DARC Layer Reduces Base-to-Collector Capacitance in SiGe BiCMOS

Solution Overview

Problem

The processing of SiGe BiCMOS devices requires pristine silicon surfaces and uniform deposition steps, but conventional hard masks like silicon nitride increase permittivity, reducing device frequency performance due to higher base-to-collector capacitance.

Innovation Solution

A dielectric anti-reflective (DARC) layer, such as silicon-rich oxynitride, is used as a hard mask during etching and as a permanent layer, maintaining device geometry integrity and reducing permittivity to enhance frequency performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a hard mask layer like silicon nitride is introduced to protect device geometry, then the geometric integrity is maintained, but the permittivity increases which increases base-to-collector capacitance and reduces device frequency performance

Engineering Contradiction:

Improvegeometric integrityVSAvoidfrequency performance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent changes the material parameter (permittivity) by selecting DARC layer material with lower permittivity than conventional hard masks like silicon nitride. This parameter change reduces base-to-collector capacitance while maintaining the hard mask function of protecting device geometry during processing.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The DARC layer serves multiple functions simultaneously: it acts as an anti-reflective coating for uniform deposition, serves as a hard mask to protect device geometry, and functions as a permanent layer in the final structure. This multi-functionality eliminates the need for separate hard mask layers that would increase permittivity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Shape

If conventional hard masks are used to maintain device geometry, then the geometric integrity is preserved, but the base-to-collector capacitance increases reducing frequency performance

Engineering Contradiction:

Improvedevice geometryVSAvoidbase-to-collector capacitance

Core Design Contradiction:

ShapeVSObject-generated harmful factors

Solution Approach 1:

The patent changes the material parameter (permittivity) by selecting DARC layer material with lower permittivity than conventional hard masks like silicon nitride. This parameter change reduces base-to-collector capacitance while maintaining the hard mask function of protecting device geometry during processing.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If multiple deposition steps are performed to ensure uniformity over large areas, then the uniformity is improved, but the process complexity increases requiring additional cleaning steps

Engineering Contradiction:

ImproveuniformityVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The DARC layer serves multiple functions simultaneously: it acts as an anti-reflective coating for uniform deposition, serves as a hard mask to protect device geometry, and functions as a permanent layer in the final structure. This multi-functionality eliminates the need for separate hard mask layers that would increase permittivity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges the anti-reflective coating function and hard mask function into a single DARC layer. This consolidation reduces the number of separate deposition and cleaning steps required, simplifying the overall process while maintaining uniformity and geometric integrity.

Inventive Principle:

Principle #5Merging (Combining)

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 DARC layer ensures uniformity and repeatability of deposition processes, maintaining device geometry and improving frequency performance by reducing base-to-collector capacitance, thus enabling higher frequency operations in SiGe BiCMOS devices.

Implementation Method 1

its high permittivity increases the SiGe HBT base-to-collector capacitance (Cbc) that directly reduces device frequency performance

Methodology Applied

Scientific EffectPermittivity: Dielectric Permittivity

Implementation Method 2

dry etching away a base opening in the DARC layer

Methodology Applied

Scientific EffectDry etching:

Implementation Method 3

wet etching away a portion of the collector dielectric layer in the base opening to provide an extended base opening to the substrate

Methodology Applied

Scientific EffectWet etching:

Implementation Method 4

performing a base deposition to form a base epitaxy region in the extended base opening

Methodology Applied

Scientific EffectEpitaxy: Epitaxy

Data Source

PatentUS9142546B2Method of making bipolar junction transistor by forming base epitaxy region on etched opening in DARC layer

Publication Date: 2015.09.22 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

A method is provided of forming a bipolar transistor device. The method comprises depositing a collector dielectric layer over a substrate in a collector active region, depositing a dielectric anti-reflective (DARC) layer over the collector dielectric layer, dry etching away a base opening in the DARC layer, and wet etching away a portion of the collector dielectric layer in the base opening to provide an extended base opening to the substrate. The method further comprises performing a base deposition to form a base epitaxy region in the extended base opening and extending over first and second portions of the DARC layer that remains as a result of the dry etching away the base opening in the DARC layer, and forming an emitter region over the base epitaxy region.