Single-Crystal Silicon Device Steep Flank Etching
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Solution Overview
Problem
Conventional KOH etching of silicon wafers results in inclined flanks with a 54.7° angle, limiting the achievement of steeper flanks necessary for enhanced mechanical stability and larger bond areas in micromechanical structures.
Innovation Solution
A 2-mask KOH etching process is employed, where masks with different opening widths are applied to both sides of the silicon wafer, allowing the third side to extend in both 111 and 110 planes, creating steeper flanks and enabling adjustable slope profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional KOH etching is used on silicon wafers, then well-defined openings with inclined walls at 54.7° are achieved, but steeper flanks cannot be implemented
Solution Approach 1:
The single etching process is segmented into two separate etching steps, each with its own mask. The first etching creates initial openings with standard inclined flanks, while the second etching steepens the flanks by removing additional material at controlled angles. This segmentation allows independent optimization of each etching step to achieve the desired steep flanks.
Solution Approach 2:
The solution transitions from a single-sided etching approach to a dual-sided etching approach. By applying masks and performing etching from both sides of the wafer, the process gains an additional dimensional control parameter, enabling the creation of steeper flanks that would be impossible with single-sided etching alone.
2Reliability
If inclined flanks at 54.7° are used, then crystallographic etching stop is achieved, but mechanical stability is reduced
Solution Approach 1:
Different regions of the flank are given different qualities through the two-step etching process. The upper portion maintains the crystallographic 111 plane orientation for etching stop reliability, while the lower portion is steepened to provide enhanced mechanical stability. This local differentiation allows both requirements to be satisfied simultaneously in different zones of the same structure.
3Ease of manufacture
If standard KOH etching is performed, then simple process is maintained, but bond area is limited
Solution Approach 1:
The first mask and first etching step perform preliminary action by creating initial openings with sufficient width to accommodate the final bond area requirement. This preliminary structure is then refined by the second etching step to achieve the final steep-flank geometry, ensuring both adequate bond area and process feasibility.
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
This method produces through openings with steeper flanks, enhancing mechanical stability and allowing for precise bonding, combining the largest possible bonding surface with improved structural stability.
Implementation Method 1
In KOH-etching of 100 silicon material, the crystallographic properties of the silicon wafer are exploited to etch precisely rectangular openings in the wafer surface
Implementation Method 2
The inclined flanks correspond to the 111 planes and actually have an etching stop character in KOH. The 111 planes have the lowest etching rates in silicon crystal by far
Data Source
AI summary
A device made of single-crystal silicon having a first side, a second side which is situated opposite to the first side, and a third side which extends from the first side to the second side, the first side and the second side each extending in a 100 plane of the single-crystal silicon, the third side extending in a first area in a 111 plane of the single-crystal silicon. The third side extends in a second area in a 110 plane of the single-crystal silicon. Furthermore, a production method for producing a device made of single-crystal silicon is described.