Method of storing GaN substrate, stored substrate, and semiconductor device and method of its manufacture
Affords a method of storing GaN substrates from which semiconductor devices of favorable properties can be manufactured, the stored substrates, and semiconductor devices and methods of manufacturing the semiconductor devices. In the GaN substrate storing method, a GaN substrate ( 1 ) is stored in an atmosphere having an oxygen concentration of 18 vol. % or less, and/or a water-vapor concentration of 12 g/m 3 or less. Surface roughness Ra of a first principal face on, and roughness Ra of a second principal face on, the GaN substrate stored by the storing method are brought to no more than 20 nm and to no more than 20 μm, respectively. In addition, the GaN substrates are rendered such that the principal faces form an off-axis angle with the (0001) plane of from 0.05° to 2° in the <1 1 00> direction, and from 0° to 1° in the <11 2 0> direction.
1. A GaN substrate storing method employing a storing device equipped with gas introduction and exhaust valves connected to respective introduction and exhaust lines, the GaN substrate storing method comprising:
a placement step of placing a plurality of device-formation-ready GaN substrates into the storing device, with the temperature of the atmosphere inside the storing device being from 5° C. to 60° C., wherein prior to said placement step, the device-formation-ready GaN substrates are each processed so as to have, along a first principal face of each of the GaN substrates, a surface roughness Ra of 20 nm or less, and so as to have, along a second principal face of each of the GaN substrates, a surface roughness Ra of 20 μm or less;
a gas-introduction/exhaust step of introducing into the storing device, via the gas-introduction lines and valves, an inert gas of not more than 18 vol. (% oxygen concentration and not more than 25 g/m 3 water-vapor concentration, and exhausting from the storing device, via the gas-exhaust lines and valves, gas of more than 18 vol. % oxygen concentration and more than 25 g/m 3 water-vapor concentration, to thereby create inside the storing device an atmosphere having an oxygen concentration of 18 vol. % or less, and a water-vapor concentration of 25 g/m 3 or less; and
a sealing step of sealing the plurality of substrates into a storage container hermetic to oxygen and water vapor.
2. A GaN substrate storing method as set forth in claim 1 , wherein in said gas-introduction/exhaust step, the atmosphere created inside the storing device is one in which the oxygen concentration is 5 vol. % or less, and the water-vapor concentration is 17 g/m 3 or less.
3. A GaN substrate storing method as set forth in claim 2 , further comprising a step, in tandem with said gas-introduction/exhaust step, of placing an oxygen scavenger and dehydrating agent inside the storing device.
4. A GaN substrate storing method as set forth in claim 1 , wherein the GaN substrates are each processed so as to have a first-principal-face surface roughness Ra of 5 nm or less, and a second-principal-face surface roughness Ra of 10 μm or less.
5. A GaN substrate storing method as set forth in claim 1 , wherein prior to said placement step, the GaN substrates are each processed so as to have an off-axis angle formed by the principal faces on said GaN substrate and its (0001) plane of between 0.05° and 2°, inclusive, in the <1 1 00 > direction, and between 0° and 1°, inclusive, in the <11 2 0> direction.
6. A GaN substrate storing method as set forth in claim 5 , wherein GaN substrates are each processed so as to have an off-axis angle of between 0.1° and 0.8°, inclusive, in the <1 1 00> direction, and between 0° and 0.6°, inclusive, in the <11 2 0> direction.
7. A GaN substrate storing method as set forth in claim 5 , wherein the plurality of substrates sealed into the storage container is stored for approximately six months.
8. A GaN substrate storing method as set forth in claim 1 , wherein the plurality of substrates sealed into the storage container is stored for approximately six months.
9. A GaN substrate storing method as set forth in claim 1 , wherein the plurality of substrates sealed into the storage container is stored for approximately six months.
10. A GaN substrate storing method as set forth in claim 1 , further comprising a step, in tandem with said gas-introduction/exhaust step, of placing an oxygen scavenger and dehydrating agent inside the storing device.