Method for manufacturing a semiconductor device

Abstract

A method for manufacturing a semiconductor device, comprising: Ion injection of a dopant into a semiconductor layer (12) formed from a group III-V compound semiconductor containing nitrogen as a group V element; Performing a first activation annealing on the semiconductor layer (12) with the ion-injected dopant using a heat treatment furnace (20) under temperature conditions of 700 °C to 900 °C to move a lattice defect (15) towards a surface of the semiconductor layer (12); and Performing a second activation annealing to locally heat a flat area of ​​the semiconductor layer (12) by striking a pulsed laser beam (22) onto the semiconductor layer (12) after the first activation annealing has been performed.

Description

Technical field

[0001] Certain embodiments of the present invention relate to a method for producing a semiconductor device which activates a doping agent which is ion-injected into a group III-V compound semiconductor which contains nitrogen as a group V element. State of the art

[0002] It is expected that a group III-V compound semiconductor containing nitrogen as a group V element, such as gallium nitride (GaN), will be applied to next-generation high-frequency power devices due to its wide bandgap capabilities. To apply GaN to various devices, a technique for locally forming a p-region or an n-region is required. A technique for forming a p-region or an n-region by ion injection of a p- or n-doping agent into a semiconductor such as silicon is established. Patent references 1 and 2 disclose a technique for forming p-GaN by ion injection of Mg, which is a p-doping agent, into GaN using an ion injection technique and by performing laser annealing. List of oppositions patent literature [PTL1] Japanese unexamined patent application publication JP002004273486A (JP 2004-273 486 A) [PTL2] Japanese unexamined patent application publication JP002013062365A (JP 2013-062 365 A) [PTL3] US patent application publication US020110316044A1 (US 2011 / 0 316 044 A1) Summary of the invention: Technical problem

[0003] In accordance with evaluations and experiments conducted by the inventors of the present application, it is unlikely that the activation rate will be sufficiently increased by using a method for injecting Mg into GaN and performing laser annealing for activation. It is desirable to provide a method for fabricating a semiconductor device that can improve the activation rate of a dopant. Solution to the problem

[0004] In accordance with one embodiment of the present invention, a method for manufacturing a semiconductor device is provided, the method comprising: ion injection of a dopant into a semiconductor layer formed from a group III-V compound semiconductor containing nitrogen as a group V element; performing a first activation annealing on the semiconductor layer with the ion-injected dopant using a heat treatment furnace under temperature conditions of 700 °C to 900 °C; and performing a second activation annealing by striking a pulsed laser beam on the semiconductor layer after the first activation annealing has been performed. Advantageous effects of the invention

[0005] By combining tempering using a heat treatment furnace with laser tempering using a pulsed laser beam, it is possible to increase the activation rate of an ion-injected dopant. Brief description of the drawings Fig. Figures 1A to 1C are sectional views showing a substrate in the middle of the fabrication process using a method for producing a semiconductor substrate in accordance with an example. Fig. Figure 2 is a view that represents a method for scanning a pulsed laser beam in time to perform a second activation annealing. Fig. Figure 3 is a graphical representation showing the results of an X-ray photoelectron spectroscopy analysis before and after a pulsed laser beam was allowed to strike a semiconductor layer 12 formed from GaN. Fig. Figure 4 is a graphical representation showing the results of a Raman spectroscopy analysis performed on a semiconductor layer into which Mg ions are injected and which is formed from GaN. Fig. 5A and Fig. 5B are graphical representations created by enlarging a portion of the results from the Fig. 4 Raman spectroscopy analyses were obtained. Fig. Figure 6 is a graphical representation showing measurement results of the surface resistance of a sample. Description of embodiments

[0006] Based on Fig. Sections 1A to 1C describe a method for manufacturing a semiconductor device in accordance with an example.

[0007] As in Fig. As shown in Figure 1A, epitaxial growth of a gallium nitride (GaN) semiconductor layer 12 is induced on a sapphire support substrate 11. The support substrate 11 and the semiconductor layer 12 are collectively referred to as a substrate 10. Magnesium (Mg) is injected into the semiconductor layer 12 as a p-type dopant. This ion injection leads to lattice defects 15 in the semiconductor layer 12.

[0008] As in Fig. As shown in Figure 1B, the substrate 10 is placed in a heat treatment furnace 20 after ion injection. A first activation annealing is performed on the semiconductor layer 12, which contains a dopant, using the heat treatment furnace 20 at temperature conditions of 700 °C to 900 °C. This first activation annealing activates a portion of the dopant injected into the semiconductor layer 12 and restores the crystallinity of an area damaged by the ion injection. Some of the lattice defects 15, particularly depletion-type defects, migrate towards the surface of the semiconductor layer 12.

[0009] As in Fig. As shown in Figure 1C, a second activation annealing step is performed by allowing a pulsed laser beam 22 to strike the semiconductor layer 12 of the substrate 10, where the first activation annealing step has been completed. The second activation annealing step is performed in a nitrogen atmosphere. When the pulsed laser beam 22 strikes the surface of the semiconductor layer 12, a flat region of the semiconductor layer 12 is locally heated. At the time of the first activation annealing step, most of the lattice defects 15 disappear ( Fig. 1B), which have moved towards the surface of the semiconductor layer 12 due to heating. The pulsed laser beam 22 uses third harmonics of a solid-state laser such as an Nd:YAG laser, an Nd:YLF laser, an Nd:YVO4 laser, and the like. Its wavelength lies in the range of 349 nm to 355 nm.

[0010] Based on Fig. 2 a method for scanning the pulsed laser beam 22 ( Fig. 1C) at the time of performing the second activation annealing. As an example, a beam spot 25 of the pulsed laser beam 22 on the surface of the semiconductor layer 12 ( Fig. 1C) a square shape with one side having a length L of approximately 100 µm. This allows the beam spot 25 to orient itself in a main scanning direction (the transverse direction in Fig. 2) on the surface of the semiconductor layer 12 while allowing the pulsed laser beam 22 ( Fig. 1C) impacts its surface.

[0011] Once the main scan has been completed, the beam spot 25 is allowed to move in a sub-scanning direction (the longitudinal direction in Fig. 2) moves, and then the next main scan is started. Overlapping widths of the beam spot 25 of second shots that are temporally adjacent in the main scan direction and in the sub-scan direction are each expressed as Wm and Ws, respectively. An overlap ratio OVm in the main scan direction and an overlap ratio OVs in the sub-scan direction are each defined using the following equation. OVm=Wm / L OVs=Ws / L.

[0012] The conditions for applying the pulsed laser beam 22 during the second activation annealing are described below. When a laser pulse of the pulsed laser beam 22 increases, the surface temperature of the semiconductor layer 12 begins to rise ( Fig. 1C) to increase, and when a laser pulse decays, the surface temperature begins to decrease. It is preferred to select a condition in which the highest achievable surface temperature, when a shot of the pulsed laser beam 22 is allowed to strike, is 900 °C or less, i.e., the dissociation temperature of nitrogen from GaN.

[0013] The result of a simulation performed by setting the pulse width to 50 ns shows that the highest achievable temperature exceeds 900 °C when the pulse energy density is 0.8 J / cm². 2 is, and that the highest achievable temperature is 900 °C or lower when the pulse energy density is 0.6 J / cm². 2 Furthermore, the highest achievable temperature does not fluctuate significantly even if the pulse energy density is the same, even if the pulse width is a different value than 50 ns.

[0014] Fig. Figure 3 shows results of the X-ray photoelectron spectroscopy analysis before and after a pulsed laser beam is directed onto the GaN semiconductor layer 12 ( Fig. 1C). The horizontal axis represents the binding energy using the unit "eV" and the vertical axis represents the photoelectron intensity using an arbitrary unit. Fig. Figure 3 shows the tip of the nitrogen (N1s) layer. The dashed line in Fig. Figure 3 shows the analysis result of the semiconductor layer before the pulsed laser beam is allowed to strike its surface. A solid line a in Fig. Figure 3 shows the analysis result of the semiconductor layer after laser annealing was carried out under conditions where the pulse energy density was 0.35 J / cm². 2The overlap ratios OVm and OVs are 90% in both the main scanning direction and the sub-scanning direction. A solid line b shows the analysis result of the semiconductor layer after laser annealing under conditions where the pulse energy density is 0.4 J / cm². 2 and the overlap ratios OVm and OVs are each 90%. A solid line c shows the analysis result of the semiconductor layer after laser annealing was performed under conditions where the pulse energy density was 0.8 J / cm². 2 is and the overlap ratios OVm and OVs are each 80%.

[0015] It is understandable that the dissociation of nitrogen in the semiconductor layer is significant when the pulse energy density is set to 0.8 J / cm². 2 is set. Under the condition of a pulse energy density of 0.35 J / cm². 2 Nitrogen dissociation occurs almost without any effect. As can be seen from the in Fig. To understand the evaluation result shown in Figure 3, the pulse energy density of the pulsed laser beam 22 at the time of the second activation annealing is preferably set to 0.35 J / cm². 2 set to suppress nitrogen dissociation in the semiconductor layer.

[0016] Fig. Figure 4 shows the results of a Raman spectroscopy analysis performed on a semiconductor layer into which Mg ions were injected and which is made of GaN. The horizontal axis represents the Raman shift using the unit "cm". -1 “and the vertical axis represents the Raman intensity. Solid lines in Fig. Figure 4 shows the analysis results of samples A to G. Sample G is a sample in which no Mg is found in semiconductor layer 12 ( Fig. 1A) has been ion-injected, and samples A to F are samples in which Mg has been ion-injected into semiconductor layer 12. Mg is injected into this layer in several phases under acceleration energies of 20 keV, 80 keV and 120 keV.

[0017] Sample A is a sample that does not undergo laser annealing after laser injection. Sample B is a sample that undergoes laser annealing after ion injection. Sample C is a sample that undergoes oven annealing at 700 °C for 20 minutes after ion injection. Sample D is a sample that undergoes oven annealing at 900 °C for 20 minutes after ion injection. Sample E is a sample that undergoes oven annealing at 700 °C for 20 minutes after ion injection, followed by laser annealing. Sample F is a sample that undergoes oven annealing at 900 °C for 20 minutes after ion injection, followed by laser annealing. Laser annealing at a pulse energy density of 0.35 J / cm² is performed on all samples B, E, and F. 2 and executed with an overlap ratio OVm of 90% and an overlap ratio OVs of 90%.

[0018] In sample G, at points of 418 cm -1 , 567.6 cm -1 and 734 cm -1 Peaks at 418 cm. -1 is based on the sapphire of the supporting substrate 11. The tip is at 567.6 cm -1 It is based on the vibration of the nitrogen in the transverse direction. The peak is at 734 cm. -1 It is based on a longitudinal optical mode. These three peaks are typical for a GaN layer whose epitaxial growth is caused on the sapphire substrate.

[0019] In sample A, peaks appear at 300 cm intervals after ion injection. -1 and 670 cm -1 These peaks are caused by lattice defects, such as holes or similar nitrogen inclusions. Naturally, many lattice defects are introduced by performing ion injection into the semiconductor layer. In samples B to F, a Raman shift of 360 cm⁻¹ occurs. -1a spike. This spike corresponds to the activation of the ion-injected Mg.

[0020] Fig. 5A and Fig. 5B are graphic representations, each created by enlarging a part of Fig. 4 were obtained. If the Raman intensities of the respective samples were in the vicinity of the Raman shift of 300 cm -1 When comparing the samples, it can be understood that the tips of samples C and D, which underwent only furnace annealing, and the tips of samples E and F, which underwent both furnace and laser annealing, are lower than the tip of sample B, which underwent only laser annealing. This indicates that furnace annealing is better suited than laser annealing for reducing lattice defects such as Ga holes.

[0021] If the Raman intensities of the respective samples are close to the Raman shift of 670 cm -1When compared, the Raman intensity of sample B, which undergoes only laser annealing, and the Raman intensity of sample C, which undergoes only furnace annealing at 700 °C, are both high. This result suggests that annealing at approximately 900 °C, i.e., above 700 °C, is beneficial for reducing lattice defects such as nitrogen holes and interstitial atoms.

[0022] If the tips of the respective samples are near the Raman shift of 360 cm -1 When compared, the tip of sample F, on which both furnace annealing at 900 °C and laser annealing are performed, is the highest. This means that the activation rate of the ion-injected Mg in sample F is the best.

[0023] Fig. Figure 6 shows measurement results of the surface resistivity of samples B, E, and F. The surface resistivity is measured using a four-probe measurement method. Fig. Figure 6 represents the current using the unit "mA" and the longitudinal axis represents the sheet resistance using the unit "Ω / Ω". The sheet resistances of samples E and F, which undergo both furnace annealing and laser annealing, are lower than the sheet resistance of sample B, which undergoes only laser annealing. Assuming that the mobility of a positive hole in GaN is 200 cm⁻¹ 2 If the coefficient of thermal conductivity (ΔV) is 1 / V · s, the surface resistance becomes 104 Ω / □ if 100% of the ion-injected Mg is activated. The fact that the surface resistance is reduced by performing both furnace annealing and laser annealing means that the activation rate of Mg is increased.

[0024] When the Hall coefficients of samples E and F, which undergo furnace annealing and laser annealing respectively, are measured, it is confirmed that both samples exhibit positive Hall coefficients. This indicates that Mg is activated and p-GaN is obtained. In contrast, no positive Hall coefficient can be obtained in sample B, which undergoes only laser annealing. When a combination of ion injection, furnace annealing, and laser annealing is used, p-GaN can be obtained.

[0025] In the example described above, GaN is used as semiconductor layer 12 ( Fig. 1A to 1C) is used and even in a case where a group III-V compound semiconductor containing nitrogen as a group V element is used, it is effective to use a combination of furnace annealing and laser annealing. Reference symbol list 10 substrate 11 Support substrate 12 Semiconductor layer 15 lattice defects 20 heat treatment furnaces 22 Pulsed laser beam 25 Ray spot OVm Overlap ratio in the main scanning direction OV's overlap ratio in the sub-scanning direction L Length of one side of the beam spot Wm Overlap width of the beam spot in the main scanning direction Ws overlap width of the beam spot in the sub-scanning direction

Claims

[1] Method for manufacturing a semiconductor device, the method comprising: Ion injection of a dopant into a semiconductor layer (12) formed from a group III-V compound semiconductor containing nitrogen as a group V element; Performing a first activation annealing on the semiconductor layer (12) with the ion-injected dopant using a heat treatment furnace (20) under temperature conditions of 700 °C to 900 °C to move a lattice defect (15) towards a surface of the semiconductor layer (12); and Performing a second activation annealing to locally heat a flat area of ​​the semiconductor layer (12) by striking a pulsed laser beam (22) onto the semiconductor layer (12) after the first activation annealing has been performed. [2] Method for manufacturing a semiconductor device according to claim 1, wherein a pulsed laser beam (22) with a wavelength of 349 nm to 355 nm, i.e. a third harmonic of a solid-state laser, is used during the execution of the second activation annealing. [3] Method for manufacturing a semiconductor device according to claim 1 or 2, wherein it is made possible that the pulsed laser beam (22) is operated under the conditions that a pulse energy density on the surface of the semiconductor layer (12) during the execution of the second activation annealing is 0.35 J / cm² 2 or less, impacts the semiconductor layer (12). [4] Method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein the annealing is carried out in a nitrogen atmosphere during the execution of the second activation annealing. [5] Method for manufacturing a semiconductor device according to any one of claims 1 to 4, wherein the crystallinity of an area damaged by ion injection of the dopant is restored during the first activation annealing, the dopant is activated and some of the lattice defects (15) in the semiconductor layer (12) move towards the surface of the semiconductor layer (12), and the lattice defects (15) which moved towards the surface of the semiconductor layer (12) at the time of the first activation annealing disappear during the second activation annealing.

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