Partial PBN Liner Plasma Generator for Film Impurity Reduction
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Solution Overview
Problem
The incorporation of boron impurities into films grown by RPCVD processes is a significant issue due to surface recombination in plasma tubes, particularly when using pyrolytic boron nitride (PBN) liners, which reduces film quality and increases manufacturing costs.
Innovation Solution
A plasma generator design featuring a pyrolytic boron nitride liner that does not extend into the plasma generation region beyond 20% of its length, maintaining low surface recombination while minimizing boron impurity incorporation, achieved by positioning the liner away from the ionizing source and using a constricted gas inlet to reduce active species loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pyrolytic boron nitride (PBN) liner is used to line the plasma tube, then surface recombination of active gas species is reduced, but boron impurities are sputtered into the growing film reducing film quality
Solution Approach 1:
The plasma tube is divided into two distinct regions: a first region without PBN liner material where plasma is generated, and a second region with PBN liner material that reduces surface recombination. This segmentation allows each region to perform its specific function without causing harmful effects to the other.
Solution Approach 2:
Different regions of the plasma tube are assigned different material properties: the first region uses materials resistant to sputtering and boron contamination, while the second region uses PBN liner material optimized for reducing surface recombination. This local differentiation of material quality resolves the contradiction between preventing impurity incorporation and maintaining active species consistency.
2Reliability
If PBN is used to construct the plasma tube, then surface recombination properties are improved, but manufacturing cost increases significantly due to difficulty in machining
Solution Approach 1:
The plasma tube is segmented into regions with different material requirements. Only the second region, where surface recombination is problematic, is lined with expensive and difficult-to-machine PBN material. The first region uses more economical and easily manufacturable materials, significantly reducing overall manufacturing cost while maintaining the necessary surface recombination resistance in the critical second region.
Solution Approach 2:
PBN liner material is applied locally only where needed (second region) rather than throughout the entire plasma tube. This localized application of high-performance material reduces material costs and simplifies manufacturing processes while still achieving the desired surface recombination resistance where it is most critical for maintaining active species consistency.
3Reliability
If the PBN liner extends into the plasma generation region, then surface recombination is reduced, but boron sputtering increases impurity levels in the film
Solution Approach 1:
The plasma tube is segmented into a first region (plasma generation zone) without PBN liner and a second region (transport zone) with PBN liner. This spatial segmentation ensures that the PBN material is present where surface recombination must be minimized, while absent from the plasma generation region where boron sputtering would contaminate the film.
Solution Approach 2:
The PBN liner material is selectively applied to the second region of the plasma tube where it provides the necessary surface recombination resistance, while the first region maintains a different material composition suitable for plasma generation without boron contamination. This local differentiation of material quality simultaneously achieves both film purity and active species consistency.
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 design effectively reduces boron impurities in the films, maintaining high quality and reducing manufacturing costs by minimizing the use of expensive PBN materials and preventing impurity incorporation, while still benefiting from low surface recombination properties.
Implementation Method 1
an ionising source adjacent the plasma tube to define a first region of the plasma tube and to expose that region to an electromagnetic field to generate active plasma species
Implementation Method 2
This surface recombination is the recombination of atoms or molecules of, for example, nitrogen which reduces the number of active atomic or molecular nitrogen species available for reaction with the metal organic reagent
Implementation Method 3
RPCVD uses the generation of plasma from a feed gas, such as nitrogen, to react with a metal organic reagent and deposit the desired material on the substrate
Data Source
AI summary
A plasma generator is described which employs a partial PBN liner not only to minimise the loss of energetic gas species during film formation but also to reduce boron impurity levels introduced into the growing film relative to the use of a complete PBN liner. The use of such a plasma generator in a film forming apparatus and method of forming a film is also described.