Semiconductor device manufacturing method

Abstract

To provide a technology capable of ensuring the quality of a separation surface when a semiconductor substrate is separated.SOLUTION: A method for manufacturing a semiconductor device comprises a step of irradiating, with laser light, a semiconductor substrate which has a p-type first semiconductor layer formed of a compound semiconductor, and also has an n-type second semiconductor layer placed on the first semiconductor layer and formed of a compound semiconductor so that the laser light converges on an interface between the first semiconductor layer and the second semiconductor layer, thereby, separating the semiconductor substrate into the first semiconductor layer and the second semiconductor layer along the interface.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a method for manufacturing a semiconductor device.

[0002] Patent Document 1 discloses a method for manufacturing a semiconductor device. In this manufacturing method, ions are first implanted into a seed substrate to a certain depth from the surface thereof to form an ion-implanted layer. In the ion-implanted layer, the energy of the implanted ions weakens the bonds between elements compared to other semiconductor regions. Then, a laser beam is irradiated from the surface of the seed substrate to impart energy to the implanted ions, thereby severing the bonds between elements and separating the semiconductor substrate from the seed substrate along the ion-implanted layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 114382 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacturing method of Patent Document 1, the implanted ions disrupt the crystal structure of the ion-implanted layer. Therefore, when the seed substrate is separated along the ion-implanted layer, the region exposed at the separation surface of the resulting semiconductor substrate has a disrupted crystal structure. Therefore, when this semiconductor substrate is used, problems arise, such as increased resistance in the semiconductor device. This specification provides a technology that can ensure the quality of the separation surface when separating the semiconductor substrate. [Means for solving the problem]

[0005] A method for manufacturing a semiconductor device disclosed in this specification includes a step of irradiating a semiconductor substrate having a p-type first semiconductor layer made of a compound semiconductor and an n-type second semiconductor layer provided on the first semiconductor layer and made of the compound semiconductor with laser light so as to be focused on an interface between the first semiconductor layer and the second semiconductor layer, thereby separating the first semiconductor layer and the second semiconductor layer along the interface.

[0006] In the above manufacturing method, the semiconductor substrate has a p-type first semiconductor layer and an n-type second semiconductor layer. Therefore, a depletion layer due to a built-in potential is formed near the interface between the first and second semiconductor layers. That is, an electric field is applied near the interface. Therefore, the Franz-Keldysh effect occurs near the interface between the first and second semiconductor layers, and long-wavelength (i.e., low-energy) laser light is easily absorbed. That is, the region near the interface between the first and second semiconductor layers has a higher light absorption efficiency than other semiconductor regions. Therefore, by irradiating the interface with laser light so that it is focused thereon, the laser light is efficiently absorbed near the interface, and the first and second semiconductor layers can be separated along the interface. Furthermore, this separation method is less likely to disrupt the crystalline structure of the semiconductor at the separation surface than separation methods that form ion-implanted layers. Therefore, this manufacturing method enables the manufacture of high-quality semiconductor devices. [Brief explanation of the drawings]

[0007] [Figure 1] 2A to 2C are diagrams showing the manufacturing process of the semiconductor device according to the first embodiment. [Figure 2] 2A to 2C are diagrams showing the manufacturing process of the semiconductor device according to the first embodiment. [Figure 3] 10 is a graph showing the results of a simulation of the relationship between the effective acceptor concentration of the first semiconductor layer and the effective donor concentration of the second semiconductor layer when a specific electric field strength is applied to the semiconductor substrate. [Figure 4] 2A to 2C are diagrams showing the manufacturing process of the semiconductor device according to the first embodiment. [Figure 5] 3 is an enlarged view showing the vicinity of an interface in the manufacturing process of the semiconductor device according to the first embodiment. [Figure 6] FIG. 2 is a diagram for explaining a depletion layer formed near the interface between a first semiconductor layer and a second semiconductor layer. [Figure 7] 1 is a graph showing the relationship between the wavelength of light irradiated onto gallium nitride, the photocurrent flowing through the gallium nitride, and the electric field intensity applied to the gallium nitride. [Figure 8] 2A to 2C are diagrams showing the manufacturing process of the semiconductor device according to the first embodiment. [Figure 9] 5A to 5C are diagrams showing the manufacturing process of a semiconductor device according to a second embodiment. [Figure 10] 10A to 10C are diagrams showing manufacturing steps of a semiconductor device according to a modified example. [Figure 11] 10A to 10C are diagrams showing manufacturing steps of a semiconductor device according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] The technical elements disclosed in this specification are listed below. Note that each of the following technical elements is independently useful.

[0009] In the manufacturing method disclosed in the present specification, the compound semiconductor may be gallium nitride. -3 ), the effective donor concentration of the second semiconductor layer is Nd (cm -3 ), and the intrinsic carrier concentration of gallium nitride is n i (cm -3 ), and the dielectric constant of gallium nitride is ε GaN (F / cm 2 ), temperature is T(K), and Boltzmann constant is k B (J / K), the following equation (1);

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[0010] When the effective acceptor concentration of the first semiconductor layer and the effective donor concentration of the second semiconductor layer satisfy the above formula, an appropriate electric field is applied near the interface between the first semiconductor layer and the second semiconductor layer due to the built-in potential, and laser light with a wavelength longer than the wavelength corresponding to the band gap of gallium nitride can be efficiently absorbed near the interface.

[0011] In one example manufacturing method disclosed in the present specification, in the step of irradiating the laser light, the laser light may be irradiated while a voltage is applied to the semiconductor substrate such that the second semiconductor layer has a higher potential than the first semiconductor layer.

[0012] In this configuration, laser light is irradiated while a reverse voltage is applied to the pn junction of the semiconductor substrate. Applying a reverse voltage to the pn junction expands the depletion layer formed near the interface between the first and second semiconductor layers. This increases the electric field applied near the interface. This increases the Franz-Keldysh effect, allowing longer wavelength laser light to be absorbed near the interface.

[0013] Example 1 A method for manufacturing a semiconductor device according to a first embodiment will be described with reference to the drawings. This manufacturing method is characterized by a process for separating a semiconductor substrate into two layers. Therefore, the manufacturing method according to this embodiment is not limited to semiconductor devices having a specific structure, but can be widely applied to semiconductor devices having semiconductor substrates made of compound semiconductors, and their semi-finished products. Below, the process for separating a semiconductor substrate made of compound semiconductors into two layers will be mainly described, and descriptions of other manufacturing processes will be omitted. Note that, with regard to other manufacturing processes for a semiconductor device, necessary processes may be performed as appropriate depending on the structure of the semiconductor device, etc.

[0014] First, as shown in Fig. 1, an n-type semiconductor layer 12 is prepared. The semiconductor layer 12 is made of gallium nitride. Note that the material of the semiconductor layer 12 is not limited to gallium nitride. The semiconductor layer 12 may be made of other compound semiconductors such as silicon carbide.

[0015] 2, p-type impurities, such as magnesium ions, are implanted into the semiconductor layer 12 to form a p-type region 14 in the surface layer of the semiconductor layer 12. Then, an ultra-high-pressure annealing (UHPA) process is performed to activate the implanted magnesium ions, thereby forming a p-type first semiconductor layer 14. The remaining n-type region of the semiconductor layer 12 becomes the second semiconductor layer 16. This results in a semiconductor substrate 20 having the second semiconductor layer 16 and the first semiconductor layer 14 provided on the second semiconductor layer 16.

[0016] When manufacturing the semiconductor substrate 20 shown in FIG. 2, the effective acceptor concentration of the first semiconductor layer 14 is set to Na (cm -3 ), and the effective donor concentration of the second semiconductor layer 16 is Nd (cm -3 ), and the intrinsic carrier concentration of gallium nitride is n i (cm -3 ), and the dielectric constant of gallium nitride is ε GaN (F / cm 2 ), temperature is T(K), and Boltzmann constant is k B (J / K), the amount of magnesium ions injected is adjusted to satisfy the following formula:

[0017]

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[0018] The effective acceptor concentration of the first semiconductor layer 14 is calculated by subtracting the n-type impurity concentration from the p-type impurity concentration in the first semiconductor layer 14. The effective donor concentration of the second semiconductor layer 16 is calculated by subtracting the p-type impurity concentration from the n-type impurity concentration in the second semiconductor layer 16. FIG. 3 shows a graph of the above formula (1). As will be described in detail later, in a semiconductor substrate 20 that satisfies the above formula (1), the electric field strength applied near the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16 is 1.2 MV / cm or more.

[0019] Next, as shown in FIG. 4 , laser light 30 is irradiated so as to be focused on the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16. Here, while the laser light 30 is focused on the interface 18, the laser light 30 is scanned along the interface 18 as indicated by arrow 32. The wavelength of the laser light 30 is approximately 400 nm. Furthermore, as shown in FIG. 5 , the focal depth d of the laser light 30 used here is significantly smaller than the thickness of the semiconductor substrate 20. Here, the laser light 30 is irradiated so that the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16 falls within the focal depth d. As a result, the laser light 30 is absorbed near the interface 18, allowing high energy to be applied to the vicinity of the interface 18. This forms crystal defects along the interface 18.

[0020] Normally, when light is incident on a semiconductor, the light is not absorbed by the semiconductor unless the energy of the light is greater than the band gap of the semiconductor. Gallium nitride has a band gap of approximately 3.4 eV (corresponding to a wavelength of approximately 365 nm), so laser light 30 with a wavelength of approximately 400 nm is generally not easily absorbed. However, when an electric field is applied to the semiconductor, the wave functions of carriers in the conduction band and valence band transition, narrowing the effective band gap of the semiconductor. This causes the absorption edge of light (i.e., the minimum energy absorbed by the semiconductor) to shift toward longer wavelengths, resulting in the so-called Franz-Keldysh effect.

[0021] In this embodiment, the first semiconductor layer 14 is p-type, and the second semiconductor layer 16 is n-type. That is, a p-n junction is formed between the first semiconductor layer 14 and the second semiconductor layer 16. Therefore, as shown in FIG. 6, a depletion layer 36 (region indicated by dotted hatching) due to a built-in potential is formed near the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16. That is, an electric field is applied near the interface 18, and the absorption edge of light near the interface 18 shifts to the longer wavelength side due to the Franz-Keldysh effect.

[0022] Figure 7 shows the photocurrent that flows when gallium nitride, which has a bandgap of approximately 3.4 eV (corresponding to a wavelength of approximately 365 nm), is irradiated with light of various wavelengths. A large photocurrent indicates that light is efficiently absorbed by gallium nitride. The horizontal axis of Figure 7 represents the electric field strength applied to gallium nitride. As shown in Figure 7, when gallium nitride is irradiated with 400 nm light, an electric field strength of 1.2 MV / cm or more is required to obtain a photocurrent of 1 nA or more. In other words, to shift the wavelength of light absorbed by gallium nitride from 365 nm to 400 nm, an electric field with an electric field strength of 1.2 MV / cm or more must be applied to gallium nitride. Note that shifting the wavelength of light absorbed by gallium nitride from 365 nm to 400 nm reduces the effective bandgap of gallium nitride by approximately 10%. The graph in FIG. 3 shows the results of a simulation of the relationship between the effective acceptor concentration of the first semiconductor layer 14 and the effective donor concentration of the second semiconductor layer 16 when the electric field strength applied to the interface 18 is 1.2 MV / cm or greater. As described above, in this embodiment, the effective acceptor concentration of the first semiconductor layer 14 and the effective donor concentration of the second semiconductor layer 16 are adjusted to satisfy the relationship of Equation (1) representing the region 50 in FIG. 3 . That is, near the interface 18 of the semiconductor substrate 20, the absorption edge of light transitions, and the effective band gap of gallium nitride is reduced by approximately 10% or more. Therefore, in this embodiment, laser light 30 having a wavelength of approximately 400 nm can be efficiently absorbed near the interface 18. Note that the laser light 30 is hardly absorbed in the region of the semiconductor substrate 20 where no electric field is applied (i.e., the region outside the depletion layer 36). Therefore, in this embodiment, light is efficiently absorbed near the interface 18, and light is hardly absorbed at positions away from the interface 18. Therefore, crystal defects can be formed in a concentrated manner near the interface 18 .

[0023] 8, the first semiconductor layer 14 is separated from the second semiconductor layer 16. For example, a support (e.g., tape) is attached to each of the surfaces of the first semiconductor layer 14 and the second semiconductor layer 16, and the two supports are pulled away from each other to separate the first semiconductor layer 14 from the second semiconductor layer 16. Because crystal defects are formed along the interface 18 in the laser irradiation step, the first semiconductor layer 14 can be separated from the second semiconductor layer 16 along the interface 18. Thereafter, a thin semiconductor device can be manufactured using the separated first semiconductor layer 14 or second semiconductor layer 16.

[0024] As described above, in this manufacturing method, in the laser irradiation step, crystal defects can be formed in a concentrated manner at the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16, and crystal defects are unlikely to be formed at positions other than the interface 18. In particular, because the laser light 30 irradiated onto the semiconductor substrate 20 has relatively low energy, the effect of the laser light 30 on semiconductor regions other than the interface 18 can be reduced. Therefore, there are fewer crystal defects present on the surfaces of the first semiconductor layer 14 and the second semiconductor layer 16 exposed after separation. In other words, a high-quality separation surface with fewer crystal defects can be obtained. Therefore, a high-quality semiconductor device can be manufactured using the separated first semiconductor layer 14 or second semiconductor layer 16.

[0025] Example 2 Next, a manufacturing method of Example 2 will be described. In Example 2, after manufacturing the semiconductor substrate 20 shown in FIG. 2 of Example 1, a power supply 44 is connected to the semiconductor substrate 20 as shown in FIG. 9. Specifically, an ohmic electrode 40 is formed on the surface of the first semiconductor layer 14, and an ohmic electrode 42 is formed on the surface of the second semiconductor layer 16. Then, the power supply 44 is connected to each of the ohmic electrodes 40, 42 in a direction such that the second semiconductor layer 16 has a higher potential than the first semiconductor layer 14. In other words, the power supply 44 is connected in a direction such that a reverse voltage is applied to the pn junction of the interface 18.

[0026] Next, with a reverse voltage applied to the pn junction of interface 18, laser light 30 is irradiated so as to be focused on interface 18, and the laser light 30 is scanned along interface 18, as in FIG. 4. This forms crystal defects along interface 18. Then, as in FIG. 8 of Example 1, semiconductor substrate 20 can be separated into first semiconductor layer 14 and second semiconductor layer 16.

[0027] In Example 2, laser light 30 is irradiated while a reverse voltage is applied to the pn junction at the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16. Applying a reverse voltage to the pn junction increases the depletion layer that spreads from the interface 18 toward each of the semiconductor layers 14 and 16. This increases the electric field strength applied near the interface 18. In other words, the Franz-Keldysh effect becomes stronger, and the absorption edge of light shifts toward longer wavelengths. Therefore, in Example 2, laser light 30 with a longer wavelength (i.e., lower energy) can be absorbed near the interface 18.

[0028] In each of the above-described embodiments, the semiconductor substrate 20 does not necessarily have to satisfy the relationship of formula (1). In the first embodiment, as described above, a depletion layer due to the built-in potential is formed at the interface 18 (p-n junction), and therefore an electric field is applied near the interface 18. Therefore, even if the semiconductor substrate 20 does not satisfy the relationship of formula (1), the effective band gap near the interface 18 becomes small, and light with wavelengths longer than approximately 365 nm is likely to be absorbed. In the second embodiment, a reverse voltage is applied to the p-n junction of the interface 18. Therefore, even if the relationship of formula (1) is not satisfied, a large electric field can be applied near the interface 18.

[0029] Furthermore, in the above-described embodiments, examples have been described in which the layers of a semiconductor substrate 20 having two stacked layers, a first semiconductor layer 14 and a second semiconductor layer 16, are separated. However, the technology disclosed herein can also be applied to a semiconductor substrate having three or more stacked layers. For example, in the state shown in FIG. 2 of Example 1, an n-type third semiconductor layer 22 may be formed on the semiconductor layer 14 as shown in FIG. 10. The third semiconductor layer 22 can be formed, for example, by epitaxially growing n-type gallium nitride. As shown in FIG. 11, the semiconductor substrate 120 thus obtained may be irradiated with laser light 130 so as to be focused on the interface 18 between the first semiconductor layer 14 and the second semiconductor layer 16, and the laser light 30 may be scanned along the interface 18 as indicated by arrow 132. Here, the laser light 130 is irradiated from the second semiconductor layer 16 side. This allows the laser light 130 to be efficiently absorbed near the interface 18, concentrating it near the interface 18 and forming crystal defects. The Franz-Keldysh effect can also occur at the interface 24 between the first semiconductor layer 14 and the third semiconductor layer 22. However, since most of the laser light 130 is absorbed near the interface 18 (i.e., most of the energy of the laser light 130 is consumed near the interface 18), there is almost no effect on the interface 24.

[0030] Although the embodiments have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings simultaneously achieves multiple objectives, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0031] 14: First semiconductor layer 16: Second semiconductor layer 18: Interface 20: Semiconductor substrate 22: Third semiconductor layer 24: Interface 30: Laser light 36: Depletion layer 40: Ohmic electrode 42: Ohmic electrode 44: Power supply 120: Semiconductor substrate 130: Laser light

Claims

1. 1. A method for manufacturing a semiconductor device, comprising: a step of irradiating a semiconductor substrate having a p-type first semiconductor layer made of a compound semiconductor and an n-type second semiconductor layer provided on the first semiconductor layer with laser light having a wavelength longer than a wavelength corresponding to a band gap of the compound semiconductor so as to focus the laser light at an interface between the first semiconductor layer and the second semiconductor layer, thereby separating the first semiconductor layer and the second semiconductor layer along the interface.

2. the compound semiconductor is gallium nitride, the laser light has a wavelength of 400 nm or less, The effective acceptor concentration of the first semiconductor layer is Na (cm －３ , the effective donor concentration of the second semiconductor layer is Nd (cm －３ ), the intrinsic carrier concentration of gallium nitride is n ｉ (cm －３ ), and the dielectric constant of gallium nitride is ε ＧａＮ (F / cm ２ ), temperature is T (K), Boltzmann constant is k Ｂ (J / K), the following formula (1) is obtained: [Equation 3] The method according to claim 1 , wherein the above formula (I) is satisfied.

3. 3. The manufacturing method according to claim 1, wherein in the step of irradiating the semiconductor substrate with the laser light, the laser light is irradiated while a voltage is applied to the semiconductor substrate such that the second semiconductor layer has a higher potential than the first semiconductor layer.

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