High-voltage Power Device Structure Design And Esd Protection

In power MOS manufacturing industry, the widely used lateral and vertical MOSFETs with their lightly doped drain structure which sustains high voltage, are applied in high voltage circuits. Power MOSFET, due to its low threshold voltage and high breakdown voltage, can be used in level shifter. Besides, CMOS flow is also used in LDMOS manufacturing, the corresponding protection device development is also a part of work in this paper.Since the vertical MOSFET has a planer channel and vertical lightly doped drain as the drift region, a bottom technique is needed to finish the drain contact in the bottom. This paper uses the surface drain contact, which is formed by a region doped in two steps, to avoid the bottom technique and reduce the cost. To adjust the breakdown voltage of N type VDMOS, the lightly doped active region in VDMOS cell is depleted. The breakdown area is altered to the PN junction with relatively large curvature radius, which increases the breakdown voltage. The process for this new structure is compatible with the normal P type LDMOS.Besides the specific structure and flow for high voltage MOS, an N type LDMOS structure can also be built based on the CMOS flow. With a different structure forming step, the new N type LDMOS structure is built up with a high breakdown voltage.Among all electrostatic discharge protection devices for HVMOS based on CMOS process flow, SCR structure is effectively used in input and output pads and inner circuit protection for its robust protection ability and low on-resistance. It is triggered by the avalanche breakdown of the PN junction, so the breakdown voltage can be tuned by adjusting the doping level of corresponding area. In its on state, SCR works on a positive feedback condition with a low on-resistance, which makes the holding voltage difficult to be adjusted. By adding a special MOS and negative feedback part to the traditional SCR structure, the holding voltage can be tuned for the increase of the on-resistance. It needs no additional process, and leads to better result.The two new structures designed in this paper have been applied in ASMC products.