Cryopump Radiation Shield Bottom Opening Design
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Solution Overview
Problem
Cryopumps face challenges in enhancing the exhaust performance of non-condensable gases, particularly in semiconductor manufacturing processes where gases like hydrogen need efficient capture and removal.
Innovation Solution
The cryopump design incorporates a two-stage cryocooler with a radiation shield and a cryopanel unit, where the radiation shield has a larger shield bottom opening than the distance between the cryopanel unit and the housing bottom, allowing for improved thermal insulation and increased adsorption area for non-condensable gases, enhancing gas capture and storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the radiation shield encloses the second cooling stage and cryopanel unit with a small shield bottom opening, then thermal insulation is improved, but the adsorption area and storage capacity for non-condensable gases are reduced
Solution Approach 1:
The radiation shield is designed with a large shield bottom opening whose dimension exceeds the distance from the cryopanel unit to the housing bottom portion. This dimensional change creates an additional storage space below the cryopanel unit, effectively increasing the storage capacity for non-condensable gases in the vertical dimension without compromising the thermal insulation provided by the radiation shield structure.
2Quantity of substance
If the shield bottom opening dimension is increased, then the adsorption area for non-condensable gases is increased, but thermal insulation performance deteriorates
Solution Approach 1:
The radiation shield acts as an intermediary structure that provides thermal insulation while incorporating a large shield bottom opening. The shield is thermally connected to the first cooling stage, which maintains it at a cryogenic temperature, allowing it to function as both a thermal barrier and an extended adsorption surface for non-condensable gases without significant heat leakage.
Solution Approach 2:
The radiation shield is maintained at a cryogenic temperature through thermal connection to the first cooling stage. This parameter change (temperature) enables the shield surface to effectively adsorb non-condensable gases even with a large opening area, as the low temperature provides the necessary adsorption capability despite the increased surface area exposed to warmer environments.
3Loss of energy
If a traditional closed radiation shield design is used, then thermal insulation is maximized, but the exhaust performance for non-condensable gases is insufficient
Solution Approach 1:
The radiation shield is segmented with a large shield bottom opening rather than being fully enclosed. This segmentation creates additional space below the cryopanel unit for non-condensable gas storage and enhances the exhaust performance by providing direct access to the adsorption surface, while the shield structure itself maintains thermal insulation for the critical cryogenic components.
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 configuration improves the exhaust performance of non-condensable gases by increasing the adsorption area and storage capacity, achieving a vacuum degree suitable for semiconductor processes with a 5% to 10% higher gas storage compared to traditional designs.
Implementation Method 1
a radiation shield which includes a shield main opening, a shield side opening, and a shield bottom opening, encloses the second cooling stage and the cryopanel unit, and is thermally connected to the first cooling stage
Implementation Method 2
The non-condensable gas can be exhausted by being adsorbed to an adsorption region cooled to a cryogenic temperature
Implementation Method 3
A cryopump is a vacuum pump which condenses or adsorbs gas molecules on a cryopanel cooled to a cryogenic temperature to capture and exhaust the gas molecules
Data Source
AI summary
A cryopump includes a second cryopanel unit which is thermally connected to a second cooling stage of a cryocooler, a radiation shield which includes a shield main opening, a shield side opening, and a shield bottom opening, and a cryopump housing having a housing bottom portion which faces the shield bottom opening. A dimension of the shield bottom opening is larger than a distance from the second cryopanel unit to the housing bottom portion.