SPLIT WELL IMPLANTATION PROCESSES FOR CMOS AND PERIPHERAL DEVICES
Manufacturing processes leverage process steps used during CMOS formation to form one or more additional type(s) of devices on the same substrate used for the CMOS formation, and at least partially in parallel with the CMOS formation processes. A first layer of implant wells may be formed at a first depth in a substrate using a first mask, and then a second layer of implant wells may be formed at a second, more shallow depth, using a second mask. CMOS devices that are part of a CMOS platform may be formed using some of the wells, while peripheral devices may be formed using remaining wells.
1 . A method of making semiconductor devices, comprising:
performing a first implantation into a substrate at a first depth using a first mask, the first mask having at least a first opening defining a first well and a second opening defining a second well;
performing a second implantation into the substrate at a second depth using a second mask, the second mask having at least a third opening defining a third well and a fourth opening defining a fourth well, and the second depth being closer to an implant surface of the substrate than the first depth;
forming a complementary metal oxide semiconductor (CMOS) device using at least the first well and the third well; and
forming a floating-body MOS transistor using at least the second well and the fourth well.
2 . The method of claim 1 , further comprising:
forming a device element of the CMOS device and a device element of the floating body MOS transistor during a single, shared process.
3 . The method of claim 1 , wherein the first implantation and the second implantation occur within a single process module.
4 . The method of claim 1 , further comprising:
defining a doughnut-shaped active area to host an isolation terminal of the floating-body MOS, using an isolation structure at a surface of the substrate.
5 . The method of claim 4 , further comprising:
forming a transistor active area inside a hole of the doughnut-shaped active area to host the floating-body MOS transistor, defined by a second isolation structure at the surface of the substrate.
6 . The method of claim 5 , further comprising:
forming a diffusion region of the floating-body MOS using the second well.
7 . The method of claim 6 , further comprising:
forming a doughnut-shaped lateral isolation diffusion under the doughnut-shaped active area, using the fourth well.
8 . The method of claim 7 , further comprising:
forming a body diffusion inside a hole of the doughnut-shaped lateral isolation diffusion.
9 . The method of claim 8 , further comprising:
forming the floating-body MOS transistor within the body diffusion.
10 . The method of claim 8 , further comprising:
forming the body diffusion together with a well implant process used to form the CMOS device.
11 . A method of making semiconductor devices, comprising:
forming CMOS devices of a CMOS platform on a substrate, the CMOS devices being formed using at least a first deep well implanted using a first mask and at least a first shallow well implanted using a second mask; and
forming at least one floating-body MOS device on the substrate, using at least a second deep well implanted using the first mask, and at least a second shallow well implanted using the second mask.
12 . The method of claim 11 , further comprising:
defining a doughnut-shaped active area to host an isolation terminal of the floating-body MOS, using an isolation structure at a surface of the substrate; and
forming a transistor active area inside a hole of the doughnut-shaped active area to host the floating-body MOS transistor, defined by a second isolation structure at the surface of the substrate.
13 . The method of claim 12 , further comprising:
forming a buried diffusion region of the floating-body MOS using the second well; and
forming a doughnut-shaped lateral isolation diffusion under the doughnut-shaped active area, using the fourth well.
14 . The method of claim 13 , further comprising:
forming a body diffusion inside a hole of the doughnut-shaped lateral isolation diffusion.
15 . The method of claim 14 , further comprising:
forming the floating-body MOS transistor within the body diffusion.
16 . The method of claim 14 , further comprising:
forming the body diffusion together with a well implant process used to form the CMOS device.
17 . A method of making semiconductor devices, comprising:
defining a doughnut-shaped active area to host an isolation terminal of a floating-body MOS, using an isolation structure at a surface of the substrate;
forming a transistor active area inside a hole of the doughnut-shaped active area, defined by a second isolation structure at the surface of the substrate;
performing a first implantation into a substrate at a first depth using a first mask, the first mask having at least a first opening defining a first well and a second opening defining a second well;
forming a buried diffusion region of the floating-body MOS using the second well;
performing a second implantation into the substrate at a second depth using a second mask, the second mask having at least a third opening defining a third well and a fourth opening defining a fourth well, and the second depth being closer to an implant surface of the substrate than the first depth;
forming a doughnut-shaped lateral isolation diffusion under the doughnut-shaped active area, using the fourth well;
forming a complementary metal oxide semiconductor (CMOS) device using at least the first well and the third well; and
forming the floating-body MOS transistor using at least the buried diffusion region and the doughnut-shaped lateral isolation diffusion.
18 . The method of claim 17 , further comprising:
forming a body diffusion inside a hole of the doughnut-shaped lateral isolation diffusion.
19 . The method of claim 18 , further comprising:
forming the floating-body MOS transistor within the body diffusion.
20 . The method of claim 19 , further comprising:
forming the body diffusion together with a well implant process used to form the CMOS device.