拡散入庫 seems to be referring to one of the many steps in the semiconductor manufacturing process.

There are two major processes in the whole manufacturing process; the first process (known in Japan as 拡散工程), and the second process (known in Japan as 組立工程), as you can see in this URL.
http://www.hama-eng.com/semiconductor/index.html
http://www.jem-net.co.jp/en/products/pro_hando_top.html

These processes are commonly outsourced to the fabrication plant located in the low-wage-cost countries, as you can see in this URL.
http://en.wikipedia.org/wiki/Semiconductor_device_fabricatio...

Therefore, for the purpose of production management, the “incoming” event occurs after the first process and before shipping out to the second process. In the third URL, the list of steps are explained at the lower half of the page. The “wafer processing” is corresponding to the first process and the rests are the second process.
Hence, “incoming from the first process/wafer process” could be the translation.

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Note added at 18 hrs (2012-06-09 15:31:36 GMT)
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I recommend not to translate 拡散 literally because there is a 拡散 (diffusion) is one of the works has to be done in the first process, as you can see in the first URL in my post. I know it is confusing but use either the “first process” or “wafer process.”

I did not posted one URL of Japanese textboard which I found during the my research. In there, people talk about the each company’s internal jargon and 拡散 is one of the topic. One guy mocked his manager because the manager did not know 拡散 means the first process and therefore the manager translate this word as diffusion.