JP4508021B2 - Manufacturing method of semiconductor light emitting device - Google Patents

Description

The present invention relates to a method of manufacturing a semiconductor light-emitting element to emit light coupled to form the electrons and holes in the semiconductor, and in particular examples of the semiconductor light emitting element has a plurality of nano-columns called columnar crystal structure About things.

  In recent years, a quantum well is formed in a III-N compound semiconductor (hereinafter referred to as a nitride) or an oxide semiconductor, and a current is applied from outside to couple electrons and holes in the quantum well. The development of solid-state light-emitting elements that emit light by making them light is remarkable. However, the fabrication of these solid state light emitting devices has the following problems.

  For example, when referring to nitride, a fundamental problem that crystal growth has is that crystal growth on a dissimilar material substrate is the main. As a general growth model for nitride heteroepitaxial growth, three-dimensional nuclei are first formed on a low-temperature buffer layer that is thinly deposited on the substrate, and as the growth proceeds further, the nuclei become larger and combine with adjacent nuclei. And a flat surface is formed. Thereafter, the two-dimensional growth is continued while maintaining a flat surface. However, when adjacent nuclei are bonded, the respective nuclei are formed independently, so that the growth planes do not coincide completely, and after bonding, many defects are formed at the nuclear interface. Many of the defects reach the crystal surface as threading dislocations. This threading dislocation acts as a non-radiative recombination center and significantly reduces the luminous efficiency of the solid state light emitting device.

Conventionally, various efforts have been made to reduce threading dislocations against such problems. As a result, the dislocation that was initially about 10 ¹⁰ cm ⁻² in the nitride crystal has been reduced to about 10 ⁵ cm ⁻² .

  As a further technique for lowering dislocations, columnar crystal structures (hereinafter referred to as nanocolumns) have begun to attract attention. The nanocolumn has a diameter of about 100 nm and forms columnar crystals independently without bonding adjacent nuclei. Therefore, the nanocolumn hardly contains threading dislocations in the crystal, and a very high quality crystal can be obtained. In addition, since the nanocolumn has a significantly larger surface area than a thin film and has a cylindrical shape, an improvement in light extraction efficiency is expected as compared with a normal thin film light emitting element.

As an example of an attempt to manufacture a solid-state light emitting device using such a nanocolumn, FIG. According to the prior art, an n-type GaN nanocolumn layer 44 and a light emitting layer 45 are formed on a silicon substrate 43 by an RF-MBE (high frequency molecular beam epitaxy) apparatus, and the p-type GaN contact layer 46 is expanded while increasing the nanocolumn diameter. Is epitaxially grown, and Ni (2 nm) / Au (3 nm) of a translucent p-type electrode is formed.
Kikuchi, Nomura, Kishino “Development of New Functional Device Materials Using Nitride Semiconductor Nanocolumn Crystals” (Applied Physics Society 2004 Autumn Conference Proceedings Vol. 1 P-W-1)

  However, in the above-described prior art, crystals having different plane orientations grow together to form a p-type electrode, and even if there are no threading dislocations in the nanocolumn, the p-type electrode formation layer (p-type GaN contact layer 46). ) Has a problem that many threading dislocations are generated. Due to the threading dislocation, most of the light generated in the light emitting layer 45 is absorbed by the substrate 43 and the p-type electrode region, and the light extraction efficiency is not improved as expected.

An object of the present invention is to provide a method of manufacturing a semiconductor light emitting element which can be further improved light extraction efficiency.

A method for manufacturing a semiconductor light emitting device according to the present invention includes an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light-emitting layer, a p-type nitride semiconductor layer or a p-type oxide semiconductor layer on a single crystal substrate. In the method for manufacturing a semiconductor light emitting device comprising a plurality of columnar crystal structures laminated in order, the step of polishing the p-type nitride semiconductor layer or the p-type oxide semiconductor layer flatly and the polished p-type nitride A step of laminating a conductive substrate on a physical semiconductor layer or a p-type oxide semiconductor layer, laminating them by applying pressure and heating, and forming the conductive substrate into a p-type electrode; and Before the bonding step , the method includes a step of irradiating at least one bonding surface side of the conductive substrate and the columnar crystal structure with a plasma containing nitrogen atoms .

  According to the above configuration, the n-type nitride semiconductor layer or the n-type oxide semiconductor layer, the light emitting layer, and the p-type nitride semiconductor layer or the p-type oxide semiconductor layer while maintaining the columnar structure on the single crystal substrate. In order to manufacture a semiconductor light emitting device having a plurality of columnar crystal structures (nanocolumns), a p-type electrode to be provided on the tip side of the nanocolumns is created by laminating conductive substrates. To do. Specifically, in the bonding, the tip of the p-type nitride semiconductor layer or the p-type oxide semiconductor layer is chemically or physically polished to make the height uniform and then flattened. Laminate the substrates and bond them by pressing and heating.

  Therefore, there is no threading dislocation that occurs when the p-type nitride semiconductor layer or the p-type oxide semiconductor layer is grown in the plane direction to form a p-type electrode in the p-type electrode made of a conductive substrate. A highly efficient semiconductor light emitting device can be manufactured taking advantage of the fact that the nanocolumn does not have threading dislocations inside.

Further, before the prior Kishirube conductive substrate is laminated step, at least one of the cemented surface of the conductive substrate and the columnar crystal structures, it has further rows step of irradiating the plasma containing nitrogen atoms, bonded thereof the surface fit than previously activated, it is possible to strengthen the binding force between the surface atoms, to lower the pressure and temperature at the time of registration lamination, it is possible to reduce damage to the element.

Furthermore, the method for manufacturing a semiconductor light emitting device of the present invention is characterized in that the step of bonding the conductive substrates is performed in a high vacuum of 10 ⁻⁶ Pa or less.

  According to said structure, the cleanliness of the bonding surface of a p-type nitride semiconductor layer or a p-type oxide semiconductor layer, and a conductive substrate can be improved, and the bonding force of surface atoms can be strengthened. Thereby, the pressure and temperature at the time of bonding can be lowered, and damage to the element can be reduced.

As described above, the method for manufacturing a semiconductor light emitting device of the present invention includes an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light emitting layer, a p-type nitride semiconductor layer, or a p-type on a single crystal substrate. In the method for manufacturing a semiconductor light emitting device including a plurality of columnar crystal structures in which an oxide semiconductor layer is sequentially stacked, the p-type nitride semiconductor layer or the p-type oxide semiconductor layer is polished flatly, and then electrically conductive. Laminating the substrates, pressing and heating them together, the conductive substrate is formed on the p-type electrode.

  Therefore, there is no threading dislocation that occurs when the p-type nitride semiconductor layer or the p-type oxide semiconductor layer is grown in the plane direction to form a p-type electrode in the p-type electrode made of a conductive substrate. Thus, a highly efficient semiconductor light emitting device can be manufactured taking advantage of the fact that the nanocolumn does not have threading dislocations inside.

[Embodiment 1]
FIG. 1 is a cross-sectional view schematically showing a manufacturing process of a light-emitting diode D1 which is a semiconductor light-emitting element according to the first embodiment of the present invention. First, an n-type GaN epilayer 2 that is an n-type substrate layer is formed on a sapphire substrate 1 via a low-temperature buffer layer (not shown), and an n-type electrode and a future electrode are formed on the surface of the n-type GaN epilayer 2. In order to make contact, n-type impurity Si is doped at a high concentration. The n-type GaN epilayer 2 becomes an n-type conductive substrate, and a nanocolumn 6 is formed thereon.

  In the present embodiment and other embodiments to be described later, it is assumed that fabrication is performed by metal organic chemical vapor deposition (MOCVD). However, the nanocolumn growth method is not limited to this, and molecular beam epitaxy is not limited thereto. It is well known that nanocolumns can be produced using an apparatus such as (MBE) or hydride vapor phase epitaxy (HVPE). Hereinafter, an MOCVD apparatus is used unless otherwise specified.

  Next, when the surface of the n-type GaN epilayer 2 is nitrided with nitrogen plasma, the growth temperature is raised from the normal GaN growth temperature, and GaN is grown in a nitrogen-excess atmosphere, a GaN crystal grows in a columnar shape. . In this growth, if a doping technique for producing a light emitting diode by normal epi growth is used, an n-type GaN nanocolumn 3, a multiple quantum well nanocolumn 4 (light emitting layer is formed; hereinafter referred to as MQW nanocolumn), a p-type GaN nanocolumn 5 can be sequentially stacked and grown. Thus, as shown in FIG. 1A, the nanocolumns 3 to 5 can be grown.

  It should be noted that in the present invention, a p-type GaN substrate 7 is bonded onto the p-type GaN nanocolumn 5 as shown in FIG. However, as shown in FIG. 1A, the nanocolumns 3 to 5 are not aligned in height in the grown state, and therefore cannot be bonded. Therefore, by using a silicon CMP technique widely used in the production of a multilayer semiconductor, the entire nanocolumns 3 to 5 are rotationally polished using a diamond paste to obtain a uniform height as shown in FIG. A nanocolumn 6 is formed. Other techniques may be used for polishing.

  Similarly, the p-type GaN substrate 7 having a flat surface by polishing is laminated on the tip of the nanocolumn 6, and a pressure of about 8 MPa is perpendicular to the bonding surface using a bonding graphite jig. In addition, when put in a furnace in that state and an appropriate temperature is applied for about 1 hour in a nitrogen atmosphere, the p-type GaN substrate 7 and the nanocolumn 6 can be bonded together as shown in FIG. .

Before this bonding, at least one of the p-type GaN substrate 7 and the nanocolumn 6 is irradiated with nitrogen plasma to activate the bonding surface, or the bonding is performed in an ultrahigh vacuum of 10 ⁻⁶ Pa or less. Further, better bonding can be performed. The former strengthens the bonding force between surface atoms by activating the surface and the latter by increasing the cleanliness of the bonded surface. Thereby, the pressure and temperature at the time of bonding can be lowered, and damage to the element can be reduced.

  Subsequently, similarly to the above, the p-type GaN substrate 7 is thinned by rotational polishing using a diamond paste to form a p-type GaN electrode formation region 8 as shown in FIG. The reason for thinning the film is that p-type GaN has an extremely high resistance compared to n-type GaN, and if the film is not thinned, the current path becomes highly resistive and the light emission efficiency of the light emitting diode is degraded.

  Thereafter, electrodes are formed using the same technique as that for manufacturing a normal light emitting diode. That is, an Au / Ni transparent conductive film 10 is formed on the thinned p-type GaN electrode formation region 8, and a region that will become an n-type electrode formation portion in the future is etched by photolithography technology and dry etching technology. The transparent conductive film 10, the p-type GaN electrode formation region 8, and the nanocolumn 6 are removed. Thereafter, the p-type electrode 11 is formed using vapor deposition, lithography, and dry etching, the n-type electrode 12 is formed in the same manner, and the structure of the light-emitting diode D1 of the present embodiment as shown in FIG. To complete.

  In this way, by forming a p-type electrode to be provided on the tip side of the nanocolumn 6 by bonding the p-type GaN substrate 7, the p-type GaN nanocolumn 5 is arranged in the plane direction in the p-type GaN substrate 7. There is no threading dislocation that would occur when grown into a p-type electrode, and a highly efficient light-emitting diode can be manufactured taking advantage of the fact that the nanocolumn has no threading dislocation inside.

[Embodiment 2]
FIG. 2 is a cross-sectional view schematically showing a manufacturing process of the light-emitting diode D2, which is a semiconductor light-emitting element according to the second embodiment of the present invention. The structure of the light-emitting diode D2 is similar to the structure of the light-emitting diode D1 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. FIG. 2A shows a state in which a p-type GaN substrate 7 is bonded to the tip of the nanocolumn 6 in the same manner as FIG. 1C described above. It should be noted that in the present embodiment, the sapphire substrate 1 Is removed and replaced with an n-type conductive substrate 19 formed by doping impurities of the same type as the n-type GaN epilayer 2.

  Specifically, after the p-type GaN substrate 7 is bonded to the tip of the nanocolumn 6, the sapphire substrate 1 is removed by irradiating a YAG laser from the sapphire substrate 1 side as shown in FIG. Such a sapphire laser lift-off technique is well-known to those skilled in the art, and the details are omitted.

  Then, the surface of the n-type conductive substrate 19 having the same polarity that does not form a pn junction with the n-type GaN epilayer 2 is irradiated with nitrogen plasma to activate the surface atoms of the bonded surface, and the n-type GaN epilayer is activated. Laminate on the surface of layer 2. At this time, the surface of the n-type GaN epilayer 2 is made sufficiently flat in advance by rotary polishing using the aforementioned diamond paste. Then, using the graphite jig, a pressure of about 8 MPa was applied perpendicularly to the bonding surface, put in the furnace in that state, and an appropriate temperature was applied for 1 hour in a nitrogen atmosphere. As shown, the n-type GaN epilayer 2 and the n-type conductive substrate 19 are bonded together. At this time, it goes without saying that better bonding is realized by performing bonding in an ultra-high vacuum as described above. This n-type conductive substrate 19 becomes an n-type electrode in the light-emitting diode D2 of the present embodiment.

  Then, as in the first embodiment, the p-type GaN substrate 7 is thinned to form the p-type GaN electrode formation region 8 by rotational polishing using a diamond paste as shown in FIG. The reason for thinning is as described above. Thereafter, a transparent conductive film 10 is deposited on the p-type GaN electrode formation region 8, and the p-type electrode 11 is formed by using normal deposition, lithography, and dry etching, as shown in FIG. Thus, the structure of the light emitting diode D2 of this embodiment is completed.

  In this way, by removing the sapphire substrate 1 on which the nanocolumns 6 are grown, and laminating an n-type conductive substrate 19 having the same polarity as that of the n-type GaN epilayer 2 instead, the n-type electrode to the p-type electrode 11 A current can flow in the thickness direction of the element, and a light-emitting diode with even higher luminance can be realized. In addition, a substrate such as a Si substrate that absorbs light at the emission wavelength of the nanocolumn 6 although it is inexpensive can be used as a substrate for growing the nanocolumn 6 by substituting the n-type conductive substrate 19 without absorption. can do.

  Since this light emitting diode D2 extracts light from the p-type GaN substrate 7 side, the n-type conductive substrate 19 has a reflectance of 80% or more of light generated in the light emitting layer (multiple quantum well nanocolumn 4). Is desirable. Instead of the n-type conductive substrate 19, a metal substrate made of, for example, a CuW alloy and capable of making ohmic contact with the n-type GaN epi layer 2 may be used.

[Embodiment 3]
FIG. 3 is a cross-sectional view schematically showing a manufacturing process of a light-emitting diode D3 which is a semiconductor light-emitting element according to the third embodiment of the present invention. The structure of the light emitting diode D3 is similar to the structure of the light emitting diode D2 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted that in the present embodiment, the above-described FIG. 1C has the p-type GaN substrate 7 bonded to the tip of the nanocolumn 6, whereas, as shown in FIG. That is, the conductive material substrate 28 is bonded.

  The bonding of the transparent conductive material substrate 28 can be made in substantially the same process, with the conditions slightly different from those of the bonding of the p-type GaN substrate 7. That is, a conductive material substrate 28 whose surface is similarly flattened by polishing is laminated on the tip of the nanocolumn 6, and a pressure of about 8 MPa is applied perpendicularly to the bonding surface using a graphite jig. When placed in a furnace in a state and an appropriate temperature is applied for 1 hour in a nitrogen atmosphere, the transparent conductive material substrate 28 can be bonded to the tip of the nanocolumn 6 as shown in FIG.

  The subsequent manufacturing process is completely the same as that of the second embodiment, and each step of FIGS. 3B to 3E is respectively replaced with each step of FIGS. 2B to 2E. It corresponds. However, unlike the p-type GaN substrate 7, the transparent conductive material substrate 28 can itself be a p-type electrode, and thus it is not necessary to form the transparent conductive film 10. Therefore, the sapphire substrate 1 is removed, the n-type conductive substrate 19 is bonded, and the transparent conductive material substrate 28 is thinned to form the transparent electrode layer 30. Thereafter, the p-type electrode 11 is directly formed.

  Therefore, the step of forming the transparent conductive film 10 can be omitted.

[Embodiment 4]
FIG. 4 is a cross-sectional view schematically showing a manufacturing process of a light-emitting diode D4 which is a semiconductor light-emitting element according to the fourth embodiment of the present invention. The structure of the light-emitting diode D4 is similar to the structure of the light-emitting diode D1 described above, and corresponding portions are denoted by the same reference numerals, and description thereof is omitted. It should be noted that in the present embodiment, the p-type GaN substrate 7 is bonded to the tip of the nanocolumn 6 in FIG. 1C described above, but as shown in FIG. That is, a transparent conductive material substrate 38 on which a reflective multilayer film (hereinafter referred to as a DBR mirror layer) 37 is laminated is bonded.

  The transparent conductive material substrate 38 is made of, for example, p-type GaAs, and the DBR mirror layer 37 is a conductive substrate on which a II-VI group distributed Bragg reflective multilayer film is formed. It is a well-known fact that this II-VI group DBR mirror layer has high reflectivity (90% or more) and is conductive (for example, reference 1: A. Murai, L. McCarthey, U. Mishra). , SPDenbaars, C. Kruse, S. Figge and D. Hommel JJAppl. Phys. Vol. 43, No. 10A, 1275 (2004)).

  In this embodiment, except that the substrate to be bonded is a transparent conductive material substrate 38 having a DBR mirror layer 37 instead of the p-type GaN substrate 7, FIGS. Since it is exactly the same as the process from 1 (c) to FIG. 1 (e), the details are omitted.

  Finally, as shown in FIG. 4D, the n-type electrode 12 formed on the n-type GaN epilayer 2 on the sapphire substrate 1 and the DBR mirror layer 37 formed on the nanocolumn 6 are provided. A light-emitting diode is obtained using the p-type electrode 41 formed on the p-type electrode formation layer 40 obtained by thinning the transparent conductive material substrate 38 as an electrode.

  A feature of the light-emitting diode D4 is that current flows from the p-type electrode 41 to the n-type electrode 12, and light is generated by recombination of electrons and holes in the MQW nanocolumn 4, and the generated light is generated by the DBR mirror layer 37. Almost all of the light is reflected and taken out from the sapphire substrate 1 side. Therefore, there is no problem even if the band gap of the GaAs layer of the transparent conductive material substrate 38 is smaller than the band gap of the InGaN layer forming the MQW nanocolumn 4, and the light absorption loss in the transparent conductive material substrate 38 is eliminated. Overall luminous efficiency can be improved.

  Usually, high reflectivity DBR mirrors are very difficult to form in the III-V group. This is because the difference in refractive index between the group III material layer and the group V material layer is small, so that a large number of layers must be stacked in order to produce the high reflectivity DBR mirror. It is. Therefore, in the prior art shown in FIG. 5, in order to form a DBR mirror layer in the p-type electrode formation layer (p-type GaN contact layer) 46, the III-V group material must be used. By attaching another transparent conductive material substrate 38 as in the present invention, the II-VI group DBR mirror layer 37 having a large refractive index difference can be used. Can be reduced.

  Further, the transparent conductive substrate 38 to be bonded is not limited to the DBR mirror layer 37 but is formed in advance, and even in the case of a metal layer having a high reflectance with respect to the emission wavelength, the light supply to the light extraction surface is similarly performed. Efficiency can be improved. Further, by using a metal substrate having a high thermal conductivity as the transparent conductive substrate 38, the heat dissipation characteristics can be improved, and the luminous efficiency can be further improved.

[Embodiment 5]
Hereinafter, a light-emitting diode that is a semiconductor light-emitting element according to the fifth embodiment of the present invention will be described. The element structure may be any of the above-described light-emitting diodes D1 to D4. It should be noted that in the above-described light emitting diodes D1 to D4, the nanocolumns 3 to 5 are made of a nitride semiconductor layer, whereas in this embodiment, the nanocolumns 3 to 5 are made of an oxide semiconductor layer.

  ZnO which is an oxide semiconductor has extremely excellent characteristics as a light-emitting element. The exciton binding energy is 60 meV, 2 to 3 times that of GaN, the internal quantum efficiency may be higher than that of GaN, and the refractive index is about 2. It is small compared to the above, and is overwhelmingly advantageous in terms of light extraction. It is also attractive from a commercial basis that the materials themselves are inexpensive.

  Therefore, although the above-described first to fourth embodiments describe a GaN-based nanocolumn that is a nitride semiconductor, a semiconductor light emitting device having exactly the same structure is also used for ZnO that is an oxide semiconductor that is similar in crystal structure. Can be produced similarly. This will be described below.

  Both GaN and ZnO have a hexagonal crystal structure, and the lattice constants of the crystals are close. The band gap is also close to 3.4 for GaN and 3.3 for ZnO. Both are direct transition semiconductors. Therefore, if a nanocolumn is formed of GaN, a nanocolumn can be formed of ZnO. In fact, in Document 2, ZnO nanocolumns (called nanorods in this document) are formed on a sapphire substrate using MOCVD (Reference 2: WIPark, YHJun, SWJung and Gyu-Chul). Yi Appl. Phys. Lett. 964 (2003)).

Regarding bonding, which is another important technique of the present invention, what is important in the bonding technique is flattening and heating / pressing. An important physical property is the coefficient of thermal expansion, whereas GaN is 5.6 × 10 ⁻⁶ / K, whereas ZnO is 2.9 × 10 ⁻⁶ / K (parallel to the c-axis), 4.7 × 10 ⁻⁶ / K (c (Perpendicular to the axis) and a value close to GaN. Therefore, it is considered that a substance that can be bonded with GaN can be bonded with ZnO.
From the above, it is considered that the light-emitting diodes D1 to D4 described in the first to fourth embodiments can also be realized with ZnO.

  By using the light emitting diodes D1 to D4 configured as described above for the lighting device, it is possible to realize a small lighting device with low power consumption in order to obtain the same luminous flux (luminance, illuminance).

It is sectional drawing which shows typically the manufacturing process of the light emitting diode which is a semiconductor light-emitting device concerning the 1st Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the light emitting diode which is a semiconductor light-emitting device based on the 2nd Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the light emitting diode which is a semiconductor light-emitting device concerning the 3rd Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the light emitting diode which is a semiconductor light-emitting device based on the 4th Embodiment of this invention. It is sectional drawing which shows typically the manufacturing process of the typical prior art semiconductor light-emitting device.

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 n-type GaN epilayer 3 n-type GaN nanocolumn 4 multiple quantum well nanocolumn 5 p-type GaN nanocolumn 6 nanocolumn 7 p-type gan substrate 8 p-type GaN electrode formation region 10 transparent conductive film 11, 41 p-type electrode 12 n Type electrode 19 n-type conductive substrate 28 transparent conductive material substrate 30 transparent electrode layer 37 Bragg reflective multilayer film 38 transparent conductive material substrates D1 to D4 Light emitting diode

Claims (2)

A plurality of columnar crystal structures in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a single crystal substrate are provided. In the method for manufacturing a semiconductor light emitting device,
Polishing the p-type nitride semiconductor layer or the p-type oxide semiconductor layer flatly ;
Laminating a conductive substrate on the polished p-type nitride semiconductor layer or p-type oxide semiconductor layer , laminating them by applying pressure and heating, and forming the conductive substrate on a p-type electrode; ,
A step of irradiating at least one bonding surface of the conductive substrate and the columnar crystal structure with a plasma containing nitrogen atoms before the step of bonding the conductive substrate. Device manufacturing method . The method for manufacturing a semiconductor light emitting element according to claim 1 , wherein the step of bonding the conductive substrate is performed in a high vacuum of 10 ⁻⁶ Pa or less.

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