Doped Glass Sidewall for Bipolar Transistor Emitter Window

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Solution Overview

Problem

Conventional bipolar transistor structures face issues with dopant uniformity and emitter-base overlap capacitance due to implanted polysilicon emitters, leading to variations in electrical parameters like current gain and potential dopant loss in oxide spacers.

Innovation Solution

The use of doped glass as a solid diffusion source on the sidewalls of the emitter window opening improves dopant uniformity and reduces emitter-base overlap capacitance, allowing for narrower emitter window openings and self-aligned extrinsic base formation, while minimizing thermal budget requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If implanted polysilicon emitter is used, then emitter structure can be formed, but dopant uniformity deteriorates and plugging effect occurs

Engineering Contradiction:

Improvedopant uniformityVSAvoidelectrical parameter uniformity

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the material parameter from polysilicon to doped glass (specifically phosphosilicate glass for NPN and borosilicate glass for PNP), which fundamentally alters the doping mechanism from ion implantation to solid diffusion, thereby achieving superior dopant uniformity and eliminating the plugging effect

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The doped glass layer is designed to be a consumable dopant source that is completely consumed during the diffusion process, replacing the reusable polysilicon emitter structure. This disposable approach ensures consistent dopant delivery without the variability associated with polysilicon implantation

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If implanted polysilicon emitter is used, then emitter can be formed, but emitter-base overlap capacitance increases

Engineering Contradiction:

Improveemitter structure stabilityVSAvoidemitter-base overlap capacitance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the dopant source function from the emitter polysilicon itself and places it in a separate doped glass layer positioned on the sidewall. This separation allows the emitter polysilicon to serve purely as the emitter contact without the plugging effect, thereby reducing emitter-base overlap capacitance

Inventive Principle:

Principle #2Taking out (Extraction)

3Productivity

If narrower emitter window openings are achieved, then device density improves, but manufacturing precision deteriorates

Engineering Contradiction:

Improvedevice densityVSAvoidemitter window opening uniformity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The doped glass sidewall acts as an intermediary dopant source that enables precise doping control in narrow emitter windows. The glass layer conformally coats the sidewall, providing a uniform dopant distribution even in sub-0.5 micron emitter windows, thus decoupling device density from manufacturing precision constraints

Inventive Principle:

Principle #24Intermediary (Mediator)

4Manufacturing precision

If significant thermals are applied to drive dopants from doped glass, then doping uniformity improves, but thermal budget increases

Engineering Contradiction:

Improvedoping uniformityVSAvoidthermal budget

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The patent optimizes the dopant concentration parameter in the doped glass (3-10 wt%) to achieve the desired doping uniformity at reduced thermal budgets. This parameter optimization allows the diffusion process to proceed effectively at lower temperatures and shorter times compared to conventional approaches

Inventive Principle:

Principle #35Parameter changes

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

This approach enhances doping uniformity, reduces emitter-base capacitance, and enables tighter spacing between base regions, improving the electrical performance and thermal efficiency of bipolar transistors.

Implementation Method 1

Use of doped glass as a solid diffusion source allows for better control of the dopant uniformity compared to implanted poly

Methodology Applied

Scientific EffectSolid diffusion: Diffusion

Data Source

PatentUS7572708B1Utilization of doped glass on the sidewall of the emitter window in a bipolar transistor structure

Publication Date: 2009.08.11 NAT SEMICON CORP

AI summary

A bipolar transistor device architecture and method of manufacture uses doped glass on the sidewall of the emitter window opening to reduce the emitter-base overlap capacitance while at the same time improving the polysilicon plugging effect. The doped glass sidewall also improves dopant loss in the oxide in the case in which an in-situ doped poly emitter is used. By using a doped sidewall glass, the sensitivity of dopant absorption that can potentially occur in un-doped spacers is removed. The proposed technique also provides a simple method for achieving narrow emitter window openings while simultaneously improving doping uniformity compared to implanted poly techniques. The technique also allows a self-aligned base to be performed, thereby allowing tighter spacing between the extrinsic base and the intrinsic base.