Selective Trench Oxidation Using a Tapered Barrier Layer
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Solution Overview
Problem
Existing methods for oxidizing high aspect ratio structures in semiconductor devices result in non-conformal oxide layers, where the upper portion is thicker than the lower portion, leading to uneven oxidation and potential device performance issues.
Innovation Solution
A method involving the formation of a non-conformal layer on the side walls of trenches using chemical vapor deposition or radical plasma processes, followed by selective oxidation to create a tapered oxide layer that is thicker at the lower portion, achieved through controlled deposition and oxidation techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional oxidation is applied to high aspect ratio structures, then the upper portion is oxidized first, but the oxide layer becomes non-conformal with thicker coverage at the top and thinner or no coverage at the bottom
Solution Approach 1:
A non-conformal nitrogen-containing layer is deposited on the upper portion of the trench sidewalls before oxidation. This preliminary layer acts as a barrier that prevents oxidizing agent penetration at the top, allowing the oxidation front to reach and uniformly oxidize the lower portions that would otherwise be deprived of oxidizing agent.
Solution Approach 2:
The nitrogen-containing layer is selectively deposited only on the upper portion of the trench sidewalls with varying thickness (thicker at top, thinner at bottom), creating local differences in oxidation resistance. This local quality modification enables the oxidizing agent to penetrate more effectively at the lower portions while being blocked at the upper portions, achieving conformal oxidation throughout the high aspect ratio structure.
2Manufacturing precision
If the oxidizing agent is applied to the upper portion first, then oxidation occurs at the top, but the oxidizing agent is depleted and cannot reach the lower portion
Solution Approach 1:
The nitrogen-containing layer serves as an intermediary barrier that modulates the interaction between the oxidizing agent and the silicon substrate. By placing this intermediate layer selectively on the upper sidewalls, it controls the release and distribution of the oxidizing agent, preventing premature consumption at the top and ensuring adequate availability reaches the lower portions for uniform oxidation.
3Manufacturing precision
If a conformal oxide layer is desired on high aspect ratio structures, then the oxidation process must ensure uniform coverage, but conventional methods produce non-conformal layers
Solution Approach 1:
The nitrogen-containing layer is deposited in advance using chemical vapor deposition or plasma processes before the oxidation step. This preliminary deposition creates a controlled barrier pattern that pre-determines the oxidation behavior, enabling conformal oxide formation on high aspect ratio structures without requiring complex in-situ oxidation control mechanisms.
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
Enables the formation of a tapered oxide layer that is thicker at the lower portion of high aspect ratio features, improving device performance consistency and yield by addressing the non-uniformity of conventional oxidation methods.
Implementation Method 1
forming a non-conformal layer on at least one side wall of a trench formed on a substrate... The non-conformal layer may include nitrogen or carbon
Implementation Method 2
forming a non-conformal layer on at least one side wall of a trench formed on a substrate... using chemical vapor deposition or radical plasma processes
Implementation Method 3
selectively oxidizing at least one trench including the non-conformal layer. The oxidation of the non-conformal layer and an exposed portion of the at least one side wall not covered by the non-conformal layer occurs to form an oxide layer
Implementation Method 4
the non-conformal layer is converted into a gas and is removed from the at least one side wall as the oxide layer forms
Data Source
AI summary
Described herein is a method for selectively oxidizing a substrate. The method includes forming a non-conformal layer on at least one side surface of a trench or a hole of a substrate. After forming the non-conformal layer, the at least one trench or at least one hole may be selectively oxidized, wherein oxidation of the non-conformal layer and an exposed portion of the at least one side wall not covered by the non-conformal layer occurs to form an oxide layer. The oxide layer is thicker at a lower portion of the at least one side wall than the upper portion of the at least one side wall, such that it tapers.