Method for efficiently reducing warping of thinned SiC wafer without damage

Abstract

The invention discloses a method for efficiently reducing warping of a thinned SiC wafer without damage, and the method comprises the steps: carrying out the thinning of a to-be-processed wafer, and obtaining a first wafer; performing laser processing on the back surface of the first wafer to obtain a second wafer; cleaning the second wafer to obtain a third wafer; and forming back metal on the back of the third wafer. According to the invention, back surface treatment is carried out on the thinned wafer by using the effects of local high temperature and rapid cooling of the laser pulse, so that the internal stress of the thinned wafer is released, the wafer warping is reduced, and the fragment risk caused by warping in the subsequent process is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor processing technology, and in particular to a method for efficiently and non-destructively reducing warpage of SiC wafers after thinning. Background Technology

[0002] Silicon carbide (SiC) materials have been widely used in power electronics due to their superior physical properties, such as high thermal conductivity, high breakdown electric field, and high saturation drift velocity. With the continuous development of semiconductor technology and increasingly demanding application scenarios for silicon carbide devices, the requirements for the mechanical strength, heat dissipation, and on-resistance of silicon carbide chips are becoming increasingly stringent. Therefore, the thinning process of silicon carbide wafers has gradually become a core technology in the manufacturing process of silicon carbide devices. Due to the extremely high hardness, wear resistance, and low fracture toughness of silicon carbide materials, diamond grinding wheels are often used for thinning during mass production to balance efficiency and quality. At the same time, the thinner the target thickness of the silicon carbide wafer, the greater the warpage after processing. Especially when the wafer thickness is less than 150μm, warpage can cause wafer transfer abnormalities, back-golding process failures, and fragmentation.

[0003] To address the issue of wafer warpage, the industry has offered various solutions. These mainly include temporary bonding to confine internal wafer stress, polishing to release internal stress, wet etching to release internal stress, and high-temperature furnace annealing to release internal stress. However, these methods not only affect the front-side device structure during actual mass production but also severely impact processing efficiency. Therefore, developing an efficient and non-destructive method to reduce warpage after SiC wafer thinning has a significant impact on the development of silicon carbide devices. Summary of the Invention

[0004] Technical objective: To address the shortcomings of existing technologies in silicon carbide device manufacturing, such as large warpage during thinning and the inefficiency and damage to the front structure caused by traditional warpage reduction processes, this invention provides a highly efficient and non-destructive method for reducing warpage after SiC wafer thinning.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution.

[0006] A method for efficiently and non-destructively reducing warpage of SiC wafers after thinning includes the following steps: S1. Thinning the wafer to be processed to obtain the first wafer; S2. Laser processing is performed on the back side of the first wafer to obtain the second wafer; S3. Clean the second wafer to obtain the third wafer; S4. Form back metal on the back side of the third wafer.

[0007] Furthermore, the thickness of the first wafer ranges from 50um to 180um.

[0008] Furthermore, the wavelength range is 355nm~527nm; the laser energy range is 2J / cm². 2 ~15J / cm 2 The focusing depth range is 5μm~30μm.

[0009] Furthermore, the laser pulse frequency range is 100Hz~2000Hz, the scanning speed range is 50mm / s~600mm / s, the spot size range is 50μm×50μm~600μm×600μm, and the laser spot duration range is 10-1000ns.

[0010] Furthermore, in S4, an ohmic contact metal material is deposited on the back side of the third wafer, and the back metal is formed after laser annealing.

[0011] Beneficial effects: This invention utilizes the local high temperature and rapid cooling effect of laser pulses to perform back-side processing on thinned wafers, releasing internal stress in the thinned wafers, reducing wafer warpage, and lowering the risk of fragmentation caused by warpage in subsequent processes. In addition, compared with traditional processing methods, this method does not damage the front-side structure and has superior production efficiency. Attached Figure Description

[0012] Figure 1 A schematic diagram of laser irradiation on the thinned surface of the SiC wafer in Example 1; Figure 2 This is a schematic diagram of the SiC wafer warpage h in Example 1; Figure 3 This is a flowchart of an efficient and non-destructive method for reducing warpage of SiC wafers after thinning, as described in Example 1. Detailed Implementation

[0013] The following description, in conjunction with the accompanying drawings and embodiments, further explains and illustrates a method for efficiently and non-destructively reducing warpage of SiC wafers after thinning.

[0014] The embodiments are for illustrative purposes only and do not constitute a limitation on the scope of the claims. Other alternative means that can be conceived by those skilled in the art are all within the scope of the claims of this invention.

[0015] Furthermore, in the description of this invention, it should be noted that the terms "central," "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Example 1

[0016] As attached Figure 1 To be continued Figure 3 As shown in the figure, this embodiment of a method for efficiently and non-destructively reducing warpage of SiC wafers after thinning includes the following steps: S1. Thinning process of the wafer to be processed to obtain a first wafer; wherein, the thinning process includes rough grinding and fine grinding of the wafer to be processed, so that the wafer to be processed is ground to the expected thickness to obtain the first wafer. In this embodiment, the thickness range of the first wafer is 50um~180um. S2, as attached Figure 1 and attached Figure 2 As shown, the back side of the first wafer is laser-processed to obtain the second wafer; the laser wavelength range is 355nm~527nm; the laser pulse frequency range is 100Hz~2000Hz; the scanning speed range is 50mm / s~600mm / s; the spot size range is 50μm×50μm~600μm×600μm; and the laser energy range is 2J / cm². 2 ~15J / cm 2 The focusing depth ranges from 5μm to 30μm. The duration of the laser spot effect ranges from 10 to 1000 ns. In this step, the laser pulse exerts a localized high temperature and rapid cooling effect on the back side of the thinned wafer, i.e., the first wafer. The back side treatment efficiently and without damage reduces the warpage of the SiC wafer after thinning.

[0017] S3. The second wafer is cleaned to obtain the third wafer. In this step, the second wafer is thoroughly cleaned to remove particles and contaminants remaining from the back grinding process, providing a clean surface for subsequent processing.

[0018] S4. Form back metal on the back side of the third wafer; deposit ohmic contact metal material on the back side of the laser-treated SiC, i.e., the back side of the third wafer, and form back metal after laser annealing; in this step, laser annealing is used to rapidly anneal the ohmic contact metal material to form back metal, so that the back metal has good ohmic contact.

[0019] The present invention provides a highly efficient and non-destructive method for reducing warpage of SiC wafers after thinning, which enables large-scale mass production of wafers. By adding a laser processing step after thinning, the warpage of the wafers after thinning is effectively reduced. Example 2

[0020] This embodiment provides a method for efficiently and non-destructively reducing warpage of SiC wafers after thinning, comprising the following steps: S1. Thinning process is performed on the 6-inch 4H-SiC wafer to be processed to obtain the first wafer; wherein, the thinning process includes rough grinding and fine grinding of the wafer to be processed, so that the wafer to be processed is ground to 180um to obtain the first wafer. S2. Laser processing is performed on the back side of the first wafer to obtain the second wafer; the laser wavelength is 527nm; the laser pulse frequency is 100Hz, the scanning speed is 300mm / s, the spot size is 400μm×400μm, and the laser energy is 6J / cm². 2 The focusing depth range is 10 μm. The duration of laser beam action is 60 ns.

[0021] S3. Perform two-fluid cleaning + RCA cleaning on the second wafer to obtain the third wafer.

[0022] S4. Form back metal on the back side of the third wafer; deposit ohmic contact metal material on the back side of the laser-treated SiC, i.e. the back side of the third wafer, and form back metal after laser annealing.

[0023] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for efficiently and non-destructively reducing warpage of SiC wafers after thinning, characterized in that, Includes the following steps: S1. Thinning the wafer to be processed to obtain the first wafer; S2. Laser processing is performed on the back side of the first wafer to obtain the second wafer; S3. Clean the second wafer to obtain the third wafer; S4. Form back metal on the back side of the third wafer.

2. The method for efficiently and non-destructively reducing warpage of SiC wafers after thinning according to claim 1, characterized in that: The thickness of the first wafer ranges from 50um to 180um.

3. The method for efficiently and non-destructively reducing warpage of SiC wafers after thinning according to claim 1, characterized in that: The laser wavelength range is 355nm~527nm; the laser energy range is 2J / cm². 2 ~15J / cm 2 The focusing depth range is 5μm~30μm.

4. The method for efficiently and non-destructively reducing warpage of SiC wafers after thinning according to claim 1, characterized in that: The laser pulse frequency range is 100Hz~2000Hz, the scanning speed range is 50mm / s~600mm / s, the spot size range is 50μm×50μm~600μm×600μm, and the laser spot duration range is 10-1000ns.

5. The method for efficiently and non-destructively reducing warpage of SiC wafers after thinning according to claim 1, characterized in that: In S4, an ohmic contact metal material is deposited on the back side of the third wafer, and the back metal is formed after laser annealing.

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