Transistor Gate Oxide Growth via Ambient Oxidation
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Solution Overview
Problem
Existing transistor fabrication methods fail to achieve low specific resistance, particularly for field-effect transistors like DEMOS transistors, where increasing oxide thickness over part of the gate oxide is necessary but not effectively addressed.
Innovation Solution
A method involving the formation of a thick oxide region below the transistor gate, which includes steps like forming a dielectric layer, depositing a barrier layer, growing an oxide region through ambient oxidizing, and implanting dopants, while incorporating this process into a standard BiCMOS flow to reduce specific resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxide thickness is increased over part of the gate oxide to lower specific resistance, then specific resistance decreases, but manufacturing complexity increases due to additional process steps
Solution Approach 1:
A thick oxide region is grown in advance during the fabrication process, before final transistor assembly. This preliminary oxide growth creates a reservoir of charge carriers that will later reduce specific resistance when the transistor is operational, eliminating the need for separate resistance-reduction steps
Solution Approach 2:
The thick oxide region acts as an intermediary structure between the substrate and the gate. It mediates the electrical characteristics by providing a controlled charge reservoir that influences channel conductivity, thereby reducing specific resistance without directly modifying the channel itself
2Reliability
If a thick oxide region is grown to reduce specific resistance, then specific resistance decreases, but process time increases
Solution Approach 1:
The thick oxide region growth is merged with the standard BiCMOS fabrication process flow. By integrating the oxide growth step into the existing process sequence rather than adding it as a separate operation, the patent achieves specific resistance reduction without proportionally increasing total fabrication time
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 method effectively reduces the specific resistance of transistors by growing a thick oxide region that affects the path of channel current, enhancing the transistor's performance.
Implementation Method 1
providing an ambient oxidizing agent after etching the portion of the barrier layer below the opening to grow an oxide region
Implementation Method 2
implanting dopants into the semiconductor substrate after removing the barrier layer
Data Source
AI summary
A method to fabricate a transistor comprises: forming a first dielectric layer on a semiconductor substrate; depositing a barrier layer on the first dielectric layer; depositing an anti-reflective coating on the barrier layer; depositing and exposing a pattern in a photoresist layer to radiation followed by etching to provide an opening; etching a portion of the anti-reflective coating below the opening; etching a portion of the barrier layer below the opening to expose a portion of the first dielectric layer; providing an ambient oxidizing agent to grow an oxide region followed by removing the barrier layer; implanting dopants into the semiconductor substrate after removing the barrier layer; removing the first dielectric layer after implanting dopants into the semiconductor substrate; and forming a second dielectric layer after removing the first dielectric layer, wherein the oxide region is grown to be thicker than the second dielectric layer.