Patent Application
20120107990
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-241044, filed on Oct. 27, 2010; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a method for manufacturing a semiconductor light emitting device and a semiconductor crystal growth apparatus.
The process for manufacturing a semiconductor light emitting device such as a light emitting diode and semiconductor laser includes a process for crystal growing a mixed crystal semiconductor on a substrate by the metal organic chemical vapor deposition (MOCVD) process. In this mixed crystal semiconductor, a plurality of group III-V compound semiconductors are mixed in a certain ratio. InGaAlN-based nitride mixed crystal semiconductors, for instance, are used in white and blue light sources. InGaAlP-based mixed crystal semiconductors, for instance, are used in red to green light sources. GaAlAs-based mixed crystal semiconductors, for instance, are used in infrared light sources. Furthermore, InGaAsP-based mixed crystal semiconductors, for instance, are used in infrared light sources for telecommunications.
In Si-based semiconductor crystal growth, the crystal itself has high purity. Hence, it is necessary to prevent autodoping of impurity from the susceptor (or tray) supporting the crystal growth substrate in the crystal growth apparatus to the crystal being grown on the substrate. Thus, as an example, the substrate is mounted on a susceptor whose surface is previously covered with the same semiconductor film as the semiconductor to be crystal grown on the substrate. The Si-based semiconductor is then crystal grown on this substrate. However, in the crystal growth of the aforementioned group III-V mixed crystal semiconductors, the purity of the crystal itself is far lower than that of the Si-based semiconductor. Hence, there is no need to concern about autodoping from the susceptor during crystal growth. In the normal MOCVD process, a substrate is mounted on the surface of the susceptor made of e.g. carbon, quartz, or SIC. The substrate surface is heated through the susceptor by a heating means such as a heater. Here, in some crystal growth apparatuses, the substrate is mounted not directly on the susceptor, but on a tray mounted on the susceptor. In this case, the substrate surface is heated through the tray. A group III raw material and a group V raw material are supplied by a raw material supply means and react on this heated substrate surface. Thus, a crystal of group III-V mixed crystal semiconductor is grown on the substrate surface. In mixed crystal semiconductors such as InGaN composed of GaN and InN, the group III-V compound semiconductor is composed of a plurality of binary compound semiconductors. In such mixed crystal semiconductors, due to non-uniformity in surface temperature on the substrate, the composition (ratio in the crystal) of the group III element and the group V element of the group III-V compound semiconductor crystal grown on the substrate becomes non-uniform within the plane. Non-uniformity in crystal composition causes variation in the emission wavelength of the light emitting device. Thus, temperature uniformity on the substrate surface is important. Hence, covering the susceptor surface with a compound semiconductor film seems to cause non-uniformity in substrate surface temperature, and has been avoided.
In general, according to one embodiment, a method is disclosed for manufacturing a semiconductor light emitting device. The method can include a crystal growth process. The crystal growth process is configured to grow a stacked structure of compound semiconductor composed of a group III element and a group V element on a substrate by a metal organic chemical vapor deposition process. The substrate is mounted on a substrate mounting portion provided on a surface of a tray placed above a heating device. The surface is located on a side opposite to the heating device. A compound semiconductor film includes at least one group III element forming the stacked structure of the compound semiconductor and at least one group V element forming the stacked structure of the compound semiconductor. The compound semiconductor film is previously formed on a surface of the substrate mounting portion before growing the stacked structure. The substrate is mounted on the substrate mounting portion via the compound semiconductor film, and the stacked structure is grown on the substrate.
Various embodiments will be described hereinafter with reference to the accompanying drawings. The figures used in describing the embodiments are schematic for ease of description. The shape, dimension, and size relation of components in the figures do not necessarily need to be identical to those shown in the figures when they are actually put into practice, but can be suitably modified as long as the effect of the invention is achieved. Embodiments are described with a case where a light emitting diode is manufactured using InGaAlN nitride mixed crystal semiconductor having InN, GaN, AlN mixed with a prescribed ratio as group III-V compound semiconductor taken as an example. Similar description is possible on other compound mixed crystal semiconductors such as InGaAlP-based, GaAlAs-based, and InGaAsP-based compound semiconductor or the like. The term InGaAlN-based nitride semiconductor is taken as including binary compound semiconductor such as InN, GaN and AlN (case where other binary compound ratio is zero) and those mixed crystals. The III-V group compound semiconductor of other materials is similarly taken as including respective group III-V binary compound semiconductors and those mixed crystals.
A first embodiment is described with reference to
By the MOCVD process, the stacked structure of group III-V compound semiconductor is grown as follows. The MOCVD-based crystal growth apparatus includes, although not shown, at least a heating means, a susceptor, a tray, and a raw material supply means. The heating means may be based on the so-called heater heating in which a current is passed in a resistor. However, it is understood that lamp heating can also be used. A susceptor including a plurality of openings is placed above the heating means. A tray is mounted in each of these openings. On the tray is mounted a substrate on which a stacked structure of group III-V compound semiconductor is to be grown.
In the crystal growth process of the method for manufacturing a semiconductor light emitting device according to the embodiment, the tray 1 shown in
A compound semiconductor film 2 is formed on the bottom surface of the depression 1a. In the embodiment, as a stacked structure of group III-V compound semiconductor, a stacked structure of InGaAlN-based nitride semiconductor is formed on the substrate 4 by the MOCVD-based crystal growth process. In this case, this compound semiconductor film 2 can be made of a nitride semiconductor containing at least one group III element constituting this stacked structure, i.e., at least one group III element of In, Ga, and Al, and a group V element, N. For instance, the compound semiconductor film 2 is formed from GaN. The compound semiconductor film 2 may be formed using the aforementioned MOCVD-based crystal growth apparatus for subsequently growing a stacked structure of nitride semiconductor. Alternatively, the compound semiconductor film 2 may be formed by another MOCVD-based crystal growth apparatus, or by an apparatus of other deposition processes such as a sputtering apparatus.
As shown in
The aforementioned heating means, not shown, is placed below the susceptor 5. The heating means supplies heat to the substrate 4 through the tray 1 mounted on the tray mounting portion 6 of the susceptor 5, the compound semiconductor film 2 formed on the bottom surface of the depression 1a of the substrate mounting portion 3 of the tray 1, and the gap 8. Here, in the entire surface of the substrate 4, heat is supplied from the heating means to the substrate through the compound semiconductor film 2 located between the substrate and the bottom surface of the depression of the tray 1. By this heat, the surface of the substrate 4 is heated. The group III raw material and the group V raw material supplied from the aforementioned raw material supply means undergo chemical reaction on the heated substrate surface. Thus, a stacked structure of InGaAlN-based nitride semiconductor is grown. Here, the detailed description of the stacked structure is omitted. For instance, in the aforementioned crystal growth process, a double heterostructure is formed on a sapphire substrate 4. In this double heterostructure, an active layer made of InGaN nitride mixed crystal semiconductor is sandwiched between cladding layers made of GaN. Subsequently, the existing process for forming a light emitting diode is performed to form a semiconductor light emitting device. To form a blue light emitting diode having an emission wavelength in the 450-nm band, the In composition of InGaN in the aforementioned active layer can be set to 20% of the entire group III raw material. That is, InGaN of the active layer is crystal grown so that the ratio (mole fraction) of InN/(InN+GaN) is 0.2.
The variation of emission wavelength of the completed light emitting diode depends on the variation of In composition of InGaN of the active layer. Hence, the variation of emission wavelength of the light emitting diode can be suppressed by suppressing the variation of In composition ratio of InGaN of the active layer in the substrate surface. The maximum and minimum of the In composition of InGaN of the active layer in the substrate surface are denoted by Max and Min, respectively. The variation thereof is defined as (Max−Min)/(Max+Min). Then, the variation of In composition of InGaN of the active layer grown by the aforementioned crystal growth process of the method for manufacturing a semiconductor light emitting device according to the embodiment was as small as 5%.
To demonstrate that this variation is small, a similar double heterostructure for comparison was formed by a crystal growth process constituting part of a method for manufacturing a semiconductor light emitting device of a comparative example. The method for manufacturing a semiconductor light, emitting device of the comparative example is described with reference to
The method for manufacturing a semiconductor light emitting device of the comparative example is generally the same as the method for manufacturing a semiconductor light emitting device according to the embodiment except for the structure of the tray for mounting a substrate. In the following, the difference in the structure of the tray, and the MOCVD-based crystal growth process using this tray are described.
Like the tray 1 used in the embodiment, the tray 1 used in the comparative example is made of e.g. SIC, quartz, or carbon and processed into the shape shown in
In contrast to the tray 1 used in the first embodiment, the compound semiconductor film 2 is not formed on the bottom surface of the depression 1a. That is, the bottom surface of the depression 1a is exposed. The tray 1 used in the embodiment includes a compound semiconductor film 2 formed on the entire bottom surface of the depression 1a of the substrate mounting portion 3. In contrast, the tray 1 used in the comparative example does not include the compound semiconductor film 2 formed on the entire bottom surface of the depression 1a of the substrate mounting portion 3. This is the difference between the method for manufacturing a semiconductor light emitting device according to the embodiment and the method for manufacturing a semiconductor light emitting device of the comparative example. The remaining configuration is the same.
The MOCVD-based crystal growth process for growing a stacked structure of InGaAlN-based nitride semiconductor using the aforementioned tray is described. This process is one process of the method for manufacturing a semiconductor light emitting device of the comparative example. As shown in
Thus, if the tray 1 is used many times in the MOCVD-based crystal growth, then as shown in
In contrast, in the MOCVD-based crystal growth process of the comparative example, when a substrate 4 is mounted on the substrate mounting portion 3 of the tray 1 as shown in
By the MOCVD-based crystal growth process in the method for manufacturing a semiconductor light emitting device of the comparative example, a double heterostructure was formed on a sapphire substrate 4 as in the embodiment. In this double heterostructure, an active layer made of InGaN nitride mixed crystal semiconductor is sandwiched between cladding layers made of GaN. As a result, the variation of In composition of InGaN of the active layer is 15%. This is significantly greater than the variation, 5%, of that grown by the MOCVD-based crystal growth process of the embodiment. It is considered that this results from the non-uniformity of surface temperature of the substrate 4 during crystal growth for the aforementioned reasons.
As described above, in the method for manufacturing a semiconductor light emitting device according to the embodiment, before a stacked structure of InGaAlN-based nitride semiconductor is grown on the substrate by the MOCVD process, a compound semiconductor film 2 is previously formed on the entire surface of the substrate mounting portion of the tray. The compound semiconductor film 2 is made of a nitride semiconductor containing at least one group III element constituting this stacked structure of nitride semiconductor, i.e., at least one group III element of In, Ga, and Al, and a group V element, N. Hence, even if InGaAlN-based nitride semiconductor deposits (9a, 9b) are formed non-uniformly along the outer periphery on the bottom surface of the depression is of the tray 1, the InGaAlN-based nitride semiconductor deposits are formed on the entire bottom surface of the depression, although there is difference in the composition of the group III element. Thus, the amount of heat supplied from the heating means to the surface of the substrate 4 through the bottom surface of the depression 1a of the tray 1 and the gap 8 is made nearly uniform across the entire surface of the substrate 4. Consequently, as an advantageous effect, the composition of the nitride mixed crystal semiconductor in the stacked structure of InGaAlN-based nitride semiconductor grown by the MOCVD-based crystal growth process of the method for manufacturing a semiconductor light emitting device according to the embodiment is uniform in the surface of the substrate 4.
In the above description of the embodiment, a stacked structure of InGaAlN-based nitride semiconductor is grown on a substrate by the MOCVD process. In the case of growing a stacked structure of InGaAlP-based compound semiconductor, the compound semiconductor film 2 can be made of a compound semiconductor containing at least one group III element of In, Ga, and Al, and a group V element, phosphorus (P). The compound semiconductor film 2 is previously formed on the substrate mounting portion of the tray 1 before crystal growth. Then, the aforementioned effect of the embodiment is achieved. In the case of growing a stacked structure of GaAlAs-based compound semiconductor, the compound semiconductor film 2 can be made of a compound semiconductor containing at least one group III element of Ga and Al, and a group V element, arsenic (As). The compound semiconductor film 2 is previously formed on the substrate mounting portion of the tray 1 before crystal growth. Then, the effect of the embodiment is achieved. In the case of growing a stacked structure of InGaAsP-based compound semiconductor, the compound semiconductor film 2 can be made of a compound semiconductor containing at least one group III element of In and Ga, and at least one group V element of As and P. The compound semiconductor film 2 is previously formed on the substrate mounting portion of the tray 1 before crystal growth. Then, the effect of the embodiment is achieved. In general, in the case of growing a stacked structure of group III-V compound semiconductor, a group III-V compound semiconductor containing at least one of the group III elements contained in this stacked structure, and at least one of the group V elements contained in this stacked structure is previously formed on the substrate mounting portion of the tray 1 before crystal growth. Then, the effect of the embodiment is achieved.
A method for manufacturing a semiconductor light emitting device according to a second embodiment is described with reference to
Also in the method for manufacturing a semiconductor light emitting device of the embodiment, before a stacked structure of InGaAlN-based nitride semiconductor is grown on the substrate by the MOCVD process, a compound semiconductor film 2 is previously formed on the entire surface of the substrate mounting portion of the tray. The compound semiconductor film 2 is made of a nitride semiconductor containing at least one group III element constituting this stacked structure of nitride semiconductor, i.e., at least one group III element of In, Ga, and Al, and a group V element, N. Hence, an effect similar to that of the first embodiment can be achieved. Furthermore, as described in the first embodiment, in general, in the case of growing a stacked structure of group III-V compound semiconductor, a group III-V compound semiconductor containing at least one of the group III elements contained in this stacked structure, and at least one of the group V elements contained in this stacked structure is previously formed on the substrate mounting portion of the tray 1 before crystal growth. Then, the effect of the embodiment is achieved.
In the examples described above, in the MOCVD-based crystal growth process in each embodiment, the tray (1, 101) mounting the substrate 4 is further mounted on the tray mounting portion 6 of the susceptor 5. In the examples of each embodiment described above, for simplicity of description, a single tray is mounted on the susceptor. However, it is understood that a plurality of trays can be mounted on the susceptor. Furthermore, the tray itself can be used as a susceptor. That is, the surface of the tray may be large enough to mount a plurality of substrates 4. In this case, the surface of the tray includes a plurality of substrate mounting portions 3. Each substrate mounting portion 3 may be formed to include the depression 1a and the step difference 1b shown in the first and second embodiment.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-241044 | Oct 2010 | JP | national |
