Resurf Bipolar Transistor Manufacturing via Base Window Trench
Solution Overview
Problem
Existing methods for manufacturing bipolar transistors face complexity in implementing the reduced surface field (Resurf) effect, which is crucial for achieving a good high-frequency performance and high base-collector junction breakdown voltage, particularly in RF power applications, due to the need for multiple photolithography steps and complex layer formations.
Innovation Solution
A simplified method involving the formation of a base window in a semiconductor substrate, followed by the creation of a trench and an isolation layer, with a second base layer forming a field plate that reshapes the electric field distribution in the collector region, allowing for simultaneous formation of the base and field plate in one process step, reducing the number of photolithography steps required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a higher doping concentration of the collector drift region is applied to increase the speed of the bipolar transistor, then the speed is improved, but the breakdown voltage between the collector region and the base region is reduced
Solution Approach 1:
The collector region is segmented into two parts: a collector drift region with higher doping concentration for improved speed, and a collector region with lower doping concentration for maintained breakdown voltage. This segmentation allows each region to optimize its function independently, resolving the speed-breakdown trade-off.
Solution Approach 2:
Different doping concentrations are applied to different locations within the collector region. The drift region adjacent to the base has higher doping for speed, while the region extending toward the collector contact has lower doping for breakdown voltage. This local quality variation enables simultaneous optimization of both parameters.
2Reliability
If the reduced surface field (Resurf) effect is implemented using a field plate with multiple photolithography steps, then the speed-breakdown trade-off is improved, but the manufacturing process complexity increases
Solution Approach 1:
The field plate formation is merged with the base contact formation into a single process step. The same photolithography pattern that defines the base contact also defines the field plate, eliminating the need for separate photolithography steps and reducing manufacturing complexity while maintaining the Resurf effect.
Solution Approach 2:
The field plate structure serves multiple functions: it provides the Resurf effect for improved breakdown voltage, acts as a base contact, and serves as an electrical connection for the collector region. This multi-functionality reduces the number of separate components and process steps required.
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 enhances the speed-breakdown trade-off by increasing the doping concentration of the collector region, thereby improving the bipolar transistor's speed and breakdown voltage, while simplifying the manufacturing process by reducing the number of photolithography steps and enabling the combined fabrication of Resurf bipolar transistors and CMOS devices.
Implementation Method 1
the Resurf effect comprises the reshaping of the electric field distribution in the collector drift region for a reverse bias situation such that a more uniform electric field distribution with a reduced maximum electric field is formed
Implementation Method 2
Bipolar transistors are important for high-frequency applications, such as optical data communication, and for RF power applications, such as power amplifier modules in wireless handset applications
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention provides for an alternative and less complex method of manufacturing a bipolar transistor comprising a field plate (17) in a trench (7) adjacent to a collector region (21), which field plate (17) employs a reduced surface field (Resurf) effect. The Resurf effect reshapes the electric field distribution in the collector region (21) such that for the same collector-base breakdown voltage the doping concentration of the collector region (21) can effectively be increased resulting in a reduced collector resistance and hence an increased bipolar transistor speed. The method comprises a step of forming a base window (6) in a first base layer (4) thereby exposing a top surface of the collector region (21) and a part of an isolation region (3). The trench (7) is formed by removing the exposed part of the isolation region (3), after which isolation layers (9,10) are formed on the surface of the trench (7). A second base layer (13) is formed on the isolation layer (10), thereby forming the field plate (17), on the top surface of the collector region (21), thereby forming a base region (31), and on a sidewall of the first base layer (4), thereby forming an electrical connection between the first base layer (4), the base region (31) and the field plate (17). An emitter region (41) is formed on a top part of the base region (31), thereby forming the Resurf bipolar transistor.