EMCCD's are the same as CCD's except that they have an extended "multiplication register (or gain register) please read link below

see here... http://www.photometrics.com/resources/learningzone/onchipmultiplicationgain.php

How can i make my own extended multiplication register and add it to a CCD chip???

As i read it, you cannot do it. I has to happen inside the CCD itself.

// Per.