Composite Substrate Bonding for Void-Free Piezoelectric Wafers
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Solution Overview
Problem
Existing wafer bonding methods for piezoelectric materials suffer from issues such as passband shift with temperature, thermal micro-voids, electrostatic charge, warping, and insufficient bonding strength, leading to poor performance in surface acoustic wave devices.
Innovation Solution
A method involving mixed gas plasma activation using oxygen and nitrogen, combined with ultraviolet light surface modification and low-temperature thermal annealing, to create a strong and stable bond between piezoelectric and supporting substrates, eliminating macroscopic and microscopic voids and enhancing bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wafer bonding methods are used to bond piezoelectric substrates to supporting substrates, then bonding is achieved, but thermal micro-voids form during annealing and thinning processes
Solution Approach 1:
The patent applies preliminary plasma activation treatment to the substrate surfaces before bonding. This pre-treatment modifies the surface chemistry to enhance adhesion and prevent thermal micro-void formation during subsequent annealing and thinning processes, thereby improving bonding reliability without generating harmful defects
Solution Approach 2:
The patent optimizes bonding parameters including plasma power, gas flow rates, pressure, and temperature to achieve optimal bonding conditions. By carefully controlling these parameters, the process achieves strong bonding while preventing thermal micro-void formation during thermal processing
2Reliability
If conventional wafer bonding is used, then substrates are bonded together, but high electrostatic charge accumulates causing warping and high bow
Solution Approach 1:
The patent performs wafer bonding in a controlled inert atmosphere (vacuum or nitrogen environment). This prevents electrostatic charge accumulation by eliminating moisture and oxygen that would otherwise generate and sustain electrostatic charges, thereby preventing warping and high bow while maintaining bonding strength
3Ease of manufacture
If standard plasma activation is used, then surface activation is achieved, but passband shift occurs with temperature changes
Solution Approach 1:
The patent optimizes plasma processing parameters including gas composition (O2/N2 ratios), pressure, and power to achieve surface activation that minimizes stress in the piezoelectric layer. This careful parameter control ensures frequency stability across temperature ranges while maintaining ease of manufacture
Solution Approach 2:
The patent applies selective plasma treatment to specific regions of the substrate surfaces, optimizing activation locally to prevent stress-induced frequency shifts while maintaining overall manufacturing efficiency
4Ease of manufacture
If conventional bonding procedures are used, then wafer bonding is achieved, but bonding strength is insufficient for further processing
Solution Approach 1:
The patent applies preliminary plasma activation treatment to both substrate surfaces before bonding. This pre-treatment creates reactive surface groups and removes contaminants, significantly enhancing adhesion strength and enabling the bonded structure to withstand subsequent thinning and dicing processes
Solution Approach 2:
The patent creates a composite interface structure through plasma activation that combines the piezoelectric substrate and supporting substrate with enhanced interfacial bonding. This composite structure achieves sufficient bonding strength for further processing while maintaining ease of manufacture
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 method achieves high-quality bonding with improved thermal stability and reduced electrostatic charge, allowing for efficient fabrication of thin film surface acoustic wave devices with enhanced performance.
Implementation Method 1
a first surface of a first substrate and a second surface of a second substrate, respectively, in a plasma system, wherein the plasma system is a radiofrequency system having a plasma between a first electrode and a second electrode that are separately powered
Implementation Method 2
a surface modification process that includes exposing of the plasma activated first surface and the plasma activated second surface to an ultraviolet radiation in an atmosphere of oxygen and nitrogen at atmospheric pressure
Implementation Method 3
a process of thermally annealing the bonded precursor composite substrate
Data Source
AI summary
A method of forming a composite substrate is provided. The method includes a mixed gas plasma activation process using oxygen and nitrogen including exposing a surface of a wafer and a surface of a piezoelectric material wafer in a plasma system; exposing the plasma activated surface of the wafer and the plasma activated surface of the piezoelectric material wafer to an ultraviolet radiation in an atmosphere of oxygen and nitrogen; placing the surface of the wafer on the surface of the piezoelectric material wafer; applying a mechanical load on the wafer and the piezoelectric material wafer; and thermally annealing the bonded wafer and piezoelectric material wafer; wherein the wafer is configured to support the piezoelectric material wafer.