Vibration Sensor Through-Hole Etching Miniaturization
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Solution Overview
Problem
Current vibration sensors face challenges in miniaturization due to large through-hole openings, high production costs, and compromised vibration characteristics, particularly when using silicon substrates for diaphragms.
Innovation Solution
A method involving isotropic etching of a sacrifice layer and crystal anisotropic etching from both front and back surfaces to form a through-hole with controlled dimensions, using protective films to prevent thin film damage and enable vent holes for balanced pressure, allowing for miniaturization and high sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If crystal anisotropic etching is performed from the back side of a (100) plane semiconductor substrate, then a through-hole is formed, but the opening area at the back side becomes large compared to the diaphragm area, making miniaturization difficult
Solution Approach 1:
The patent performs etching from both the front side and back side of the substrate to form the through-hole. By approaching from two dimensions (front and back surfaces), the opening areas at both surfaces can be reduced while still achieving complete penetration, thus enabling miniaturization of the sensor.
Solution Approach 2:
The etching process is divided into two separate operations: front side etching and back side etching. Each etching operation creates a portion of the through-hole, and the combined effect produces a complete through-hole with reduced opening areas at both surfaces compared to single-sided etching.
2Area of stationary object
If the thickness of the semiconductor substrate is reduced to reduce the back surface opening area ratio, then the opening area ratio decreases, but the substrate strength lowers and handling becomes difficult
Solution Approach 1:
Instead of reducing substrate thickness to control the opening area ratio, the patent uses dual-sided etching to achieve precise control of opening areas while maintaining adequate substrate thickness for mechanical strength and handling.
Solution Approach 2:
The patent changes the etching parameters (etching from both sides with controlled depths) to achieve the desired opening area ratio without compromising substrate thickness, thereby maintaining substrate strength while controlling the opening geometry.
3Volume of moving object
If DRIE or ICP vertical etching is used to miniaturize the sensor, then the through-hole does not spread in truncated pyramid shape, but device cost is high and wafer processing productivity is not satisfactory
Solution Approach 1:
The patent uses conventional wet etching methods with controlled parameters (etching from both front and back sides) to achieve vertical through-holes without requiring expensive DRIE or ICP equipment, thereby maintaining high productivity and low cost while achieving miniaturization.
Solution Approach 2:
The patent discards the need for expensive specialized equipment (DRIE, ICP) by using conventional wet etching processes, achieving the same miniaturization effect through a more cost-effective and productive approach suitable for wafer-scale processing.
4Area of stationary object
If crystal anisotropic etching is performed from the front side to avoid large opening area, then an etching hole must be opened in the diaphragm, which adversely affects vibration characteristics and strength
Solution Approach 1:
The patent performs etching from the back side of the substrate instead of the front side, allowing formation of the through-hole without creating etching holes in the diaphragm. This approach maintains the integrity and vibration characteristics of the diaphragm while achieving the desired opening area control.
Solution Approach 2:
Instead of etching from the front side (diaphragm side), the patent inverts the approach and etches from the back side of the substrate, thereby avoiding damage to the diaphragm while still achieving precise control of the through-hole opening area.
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 miniaturization of vibration sensors, reduces production costs, and enhances sensitivity and acoustic compliance by controlling the through-hole dimensions and incorporating vent holes for balanced pressure.
Implementation Method 1
performing crystal anisotropic etching on a semiconductor substrate from both front and back surfaces
Implementation Method 2
isotropic etching of a sacrifice layer and crystal anisotropic etching from both front and back surfaces
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(d)
Figure 3(a)~3(d)
AI summary
A protective film (20) of an SiO2 thin film is formed on a front surface of an Si substrate (12), and a part of the protective film (20) is removed to form an etching window (22). A sacrifice layer (23) of polycrystalline Si is formed in the etching window (22). A protective film (24) of SiO2 is formed on the front surface of the Si substrate (12) from the top of the sacrifice layer (23), and a thin film (13) as an element formed of polycrystalline Si is further formed on the protective film (24). A backside etching window (26) is opened in a protective film (21) on the back side of the Si substrate (12). The Si substrate (12) is soaked in TMAH to perform crystal anisotropic etching in the Si substrate (12) through the backside etching window (26) to provide a through-hole (14) in the Si substrate (12).; When the sacrifice layer (23) is exposed to the interior of the through-hole (14), the sacrifice layer (23) is etching-removed to provide a gap (19) between the protective film (24) and the Si substrate (12) and crystal anisotropic etching of the Si substrate (12) is carried out from its front side and backside.