Polysilicon Resistor Embedded in Shallow Trench Isolation
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Solution Overview
Problem
Conventional integrated circuit designs face challenges in scaling down field effect transistors and semiconductor resistors to achieve higher integration density, as polysilicon resistors are heavily influenced by gate electrode fabrication processes, leading to variability in resistance and capacitive coupling between adjacent devices.
Innovation Solution
A method is developed to form polysilicon resistors independently within shallow trench isolation regions, decoupling them from gate electrodes, allowing for precise control of dopant concentration and resistance values, and integrating them before or after well implants, thus isolating them from substrate noise and capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polysilicon resistors are formed using conventional gate electrode fabrication processes, then the resistors can be created simultaneously with transistors, but the resistance values and properties become highly variable and dependent on gate process changes
Solution Approach 1:
The patent segments the resistor formation process from the gate electrode fabrication process. Resistors are formed independently within shallow trench isolation regions using separate patterning and doping steps, allowing precise control of resistance values without being affected by gate process variations.
Solution Approach 2:
The patent extracts the resistor formation from the gate electrode process by placing resistors in shallow trench isolation regions between active transistors. This separation removes resistors from the gate fabrication sequence, making resistance properties independent of gate height, doping, and integration changes.
2Device complexity
If polysilicon resistors are formed in conventional locations, then the layout is simple, but capacitive coupling and electrical interaction between adjacent devices increases
Solution Approach 1:
The patent uses shallow trench isolation regions as intermediary structures to host resistors. These STI regions act as isolating mediators between active transistors, reducing capacitive coupling and electrical interaction while maintaining a relatively simple overall layout.
3Productivity
If polysilicon resistors are formed before well implants, then the process sequence is simplified, but the resistors are exposed to substrate noise and process variations
Solution Approach 1:
The patent performs well implantation and substrate preparation before forming resistors in the shallow trench isolation regions. This preliminary action ensures that the substrate is properly prepared and noise-minimized before resistor fabrication, improving performance stability while maintaining efficient process sequencing.
Data Source
AI summary
Forming a polysilicon embedded resistor within the shallow trench isolations separating the active area of two adjacent devices, minimizing the electrical interaction between two devices and reducing the capacitive coupling or leakage therebetween. The precision polysilicon resistor is formed independently from the formation of gate electrodes by creating a recess region within the STI region when the polysilicon resistor is embedded within the STI recess region. The polysilicon resistor is decoupled from the gate electrode, making it immune to gate electrode related processes. The method forms the polysilicon resistor following the formation of STIs but before the formation of the p-well and n-well implants. In another embodiment the resistor is formed following the formation of the STIs but after the formation of the well implants.