Method Of Integrating Poly Silicon Diodes With Different Breakdown Voltages Into A Discrete Power MOSFET Structure

It is becoming highly desirable to integrate diodes with different breakdown characteristics into power MOSFET devices for smart discrete applications (one example could be a temperature sensing diode and a power MOSFET gate protection diode). Traditional methods of integrating power MOSFET and Poly Diodes use a p- poly implant to optimize poly diode characteristics such as breakdown voltages. These methods allow only single p- concentration in the diodes thus formed. If two types of poly diodes with different breakdown characteristics are required, additional mask steps are traditionally needed to fabricate two p- areas in the polysilicon with different dopant concentrations. This results in increased complexity and manufacturing cost. ...

Method Of Integrating Poly Silicon Diodes With Different Breakdown Voltages Into A Discrete Power MOSFET Structure

It is becoming highly desirable to integrate diodes with different breakdown characteristics into power MOSFET devices for smart discrete applications (one example could be a temperature sensing diode and a power MOSFET gate protection diode). Traditional methods of integrating power MOSFET and Poly Diodes use a p- poly implant to optimize poly diode characteristics such as breakdown voltages. These methods allow only single p- concentration in the diodes thus formed. If two types of poly diodes with different breakdown characteristics are required, additional mask steps are traditionally needed to fabricate two p- areas in the polysilicon with different dopant concentrations. This results in increased complexity and manufacturing cost.

Instead, a new method is proposed where the two poly diodes (see Integrated MOSFET Poly Diode drawing) with different characteristics are formed using a single mask step. This is done by using a mask (Mask Layout Drawing) that allows an open window for p- base mask thus the total doping of poly diode B is the sum of the p- poly implant and the p- base mask/implant (see Table 1). Thus poly diode B has a lower breakdown voltage than poly diode A without any process changes or additional masking steps.

Power MOSFET Cell

Poly Diode A

Poly Diode B

Active area mask

YES

NO

NO

Gate Oxidation

YES

NO

NO

Polysilicon Deposition

YES

YES

YES

p- poly implant

YES

YES

YES

Gate electrode/diode mask

YES

YES

YES

p- base mask/implant

YES

NO

YES

p+ mask

YES

NO

NO

n+ mask

YES

YES

YES

Contact mask

YES

YES

YES

Metal Mask

YES

YES

YES

TABLE 1

INTEGRATED MOSFET /POLY DIODES

MASK LAYOUT DRAWING