Polycrystalline CVD Diamond Wafer Segmentation for Cracking Reduction
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Solution Overview
Problem
The challenge in growing polycrystalline CVD synthetic diamond wafers is the incorporation of impurities and defects during the synthesis process, which affects thermal conductivity and stiffness, leading to issues like wafer cracking and non-uniform thermal performance, especially when trying to achieve thicker wafers.
Innovation Solution
The method involves growing a polycrystalline CVD diamond wafer to a first thickness, cutting it into smaller wafers, and then continuing growth in a second reactor with different conditions to achieve a combined thickness, reducing temperature differences and strain, and allowing for different properties at various points in the material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the wafer thickness is increased to improve heat spreading functionality and stiffness, then thermal performance and rigidity are improved, but the rate of impurity and defect incorporation increases leading to wafer cracking
Solution Approach 1:
The diamond wafer growth process is divided into multiple sequential stages, with each stage producing a portion of the final thickness. The wafer is grown to an intermediate thickness, removed from the substrate, cut into smaller wafers, and then regrown on new substrates to achieve the final thickness. This segmentation allows the total thickness to be accumulated without the continuous stress and defect accumulation that would occur in a single growth run.
2Area of stationary object
If the wafer diameter is increased to improve heat spreading functionality, then thermal performance is improved, but the rate of impurity and defect incorporation increases particularly at the periphery
Solution Approach 1:
Large diameter wafers are grown in multiple sequential stages rather than in a single continuous growth process. By removing the wafer from the substrate between growth stages and cutting it into smaller wafers that are then regrown on new substrates, the process maintains better control over impurity and defect incorporation throughout the entire wafer area, including the periphery.
3Productivity
If the growth rate is increased to improve productivity, then manufacturing efficiency is improved, but the rate of impurity and defect incorporation increases
Solution Approach 1:
The overall thickness requirement is divided into multiple growth stages, each producing a portion of the final thickness. This allows the process to accumulate total thickness over time while maintaining controlled growth rates in each individual stage, thereby reducing the incorporation rate of impurities and defects compared to attempting to grow the entire thickness in a single high-rate process.
4Length of stationary object
If continuous growth is performed to achieve thick wafers, then final thickness is achieved, but temperature differences and strain increase leading to wafer cracking
Solution Approach 1:
The continuous growth process is interrupted by removing the wafer from the substrate at an intermediate thickness, cutting it into smaller wafers, and regrowing on new substrates. This segmentation breaks up the continuous accumulation of temperature differences and strain that would occur in uninterrupted growth, allowing stress relief and reducing the likelihood of wafer cracking in the final thick product.
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 enhances yield by early identification of growth issues, reduces wafer cracking, and allows for polycrystalline diamond growth with varied properties, resulting in improved thermal conductivity and mechanical stability, particularly in achieving thicker wafers with reduced defects.
Implementation Method 1
A microwave plasma activated CVD diamond synthesis system typically comprises a plasma reactor vessel coupled both to a supply of source gases and to a microwave power source. The plasma reactor vessel is configured to form a resonance cavity supporting a standing microwave. Source gases including a carbon source and molecular hydrogen are fed into the plasma reactor vessel and can be activated by the standing microwave to form a plasma in high field regions.
Implementation Method 2
If a suitable substrate is provided in close proximity to the plasma, reactive carbon containing radicals can diffuse from the plasma to the substrate and be deposited thereon.
Implementation Method 3
Atomic hydrogen can also diffuse from the plasma to the substrate and selectively etch off non-diamond carbon from the substrate such that diamond growth can occur.
Data Source
AI summary
A method of fabricating a polycrystalline CVD synthetic diamond wafer is disclosed. A first polycrystalline CVD synthetic diamond wafer is grown using a CVD process to a first thickness on a substrate. A second smaller wafer is cut from the polycrystalline CVD synthetic diamond wafer. The second smaller wafer is located on a carrier, and further polycrystalline CVD synthetic diamond material is grown on the second smaller wafer to a second thickness to give a polycrystalline CVD synthetic diamond material having a total thickness of the combined first and second thicknesses.