METHOD FOR MANUFACTURING A SEMICONDUCTOR DEVICE

Abstract

Method for manufacturing a semiconductor device comprising: Applying a laser beam to a plane (3) extending to a predetermined depth in a semiconductor substrate (1) from one side of a second principal surface (1b) of the semiconductor substrate (1), wherein the side of the second principal surface (1b) is opposite to one side of a first principal surface (1a) of the semiconductor substrate (1) on which a device structure (10) containing a channel (CH) is formed; Detaching a device layer (2) containing the device structure (10) from the semiconductor substrate (1) along the plane (3) onto which the laser beam (L) is applied, wherein The laser beam (L) is applied in such a way that the power density in the plane (3), which extends to the predetermined depth in the semiconductor substrate (1), is lower in a region corresponding to the channel (CH) in a thickness direction of the semiconductor substrate (1) than in a remaining region.

Description

[0001] The present invention relates to a method for manufacturing a semiconductor device.

[0002] A technique has been developed for forming a device pattern on a main surface of a semiconductor substrate and then peeling a device layer on which the device pattern is formed from the semiconductor substrate. By using such a technique, it is possible to reuse the semiconductor substrate from which the device layer has been peeled. Furthermore, it is possible to reduce the manufacturing cost of semiconductor devices. For example, JP 2020-102520 A discloses a technique for forming a modified layer within a semiconductor substrate by irradiating a plane extending to a predetermined depth within the semiconductor substrate with a laser beam and peeling the device layer from the semiconductor substrate along the plane on or in which the modified layer was formed.

[0003] US 2021 / 0 197 314 A1 discloses a method for manufacturing a semiconductor device, comprising: applying a laser beam to a plane extending to a predetermined depth in a semiconductor substrate, wherein a side of the second main surface is opposite to a side of a first main surface of the semiconductor substrate on which a device structure including a channel is formed; peeling a device layer including the device structure from the semiconductor substrate along the plane to which the laser beam is applied, wherein the laser beam is applied in the application of the laser beam such that a power density in the plane extending to the predetermined depth in the semiconductor substrate is lower in one region than in a remaining region.

[0004] JP 2020 - 102 520 A discloses a method for manufacturing a semiconductor device in which a laser is used from a second main surface of the semiconductor substrate.

[0005] According to studies conducted by the inventors of the present application, it was found that a portion of the laser beam that is not absorbed at a focal point reaches the device structure and leads to a change in the electrical properties of the device structure. In particular, it was found that the laser beam that reaches the device structure leads to changes in a leakage current and a shift in the threshold voltage. Therefore, it is an object of the invention to provide a method for manufacturing a semiconductor device that avoids changes in the electrical properties of such device structures. This object is achieved by a method for manufacturing a semiconductor device having the features of claim 1. The dependent claims are directed to advantageous developments of the invention.

[0006] According to one aspect of the present invention, a method for manufacturing a semiconductor device includes: applying a laser beam to a plane extending to a predetermined depth in a semiconductor substrate from the side of a second surface of the semiconductor substrate opposite to a first surface on which a device structure having a channel is formed; and peeling a device layer in which the device structure is formed from the semiconductor substrate along the plane. In applying the laser beam, the laser beam is applied to the plane extending to the predetermined depth such that a power density of the laser beam is lower in a region corresponding to the channel of the device structure in a thickness direction of the semiconductor substrate than in the other region.

[0007] In this case, "the plane extending to the predetermined depth of the semiconductor substrate" refers to a plane extending in a direction orthogonal to the thickness direction of the semiconductor substrate and having a predetermined thickness taking into account the expansion or dispersion of the focal points of the laser beams. "The region corresponding to the channel of the device structure in the thickness direction of the semiconductor substrate" or "the region corresponding to the lower side of the channel of the device structure" refers to a region including at least a part of a region overlapping with the channel of the device structure when the semiconductor substrate is viewed in the thickness direction, that is, in the thickness direction of the semiconductor substrate. "The power density of the laser beam" refers to the light intensity of the laser beam per unit area.Unit area on the plane extending to the predetermined depth in the semiconductor substrate when the semiconductor substrate is viewed in the thickness direction. In such a method, the power density of the laser beam is lower at least in the region corresponding to the channel of the device structure than in the remaining region, and may include a case where the power density of the laser beam is substantially zero in the region corresponding to the channel of the device structure.

[0008] According to such a method, the power density of the laser beam applied to the region corresponding to the channel of the device structure is low. For this reason, the light intensity of the laser beam not absorbed at the focal point is reduced in the region corresponding to the channel of the device structure. Therefore, it is possible to prevent a portion of the laser beam not absorbed at the focal point from reaching the channel of the device structure. As a result, changes in the electrical properties of the device structure can be prevented.

[0009] Objects, features, and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings, in which the same parts are designated by the same reference numerals. In the drawings: Fig. 1 is a diagram showing a flow of a manufacturing process of a semiconductor device including a laser application process, a detachment process, and a dicing process; Fig. 2 is a diagram schematically showing a cross section of a semiconductor substrate in the manufacturing process of the semiconductor device; Fig. 3 is a diagram schematically showing a cross section of a unit cell of a device structure formed adjacent to an upper surface of the semiconductor substrate; Fig. 4 is a diagram schematically showing a cross section of the semiconductor substrate in the manufacturing process of the semiconductor device; Fig. 5 is a diagram schematically showing a cross section of the semiconductor substrate in the manufacturing process of the semiconductor device; Fig. 6 is a diagram schematically showing a cross section of the semiconductor substrate in the manufacturing process of the semiconductor device; Fig. 7 is a diagram showing a flow of a first example of the laser application process; Fig. 8 is a plan view of a semiconductor substrate for explaining a plurality of application position coordinates set in the first example of the laser application process; Fig. 9 is a plan view of a semiconductor substrate for explaining a plurality of channel position coordinates set in the first example of the laser application process; Fig. 10 is a plan view of a semiconductor substrate for explaining respective positions of first application position coordinates and second application position coordinates into which application position coordinates are categorized in the first example of the laser application process; Fig. 11 is a diagram showing a flow of a second example of the laser application process; Fig. 12 is a diagram schematically showing a cross section of a semiconductor substrate in a step of the second example of the device shown in Fig. 11 shows the laser application process; Fig. 13 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the second example of the device shown in Fig. 11 shows the laser application process; Fig. 14 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the second example of the device shown in Fig. 11 shows the laser application process; Fig. 15 is a diagram showing a flow of a third example of the laser application process; Fig. 16 is a diagram schematically showing a cross section of a semiconductor substrate in a step of the third example of the device shown in Fig. 15 shows the laser application process; Fig. 17 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the third example of the device shown in Fig. 15 shows the laser application process; Fig. 18 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the third example of the device shown in Fig. 15 shows the laser application process; Fig. 19 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the third example of the device shown in Fig. 15 shows the laser application process; Fig. 20 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the third example of the device shown in Fig. 15 shows the laser application process; Fig. 21 is a diagram showing a flow of a fourth example of the laser application process; Fig. 22 is a diagram schematically showing a cross section of a semiconductor substrate in a step of the fourth example of the device shown in Fig. 21 shows the laser application process; Fig. 23 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the fourth example of the device shown in Fig. 21 shows the laser application process; Fig. 24 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the fourth example of the device shown in Fig. 21 shows the laser application process; Fig. 25 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the fourth example of the device shown in Fig. 21 shows the laser application process; and Fig. 26 is a diagram schematically showing a cross section of the semiconductor substrate in a step of the fourth example of the device shown in Fig. 21 shows the laser application process.

[0010] A method for manufacturing a semiconductor device disclosed herein may include a laser application process and a stripping process. In the laser application process, a laser beam is applied to a plane in a semiconductor substrate extending to a predetermined depth in the semiconductor substrate. The semiconductor substrate is not particularly limited but may be a compound semiconductor substrate. For example, the semiconductor substrate may be made of a nitride semiconductor containing gallium nitride, silicon carbide, or gallium oxide. By the method for manufacturing a semiconductor device disclosed herein, the semiconductor substrate can be reused. Thus, the method for manufacturing a semiconductor device disclosed herein may be useful for a semiconductor substrate of an expensive compound semiconductor.

[0011] The semiconductor substrate has a first main surface and a second main surface opposite to the first main surface, and a device structure having a channel is formed adjacent to the first main surface. The type of device structure is not particularly limited but may be, for example, a switching element structure. For example, a metal-oxide-semiconductor field-effect transistor (MOSFET) or an insulated-gate bipolar transistor (IGBT) can be used as the type of switching element structure.

[0012] In the laser application process, a laser beam is applied to a predetermined depth of the semiconductor substrate from the second main surface where the device structure is not formed. In the stripping process, a device layer in which the device structure is formed is stripped from the semiconductor substrate along the plane irradiated with the laser beam. In the laser application process, the laser beam is applied in the plane extending to the predetermined depth in the semiconductor substrate such that a power density of the laser beam in a region corresponding to the channel in a thickness direction of the semiconductor substrate is lower than in the remaining region.

[0013] According to one aspect of the manufacturing method described above, the laser application process may include the following steps: preparing laser application coordinate data including a plurality of application position coordinates that determine positions for applying the laser beam to the semiconductor substrate in a two-dimensional coordinate system that defines in-plane positions in the semiconductor substrate, that is, positions in a plane of the semiconductor substrate; preparingCreating channel coordinate data including one or more channel position coordinates that determine a position of the channel of the device structure in the two-dimensional coordinate system; categorizing the application position coordinates into one or more first application position coordinates not included in the one or more channel position coordinates and one or more second application coordinates included in the one or more channel position coordinates; and applying the laser beam to the predetermined depth in the semiconductor substrate at one or more positions corresponding to the one or more first application position coordinates, while refraining from applying the laser beam to the predetermined depth at one or more positions corresponding to the one or more second application position coordinates.

[0014] In such a method, by controlling the application of the laser beam in the plane extending to the predetermined depth in the semiconductor substrate based on the first application position coordinates and the second application position coordinates, the power density of the laser beam may be smaller in the region corresponding to the channel of the device structure in the thickness direction of the semiconductor substrate than in the other region.

[0015] According to one aspect of the manufacturing method described above, the laser application process may include the following steps: disposing a laser shielding film for shielding the laser beam in a region corresponding to the channel of the device structure in the thickness direction of the semiconductor substrate; and applying the laser beam to the predetermined depth in the semiconductor substrate above the laser shielding film. In this case, "disposing the laser shielding film" means that the laser shielding film is present at least in the region corresponding to the channel in the thickness direction of the semiconductor substrate.Although there is no particular limitation, examples of disposing the laser shielding film may include disposing the laser shielding film on the second main surface of the semiconductor substrate or in an interior of the semiconductor substrate as a film, disposing the laser shielding film on the second main surface of the semiconductor substrate, and disposing the laser shielding film separately from the second main surface of the semiconductor substrate.

[0016] In such a method, since the laser shielding film blocks the laser beam, the power density of the laser beam in the plane extending to the predetermined depth in the semiconductor substrate may be lower in the region corresponding to the channel in the thickness direction of the semiconductor substrate than in the remaining region.

[0017] Disposing the laser shielding film may include the following steps: forming the laser shielding film entirely over the second main surface of the semiconductor substrate as a film; and partially removing the laser shielding film so that the laser shielding film is left in the region corresponding to the channel of the device structure in the thickness direction of the semiconductor substrate. By such a method, the laser shielding film can be formed on the second main surface of the semiconductor substrate.

[0018] Disposing the laser shielding film may include the following steps: forming the laser shielding film over an entire surface of a base substrate as a film; partially removing the laser shielding film so that the laser shielding film is left in a region corresponding to a formation position where the channel of the device structure is to be formed; and forming an epitaxial layer on the surface of the base substrate as a film, thereby forming the semiconductor substrate. The "region corresponding to the formation position where the channel of the device structure is to be formed" means the region corresponding to the channel of the device structure in the thickness direction of the semiconductor substrate when the device structure is formed on the semiconductor substrate. By such a method, the laser shielding film can be formed within the semiconductor substrate.

[0019] According to one aspect of the manufacturing method described above, applying the laser beam may include the steps of: forming a mask over the entire second main surface of the semiconductor substrate as a film; partially removing the mask so that a region corresponding to the channel in the thickness direction of the semiconductor substrate is opened; and forming a damage region by applying damage to the portion of the second main surface of the semiconductor substrate exposed from the mask; removing the mask after forming the damage region; and applying the laser beam to the predetermined depth of the semiconductor substrate over the damage region. The surface roughness of the second main surface of the semiconductor substrate is increased in the damage region. Therefore, the amount ofThe amount of laser beam transmitted through the damage region is greatly reduced by reflection and / or scattering. By such a method, the power density of the laser beam in the plane extending to the predetermined depth in the semiconductor substrate can be lower in the region corresponding to the channel in the thickness direction of the semiconductor substrate than in the remaining region, because the damage region blocks the laser beam.

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0021] First, a laser application process, a detachment process, and a dicing process of a semiconductor device manufacturing method will be described with reference to the drawings. Next, some examples of the laser application process of the present invention will be described in detail. Note that, in the semiconductor device manufacturing method, known techniques can be used for processes other than the laser application process, the detachment process, and the dicing process. For example, a device structure can be manufactured using a known technique.

[0022] Fig. Fig. 1 shows a flow of a manufacturing process including a laser application process (S1), a detachment process (S2), and a dicing process (S3). In a method for manufacturing a semiconductor device disclosed herein, a plurality of semiconductor devices, also referred to as chips, are manufactured by performing these processes for a semiconductor substrate 1, which is Fig. 2 is shown.

[0023] As it is in Fig. As shown in Figure 2, the semiconductor substrate 1 has an upper surface 1a and a lower surface 1b that are planar and extend parallel to each other. The upper surface 1a and lower surface 1b are also referred to as main surfaces. The upper surface 1a and lower surface 1b are also referred to as the first main surface and the second main surface. Although the semiconductor substrate 1 is not particularly limited, the semiconductor substrate 1 in this example is a gallium nitride substrate. A plane 3 extending to a predetermined depth in the semiconductor substrate 1 is a plane irradiated with a laser beam, that is, a plane on which a plurality of laser focal points are concentrated. In this specification, a part of the semiconductor substrate 1 above the laser irradiation plane 3, that is, a part to be peeled off from the semiconductor substrate 1, is referred to as a device layer 2.The device layer 2 of the semiconductor substrate 1 is formed with a device structure having a channel.

[0024] Fig. Figure 3 shows a unit cell of a device structure 10 formed within the device layer 2 of the semiconductor substrate 1. Although there is no limitation in this regard, the device structure 10 is, for example, a vertical MOSFET. The device structure 10 has a drain region 12 of the n + -type, a drift region 14 of n-type, a body region 16 of p-type, a source region 18 of n +-type and a planar insulated gate 19. The drain region 12 is arranged at a position exposed from the lower surface 1b of the semiconductor substrate 1. The drift region 14 is arranged between the drain region 12 and the body region 16. A part of the drift region 14 that lies on the upper surface 1a of the semiconductor substrate 1 is referred to as a JFET region 14a. The body region 16 is arranged at a position that lies on the upper surface 1a of the semiconductor substrate 1 and is arranged to separate the drift region 14 and the source region 18 from each other. A part of the body region 16 that is arranged between the JFET region 14a of the drift region 14 and the source region 18 is referred to as a channel CH. The source region 18 is arranged at a position located on the upper surface 1a of the semiconductor substrate 1.The insulated gate 19 is arranged to cover a portion of the upper surface 1a of the semiconductor substrate 1 and is arranged facing the channel CH of the body region 16. The electron density in an inversion layer created in the channel CH of the body region 16 is controlled according to the voltage applied to the insulated gate 19, so that an on-state and off-state of the device structure 10 are controlled. Thus, the channel CH is defined as a region where the carrier density is controlled by the gate.

[0025] In the laser application process (S1 in Fig. 1) a laser beam L is applied to the plane 3 extending at the predetermined depth in the semiconductor substrate 1, as shown in Fig. 4. The laser beam L is applied from the lower surface 1b of the semiconductor substrate 1, where the device structure 10 is not formed. The laser beam L is applied such that it is focused to the predetermined depth in the semiconductor substrate 1. The laser beam L has a wavelength range that transmits through the semiconductor substrate 1, in this example, the gallium nitride substrate. At the position of the focal point, the crystal constituting the semiconductor substrate 1, for example, a single crystal of gallium nitride, is heated and decomposed. As a result, an extraction layer of atoms constituting the crystal of the semiconductor substrate 1 is formed at the positions of the focal points as a modified layer. In this example, the extraction layer is made of gallium. 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 is lower than that of the surrounding crystal.

[0026] In the laser application process, the laser beam L is applied such that the power density of the laser beam L in the plane 3 extending to the predetermined depth in the semiconductor substrate 1 is lower in a region corresponding to the channel CH of the device structure 10 in a thickness direction of the semiconductor substrate than in the remaining region. In other words, the laser beam L is applied such that the power density of the laser beam L is lower in a region corresponding to a lower side of the channel CH than in the remaining region in the plane 3. Specifically, the laser beam L is applied such that the power density of the laser beam L is lower in a region corresponding to at least a part of the channel CH of the device structure 10 in a plan view, that is, in a direction orthogonal to the surface of the semiconductor substrate 1, than in the remaining region.For example, the laser beam L is applied such that the power density of the laser beam L is lower in a region including the entire region corresponding to the channel CH of the device structure 10 in the thickness direction of the semiconductor substrate 1 than in the remaining region. Various examples of forming such a power density distribution in the laser application process will be described later. Due to such a power density distribution, the intensity of the laser beam L not absorbed at the focal point is reduced in the region below the channel CH of the device structure 10. Therefore, it is possible to prevent a part of the unabsorbed laser beam from reaching the channel CH of the device structure 10. As a result, changes in the electrical characteristics of the device structure 10 can be prevented.

[0027] In the detachment process (S2 in Fig. 1) the device layer 2 in which the device structure 10 has been formed is detached from the semiconductor substrate 1 along the plane 3 which is or has been irradiated with the laser beam L, as shown in Fig. 5. Since the strength of the semiconductor substrate 1 at the laser-irradiated plane 3 is reduced due to the formation of the modified layer, the device layer 2 can be satisfactorily peeled off the semiconductor substrate 1. The semiconductor substrate 1 from which the device layer 2 has been removed is reused for further manufacturing of semiconductor devices. After polishing and etching the peeling surface of the semiconductor substrate 1 from which the device layer 2 has been removed, a device layer is film-formed on the peeling surface using an epitaxial crystal growth technique, and a device structure is formed in the film-formed device layer.

[0028] In the isolation process (S3 in Fig. 1), the device layer 2, which has been peeled off from the semiconductor substrate 1, is subjected to a polishing process, an electrode formation process, and the like. Then, the device layer 2 is cut into devices (dices) as shown in Fig. 6. In this way, the semiconductor device is manufactured.

[0029] Specific examples of the laser application process are described below. <Erstes Beispiel des Laseranwendungsprozesses>

[0030] A first example of the laser application process is given with reference to the Fig. 7 to 10. In the first example of the laser application process, laser application coordinate data are first created or prepared (S11 in Fig. 7). The laser application coordinate data contains several application position coordinates 22, as shown in Fig. 8. The application position coordinates 22 are coordinates for determining the positions for applying the laser beam L in the semiconductor substrate 1 in a two-dimensional coordinate system that defines in-plane positions of the semiconductor substrate 1. One pulse of the laser beam L is applied to one application position coordinate 22. Although there is no particular limitation, the application position coordinates 22 are set in a matrix form, in which, in this example, the application position coordinates 22 are arranged at equal intervals in the vertical direction and the horizontal direction.

[0031] As it is in Fig. 9, channel coordinate data containing one or more channel position coordinates 24 in the two-dimensional coordinate system are then created or prepared (S12 in Fig. 7). The one or more channel position coordinates 24 are coordinates for determining the position of the channel or channels (see channel CH in Fig. 3) the device structures 10 formed adjacent to the upper surface 1a of the semiconductor substrate 1. In this example, the channel position coordinates 24 are set in a matrix form in which the channel position coordinates 24 are arranged at equal intervals in the vertical direction and the horizontal direction. Since the channel CH of the device structure 10 has an area, the respective channel position coordinates 24 are set such that the area of ​​the channel CH can be specified. The channel position coordinates 24 can be set using mask data for photolithography to form the device structures 10.Alternatively, the channel position coordinates 24 may be set based on the positions of the channels CH specified in an image of the upper surface 1a of the semiconductor substrate 1 obtained after the device structures 10 are formed on the upper surface 1a of the semiconductor substrate 1.

[0032] As it is in Fig. 10, the application position coordinates 22 included in the laser application coordinate data are then categorized into a plurality of first application position coordinates 22a and a plurality of second application position coordinates 22b (S13 in Fig. 7). Among the application position coordinates 22, the first application position coordinates 22a are coordinates not included in the channel position coordinates 24. Among the application position coordinates 22, the second application position coordinates 22b are coordinates included in the channel position coordinates 24.

[0033] In the first example of the laser application process, the laser beam L is applied to the interior of the semiconductor substrate 1 based on the first application position coordinates 22a and second application position coordinates 22b created as described above (S14 in Fig. 7). Specifically, the laser beam L is applied to a portion at the predetermined depth within the semiconductor substrate 1 corresponding to the first application position coordinate 22a, but the laser beam L is not applied to a portion at the predetermined depth within the semiconductor substrate 1 corresponding to the second application position coordinate 22b. The laser beam L is applied such that the power density of the laser beam L in the plane 3 extending at the predetermined depth in the semiconductor substrate 1 is lower in the region corresponding to the lower side of the channel CH of the device structure than in the remaining region. As a result, it is possible to prevent a part of the laser beam L that is not absorbed at the focal point at the predetermined depth of the semiconductor substrate 1 from reaching the channel CH of the device structure 10.

[0034] Alternatively, the laser beam L may be applied to the portion corresponding to the second application position coordinate 22b at the predetermined depth in the semiconductor substrate 1 with a smaller application energy than that for the portion corresponding to the first application position coordinate 22a at the predetermined depth of the semiconductor substrate 1. In this case, too, the laser beam L may be applied such that the power density in the region corresponding to the lower side of the channel CH of the device structure 10 is lower than in the remaining region. Therefore, it is possible to prevent a part of the laser beam L that is not absorbed at the focal point from reaching the channel CH of the device structure 10. In this example, the device layer 2 can be satisfactorily peeled off from the semiconductor substrate 1 in the peeling process.The control of the application energy of the laser beam L is not particularly limited, but can be achieved by controlling a spatial light modulator (SLM) of a reflective liquid crystal such as a liquid crystal on silicon substrate (LCOS) or an attenuator. <Zweites Beispiel des Laseranwendungsprozesses>

[0035] A second example of the laser application process is described with reference to the Fig. 11 to 14. In the cross sections of the Fig. 12 to 14, the unit cells of the device structures 10 formed adjacent to the upper surface 1a of the semiconductor substrate 1 are shown in a simplified manner. In the second example of the laser application process (S21 in Fig. 11), first, a laser shielding film 32a is formed on the entire lower surface 1b of the semiconductor substrate 1, as shown in Fig. 12. The laser shielding film 32 is a film that reflects the laser beam L or a film that is not transparent to the laser beam L. The laser shielding film 32 is not particularly limited, but may be, for example, an Al film or an Au film with a thickness of about 1 μm. Alternatively, the laser shielding film 32 may be a black matrix used in a color filter of a liquid crystal panel.

[0036] As it is in Fig. 13, the laser shielding film 32 is then partially removed using an etching technique, so that portions of the laser shielding film 32 corresponding to the lower side of the channels CH of the semiconductor devices 10 remain (S22 in Fig. 11). Specifically, the laser shielding film 32 is left at least in a portion of the region corresponding to the channel CH of the device structure 10 when the semiconductor substrate 1 is viewed in the direction orthogonal to the surface of the semiconductor substrate 1, that is, in the thickness direction of the semiconductor substrate 1. For example, the laser shielding film 32 is left in the entire region overlapping the channel CH of the device structure 10 in the thickness direction of the semiconductor substrate 1.

[0037] As it is in Fig. 14, the laser beam L is then applied to the predetermined depth in the semiconductor substrate 1 from the side of the lower surface 1b of the semiconductor substrate 1 (S23 in Fig. 11). The laser beam L is applied to the predetermined depth of the semiconductor substrate 1 through the laser shielding film 32. Since the laser shielding film 32 shields the laser beam L, the power density of the laser beam L in the plane 3 extending to the predetermined depth in the semiconductor substrate 1 becomes lower in the region corresponding to the lower side of the channel CH of the device structure 10 than in the remaining region. As a result, it is possible to prevent a part of the laser beams L that are not absorbed at the focal point at the predetermined depth of the semiconductor substrate 1 from reaching the channel CH of the device structure 10, as shown by the dashed lines in Fig. 14 is shown. <Drittes Beispiel des Laseranwendungsprozesses>

[0038] A third example of the laser application process is described with reference to the Fig. 15 to 20. The third example of the laser application process is characterized by forming a laser shielding film within the semiconductor substrate 1 before forming the device structures 10. As shown in Fig. 16, in the third example of the laser application process, first, a laser shielding film 42 is formed entirely on a surface of a base substrate 100 (S31 in Fig. 15). The material of the laser shielding film 42 may be the same as that of the laser shielding film 32 used in the second example of the laser application process.

[0039] As it is in Fig. 17, the laser shielding film 42 is partially removed using an etching technique so that the laser shielding film 42 is left in a region corresponding to a formation position in which the channel CH of the device structure 10 is to be formed later (S32 in Fig. 15.).

[0040] As it is in Fig. 18, an epitaxial layer 110 is subsequently formed on the surface of the base substrate 100 using an epitaxial technique as a film, thereby forming the semiconductor substrate 1 (S33 in Fig. 15). In this way, the laser shielding film 42 is formed so as to be embedded in the semiconductor substrate 1.

[0041] As it is in Fig. 19, the device structures 10 are subsequently formed adjacent to the upper surface 1a of the semiconductor substrate 1 (S34 in Fig. 15). The laser shielding film 42 embedded in the semiconductor substrate 1 overlaps at least a portion of the area corresponding to the channel CH of the device structure 10 when the semiconductor substrate 1 is viewed in the direction orthogonal to the surface of the semiconductor substrate 1. For example, the laser shielding film 42 covers the entire area corresponding to the channel CH of the device structure 10.

[0042] As it is in Fig. 20, the laser beam L is then applied to the predetermined depth of the semiconductor substrate 1 from the lower surface 1b (S35 in Fig. 15). The laser beam L is applied to the predetermined depth of the semiconductor substrate 1 through the laser shielding film 42. Since the laser shielding film 42 shields the laser beam L, the power density of the laser beam L in the plane 3 extending to the predetermined depth in the semiconductor substrate 1 becomes lower in the region corresponding to the lower side of the channel CH of the device structure 10 than in the remaining region. As a result, it is possible to prevent a part of the laser beams L that are not absorbed at the focal point at the predetermined depth of the semiconductor substrate 1 from reaching the channel CH of the device structure 10, as shown by the dashed lines in Fig. 20 is shown. <Viertes Beispiel des Laseranwendungsprozesses>

[0043] A fourth example of the laser application process is described with reference to the Fig. 21 to 26. As described in Fig. 22, in the fourth example of the laser application process, first, a mask 52 is formed on the entire lower surface 1b of the semiconductor substrate 1 (S41 in Fig. 21). The mask 52 is not particularly limited, but may be, for example, a photoresist.

[0044] As it is in Fig. 23, the mask 52 is then partially removed using an etching technique so that a region of the mask 52 corresponding to the lower side of the channel CH of the device structure 10 is opened (S42 in Fig. 21). Specifically, the mask 52 is left in such a way that at least a portion of the region overlapping the channel CH of the device structure 10 is opened when the semiconductor substrate 1 is viewed in the direction orthogonal to the surface of the semiconductor substrate 1. For example, the mask 52 is formed such that the entire region overlapping the channel CH of the device structure 10 is opened.

[0045] As it is in Fig. 24, the lower surface 1b of the semiconductor substrate 1 exposed from the mask 52 is subsequently damaged to form a damage region 54 (S43 in Fig. 21). The treatment for forming the damage region 54 is not particularly limited, but may be a wet etching treatment, a dry etching treatment with plasma application, or an ion implantation treatment with inert ions such as nitrogen ions or argon ions. The damage region 54 is a region where the surface roughness is higher after such treatment.

[0046] As it is in Fig. 25, the mask 52 is then removed using an etching technique (S44 in Fig. 21).

[0047] As it is in Fig. 26, the laser beam L is then applied to the predetermined depth of the semiconductor substrate 1 from the lower surface 1b of the semiconductor substrate 1 (S45 in Fig. 21). The laser beam L is also applied through the damage region 54 to the predetermined depth of the semiconductor substrate 1. Since the damage region 54 blocks the laser beam L by reflection and / or scattering, the laser beam L is applied such that the power density in the plane 3 extending to the predetermined depth in the semiconductor substrate 1 is lower in the region corresponding to the lower side of the channel CH of the device structure 10 than in the remaining region. As a result, it is possible to prevent a part of the laser beams L that are not absorbed at the focal point in the predetermined depth of the semiconductor substrate 1 from reaching the channel CH of the device structure 10, as shown by the dashed lines in Fig. 26 is shown.

Claims

[1] A method of manufacturing a semiconductor device, comprising: Applying a laser beam to a plane (3) extending to a predetermined depth in a semiconductor substrate (1) from a side of a second main surface (1b) of the semiconductor substrate (1), the side of the second main surface (1b) being opposite to a side of a first main surface (1a) of the semiconductor substrate (1) on which a device structure (10) containing a channel (CH) is formed; Detaching a device layer (2) containing the device structure (10) from the semiconductor substrate (1) along the plane (3) to which the laser beam (L) is applied, wherein the laser beam (L) is applied in the application of the laser beam (L) such that a power density in the plane (3) extending at the predetermined depth in the semiconductor substrate (1) is lower in a region corresponding to the channel (CH) in a thickness direction of the semiconductor substrate (1) than in a remaining region. [2] The method of claim 1, wherein applying the laser beam includes: Creating laser application coordinate data containing a plurality of application position coordinates (22) for determining positions in the semiconductor substrate (1) for applying the laser beam in a two-dimensional coordinate system defining in-plane positions of the semiconductor substrate (1); Creating channel coordinate data containing one or more channel position coordinates (24) for determining the position of the channel (CH) in the two-dimensional coordinate system; Categorizing the application position coordinates (22) of the laser application coordinate data into one or more first application position coordinates (22a) not included in the one or more channel position coordinates and one or more second application coordinates (22b) included in the one or more channel position coordinates (24); and Applying the laser beam to the predetermined depth in the semiconductor substrate (1) at one or more positions corresponding to the one or more first application position coordinates (22a) without applying it to one or more positions corresponding to the one or more second application coordinates (22b). [3] The method of claim 1, wherein applying the laser beam includes: Creating laser application coordinate data containing a plurality of application position coordinates (22) for determining positions in the semiconductor substrate (1) for applying the laser beam in a two-dimensional coordinate system defining in-plane positions of the semiconductor substrate (1); Creating channel coordinate data containing one or more channel position coordinates (24) for determining the position of the channel (CH) in the two-dimensional coordinate system; Categorizing the application position coordinates (22) of the laser application coordinate data into one or more first application position coordinates (22a) not included in the one or more channel position data and one or more second application coordinates (22b) included in the one or more channel position coordinates (24); and Applying the laser beam to the predetermined depth in the semiconductor substrate (1) at one or more positions corresponding to the one or more first application position coordinates (22a), wherein the application at the one or more positions corresponding to the one or more second application position coordinates (22b) is performed with a smaller application energy than that at the one or more positions corresponding to the one or more first application position coordinates (22a). [4] The method of claim 1, wherein applying the laser beam includes: Arranging a laser shielding film (32, 42) for shielding the laser beam in a region corresponding to the channel (CH) of the device structure (10) in the thickness direction of the semiconductor substrate (1); and Applying the laser beam to the predetermined depth of the semiconductor substrate (1) via the laser shielding film (32, 42). [5] The method according to claim 4, wherein disposing the laser shielding film (32, 42) includes: Forming the laser shielding film (32) on the entire second main surface (1b) of the semiconductor substrate (1); and partially removing the laser shielding film (32) so that the laser shielding film (32) is left in the region corresponding to the channel (CH) of the device structure (10) in the thickness direction of the semiconductor substrate (1). [6] The method according to claim 4, wherein disposing the laser shielding film (32, 42) includes: Forming the laser shielding film (42) entirely on a surface of a base substrate (100); partially removing the laser shielding film (42) so that the laser shielding film (42) is left in a region corresponding to a formation position at which the channel (CH) of the device structure (10) is to be formed; and Forming an epitaxial layer (110) on the surface of the base substrate (100), thereby forming the semiconductor substrate (1). [7] The method of claim 1, wherein applying the laser beam includes: Forming a mask (52) on the entire second main surface (1b) of the semiconductor substrate (1); Removing a part of the mask (52) so that a region corresponding to the channel (CH) of the device structure (10) in the thickness direction of the semiconductor substrate (1) is opened; Forming a damage region (54) by applying damage to a portion of the semiconductor substrate (1) exposed from the mask (52); Removing the mask (52) after forming the damaged area (54); and Applying the laser beam (L) to the predetermined depth of the semiconductor substrate (1) over the damage area (54). [8] Method according to one of claims 1 to 7, wherein the semiconductor substrate (1) consists of a compound semiconductor.

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