High voltage lateral double-diffused metal oxide semiconductor field effect transistor (LDMOSFET) having a deep fully depleted drain drift region
Disclosed are semiconductor structures. Each semiconductor structure can comprise a substrate and at least one laterally double-diffused metal oxide semiconductor field effect transistor (LDMOSFET) on the substrate. Each LDMOSFET can have a fully-depleted deep drain drift region (i.e., a fully depleted deep ballast resistor region) for providing a relatively high blocking voltage. Different configurations for the drain drift regions are disclosed and these different configurations can also vary as a function of the conductivity type of the LDMOSFET. Additionally, each semiconductor structure can comprise an isolation band positioned below the LDMOSFET and an isolation well positioned laterally around the LDMOSFET and extending vertically to the isolation band such that the LDMOSFET is electrically isolated from both a lower portion of the substrate and any adjacent devices on the substrate.
1. A semiconductor structure comprising:
a semiconductor substrate having a top surface and a first type conductivity;
a transistor on said substrate, said transistor comprising:
a first intra-transistor well in said substrate and having said first type conductivity;
a second intra-transistor well in said substrate, positioned laterally adjacent to said first intra-transistor well and having a second type conductivity;
a third intra-transistor well in said substrate, positioned laterally adjacent to said second intra-transistor well and having said first type conductivity;
a fourth intra-transistor well in said substrate, positioned laterally adjacent to said third intra-transistor well and having said second type conductivity;
a drain region within said first intra-transistor well at said top surface of said substrate, said drain region having said first type conductivity;
a source region within said fourth intra-transistor well at said top surface of said substrate, said source region having said first type conductivity; and
an intra-transistor band in said substrate below and in contact with said first intra-transistor well, said second intra-transistor well, said third intra-transistor well and said fourth intra-transistor well, said intra-transistor band having said first type conductivity;
a first isolation well positioned laterally around said transistor and having said second type conductivity;
a second isolation well positioned laterally between said fourth intra-transistor well and said first isolation well, said second isolation well having said first type conductivity and extending vertically to said intra-transistor band; and,
an isolation band in said substrate and having said second type conductivity, said isolation band being below said isolation well and said intra-transistor band such that said transistor is electrically isolated from a lower portion of said substrate,
said intra-transistor band having a drain drift region between said third intra-transistor well and said isolation band.
2. The semiconductor structure of claim 1 , said drain drift region being fully depleted.
3. The semiconductor structure of claim 1 , further comprising a gate structure on said top surface closer to said source region than said drain region, said gate structure having a first side above said third intra-transistor well and a second side above said fourth intra-transistor well.
4. The semiconductor structure of claim 1 , said third intra-transistor well being any one of immediately adjacent to said fourth intra-transistor well and physically separated from said fourth intra-transistor well.
5. The semiconductor structure of claim 1 , further comprising a contact region having said second type conductivity within said second intra-transistor well at said top surface of said substrate.
6. The semiconductor structure of claim 1 , said transistor comprising a P-type transistor.
7. The semiconductor structure of claim 6 , further comprising an N-type transistor on said substrate positioned laterally adjacent to said first isolation well, said isolation band extending laterally below said N-type transistor.