JP2014237575A - PRODUCTION METHOD OF SiC MATERIAL, AND SiC MATERIAL LAMINATE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an SiC material capable of producing an SiC material in a short time, and improving yield, and to provide an SiC material laminate.SOLUTION: When producing an SiC material, after growing a p-type SiC layer on a seed crystal substrate, an n-type SiC layer is grown on the p-type SiC layer, and energy of laser is absorbed into the p-type SiC layer, and the n-type SiC layer is exfoliated from the seed crystal substrate side by laser lift-off.

Description

  The present invention relates to a method for producing a SiC material and a SiC material laminate.

  As a light emitting element using a pn junction of a compound semiconductor, an LED (light emitting diode) has been widely put into practical use, and is mainly used for light transmission, display, and illumination. In the white LED, since the energy conversion efficiency is insufficient as compared with the existing fluorescent lamp, a significant improvement in efficiency is necessary for general lighting applications. Furthermore, many problems remain for realizing high color rendering properties, low cost, and high luminous flux LEDs.

  As a white LED currently on the market, a blue light emitting diode element mounted on a lead frame, a yellow phosphor layer made of YAG: Ce over the blue light emitting diode element, and a transparent material such as an epoxy resin covering them. What is provided with the mold lens which becomes. In this white LED, when blue light is emitted from the blue light emitting diode element, part of the blue light is converted into yellow light when passing through the yellow phosphor. Since blue and yellow are complementary to each other, when blue light and yellow light are mixed, white light is obtained. The white LED is required to improve the performance of the blue light-emitting diode element in order to improve efficiency and improve color rendering.

  As a blue light-emitting diode element, on an n-type SiC substrate, a buffer layer made of AlGaN, an n-type GaN layer made of n-GaN, a multiple quantum well active layer made of GaInN / GaN, an electron block layer made of p-AlGaN, It is known that a p-type contact layer made of p-GaN is continuously laminated in this order from the SiC substrate side. In this blue light emitting diode element, a p-side electrode is formed on the surface of the p-type contact layer, an n-side electrode is formed on the back surface of the SiC substrate, and a voltage is applied between the p-side electrode and the n-side electrode. Thus, blue light is emitted from the multiple quantum well active layer. Here, since the SiC substrate is conductive, unlike the blue light emitting diode element using the sapphire substrate, electrodes can be arranged above and below, simplifying the manufacturing process, in-plane current uniformity, chip area The effective use of the light emission area with respect to can be achieved.

  Furthermore, a light-emitting diode element that independently generates white light without using a phosphor has been proposed (see, for example, Patent Document 1). In this light emitting diode element, a fluorescent SiC substrate having a first SiC layer doped with B and N and a second SiC layer doped with Al and N is used instead of the n-type SiC substrate of the blue light emitting diode element described above. Near ultraviolet light is emitted from the multiple quantum well active layer. Near-ultraviolet light is absorbed by the first SiC layer and the second SiC layer, and is converted from green to red visible light by the first SiC layer, and from blue to red visible light by the second SiC layer. As a result, white light close to sunlight is emitted from the fluorescent SiC substrate.

  By the way, in Patent Document 1, a fluorescent SiC material is grown by a sublimation method, a CVD method or the like, and the obtained SiC single crystal is mechanically cut using a wire saw or the like to form a fluorescent SiC substrate.

Japanese Patent No. 4153455

  However, the method of manufacturing a SiC material described in Patent Document 1 has a problem in that since the fluorescent SiC material is mechanically cut with a wire saw or the like, the time required for manufacturing is long and the yield is poor.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a SiC material manufacturing method and SiC capable of manufacturing a SiC material in a short time and improving the yield. The object is to provide a material laminate.

  In order to achieve the object, in the present invention, a p-type layer growth step for growing a p-type SiC layer on a seed crystal substrate, and an n-type layer growth step for growing an n-type SiC layer on the p-type SiC layer, And a laser lift-off process in which the p-type SiC layer absorbs laser energy and the n-type SiC layer is peeled off from the seed crystal substrate side.

  In the SiC fluorescent material, the p-type SiC layer may include at least one of Al or B as an impurity, and the n-type SiC layer may include undoped or N as an impurity.

  In the SiC fluorescent material, the n-type SiC layer may be a fluorescent material containing N as a donor impurity and containing at least one of Al or B as an acceptor impurity.

  In the SiC fluorescent material, the p-type SiC layer and the n-type SiC layer are grown by a sublimation method in the p-type layer growth step and the n-type layer growth step, and the n-type layer growth step. The n-type SiC layer may be grown in a hydrogen-containing atmosphere.

  Further, in the SiC fluorescent material, after the n-type layer growth step, a second p-type layer growth step of growing a second p-type SiC layer on the n-type SiC layer, and the second p-type layer After the layer growth step, a second n-type layer growth step of growing a second n-type SiC layer on the second p-type SiC layer, and in the laser lift-off step, the p-type SiC The layer and the second p-type SiC layer may absorb laser energy, and the n-type SiC layer and the second n-type SiC layer may be separated from the seed crystal substrate side.

  The SiC fluorescent material further includes a group III nitride semiconductor layer growth step of growing a group III nitride semiconductor layer including a light emitting layer on the n type SiC layer after the n type layer growth step, and the laser In the lift-off process, the n-type SiC layer and the group III nitride semiconductor layer may be separated from the seed crystal substrate side.

  The present invention also provides a SiC material stack including a seed crystal substrate, a p-type SiC layer grown on the seed crystal substrate, and an n-type SiC layer grown on the p-type SiC layer. Is done.

  In the SiC fluorescent material, the n-type SiC layer is a fluorescent material made of SiC crystal in which carbon atoms are arranged at cubic sites and hexagonal sites, and doped with donor impurities and acceptor impurities. The ratio of the donor impurity substituted for the carbon atom of the cubic site to the donor impurity substituted for the atom may be larger than the ratio of the cubic site to the hexagonal site in the crystal structure.

  According to the present invention, a SiC material can be manufactured in a short time, and the yield can be improved.

FIG. 1 is a schematic cross-sectional view of a light-emitting diode element showing an embodiment of the present invention. FIG. 2 is a schematic diagram of a 6H-type SiC crystal. FIG. 3 is an explanatory diagram schematically showing how light incident on the SiC substrate is converted into fluorescence. FIG. 4 is a flowchart showing a method for producing a SiC fluorescent material. FIG. 5 is an explanatory diagram of a crystal growth apparatus. FIG. 6 shows the growth process of the SiC material, (a) shows a state in which the first p-type SiC layer is formed on the seed crystal substrate, and (b) shows the first on the first p-type SiC layer. (C) shows a state in which a second p-type SiC layer is formed on the first n-type SiC layer. FIG. 7 shows the growth process of the SiC material, (a) shows a state in which the second n-type SiC layer is formed on the second p-type SiC layer, and (b) shows n sets on the seed crystal substrate. A state in which a p-type SiC layer and an n-type SiC layer are formed is shown. FIG. 8 is a schematic explanatory diagram of a laser irradiation apparatus. FIG. 9 is a graph showing the relationship between the wavelength and the absorption coefficient for the sample body A, the sample body B, and the sample body C. FIG. 10 is a graph showing the relationship between the wavelength and the absorption coefficient for the sample body B, the sample body D, the sample body E, the sample body F, and the sample body G. 11A and 11B are explanatory views of laser lift-off, in which FIG. 11A shows a state where a laser beam is focused on the n-th p-type SiC layer, and FIG. 11B shows a state where the n-th n-type SiC layer is irradiated. The state after peeling by laser lift-off is shown. 12A and 12B are explanatory diagrams of laser lift-off, in which FIG. 12A shows a state in which the second p-type SiC layer is focused and irradiated with a laser, and FIG. 12B shows the first p-type SiC layer. It shows a state in which the laser is irradiated with the focus. FIG. 13 shows a modified example, (a) shows a state in which the layer structure of the light-emitting diode element is formed on the seed crystal substrate via the p-type SiC layer, and (b) focuses on the p-type SiC layer. The state in which the laser is irradiated is shown. FIG. 14 shows the relative emission intensities of the sample body H and the sample body I, the room temperature carrier concentration, the difference between the donor impurity and the acceptor impurity, the ratio of the difference to the hole, the donor forming the shallow donor level, and the deep donor level. It is a table | surface which shows the ratio of the donor to form. FIG. 15 is a graph showing the relationship between the wavelength and the transmittance of the sample body H, the sample body I, and the sample body J.

  1 to 4 show an embodiment of the present invention, and FIG. 1 is a schematic cross-sectional view of a light-emitting diode element.

  As shown in FIG. 1, the white light emitting diode 1 is a light emitting device composed of a SiC substrate 10 doped with boron (B) and nitrogen (N), and a plurality of nitride semiconductor layers formed on the SiC substrate 10. Part 20. When light is incident on the SiC substrate 10 from the light emitting unit 20, the incident light is absorbed by the SiC substrate 10 and fluorescence due to impurity levels is generated.

As shown in FIG. 2, SiC substrate 10 is formed of 6H-type SiC crystal having a periodic structure for every six layers, and contains nitrogen as a donor impurity and boron as an acceptor impurity. Although the manufacturing method of the SiC substrate 10 is arbitrary, it can be manufactured by growing a SiC crystal by, for example, a sublimation method or a chemical vapor deposition method. At this time, the concentration of nitrogen in SiC substrate 10 can be arbitrarily set by appropriately adjusting the partial pressure of nitrogen gas (N ₂ ) in the atmosphere during crystal growth. On the other hand, the boron concentration of boron in SiC substrate 10 can be arbitrarily set by mixing an appropriate amount of boron alone or a boron compound with the raw material.

  Here, the 6H-type SiC crystal has a cubic site ratio of 2/3 and a hexagonal site ratio of 1/3. Normally, nitrogen, which is a donor impurity, is arranged at each site at the same rate as the existing rate of each site. That is, in the case of 6H-type SiC, 2/3 of nitrogen is substituted with cubic site carbon atoms, and 1/3 of nitrogen is substituted with hexagonal site carbon atoms. However, since the SiC crystal of this embodiment is manufactured through a step of manipulating the donor so as to increase the donor impurity concentration of the cubic site, the carbon of the cubic site with respect to the donor impurity substituted with the carbon atom of the hexagonal site. The ratio of donor impurities substituted for atoms is larger than the ratio of cubic sites to hexagonal sites in the crystal structure.

  As shown in FIG. 1, the light emitting unit 20 includes a buffer layer 21 made of AIGaN, a first contact layer 22 made of n-GaN, a first cladding layer 23 made of n-AIGaN, A multiple quantum well active layer 24 composed of GalnN / GaN, an electron block layer 25 composed of p-AIGaN, a second cladding layer 26 composed of p-AIGaN, and a first cladding layer composed of p-GaN. The two contact layers 27 are continuously provided in this order from the SiC substrate 10 side. The light emitting unit 20 is stacked on the SiC substrate 10 by, for example, an organic metal compound vapor deposition method. A p-electrode 31 made of Ni / Au is formed on the surface of the second contact layer 27. Further, the first contact layer 22 is exposed by etching in the thickness direction from the second contact layer 27 to a predetermined position of the first contact layer 22, and the n electrode 32 made of Ti / Al / Ti / Au is exposed at this exposed portion. Is formed.

In the present embodiment, the multiple quantum well active layer 108 is made of Ga _0.95 ln _0.05 N / GaN, and the peak wavelength of light emission is 385 nm. The peak wavelength in the multiple quantum well active layer 24 can be arbitrarily changed. In addition, it includes at least a first conductivity type layer, an active layer, and a second conductivity type layer. When a voltage is applied to the first conductivity type layer and the second conductivity type layer, the active layer is formed by recombination of electrons and holes. As long as light is emitted, the layer structure of the light emitting unit 20 is arbitrary.

  When a forward voltage is applied to the p-electrode 31 and the n-electrode 32 of the white light-emitting diode 1 configured as described above, a current is injected into the light-emitting portion 20, and the peak wavelength in the near-ultraviolet region in the multiple quantum well active layer 24 Is emitted. The emitted near-ultraviolet light is incident on the SiC substrate 10 doped with acceptor impurities and donor impurities, and almost all is absorbed. In SiC substrate 10, fluorescence is generated by recombination of donor electrons and acceptor holes using near ultraviolet light as excitation light, and light is emitted from yellow to red. Thereby, the white light emitting diode 1 emits warm white light, and light suitable for illumination is emitted to the outside.

Here, the fluorescence action in SiC substrate 10 will be described with reference to FIG. FIG. 3 is an explanatory diagram schematically showing how light incident on the SiC substrate is converted into fluorescence.
Since SiC substrate 10 which consists mainly of SiC crystal, the band gap energy _{E g} of 6H-type SiC crystal is formed.
When light is incident on the SiC substrate 10, free electrons a are excited from the valence band E2 to the conduction band E1, and free holes b are generated in E2. Then, in a short time of several ns to several μs, the free electron a relaxes to the donor levels N _SD and N _DD to become donor electrons a _S ′ and a _D ′, and the free hole b becomes the acceptor level N. It relaxes to _A and becomes an acceptor hole b ′.
Here, it has been found that a cubic site donor forms a deep donor level N _DD and a hexagonal site donor forms a shallow donor level N _SD .

The donor electron a _D ′ relaxed to the deep donor level N _DD is used for donor-acceptor pair (DAP) emission and recombines with the acceptor hole b ′. The photons c having the energy corresponding to the transition energy _{(E g -E} DD _{-E A)} is discharged to the outside of the SiC substrate 10. Wavelength photons c emitted to the outside of the SiC substrate 10 is dependent on the transition energy _{(E g -E DD -E A)} .
On the other hand, the shallow donor level N donor relaxed to _SD electron a _{S 'is} used for in-band absorption of the Γ-band, an acceptor hole b' does not recombine with. That is, it does not contribute to light emission.

In order to accurately perform donor-acceptor pair emission, the carrier concentration at room temperature in the SiC crystal is preferably smaller than the difference between the donor concentration and the acceptor concentration.
Furthermore, since the ionization energy of nitrogen is smaller than that of boron, a certain amount of nitrogen is ionized at room temperature. Then, the excited donor electron a _D ′ again transitions to the conduction band E1, and the donor electron a _D ′ paired with the acceptor hole b ′ becomes insufficient. The acceptor hole b ′ without the pair of donor electrons a _D ′ cannot contribute to fluorescence emission, and energy for exciting the acceptor hole b ′ is wasted. That is, by setting the nitrogen concentration higher than the boron concentration in anticipation of the amount of nitrogen to be ionized in advance so that the donor electrons a _D ′ and acceptor holes b ′ can be recombined without excess or deficiency, high fluorescence quantum efficiency Can be realized.

Next, a manufacturing method of the SiC fluorescent material will be described with reference to FIG. FIG. 4 is a flowchart showing a method for producing a SiC fluorescent material.
As shown in FIG. 4, this SiC fluorescent material manufacturing method includes a first p-type layer growth step S1, a first n-type layer growth step S2, a second p-type layer growth step S3, 2 n-type layer growth step S4, n-th p-type layer growth step S5, n-th n-type layer growth step S6, and laser lift-off step S7. Here, n is the number of pairs of p-type SiC layer and n-type SiC layer formed on the seed crystal substrate, and n in FIG. 4 is an integer of 3 or more.

FIG. 5 is an explanatory diagram of a crystal growth apparatus.
As shown in FIG. 5, the crystal growth apparatus 100 includes an inner container 130 in which the seed crystal substrate 110 and the raw material 120 are disposed, a housing tube 140 that houses the inner container 130, and a heat insulating container 150 that covers the inner container 130. , An introduction pipe 160 for introducing gas into the accommodation pipe 140, a flow meter 170 for measuring the flow rate of the gas introduced from the introduction pipe 160, a pump 180 for adjusting the pressure in the accommodation pipe 140, and the outside of the accommodation pipe 140 And an RF coil 190 for heating the seed crystal substrate 110.

The inner container 130 is made of, for example, graphite, and includes a crucible 131 that opens upward and a lid 132 that closes the opening of the crucible 131. A seed crystal substrate 110 made of single crystal SiC is attached to the inner surface of lid 132. Further, the sublimation recrystallization raw material 120 is accommodated in the crucible 131. In this embodiment, the raw material 120 uses SiC crystal powder and B source powder. Examples of the B source include LaB ₆ , B ₄ C, TaB ₂ , NbB ₂ , ZrB ₂ , HfB ₂ , BN, B-containing carbon, and the like.

In manufacturing the SiC fluorescent material, first, the crucible 131 filled with the raw material 120 is closed with the lid 132, and the crucible 131 is installed inside the housing tube 140 with a support rod made of graphite, and then the inner container 130 is covered with the heat insulating container 150. . Then, Ar gas, N ₂ gas, and H ₂ gas are flowed as an atmosphere gas through the flow meter 170 into the accommodation tube 140 through the introduction tube 160. Subsequently, the raw material 120 is heated using the RF coil 190, and the pressure in the housing tube 140 is controlled using the pump 180.

  Specifically, the pressure in the storage tube 140 is set to be between 0.03 Pa and 600 Pa, and the initial temperature of the seed crystal substrate 110 is set to at least 1100 ° C. The initial temperature is preferably 1500 ° C. or lower, and more preferably 1400 ° C. or lower. And the temperature gradient between the raw material 120 and the seed crystal substrate 110 is set between 1 degreeC and 10 degreeC.

  Next, the seed crystal substrate 110 is heated from the initial temperature at a rate of 15 ° C./min to 25 ° C./min and raised to the growth temperature. The growth temperature is preferably between 1700 ° C and 1900 ° C. The growth rate is preferably between 10 μm / hour and 200 μm / hour.

  Thereby, the raw material 120 is transported by being diffused in the direction of the seed crystal substrate 110 by the concentration gradient formed based on the temperature gradient after sublimation. The growth of the SiC fluorescent material is realized by recrystallizing the source gas arriving at the seed crystal substrate 110 on the seed crystal. The doping concentration of the SiC crystal can be controlled by adding an impurity gas to the atmosphere gas during crystal growth and adding an impurity element or compound thereof to the raw material powder.

  FIG. 6 shows the growth process of the SiC material, (a) shows a state in which the first p-type SiC layer is formed on the seed crystal substrate, and (b) shows the first on the first p-type SiC layer. (C) shows a state in which a second p-type SiC layer is formed on the first n-type SiC layer. FIG. 7 shows the growth process of the SiC material, (a) shows a state in which the second n-type SiC layer is formed on the second p-type SiC layer, and (b) shows n sets on the seed crystal substrate. A state in which a p-type SiC layer and an n-type SiC are formed is shown.

  In the present embodiment, as shown in FIG. 6A, first, a first p-type SiC layer 210 is grown on a seed crystal substrate 110 (first p-type layer growth step: S1). In the present embodiment, a B compound is added to the raw material 120, and the first p-type SiC layer 210 contains B as an impurity element. The thickness of the first p-type SiC layer 210 is, for example, 10 μm to 50 μm. Since the first p-type SiC layer 210 functions as a light absorption layer in the laser lift-off step S7, the thickness, impurity concentration, etc. are arbitrary as long as the function as the light absorption layer is achieved.

Next, as shown in FIG. 6B, a first n-type SiC layer 220 is grown on the first p-type SiC layer 210 (first n-type layer growth step: S2). In the present embodiment, N ₂ gas is added to the atmospheric gas during crystal growth, and the first n-type SiC layer 220 contains B and N as impurity elements. Further, H ₂ gas is added to the atmospheric gas during crystal growth, thereby suppressing substitution of donor impurities with carbon atoms of hexagonal sites and promoting substitution of carbon sites with cubic sites. The thickness of the first n-type SiC layer 220 is, for example, 200 μm to 300 μm. Since the first n-type SiC layer 220 is used as the SiC substrate 10 of the white light emitting diode 1, it is desirable that the first n-type SiC layer 220 is designed so that no mechanical processing is required regarding the thickness after the laser lift-off.

  Here, the mechanism by which substitution of donor impurities with carbon atoms at cubic sites is promoted is considered as follows. First, hydrogen atoms react with carbon atoms at the atomic step ends on the crystal growth surface to form C—H bonds. Next, the bonding force between the carbon atoms and the surrounding silicon atoms is weakened, and carbon vacancies are generated due to the elimination of the carbon atoms. And the probability that nitrogen will be taken into the carbon vacancies increases. Here, there is a difference in the bonding strength of the Si atoms around the carbon atom of the hexagonal site and the carbon atom of the cubic site, and the carbon atom of the cubic site has a weaker bonding force, so carbon vacancies are generated by hydrogen atoms. For this reason, it is considered that substitution of carbon atoms and nitrogen atoms in the cubic site is selectively promoted.

  Thus, the SiC crystal produced through the donor operation step that promotes the substitution of carbon atoms and nitrogen atoms of cubic sites rather than hexagonal sites, such as the growth of SiC fluorescent materials in a hydrogen-containing atmosphere, is hexagonal. The ratio of the donor impurity substituted for the carbon atom of the cubic site to the donor impurity substituted for the carbon atom of the site is larger than the ratio of the cubic site to the hexagonal site in the crystal structure.

  The SiC crystal manufactured in this way has a higher proportion of donor impurities contributing to light emission than the conventional one produced without going through the donor operation step. Therefore, when the donor-acceptor pair (DAP) light is emitted. The luminous efficiency of can be improved. At this time, it is preferable that the absorptivity of the visible light region in the SiC crystal is the same as that in the case of no addition of impurities, since there are few shallow level donors.

  Further, as shown in FIG. 6C, a second p-type SiC layer 230 is grown on the first n-type SiC layer 220 under the same conditions as the first p-type SiC layer 210 (first 2 p-type layer growth step: S3). Furthermore, as shown in FIG. 7A, the second n-type SiC layer 240 is grown on the second p-type SiC layer 230 under the same conditions as the first n-type SiC layer 220 ( Second n-type layer growth step: S4). In this way, the p-type SiC layer and the n-type SiC layer are alternately stacked in this order, and as shown in FIG. 7B, the n-th p-type SiC layer 250 and the n-th n-type SiC layer Stack up to 260 (n-th p-type layer growth step: S5, n-th n-type layer growth step: S6). Thereby, SiC material laminate 290 in which a plurality of p-type SiC layers and n-type SiC layers on seed crystal substrate 110 are laminated is manufactured.

Next, each n-type SiC layer 220, 240, 260 is peeled off by a laser lift-off method (laser lift-off process: S7). FIG. 8 is a schematic explanatory diagram of a laser irradiation apparatus.
As shown in FIG. 8, a laser irradiation apparatus 300 is a laser oscillator 310 that oscillates a laser beam, a mirror 320 that changes the direction of the oscillated laser beam, an optical lens 330 that focuses the laser beam, and a laser beam irradiation target. A stage 340 for supporting the work object, that is, the joined body 160 is provided. The laser irradiation apparatus 300 may include a housing 350 that maintains the laser beam path in a vacuum state.

  The laser oscillator 310 can use a second harmonic of a YAG laser or the like. The beam emitted from the laser oscillator 310 is reflected by the mirror 320 and its direction is changed. A plurality of mirrors 320 are provided to change the direction of the laser beam. The optical lens 330 is positioned above the stage 340 and focuses the laser beam incident on the SiC material stack 290.

  Stage 340 moves in the x direction and / or y direction by a moving means (not shown), and moves SiC material stack 290 placed thereon. The laser beam is irradiated through the seed crystal substrate 110 and the n-type SiC layers 220, 240, and 260 and is absorbed by the p-type SiC layers 210, 230, and 250. Since p-type SiC layers 210, 230, and 250 have a large absorption peak in the visible light region, the absorption coefficient of the laser is larger than that of n-type SiC layers 220, 240, and 260. Therefore, the p-type SiC layers 210, 230, and 250 can function as a light absorption layer, and the n-type SiC layers 220, 240, and 260 can be peeled off.

  Here, when a plurality of sample bodies of p-type SiC and n-type SiC were produced, it was visually confirmed that p-type SiC has a larger absorption coefficient in the visible region than n-type SiC. Specifically, when a plurality of p-type SiC doped with Al as an impurity was produced, a black or dark green sample body was obtained, and it was visually confirmed that the absorption coefficient was large in the visible region. Further, when an n-type SiC doped with Al and N as impurities is produced, a transparent or light green sample body is obtained, and it is visually confirmed that the absorption coefficient is small in the visible region. That is, when p-type SiC doped with Al and n-type SiC doped with Al and N are stacked and irradiated with a laser in the visible region, light is absorbed by the p-type SiC.

  Further, when p-type SiC doped with B as an impurity was produced, a black or dark green sample body was obtained, and it was visually confirmed that the absorption coefficient was large in the visible region. Further, when n-type SiC doped with B and N as impurities was produced, a transparent or light green sample body was obtained, and it was visually confirmed that the absorption coefficient was small in the visible region. That is, when p-type SiC doped with B and n-type SiC doped with B and N are stacked and irradiated with a laser in the visible region, light is absorbed by the p-type SiC.

In the case of n-type SiC doped with a donor impurity and an acceptor impurity, the difference between the concentration N _D of the donor impurity such as N and the concentration N _A of the acceptor impurity such as Al and B (N _D −N _A ) is It has been confirmed that the n-type SiC of at least 1 × 10 ¹⁹ or less is almost transparent. Actually, a laser having a wavelength of 532 nm, a spot diameter of 3 mm, and a peak power of 0.1 to 1 .mu.m is applied to a laminated body of n-type SiC containing donor impurities and acceptor impurities and p-type SiC containing acceptor impurities. When irradiation was performed from the n-type SiC side under the condition of 0 MW / pulse, energy was not absorbed by n-type SiC but was absorbed by p-type SiC.

Furthermore, the relationship between the wavelength and the absorption coefficient was actually measured for a plurality of sample bodies.
FIG. 9 is a graph showing the relationship between the wavelength and the absorption coefficient for the sample body A, the sample body B, and the sample body C. The sample body A was p-type SiC doped with Al, and the concentration of Al was set to 1.5 × 10 ¹⁹ / cm ³ . The sample body B is undoped n-type SiC. The sample body C was n-type SiC doped with Al and N, and the Al concentration was 4 × 10 ¹⁸ / cm ³ and the N concentration was 5.5 × 10 ¹⁸ / cm ³ . As shown in FIG. 9, p-type SiC has a significantly larger absorption coefficient in a region of 420 nm or more than n-type SiC. It is understood that the n-type SiC may be undoped SiC like the sample body B or SiC doped with Al as the acceptor impurity and N as the donor impurity like the sample body C. The The sample body C is fluorescent SiC that emits blue light when excited by near ultraviolet light.

FIG. 10 is a graph showing the relationship between the wavelength and the absorption coefficient for the sample body B, the sample body D, the sample body E, the sample body F, and the sample body G. The sample body D was p-type SiC doped with B, and the concentration of B was 5 × 10 ¹⁸ / cm ³ . The sample body E was n-type SiC doped with B and N, and the concentration of B was 6 × 10 ¹⁷ / cm ³ and the concentration of N was 1 × 10 ¹⁹ / cm ³ . The sample body F was n-type SiC doped with B and N, and the concentration of B was 4 × 10 ¹⁷ / cm ³ and the concentration of N was 2.6 × 10 ¹⁸ / cm ³ . The sample body G was n-type SiC doped with B and N, and the concentration of B was 8.95 × 10 ¹⁷ / cm ³ and the concentration of N was 2.5 × 10 ¹⁸ / cm ³ . As shown in FIG. 10, p-type SiC has a significantly larger absorption coefficient in a region of 450 nm or more than n-type SiC.

As for the sample body E, the sample body F, and the sample body G, the absorption coefficient is relatively low in the region of 450 nm or more and 580 nm or less and the region of 680 nm or more. Therefore, it is preferable that the wavelength of the laser is 450 nm or more and 580 nm or less or 680 nm or more because the difference in absorption coefficient from p-type SiC increases. Even in the region of more than 580 nm and less than 680 nm, although the absorption coefficient of the sample body E is relatively high, the absorption coefficients of the sample body F and the sample body G are relatively low. This is thought to be due to the difference in concentration _{N A} of the acceptor impurity concentration _{N D} of the donor impurity of each sample body _(N D -N _A), the difference _(N D -N _A) is the sample body E The sample body F is 9.4 × 10 ¹⁸ / cm ³ , the sample body F is 2.2 × 10 ¹⁸ / cm ³ , and the sample body G is 1.6 × 10 ¹⁸ / cm ³ . Therefore, if the difference between the concentration _{N A} of the acceptor impurity concentration _{N D} of the donor impurities _(N D -N _A) and 2.2 × ¹⁰ 18 / cm ³ or less, preferably Nari low absorption coefficient in the entire wavelength region .

  11A and 11B are explanatory views of laser lift-off, in which FIG. 11A shows a state where a laser beam is focused on the n-th p-type SiC layer, and FIG. 11B shows a state where the n-th n-type SiC layer is irradiated. The state after peeling by laser lift-off is shown. FIG. 12 is an explanatory diagram of laser lift-off, in which (a) shows a state in which a laser beam is focused on the second p-type SiC layer, and (a) shows the first p-type SiC layer. It shows a state in which the laser is irradiated with the focus.

  In laser lift-off, first, as shown in FIG. 11A, the laser is focused on the n-th p-type SiC layer 250 farthest from the seed crystal substrate 110, and the first n-type SiC layer 260 passes through the n-th SiC layer 260. The n p-type SiC layer 250 absorbs the laser beam. Thereby, as shown in FIG. 11B, the n-th n-type SiC layer 260 is peeled off from the seed crystal substrate 110 side.

  In this manner, the n-type SiC layer is sequentially peeled from the side opposite to the seed crystal substrate 110. Then, as shown in FIG. 12A, the second p-type SiC layer 230 absorbs the laser beam to peel off the second n-type SiC layer 240, and as shown in FIG. All the n-type SiC layers 220, 240, and 260 are peeled from the seed crystal substrate 110 side by causing the p-type SiC layer 210 to absorb the laser light and peeling the first n-type SiC layer 220. The seed crystal substrate 110 from which all the n-type SiC layers 220, 240, and 260 have been peeled can be reused.

  In this manner, p-type SiC layers 210, 230, 250 are formed between seed crystal substrate 110 and n-type SiC layers 220, 240, 260, and laser light is absorbed by p-type SiC layers 210, 230, 250. Thus, an n-type SiC material can be obtained. At this time, the p-type SiC layers 210, 230, and 250 may have a thickness that allows them to function as an absorption layer. For example, the p-type SiC layers 210, 230, and 250 may be significantly thinner than the thickness of the cutting allowance when mechanically dividing and peeling off. it can. Therefore, the yield when manufacturing the SiC material can be dramatically improved. For example, when a SiC material is mechanically divided using a wire saw, a cutting allowance of about 400 μm is necessary. However, in the case of a p-type SiC layer as a light absorption layer, the thickness is about 1/40 of about 10 μm. be able to.

  In addition, since the p-type SiC layers 210, 230, and 250 absorb the laser beam and are peeled off, the SiC material is not mechanically damaged as in the case of mechanical peeling. Thereby, a good quality SiC material with little damage can be obtained. Furthermore, if the laser beam is irradiated, the SiC material can be manufactured in a short time without requiring time for processing unlike the case of mechanical peeling.

  The SiC crystal thus peeled off becomes the SiC substrate 10 of the light emitting diode element 1 as it is. Thereafter, a group III nitride semiconductor is epitaxially grown on SiC substrate 10. In the present embodiment, the buffer layer 21, the first contact layer 22, the first cladding layer 23, the multiple quantum well active layer 24, the electron block layer 25, the second cladding layer 26, and the first cladding layer are formed by, for example, metal organic compound vapor deposition. Two contact layers 27 are grown. After the nitride semiconductor layer is formed, the electrodes 31 and 32 are formed and divided into a plurality of light emitting diode elements 1 by dicing, whereby the light emitting diode element 1 is manufactured. Here, the SiC substrate 10 shown in FIG. 1 can be used as a phosphor plate instead of the substrate of the light-emitting diode element 1.

FIG. 13 shows a modified example, (a) shows a state in which the layer structure of the light-emitting diode element is formed on the seed crystal substrate via the p-type SiC layer, and (b) focuses on the p-type SiC layer. The state in which the laser is irradiated is shown.
In the embodiment, the n-type SiC layer is peeled from the side opposite to the seed crystal substrate 110. For example, as shown in FIG. 13B, the n-type SiC layer is peeled from the seed crystal substrate 110 side. Is also possible. If the seed crystal substrate 110 is an n-type SiC material such as undoped, for example, the laser beam is not absorbed in the same manner as each n-type SiC layer. The laser beam is not absorbed before reaching the type SiC layer. Further, the number of p-type SiC layers and n-type SiC layers formed on seed crystal substrate 110 is also arbitrary.

  In the above embodiment, p-type and n-type SiC materials are sequentially stacked on the seed crystal substrate 110 to obtain a plurality of n-type SiC materials. For example, FIG. As shown, the layer structure of the light-emitting diode element 1 may be formed via the p-type SiC layer 210. In this case, after the p-type SiC layer 210 and the n-type SiC layer 10 are sequentially formed on the seed crystal substrate 110, a group III nitride semiconductor is epitaxially grown on the n-type SiC layer 10. Thereafter, as shown in FIG. 13B, the light-emitting diode element 1 can be obtained by causing the p-type SiC layer 210 to absorb the laser light.

  Moreover, in the said embodiment, although the n-type SiC layer showed what is a fluorescent material, of course, it is good also as SiC materials other than a fluorescent material. The point is that a p-type SiC material is interposed between the seed crystal substrate and the n-type SiC material, and the p-type SiC material absorbs the laser beam.

  If the n-type SiC layer is a fluorescent material, the n-type SiC layer is preferably a fluorescent material containing N as a donor impurity and at least one of Al or B as an acceptor impurity. In this case, if the impurity of the p-type SiC layer is the same material as the acceptor impurity of the n-type SiC layer, it is easy to produce a SiC material stack. That is, the p-type SiC layer preferably contains at least one of Al or B as an impurity.

  In the above embodiment, the SiC fluorescent material is obtained by the sublimation method. However, the SiC fluorescent material may be obtained by the CVD method or the like. In addition, by attaching hydrogen gas during crystal growth, carbon atoms of hexagonal sites are preferentially substituted for donor impurities. However, other methods can be used, for example, the ratio of Si to C It is also possible by accurately controlling.

  Moreover, in the said embodiment, although what used SiC fluorescent material as a board | substrate of the light emitting diode element 1 was shown, it can also utilize as a fluorescent substance separate from a light source. For example, the SiC fluorescent material can be used as a powder or can be used in the form of a plate.

  Moreover, although what used N and B as a donor and acceptor of an n-type SiC fluorescent material was shown, it can be made to light-emit on the short wavelength side rather than the combination of N and B by using N and Al, for example. In addition, Al and B may be added together with N. Further, as the donor and acceptor of the n-type SiC fluorescent material, other group V elements such as P, As, Sb, Ga, In, Al and group III elements can be used, and further, Ti, Cr, etc. It is also possible to use group II elements such as transition metals and Be, and the donor and acceptor can be appropriately changed as long as they can be used as donor impurities and acceptor impurities in the SiC crystal.

  In addition, in the 6H type SiC crystal as the SiC fluorescent material, the ratio of the donor impurity substituted for the carbon atom of the cubic site to the donor impurity substituted for the carbon atom of the hexagonal site is such that the cubic site relative to the hexagonal site in the crystal structure is Although the ratio is larger than the ratio, any other polytype SiC crystal can be applied as long as it has a cubic site and a hexagonal site, such as a 4H type SiC crystal.

  Here, in fact, in the 6H-type SiC crystal, the ratio of the donor impurity substituted for the carbon atom of the cubic site relative to the donor impurity substituted for the carbon atom of the hexagonal site is such that the cubic site relative to the hexagonal site in the crystal structure is A sample body H larger than the ratio was produced. In addition, for comparison, in the 6H-type SiC crystal, the ratio of the donor impurity substituted for the carbon atom of the cubic site to the donor impurity substituted for the carbon atom of the hexagonal site is the ratio of the cubic site to the hexagonal site in the crystal structure. A sample body I having the same ratio was produced.

Specifically, the sample bodies H and I were manufactured using the crystal growth apparatus shown in FIG. 5, and nitrogen was used as a donor impurity and boron was used as an acceptor impurity. Nitrogen was added by containing N ₂ gas in the atmosphere gas during crystal growth, and boron was added by containing B compound in the raw material 120. More specifically, the sample bodies H and I were manufactured at an initial temperature of 1100 ° C., a growth temperature of 1780 ° C., and a growth rate of 100 μm / hour. The sample body H, in the housing but within 140 in addition to the Ar gas and _{N 2} gas was introduced into the _{H 2} gas, the pressure in the reservoir tube 140 was prepared as a 0.08 Pa. In addition, the sample body I was prepared by setting the pressure in the storage tube 140 to 30 Pa in addition to Ar gas and N ₂ gas in the storage chamber 140.

  The relative emission intensities, the room temperature carrier concentration, the difference between the donor impurity and the acceptor impurity, the ratio of the difference to the hole (Hall), the donor forming the shallow donor level, When the ratio of the donors forming the donor level was measured, it was as shown in FIG. FIG. 14 shows the relative emission intensities of the sample body H and the sample body I, the room temperature carrier concentration, the difference between the donor impurity and the acceptor impurity, the ratio of the difference to the hole, the donor forming the shallow donor level, and the deep donor level. It is a table | surface which shows the ratio of the donor to form. Here, Hall means the carrier concentration obtained by measuring the Hall effect at room temperature.

  As is clear from FIG. 14, in the sample body H, by adding hydrogen during crystal growth, the substitution of the donor impurity with the carbon atom of the hexagonal site was suppressed, and the substitution of the cubic site with the carbon atom was promoted. . As a result, the emission intensity was four times that of the sample body I. Further, regarding the sample body H, it is understood that the carrier concentration at room temperature is smaller than the difference between the donor concentration and the acceptor concentration, and that the donor-acceptor pair emission is accurately performed. Further, in the sample body H, since the ratio of the difference between the donor concentration and the acceptor concentration with respect to the holes is smaller than that of the sample body I, compared to the sample body I, nitrogen as a donor generates extra free carriers. It is understood that this contributes to donor-acceptor pair emission without any problem.

  Further, the transmittance and the absorption coefficient of the sample body H and the sample body I were measured. For comparison, a sample body J made of 6H-type SiC crystal containing no impurities was prepared and compared with the transmittance. Here, the sample body J was manufactured at an initial temperature of 1100 ° C., a growth temperature of 1780 ° C., and a growth rate of 100 μm / hour. FIG. 15 is a graph showing the relationship between the wavelength and the transmittance of the sample body H, the sample body I, and the sample body J.

  As shown in FIG. 15, the sample body H has a transmittance in the visible light region that is comparable to that of the sample body J to which no impurities are added, and it is understood that there are relatively few shallow level donors. On the other hand, it is understood that the sample body I has a transmittance in the visible light region smaller than that of the sample body J, and there are relatively many shallow level donors.

DESCRIPTION OF SYMBOLS 1 Light emitting diode element 10 SiC substrate 21 Buffer layer 22 1st contact layer 23 1st clad layer 24 Multiple quantum well active layer 25 Electron block layer 26 2nd clad layer 27 2nd contact layer 31 p electrode 32 n electrode 100 Crystal growth apparatus DESCRIPTION OF SYMBOLS 110 Seed crystal substrate 120 Raw material 130 Inner container 131 Crucible 132 Lid 140 Housing pipe 150 Thermal insulation container 160 Introduction pipe 170 Flowmeter 180 Pump 190 RF coil 210 1st p-type SiC layer 220 1st n-type SiC layer 230 2nd p-type SiC layer 240 second n-type SiC layer 250 n-th p-type SiC layer 260 n-th n-type SiC layer 300 laser irradiation device 310 laser oscillator 320 mirror 330 optical lens 340 stage 350 housing

Claims (2)

A seed crystal substrate;
A p-type SiC layer grown on the seed crystal substrate;
A SiC material stack including an n-type SiC layer grown on the p-type SiC layer. The n-type SiC layer is
It is a fluorescent material composed of SiC crystals in which carbon atoms are arranged at cubic sites and hexagonal sites, and doped with donor impurities and acceptor impurities,
The SiC material stack according to claim 1, wherein the ratio of the donor impurity substituted for the carbon atom of the cubic site to the donor impurity substituted for the carbon atom of the hexagonal site is larger than the ratio of the cubic site to the hexagonal site in the crystal structure. body.

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