Method and System for Fabricating a Bipolar Junction Transistor (BJT) with Feed-Forward Control of Base Oxide Thickness for Improved Emitter-Base Junction Control
Publication Date: 2010-Dec-15
The IP.com Prior Art Database
A method and system for fabricating a Bipolar Junction Transistor (BJT) with feed-forward control of base oxide thickness for improved emitter-base junction control is disclosed. The method involves measuring the oxide thickness and adjusting the oxide etches to maintain a constant post etch oxide thickness, thereby controlling the transistor characteristics.
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Method and System for Fabricating a Bipolar Junction Transistor (BJT) with Feed-Forward Control of Base Oxide Thickness for Improved Emitter -Base Junction Control
Disclosed is a method and system for fabricating a Bipolar Junction Transistor (BJT) with feed-forward control of base oxide thickness for improved emitter-base junction control. The N-P-N properties of the BJT are set by base oxide thickness, through the impact that the base oxide thickness has on the emitter dopant diffusion towards the base post emitter etch. As such, a feed-forward control mechanism is used to control the post emitter etch base oxide thickness of the BJT using emitter etch adjustment. This results in improved control of the N-P-N properties of the BJT, as emitter-base
junction characteristics are set by the amount of remaining oxide prior to oxide removal
and emitter poly deposition through the impact on emitter dopant diffusion. A thin base oxide results paradoxically in a higher residual oxygen contamination at the emitter-base interface, and a retarded diffusion of emitter doping towards the base. This results in a higher emitter-base junction breakdown (BVEBO), a lower collector current IC, an increased base current IB through an increase in recombination, a reduced gain (beta), an increased emitter resistance RE and a decreased pinched intrinsic base resistance.
Fig. 1 illustrates a base-emitter interface process. As depicted in fig. 1, a base oxide is deposited on top of base region (LTE). This is depicted in step 1. The base oxide thickness is measured prior to emitter (EX) etch. As such, the thickness of the base oxide varies across wafer and from wafer to wafer. Thereafter, the base oxide and layers above the base oxide are etched using the emitter (EX) etch and spacer etch. The emitter (EX) etch time and the...