Silicon Hairspring Fabrication via DRIE and Oxidation
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Solution Overview
Problem
The existing process for fabricating silicon hairsprings suffers from significant geometric and stiffness variations due to etching dispersion, leading to inconsistent dimensional accuracy and thermal compensation in resonator assemblies.
Innovation Solution
A process involving SOI wafers with precise layering and etching techniques, including photolithography, deep reactive-ion etching, and oxidation steps, to achieve a silicon hairspring with controlled dimensions and stiffness, ensuring high dimensional accuracy and thermal compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching methods are used to fabricate silicon hairsprings, then the fabrication process is simple, but geometric dispersion and stiffness variation are significant
Solution Approach 1:
The patent applies preliminary action by pre-defining the hairspring geometry through photolithography masking before etching. The resist mask is formed with precise dimensions, and the etching process follows this pre-defined pattern, ensuring geometric precision is established before the actual material removal occurs.
Solution Approach 2:
The patent replaces conventional mechanical etching methods with deep reactive-ion etching (DRIE), which uses plasma chemistry and ion bombardment to achieve precise, anisotropic etching. This substitution of the etching mechanism enables superior geometric control and reduced dispersion compared to traditional mechanical approaches.
2Productivity
If multiple hairsprings are etched in a silicon wafer, then productivity increases, but geometric dispersion between hairsprings increases
Solution Approach 1:
The patent segments the fabrication process into distinct stages: photolithography patterning, DRIE etching, and release. Each stage is optimized independently, allowing multiple hairsprings to be fabricated simultaneously while maintaining consistent geometry through the segmented approach. The photolithography step creates identical masks for all hairsprings, ensuring geometric consistency across batches.
Solution Approach 2:
The patent controls etching parameters (plasma power, gas flow, temperature) to maintain consistency across multiple hairsprings etched in the same wafer. By precisely controlling these parameters during DRIE, the process achieves uniform etch rates and geometric fidelity across all hairsprings, reducing dispersion even when fabricating multiple devices simultaneously.
3Reliability
If the hairspring dimensions are not precisely controlled, then fabrication is easier, but thermal compensation performance deteriorates
Solution Approach 1:
The patent incorporates feedback by measuring the actual stiffness of etched hairsprings and using this information to adjust subsequent fabrication parameters. The stiffness measurement provides feedback on the achieved geometry, allowing real-time correction of etching conditions to maintain precise dimensional control and ensure proper thermal compensation performance.
Solution Approach 2:
The patent replaces less precise etching methods with DRIE, which provides superior control over etch depth, profile, and uniformity. This substitution enables precise dimensional control necessary for thermal compensation while maintaining a manageable fabrication process through automated plasma control and real-time monitoring.
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 process results in a silicon hairspring with precise dimensions and stiffness, providing enhanced thermal compensation and stability in resonator assemblies, reducing temperature drifts and electrostatic interference sensitivity.
Implementation Method 1
b) growing a silicon oxide layer on the surface of the wafer
Implementation Method 2
e) carrying out deep reactive-ion etching in order to form the silicon hairspring
Implementation Method 3
i) oxidizing the hairspring formed in order to transform said thickness of silicon-based material to be removed into silicon dioxide
Data Source
AI summary
A process for fabricating a hairspring having a final stiffness includes the steps of fabricating a hairspring to thickened dimensions, and determining the initial stiffness of the hairspring formed in order to remove the volume of material to obtain the hairspring having the dimensions required for said final stiffness.