

[0001] The present invention relates to a method for depositing a layer of elements of main group III and V on a SiC surface of a silicon substrate in a process chamber of a CVD reactor. The SiC surface is formed by a first chemical reaction between a first gaseous starting material containing carbon and the surface of the Si substrate at a first elevated temperature of the substrate. The layer is formed by a second chemical reaction between a second gaseous starting material containing an element of main group III and a third gaseous starting material containing an element of main group V at a second elevated temperature. [Background technology]

[0002] Patent document 1 discloses a method for depositing AlN or GaN on a Si substrate, in which an opening is made in the top of the substrate, thereby imparting a high level of roughness to the substrate. At temperatures between 800°C and 1400°C, propane, methane, or butane is supplied to a process chamber containing the substrate to be coated to carbonize the surface. The objective is to form a SiC layer at least 0.1 nanometers thick and up to 100 nanometers thick, on which a III-V layer is deposited.

[0003] Patent Document 2 discloses a method for depositing gallium nitrite on a silicon substrate, in which the surface is first converted to SiC by introducing a hydrocarbon, such as ethylene, and then epitaxially growing SiC on top of it. A III-V layer is then deposited on this SiC layer.

[0004] In Patent Documents 3 and 4, a Si substrate is placed in a reactor and heated to a high temperature. The substrate is first hydrogen-treated at 1100°C to form a hydrogen-terminated surface. At the same temperature, a low mass flow rate of TMAl is supplied to the process chamber. TMAl decomposes to AlCH on the substrate, leaving behind methyl residues. The methyl residues decompose into carbon and hydrogen. The carbon bonds with silicon atoms in the substrate, forming a monolayer of SiC on the surface. The remaining aluminum can diffuse into the substrate. AlSi can be synthesized there, but it may also remain on the surface and have a catalytic effect during the subsequent deposition of the III-V layer. The III-V layer deposited here is converted to GaN by increasing the TMAl flow rate and simultaneously injecting ammonia.

[0005] Patent Document 5 discloses a method for MOCVD deposition of GaN layers: Prior to the deposition process, the process chamber is cleaned with HCl in the absence of a substrate. Patent Document 6 describes a method for depositing an indium-containing layer on a Si substrate. The substrate is preheated to a high temperature of 1000 to 1100°C, and exposed to a low flow rate of an indium-containing organic compound, thereby forming a SiC layer on the substrate surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2005 / 0263754 [Patent Document 2] US Patent Application Publication No. 2004 / 0029365 [Patent Document 3] European Patent No. 1 842 941 [Patent Document 4] European Patent Application Publication No. 1 842 940 [Patent Document 5] US Patent Application Publication No. 2010 / 0273291 [Patent Document 6] European Patent Application Publication No. 3 503 163 [Patent Document 7] DE 10 2013 104 105 Summary of the Invention [Problem to be solved by the invention]

[0007] The methods described in the above-mentioned patents JP 2003-122266 and JP 2003-122266 result in layers with poor surface quality. The variants described in the above-mentioned patents JP 2003-122266 and JP 2003-122266 allow for the formation of SiC layers using metal-containing starting materials, which improve the layer quality. However, these variants run the risk that metal atoms remaining on the surface or diffusing into the substrate can adversely affect the electronic properties of the III-V layer, especially if the III-V layer is a nitrogen-containing layer.

[0008] A common problem with all the above methods is that if the deposition method is repeated, especially if repeated multiple times, metal atoms may become incorporated into the silicon substrate.

[0009] It is also known in the prior art to pretreat silicon substrates at relatively low temperatures below 150° C. by introducing organometallic compounds of elements of main group III (for example aluminium).

[0010] The present invention aims to improve the above-mentioned method so that the above-mentioned drawbacks are eliminated. [Means for solving the problem]

[0011] This object is achieved by the technical measures specified in the claims, and the dependent claims are not only developments of the method described in claim 1 but also independent solutions to this object.

[0012] This object is achieved by a method comprising the following method steps: a. providing a CVD reactor having a gas inlet member for introducing a reactive gas into a process chamber of the CVD reactor, the CVD reactor having a heating device capable of heating a susceptor to an elevated temperature and a gas outlet member capable of exhausting decomposition products of the process gas from the process chamber; b. providing a cleaning gas having properties that chemically react with metal residues on the surfaces of the process chamber at a cleaning temperature to produce a gas containing the metal residues. c. providing a carbon-containing reactant gas that is free of any metals d. Providing a first gaseous starting material comprising a main group III element and a second gaseous starting material comprising a main group V element. e. heating the process chamber surfaces to a cleaning temperature f. introducing a cleaning gas into the process chamber to remove the metal residues by producing a gas containing the metal residues and removing the gas through the gas outlet member; g. purging the process chamber with an inert gas h. Loading at least one silicon substrate onto a susceptor. i. heating the substrate to a first elevated temperature j. introducing a carbon-containing reactive gas into the process chamber to chemically react the carbon-containing gas with the Si surface of the substrate, thereby forming a SiC surface that is as closed as possible; k. heating the substrate to a second elevated temperature. l. depositing a III-V layer on the SiC surface by introducing first and second gaseous starting materials into the process chamber;

[0013] It is of primary importance here that method steps b, e, and f are performed in the absence of a substrate, thereby ensuring that the introduction of cleaning gas into the process chamber does not leave metal residues on the surface from previous processes. It is also important that method steps j to l are performed immediately one after the other. For this purpose, it is particularly advantageous if the first elevated temperature coincides with the second elevated temperature. The deposition of the III-V layer (step l) is performed immediately after the formation of the SiC surface (step j). All steps are performed in the same process chamber.

[0014] Before the substrate is actually coated with the III-V layer, a cleaning method is used to remove any parasitic coatings that formed on the process chamber surfaces during the previous coating process. These layers contain gallium. Only after these surfaces are metal-free, i.e., gallium-free, can a silicon substrate be introduced into the process chamber. This can take the form of a pretreated silicon substrate, where the native oxide has been removed by pretreatment at high temperature in a hydrogen atmosphere. This substrate pretreatment can be performed in a separate process chamber; however, it can also be performed in the same process chamber. For example, after the cleaning step, hydrogen can be supplied to the process chamber at high temperature before the SiC surface is formed. This is preferably performed in the presence of the substrate, thereby removing the oxide from the substrate surface by reaction with the hydrogen. At least one silicon substrate has a diameter of 150 mm or more. The thickness of the substrate is less than 1.2 mm. A substrate with a diameter of 300 mm has a thickness of 1.5 mm. Therefore, the thickness of the substrate ranges from 1 mm to 2 mm. Usable substrates are polished silicon substrates with smooth surfaces on which a layered structure containing multiple layers can be deposited. The carbon-containing reactant gas is a hydrocarbon, such as methane, ethane, propane, butane, or ethylene. It may also take the form of an alkane, alkene, or alkyne. The main group III and main group V gaseous starting materials may be organometallic compounds of main group III and hydrides of main group V. The main group III element is preferably aluminum or gallium, and the main group V element is preferably nitrogen. The method particularly allows for the deposition of an AlN or GaN layer on a silicon substrate, in which case the silicon surface of the substrate is carbonized beforehand. The carbonization is carried out so that no reaction occurs between the organometallic starting material and the silicon surface during the deposition of the III-V layer. The SiC layer may be polycrystalline. The cleaning step and the deposition of the III-V layer can be carried out at a temperature between 950°C and 1100°C, between 1000°C and 1060°C, or between 970°C and 1000°C. The temperature for carbonizing the silicon surface is preferably the same as the temperature for depositing the III-V layer. During the transition period, a carbon-containing reactant gas can be present in the process chamber simultaneously with the main group III and main group V reactant gases. The molar flow rate of the carbon-containing gas into the process chamber can be in the range of 0.1% to 0.3% of the total molar flow rate.

[0015] After the deposition of the III-V layer, or after depositing additional layers on this initial III-V layer, the process chamber can be evacuated. After removing the substrate, the process chamber is closed and steps e and f are performed. The process chamber surfaces, particularly those with parasitic coatings of metals such as Al or Ga, are cleaned during the initial deposition of the III-V layer. These metals are removed during this cleaning process. One or more substrates can then be loaded into the process chamber and the coating procedure described above can be repeated. This procedure involves first heating the substrate to remove native oxide from the silicon substrate and forming a SiC monolayer, followed by the deposition of at least one III-V layer.

[0016] The cleaning method before loading the substrate onto the susceptor can be performed using the cleaning procedure described in Patent Document 7. The first cleaning step is performed at a high temperature in the range of 1000°C to 1300°C, and essentially only hydrogen is introduced into the process chamber. The total pressure is 50 mbar to 900 mbar, preferably about 100 mbar, and 10 to 100 slm of H2 is introduced into the process chamber for about 10 to 60 minutes. This converts the GaN deposited on the process chamber walls to NH3. Any silicon oxide layer present is reduced. Optionally, in a second cleaning step, other metal components are removed from the surface. This step is performed at a low pressure, preferably less than 100 mbar. The susceptor temperature here is 800°C to 900°C. During this step, Cl2 and N2 can be supplied to the process chamber. During this decomposition step, the metals react to form volatile chlorides, which are exhausted through the gas outlet.

[0017] The method according to the present invention also has an advantage over the previously described method of pretreating the silicon substrate with an organometallic compound, e.g., an organometallic aluminum compound, at low temperatures, because it does not require time-consuming cooling of the process chamber to temperatures below 750° C. after removing the oxide layer from the surface of the silicon substrate at temperatures above 1000° C. Therefore, the method of the present invention also reduces cycle time. [Brief explanation of the drawings]

[0018] The invention will now be explained in more detail with reference to exemplary embodiments and with reference to the accompanying drawings. [Figure 1] FIG. 1 shows a schematic diagram of a CVD reactor. DETAILED DESCRIPTION OF THE INVENTION

[0019] The CVD reactor 7 has an airtight housing within which a gas inlet member 1 is provided, by means of which process gases 9, 10, including various reactive gases, supplied by a gas supply system 15, can be introduced into the process chamber 2.

[0020] The process chamber 2 contains a susceptor 4 which can be heated to the process temperature from below by a heating device 3. The decomposition products are exhausted from the process chamber by a gas outlet member 5. The decomposition products can be directed to a gas cleaning system 16.

[0021] A controller 17 is provided which is capable of controlling valves and mass flow controllers (not shown) for introducing gases from gas sources 8 , 9 , 10 , 11 , 13 into the process chamber 2 .

[0022] For the purpose of depositing a III-V layer on a silicon substrate, the process chamber 2 is first prepared for processing and a first cleaning step is performed to remove metal residues remaining on the surface of the walls of the process chamber 2 from the previous process. This is done without the presence of a substrate 6 inside the process chamber 2. Chlorine or ammonia, or ammonia followed by chlorine, can be supplied to the process chamber 2.

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

[0024] Hydrogen is supplied to the process chamber to remove oxides from the surface of the substrate, although this pretreatment process, i.e., the process of removing oxides from the surface of the silicon substrate, can also be performed in a separate process chamber from which the substrate is removed and brought into the cleaned process chamber.

[0025] Next, a carbon-containing gas, such as an alkane, is supplied to the process chamber through the gas inlet member 5. The carbon in the carbon-containing gas reacts with the substrate surface at temperatures above 970°C, preferably in the range of 970°C to 1000°C, to form a SiC monolayer. The reaction takes 4 to 10 seconds. The flow rate of the carbon-containing gas is 66 sccm or greater, which saturates the substrate surface. For a total hydrogen flow rate of approximately 180 slm (i.e., approximately 8 mol / min), the ethylene flow rate should be 0.5 to 50 mmol / min. The C2H4 concentration in H2 should be 0.006 to 0.6% (60 to 6000 ppm) when the pressure in the process chamber is 35 to 300 mbar.

[0026] Immediately after, or while the carbon-containing gas is still being supplied to the process chamber, a process gas consisting of an organometallic aluminum compound and ammonia, along with an inert gas (e.g., hydrogen, nitrogen, or a noble gas), is supplied through the gas inlet member 5 to the process chamber 2, forming an AlN layer on the SiC monolayer, which can be done at the same temperature.

[0027] The process chamber 2 is then purged with an inert gas or further layers are deposited, in particular one layer of the subsequently deposited layer sequence containing gallium, in particular a GaN layer.

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

[0029] Prior to the introduction of a gas containing a metal, particularly a group III metal, a carbon-containing, metal-free reactive gas is supplied to the process chamber, where it reacts with the silicon surface of the substrate to convert it. Furthermore, it is important that the substrate be heated in a metal-free environment, which requires prior cleaning of the substrate environment using an appropriate method. The gas supply system 15 can include a cleaning gas source 8, e.g., a chlorine-containing gas; a process gas source 9, e.g., a gallium-containing gas; an additional process gas source 10, e.g., a nitrogen-containing gas; and a carbon-containing gas source 11. The gases are supplied via supply lines to the process chamber 2, where they undergo a chemical reaction. Reaction products 12 are generated and sent to a gas cleaning system 16 through a gas outlet.

[0030] This is particularly advantageous in industrial production processes where the same layer sequence is deposited multiple times in succession in the process chamber 2, at least one of the layer sequences containing gallium, which is deposited on the surfaces of the process chamber 2 during the deposition process. Any gallium remaining in the process chamber is removed by rinsing the process chamber before each deposition process. This prevents the formation of gallium gas, which may have a corrosive effect on the silicon surface of the substrate, when the process chamber 2 is heated in the presence of the substrate 6.

[0031] The foregoing describes the inventions contained in this application as a whole, each of which independently advances the prior art by at least one combination of the following features, and which may combine any two, more, or all of these feature combinations:

[0032] 1. A method for depositing a layer of main group III and V elements on a silicon substrate, comprising: a. providing a CVD reactor R having a gas inlet member 1 for introducing a reaction gas into a process chamber 2 of the CVD reactor, the CVD reactor R having a heating device 3 capable of heating a susceptor 4 to a high temperature and a gas outlet member 5 capable of discharging decomposition products of the process gas from the process chamber 2; b. providing a cleaning gas 8 having properties that chemically react with metal residues on the surfaces of the process chamber 2 at a cleaning temperature to produce a gas containing the metal residues; c. providing a carbon-containing reaction gas 11 that does not contain any metals; d. Providing a first gaseous starting material 9 comprising a main group III element and a second gaseous starting material 10 comprising a main group V element; e. heating the surfaces of the process chamber 2 that do not contain a substrate and have metal residues on their surfaces to a cleaning temperature TR; f. introducing a cleaning gas 8 into the process chamber 2 to remove metal residues by generating a gas 12 containing the metal residues and removing this gas through the gas outlet member 5; g. purging the process chamber 2 with an inert gas 13; h. loading at least one silicon substrate 6 onto the susceptor 4; i. heating the substrate to a first elevated temperature T1; j. introducing a carbon-containing reactive gas 11 into the process chamber 2 to chemically react the carbon-containing gas 11 with the Si surface of the substrate 6, thereby forming a SiC surface; k. heating the substrate to a second elevated temperature T2; l. depositing a III-V layer on the SiC surface by introducing first and second gaseous starting materials 9, 10 into the process chamber 2; All steps are performed consecutively in the same process chamber 2, with steps j, k, and l being performed immediately one after the other.

[0033] A method characterized in that, before the formation of the SiC surface (step j), hydrogen is supplied to a separate process chamber 2 or to the same process chamber 2 in which the substrate 6 is placed, and then this process chamber 2 containing hydrogen is heated to a third elevated temperature T3.

[0034] A method characterized in that the first reaction starting material 9 is an organometallic compound, or an organometallic gallium compound, or an aluminum compound, and the second reaction starting material 10 is a hydride or NH3.

[0035] The method is characterized in that the carbon-containing reaction gas 11 is a hydrocarbon or is C2H4.

[0036] The method is characterized in that the cleaning gas (8) contains ammonia or chlorine, and the cleaning temperature is 1000°C to 1300°C.

[0037] 1. A method according to claim 1, wherein the SiC surface is formed at a first temperature T1 of 950°C to 1050°C or 970°C to 1000°C, and the introduction of the carbon-containing reactive gas is continued until the Si surface of the substrate is completely saturated with SiC, or the duration of the introduction is at least 2 seconds or 4 to 10 seconds.

[0038] The method is characterized in that the deposition of the III-V layer is carried out at a temperature between 1000°C and 1060°C.

[0039] The method is characterized in that the second elevated temperature T2 corresponds to the first elevated temperature T1, and steps j and l are performed in immediate succession.

[0040] The method is characterized in that the introduction of the first and second gaseous starting materials (9, 10) occurs immediately after the introduction of the carbon-containing reactive gas (11) into the process chamber (2), so that the carbon-containing gas (11) is present in the process chamber (2) at the start of deposition of the layer.

[0041] The method is characterized in that the carbon-containing reactant gas 11 is introduced at a total molar flow rate of less than 15 μmol / min and / or the partial molar flow rate of the carbon-containing reactant gas 11 is less than 0.3% of the total molar flow rate.

[0042] 10. The method of claim 1, wherein steps j, k, and l are performed at a process chamber pressure of at least 25 mbar and at most 800 mbar, or at least 35 mbar and at most 75 mbar, or at least 35 mbar and at most 145 mbar.

[0043] All disclosed features are essential to the invention (both by themselves and in combination with one another). The disclosure of the present application incorporates in its entirety the disclosures of the relevant / additional priority documents (copies of earlier applications), with the aim of incorporating the features of these documents into the claims of the present application. The dependent claims are characterized by independent, inventive further developments of the prior art, even without the features of the claims cited therein, in particular for the purpose of filing a divisional application based on these claims. The invention specified in each claim may additionally have one or more features specified in the preceding description, in particular those given reference signs and / or specified in the sign explanations. The present invention also relates in particular to design forms in which individual features set out in the preceding description are not implemented, insofar as they are clearly unnecessary for the respective intended use or can be replaced by other means having the same technical effect. [Explanation of symbols]

[0044] 1 Gas inlet member 2. Process chamber 3 Heating device 4 susceptor 5 Gas outlet member 6 PCB 7 CVD reactor 8 Cleaning gas source 9 Process Gas Source III 10 Process gas source V 11 Sources of carbon-containing gases 12 Residual gas 13 Inert gas source 15 Gas Supply System 16 Gas Purification System 17 Control Unit R CVD reactor TR Wash Temperature T1 First temperature T2 Second temperature T3 Third temperature

Claims

1. 1. A method for depositing a layer of main group III and V elements on a silicon substrate, comprising: a) providing a CVD reactor (R) having a gas inlet member (1) for supplying a reactive gas to a process chamber (2) of the CVD reactor, the CVD reactor (R) having a heating device (3) capable of heating a susceptor (4) to a high temperature, and a gas outlet member (5) capable of exhausting decomposition products of the process gas from the process chamber (2); b. providing a cleaning gas (8) having properties to chemically react with metal-containing and III and V main group compound residues, such as GaN or AlN, on the surfaces of the process chamber (2) at a cleaning temperature to produce a gas (12) containing said residues; c. Providing a carbon-containing reaction gas (11) that is free of any metals; d. Providing a first gaseous starting material (9) containing a main group III element and a second gaseous starting material (10) containing a main group V element; e. Heating the surfaces of the process chamber (2) to a cleaning temperature (TR); f. introducing said cleaning gas (8) into said process chamber (2) to remove said residues by producing said gas (12) containing said residues and removing said gas (12) through said gas outlet member (4); g. purging the process chamber (2) with an inert gas (13); h. Loading at least one substrate (6) made of silicon onto said susceptor (4); i. heating the substrate to a first elevated temperature (T1); j) introducing the carbon-containing reactive gas (11) into the process chamber (2) to chemically react the carbon-containing gas (11) with the Si surface of the substrate (6) to form a SiC surface; k. heating the substrate to a second elevated temperature (T2); l. depositing a III-V layer on the SiC surface by introducing the first and second gaseous starting materials (9, 10) into the process chamber (2); A method in which all steps are performed sequentially in the same process chamber (2), with steps j, k, and l being performed immediately following one another.

2. 2. The method according to claim 1, characterized in that before the formation of the SiC surface (step j), hydrogen is supplied to a separate chamber or to the same process chamber (2) in which the substrate (6) is placed, and then this process chamber (2) containing hydrogen is heated to a third temperature (T3).

3. The first reactive starting material (9) is an organometallic compound, an organometallic gallium compound, or an aluminum compound, and the second reactive starting material (10) is a hydride or NH ３ 3. The method according to claim 1 or 2, wherein

4. The carbon-containing reaction gas (11) is a hydrocarbon, or ２ H ４ The method according to any one of claims 1 to 3, wherein

5. 5. The method according to any one of claims 1 to 4, wherein the cleaning gas (8) contains ammonia or a halogen, and the cleaning temperature is between 1000°C and 1300°C.

6. 6. The method according to claim 1, wherein the SiC surface is formed at a first temperature (T1) of 950°C to 1050°C, or 970°C to 1000°C, and the introduction of the carbon-containing reactive gas lasts until the Si surface of the substrate is fully saturated with SiC, or the duration of the introduction is at least 2 seconds, or 4 to 10 seconds.

7. The method according to any of the preceding claims, wherein the deposition of the III-V layer is carried out at a temperature between 1000°C and 1100°C, or between 1000°C and 1060°C.

8. 8. A method according to any one of claims 1 to 7, characterized in that the second elevated temperature (T2) coincides with the first elevated temperature (T1) and steps j and l are carried out in immediate succession.

9. 9. The method according to claim 1, wherein the introduction of the first and second gaseous starting materials (9, 10) takes place immediately after the introduction of the carbon-containing reaction gas (11) into the process chamber (2), so that the carbon-containing reaction gas (11) is present in the process chamber (2) at the start of deposition of the layer.

10. 10. The method according to any one of claims 1 to 9, characterized in that the carbon-containing reaction gas (11) is introduced at a total molar flow rate of 15 mmol / min.

11. 11. A method according to any one of claims 1 to 10, characterized in that the partial molar flow rate of the carbon-containing reaction gas (11) is less than 0.3% of the total molar flow rate.

12. 12. The method of any one of claims 1 to 11, wherein steps j, k, l of claim 1 are performed at a process chamber pressure of at least 25 mbar and at most 800 mbar, or at least 35 mbar and at most 75 mbar, or at least 35 mbar and at most 145 mbar.

13. A method characterized by one or more of the features according to any one of the preceding claims.

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