Method for depositing crystalline semiconductors onto a substrate

Abstract

The invention relates to a method for depositing crystalline semiconductors onto a substrate. In the method, a voltage is applied between a metal sputtering target and an anode of a magnetron sputtering system in order to ignite a magnetron discharge, during which a particle flow from the sputtering target to the substrate takes place and the reactive gas is excited to form a first amount of activated reactive-gas plasma, wherein a crystalline semiconductor epitaxially grows on the substrate. In the method, during the deposition of a semiconductor on the substrate an additional power feed into the reactive-gas plasma is implemented, by means of which the reactive gas is excited to form a second amount of activated reactive-gas plasma which is greater than the first amount of activated reactive-gas plasma but which has the result that the particle flow from the sputtering target to the substrate remains the same or increases only less than proportionally to the increase from the first amount of activated reactive-gas plasma to the second amount of activated reactive-gas plasma.

Description

[0001] Fraunhofer Society...eV

[0002] P149799PC00

[0003] Method for depositing crystalline semiconductors onto a substrate

[0004] A method for depositing crystalline semiconductors onto a substrate is provided. In this method, an electrical voltage is applied between a metallic sputtering target and the anode of a magnetron sputtering unit to trigger a magnetron discharge. This discharge causes a particle flux from the sputtering target to the substrate and excites the reactive gas to an initial quantity of activated reactive gas plasma, resulting in the epitaxial growth of a crystalline semiconductor on the substrate.In this process, during the deposition of a semiconductor onto the substrate, additional power is injected into the reactive gas plasma. This excites the reactive gas to produce a second quantity of activated reactive gas plasma, which is higher than the first. However, the particle flux from the sputtering target to the substrate remains constant or increases only disproportionately less than the increase in the second quantity of activated reactive gas plasma. There is a current need to deposit group III nitrides of the periodic table onto a substrate at high rates, using reactive PVD deposition in a single-crystal, epitaxial manner. Gallium is less reactive with a reactive gas (e.g., nitrogen, but also oxygen) during reactive deposition than aluminum. GaN has an enthalpy of formation of approximately -110 kJ / mol, and AIN has an enthalpy of formation of approximately...320 kJ / mol. Therefore, metallic gallium droplets can form on the substrate during reactive sputtering. This effect is more pronounced at technologically preferred substrate temperatures below 1000°C.

[0005] It is known that this droplet formation must be managed during growth. Furthermore, it is known that in all common epitaxy methods for GaN, gallium droplet formation on the substrate can be a problem depending on the substrate temperature.

[0006] To avoid this problem, it is known that increasing the substrate temperature causes additional gallium to evaporate from the substrate, resulting in layers of sufficient quality. However, this approach is technically inefficient because high growth rates cannot be achieved and the efficiency / yield decreases significantly. Furthermore, this measure does not allow deposition on substrates that are unstable at higher temperatures (e.g., temperatures above 800 °C). Similar problems are likely to occur with other material combinations if the reactivity between the metal and the reactive gas is too low.

[0007] Furthermore, limiting the gallium particle flux is known to avoid this problem. However, the disadvantage of this approach is that it limits the possible growth rates of crystalline semiconductor on the substrate, thus significantly slowing down the process.

[0008] Furthermore, to avoid this problem, it is known to increase the process reactivity, for example by using ammonia or hydrazine instead of nitrogen as the reactive gas. However, this in turn leads to the incorporation of hydrogen into the semiconductor layers. This effect is further amplified at the targeted growth temperatures of <800°C. Based on this, the object of the present invention is to provide a method and a system for depositing crystalline semiconductors onto a substrate that overcomes at least one disadvantage of the prior art. In particular, the method and the system should make it possible to prevent metal droplet formation on the substrate even at low growth temperatures (<800°C) and to produce crystalline semiconductor layers of high quality and / or high speed (i.e., high efficiency or yield per unit time).

[0009] The problem is solved by the method with the features of claim 1 and the system with the features of claim 8. The dependent claims describe advantageous further developments.

[0010] According to the invention, a method for depositing crystalline semiconductors onto a substrate is provided, comprising or consisting of the following steps: a) providing a magnetron sputtering system comprising a vacuum chamber, a gas source containing a noble gas and a reactive gas, a magnetron, wherein the magnetron is equipped with a metallic sputtering target suitable for chemically reacting with the reactive gas to form a semiconductor, an anode, wherein the anode is selected from the group consisting of a magnetron anode, the wall of the vacuum chamber, and combinations thereof, an electrical voltage source suitable for supplying an electrical voltage (e.g., a DC voltage, pulsed DC voltage, or AC voltage), and a substrate; b) applying an electrical voltage (e.g.,a DC voltage, pulsed DC voltage or AC voltage) between the metallic sputtering target and the anode via the electrical voltage source to trigger a magnetron discharge, in which a particle flow occurs from the sputtering target to the substrate and in which the reactive gas is excited to a first quantity of activated reactive gas plasma, wherein a semiconductor is deposited on the substrate such that the semiconductor grows epitaxially on the substrate to form a crystalline semiconductor; characterized in that during the deposition of a semiconductor on the substrate an additional power injection into the reactive gas plasma is realized, by which the reactive gas is excited to a second quantity of activated reactive gas plasma, wherein the sum of the first quantity of activated reactive gas plasma and the second quantity of activated reactive gas plasma is higher than the first quantity of activated reactive gas plasma, but by the (i.e.(due to the additional power input) the particle flux from the sputter target to the substrate remains the same or increases only disproportionately to the increase in the first amount of activated reactive gas plasma to the second amount of activated reactive gas plasma.

[0011] An activated reactive gas plasma is understood to mean, in particular, that the reactive gas in the plasma is present in dissociated form, ionized form, excited form and / or in radical form (or that the atoms or molecules of the reactive gas are present in said form).

[0012] The inventive method makes it possible to prevent droplet formation of metal on the substrate even at low growth temperatures (<800 °C) and to provide crystalline semiconductor layers with high quality and high speed.

[0013] The prevention of droplet formation is achieved by influencing the plasma via additional power injection. This power injection is additional because it is applied alongside the power used for the actual plasma discharge in the process. The additional power injection activates the reactive gas in the vacuum chamber in the gas phase, resulting in the generation of more activated reactive gas. This increased generation of activated reactive gas in the vacuum chamber reduces the reaction enthalpy of the metal (e.g., Ga) sputtered by the magnetron with the reactive gas (e.g., N₂) to form a semiconductor (e.g., GaN). This means that the formation of metal droplets on the substrate can be reduced or even completely prevented. Furthermore, virtually the entire metal particle stream reacts, which correspondingly increases the yield (rate) of the process compared to evaporating the metallic droplets.This allows for the production of high-quality crystalline semiconductor layers. Since the reduction or prevention of droplet formation also occurs at low substrate temperatures, high growth rates can be ensured, meaning the crystalline semiconductor layers can be produced on the substrate at high speed.

[0014] In the method according to the invention, the substrate is preferably heated to a temperature in the range of <1000 °C, preferably in the range of <800 °C.

[0015] The process can also be used to deposit a doped semiconductor onto the substrate.

[0016] In step a) of the process, a magnetron sputtering system can be provided which includes a vacuum pump, wherein the vacuum pump is preferably used to create a vacuum in the vacuum chamber before carrying out a reactive deposition, the pressure of which is in the range of < 1-10'6 Pa is located.

[0017] Furthermore, in step a) of the process, a magnetron sputtering system can be provided containing a gas source that includes argon as the noble gas and / or a reactive gas selected from the group consisting of nitrogen, ammonia, oxygen, and combinations thereof. The reactive gas can also contain hydrogen. Furthermore, the reactive gas can be free of molecules or atoms containing or consisting of hydrogen. The advantage of this is that it ensures the deposition of a hydrogen-free, crystalline semiconductor layer on the substrate.

[0018] Furthermore, in step a) of the process, a magnetron sputtering system can be provided, which contains a magnetron configured as a double-ring magnetron. Here, a double-ring magnetron is understood to be an embodiment of the magnetron that has two concentrically arranged, galvanically isolated target rings. Its metallic sputtering target preferably consists of gallium and / or aluminum; optionally, all metallic sputtering targets of the magnetron consist of gallium and / or aluminum.

[0019] Apart from that, in step a) of the method a magnetron sputtering system can be provided which includes an electrical voltage source suitable for supplying an electrical voltage in the range of 100 to 400 volts, wherein the electrical voltage preferably has a frequency in the range of up to 100 kHz (i.e., is an alternating voltage or a pulsed direct voltage).

[0020] In this method, the additional power input can be provided via the electrical voltage source (of the magnetron sputtering system), preferably with an additional electrical voltage (e.g., alternating current or pulsed direct current) coupled into the electrical voltage source. This additional voltage has a higher frequency than the electrical voltage applied between the magnetron and the substrate for depositing a semiconductor onto the substrate. The higher frequency is, in particular, a frequency in the range of > 13.56 MHz. This embodiment has the advantage of being particularly cost-effective, as no separate plasma source is required for the additional power input and excitation of the reactive gas (i.e., for influencing the plasma).

[0021] Furthermore, the additional power input can be provided (alternatively or additionally) via a separate plasma source that is different from the magnetron. The separate plasma source is preferably selected from the group consisting of ion sources, microwave plasma sources, RF plasma sources, hollow cathode sources and combinations thereof, wherein the RF plasma source is preferably an ICP-excited RF plasma source or a CCP-excited RF plasma source.

[0022] The metallic sputtering target can consist of a metal selected from the group consisting of gallium, aluminium and combinations thereof, with the metal preferably being gallium.

[0023] The magnetron sputtering system provided in step a) may include a temperature control device for tempering the substrate. The substrate can be tempered to a temperature of < 800 °C by the temperature control device.

[0024] The magnetron sputtering system provided in step a) can include a detector suitable for detecting metal droplets on the substrate. In this process, the detector is preferably used for detecting metal droplets on the substrate.

[0025] In a preferred embodiment of the method, the level of additional power input is regulated based on at least one detection signal from the detector. This control loop (i.e., feedback mechanism) ensures that no metal droplets (e.g., gallium droplets) form on the substrate.

[0026] The detector can be selected from the group consisting of optical emission detector, optical transmission detector, optical reflection detector and combinations thereof, wherein the detector is in particular a combination of optical transmission detector and optical reflection detector.

[0027] According to the invention, a system for depositing crystalline semiconductors onto a substrate is further provided, comprising or consisting of: a) a magnetron sputtering system comprising a vacuum chamber, a gas source containing a noble gas and a reactive gas, a magnetron, wherein the magnetron is equipped with a metallic sputtering target suitable for chemically reacting with the reactive gas to form a semiconductor, an anode, wherein the anode is selected from the group consisting of a magnetron anode, the wall of the vacuum chamber and combinations thereof, an electrical voltage source suitable for supplying an electrical voltage (e.g., a DC voltage, pulsed DC voltage or AC voltage), a substrate; b) a control unit;wherein the control unit is configured to cause the electrical voltage source to apply an electrical voltage (e.g. a DC voltage, pulsed DC voltage or AC voltage) between the metallic sputtering target and the anode to trigger a magnetron discharge, in which a particle flux from the sputtering target to the substrate occurs and in which the reactive gas is excited to an initial amount of activated reactive gas plasma, such that a semiconductor is deposited on the substrate in such a way that the semiconductor grows epitaxially on the substrate to form a crystalline semiconductor;characterized in that the control unit is configured to cause an additional power injection into the reactive gas plasma during the deposition of a semiconductor on the substrate, whereby the reactive gas is excited to a second quantity of activated reactive gas plasma, wherein the sum of the first quantity of activated reactive gas plasma and the second quantity of activated reactive gas plasma is higher than the first quantity of activated reactive gas plasma, but through the (i.e., through the additional power injection) the particle flux from the sputtering target to the substrate remains the same or increases only disproportionately less than the increase in the first quantity of activated reactive gas plasma to the second quantity of activated reactive gas plasma.

[0028] With the system according to the invention, it is possible to prevent droplet formation of metal suitable for chemical reaction with a reactive gas to form a semiconductor on the substrate, even at low growth temperatures (<800 °C), and to provide crystalline semiconductor layers with high quality and high speed.

[0029] The control unit of the system according to the invention can be configured (e.g., a heating element of the system according to the invention) to heat the substrate to a temperature in the range of <1000 °C, preferably in the range of <800 °C.

[0030] The system can deposit a doped semiconductor onto the substrate. The magnetron sputtering unit of the system can include a vacuum pump. The control unit is preferably configured to cause the vacuum pump to establish a vacuum in the vacuum chamber before performing reactive deposition, with a pressure in the range of < 1 10 -6 Pa is located.

[0031] Furthermore, the magnetron sputtering unit of the plant may contain a gas source containing argon as the noble gas and / or a reactive gas selected from the group consisting of nitrogen, ammonia, oxygen, and combinations thereof. The reactive gas may also contain hydrogen. Furthermore, the reactive gas may be free of molecules or atoms containing or consisting of hydrogen.

[0032] Apart from that, the magnetron sputtering system of the plant can contain a magnetron designed as a double-ring magnetron, wherein its metallic sputtering target preferably consists of gallium and / or aluminium, optionally all metallic sputtering targets of the magnetron consist of gallium and / or aluminium.

[0033] Furthermore, the magnetron sputtering system of the plant may include an electrical voltage source suitable for supplying an electrical voltage in the range of 100 to 400 volts, wherein the electrical voltage preferably has a frequency in the range of up to 100 kHz (i.e., is a pulsed DC voltage or an AC voltage).

[0034] The control unit of the system can be configured to supply the additional power via the electrical voltage source, with the control unit preferably being configured to couple an additional electrical voltage (e.g., alternating current or pulsed direct current) into the electrical voltage source, which has a higher frequency than the electrical voltage applied between the magnetron and the substrate for depositing a semiconductor onto the substrate. The higher frequency is, in particular, a frequency in the range of > 13.56 MHz.

[0035] Furthermore, the system can include a separate plasma source, distinct from the system's magnetron (as the primary plasma source), and the system's control unit can be configured to supply additional power via the separate plasma source. The separate plasma source is preferably selected from the group consisting of ion sources, microwave plasma sources, RF plasma sources, hollow cathode sources, and combinations thereof, wherein the RF plasma source is preferably an ICP-excited RF plasma source or a CCP-excited RF plasma source.

[0036] The metallic sputtering target can consist of a metal selected from the group consisting of gallium, aluminium and combinations thereof, with the metal preferably being gallium.

[0037] The magnetron atomization system of the plant may include a temperature control device for temperature control of the substrate, wherein the control unit of the plant may be configured to cause the temperature control device to temperature the substrate to a temperature of < 800 °C.

[0038] Furthermore, the magnetron sputtering system of the plant can include a detector suitable for detecting metal droplets on the substrate, wherein the control unit is preferably configured to cause the detector to detect metal droplets on the substrate.

[0039] In a preferred embodiment, the control unit of the system is configured to regulate the level of additional power input based on at least one detection signal from the detector (i.e., to establish a control loop).

[0040] The detector can be selected from the group consisting of optical emission detector, optical transmission detector, optical reflection detector and combinations thereof, wherein the detector is in particular a combination of optical transmission detector and optical reflection detector.

[0041] The system can be configured to carry out the method according to the invention. Preferably, the control unit of the system is configured to initiate the execution (of steps) of the method according to the invention.

Claims

Fraunhofer Society...eV P149799PC00 Patent claims 1. A method for depositing crystalline semiconductors onto a substrate, comprising or consisting of the following steps: a) providing a magnetron sputtering apparatus comprising a vacuum chamber, a gas source containing a noble gas and a reactive gas, a magnetron wherein the magnetron is equipped with a metallic sputtering target suitable for chemically reacting with the reactive gas to form a semiconductor, an anode wherein the anode is selected from the group consisting of a magnetron anode, a wall of the vacuum chamber and combinations thereof, an electrical voltage source suitable for supplying an electrical voltage, a substrate;b) Applying an electrical voltage between the metallic sputtering target and the anode via the electrical voltage source to trigger a magnetron discharge, in which a particle flow occurs from the sputtering target to the substrate and in which the reactive gas is excited to a first quantity of activated reactive gas plasma, wherein a semiconductor is deposited on the substrate in such a way that the semiconductor grows epitaxially on the substrate to form a crystalline semiconductor; characterized in that an additional power input into the reactive gas plasma is realized during the deposition of a semiconductor on the substrate; - by which the reactive gas is excited to a second quantity of activated reactive gas plasma, wherein a sum of the first quantity of activated reactive gas plasma and the second quantity the amount of activated reactive gas plasma is higher than the first amount of activated reactive gas plasma, but - through which the particle flux from the sputter target to the substrate remains the same or increases only disproportionately to the increase of the first amount of activated reactive gas plasma to the second amount of activated reactive gas plasma.

2. Method according to the preceding claim, characterized in that in step a) a magnetron sputtering system is provided which i) includes a vacuum pump, wherein the vacuum pump is preferably used to create a vacuum in the vacuum chamber prior to carrying out a reactive deposition, the pressure of which is in the range of < 1 10 -6Pa; and / or ii) contains a gas source containing argon as the noble gas and / or containing as the reactive gas a gas selected from the group consisting of nitrogen, ammonia, oxygen and combinations thereof, wherein optionally the reactive gas additionally contains hydrogen or is free of molecules or atoms containing or consisting of hydrogen; and / or iii) contains a magnetron configured as a double-ring magnetron, wherein its metallic sputtering target preferably consists of gallium and / or aluminum, optionally all metallic sputtering targets of the magnetron consist of gallium and / or aluminum; and / or iv) contains an electrical voltage source suitable for supplying an electrical voltage in the range of 100 to 400 volts, wherein the electrical voltage preferably has a frequency in the range of up to 100 kHz.

3. Method according to one of the preceding claims, characterized in that the additional power supply is provided via the electrical voltage source, wherein preferably an additional electrical voltage is coupled into the electrical voltage source. is a frequency higher than the electrical voltage applied between the magnetron and the substrate for depositing a semiconductor on the substrate, wherein the higher frequency is in particular a frequency in the range of > 13.56 MHz.

4. Method according to one of the preceding claims, characterized in that the additional power input is provided via a separate plasma source which is different from the magnetron, wherein the separate plasma source is preferably selected from the group consisting of ion source, microwave plasma source, RF plasma source, hollow cathode sources and combinations thereof, wherein the RF plasma source is preferably an ICP-excited RF plasma source or CCP-excited RF plasma source.

5. Method according to one of the preceding claims, characterized in that the metallic sputtering target consists of a metal selected from the group consisting of gallium, aluminium and combinations thereof, wherein the metal is preferably gallium.

6. Method according to one of the preceding claims, characterized in that the magnetron sputtering system includes a temperature control device for temperature control of the substrate, wherein the substrate is temperature-controlled to a temperature of < 800 °C by the temperature control device.

7. A method according to any of the preceding claims, characterized in that the magnetron sputtering system includes a detector suitable for detecting metal droplets on the substrate, wherein the detector is preferably used for detecting metal droplets on the substrate, and particularly preferably i) the level of additional power input is regulated based on at least one detection signal from the detector; and / or ii) the detector is selected from the group consisting of optical emission detector, optical transmission detector, optical reflection detector and combinations thereof, wherein the detector is in particular a combination of optical transmission detector and optical reflection detector.

8. Apparatus for the deposition of crystalline semiconductors on a substrate, comprising or consisting of: a) a magnetron sputtering apparatus comprising a vacuum chamber, a gas source containing a noble gas and a reactive gas, a magnetron, wherein the magnetron is equipped with a metallic sputtering target suitable for chemically reacting with the reactive gas to form a semiconductor, an anode, wherein the anode is selected from the group consisting of a magnetron anode, a wall of the vacuum chamber and combinations thereof, an electrical voltage source suitable for supplying an electrical voltage, a substrate; b) a control unit;wherein the control unit is configured to cause the electrical voltage source to apply an electrical voltage between the metallic sputtering target and the anode to trigger a magnetron discharge, in which a particle flux from the sputtering target to the substrate occurs and in which the reactive gas is excited to a first quantity of activated reactive gas plasma, such that a semiconductor is deposited on the substrate in such a way that the semiconductor grows epitaxially on the substrate to form a crystalline semiconductor; characterized in that the control unit is configured to cause an additional power input into the reactive gas plasma during the deposition of a semiconductor on the substrate; - by which the reactive gas is excited to a second quantity of activated reactive gas plasma, wherein the sum of the first quantity of activated reactive gas plasma and the second quantity of activated reactive gas plasma is higher than the first quantity of activated reactive gas plasma, but - through which the particle flux from the sputter target to the substrate remains the same or increases only disproportionately to the increase of the first amount of activated reactive gas plasma to the second amount of activated reactive gas plasma.

9. System according to claim 8, characterized in that the magnetic ron demineralization system i) includes a vacuum pump, wherein the control unit is preferably configured to cause the vacuum pump to establish a vacuum in the vacuum chamber prior to performing a reactive deposition, the pressure of which is in the range of < 1-10 6Pa; and / or ii) contains a gas source containing argon as the noble gas and / or a reactive gas selected from the group consisting of nitrogen, ammonia, oxygen and combinations thereof, wherein the reactive gas optionally also contains hydrogen; and / or iii) contains a magnetron configured as a double-ring magnetron, wherein its metallic sputtering target preferably consists of gallium and / or aluminum, optionally all metallic sputtering targets of the magnetron consist of gallium and / or aluminum; and / or iv) contains an electrical voltage source suitable for supplying an electrical voltage in the range of 100 to 400 volts, wherein the electrical voltage preferably has a frequency in the range of up to 100 kHz.

10. System according to one of claims 8 or 9, characterized in that the control unit of the system is configured to provide additional Power is supplied via the electrical voltage source, wherein the control unit is preferably configured to couple an additional electrical voltage into the electrical voltage source, which has a higher frequency than the electrical voltage applied between the magnetron and the substrate for depositing a semiconductor on the substrate, wherein the higher frequency is in particular a frequency in the range of > 13.56 MHz.

11. System according to one of claims 8 to 10, characterized in that the system includes a separate plasma source which is different from the magnetron of the system, wherein the control unit of the system is configured to allow the additional power input via the separate plasma source, wherein the separate plasma source is preferably selected from the group consisting of ion source, microwave plasma source, RF plasma source, hollow cathode sources and combinations thereof, wherein the RF plasma source is preferably an ICP-excited RF plasma source or a CCP-excited RF plasma source.

12. Plant according to one of claims 8 to 11, characterized in that the metallic sputtering target consists of a metal selected from the group consisting of gallium, aluminium and combinations thereof, wherein the metal is preferably gallium.

13. Plant according to one of claims 8 to 12, characterized in that the magnetron atomizing plant includes a temperature control device for temperature control of the substrate, wherein the control unit of the plant is configured to cause the temperature control device to temperature the substrate to a temperature of < 800 °C.

14. System according to any one of claims 8 to 13, characterized in that the magnetron sputtering system includes a detector suitable for detecting metal droplets on the substrate, wherein the control unit is preferably configured to cause the detector to detect metal droplets on the substrate and particularly preferably i) the control unit is configured to regulate the level of additional power input based on at least one detection signal from the detector; and / or ii) the detector is selected from the group consisting of optical emission detector, optical transmission detector, optical reflection detector and combinations thereof, wherein the detector is in particular a combination of optical transmission detector and optical reflection detector.

15. Plant according to one of claims 8 to 14, characterized in that the plant is configured to carry out the method according to one of claims 1 to 7, wherein preferably the control unit of the plant is configured to initiate the execution of the method according to one of claims 1 to 7.