Method for forming a bipolar junction transistor and a metal oxide semiconductor field effect transistor
A method for forming BiCMOS integrated circuits and structures formed according to the method. After forming doped wells and gate stacks for the CMOS devices and collector and base regions for the bipolar junction transistor, an emitter layer is formed within an emitter window. A dielectric material layer is formed over the emitter layer and remains in place during etching of the emitter layer and removal of the etch mask. The dielectric material layer further remains in place during source/drain implant doping and activation of the implanted source/drain dopants. The dielectric material layer functions as a thermal barrier, to limit out-diffusion of the emitter dopants during the activation step.
1. A method for forming a bipolar junction transistor and a metal oxide semiconductor field effect transistor in a semiconductor layer, comprising:
forming first MOSFET structures in a MOSFET region of a semiconductor layer;
forming bipolar junction transistor structures including forming an extrinsic base material layer over the semiconductor layer and an emitter material layer overlying the extrinsic base material layer in a bipolar junction transistor region of the semiconductor layer;
forming a first material layer over the emitter material layer and the extrinsic base material layer;
patterning the first material layer using a hardmask to form a thermal barrier layer over the emitter material layer and the extrinsic base material layer;
patterning the emitter material layer with the hardmask to form a patterned emitter;
patterning the extrinsic base material layer;
forming second MOSFET structures in the MOSFET region; and
heating the semiconductor layer with the thermal layer in place.
2. The method of claim 1 wherein forming first MOSFET structures in the MOSFET region further comprises:
forming an isolation region;
forming a doped tub region;
forming a gate stack; and
forming lightly doped regions.
3. The method of claim 1 wherein forming bipolar junction transistor structures comprises:
forming a bipolar junction transistor collector;
depositing a base polysilicon layer, wherein the extrinsic base material layer comprises the base polysilicon layer; and
depositing an emitter polysilicon layer, wherein the emitter material layer comprises the emitter polysilicon layer.
4. The method of claim 1 wherein the first material layer comprises a silicon oxynitride layer, a silicon nitride layer, a silicon carbide layer or a silicon dioxide layer having a thickness of about 30 to about 60 nm.
5. The method of claim 1 wherein the first MOSFET structures comprise a doped tub region and a gate stack, and wherein the step of forming second MOSFET structures comprises forming gate stack spacers adjacent the gate stack and forming source/drain regions in the doped tub region, and wherein the step of heating comprises heating the semiconductor layer to activate dopants forming the source/drain regions.
6. The method of claim 1 wherein patterning the first material layer and the emitter material layer using the hardmask comprises patterning the hardmask using a patterned photoresist mask.
7. The method of claim 1 wherein patterning the hardmask includes using a plasma etch comprising a mixture of carbon-fluorine gases.
8. The method of claim 7 wherein etching the first material layer comprises using a plasma etch process employing C 2 F 6 and oxygen and etching the emitter material layer includes using a plasma etch process employing chlorine, hydrogen bromine and a mixture of helium and oxygen.
9. The method of claim 1 further comprising removing the thermal barrier layer after heating.