Isolation Trench with Nitride Spacers for Void-Free Oxide Fill
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Solution Overview
Problem
Conventional shallow trench isolation methods in semiconductor devices face challenges with high aspect ratio trenches, leading to voids and oxidation issues, which compromise electrical isolation and device performance, especially when exposed to high temperatures.
Innovation Solution
A method involving forming a trench, creating an oxide layer and nitride sidewalls, etching a deeper trench, densifying the region, and filling it with a high-density plasma CVD process, while using a nitride layer to protect silicon from oxidation, ensuring effective isolation without voids or oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a deep isolation trench with high aspect ratio is formed to improve device isolation, then electrical isolation between devices is improved, but voids or seams appear in the insulating layer due to incomplete filling
Solution Approach 1:
The trench filling process is segmented into multiple deposition steps with alternating orientations. The first insulating layer is deposited with a first orientation, then a second insulating layer is deposited with a second orientation different from the first. This segmentation of the filling process allows each layer to compensate for voids in the previous layer, achieving complete trench filling without voids or seams.
Solution Approach 2:
The solution introduces an additional dimension to the filling process by varying the deposition orientation. Instead of simply increasing deposition thickness in one direction, the method changes the orientation dimension of insulating layer deposition, allowing material to reach all areas of the high aspect ratio trench effectively.
2Ease of manufacture
If silicon is exposed to high ambient temperatures during trench formation, then trench isolation can be formed, but silicon and polysilicon become oxidized resulting in undesirable property changes
Solution Approach 1:
A liner layer is introduced as an intermediary between the silicon substrate and the high-temperature processing environment. This liner layer acts as a protective barrier that prevents direct oxidation of silicon and polysilicon during trench isolation formation at high temperatures, while still allowing the isolation process to proceed effectively.
3Stability of the object's composition
If the opening at the top of the trench is closed-off before complete filling during insulating layer deposition, then sidewall insulation is improved, but void regions are created in the trench
Solution Approach 1:
The deposition process uses periodic action with alternating orientations. The first insulating layer is deposited with a first orientation, then the second insulating layer is deposited with a second orientation. This periodic alternation ensures that when one orientation closes the top opening, the next orientation can still deposit material into the trench volume, preventing void formation while maintaining sidewall insulation.
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 provides robust, high-aspect ratio trench isolation with improved electrical isolation and resistance to high temperatures, reducing the risk of short circuits and extending device lifetime.
Implementation Method 1
an insulating layer is deposited using high-density plasma chemical vapor deposition (HPDCVD)
Implementation Method 2
forming an oxide layer on the bottom and sidewalls of the trench... using a nitride layer to protect silicon from oxidation
Data Source
AI summary
A method of forming and resulting isolation region, which allows for densification of an oxide layer in the isolation region. One exemplary embodiment of the method includes the steps of forming a first trench, forming an oxide layer on the bottom and sidewalls of the trench, forming nitride spacers on the lined trench, and thereafter etching the silicon beneath the first trench to form a second trench area. An oxide layer is then deposited to fill the second trench. Densification of the isolation region is possible because the silicon is covered with nitride, and therefore will not be oxidized. Light etches are then performed to etch the oxide and nitride spacer area in the first trench region. A conventional oxide fill process can then be implemented to complete the isolation region.