HBT Fabrication Using SIC Mask Edge Effects
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Solution Overview
Problem
There is a need for a scalable and cost-effective method to fabricate Heterojunction Bipolar Transistors (HBTs) that reduces the Kirk Effect while maintaining or increasing collector-base breakdown voltage, which is challenging with conventional approaches that often compromise on power efficiency and complexity.
Innovation Solution
A method utilizing the resist mask edge effect during the formation of selectively implanted collector regions to create shallow secondary increased-doping regions, enhancing base-collector capacitance without decreasing the collector-base breakdown voltage, by employing a multiple-opening SIC implant mask to direct dopants and form both primary and secondary increased-doping regions simultaneously.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional single-mask SIC implant is used, then fabrication is simple, but secondary increased-doping regions near the surface are not formed
Solution Approach 1:
The patent applies segmentation by dividing the implant mask into multiple openings instead of using a single continuous mask region. This segmentation of the SIC implant mask allows different portions of the dopant flux to be directed through separate openings, creating distinct primary and secondary increased-doping regions. The segmented mask structure enables precise control over the doping profile while maintaining a single-implant-process fabrication approach.
2Speed
If HBTs are scaled for higher performance, then operating frequency increases, but power efficiency and voltage handling are compromised
Solution Approach 1:
The patent applies parameter changes by modifying the doping concentration parameter at the base-collector junction through the multiple-opening SIC implant mask. By creating secondary increased-doping regions with higher doping concentration near the junction, the patent changes the electrical parameters of the HBT to reduce the Kirk Effect and improve power efficiency, enabling scaled HBTs to maintain high voltage handling capability while operating at higher frequencies.
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 results in HBTs with improved operating characteristics, specifically enhanced Ft*BVceo metrics, indicating increased transistor switching speed and breakdown voltage, while maintaining a low-cost and scalable fabrication process compatible with existing flows.
Implementation Method 1
the SIC implant process involves directing the implanted SIC dopant through an SIC implant mask formed by patterning a photoresist layer to include multiple mask openings that expose corresponding upper surface sections over each HBT's designated collector region. When directing the SIC dopant through the mask, first portions of the implanted SIC dopant pass directly through the multiple mask openings and enter the substrate perpendicular to the exposed corresponding surface sections, thereby forming one or more primary increased-doping regions below the substrate surface at a depth determined by the SIC implant process parameters
Implementation Method 2
the multiple mask-opening configuration also causes second portions of the SIC dopant to be subjected to mask edge effects generated by each of the multiple mask openings (e.g., to deflected by side edges of each mask opening toward the center of each mask opening), whereby the second dopant portions are slowed and enter the exposed substrate surface sections at an angle such that they form secondary increased-doping regions in the collector region between primary increased-doping regions and the corresponding substrate surface sections below each mask opening
Implementation Method 3
A heterojunction bipolar transistor (HBT) is a type of bipolar junction transistor (BJT) that utilizes different semiconductor materials to form the HBT's emitter, collector and base structures, thereby creating a heterojunction
Data Source
AI summary
A heterojunction bipolar transistor (HBT) is fabricated using a selectively implanted collector (SIC) implant mask including multiple openings located over the HBT's collector region. During the SIC implant process, resist mask edge (well proximity) effects caused by the SIC dopant passing through the multiple openings generates multiple secondary shallow increased-doping regions in the collector region adjacent to the substrate surface, where the mask openings are sized such that each secondary increased-doping region has a doping concentration that is comparable to primary increased-doping regions, which are simultaneously formed deeper in the SIC region. A base structure and an emitter structure are then formed over the SIC region using known techniques. The secondary increased-doping regions produce enhanced base-collector junction between the SIC region and the base structure that measurably decreases Kirk Effect by way of enhancing the HBT's cutoff frequency (Ft) and break-down voltage (BVCEO).