Cryogenic Etching of Photolithographic Substrates
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Solution Overview
Problem
Current photolithographic processes face challenges in achieving precise feature profiles and critical dimension (CD) performance due to dimensional changes and sloped feature profiles during etching, particularly in high-density areas, which affect the optical performance of photomasks.
Innovation Solution
A method involving cooling the photolithographic substrate to less than -30°C before etching, using a plasma system with controlled temperature and processing gases, and modulating the plasma process conditions to minimize CD bias and improve feature profiles, including multiple temperature control steps and inert gas handling within a vacuum chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithographic etching is performed at room temperature, then the etching process can be completed, but dimensional changes and sloped feature profiles occur leading to poor CD performance
Solution Approach 1:
The patent applies parameter changes by cooling the substrate to cryogenic temperatures (below -30°C, preferably below -70°C) before and during the etching process. This temperature parameter change fundamentally alters the etching chemistry and physics, resulting in vertical feature profiles and eliminating the sloped profiles that occur at room temperature, thereby resolving the CD performance issue
Solution Approach 2:
The patent utilizes phase transitions of the substrate temperature from room temperature to cryogenic temperatures. This phase transition in thermal state changes the material properties and reaction kinetics during etching, enabling precise dimensional control and eliminating the dimensional changes that normally occur during conventional etching
2Manufacturing precision
If substrate temperature is not controlled during plasma etching, then the process is simpler, but CD bias increases and feature profiles deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-cooling the substrate to cryogenic temperatures before initiating the plasma etching process. This preliminary temperature control step ensures that the substrate maintains optimal temperature conditions throughout etching, preventing CD bias and profile deterioration without requiring complex real-time temperature adjustment systems during the etch itself
Solution Approach 2:
The patent replaces complex active temperature control mechanisms during etching with a simpler approach: pre-cooling the substrate and maintaining it at cryogenic temperatures through thermal isolation and cryogenic cooling infrastructure. This substitution reduces the need for complex feedback control systems while achieving superior CD bias control
3Productivity
If high circuit density is achieved by decreasing feature sizes, then device performance improves, but photolithographic precision becomes more difficult to maintain
Solution Approach 1:
The patent applies parameter changes by using cryogenic temperature control during etching to achieve unprecedented precision in feature size control. This temperature parameter change enables the etching process to maintain vertical profiles and consistent dimensions even at the smallest feature sizes required for high circuit density, directly supporting continued scaling
Solution Approach 2:
The patent utilizes cryogenic gas flows (pneumatic system) to cool and maintain the substrate at low temperatures during etching. This pneumatic cooling approach provides uniform temperature distribution across the substrate surface, ensuring consistent etching conditions and precision across all features regardless of size, thereby enabling high circuit density with maintained precision
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 results in improved feature profiles with reduced CD bias and enhanced etch selectivity, leading to better optical performance and fidelity in photomask fabrication by maintaining low substrate temperatures and optimizing plasma processing conditions.
Implementation Method 1
introducing at least one processing gas into said vacuum chamber; igniting a plasma from said processing gas; processing the photolithographic substrate using said plasma
Implementation Method 2
cooling the photolithographic substrate to less than minus thirty degrees Celsius, before the photolithographic substrate is etched
Data Source
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AI summary
The present invention provides a method for processing a photolithographic substrate within a vacuum chamber. The method comprising the steps of cooling the photolithographic substrate to a target temperature before the photolithographic substrate is processed within the vacuum chamber. At least one processing gas is introduced into the vacuum chamber. After the photolithographic substrate is at the target temperature, a plasma is ignited from the processing gas wherein the photolithographic substrate is processed using the plasma. Upon completion of the processing, the photolithographic substrate is unloaded from the vacuum chamber.