Effusion Cell Aperture Design for MBE Substrate Loading
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Solution Overview
Problem
Existing molecular beam epitaxy (MBE) vacuum chambers face issues with substrate loading and unloading compatibility with standard semiconductor equipment, limited crucible capacity for liquid sources, contamination from deposits, and silicon substrate defects due to high-temperature processing and edge-based support.
Innovation Solution
The apparatus features a vacuum chamber with a crucible having an aperture in the side wall closer to the first end, allowing for a conical part to direct atoms or molecules downwards at an angle, increasing crucible capacity, and using a deposition shield to prevent contamination, while supporting silicon substrates from the back to prevent defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the substrate growth surface faces down in MBE vacuum chambers, then substrate loading and unloading can be performed using carrier rings, but this configuration is incompatible with existing semiconductor process equipment which typically have the growth surface facing up
Solution Approach 1:
The patent inverts the conventional substrate orientation by positioning the growth surface facing up instead of facing down. This inversion allows direct compatibility with semiconductor process equipment while maintaining efficient material deposition through the redesigned crucible aperture configuration
2Quantity of substance
If conventional crucibles are used with liquid source materials, then the apparatus can operate, but the crucible capacity is limited and the surface area of the melt diminishes causing diminishing material flux to the substrate
Solution Approach 1:
The patent introduces a side wall aperture in addition to the conventional top opening, utilizing a different spatial dimension for material effusion. This allows the crucible to maintain constant melt surface area while increasing overall capacity, thereby sustaining material flux throughout the deposition process
Solution Approach 2:
The crucible is divided into multiple effusion paths: a top aperture and side wall apertures. This segmentation allows different portions of the crucible to contribute to material flux independently, maintaining productivity while increasing total capacity
3Temperature
If high temperatures are used for evaporation, then material can be evaporated effectively, but deposits accumulate on chamber walls and structures which can fall into the crucible and contaminate the source material
Solution Approach 1:
The patent extracts the substrate from the direct path of falling deposits by positioning it on a stage below the crucible aperture. The deposition shield further isolates the substrate area, removing the contamination hazard while maintaining high temperature evaporation conditions
4Temperature
If silicon substrates are processed at high temperatures with edge-based support, then evaporation can be performed, but slip lines and similar defects occur on the substrate
Solution Approach 1:
The patent introduces a deposition shield as an intermediary element that protects the substrate from direct exposure to falling deposits. This shield allows high temperature processing to continue while preventing the formation of defects on the substrate surface
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 enhances compatibility with semiconductor handlers, maintains constant deposition rate, reduces contamination, and prevents substrate defects, enabling high-temperature processing of large diameter silicon substrates without slip lines.
Implementation Method 1
The source material is heated to the point where it starts to evaporate. The vacuum allows atoms or molecules to evaporate freely in the chamber and the atoms and molecules subsequently condense on substrate surfaces.
Implementation Method 2
allowing for a conical part to direct atoms or molecules downwards at an angle
Implementation Method 3
using a deposition shield to prevent contamination
Implementation Method 4
the atoms and molecules subsequently condense on substrate surfaces
Data Source
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AI summary
The present invention relates to an apparatus for evaporation comprising a vacuum chamber (12), a substrate stage (2) defining a substrate plane (26) and at least one effusion cell (6), the effusion cell comprising a crucible (7) having a volume, wherein said effusion cell, crucible and substrate stage are arranged inside the vacuum chamber. The crucible comprises a first end (14), a second end (15), at least one side wall (16) and an aperture (17). In a typical apparatus according to the invention the aperture is situated in the first wall or in a side wall closer to the first end than the second end, the second end arranged closer to the substrate plane than the first end. The invention also relates to a crucible for evaporation, having a volume, comprising a first end, a second end, at least one side wall and an aperture. The invention further relates to a method of growing a film on a substrate.