Selective Silicon Oxide Etching via Ammonium Salt Formation
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Solution Overview
Problem
Current semiconductor manufacturing techniques face challenges in achieving selective dry etch removal of silicon oxide relative to silicon nitride, particularly in etching contacts of <5 nm, where the fluorinated carbon layer formed during etching with fluorocarbon or hydrofluorocarbon gases affects the etch rate and selectivity.
Innovation Solution
A method involving sequential plasma exposures of H2 and HF or F2 gases to form a silicon oxide surface layer with reduced oxygen content and an ammonium salt layer on silicon nitride, followed by a halogen-containing gas to selectively etch the silicon oxide film, with repeated cycles for enhanced selectivity, utilizing conventional plasma processing systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluorocarbon or hydrofluorocarbon gases are used for dry etching of silicon oxide, then etching capability is achieved, but a fluorinated carbon layer is formed that reduces etch selectivity and controls etch rate poorly
Solution Approach 1:
The patent applies preliminary action by forming an ammonium salt layer on the silicon nitride surface before the etching process. This layer is created through plasma exposure to H2 and HF or F2 gases, which deposit ammonium salts that protect the silicon nitride during subsequent halogen-containing gas etching, thereby preventing the formation of harmful fluorinated carbon layers on the nitride surface
Solution Approach 2:
The ammonium salt layer acts as an intermediary protective layer between the halogen-containing etching gas and the silicon nitride film. This mediator prevents direct interaction that would otherwise form fluorinated carbon layers, while allowing controlled etching of the silicon oxide film through the alternating plasma cycles
2Manufacturing precision
If conventional plasma etching is used to remove silicon oxide, then etching is achieved, but selective removal relative to silicon nitride is difficult to achieve
Solution Approach 1:
The patent employs periodic action through alternating plasma exposure cycles. The substrate is repeatedly exposed to different plasma gases (H2/HF or F2, then halogen-containing gas) in sequential cycles. Each cycle builds up the ammonium salt layer and performs selective etching, with repetition enhancing selectivity while using conventional plasma processing equipment
Solution Approach 2:
The process utilizes parameter changes by alternating between different plasma gas compositions and exposure conditions. The plasma gas type, pressure, and exposure time are varied between cycles to selectively form the protective ammonium salt layer on silicon nitride while enabling etching of silicon oxide, achieving high selectivity through dynamic parameter adjustment
3Manufacturing precision
If repeated plasma cycles are used to enhance selectivity, then etching precision is improved, but processing time increases
Solution Approach 1:
The patent maintains continuity of useful action by designing alternating plasma cycles where each cycle contributes productively to the overall etching process. The H2/HF or F2 plasma cycle continuously builds the protective ammonium salt layer, while the halogen-containing gas cycle continuously removes silicon oxide. This continuous alternating action achieves precise depth control without excessive idle time, as both phases perform useful functions
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 method provides highly controllable and selective etching of silicon oxide relative to silicon nitride, avoiding excessive etching of silicon nitride and allowing for precise control over etch depth, while forming an ammonium salt layer that acts as an etch blocking layer, differing from conventional processes by forming an ammonium salt in a bottom-up manner.
Implementation Method 1
exposing the substrate to a plasma-excited treatment gas containing 1) H2 and 2) HF, F2, or both HF and F2
Implementation Method 2
form a silicon oxide surface layer with reduced oxygen content on the silicon oxide film and form an ammonium salt layer on the silicon nitride film
Implementation Method 3
exposing the substrate to a plasma-excited halogen-containing gas that reacts with and removes the silicon oxide surface layer
Implementation Method 4
halogen-containing gas that reacts with and removes the silicon oxide surface layer from the silicon oxide film
Data Source
AI summary
A method for selective plasma etching of silicon oxide relative to silicon nitride. The method includes a) providing a substrate containing a silicon oxide film and a silicon nitride film, b) exposing the substrate to a plasma-excited treatment gas containing 1) H2 and 2) HF, F2, or both HF and F2, to form a silicon oxide surface layer with reduced oxygen content on the silicon oxide film and form an ammonium salt layer on the silicon nitride film, c) exposing the substrate to a plasma-excited halogen-containing gas that reacts with and removes the silicon oxide surface layer from the silicon oxide film, and d) repeating steps b) and c) at least once to further selectively etch the silicon oxide film relative to the ammonium salt layer on the silicon nitride film. The ammonium salt layer may be removed when the desired etching has been achieved.