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A process is provided for doping the sidewalls and bottom of a trench formed in a semiconductor substrate, which is particularly useful for field-effect transistor (FET) isolation.
English (United States)
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Doped Trench Isolation Process
A process is provided for doping the sidewalls and bottom of a trench formed
in a semiconductor substrate, which is particularly useful for field-effect transistor
As illustrated in Fig. 1, a semiconductor substrate 10, preferably of lightly
doped P type conductivity, has a layer of silicon dioxide 12 grown thereon over
which is disposed a layer of photoresist 14. An opening 16 is formed by known
techniques through photoresist and silicon dioxide layers 14 and 12, respectively,
to expose the surface of substrate 10.
Through opening 16, P type ions, e.g., boron, are implanted into substrate 10. As indicated in Fig. 1, multiple implants I/Ia, I/Ib and I/Ic are made with, e.g.,
implant I/Ia being introduced at an intensity of 190 KeV implant, I/Ib at an
intensity of 115 KeV and implant I/Ic at an intensity of 70 KeV, all at a dose of 2 x
10/13/ ions/cm/2/. If desired, one implant may be employed having a varying
gradient. After the ions have been implanted into substrate 10 and the
photoresist layer 14 removed, a known heat treatment is performed to form a
uniformly doped P type pocket 18, as indicated in Fig. 2, having boundaries
diffused beyond opening 16.
Using the original opening 16 in the silicon dioxide layer 12,
a trench 20 is formed by reactive ion etching techniques in substrate
10 with a portion of P type pocket 18 remaining around the sidewalls
and bottom of trench 20. If additional dopant is required at th...