1. Field of the Invention
The present invention relates to an MOCVD apparatus and method for forming an epitaxial film on a target substrate by means of MOCVD (Metal Organic Chemical Vapor Deposition).
2. Description of the Related Art
In manufacturing opto-electronics devices, such as a light-emitting diode (LED), laser diode, and photo diode, MOCVD is utilized. For example, in the process of manufacturing LEDs, a group III–V nitride film expressed by a general formula AlxGayInzN (where x+y+z=1, x≧0, y≧0, z≧0) is epitaxially grown on a sapphire substrate by means of MOCVD.
MOCVD is suitable for film-formation of a compound semiconductor film, as compared with LPE (Liquid Phase Epitaxy) and VPE (Vapor Phase Epitaxy). For example, in the case of LPE, a large degree of Al segregation coefficient makes it difficult to grow a predetermined film. In the case of VPE, a process raw material reacts with the wall of an epitaxial growth reaction chamber, thereby making it difficult to grow a predetermined film.
Where an AlxGayInzN (where x+y+z=1, x≧0, y≧0, z≧0) film is formed by means of MOCVD, an operation is performed, as follows. First, a target substrate is loaded into a process chamber, and placed on a susceptor (worktable) having being heated to a predetermined temperature by a heater. Then, one or more of organic metal raw materials, such as trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI), and ammonia are fed as process raw materials, along with a carrier gas, such as hydrogen or nitrogen, into a process chamber. Then, the process raw materials cause reaction and decomposition (reaction of the organic metal with ammonia) in the process chamber, and components thereby provided form an epitaxial film on a target substrate.
The epitaxial film is expressed by a general formula AlxGayInzN (where x+y+z=1, x≧0, y≧0, z≧0). For example, the epitaxial film is an aluminum nitride film, gallium nitride film, indium nitride film, aluminum-gallium nitride film, aluminum-indium nitride film, or gallium-indium nitride film (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2002-246323 (paragraph number 0005)).
According to the present inventors, a problem has been found in opto-electronics devices manufactured by conventional MOCVD apparatuses, in that the wavelength or brightness of emitted light differs between wafer lots (between devices belonging to different lots). As described later, this is though to be attributed to a low reproducibility in the composition of an epitaxial film, which is due to the structure of a raw material supply section in conventional MOCVD apparatuses.