Polysilicon Contact Plug Seam Suppression via Layered Deposition
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Solution Overview
Problem
In semiconductor device manufacturing, the formation of fine contact plugs is hindered by the formation of seams between wiring lines, leading to increased contact resistance due to insulating film penetration into voids, which reduces the contact surface area and increases resistance defects.
Innovation Solution
A two-layer configuration of high-concentration and low-concentration polysilicon is used between wiring lines, with the high-concentration polysilicon as an underlying film and the low-concentration polysilicon as an embedded film, allowing for controlled etching and reduced void formation, thereby minimizing insulating film penetration and maintaining contact surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If doped polysilicon is deposited conformally to fill the space part between wiring lines, then the space is completely filled, but a seam forms in the central portion leading to void formation and increased contact resistance
Solution Approach 1:
The polysilicon filling process is segmented into two distinct deposition steps: first depositing doped polysilicon to a partial thickness, then depositing undoped polysilicon to complete the filling. This segmentation prevents seam formation by avoiding excessive doped polysilicon accumulation that would create protrusions and subsequent voids after etching.
Solution Approach 2:
Different regions of the polysilicon structure are assigned different material properties: the lower portion uses doped polysilicon with specific electrical characteristics, while the upper portion uses undoped polysilicon with different etching characteristics. This local differentiation allows the seamless filling without compromising contact quality.
2Ease of operation
If the doped polysilicon is etched back to expose sidewalls of insulating line patterns, then the dividing mask can be formed, but the seam part is more readily etched forming a slit and void
Solution Approach 1:
The etching process exhibits local selectivity based on material composition: doped polysilicon etches faster than undoped polysilicon. This creates a controlled recession pattern where the doped lower layer recedes more, exposing the sidewalls for mask formation, while the undoped upper layer maintains structural integrity and prevents void formation at the seam location.
Solution Approach 2:
The polysilicon structure is segmented into doped and undoped layers with different etching rates, enabling selective etching that achieves sidewall exposure without creating harmful voids. The segmentation allows the etching process to differentiate between functional regions.
3Quantity of substance
If insulating film is deposited to fill the groove, then the groove is completely filled, but the insulating film penetrates into the void and reduces contact surface area
Solution Approach 1:
The undoped polysilicon layer is deposited in advance to prevent void formation before the insulating film deposition step. This preliminary action eliminates the root cause of the problem, ensuring that when the insulating film is subsequently deposited to fill the groove, there are no voids for the insulating film to penetrate into, thus preserving the full contact surface area.
4Device complexity
If a single-layer doped polysilicon is used, then the process is simple, but seams form and lead to high-resistance defects
Solution Approach 1:
The polysilicon structure is transformed from a single-layer homogeneous material to a composite structure with doped and undoped layers. Each layer contributes different properties: the doped layer provides electrical conductivity and forms the dividing mask, while the undoped layer provides structural integrity and prevents seam formation. This composite approach eliminates high-resistance defects while maintaining reasonable process complexity.
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 suppresses slit expansion and reduces contact resistance by minimizing void formation and insulating film penetration, enhancing the manufacturing of fine contact plugs with improved surface area and reduced defects.
Implementation Method 1
a first silicon film, containing an impurity having a first concentration, is deposited to a thickness that does not fill the first space portion; a second silicon film, containing an impurity having a second concentration, is deposited to a thickness that fills the first space portion
Implementation Method 2
a groove is formed in the silicon filler body, and then heat treatment is applied to adjust the impurity concentration in the divided silicon filler body to a third concentration
Data Source
AI summary
In one device, a first space partitioned by first and second line patters is filled with a multilayer film that is composed of a first silicon film having a high impurity concentration relative to a standard plug impurity concentration and a second silicon film having a low impurity concentration relative to the standard plug impurity concentration, and is divided by forming a groove using a mask film on the side wall of the second line pattern. As a result, expansion of a seam, which is formed only on the second silicon film having a low impurity concentration, is suppressed. After that, an isolation insulating film is embedded in the groove and impurity diffusion is carried out by a heat treatment, so that divided plugs as a whole are made to have the standard plug impurity concentration.