Polysilicon Deep Trench Fill via Segmented Doping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor devices with deep trench structures face challenges in achieving low sheet resistance using in situ doped polysilicon, which causes dopant contamination and stress, and undoped polysilicon requires long thermal drives for uniform dopant distribution, affecting buried layers.
Innovation Solution
A method involving forming a deep trench with a dielectric liner, depositing an undoped first polysilicon layer, implanting dopants, and then forming a second polysilicon layer, followed by a thermal drive anneal to activate and diffuse the dopants, while removing polysilicon from the top surface to achieve low resistance without contaminating the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If in situ doped polysilicon is deposited to achieve low sheet resistance, then the sheet resistance is reduced, but dopant contamination on the backside of the substrate and stress in the semiconductor device occur
Solution Approach 1:
The polysilicon filling process is segmented into two distinct stages: first depositing undoped polysilicon to avoid contamination, then selectively doping only the portion within the trench after formation. This segmentation separates the harmful doping step from the substrate, eliminating dopant contamination on the backside while still achieving low sheet resistance in the trench region.
Solution Approach 2:
The undoped polysilicon is deposited in advance before any doping occurs. This preliminary action creates a clean polysilicon layer that can be selectively doped later using implantation techniques, ensuring that doping only affects the intended trench region and not the entire substrate, thereby preventing contamination and stress.
2Manufacturing precision
If undoped polysilicon is deposited and implanted at the top surface, then dopant distribution uniformity is achieved, but a long thermal drive is required which adversely affects doped structures in the substrate
Solution Approach 1:
The doping process is applied locally only to the polysilicon within the deep trench structure, rather than uniformly across the entire substrate. This localized doping approach allows for precise control of dopant distribution in the trench region while minimizing thermal exposure and protecting other doped structures in the substrate from adverse effects.
Solution Approach 2:
The patent replaces the conventional thermal diffusion method with ion implantation for dopant introduction. This substitution eliminates the need for prolonged thermal drives, as ion implantation can achieve uniform dopant distribution through direct physical implantation followed by a brief thermal anneal for activation, thereby protecting sensitive substrate structures.
3Manufacturing precision
If a long thermal drive is used to achieve uniform dopant distribution, then dopant uniformity is improved, but doped structures in the substrate such as buried layers are adversely affected
Solution Approach 1:
The processing is segmented so that doping occurs only after the deep trench structure is formed, allowing selective doping of the trench-filled polysilicon while leaving other substrate regions, including buried layers, unaffected by the doping process. This segmentation protects buried layer integrity while achieving uniform dopant distribution in the trench region.
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 allows for low resistance deep trench structures with reduced dopant contamination and stress, enabling efficient dopant distribution without adverse effects on buried layers, thus improving semiconductor device performance and reliability.
Implementation Method 1
A thermal drive anneal activates and diffuses the dopants
Implementation Method 2
A thermal drive anneal activates and diffuses the dopants
Implementation Method 3
Dopants are implanted into the first polysilicon layer
Data Source
Figure 1
Figure 2A
Figure 2B
AI summary
A semiconductor device (100) is formed by forming a deep trench (120) in a substrate (102) and a dielectric liner (116) on sidewalls (118) of the deep trench (120). A first undoped polysilicon layer (122) is formed on the semiconductor device (100), extending into the deep trench (120) on the dielectric liner (116), but not filling the deep trench (120). Dopants are implanted into the first polysilicon layer (122). A second layer of polysilicon (124) is formed on the first layer of polysilicon (122). A thermal drive anneal activates and diffuses the dopants. In one version, the dielectric liner (116) is removed at the bottom of the deep trench (120) before the first polysilicon layer (122) is formed, so that the polysilicon (122) in the deep trench (120) provides a contact to the substrate (102). In another version, the polysilicon (122) in the deep trench (120) is isolated from the substrate (102) by the dielectric liner (116).