1. Technical Field
The present invention relates to compound-semiconductor-substrate packaging methods for preventing degradation in quality during storage of compound semiconductor substrates employed in semiconductor device manufacturing.
2. Description of the Related Art
Methods whereby compound semiconductor substrates are stored within a non-oxidizing atmosphere so that the compound semiconductor substrates will not give rise to oxidation or other detriment to quality during storage have been proposed. For example, Japanese Unexamined Pat. App. Pub. No. 2003-175906 discloses a method of packaging semiconductor wafers in which a semiconductor-wafer-storing container and a deoxygenating/dehydrating agent are put into a bag having gas-barrier properties, top of the bag is hermetically sealed, and the bag is kept sealed for a time period sufficient for the oxygen and moisture in the wafer container interior and the bag interior to be absorbed by the deoxygenating/dehydrating agent, after which, with the sealed state left undisturbed, the bag is isolated by a sealing-off partition into a zone in the pouch interior where the wafer container is present and a zone therein where the deoxygenating/dehydrating agent is present.
A problem with the semiconductor wafer packaging method of Pat. App. Pub. No. 2003-175906, however, is that it includes a step whereby the wafer container, which is not gastight, and the deoxygenating/dehydrating agent are sealed into the same space, and because the deoxygenating/dehydrating agent, which is ordinarily a fine powder, gives off particles, impurities from the rising particles adhere to the semiconductor wafers.
What is more, the problem of raising particles from the deoxygenating/dehydrating agent can make it impossible to reduce pressure of the interior of a pouch into which a wafer container has been inserted together with a deoxygenating/dehydrating agent, on account of which a large volume of oxygen and moisture will remain in the pouch interior. A considerable amount of time is necessary for the deoxygenating/dehydrating agent to remove such large volume of oxygen and/or moisture, and in the meantime the surface of the semiconductor wafers is consequently liable to oxidize.
Also, so as to make it possible to form a gastight closure in the pouch by means of a heat seal, at least a sealing portion of the pouch is formed from polyethylene (PE), which has a high oxygen transmission rate, as a consequence of which when semiconductor wafers are stored for long periods, oxygen and/or water enters the pouch interior through the sealing portion, leaving the semiconductor wafers susceptible to surface oxidation.
Still further, with compound semiconductor substrates, one or more epitaxial layers is grown onto the front surface without, ordinarily, any special treatment of the substrate surface being carried out. A problem therein has been that should a thick oxidation layer form on the front surface of the compound semiconductor substrate, oxygen remains behind at the interface between the substrate and the epitaxial layer grown onto its front surface, which is deleterious to device properties.