Method for improving RTA annealing stability of SiC device and semiconductor device

Abstract

The invention belongs to the technical field of semiconductor device manufacturing, and particularly relates to a method for improving RTA annealing stability of a SiC device and a semiconductor device.The method comprises the following steps that a Ni metal layer is formed on the front face of a SiC wafer through a sputtering method; forming carbon films on the front surface and the back surface of the SiC wafer by adopting a PVD (Physical Vapor Deposition) magnetron sputtering method; directly putting the SiC wafer of which the front surface and the back surface are protected by the carbon film into an RTA cavity, and carrying out RTA rapid annealing to form NiSi alloy; after RTA annealing, the carbon film on the surface of the SiC wafer is removed through oxidation, the SiC wafer is protected by depositing the carbon film twice on the front face and the back face, the direct annealing process of the SiC wafer is achieved through the high-temperature stability, good heat conductivity and strong light absorption of the carbon film, tray-free box heating is achieved, the temperature controllability of the SiC annealing process is enhanced, and the stability of the RTA process is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor device manufacturing, and particularly relates to a method for improving the RTA annealing stability of SiC devices and a semiconductor device. Background Art

[0002] As a third-generation semiconductor material, SiC material has many excellent properties, such as high temperature resistance, high voltage resistance, and radiation resistance. Therefore, SiC devices have obvious advantages compared with traditional devices and are consistently considered to be the most potential semiconductor devices. However, some unique properties of SiC material also bring new requirements for its process manufacturing technology.

[0003] Since the SiC wafer is a semi-transparent material, the mainstream rapid thermal annealing to form an alloy requires a tray for the conventional RTA annealing to carry out an effective annealing process. On the one hand, it increases the cost of the additional tray, and on the other hand, it brings uncontrollability and uncertainty of the temperature inside the tray, making it impossible to confirm the RTA annealing process temperature and difficult to ensure the stability of the SiC device RTA annealing process. Therefore, the temperature monitoring of SiC during RTA annealing in the preparation process of SiC devices has become a technical difficulty. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the RTA annealing stability of SiC devices.

[0005] The present invention provides a method for improving the RTA annealing stability of SiC devices, including the following steps: S1. Form a Ni metal layer on the front surface of the SiC wafer by sputtering; S2. Form a carbon film on the front and back surfaces of the SiC wafer by magnetron sputtering; S3. Place the SiC wafer protected by the carbon film on both the front and back directly in the RTA cavity and perform RTA annealing to form a NiSi alloy; S4. After RTA annealing, oxidize to remove the carbon film on the surface of the SiC wafer.

[0006] Optionally, the sputtering method in step S1 includes the following steps: Transfer the SiC wafer into the process cavity and deposit a layer of metal Ni on the front surface of the SiC by PVD DC magnetron sputtering.

[0007] Optionally, the thickness of the Ni metal layer is 160 - 200 nm.

[0008] Optionally, in step S2, the magnetron sputtering method includes the following steps: On the front surface of the SiC wafer, a surface of metal Ni has been formed, and a carbon film with a thickness of 80 - 110 nm is formed by DC pulsed magnetron sputtering; then on the back surface of the SiC wafer, a carbon film with a thickness of 80 - 110 nm is formed by PVD DC magnetron sputtering.

[0009] Optionally, the process parameters of the DC pulsed magnetron sputtering are: DC power is 1000 W, pulsed power is 500 W, the flow rate of process gas Ar is 150 sccm, the rotation speed of the Table is 15 revolutions per minute, the target - substrate distance is 85 mm, the butterfly valve is controlled at 20%, and the sputtering time is 50 min.

[0010] Optionally, the method for forming NiSi alloy by RTA annealing includes the following steps: Put the SiC wafer with carbon films on both the front and back sides into an RTA machine, evacuate the air. After the vacuum degree reaches 1E - 5 Torr, introduce an inert gas, then evacuate again, repeat this process several times to remove all water vapor; then, in an inert gas atmosphere, rapidly heat up at a heating rate of 3 - 5 °C / s to reach 360 - 450 °C, and then heat up to the annealing temperature of 950 - 1100 °C at a heating rate of 10 - 15 °C / s, and hold for 350 - 450 s to complete the RTA rapid annealing process, and form NiSi alloy on the surface of the SiC wafer and the Ni metal layer.

[0011] Optionally, the method for oxidizing and removing the carbon film includes the following steps: Put the SiC wafer that has completed RTA annealing into a radio - frequency de - bonding machine with the front side facing down, first remove the carbon film on the back side; after the carbon film on the back side is removed completely, flip the wafer using the same process to remove the carbon film on the front side, thus removing the double - sided carbon film completely.

[0012] Optionally, the process parameters for oxidizing and removing the carbon film are: set the power of the radio - frequency de - bonding machine to 1000 - 1200 W, the oxygen flow rate to 2600 - 3000 sccm, the air pressure to 1 Torr, the heating temperature to 200 - 230 °C, and the process time to 25 - 35 s.

[0013] Optionally, before forming the Ni metal layer, the SiC wafer is cleaned using the RCA standard cleaning method.

[0014] A semiconductor device is fabricated using the method described above.

[0015] The beneficial effect of the present invention is that the present invention combines two - time carbon film sputtering and RTA annealing processes. First, a layer of Ni metal is sputtered on the SiC surface, and two - time front - and - back - side carbon film sputtering is carried out using room - temperature magnetron sputtering. After the carbon film wraps the SiC surface, it is directly put into RTA annealing without using a heating tray box. After the RTA annealing process is completed, the carbon film is removed by forming oxygen plasma through a radio - frequency de - bonding machine.

[0016] The present invention adopts a mature magnetron sputtering process and an oxygen plasma thin film etching process. The process steps are simple. The SiC wafer is protected by depositing carbon films on both the front and back sides. The direct annealing process of the SiC wafer is realized by utilizing the high-temperature stability, good thermal conductivity, and strong light absorption of the carbon film, achieving heating without a tray box, enhancing the temperature controllability of the SiC annealing process, and improving the stability of the RTA process. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of forming a Ni layer on the surface of the SiC wafer provided by the present invention; Figure 2 It is a schematic diagram of forming a carbon film provided by the present invention; Figure 3 It is a schematic diagram of the RTA annealing step of the SiC wafer provided by the present invention; Figure 4 It is a schematic diagram of the SiC semiconductor device with the carbon film removed provided by the present invention. Detailed Embodiments

[0018] The present invention provides a method for improving the RTA annealing stability of SiC devices, including the following steps: S1. A Ni metal layer is formed on the front side of the SiC wafer by sputtering; S2. Carbon films are formed on the front and back sides of the SiC wafer by PVD magnetron sputtering; S3. The SiC wafer protected by carbon films on both the front and back sides is directly placed in the RTA cavity for RTA annealing to form a NiSi alloy; S4. After RTA annealing, the carbon film on the surface of the SiC wafer is removed by oxidation.

[0019] Compared with the prior art, the present invention combines the two-time carbon film sputtering and RTA annealing processes. First, a layer of Ni metal is sputtered on the SiC surface, and the two-time front and back carbon film sputtering is carried out by room-temperature magnetron sputtering. After the carbon film wraps the SiC surface, it is directly placed in the RTA annealing without using a heating tray box. After the RTA annealing process is completed, the carbon film is removed by forming oxygen plasma through a radio frequency degumming machine. The present invention adopts a mature magnetron sputtering process and an oxygen plasma thin film etching process. The process steps are simple. The SiC wafer is protected by depositing carbon films on both the front and back sides. The direct annealing process of the SiC wafer is realized by utilizing the high-temperature stability, good thermal conductivity, and strong light absorption of the carbon film, achieving heating without a tray box, enhancing the temperature controllability of the SiC annealing process, and improving the stability of the RTA process.

[0020] It should be noted that: High-temperature activation: The impurity ions implanted into the SiC material are basically in the interstitial positions of the lattice. In order to make these impurity ions substitute into the lattice point positions, the ion-implanted SiC material needs to be subjected to high-temperature activation annealing. The annealing temperature is generally higher than 1400 °C for N-type impurities and 1600 °C - 1800 °C for P-type impurities. At such a high annealing temperature, the silicon in SiC will volatilize and redeposit, resulting in the appearance of step clusters on the surface of the annealed wafer, deteriorating the surface morphology of the wafer, and thus seriously affecting the device performance. To solve this problem, generally, a protective layer is covered on the surface of the SiC wafer during high-temperature activation annealing to inhibit the volatilization and deposition of silicon. Currently, the most widely used is the carbon protective film. This is because, first, carbon does not react with SiC at high temperatures; second, the carbon protective film has a certain hardness and effectively inhibits the precipitation of silicon in SiC. Generally, photoresist is carbonized into a carbon film, and PVD sputtered carbon film is also used, both of which only form a layer on the front side for protection.

[0021] RTA annealing: Deposit a layer of metal, such as Ni, on the SiC surface, and anneal at about 900 °C to form a NiSi alloy to obtain good ohmic contact on the device.

[0022] High-temperature activation and RTA are two processing techniques with completely different functions. High-temperature activation uses a resistance wire for heating, mainly through heat conduction. Only a layer of carbon film protective layer needs to be deposited on the front side, and almost all activation annealing uses photoresist, which is carbonized to form a carbon film to achieve the protection effect on the SiC surface under high-temperature conditions; RTA annealing uses Lam for heating, through heat radiation. Therefore, for SiC wafers, high-temperature activation does not require box heating, while RTA annealing uses a graphite box for heating.

[0023] Example 1 SiC wafer cleaning: The SiC wafer is cleaned using standard RCA cleaning. RTA cleaning includes SC-1, SC-2, DHF, and deionized water rinsing. SC-1 is a mixed solution of ammonia water, hydrogen peroxide, and water with a ratio of 1:1:20, at a temperature of 70 °C. SC-2 is a mixed solution of hydrochloric acid, hydrogen peroxide, and water with a ratio of 1:1:5, at a temperature of 60 °C. DHF is hydrofluoric acid with a dilution ratio of 1:100, at a temperature of 25 °C. Immerse the SiC wafer in the SC-1 solution for 2 minutes to remove surface particles, pass through the SC-2 solution for 3 minutes to remove surface metal contaminants, then immerse in DHF for 30 seconds, rinse with deionized water for 30 seconds, and finally spin dry.

[0024] Front sputtering of Ni metal: After the SiC wafer is cleaned by RCA, a layer of metal Ni is deposited on the front of the SiC using a PVD DC magnetron sputtering machine. The base pressure of the machine reaches 1E-7 Torr. The SiC wafer is transferred into the process chamber. The sputtering power is 2000 W, the flow rate of the process gas Ar is 18 sccm, the flow rate of Ar on the back is 20 sccm, the target-substrate distance is 40 mm, the process pressure is 5 mTorr, the deposition time is 20 s, and the thickness of the generated Ni layer is 180 nm, as Figure 1 shown.

[0025] Deposition of carbon films on the front and back: On the surface of the SiC wafer where metal Ni has been formed on the front, a carbon film with a thickness of 100 nm is sputtered using DC pulse control sputtering. The process parameters are a DC power of 1000 W, a pulse power of 500 W, a flow rate of the process gas Ar of 150 sccm, a Table rotation speed of 15 revolutions per minute, a target-substrate distance of 85 mm, a butterfly valve control at 20%, and a sputtering time of 50 min to form a carbon film with a thickness of 100 nm. After the process is completed, it is transferred out of the PVD machine and flipped. The front with the carbon film protection will not cause scratches. Using the same process parameters as above, a carbon film with a thickness of 100 nm is deposited on the back of the SiC. In this way, 100-nm carbon films on the front and back of the SiC are completed, as Figure 2 shown.

[0026] RTA annealing to form NiSi alloy: The SiC wafer with 100 nm deposited on both the front and back is placed in an RTA machine and evacuated. After the vacuum degree reaches 1E-5 Torr, N2 is flushed for 30 s and evacuated for 1 min, and this is repeated 3 times. After the water vapor is removed completely, 1000 sccm of Ar is introduced as the annealing protective atmosphere, and the gas is continuously introduced until the chamber pressure reaches standard atmospheric pressure. It is rapidly heated at a heating rate of 5 °C / s to reach 400 °C, and then heated to the annealing temperature of 1000 °C at a heating rate of 10 °C / s and held for 400 s to complete the RTA rapid annealing process and form the NiSi alloy, as Figure 3 shown.

[0027] Removing the carbon film: For the SiC wafer that has completed annealing, first remove the carbon film on the back. Place the wafer face down in a radio frequency degumming machine, set the power to 1000 W, the O2 flow rate to 3000 sccm, the process pressure to 1 Torr, the heating temperature to 230 °C, and the process time to 30 s. After the carbon film on the back is removed completely, use the same process menu to flip the wafer and remove the carbon film on the front, so as to completely remove the carbon film on both sides. The specific contact resistance obtained by this method is lower than 1.5E-6 Ω∙cm 2 , as Figure 4 shown.

[0028] By depositing a carbon film on the front and back, the pyrometer temperature during the RTA annealing process shows 1000 °C, and the set temperature is the actual annealing temperature; if box heating is used, the pyrometer temperature shows 1000 °C, but in fact the temperature inside the box reaches 1050 °C. There is a gap between the heating box and the lid, and the difference in the airflow field in the gap increases the temperature difference between the center and the edge of the SiC wafer, resulting in poor in-wafer uniformity. Therefore, the stability of the RTA process is improved.

[0029] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the present application is limited to these examples; under the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of brevity.

[0030] One or more embodiments of the present application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application shall be included within the protection scope of the present application.

Claims

1. A method for improving the RTA annealing stability of SiC devices, characterized in that, It includes the following steps: S1. Form a Ni metal layer on the front side of the SiC wafer by sputtering method; S2. Form a carbon film on the front and back sides of the SiC wafer by magnetron sputtering method; S3. Place the SiC wafer protected by the carbon film on both sides directly in the RTA chamber for RTA annealing to form NiSi alloy; S4. After RTA annealing, oxidize to remove the carbon film on the surface of the SiC wafer.

2. The method for improving the RTA annealing stability of SiC devices according to claim 1, characterized in that, The sputtering method in step S1 includes the following steps: Transfer the SiC wafer into the process chamber and deposit a layer of metal Ni on the front side of the SiC by PVD DC magnetron sputtering.

3. The method for improving the RTA annealing stability of SiC devices according to claim 1, characterized in that, The thickness of the Ni metal layer is 160 - 200 nm.

4. The method for improving the RTA annealing stability of SiC devices according to claim 1, characterized in that, In step S2, the magnetron sputtering method includes the following steps: On the surface of the SiC wafer where metal Ni has been formed on the front side, form a carbon film with a thickness of 80 - 110 nm by DC pulsed magnetron sputtering; then on the back side of the SiC wafer, form a carbon film with a thickness of 80 - 110 nm by PVD DC magnetron sputtering.

5. The method for improving the RTA annealing stability of SiC devices according to claim 4, characterized in that, The process parameters of the DC pulsed magnetron sputtering are: DC power is 1000 W, pulsed power is 500 W, the flow rate of process gas Ar is 150 sccm, the rotation speed of the Table is 15 revolutions / min, the target-substrate distance is 85 mm, the butterfly valve is controlled at 20%, and the sputtering time is 50 min.

6. The method for improving the RTA annealing stability of SiC devices according to claim 1, characterized in that, The method for forming NiSi alloy by RTA annealing includes the following steps: Place the SiC wafer with carbon films on both sides into the RTA machine, evacuate the air. After the vacuum degree reaches 1E - 5 Torr, fill in inert gas, and then evacuate the air again. Repeat this process several times to remove all water vapor; then, in an inert gas atmosphere, rapidly heat up at a heating rate of 3 - 5 °C / s to reach 360 - 450 °C, and then heat up to the annealing temperature of 950 - 1100 °C at a heating rate of 10 - 15 °C / s, and hold for 350 - 450 s to complete the RTA rapid annealing process, and form NiSi alloy on the surface of the SiC wafer and the Ni metal layer.

7. The method for improving the RTA annealing stability of SiC devices according to claim 1, characterized in that, The method for oxidizing and removing the carbon film includes the following steps: Place the SiC wafer that has completed RTA annealing with the front side facing down into the radio frequency degumming machine to first remove the carbon film on the back side; after the carbon film on the back side is removed cleanly, turn over the wafer using the same process to remove the carbon film on the front side, so as to remove the carbon film on both sides cleanly.

8. The method for improving the RTA annealing stability of SiC devices according to claim 7, characterized in that, The process parameters for oxidizing and removing the carbon film are: set the power of the radio frequency degumming machine to 1000 - 1200 W, the oxygen flow rate to 2600 - 3000 sccm, the air pressure to 1 Torr, the heating temperature to 200 - 230 °C, and the process time to 25 - 35 s.

9. The method for improving the RTA annealing stability of SiC devices according to any one of claims 1-8, characterized in that, It also includes cleaning the SiC wafer by RCA standard cleaning method before forming the Ni metal layer.

10. A semiconductor device, characterized in that, It is made by using the method described in any one of claims 1 - 9.

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