EMITTER BALLAST RESISTOR WITH ENHANCED BODY EFFECT TO IMPROVE THE SHORT CIRCUIT WITHSTAND CAPABILITY OF POWER DEVICES

摘要

PURPOSE: An emitter ballast resistor with enhanced body effect to improve the short circuit withstand capability of power devices is provided to accurately control the size and resistance of a ballast resistor the resistor without having to use a mask layer and a source/ emitter ballast resistor aligned with a side-wall spacer having a cellular gate structure. CONSTITUTION: The device includes an N-type substrate(12) with a highly P-doped anode layer on the bottom covered by a highly n-doped drain layer(6). P-well(30) is in the bulk of the wafer near the top surface thereof. The surface of the P-well(30) has a highly doped P-type layer(32). The P-well(30) extends along the length of the device in the z direction, i.e., into the paper. On the top surface of the substrate(12) portions of the gate are opposite each other. The gate portions include a gate oxide layer(14) on the surface of the substrate. The gate(16) includes a number of parallel gate fingers. The fingers are conventionally connected to each other to form a single gate. In the striped gate version the gate portions are elongated fingers; in the cellular version the gate portions are on the opposite boundaries of the cell. On top of the gate oxide layer(14) there is a layer of doped polysilicon(16). Covering the doped polysilicon(16) is a silicon dioxide layer(18) that includes sidewall spacers(19). Sidewall spacers(19) also run the z length of the P-wells(30). Beneath the sidewall spacers(19) are elongated ballast resistors(20). These resistors are tied together by N+ contact areas(40) that extend from one ballast resistor across the surface of the semiconductor to the other ballast resistor. Thus, the emitter region of the device includes a plurality of N+ contact regions that extend generally in the x direction across the surface of the substrate(12). The ballast resistors extend in the z direction on opposite sides of the P-well structure(30).