Manufacturing method for semiconductor devices
Deformation prevention layers on semiconductor substrates address the deformation issues in laser lift-off processes, enabling precise peeling and substrate reuse by suppressing gas-induced deformation and maintaining laser focus.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- DENSO CORP
- Filing Date
- 2022-12-12
- Publication Date
- 2026-06-04
AI Technical Summary
The deformation of semiconductor substrates during laser lift-off processes due to gas generation and crystal structure breakage leads to variations in laser condensing positions and potential damage, particularly in nitride semiconductors like gallium nitride.
Formation of deformation prevention layers on both sides of the semiconductor substrate before laser irradiation, using materials with specific properties to suppress substrate deformation and facilitate clean peeling of the device layer.
The deformation prevention layers effectively prevent substrate deformation, ensuring precise laser focusing and clean peeling, allowing reuse of the substrate and reducing manufacturing costs.
Smart Images
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Abstract
Description
Technical Field
[0001] The technology disclosed in this specification relates to a method for manufacturing a semiconductor device.
[0002] After forming a device structure on one main surface side of a semiconductor substrate, a laser is irradiated into the semiconductor substrate to form a modified layer, and a device layer on which the device structure is formed is peeled off from the remaining layers of the semiconductor substrate along the modified layer. A technology has been developed. By using this laser lift-off technology, the semiconductor substrate after the device layer is peeled off can be reused, so that the manufacturing cost of the semiconductor device can be reduced. Patent Documents 1 and 2 disclose an example of a method for manufacturing a semiconductor device using the laser lift-off technology.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In a portion where a modified layer is formed in a semiconductor substrate, the crystal structure may be broken by laser irradiation, and atoms constituting the semiconductor may be vaporized. For example, when the semiconductor substrate is made of a nitride semiconductor, it is known that nitrogen gas is generated at the site of the modified layer. When gas is generated inside the semiconductor substrate, the semiconductor substrate expands and the semiconductor substrate is deformed. The deformation of the semiconductor substrate may cause variations in the condensing position of the laser irradiation or cause damage to the semiconductor substrate. This specification provides a technology for suppressing the deformation of a semiconductor substrate in a method for manufacturing a semiconductor device using the laser lift-off technology.
Means for Solving the Problems
[0005] A method for manufacturing a semiconductor device disclosed herein may include a deformation prevention layer formation step of forming a first deformation prevention layer (30) on the first main surface of a semiconductor substrate (1) having a first main surface (1a) and a second main surface (1b), and forming a second deformation prevention layer (40) on the second main surface of the semiconductor substrate, wherein a device structure is formed on the first main surface side of the semiconductor substrate; a laser irradiation step of irradiating the semiconductor substrate with a laser that penetrates the second deformation prevention layer formed on the second main surface of the semiconductor substrate, wherein the laser is irradiated onto a surface (3) extending to a predetermined depth within the semiconductor substrate; and a peeling step of peeling off the device layer (2) on which the device structure is formed from the remaining layers of the semiconductor substrate along the surface irradiated with the laser. The type of semiconductor substrate may be various types of semiconductor substrates containing atoms that vaporize upon irradiation with the laser. The type of device structure is not particularly limited, but may be, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a HEMT (High Electron Mobility Transistor), or a structure for forming a diode.
[0006] In the above manufacturing method, deformation prevention layers are formed on both sides of the semiconductor substrate before the laser irradiation step. Therefore, even if gas is generated inside the semiconductor substrate during the laser irradiation step, deformation of the semiconductor substrate is suppressed. [Brief explanation of the drawing]
[0007] [Figure 1] This diagram shows the flow chart of the device structure formation process, deformation prevention layer formation process, laser irradiation process, peeling process, and dicing process in the manufacturing method of a semiconductor device. [Figure 2] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Figure 3]This diagram schematically shows a cross-sectional view of a unit cell of a device structure formed on the upper surface of a semiconductor substrate. [Figure 4] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Figure 5] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Figure 6] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Figure 7] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Figure 8] This is an enlarged cross-sectional view of a key part of a semiconductor substrate during the manufacturing process of a semiconductor device, and schematically shows an enlarged cross-sectional view of a key part near the peripheral edge on the lower side of the semiconductor substrate. [Figure 9] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Figure 10] This diagram schematically shows a cross-sectional view of a semiconductor substrate during the manufacturing process of a semiconductor device. [Modes for carrying out the invention]
[0008] As shown in Figure 1, the method for manufacturing a semiconductor device using the laser peeling technology disclosed herein comprises a device structure formation step (step S1), a deformation prevention layer formation step (S2), a laser irradiation step (step S3), a peeling step (step S4), and a dicing step (step S5). By performing these steps on the semiconductor substrate 1 shown in Figure 2, multiple semiconductor devices (also called chips) can be manufactured using this manufacturing method.
[0009] As shown in Figure 2, the semiconductor substrate 1 has an upper surface 1a and a lower surface 1b, both of which are planar and extend parallel to each other. These upper surface 1a and lower surface 1b are also referred to as the main surfaces. The semiconductor substrate 1 further has a side surface 1c that is perpendicular to the upper surface 1a and lower surface 1b and connects the upper surface 1a and lower surface 1b. The semiconductor substrate 1 is not particularly limited, but may be a nitride semiconductor substrate, for example. Specifically, the semiconductor substrate 1 may be a substrate made of gallium nitride (GaN), for example. The surface 3 extending to a predetermined depth of the semiconductor substrate 1 is, as will be described later, the surface to which the laser is irradiated, that is, the surface where multiple laser focal points converge (hereinafter referred to as the "focusing surface"). The depth of the focusing surface 3 is closer to the upper surface 1a than to the lower surface 1b of the semiconductor substrate 1. In this specification, the portion of the semiconductor substrate 1 above the focusing surface 3, that is, the portion that is peeled off from the semiconductor substrate 1, is referred to as the device layer 2.
[0010] In the device structure formation process (step S1 in Figure 1), a device structure is formed within the device layer 2 of the semiconductor substrate 1. Figure 3 shows a unit cell of the device structure 10 formed within the device layer 2 of the semiconductor substrate 1 after the device structure formation process has been carried out. The device structure 10 is not particularly limited, but may be, for example, a vertical MOSFET.
[0011] The device structure 10 is n + A drain region 12 of type n, a drift region 14 of type n, a body region 16 of type p, and n + It comprises a type source region 18 and a planar type MOS structure 20.
[0012] The drain region 12 is located in a position exposed to the lower surface 1b of the semiconductor substrate 1. The drift region 14 is located between the drain region 12 and the body region 16. A portion of the drift region 14 located in a position exposed to the upper surface 1a of the semiconductor substrate 1 is called the JFET region 14a. The body region 16 is located in a position exposed to the upper surface 1a of the semiconductor substrate 1 and is positioned to separate the drift region 14 and the source region 18. A portion of the body region 16 located between the JFET region 14a of the drift region 14 and the source region 18 is called the channel region CH. The source region 18 is located in a position exposed to the upper surface 1a of the semiconductor substrate 1.
[0013] The MOS structure 20 is provided so as to cover a portion of the upper surface 1a of the semiconductor substrate 1, and comprises a gate insulating film 22 and a gate electrode 24. The gate electrode 24 faces the channel region CH of the body region 16 via the gate insulating film 22. In the device structure 10, the electron density of the inversion layer generated in the channel region CH of the body region 16 is controlled according to the gate voltage applied to the gate electrode 24.
[0014] As shown in Figure 4, in the deformation prevention layer formation process (step S2 in Figure 1), a first deformation prevention layer 30 is formed over the entire upper surface 1a of the semiconductor substrate 1, and a second deformation prevention layer 40 is formed over the entire lower surface 1b of the semiconductor substrate 1. The materials of these deformation prevention layers 30 and 40 are not particularly limited. The materials of these deformation prevention layers 30 and 40 may have a higher Young's modulus than the semiconductor substrate 1, or they may have a lower Young's modulus than the semiconductor substrate 1. The first deformation prevention layer 30 and the second deformation prevention layer 40 may use the same material, or they may use different materials.
[0015] The first anti-deformation layer 30 may be an organic material in consideration of stress reduction for the device structure formed on the upper surface 1a of the semiconductor substrate 1 and adhesion to the upper surface 1a of the semiconductor substrate 1. The first anti-deformation layer 30 may be, for example, a resin (such as a thermosetting resin or an ultraviolet curable resin). Alternatively, the first anti-deformation layer 30 may be a surface protection tape widely used in semiconductor manufacturing processes.
[0016] In addition to materials similar to those of the first anti-deformation layer 30, the second anti-deformation layer 40 may be a ceramic, a metal material, a crystal material, or a combination thereof. These materials may be directly bonded to the lower surface 1b of the semiconductor substrate 1, or may be formed on the lower surface 1b of the semiconductor substrate 1 using a film forming technique (such as sputtering technique, evaporation technique, or plasma film forming technique).
[0017] In this example, resins are used for both the first anti-deformation layer 30 and the second anti-deformation layer 40. Note that the thicknesses of the first anti-deformation layer 30 and the second anti-deformation layer 40 are not particularly limited and may be appropriately adjusted so as to suppress deformation of the semiconductor substrate 1 in the laser irradiation process described later.
[0018] As shown in FIG. 5, in the laser irradiation process (step S3 in FIG. 1), the laser is irradiated onto the condensing surface 3 extending to a predetermined depth of the semiconductor substrate 1. The laser is irradiated so as to be condensed at a predetermined depth of the semiconductor substrate 1 from the lower surface 1b of the semiconductor substrate 1 where the device structure is not formed. The laser is a laser in a wavelength range having permeability to the semiconductor substrate 1 (a gallium nitride substrate in this example) and the second anti-deformation layer 40. The laser is not particularly limited, and may be a visible light laser, for example, a green laser. At the position of the condensing point, the crystal (a single crystal of gallium nitride in this example) constituting the semiconductor substrate 1 is heated and decomposed, and a modified layer is formed. The strength of the modified layer is lower than that of the crystal constituting the semiconductor substrate 1. Therefore, the strength of the modified layer becomes lower than that of the surrounding crystals.
[0019] Nitrogen gas is generated during the process of forming a modified layer inside the semiconductor substrate 1. When nitrogen gas is generated inside the semiconductor substrate 1, the semiconductor substrate 1 tends to expand and deform. However, deformation prevention layers 30 and 40 are formed on both sides of the semiconductor substrate 1. Therefore, even if nitrogen gas is generated inside the semiconductor substrate 1, deformation of the semiconductor substrate 1 is suppressed. As a result, variations in the focusing position of the laser irradiation and damage to the semiconductor substrate 1 are suppressed.
[0020] As shown in Figure 6, in the peeling process (step S4 in Figure 1), the device layer 2 on which the device structure 10 is formed is peeled off from the remaining layers of the semiconductor substrate 1 along the focusing surface 3 irradiated with the laser. Since the strength of the focusing surface 3 is reduced due to the formation of the altered layer, the device layer 2 is peeled off cleanly from the remaining layers of the semiconductor substrate 1. In this peeling process, the deformation prevention layers 30 and 40 remain on both sides of the semiconductor substrate 1. In this way, the deformation prevention layers 30 and 40 can also function as surface protective films in the peeling process. The semiconductor substrate 1 after the device layer 2 has been peeled off is reused in the manufacture of semiconductor devices. For example, after polishing and etching the peeled surface of the semiconductor substrate 1, the device layer can be formed on the peeled surface using epitaxial crystal growth technology, thereby forming a device structure on the formed device layer.
[0021] As shown in Figure 7, in the dicing process (step S5 in Figure 1), after polishing and electrode formation processes are performed on the device layer 2 peeled off from the semiconductor substrate 1, multiple devices (also called dies) are cut out from the device layer 2, and the semiconductor device is completed.
[0022] Other features and variations of the above manufacturing method are described below.
[0023] Figure 8 is an enlarged cross-sectional view of the main part near the periphery of the lower surface 1b of the semiconductor substrate 1. Generally, the periphery of the main surface of a semiconductor substrate is often curved. For this reason, as shown in Figure 8, an end curved surface 1d is formed on the periphery of the lower surface 1b of the semiconductor substrate 1, extending between the lower surface 1b and the side surface 1c. The laser irradiated in the laser irradiation process is irradiated from a direction perpendicular to the lower surface 1b of the semiconductor substrate 1. For this reason, if the second deformation prevention layer 40 is not formed, the laser is refracted by the end curved surface 1d of the semiconductor substrate 1. As a result, the laser may not be focused at both ends of the focusing surface 3 of the semiconductor substrate 1.
[0024] As shown in Figure 8, the second deformation prevention layer 40 extends laterally beyond the side surface 1c of the semiconductor substrate 1 and is formed to cover the curved edge surface 1d of the semiconductor substrate 1. The difference in refractive index between the second deformation prevention layer 40 and the semiconductor substrate 1 is smaller than the difference in refractive index between air and the semiconductor substrate 1. Therefore, when the second deformation prevention layer 40 is formed to cover the curved edge surface 1d of the semiconductor substrate 1, the refraction of the laser passing through the interface between the second deformation prevention layer 40 and the curved edge surface 1d of the semiconductor substrate 1 is suppressed. Furthermore, when observed along the laser irradiation direction, a flat surface 40a of the second deformation prevention layer 40 exists in the range R1 where the curved edge surface 1d of the semiconductor substrate 1 exists. Therefore, the refraction of the laser when incident on the second deformation prevention layer 40 is also suppressed. As a result, in the laser irradiation process, the laser can be well focused to both ends of the focusing surface 3 of the semiconductor substrate 1. When the laser is well focused on both ends of the focusing surface 3 of the semiconductor substrate 1, the altered layer can extend to the side surface 1c of the semiconductor substrate 1. As a result, the altered layer is exposed on the side surface 1c of the semiconductor substrate 1, and some of the nitrogen gas generated during the laser irradiation process can be well discharged from the side surface of the semiconductor substrate 1. As a result, even if nitrogen gas is generated inside the semiconductor substrate 1, deformation of the semiconductor substrate 1 is suppressed. In order to well discharge nitrogen gas from the side surface 1c of the semiconductor substrate 1, it is desirable that the deformation prevention layers 30 and 40 are not covered on the portion of the side surface 1c of the semiconductor substrate 1 where the focusing surface 3 is exposed.
[0025] As shown in Figure 9, a removal process may be performed before the laser irradiation process to remove the periphery of the upper surface 1a of the semiconductor substrate 1, so that the side surface 1c on the upper surface 1a side of the semiconductor substrate 1 is located inside the semiconductor substrate 1 compared to the side surface 1c on the lower surface 1b side of the semiconductor substrate 1. In other words, the upper surface 1a of the semiconductor substrate 1 is edge-trimmed so that when the semiconductor substrate 1 is viewed from above, the periphery of the upper surface 1a is located inside the periphery of the lower surface 1b. The removal process may be performed before or after the deformation prevention layer formation process. The offset length L1 between the side surface 1c on the upper surface 1a side and the side surface 1c on the lower surface 1b side of the semiconductor substrate 1 is greater than the width of the range R1 (see Figure 8) where the edge curved surface 1d of the lower surface 1b of the semiconductor substrate 1 exists. The light-gathering surface 3 of the semiconductor substrate 1 is exposed on the side surface 1c on the upper surface 1a side of the semiconductor substrate 1, which is located inside the semiconductor substrate 1.
[0026] In the laser irradiation process, the laser focused on the focusing surface 3 is incident into the semiconductor substrate 1 from the flat lower surface 1b, which is inside the curved edge surface 1d of the semiconductor substrate 1. Therefore, in the laser irradiation process, the laser can be well focused on both ends of the focusing surface 3 of the semiconductor substrate 1.
[0027] As shown in Figure 10, the first deformation prevention layer 30 may have an adhesive layer 32 and a support substrate 34. The adhesive layer 32 is made of an organic material and is not particularly limited, but may be, for example, a double-sided tape commonly used in semiconductor manufacturing processes. The support substrate 34 is fixed to the upper surface 1a of the semiconductor substrate 1 via the adhesive layer 32 and is made of a material with a higher Young's modulus than the semiconductor substrate 1. The support substrate 34 is a flat substrate that extends parallel to the main surface of the semiconductor substrate 1 and extends laterally beyond the side surface 1c of the semiconductor substrate 1. The support substrate 34 is not particularly limited, but may be, for example, a glass substrate or a sapphire substrate. The second deformation prevention layer 40 also has an adhesive layer 42 and a support substrate 44. The adhesive layer 42 and support substrate 44 of the second deformation prevention layer 40 can be made of the same materials as the adhesive layer 32 and support substrate 34 of the first deformation prevention layer 30.
[0028] Both of these deformation-preventing layers 30 and 40 have support substrates 34 and 44 with a high Young's modulus. Therefore, even if nitrogen gas is generated inside the semiconductor substrate 1 during the laser irradiation process, deformation of the semiconductor substrate 1 is suppressed.
[0029] The features of the technology disclosed herein are summarized below. Note that the technical elements described below are independent elements that exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing.
[0030] (Feature 1) A method for manufacturing a semiconductor device, A deformation prevention layer formation step comprising forming a first deformation prevention layer (30) on the first main surface of a semiconductor substrate (1) having a first main surface (1a) and a second main surface (1b), and forming a second deformation prevention layer (40) on the second main surface of the semiconductor substrate, wherein a device structure is formed on the first main surface side of the semiconductor substrate. A laser irradiation step in which a laser is irradiated into the semiconductor substrate by passing through the second deformation prevention layer formed on the second main surface of the semiconductor substrate, wherein the laser is irradiated onto a surface (3) extending to a predetermined depth within the semiconductor substrate. A peeling step of peeling the device layer (2) on which the device structure is formed from the remaining layers of the semiconductor substrate along the surface irradiated with the laser, A method for manufacturing a semiconductor device, comprising:
[0031] (Feature 2) The method for manufacturing a semiconductor device according to feature 1, wherein at least one of the first deformation prevention layer and the second deformation prevention layer has an organic material layer.
[0032] (Feature 3) At least one of the first deformation prevention layer and the second deformation prevention layer has a support substrate, The method for manufacturing a semiconductor device according to Feature 1, wherein the support substrate has a Young's modulus greater than that of the semiconductor substrate.
[0033] (Feature 4) The semiconductor substrate has a curved end surface (1d) at the periphery of the second main surface, The method for manufacturing a semiconductor device according to any one of features 1 to 3, wherein in the deformation prevention layer formation step, the second deformation prevention layer is formed so as to cover the end curved surface.
[0034] (Feature 5) The method for manufacturing a semiconductor device according to feature 4, wherein in the deformation prevention layer formation step, the second deformation prevention layer is formed so as not to cover the portion of the side surface (1c) of the semiconductor substrate that extends to a predetermined depth within the semiconductor substrate and is exposed.
[0035] (Feature 6) Prior to the laser irradiation step, the method further includes a removal process in which the peripheral edge of the first main surface of the semiconductor substrate is removed, and the side surface of the semiconductor substrate on the first main surface side is positioned further inward than the side surface of the semiconductor substrate on the second main surface side. The method for manufacturing a semiconductor device according to any one of features 1 to 5, wherein in the laser irradiation step, a surface extending to a predetermined depth within the semiconductor substrate is exposed on the side surface of the semiconductor substrate on the first main surface side.
[0036] (Feature 7) A method for manufacturing a semiconductor device according to any one of features 1 to 6, wherein the semiconductor substrate is a nitride semiconductor.
[0037] Although embodiments have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness. [Explanation of Symbols]
[0038] 1: Semiconductor substrate, 2: Device layer, 3: Light-gathering surface, 30: First deformation prevention layer, 32, 42: Adhesive layer, 34, 44: Support substrate, 40: Second deformation prevention layer
Claims
1. A method for manufacturing a semiconductor device, A deformation prevention layer formation step comprising forming a first deformation prevention layer (30) on the first main surface of a semiconductor substrate (1) having a first main surface (1a) and a second main surface (1b), and forming a second deformation prevention layer (40) on the second main surface of the semiconductor substrate, wherein a device structure is formed on the first main surface side of the semiconductor substrate. A laser irradiation step in which a laser is irradiated into the semiconductor substrate by passing through the second deformation prevention layer formed on the second main surface of the semiconductor substrate, wherein the laser is irradiated onto a surface (3) extending to a predetermined depth within the semiconductor substrate. A peeling step in which the device layer (2) on which the device structure is formed is peeled off from the remaining layers of the semiconductor substrate along the surface irradiated with the laser, A method for manufacturing a semiconductor device, comprising:
2. The method for manufacturing a semiconductor device according to claim 1, wherein at least one of the first deformation prevention layer and the second deformation prevention layer has an organic material layer.
3. At least one of the first deformation prevention layer and the second deformation prevention layer has a support substrate, The method for manufacturing a semiconductor device according to claim 1, wherein the support substrate has a Young's modulus greater than that of the semiconductor substrate.
4. The semiconductor substrate has a curved end surface (1d) at the periphery of the second main surface, The method for manufacturing a semiconductor device according to claim 1, wherein in the deformation prevention layer formation step, the second deformation prevention layer is formed so as to cover the end curved surface.
5. The method for manufacturing a semiconductor device according to claim 4, wherein in the deformation prevention layer formation step, the second deformation prevention layer is formed such that it does not cover the portion of the side surface (1c) of the semiconductor substrate in which a surface extending to a predetermined depth within the semiconductor substrate is exposed.
6. Prior to the laser irradiation step, the method further includes a removal process in which the peripheral edge of the first main surface of the semiconductor substrate is removed, so that the side surface of the semiconductor substrate on the first main surface side is positioned further inward than the side surface of the semiconductor substrate on the second main surface side. The method for manufacturing a semiconductor device according to claim 1, wherein in the laser irradiation step, a surface extending to a predetermined depth within the semiconductor substrate is exposed on the side surface of the semiconductor substrate on the first main surface side.
7. The method for manufacturing a semiconductor device according to any one of claims 1 to 6, wherein the semiconductor substrate is a nitride semiconductor.