Thermally Oxidized Composite Substrate Defect Reduction
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Solution Overview
Problem
High-temperature processing of heterogeneous composite substrates, such as SOQ and SOS, results in micro-cracks and defects due to significant differences in thermal expansion coefficients between the handle substrate and the silicon thin film, leading to issues with gate oxide film formation and device performance.
Innovation Solution
A previous heat treatment at temperatures ranging from 650°C to 850°C is applied to the handle substrate before high-temperature oxidative treatment, to reduce defects and stress, and enhance bond strength, thereby minimizing micro-cracks and defects in the thermally oxidized heterogeneous composite substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature treatment in excess of 850°C is applied to form gate oxide film, then gate oxide film formation is achieved, but micro-cracks and defects are generated due to thermal expansion difference
Solution Approach 1:
The patent applies a preliminary heat treatment at 650-850°C before the high-temperature gate oxide formation process. This preliminary treatment pre-stresses the silicon film and bonding interface, allowing the subsequent high-temperature process to proceed without generating micro-cracks. The preliminary action prepares the structure to withstand the thermal stress of the main process.
Solution Approach 2:
The patent changes the temperature parameter by introducing an intermediate heat treatment step at 650-850°C between room temperature and the high-temperature gate oxide formation process. This parameter change creates a gradual thermal transition that prevents sudden stress concentration and micro-crack formation while still enabling complete oxide formation.
2Adaptability or versatility
If heterogeneous materials are bonded to form composite substrates, then substrate functionality is improved, but bond strength is insufficient under high-temperature stress
Solution Approach 1:
The preliminary heat treatment at 650-850°C serves to pre-stress the bonding interface between heterogeneous materials before the high-temperature gate oxide formation. This preliminary action strengthens the bond by allowing thermal equilibrium to be established and stress distribution to be optimized in advance, preventing bond failure during the main high-temperature process.
3Quantity of substance
If thermal oxidation is performed at high temperature, then oxide layer is formed, but stress concentration causes defects
Solution Approach 1:
The preliminary heat treatment at 650-850°C pre-stresses the silicon film and distributes thermal stress uniformly across the wafer before the high-temperature oxidation process. This preliminary action ensures that when the high-temperature oxidation occurs, the stress is already managed, preventing stress concentration and defect formation while still achieving complete oxide layer formation.
Solution Approach 2:
The patent introduces an intermediate temperature parameter (650-850°C) between the initial state and the high-temperature oxidation process. This parameter change allows the system to undergo gradual thermal expansion and stress distribution, preventing sudden stress concentration that would lead to defects during oxide layer formation.
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 significantly reduces the number of defects in thermally oxidized heterogeneous composite substrates, as evidenced by reduced HF defects in immersion tests, improving the quality and reliability of the substrates for optoelectronic and high-frequency device applications.
Implementation Method 1
The cause originating from the heterogeneous composite substrate is a substantial difference in coefficient of expansion between the support substrate known as 'handle substrate' and the upper layer or silicon thin film
Implementation Method 2
The previous heat treatment is also regarded as a treatment for averaging localized stresses over the entire wafer surface
Implementation Method 3
High-temperature treatment, specifically oxidative treatment is carried out subsequent to the previous heat treatment
Data Source
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AI summary
A thermally oxidized heterogeneous composite substrate provided with a single crystal silicon film on a handle substrate, said heterogeneous composite substrate being obtained by, prior to a thermal oxidization treatment at a temperature exceeding 850°C, conducting an intermediate heat treatment at 650-850°C and then conducting the thermal oxidization treatment at a temperature exceeding 850°C. According to the present invention, a thermally oxidized heterogeneous composite substrate with a reduced number of defects after thermal oxidization can be obtained.