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

Publishing Venue

The IP.com Prior Art Database

Abstract

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.

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