Glass Substrate Thermal Expansion and Alkali Ion Diffusion
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Solution Overview
Problem
In the wafer-level package technology, the difference in thermal expansion coefficients between silicon and glass substrates leads to residual strain in silicon substrates, and there is a risk of alkali ion diffusion from glass substrates into silicon substrates during heat treatment.
Innovation Solution
A glass substrate with specific thermal expansion coefficients (2.70-3.20 ppm/°C at 50-100°C and 3.45-3.95 ppm/°C at 200-300°C) and a low alkali metal oxide content (0-0.1% molar percentage) is developed, along with a method involving a melting step, refining, forming, and cooling to minimize residual strain and alkali ion diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thermal expansion coefficient of glass substrate is matched to silicon substrate, then residual strain is reduced, but alkali ion diffusion risk increases during heat treatment
Solution Approach 1:
The patent changes the chemical composition parameters of the glass substrate, specifically limiting alkali metal oxide content to 0-0.1% and adjusting the ratio of alkaline earth metal oxides (MgO: 5-15%, CaO: 10-20%, SrO: 5-15%, BaO: 5-15%). This compositional parameter change allows the glass to maintain thermal expansion matching with silicon (2.5-3.5 ppm/°C) while reducing alkali ion diffusion during heat treatment, thus resolving the contradiction between reducing residual strain and preventing alkali ion contamination.
Solution Approach 2:
The patent creates a composite glass material system that combines multiple oxide components (SiO2: 60-70%, Al2O3: 5-15%, B2O3: 5-15%, MgO: 5-15%, CaO: 10-20%, SrO: 5-15%, BaO: 5-15%) in specific proportions. This composite composition achieves both thermal expansion matching with silicon substrate and resistance to alkali ion diffusion, resolving the technical contradiction by integrating multiple material properties into a single glass formulation.
2Object-affected harmful factors
If alkali metal oxide content in glass substrate is reduced, then alkali ion diffusion is prevented, but manufacturing complexity increases
Solution Approach 1:
The patent simplifies the manufacturing process by establishing clear compositional parameters: total alkali metal oxides (Na2O + K2O) ≤ 0.1%, and specific ranges for alkaline earth metal oxides (MgO: 5-15%, CaO: 10-20%, SrO: 5-15%, BaO: 5-15%). These defined parameters provide a straightforward formulation guide for manufacturers, reducing complexity while ensuring low alkali ion diffusion. The use of common oxide components with specified ranges makes the manufacturing process manageable.
3Reliability
If thermal expansion coefficient matching is improved, then residual strain is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent achieves thermal expansion coefficient control (2.5-3.5 ppm/°C) matching silicon substrate by using a composite glass system with multiple oxide components in balanced proportions. The combination of SiO2 (60-70%), Al2O3 (5-15%), B2O3 (5-15%), and alkaline earth metal oxides creates a material whose thermal expansion can be tuned within a practical range, reducing the precision burden on manufacturing while ensuring compatibility with silicon substrates.
Solution Approach 2:
The patent provides a compositional parameter framework that guides manufacturers to achieve the desired thermal expansion coefficient range (2.5-3.5 ppm/°C). By specifying ranges for key components (particularly alkaline earth metal oxides) rather than exact values, the patent balances manufacturing precision requirements with the need for thermal expansion matching, making the specification achievable in practice.
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 residual strain in silicon substrates and prevents alkali ion diffusion, enhancing the reliability and performance of silicon substrates in heat treatment processes.
Implementation Method 1
a melting step of heating glass raw materials to obtain a molten glass
Implementation Method 2
an average thermal expansion coefficient α50/100 at 50° C. to 100° C. of 2.70 ppm/° C. to 3.20 ppm/° C.; an average thermal expansion coefficient α200/300 at 200° C. to 300° C. of 3.45 ppm/° C. to 3.95 ppm/° C.
Implementation Method 3
a cooling step of gradually cooling the glass ribbon to a room temperature state
Data Source
AI summary
The present invention provides a glass substrate in which in a heat treatment step of sticking a silicon substrate and a glass substrate to each other, an alkali ion is hardly diffused into the silicon substrate, and a residual strain generated in the silicon substrate is small. A glass substrate of the present invention has: an average thermal expansion coefficient α50/100 at 50° C. to 100° C. of 2.70 ppm/° C. to 3.20 ppm/° C.; an average thermal expansion coefficient α200/300 at 200° C. to 300° C. of 3.45 ppm/° C. to 3.95 ppm/° C.; a value α200/300/α50/100 obtained by dividing the average thermal expansion coefficient α200/300 at 200° C. to 300° C. by the average thermal expansion coefficient α50/100 at 50° C. to 100° C. of 1.20 to 1.30; and a content of an alkali metal oxide being 0% to 0.1% as expressed in terms of a molar percentage based on oxides.