Two-Step Etching for Group III-N HEMT Metal Contact Depth Control
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Solution Overview
Problem
Conventional methods for forming metal contacts in group III-N HEMTs often result in uncontrollable depths, leading to the exposure of the channel layer, which affects the reliability and performance of the transistors.
Innovation Solution
A two-step etching process using specific gas combinations, initially with BCl3 and SF6, and subsequently with BCl3 and Cl2, is employed to form and deepen metal contact openings in the barrier layer without extending into the channel layer, allowing precise control of the contact depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-step etching process is used to form metal contact openings, then the manufacturing process is simple and fast, but the depth control is poor and the channel layer may be exposed
Solution Approach 1:
The etching process is divided into two distinct steps: a first etching step using BCl3 and SF6 gas mixture to create initial openings, and a second etching step using BCl3 and Cl2 gas mixture to deepen the openings. This segmentation allows each step to be optimized for its specific function, achieving both efficiency and precision in contact opening formation.
2Reliability
If the etching process continues until the channel layer is exposed, then the barrier layer is fully accessed for good ohmic contact, but the transistor reliability deteriorates
Solution Approach 1:
The patent uses the barrier layer itself as an intermediary to control etching depth. By monitoring and controlling the etching process to stop at a predetermined depth within the barrier layer (without exposing the channel layer), the method achieves reliable ohmic contact while maintaining transistor integrity and reliability.
3Manufacturing precision
If different gas combinations are used in sequential etching steps, then the depth control precision is improved, but the process complexity increases
Solution Approach 1:
The patent changes the chemical composition parameters of the etching gas mixture between steps. The first step uses BCl3 and SF6 for initial opening formation, while the second step uses BCl3 and Cl2 for controlled deepening. This parameter change allows optimization of etching rate and selectivity for each stage, achieving precise depth control.
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 method enables controlled depths of metal contact openings, preventing exposure into the channel layer and enhancing the reliability and performance of group III-N HEMTs by ensuring accurate formation of ohmic contacts within the barrier layer.
Implementation Method 1
etching a layered structure with a first gas combination to form a number of metal contact openings... etching the layered structure with a second gas combination to deepen the first bottom surface of each metal contact opening
Data Source
AI summary
Metal contact openings are etched in the barrier layer of a group III-N HEMT with a first gas combination that etches down into the barrier layer, and a second gas combination that etches further down into the barrier layer to a depth that lies above the top surface of a channel layer that touches and lies below the barrier layer.