SUBSTRATE RECLAIMING METHOD AND SiC SUBSTRATE RECLAIMING METHOD

Abstract

To provide a substrate reclaiming method for a wafer for manufacturing a semiconductor device, in which a gallium compound layer is laminated on a substrate, in which a substrate is reclaimed by removing the gallium compound layer by plasma etching without mechanical blasting, grinding, or polishing, which would introduce a damaged layer, and a SiC substrate reclaiming method.SOLUTION: A method for reclaiming a semiconductor device manufacturing wafer 100 having a single or multiple gallium compound layers 102, 103 stacked on a substrate 101 includes the steps of generating a plasma based on an etching gas consisting of a carrier gas and hydrogen gas, or a process gas to which an oxidizing gas having an effect of oxidizing metallic gallium has been added, and removing the entire gallium compound layer by plasma etching when the gallium compound layer is a single layer, or removing the entire layer or an upper portion when the gallium compound layer is multiple layers, and a cleaning step for removing any deposits adhering to the substrate surface.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present invention relates to a method for regenerating a substrate of a wafer for manufacturing a semiconductor device in which a gallium compound layer is formed on a substrate, and a method for regenerating a SiC substrate.

Background Art

[0002] GaN becomes a device with excellent high-power and high-frequency characteristics and is mainly used as a device for communication base stations and satellites. Further, GaN is used as a semiconductor material such as a light-emitting diode (LED), a laser diode (LD), and a power device used for power conversion. When using a currently mainstream GaN on Si (hereinafter, referred to as "GaN / Si" in the specification) wafer, while it is inexpensive, the defect density of the epitaxial GaN layer tends to be high due to the misfit of the lattice constants of Si and GaN, and good device characteristics cannot be obtained. On the other hand, in the case of a GaN on SiC (hereinafter, referred to as "GaN / SiC" in the specification) wafer, while the SiC substrate is expensive, the lattice constants of GaN and SiC are close, and an epitaxial GaN layer with few defects can be obtained, so a high-performance device can be obtained.

[0003] In GaN-HEMT, since defects and dislocations in the epitaxial GaN layer greatly affect device characteristics, it is necessary to form the GaN layer with a low defect density. Therefore, in the GaN / SiC wafer used for GaN-HEMT, an epitaxial GaN layer is actually formed on the SiC substrate via a buffer layer for gradually matching the lattice constants. Here, AlGaN or the like is used for the buffer layer.

[0004] When mass-producing semiconductor devices using GaN / SiC wafers, a large number of used GaN / SiC wafers are generated in the prototype production for optimizing device manufacturing equipment prior to mass production. Also, a certain amount of defective products are generated during the mass production process due to the yield. Of course, defective products also occur during the manufacturing process and transportation process of GaN / SiC wafers. Recycling these unusable GaN / SiC wafers, especially recycling the SiC substrates, is important for reducing manufacturing costs.

[0005] The conventional method for recycling GaN / SiC wafers is carried out in the following steps. (1) Grind and polish to remove the GaN layer and the buffer layer. At this time, about 5 to 10 μm of the SiC substrate is also cut off. (2) Finish the rough SiC surface to about Ra 0.2 nm by lapping and polishing. In this case, plasma etching may be combined to remove mechanical damage. (3) Deposit a buffer layer on the polished SiC surface. (4) Deposit an epitaxial GaN layer on the buffer layer. Usually, the processes up to (1) and (2) are referred to as the recycling of the SiC substrate.

[0006] Specifically, Patent Document 1 discloses a method for recycling a substrate of a semiconductor device wafer in which a group III nitride compound semiconductor layer such as GaN is formed on a SiC substrate or a sapphire substrate via a buffer layer. After removing the stacked semiconductor layer including the buffer layer by a blasting process, heat treatment is performed at about 1400 °C, and further polishing is carried out. Also, Patent Document 2 discloses a method for recycling a SiC substrate having a nitride layer formed on the surface side. By polishing the surface side of the SiC substrate using a polishing pad while supplying an acidic polishing liquid to remove the nitride layer, it is said that deep damage such as blasting is not introduced. However, since both methods involve mechanical processing such as blasting and polishing steps, a mechanical damage layer is introduced into the substrate, whether large or small, and the crystal structure is disturbed. Therefore, an additional process for removing the damage layer is required, inevitably increasing the man-hours and also increasing the removal amount of the SiC substrate.

Prior Art Documents

Patent Documents

[0007] Patent Document 1 Japanese Patent Application Laid-Open No. 2011-086672 Patent Document 2 Japanese Patent Application Laid-Open No. 2021-077757 Summary of the Invention Problems to be Solved by the Invention

[0008] Therefore, in view of the above situation, the problem to be solved by the present invention is to provide a substrate regeneration method and a SiC substrate regeneration method for a semiconductor device manufacturing wafer having a gallium compound layer laminated on a substrate, in which the gallium compound layer is removed by plasma etching to regenerate the substrate without performing mechanical blasting, grinding, or polishing that introduces a damage layer. Means for Solving the Problems

[0009] In order to solve the above problems, the present invention provides a substrate regeneration method and a SiC substrate regeneration method configured as follows.

[0010] [Configuration 1] A method for regenerating a SiC substrate in a semiconductor device manufacturing wafer having a single layer or a plurality of gallium compound layers laminated on a substrate (SiC / Si substrate) in which an epitaxial SiC layer is formed on a single crystal SiC substrate or a single crystal Si substrate, comprising: generating plasma based on an etching gas composed of a carrier gas and hydrogen gas, removing all of the gallium compound layer by plasma etching, and leaving only the SiC substrate or the SiC / Si substrate; a cleaning step of removing deposits adhering to the surface of the SiC substrate or the SiC / Si substrate; A method for regenerating a SiC substrate having the above steps.

[0011] [Configuration 2] The gallium compound layer has an epitaxial GaN layer on the uppermost layer, and between the substrate and the GaN layer, Al for matching the lattice constant x Ga (1-x) N (0 ≦ x ≦ 1) or In y Ga (1-y) has a buffer layer composed of N (0 ≦ y ≦ 1). The method for regenerating the SiC substrate according to Configuration 1.

[0012] [Configuration 3] Using the elements constituting the buffer layer as monitor elements, detecting the presence of free monitor elements during plasma etching with a spectroanalyzer, After the spectroanalyzer detects the monitor element, turning off the plasma when it is no longer detected or after a predetermined time from when it is no longer detected. The method for regenerating the SiC substrate according to Configuration 2.

[0013] [Configuration 4] On a substrate (SiC / Si substrate) on which an epitaxial SiC layer is formed on a single-crystal SiC substrate or a single-crystal Si substrate, Al x Ga (1-x) N (0 ≦ x ≦ 1) or In y Ga (1-y) Preparing a wafer for manufacturing a semiconductor device on which an epitaxial GaN layer is formed through a buffer layer composed of N (0 ≦ y ≦ 1), Generating plasma based on a process gas in which an oxidizing gas having an action of oxidizing metallic gallium is added to an etching gas composed of a carrier gas and hydrogen gas, and removing the GaN layer and the buffer layer by plasma etching, During plasma etching, detecting free Al or In with a spectroanalyzer, and turning off the plasma when the Al or In is no longer detected after being detected by the spectroanalyzer. A cleaning step of removing deposits adhering to the surface of the SiC substrate or SiC / Si substrate, The method for regenerating the SiC substrate having the above steps.

[0014] [Configuration 5] The oxidizing gas contains oxygen gas, water vapor, or both oxygen gas and water vapor, The method for regenerating the SiC substrate according to Configuration 4.

[0015] [Configuration 6] In the local plasma etching where the plasma generation region is smaller than the area of the GaN layer, in the step of removing the entire wafer surface by plasma etching by raster scanning, the plasma is turned off when Al or In is no longer detected by the spectroscopic analyzer in the entire path of the raster scan. The method for regenerating the SiC substrate according to Configuration 4 or 5.

[0016] [Configuration 7] Before the substrate is exposed, at least the supply of the oxidizing gas is stopped. The method for regenerating the SiC substrate according to Configuration 5.

[0017] [Configuration 8] A method for regenerating a substrate in a semiconductor device manufacturing wafer on which a single-layer or multiple-layer gallium compound layer is laminated, Generating plasma based on a process gas in which an oxidizing gas having an effect of oxidizing metallic gallium is added to an etching gas composed of a carrier gas and hydrogen gas, and removing all of the gallium compound layer when the gallium compound layer is a single layer, or removing all or the upper layer portion when the gallium compound layer is a multiple layer by plasma etching, A cleaning step of removing deposits adhering to the substrate surface, A substrate regeneration method having

[0018] [Configuration 9] The oxidizing gas contains oxygen gas, water vapor, or both oxygen gas and water vapor, The substrate regeneration method according to Configuration 8.

[0019] [Configuration 10] The substrate is any one of a single crystal SiC substrate, a substrate (SiC / Si substrate) having an epitaxial SiC layer formed on a single crystal Si substrate, a sapphire substrate, and a single crystal Si substrate, and the substrate regeneration method according to Configuration 8 or 9.

[0020] [Configuration 11] The gallium compound layer has an epitaxial GaN layer on the uppermost layer, and has a buffer layer for matching the lattice constants between the substrate and the GaN layer. The substrate regeneration method according to Configuration 10.

[0021] [Configuration 12] The buffer layer contains an element different from the substrate constituent element and the GaN layer constituent element, and this element is used as a monitor element. During plasma etching, the presence of the free monitor element is detected by a spectroscopic analyzer. When the spectroscopic analyzer detects the monitor element, the plasma is turned off. Alternatively, after the spectroscopic analyzer detects the monitor element and the detection stops, the plasma is turned off. The substrate regeneration method according to Configuration 11.

[0022] [Configuration 13] The gallium compound layer has at least an epitaxial GaN layer on the uppermost layer. The wafer for semiconductor device manufacturing has a layer structure composed of a plurality of layers with the substrate. When different elements exist in both compositions with the interface of the layer structure as the boundary to be left by plasma etching as the boundary, the end point of the plasma is detected using that element as a monitor element. The substrate regeneration method according to Claim 10.

[0023] [Configuration 14] The substrate is a single crystal SiC substrate or a SiC / Si substrate. The gallium compound layer has an epitaxial GaN layer on the uppermost layer. Before the substrate is exposed, at least the supply of the oxidizing gas is stopped. The substrate regeneration method described in Configuration 9.

Effects of the Invention

[0024] The substrate regeneration method of the present invention and the SiC substrate regeneration method thus formed have the following effects.

[0025] For the regeneration of the substrate of a wafer for manufacturing a semiconductor device having a gallium compound layer laminated on the substrate, the gallium compound layer is removed using hydrogen plasma etching without performing mechanical blasting, grinding, or polishing. Therefore, a damage layer is not introduced into the substrate, and the thickness of the substrate does not decrease. A high-quality regenerated substrate can be obtained, and effective utilization of resources can be achieved. In particular, when the substrate is an expensive SiC substrate, SiC / Si substrate, or sapphire substrate, the cost reduction effect in semiconductor device manufacturing is significant.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0027] The present invention is a method for regenerating a substrate of a wafer for semiconductor device manufacturing in which a single layer or a plurality of layers of gallium compound layers are laminated on a substrate. The method removes the gallium compound layer formed on the substrate by plasma etching using hydrogen plasma and regenerates the base substrate to a reusable state. The present invention does not use fluorine-based gases or chlorine-based gases, which have problems with safety and environmental impact, and it is possible to process gallium compounds by plasma etching with high efficiency.

[0028] A GaN wafer for semiconductor device manufacturing is provided with a buffer layer for taking lattice number consistency on a single-crystalline substrate, and an epitaxial layer of GaN is formed thereon. As the substrate, there are single-crystalline SiC, sapphire (Al 2 O 3 ), and single-crystalline Si. In the case of single-crystalline SiC, in addition to bulk SiC, a substrate (SiC / Si substrate) in which 3C-SiC(111) is heteroepitaxially grown on a single-crystalline Si substrate may also be used.

[0029] Specifically, a sapphire or SiC substrate is introduced into a growth furnace. First, AlN, AlGaN, and GaN low-temperature deposition layers of about several tens of nm are sequentially formed on this substrate as a buffer layer, and an epitaxial GaN layer is grown thereon. Note that the buffer layer can be represented as Al x Ga (1-x) N(0≦x≦1), and the composition gradually changes or changes stepwise from x = 1 to 0 from the underlying substrate. Also, as the buffer layer, there are In y Ga (1-y) N(0≦y≦1) and InAlN.

[0030] In the present invention, the gallium compound layer present on the substrate includes a buffer layer in addition to the uppermost GaN layer, which is a concept. Also, a wafer for manufacturing a semiconductor device provided with a single crystal GaP layer and a single crystal GaAs layer on the uppermost layer is also an object of the present invention.

[0031] Next, based on the embodiments shown in the accompanying drawings, the present invention will be described in more detail. FIG. 1 shows a plasma processing apparatus for carrying out the substrate regeneration method of the present invention. The present invention is not limited to the illustrated embodiments, and it can be configured with a processing apparatus for uniformly plasma etching the entire processing surface of the workpiece, or a plasma CVM (Chemical Vaporization Machining) apparatus for locally plasma etching a part of the processing surface of the workpiece to create an arbitrary shape.

[0032] Also, in this embodiment, atmospheric pressure plasma is used, but reduced pressure plasma may also be used. The pressure of the process gas of the present invention is in the range of several kPa to atmospheric pressure. Here, the "atmospheric pressure" includes a range of pressures slightly higher than atmospheric pressure when an atmospheric pressure release type plasma head is used because it is necessary to generate the flow of the process gas.

[0033] In this technology, in order to plasma etch a gallium compound, an etching gas is used which is a mixture of a carrier gas composed of a carrier gas such as He or Ar and hydrogen gas as a reaction gas. Incidentally, as a reaction product of the gallium compound, when a fluorine-based gas is used, GaF 3 (boiling point 1000 °C), when a chlorine-based gas is used, GaCl 3 (boiling point 201 °C), when hydrogen gas is used, Ga 2 H 6(Boiling point -50 °C) is generated. Thus, using hydrogen gas is advantageous because the reaction product volatilizes without heating the gallium compound. Here, although most of the gallium compound is removed outside the plasma by hydrogen plasma etching, in order to suppress a part of the volatilized gallium from aggregating to become metallic gallium, an oxidizing gas having an action of oxidizing metallic gallium may be added to the etching gas. Incidentally, since the etching rate of gallium oxide by hydrogen plasma is high, the adhesion of metallic gallium to the substrate is almost eliminated. As the oxidizing gas, oxygen gas (O 2 ), water vapor (H 2 O), hydrogen peroxide (H 2 O 2 ) is used.

[0034] The wafer (work W) for manufacturing a semiconductor device targeted in the present invention typically has a layer structure such as 2 μm thick GaN(0001) / 1.5 μm thick nitride buffer layer / SiC(111).

[0035] The plasma processing apparatus (plasma etching apparatus) shown in FIG. 1 has a conductive holding stage 2 for holding a work W and a nozzle-type electrode 3 disposed to face each other in a chamber 1. In order to generate plasma based on a process gas in the space between the work W and the nozzle-type electrode 3, a high-frequency power source 4 that applies a high-frequency voltage between the holding stage 2 and the nozzle-type electrode 3, a gas supply system 5 that supplies a process gas through a flow path of the nozzle-type electrode 3 to a plasma generation region P, and a gas exhaust system 6 for exhausting the process gas in the chamber 1. In order to relatively displace the work W and the nozzle-type electrode 3, in the present embodiment, the holding stage 2 is provided on an XY table 7 installed at the bottom of the chamber 1. Incidentally, the structure including the nozzle-type electrode 3 is fixed to the chamber 1 via an insulator 8, and the chamber 1 is grounded. And a spectroscopic analyzer 9 for monitoring is arranged at a position facing the plasma generation region P between the work W and the nozzle-type electrode 3. Incidentally, as monitoring means other than the spectroscopic analyzer, means by gas analysis (mass spectrometry) and plasma impedance analysis can also be mentioned.

[0036] In the plasma processing apparatus of this embodiment, a temperature control system combining a heater and an appropriate cooling device, and a thermocouple for temperature measurement are provided on the holding table 2. Further, the nozzle-type electrode 3 is provided with a gas supply path 10 inside, and the process gas supplied from the gas supply system 5 is guided to the tip and ejected from the ejection port 11. Then, while ejecting the process gas from the ejection port 11 of the nozzle-type electrode 3, a high-frequency voltage is applied from the high-frequency power supply 4 to generate high-frequency plasma based on the process gas in the plasma generation region P. The gallium compound layer of the work W exposed to the hydrogen plasma is removed by plasma etching. In the present invention, the structure of the nozzle-type electrode 3 and the method of generating plasma are not particularly limited. In this embodiment, the frequency of the high-frequency power supply 4 is 13.56 MHz, but plasma may be generated using microwaves of 150 MHz or 2.45 GHz.

[0037] In the plasma processing apparatus shown in FIG. 1, by using the local plasma generated near the tip of the nozzle-type electrode 3 and scanning the plasma generation region P over the entire surface of the work W, the gallium compound layer is uniformly removed. When there is non-uniformity in the thickness of the gallium compound layer on the surface of the work W, the processing amount of each part is controlled by the residence time of the plasma. For that purpose, the pre-processing shape profile of the processing surface of the work W and the profile of the stationary processing marks are acquired in advance, the difference between the pre-processing shape profile and the target shape profile is taken to obtain the processing amount distribution, the XY table 7 is driven based on the created NC processing data, and the work W is displaced with respect to the nozzle-type electrode 3, that is, the plasma generation region P is scanned on the processing surface of the work W.

[0038] Chlorine-based gases and fluorine-based gases that have been conventionally used as etching gases have a large processing rate, but they are gases with a large environmental impact and thus have the drawback of high costs for handling and recovery processing. Therefore, in the present invention, an etching gas in which hydrogen gas is diluted with a carrier gas is used. As the carrier gas, He is used in this embodiment, but Ar may also be used. A specific example of the gas supply system 5 is shown in FIG. 2, and a specific example of the exhaust system 6 is shown in FIG. 3. As shown in FIG. 2(a), the gas supply system 5 supplies He gas supplied from a helium gas cylinder 12 via a valve 13 and a mass flow controller (MFC) 14, and H 2 gas supplied from a hydrogen gas cylinder 15 via a valve 16 and a mass flow controller 17 are mixed to prepare an etching gas, which is sent from a gas supply pipe 18 to a supply path 10 of the nozzle-type electrode 3. Incidentally, regulators (not shown) are connected to each cylinder so that a gas at a predetermined pressure can be sent out. As shown in FIG. 3, the exhaust system 6 is composed of a vacuum pump 19 for initially evacuating the inside of the chamber and a decontamination cylinder 20. When the process gas is at atmospheric pressure, the exhaust flow path is switched by two valves 21 and 22 so that it can be directly exhausted into the atmosphere through the decontamination cylinder 20 without passing through the vacuum pump 19. In the figure, reference numeral 23 is a pressure gauge.

[0039] As a result of spot processing of small piece samples of GaN and Ga 2 O 3 by test processing using hydrogen gas (diluted with helium) as the etching gas, for GaN, a processing rate of 4 μm / min (processing conditions: He:H 2 = 90:10, RF power 130 W, processing time 5 minutes, gas flow rate 500 sccm) was obtained, and for Ga 2 O 3 it was 60 μm / min (processing conditions, He:H 2It has been found that a high processing speed (90:10, RF power 130 W, processing time 3 minutes, gas flow rate 500 sccm) can be obtained. However, the surface of the sample that had been polished to a mirror finish before processing turned brownish due to the adhesion of metallic Ga after processing. Fig. 4 shows a scanning electron microscope image of the GaN surface after processing. However, it has been confirmed that gallium compounds are efficiently discharged outside the plasma by hydrogen plasma etching, and only a part of them has adhered to the sample surface as metallic Ga, indicating that the effect of hydrogen plasma etching on gallium compounds is significant.

[0040] Regarding GaN, it has also been confirmed that the processing rate increases with an increase in the gas flow rate of the etching gas (see Fig. 5), and a tendency for a maximum in the processing rate is observed when the hydrogen gas concentration is around 5% (see Fig. 6). Also, it has been confirmed that the processing rate increases with an increase in the input power (see Fig. 7), and increases with an increase in the sample stage temperature but shows a saturation tendency (see Fig. 8). On the other hand, for Ga 2 O 3 it has been found that the processing rate is maximum when the sample stage temperature is 50 °C, but the dependence on temperature is small. Practically, the hydrogen gas concentration in the process gas is preferably in the range of 2 to 10%, more preferably in the range of 3 to 7%.

[0041] It has been found that gallium compounds can be processed with high efficiency by plasma etching using the etching gas composed of the aforementioned carrier gas and hydrogen gas. However, there is a phenomenon in which particles of metallic Ga adhere to the surface of the gallium compound after etching. In response to this, it has been found that by adding an oxidizing gas for oxidizing metallic Ga so that it is easily etched by hydrogen radicals to the etching gas composed of hydrogen gas, the adhesion of metallic Ga to the surface can be prevented. Here, as specific examples of the oxidizing gas, from a practical point of view, water vapor (H 2 O molecules), oxygen gas (O 2 molecules), or hydrogen peroxide vapor (H 2 O 2) can be mentioned. By adding an oxidizing gas, metallic Ga is oxidized, and vaporization is promoted by the reaction with hydrogen radicals. Fig. 9 shows the processing results (processing conditions: He:H 2 :O 2 =92:4:4, RF power 100 W, processing time 3 minutes, gas flow rate 500 sccm, temperature 80 °C) when oxygen gas is added as the oxidizing gas, and it can be seen that no metallic Ga exists on the surface of GaN after processing.

[0042] Fig. 2(b) shows a gas supply system 5 that supplies a process gas in which water vapor is added as an oxidizing gas to the aforementioned etching gas. This gas supply system 5 mixes the He gas supplied from the helium gas cylinder 12 via the mass flow controller 14 and the H 2 gas supplied from the hydrogen gas cylinder 15 via the mass flow controller 17 to form a process gas, and passes the process gas through the water in the airtight water tank 24 to vaporize and mix the water vapor to prepare the process gas.

[0043] Fig. 2(c) shows a gas supply system 5 that supplies a process gas in which oxygen gas is added as an oxidizing gas to the aforementioned etching gas. This gas supply system 5 mixes the He gas supplied from the helium gas cylinder 12 via the mass flow controller 14 and the H 2 gas supplied from the hydrogen gas cylinder 15 via the mass flow controller 16 to form a process gas, and mixes the O 2 gas supplied from the oxygen gas cylinder 25 via the valve 26 and the mass flow controller 27 to the process gas to prepare the process gas.

[0044] In this way, when plasma etching of a gallium compound is performed using a process gas composed of He / H 2 / O 2 , no spherical deposits can be seen on the surface after processing, and a shiny processed surface can be obtained. Instead of O 2 gas, when H 2 O is added, the same effect is confirmed. H 2During plasma processing with a process gas containing gas, the metallic Ga formed on the surface is rapidly oxidized by oxygen radicals or OH radicals in the plasma and is considered to be etched with high efficiency by hydrogen radicals.

[0045] FIG. 10 shows a wafer 100 for manufacturing a semiconductor device, which is the object of the present invention. The wafer 100 for manufacturing a semiconductor device is obtained by epitaxially growing a GaN layer 102 on a single crystal SiC substrate 101, and has a buffer layer 103 made of a gallium compound between the two. The buffer layer 103 is Al x Ga (1-x) N (0 ≦ x ≦ 1) or In y Ga (1-y) N (0 ≦ y ≦ 1). In this technology, for the regeneration that leaves only the single crystal SiC substrate, the elements constituting the buffer layer 103 are used as monitor elements (Ga, N, Al, or In), and for the regeneration that leaves the buffer layer 103, the elements of the buffer layer 103 different from the compositions of the single crystal SiC substrate 101 and the GaN layer 102 are used as monitor elements (Al or In) and used for the control to stop plasma etching. The control includes control to turn off the plasma itself (OFF) and control to stop the supply of a specific gas.

[0046] Here, the results of spot processing (etching) of GaN and SiC with only hydrogen gas and a mixed gas of hydrogen gas and oxygen gas are shown in FIGS. 11 to 14. FIG. 11 shows the processing profile of GaN when the processing conditions are He:H 2 = 95:5, RF power 180 W, processing time 5 minutes, and gas flow rate 500 sccm, and the processing rate is 2 to 3 μm / min. FIG. 12 shows the processing profile of GaN when the processing conditions are He:H 2 :O 2 = 93:4:3, RF power 180 W, processing time 15 minutes, and gas flow rate 500 sccm, and the processing rate is about 3 μm / min. FIG. 13 shows the processing conditions where He:H 2=96:4, RF power 180W, processing time 15 minutes, and gas flow rate 500 sccm. This is the processing profile of SiC, and the processing rate is at most 0.1 μm / min. Figure 14 shows the processing conditions of He:H 2 :O 2 =93:4:3, RF power 180W, processing time 15 minutes, and gas flow rate 500 sccm. This is the processing profile of SiC, and it can be seen that the unevenness is severe and the surface is greatly rough.

[0047] In the case of GaN, it was well processed with either only hydrogen gas or a mixed gas of hydrogen gas and oxygen gas. However, as described above, when using only hydrogen gas, fine metallic Ga adheres to the surface. In the case of SiC, it was hardly processed with only hydrogen gas, but the surface state changed greatly with a mixed gas of hydrogen gas and oxygen gas. When processed with a mixed gas of hydrogen gas and oxygen gas, the surface of SiC is black and rough, and the deposits cannot be removed even with a little rubbing. The phenomenon when SiC is processed with a mixed gas of hydrogen gas and oxygen gas is speculated as follows. First, since SiC was hardly processed without oxygen, it is speculated that the strong Si-C bond is broken by oxygen radicals, making it possible to be etched with hydrogen plasma. And the deposits act as a mask to prevent processing, resulting in a larger uneven structure. From this, when the surface of the SiC substrate appears, it is necessary to at least stop the supply of oxygen gas so that oxygen radicals do not act on the SiC substrate. However, if only stopping the oxygen gas has little effect, it is also necessary to stop the supply of high-frequency power and turn off the plasma.

[0048] In addition, in this embodiment, a method of blowing the etching gas from the central flow path of the nozzle-type electrode 3 is shown. However, if a method of sucking the etching gas with the nozzle-type electrode 3 is adopted, there is a possibility of suppressing the adhesion of the etching product to the surface of the workpiece W by quickly exhausting it from the plasma generation region P to the outside of the system.

Example

[0049] <SiC Substrate Regeneration Method 1 Leaving Only the SiC Substrate> As shown in Fig. 15(a), a plasma based on an etching gas composed of a carrier gas and hydrogen gas is generated between the surface of the wafer 100 for semiconductor device manufacturing and the tip of the nozzle-type electrode 3, and this plasma generation region P is scanned along the surface of the wafer 100 for semiconductor device manufacturing to remove the GaN layer 102 (gallium compound layer). In the present embodiment, an example of processing by local plasma etching in which the plasma generation region P is smaller than the area of the GaN layer 102 is shown, and the entire surface of the GaN layer 102 is raster scanned.

[0050] During plasma etching, the plasma is constantly monitored by the spectroscopic analyzer 9. In this case, the element constituting the buffer layer 103 is used as a monitoring element (Ga, N, Al or In), and the presence of the free monitoring element during plasma etching is detected by the spectroscopic analyzer 9. When Al or In is selected as the monitoring element, as shown in Fig. 15(b), the uppermost GaN layer 102 is removed and the buffer layer 103 (gallium compound layer) appears. At the same time as the plasma etching of the buffer layer 103 starts, Al or In in its composition is detected by the spectroscopic analyzer 9, and a signal is sent to the control system. Then, when the control system processes the signal of the spectroscopic analyzer 9 and turns off the plasma when the presence of Al or In detected by the spectroscopic analyzer 9 is no longer detected, as shown in Fig. 15(c), the buffer layer 103 is removed and the SiC substrate 101 remains. Note that the same applies when using a substrate (SiC / Si substrate) in which an epitaxial SiC layer is formed on a single crystal Si substrate instead of the single crystal SiC substrate.

[0051] Then, after the removal process of the gallium compound layer (GaN layer 102 and buffer layer 103) by plasma etching is completed, a cleaning process is performed to remove the deposits adhering to the surface of the SiC substrate 101. If the deposit is metallic Ga, it can be removed with an acidic or alkaline cleaning solution. At that time, by performing heating, metallic Ga can be removed more reliably. Incidentally, when the work W (wafer 100 for manufacturing a semiconductor device) is heated during etching, the amount of metallic Ga adhering to its surface can be reduced. By appropriately cleaning with a cleaning solution and cleaning means according to the type of deposit, it can be regenerated as a clean and undamaged SiC substrate. Of course, a cleaning solution that hardly affects the SiC substrate is used.

[0052] In the case of etching with hydrogen plasma, after the spectroscopic analyzer 9 detects the presence of Al or In, it is not necessary to immediately turn off the plasma when the detection stops. The plasma may be turned off after a predetermined time from the point when the detection stops. This is because while the SiC substrate 101 is hardly etched by hydrogen plasma, the metallic Ga adhering to the surface of the SiC substrate 101 is etched by hydrogen plasma. Here, the predetermined time is the time until the metallic Ga adhering to the surface of the SiC substrate 101 is etched away by hydrogen plasma, or the time when the metallic Ga remains to such an extent that it can be easily removed by the cleaning process.

[0053] Here, when N or Ga is selected as the monitor element, when the etching of the uppermost GaN layer 102 starts, the presence of the monitor element will be detected by the spectroscopic detector 9. Although the starting point of the etching of the buffer layer 103 containing the same element is unknown, the end point of the etching of the buffer layer 103 can be known when the monitor element is no longer detected by the spectroscopic detector 9, which is sufficient. However, when Ga is selected as the monitor element, even after the buffer layer 103 is removed, if metallic Ga exists on the surface of the SiC substrate 101, the spectroscopic analyzer 9 will continue to detect Ga. Therefore, when Ga is no longer detected, the hydrogen plasma can be turned off, which simplifies the control. This operation mode is the same as the control with the aforementioned predetermined time added. In addition, when the monitor element is Ga or N, it is detected by the spectroscopic analyzer 9 from the time when the etching of the GaN layer 102 starts. Therefore, it is difficult to detect the boundary between the GaN layer 102 and the buffer layer 103. However, this is not a problem when the buffer layer 103 is also removed.

Example

[0054] <SiC substrate regeneration method 2 that only leaves the SiC substrate> The SiC substrate regeneration method of this example is On the single-crystalline SiC substrate 101, Al x Ga (1-x) N (0 ≦ x ≦ 1) or In y Ga (1-y) Prepare a wafer 100 for manufacturing a semiconductor device in which an epitaxial GaN layer 102 is formed through a buffer layer 103 composed of N (0 ≦ y ≦ 1). Generate plasma based on a process gas in which an oxidizing gas having an effect of oxidizing metallic gallium is added to an etching gas composed of a carrier gas and a hydrogen gas, and remove the GaN layer and the buffer layer by plasma etching. During plasma etching, detect free Al or In with a spectroscopic analyzer, and turn off the plasma when Al or In is no longer detected after being detected by the spectroscopic analyzer. A cleaning process for removing deposits adhering to the surface of the SiC substrate or the SiC / Si substrate. has

[0055] Specifically, as shown in Fig. 15(a), a plasma based on a process gas in which an oxidizing gas (oxygen gas in this embodiment) that oxidizes metallic gallium is added to an etching gas composed of a carrier gas and hydrogen gas is generated between the surface of the wafer 100 for semiconductor device manufacturing and the tip of the nozzle-type electrode 3, and this plasma generation region P is scanned along the surface of the wafer 100 for semiconductor device manufacturing to remove the GaN layer 102 (gallium compound layer). As shown in Fig. 15(b), when the uppermost GaN layer 102 is removed and the buffer layer 103 (gallium compound layer) appears, plasma etching of the buffer layer 103 starts, and at the same time, Al or In in its composition is detected by the spectroscopic analyzer 9. Even if the presence of Al or In is detected by the spectroscopic analyzer 9, plasma etching is continued without interrupting the power supply from the high-frequency power supply 4, and the buffer layer 103 is removed following the GaN layer 102. While the buffer layer 103 is being plasma-etched, the presence of Al or In, which is the monitoring element, is continuously detected by the spectroscopic analyzer 9.

[0056] Then, as shown in Fig. 15(c), when the buffer layer 103 is completely removed, the presence of Al or In is no longer detected by the spectroscopic analyzer 9. Immediately, a signal is sent to the control system to cut off the power supply from the high-frequency power supply 4 to extinguish the plasma (turn it OFF), thereby regenerating the substrate consisting only of the single-crystalline SiC substrate 101. Incidentally, when the SiC substrate is exposed completely and exposed to the plasma containing the oxidizing gas, the surface of the SiC becomes rough as described above. Therefore, instead of cutting off the power supply, at least the supply of the oxidizing gas may be stopped, or the supply of the etching gas may be stopped simultaneously with the cutting off of the power supply. Incidentally, since the adhesion of the metal Ga to the surface is suppressed by adding the oxidizing gas, there is almost no metal Ga on the surface of the SiC substrate 101 after turning off the plasma. However, after the buffer layer 103 is completely removed (Al or In is not detected), the supply of the oxygen gas may be stopped, etched with only the hydrogen gas for a short time, and then the power supply may be cut off. Thereby, even if the metal Ga remains on the surface of the SiC substrate 101, it can be completely removed by etching.

[0057] When the scanning for relatively displacing the workpiece W and the nozzle-type electrode 3 is a raster scan, in the actual plasma control, in order to remove the entire surfaces of the GaN layer 102 and the buffer layer 103, after the presence of Al or In is no longer detected by the spectroscopic analyzer 9 in the entire path of the raster scan, the plasma is turned OFF.

Example

[0058] <Method for regenerating SiC substrate leaving buffer layer> In the above-described Example 2, when the uppermost GaN layer 102 is removed and the buffer layer 103 (gallium compound layer) appears, plasma etching of the buffer layer 103 starts, and at the same time, Al or In in its composition is detected by the spectroscopic analyzer 9. Immediately, the power supply from the high-frequency power supply 4 is cut off to extinguish the plasma (turn it OFF). As shown in FIG. 15(b), a substrate with a buffer layer in which the buffer layer 103 remains on the single-crystalline SiC substrate 101 is regenerated. Even if the plasma etching is stopped in this state, almost no metallic Ga exists on the surface of the buffer layer 103. Thereafter, the cleaning process is performed in the same manner as described above.

Example

[0059] <Method for regenerating substrate> A method for regenerating a substrate in a semiconductor device manufacturing wafer 100 on which a single layer or a plurality of layers of gallium compound layers are stacked will be described. The substrate 101 is any one of a single-crystalline SiC substrate, a substrate in which an epitaxial SiC layer is formed on a single-crystalline Si substrate (SiC / Si substrate), a sapphire substrate, and a single-crystalline Si substrate. However, the true value of the present invention lies in the regeneration of the substrate in the semiconductor device manufacturing wafer 100 provided with a more expensive substrate.

[0060] Basically, it is the same as the above-described example. First, the semiconductor device manufacturing wafer 100 is set in the above-described plasma etching apparatus. Plasma is generated based on a process gas in which an oxidizing gas having an action of oxidizing metallic gallium is added to an etching gas composed of a carrier gas and hydrogen gas. After performing a step of removing all of the gallium compound layer when the gallium compound layer is a single layer, or all or the upper layer portion when the gallium compound layer is a plurality of layers, by plasma etching, a cleaning step of removing deposits adhering to the substrate surface is performed. Here, the oxidizing gas is the same as described above, namely oxygen gas, water vapor, or a gas containing oxygen gas and water vapor. When all of the gallium compound layer is removed, it becomes a substrate regeneration method in which only the substrate remains. When only the upper layer portion is removed in the case where the gallium compound layer is a plurality of layers, it typically becomes a substrate regeneration method with a buffer layer.

[0061] Specifically, the gallium compound layer has an epitaxial GaN layer 102 on the uppermost layer and a buffer layer 103 for matching the lattice constants between the substrate 101 and the GaN layer 102. The buffer layer 103 contains an element different from the constituent elements of the substrate 101 and the GaN layer 102. By using this element as a monitor element, it is possible to select substrate regeneration that leaves the buffer layer 103 or removes it up to the buffer layer 103.

[0062] That is, during plasma etching, the presence of the free monitor element is detected by a spectroscopic analyzer. When the plasma is turned off at the time when the spectroscopic analyzer 9 detects the monitor element, the substrate with the buffer layer 103 remaining can be regenerated. When the plasma is turned off at the time when the monitor element is no longer detected after being detected by the spectroscopic analyzer 9, the substrate can be regenerated leaving only the substrate. Also in this case, it is necessary to stop the supply of at least the oxidizing gas before the substrate is exposed so as not to damage the substrate by oxygen radicals.

[0063] The substrate 101 is a single-crystalline SiC substrate or an SiC / Si substrate, and when the buffer layer is Al x Ga (1-x) N (0 ≦ x ≦ 1) or In y Ga (1-y) N (0 ≦ y ≦ 1), and when the monitor element is Al or In, it is the same as in Example 2 and Example 3. When the substrate 101 is sapphire (Al 2 O 3 ), since an AlN low-temperature buffer layer or a GaN low-temperature buffer layer is used for the buffer layer 103, it is not possible to use an element different from the constituent elements of the substrate 101 and the GaN layer 102 as a monitor element. However, if at least an element different from the substrate 101 is used as a monitor element (for example, N or Ga), it is possible to detect the end point of removing the buffer layer 103. Also, in the case of an AlN low-temperature buffer layer, if Ga or Al is used as a monitor element, it is also possible to regenerate the substrate leaving the buffer layer.

[0064] Therefore, generally, the gallium compound layer has at least an epitaxial GaN layer 102 in the uppermost layer, and assuming that the wafer 100 for semiconductor device manufacturing forms a laminated structure composed of multiple layers with the substrate 101, when different elements exist in both compositions across the interface of the laminated structure, with the interface to be left by plasma etching as the boundary, it is possible to detect the endpoint of the plasma using that element as a monitor element.

Explanation of Reference Signs

[0065] W Workpiece, P Plasma generation region, 1 Chamber, 2 Holding stage, 3 Nozzle-type electrode, 4 High-frequency power supply, 5 Gas supply system, 6 Gas exhaust system, 7 XY table, 8 Insulator, 9 Spectroanalyzer, 10 Supply path, 11 Jet outlet, 12 Helium gas cylinder, 13 Valve, 14 Mass flow controller, 15 Hydrogen gas cylinder, 16 Valve, 17 Mass flow controller, 18 Gas supply pipe, 19 Vacuum pump, 20 Decontamination cylinder, 21 Valve, 22 Valve, 23 Pressure gauge, 24 Airtight water tank, 25 Oxygen gas cylinder, 26 Valve, 27 Mass flow controller, 100 Wafer for semiconductor device manufacturing, 101 Single-crystal SiC substrate, 102 GaN layer, 103 Buffer layer.

Claims

1. A method for regenerating a SiC substrate in a semiconductor device manufacturing wafer in which a single-layer or multiple-layer gallium compound layer is laminated on a substrate (SiC / Si substrate) having an epitaxial SiC layer formed on a single-crystalline SiC substrate or a single-crystalline Si substrate, comprising: generating a plasma based on an etching gas composed of a carrier gas and hydrogen gas, removing all of the gallium compound layer by plasma etching, and leaving only the SiC substrate or the SiC / Si substrate; a cleaning step of removing deposits adhering to the surface of the SiC substrate or the SiC / Si substrate; A method for regenerating a SiC substrate having the above steps.

2. The gallium compound layer has an epitaxial GaN layer on the uppermost layer, and between the substrate and the GaN layer, Al ｘ Ga （１－ｘ） N (0 ≦ x ≦ 1) or In ｙ Ga （１－ｙ） has a buffer layer composed of N (0 ≦ y ≦ 1). The method for regenerating a SiC substrate according to Claim 1.

3. Using the element constituting the buffer layer as a monitor element, detecting the presence of the free monitor element during plasma etching with a spectroscopic analyzer, after the spectroscopic analyzer detects the monitor element, turning off the plasma when the detection stops or after a predetermined time from the time when the detection stops; The method for regenerating a SiC substrate according to Claim 2.

4. On a substrate (SiC / Si substrate) having an epitaxial SiC layer formed on a single crystal SiC substrate or a single crystal Si substrate, Al ｘ Ga （１－ｘ） N (0 ≤ x ≤ 1) or In ｙ Ga （１－ｙ） A step of preparing a semiconductor device manufacturing wafer on which an epitaxial GaN layer is formed through a buffer layer made of N (0 ≤ y ≤ 1). generating a plasma based on a process gas in which an oxidizing gas having an action of oxidizing metallic gallium is added to an etching gas composed of a carrier gas and hydrogen gas, and removing the GaN layer and the buffer layer by plasma etching; detecting free Al or In with a spectroscopic analyzer during plasma etching, and turning off the plasma when the detection of the Al or In by the spectroscopic analyzer stops; a cleaning step of removing deposits adhering to the surface of the SiC substrate or the SiC / Si substrate; A method for regenerating a SiC substrate having the above steps.

5. The oxidizing gas contains oxygen gas, water vapor, or both oxygen gas and water vapor. The method for regenerating a SiC substrate according to Claim 4.

6. In the step of performing local plasma etching where the plasma generation region is smaller than the area of the GaN layer and removing the entire wafer surface by plasma etching by raster scanning, turning off the plasma when the detection of Al or In stops in the entire path of the raster scanning; The method for regenerating a SiC substrate according to Claim 4 or 5.

7. stopping the supply of at least the oxidizing gas before the substrate is exposed; The method for regenerating a SiC substrate according to Claim 5.

8. A method for substrate regeneration in a wafer for manufacturing a semiconductor device, on which a single-layer or multiple-layer gallium compound layer is laminated on a substrate, comprising: generating plasma based on a process gas in which an oxidizing gas having an action of oxidizing metallic gallium is added to an etching gas composed of a carrier gas and hydrogen gas, and removing all of the gallium compound layer when the gallium compound layer is a single layer, or removing all or the upper layer portion of the gallium compound layer by plasma etching when the gallium compound layer is multiple layers; a cleaning step of removing deposits adhering to the substrate surface; A substrate regeneration method comprising the above steps.

9. The oxidizing gas contains oxygen gas, water vapor, or both oxygen gas and water vapor. The substrate regeneration method according to claim 8.

10. The substrate is any one of a single crystal SiC substrate, a substrate in which an epitaxial SiC layer is formed on a single crystal Si substrate (SiC / Si substrate), a sapphire substrate, and a single crystal Si substrate. The substrate regeneration method according to claim 8 or 9.

11. The gallium compound layer has an epitaxial GaN layer on the uppermost layer, and has a buffer layer for matching the lattice constants between the substrate and the GaN layer. The substrate regeneration method according to claim 10.

12. The buffer layer contains an element different from the substrate constituent element and the GaN layer constituent element, and this element is used as a monitor element. During plasma etching, the presence of the free monitor element is detected by a spectroscopic analyzer. Turn off the plasma when the spectroscopic analyzer detects the monitor element. Or turn off the plasma when the spectroscopic analyzer detects the monitor element and then the monitor element is no longer detected. The substrate regeneration method according to claim 11.

13. The gallium compound layer has at least an epitaxial GaN layer on the uppermost layer. The wafer for manufacturing a semiconductor device has a layer structure composed of multiple layers together with the substrate. When different elements exist in both compositions with the interface of the layer structure as the boundary to be left by plasma etching, the end point of the plasma is detected using that element as a monitor element. The substrate regeneration method according to claim 10.

14. The substrate is a single crystal SiC substrate or a SiC / Si substrate. The gallium compound layer has an epitaxial GaN layer on the uppermost layer. Stop supplying at least the oxidizing gas before the substrate is exposed. The substrate regeneration method according to claim 9.

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