Polycrystalline Diamond Bonded Substrate With Wafer-Bow Compensation
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Solution Overview
Problem
Wafer-bow induced by mismatched coefficients of thermal expansion between silicon and polycrystalline diamond layers is not effectively addressed in existing technologies, leading to undesirable deflection and bonding challenges.
Innovation Solution
A wafer structure is developed with a polycrystalline diamond layer on one side and a bow-compensation layer on the other, along with surface preparation techniques such as chemical-mechanical polishing and plasma activation to create dangling bonds for contact bonding, allowing for reduced wafer-bow and low-temperature bonding of substrates like gallium nitride and silicon carbide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polycrystalline diamond layer is deposited on a silicon-containing layer, then the thermal conductivity and hardness are improved, but wafer-bow increases due to mismatched coefficients of thermal expansion
Solution Approach 1:
A bow-compensation layer is deposited on the back side of the silicon-containing layer before bonding, specifically designed to counteract the wafer-bow that will be induced by the polycrystalline diamond layer. This preliminary action prevents the shape distortion before it occurs during bonding.
Solution Approach 2:
The coefficient of thermal expansion of the silicon-containing layer is modified by depositing a bow-compensation layer with specific thermal expansion properties. This changes the overall thermal expansion parameter of the substrate to match the polycrystalline diamond layer, eliminating wafer-bow while maintaining the hardness benefits.
2Strength
If conventional bonding methods are used for substrates with mismatched thermal expansion coefficients, then bonding strength is achieved, but high temperatures are required causing thermal damage
Solution Approach 1:
The bonding process is transformed from a high-temperature thermal bonding process to a low-temperature plasma activation process. This parameter change in the bonding mechanism allows strong bonding to be achieved without the thermal damage associated with conventional high-temperature methods.
Solution Approach 2:
The thermal bonding mechanism is replaced with a plasma-based chemical activation mechanism. Instead of relying on heat to create bonding, plasma activation creates dangling bonds that enable strong adhesion at low temperatures, substituting a mechanical/thermal process with a chemical/plasma process.
3Manufacturing precision
If the surface roughness of polycrystalline diamond is reduced by polishing, then bonding quality is improved, but the process complexity and time increase
Solution Approach 1:
A separate bow-compensation layer is introduced as an intermediary component on the back side of the substrate. This layer serves the dual function of compensating for wafer-bow and potentially providing a smoother bonding surface, eliminating the need for complex polishing processes on the diamond layer itself.
Solution Approach 2:
The substrate structure is segmented into multiple functional layers: the polycrystalline diamond layer for hardness and thermal conductivity, the silicon-containing layer for structural support, and the bow-compensation layer for shape control and surface quality. This segmentation allows each layer to be optimized independently without requiring complex processing of the diamond layer.
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
The solution effectively reduces wafer-bow to less than 50 microns, enabling reliable low-temperature bonding of substrates with mismatched thermal expansion coefficients, improving bonding surface roughness and facilitating contact bonding between diverse materials.
Implementation Method 1
performing an activation process on a surface of a first substrate, to create dangling bonds on at least that surface, and then contact bonding the surface of the first substrate to a surface of a second substrate. The activation process may be, for example, a plasma activation process.
Implementation Method 2
The wafer-bow that is reduced or eliminated can be induced by a mis-match between the coefficients of thermal expansion of the respective materials of the layer containing silicon and the layer of polycrystalline diamond.
Implementation Method 3
Contact bonding of the substrates may be initially established by Van der Waals forces.
Implementation Method 4
the surface roughness of the material other than diamond is reduced by chemical-mechanical polishing, ion milling, and/or magnetorheological finishing
Data Source
AI summary
A wafer has a layer containing silicon, a layer of polycrystalline diamond deposited on the silicon-containing layer, and a bow-compensation layer on the other side of the silicon-containing layer for reducing wafer-bow. A method of making a bonded structure includes an activation process for creating dangling bonds on the surface of one substrate, followed by contact-bonding the surface to a second substrate at low temperature. A bonded structure may include two substrates contact bonded to each other, one substrate including a layer containing silicon, a layer of polycrystalline diamond, a bow-compensation layer for reducing wafer-bow of the first substrate, and the other substrate including gallium nitride, silicon carbide, lithium niobate, lithium tantalate, gallium arsenide, indium phosphide, or another suitable material other than diamond.