Polysilicon Emitter Bipolar Transistor for High hFE Control
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Solution Overview
Problem
Conventional bipolar transistors face limitations in achieving high current gain (hFE) values greater than 1000 due to challenges in controlling the narrow and lowly doped base region, leading to process spread variations and yield loss, and are unable to enter saturation at high collector currents without compromising device performance.
Innovation Solution
A bipolar transistor semiconductor device with a polysilicon emitter region and a collector on the wafer back side, where the emitter region is formed by depositing polysilicon and implanting a high dose of dopants, allowing for a high emitter Gummel number and a well-controlled narrow base, reducing thermal budget and process spread, and enabling hFE values of 1000 or higher without yield loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional diffusion processes are used to create highly doped emitters and lowly doped narrow bases, then high current gain (hFE) is achieved, but process spread variations increase and manufacturing precision deteriorates
Solution Approach 1:
The patent changes the fundamental parameter of emitter material from conventional silicon to polysilicon. This material parameter change enables achieving high emitter doping concentrations (high emitter Gummel number) without the process spread variations that plague traditional diffusion methods. The polysilicon emitter can be deposited with precise thickness control and then heavily doped in a single step, eliminating the need for prolonged high-temperature diffusion processes that cause base width variations and process spread.
2Reliability
If the base region is made narrower and less doped to increase current gain, then hFE improves, but device complexity and difficulty of manufacture increase
Solution Approach 1:
The patent performs preliminary doping of the base region before emitter formation. The base is pre-doped to a low doping concentration and precise width is established before the polysilicon emitter is deposited and heavily doped. This preliminary action allows the base dimensions and doping to be set once and fixed, avoiding subsequent variations that would occur during emitter diffusion. The sequence is carefully orchestrated to establish the narrow, lowly doped base first, then add the heavily doped polysilicon emitter on top.
3Reliability
If conventional silicon emitters are used with high doping, then emitter efficiency is improved, but thermal budget increases causing base width variations
Solution Approach 1:
The patent replaces the thermal diffusion mechanism with a deposition and implantation mechanism. Instead of using high-temperature thermal diffusion to dope the emitter (which increases thermal budget and causes base width variations), the patent deposits polysilicon material and then uses ion implantation or in-situ doping to achieve heavy doping. This substitution of the doping mechanism eliminates the prolonged high-temperature exposure that causes thermal budget issues and subsequent base width variations while maintaining high emitter efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves double the current gain of conventional bipolar transistors, allowing it to enter saturation with half the base current, reducing power losses and enabling high power applications in a compact, energy-efficient form.
Implementation Method 1
the emitter region is formed by depositing polysilicon and implanting a high dose of dopants
Implementation Method 2
the emitter region is formed by depositing polysilicon and implanting a high dose of dopants
Data Source
AI summary
The present disclosure relates to a bipolar transistor semiconductor device including: a substrate layer, a collector epitaxial layer supported by the substrate layer, a base region supported by a portion of the collector epitaxial layer, and an emitter region supported by a portion of the base region. The emitter region includes a polysilicon material.