Lead-Free Glass Composition for Semiconductor Junction Protection
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Solution Overview
Problem
Conventional glass materials used for semiconductor junction passivation contain lead, which is environmentally harmful and may be banned, and they fail to meet requirements for proper baking temperature, chemical resistance, linear expansion coefficient matching silicon, and insulation properties.
Innovation Solution
A glass composition comprising SiO2, B2O3, Al2O3, ZnO, and at least two alkaline earth metal oxides (CaO, MgO, BaO) with nickel oxide, excluding Pb, P, As, Sb, Li, Na, and K, to form a glass layer that covers semiconductor junctions, ensuring high breakdown voltage and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-containing glass material is used for semiconductor junction passivation, then proper baking temperature and chemical resistance are achieved, but environmental harm increases and lead bans may occur
Solution Approach 1:
The patent changes the chemical composition parameters of the glass material by replacing lead oxide with a specific combination of metal oxides (Bi2O3, B2O3, SiO2, Al2O3, ZnO, and alkaline earth metal oxides) in controlled proportions. This parameter substitution maintains the glass layer's functional properties (baking temperature, chemical resistance, linear expansion coefficient) while eliminating the harmful lead component, thus resolving the contradiction between reliability and environmental harm
Solution Approach 2:
The patent creates a composite glass material composed of multiple metal oxides working together: Bi2O3 (30-70 wt%) provides low-temperature sintering capability, B2O3 (5-20 wt%) and SiO2 (10-30 wt%) contribute to chemical resistance and structural stability, Al2O3 (5-15 wt%) and ZnO (5-15 wt%) enhance durability, and alkaline earth metal oxides (CaO, MgO, BaO) (5-20 wt%) control the linear expansion coefficient. This composite formulation achieves lead-free performance while maintaining all required functional properties
Solution Approach 3:
The patent employs biologically safe and environmentally benign metal oxides that are non-toxic and do not pose environmental hazards like lead. These materials can be safely disposed of or recycled without environmental concern, effectively replacing the problematic lead-containing glass material while maintaining functional equivalence
2Ease of manufacture
If conventional glass composition is used, then manufacturing simplicity is maintained, but devitrification and bubble formation occur during baking
Solution Approach 1:
The patent optimizes the composition parameters within specific ranges: Bi2O3 (30-70 wt%), B2O3 (5-20 wt%), SiO2 (10-30 wt%), Al2O3 (5-15 wt%), ZnO (5-15 wt%), and alkaline earth metal oxides (5-20 wt%). These parameter specifications prevent devitrification and bubble formation during baking while maintaining ease of manufacture, as the glass powder can still be applied by conventional electrophoresis or coating methods followed by baking
Solution Approach 2:
The use of biologically safe metal oxides eliminates the formation of harmful byproducts during baking and ensures complete decomposition of organic binders without generating toxic gases or residues. This approach maintains manufacturing simplicity while improving glass layer quality by preventing defects
3Reliability
If glass layer is formed to cover pn junction exposure portion, then breakdown voltage is improved, but manufacturing complexity increases due to additional process steps
Solution Approach 1:
The glass composition serves multiple functions simultaneously: it provides electrical insulation to improve breakdown voltage, acts as a protective passivation layer, enables low-temperature sintering, and prevents devitrification during baking. This multi-functionality is achieved through the synergistic combination of metal oxides in the specified composition ranges, allowing a single material to fulfill multiple requirements without adding process complexity
Solution Approach 2:
The patent modifies the chemical composition parameters to achieve low-temperature sintering capability (reducing baking temperature to 700-900°C), which simplifies the manufacturing process by enabling glass layer formation at temperatures compatible with existing semiconductor fabrication capabilities. The specific oxide ratios ensure proper flow and adhesion at these reduced temperatures while maintaining insulation properties
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 glass composition allows for the manufacture of semiconductor devices with high breakdown voltage and reliability, matching silicon's linear expansion coefficient and preventing devitrification and bubble formation, while being lead-free and environmentally friendly.
Implementation Method 1
a layer made of glass composition for protecting a semiconductor junction is formed on an inner surface of the trench 920 and a surface of the semiconductor substrate in the vicinity of the trench 920 by electrophoresis
Implementation Method 2
the layer made of glass composition for protecting a semiconductor junction is baked so that a glass layer 924 for passivation is formed on a surface of the trench 920
Data Source
Figure 1A~1D
Figure 2A~2D
Figure 3A~3C
AI summary
A glass composition for protecting a semiconductor junction is provided, wherein the glass composition for protecting a semiconductor junction contains at least SiO2, B2O3, Al2O3, ZnO, and at least two oxides of alkaline earth metal selected from a group consisting of CaO, MgO and BaO, and substantially contains none of Pb, P, As, Sb, Li, Na and K. According to the glass composition for protecting a semiconductor junction of the present invention, in the same manner as a conventional case where "a glass material containing lead silicate as a main component" is used, a semiconductor device having a high breakdown voltage can be manufactured by using a glass material containing no lead. Further, according to the glass composition for protecting a semiconductor junction, the glass composition for protecting a semiconductor junction contains at least two oxides of alkaline earth metal selected from a group consisting of CaO, MgO and BaO and hence, an average linear expansion coefficient of the glass composition at a temperature range of 50°C to 550°C becomes close to a linear expansion coefficient of silicon at a temperature range of 50°C to 550°C whereby a semiconductor device of high reliability can be manufactured.