Example: N wafer originally has a unifo 5×10N/nwee dopant level, e.g. donor p-type gau e n- type background Predep plus drive-in 3X10 introduces a second dopal an acceptor At a certain depth, a p-n junction is formed N a third pre-dep of donor can then be done to make an npn transistor N Problem 0 *eb *be can only make profiles consisting of st Emitter Base Collector Gausslans centered at the 01,01.4 xm一 substrate surface Bipolar transistor formation by successive diffusions 3.155J/6.152J.2003Example: wafer originally has a uniform dopant level, e.g. donor. Predep plus drive-in introduces a second dopant, an acceptor. At a certain depth, a p-n junction is formed. A third pre-dep of donor can then be done to make an npn transistor. Problem: can only make profiles consisting of superposed Gaussians centered at the substrate surface. 3.155J/6.152J, 2003 4