Multiple doping level bipolar junctions transistors and method for forming
View Patent ↗A process for forming bipolar junction transistors having a plurality of different collector doping densities on a semiconductor substrate and an integrated circuit comprising bipolar junction transistors having a plurality of different collector doping densities. A first group of the transistors are formed during formation of a triple well for use in providing triple well isolation for complementary metal oxide semiconductor field effect transistors also formed on the semiconductor substrate. Additional bipolar junction transistors with different collector doping densities are formed during a second doping step after forming a gate stack for the field effect transistors. Implant doping through bipolar transistor emitter windows forms bipolar transistors having different doping densities than the previously formed bipolar transistors. According to one embodiment of the present invention, bipolar junction transistors having six different collector dopant densities (and thus six different breakdown characteristics) are formed.
1. A process for forming bipolar junction transistors in a semiconductor substrate, the process comprising:
forming first doped tub regions of a first dopant type within the substrate in a first metal oxide semiconductor field effect transistor (MOSFET) regions of the substrate;
concurrently forming doped sinker regions of a second dopant type, opposite in type to the first dopant type, within first, second, third and fourth bipolar junction transistor (BJT) regions in the substrate and forming second doped tub regions with the second dopant type in second MOSFET regions;
concurrently forming subcollector regions within the first, second and fourth BJT regions and forming triple well regions within the first MOSFET regions all with the second dopant type, wherein the triple well regions and the second doped tub regions cooperate to electrically isolate the first doped tub regions of the first MOSFET regions from the substrate, and wherein each one of the subcollector regions cooperate with respective doped sinker regions in the first, second and fourth BJT regions;
forming gate electrodes over triple wells in the first MOSFET regions and over the second doped tub regions in the second MOSFET regions;
concurrently doping unmasked portions of the doped sinker regions in the first, second, third and fourth BJT regions and the first doped tub regions with the second type dopant, including forming source/drain regions adjacent the gate electrodes in the first MOSFET regions; and
doping the third and fourth BJT regions with the second dopant type to form a subcollector in the third BJT region and further doping the subcollector in the fourth BJT region.
2. The process of claim 1 further including:
forming a bipolar junction transistor structure for cooperating with the doped sinker regions and the subcollector region in the first BJT region to form a first bipolar junction transistor in the first BJT region;
forming a bipolar junction transistor structure for cooperating with the doped sinker regions and the subcollector region in the second BJT region to form a second bipolar junction transistor in the second BJT region;
forming a bipolar junction transistor structure for cooperating with the doped sinker regions and the subcollector region in the third BJT region to form a third bipolar junction transistor in the third BJT region; and
forming a bipolar junction transistor structure for cooperating with the fourth doped sinker region and the fourth subcollector region to form a fourth bipolar junction transistor;
wherein the first, second, third and fourth bipolar junction transistors exhibit breakdown characteristics in the following order beginning with the bipolar junction transistor having the highest breakdown voltage, the first bipolar junction transistor, the third bipolar junction transistor, the second bipolar junction transistor and the fourth bipolar junction transistor.
3. The process of claim 1 wherein forming the gate electrodes occurs after concurrently forming the first, second, and fourth subcollector regions and the triple well regions.
4. The process of claim 3 wherein forming the gate electrodes occurs prior to forming a subcollector in the third BJT region and further doping the subcollector in the fourth BJT region.
5. The process of claim 1 wherein concurrently forming subcollectors in the first, second, third, and fourth BJT regions and the triple wells in the MOSFET regions comprise using an n-type dopant.
6. The process of claim 5 wherein doping to form the subcollector regions and the triple well regions further comprise implanting phosphorous at a dose of about 2E13 per cubic cm.
7. The process of claim 1 further comprising forming material layers overlying the substrate and forming emitter windows within one or more of the material layers in the first, second, third and fourth BJT regions after forming the subcollectors in the first, second, third and fourth BJT regions.