Uniform Sacrificial Silicon Nitride Etch Using Two-Step Vapor Process
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Solution Overview
Problem
Conventional methods for removing sacrificial silicon nitride features in integrated circuits, such as hot phosphoric acid etching and plasma etching, result in non-uniformity and damage to silicon dioxide and silicon features due to etch micro loading effects and difficulty in controlling etch uniformity and selectivity.
Innovation Solution
A two-step oxidized layer etch process using fluorine-containing etch reagents, free of ammonia, is employed to remove the surface layer of oxidized silicon and subsequently the sacrificial silicon nitride feature, with the process conducted at controlled temperatures and in an oxygen-free ambient to minimize damage to surrounding silicon dioxide and silicon components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hot phosphoric acid etch is used to remove silicon nitride, then the silicon nitride feature is removed, but non-uniform removal occurs due to etch micro loading effects
Solution Approach 1:
The patent changes the chemical parameters of the etch process by using a vapor-phase etch with specific gas compositions (Cl2, BCl3, or CCl4) at controlled temperatures (25-40°C), replacing the liquid hot phosphoric acid etch. This parameter change enables uniform removal across different feature sizes by eliminating micro-loading effects inherent in liquid etching.
Solution Approach 2:
The patent replaces the chemical mechanism of liquid hot phosphoric acid etching with a vapor-phase chemical etching mechanism. The vapor-phase process provides more uniform reactant distribution and eliminates the micro-loading effects that occur in liquid etching, where etch rate varies with feature geometry and local concentration effects.
2Ease of manufacture
If dilute hydrofluoric acid etch is used to remove oxidized silicon layer, then the surface layer is removed, but thin layers of silicon nitride and silicon dioxide are undesirably removed
Solution Approach 1:
The patent changes the etch chemistry from hydrofluoric acid to vapor-phase chlorine-based or boron-based etchants at controlled temperatures. This parameter change provides selective removal of oxidized silicon while preserving silicon nitride and silicon dioxide, as the vapor-phase etchants exhibit different selectivity characteristics compared to liquid HF.
Solution Approach 2:
The patent uses a vapor-phase etch process conducted in a controlled atmosphere with specific gas compositions. This inert environment approach allows precise control over which materials are etched, enabling selective removal of the oxidized silicon layer without attacking the underlying silicon nitride or silicon dioxide structures.
3Ease of manufacture
If plasma oxide etch is used to remove oxidized silicon, then the surface layer is removed, but etch uniformity and etch rate are difficult to control causing damage to exposed silicon
Solution Approach 1:
The patent changes from plasma oxide etch to vapor-phase etching with controlled gas compositions (Cl2, BCl3, or CCl4) and temperatures (25-40°C). This parameter change provides excellent control over etch rate and uniformity, as the vapor-phase process allows precise control of reactant partial pressures and temperature, eliminating the uniformity control difficulties of plasma processes.
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 ensures uniform and selective removal of the sacrificial silicon nitride feature without damaging adjacent silicon dioxide or silicon components, maintaining performance uniformity and reducing the risk of exposing active areas and gates.
Implementation Method 1
removing a surface layer of oxidized silicon from the sacrificial silicon nitride feature using a two-step etch process... While the integrated circuit is in the two-step oxidized layer etch tool, without exposing the integrated circuit to an ambient containing more than 1 torr of oxygen, at least a portion of the sacrificial silicon nitride feature is removed using fluorine-containing etch reagents
Implementation Method 2
subsequently heating the integrated circuit to 80° C. to 120° C. while in the two-step oxidized layer etch tool to remove etch by-products
Data Source
AI summary
An integrated circuit may be formed by forming a sacrificial silicon nitride feature. At least a portion of the sacrificial silicon nitride feature may be removed by placing the integrated circuit in a two-step oxidized layer etch tool and removing a surface layer of oxidized silicon from the sacrificial silicon nitride feature using a two-step etch process. The two-step etch process exposes the integrated circuits to reactants from a plasma source at a temperature less than 40° C. and subsequently heating the integrated circuit to 80° C. to 120° C. while in the two-step oxidized layer etch tool. While the integrated circuit is in the two-step oxidized layer etch tool, without exposing the integrated circuit to an ambient containing more than 1 torr of oxygen, at least a portion of the sacrificial silicon nitride feature is removed using fluorine-containing etch reagents, substantially free of ammonia.