Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2001-10-16
2004-08-24
Norton, Nadine G. (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
Reexamination Certificate
active
06780239
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystal growth method, a crystal growth apparatus, a group-III nitride crystal, and a group-III nitride semiconductor device. In particular, the present invention relates to a crystal growth method and a crystal growth apparatus for a group-III nitride crystal, the group-III nitride crystal, and a group-III nitride semiconductor device-employing the group-III nitride crystal applicable to a blue light source for an optical disk drive, for example.
2. Description of the Related Art
Now, a InGaAlN-family (group-III nitride) device used as violet through blue through green light sources is produced by a crystal growth process employing an MO-CVD method (organic metal chemical vapor phase growth method), an MBE method (molecular beam crystal growth method), etc. on a sapphire or SiC substrate in most cases. In using sapphire or SiC as a substrate, crystal defect caused due to a large expansivity difference and/or lattice constant difference from a group-III nitride may occur frequently. By this reason, there is a problem that the device characteristic may become worth, it may be difficult to lengthen the life of the light-emission device, or the electric power consumption may become larger.
Furthermore, since a sapphire substrate has an insulating property, drawing of an electrode from the substrate like in another conventional light-emission device is impossible, and therefore, drawing the electrode from the nitride semiconductor surface on which crystal was grown is needed. Consequently, the device area may have to be enlarged, and, thereby, the costs may increase. Moreover, chip separation by cleavage is difficult for a group-III nitride semiconductor device produced on a sapphire substrate, and it is not easy to obtain a resonator end surface needed for a laser diode (LD) by cleavage, either. By this reason, a resonator end surface formation according to dry etching, or, after grinding a sapphire substrate to the thickness of 100 micrometers or less, a resonator end surface formation in a way near cleavage should be performed. Also in such a case, it is impossible to perform formation of a resonator end surface and chip separation easily by a single process like for another conventional LD, and, also, complication in process, and, thereby, cost increase may occur.
In order to solve these problems, it has been proposed to reduce the crystal defects by employing a selective lateral growth method and/or another technique for forming a group-III nitride semiconductor film on a sapphire substrate.
For example, a document ‘Japanese Journal of Applied Physics, Vol. 36 (1967), Part 2, No. 12A, pages L1568-1571’ (referred to as a first prior art, hereinafter) discloses a laser diode (LD) shown in FIG.
1
. This configuration is produced as follows: After growing up a GaN low-temperature buffer layer
2
and a GaN layer
3
, one by one, on a sapphire substrate
1
by an MO-VPE (organometallic vapor phase epitaxy) apparatus, an SiO
2
mask
4
for selective growth is formed. This SiO
2
mask
4
is formed through photo lithography and etching process, after depositing a SiO
2
film by another CVD (chemistry vapor phase deposition) apparatus. Next, on this SiO
2
mask
4
, again, a GaN film
3
′ is grown up to a thickness of 20 micrometers by the MO-VPE apparatus, and, thereby, GaN grows laterally selectively, and, as a result, the crystal defects are reduced as compared with the case where the selective lateral growth is not performed. Furthermore, prolonging of the crystal defect toward an activity layer
6
is prevented by provision of a modulation doped strained-layer superlattice layer (MD-SLS)
5
formed thereon. Consequently, as compared with the case where the selective lateral growth and modulation doped strained-layer superlattice layer are not used, it becomes possible to lengthen the device life.
In the case of this first prior art, although it becomes possible to reduce the crystal defects as compared with the case where the selective lateral growth of a GaN film is not carried out on a sapphire substrate, the above-mentioned problems concerning the insulating property and cleavage by using a sapphire substrate still remain. Furthermore, as the SiO
2
mask formation process is added, the crystal growth by the MO-VPE apparatus is needed twice, and, thereby, a problem that a process is complicated newly arises.
As another method, for example, a document ‘Applied Physics Letters, Vol. 73, No. 6, pages 832-834 (1998)’ (referred to as a second prior art, hereinafter) discloses application of a GaN thick film substrate. By this second prior art, a GaN substrate is produced, by growing up a 200-micrometer GaN thick film by an H-VPE (hydride vapor phase growth) apparatus after 20-micrometer selective lateral growth according to the above-mentioned first prior art, and, then, grinding the GaN substrate thus having grown to be the thick film from the side of the sapphire substrate so that it may have the thickness of 150 micrometers. Then, the MO-VPE apparatus is used on this GaN substrate, crystal growth processes required for a LD device are performed, one by one, and, thus, the LD device is produced. Consequently, it becomes possible to solve the above-mentioned problems concerning the insulating property and cleavage by using the sapphire substrate in addition to solving the problem concerning the crystal defects.
A similar method is disclosed by Japanese Laid-Open Patent Application No. 11-4048.
FIG. 7
shows a typical figure thereof.
However, further, the process is more complicated in the second prior art, and, requires the higher costs, in comparison to the first prior art. Moreover, in growing up the no less than 200 micrometer GaN thick film by the method of the second prior art, a stress occurring due to a lattice constant difference and a expansivity difference from the sapphire of the substrate becomes large, and a problem that the curvature and the crack of the substrate arise may newly occur. Moreover, even by performing such a complicated process, the crystal defective density can be reduced to only on the order of 10
6
/cm
2
. Thus, it is not possible to obtain a practical semiconductor device.
In order to avoid this problem, setting to 1 mm or more thickness of an original substrate (sapphire and spinel are the most desirable materials as the substrate) from which a thick film grows is proposed by Japanese Laid-Open Patent Application No. 10-256662. According thereto, no curvature nor crack arise in the substrate even when the GaN film grows in 200 micrometers of thickness by applying this substrate having the thickness of 1 mm or more. However, a substrate thick in this way has a high cost of the substrate itself, and it is necessary to spend much time on polish thereof, and leads to the cost rise of the polish process. That is, as compared with the case where a thin substrate is used, the cost becomes higher by using the thick substrate. Moreover, although no curvature nor crack arise in the substrate after growing up the thick GaN film in using the thick substrate, curvature and/or crack may occur as stress relief occurs during the process of polish. By this reason, even when the thick substrate is used, the GaN substrate having a high crystal quality and having such a large area that it can be practically used for an ordinary semiconductor device manufacturing process cannot be easily produced.
A document ‘Journal of Crystal Growth, Vol. 189/190, pages. 153-158 (1998)’ (referred to as a third prior art, hereinafter) discloses that a bulk crystal of GaN is grown up, and it is used as a homoepitaxial substrate. According to this technique, under the high temperature in the range between 1400 and 1700° C., and under the very high nitrogen pressure of 10 kilobars, crystal growth of the GaN is performed from a Ga liquid. In this case, it becomes possible to grow up a group-III nitride semiconductor film required for a device by using this GaN substrate. Therefore, it is pos
Aoki Masato
Sarayama Seiji
Shimada Masahiko
Yamane Hisanori
Anderson Matthew A.
Cooper & Dunham LLP
Norton Nadine G.
Ricoh & Company, Ltd.
LandOfFree
Crystal growth method, crystal growth apparatus, group-III... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Crystal growth method, crystal growth apparatus, group-III..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Crystal growth method, crystal growth apparatus, group-III... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3361320