Plasma Etching Method for Silicon Substrate Tapering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional plasma etching methods for forming tapering etching structures in silicon substrates often result in bowing shapes due to uneven etching, leading to surface roughness and difficulties in uniform deposition, and the use of fluorocarbon gases can cause high surface roughness and non-uniform etch-resistant layers.
Innovation Solution
A two-step plasma etching method using SF6 and N2 gases in the first step, followed by SF6 and O2 gases in the second step, to control the taper state and surface roughness, forming a smooth tapering etching structure without bowing by using the O2 plasma-generated etch-resistant layer for depth etching and the N2 plasma-generated layer for width etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If oxygen gas plasma is used to form an oxide film as etch-resistant layer, then the side wall is protected and etching proceeds in depth direction, but the upper portion of the side wall becomes hollowed out in arc shape (bowing shape) and surface roughness increases
Solution Approach 1:
The etching process is divided into two distinct steps: first forming a polymer film layer using fluorocarbon gas, then forming an oxide film layer using oxygen gas. This segmentation allows each layer to perform its specific function without interfering with the other, preventing the bowing shape while maintaining etching precision
Solution Approach 2:
The polymer film is formed as a preliminary etch-resistant layer before the oxide film formation. This preliminary layer protects the side wall during the subsequent oxide film formation and etching process, preventing the bowing shape that occurs when oxygen plasma is used alone
2Manufacturing precision
If fluorocarbon gas is used to form a polymer film as etch-resistant layer, then the side wall is protected, but the surface of the side wall becomes rough and uniformity is poor
Solution Approach 1:
The patent combines two different etch-resistant layer materials (polymer film from fluorocarbon gas and oxide film from oxygen gas) into a composite protective structure. The polymer film provides initial protection and the oxide film provides smooth, uniform protection, merging the advantages of both materials to achieve both side wall protection and surface smoothness
Solution Approach 2:
The etch-resistant structure is formed as a composite of two different materials: a polymer film layer and an oxide film layer. This composite structure combines the protective properties of the polymer with the smooth, uniform properties of the oxide film, resolving the contradiction between protection and surface quality
3Device complexity
If conventional single-step etching with oxygen gas is used, then the process is simple, but bowing shape is formed and subsequent deposition uniformity is poor
Solution Approach 1:
The etching process is segmented into two sequential steps with different gas compositions: first fluorocarbon-based polymer film formation, then oxygen-based oxide film formation and etching. This segmentation increases process complexity slightly but dramatically improves etching shape accuracy by preventing bowing
Solution Approach 2:
The polymer film formation is performed as a preliminary step before the main etching process. This preliminary action prepares the side wall with a protective layer that prevents bowing during subsequent etching, ensuring accurate etching shape while maintaining a structured and controllable process
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 enables the formation of a tapering etching structure with a smooth surface and high etching speed, preventing bowing shapes and achieving uniformity, which is essential for subsequent deposition processes.
Implementation Method 1
plasma is generated from a gas mixture of SF6 and N2 to thereby etch a silicon substrate
Implementation Method 2
the silicon substrate is etched by the plasma generated from the SF6 gas
Implementation Method 3
an etch-resistant layer is formed on the silicon substrate by the plasma generated from the N2 gas
Implementation Method 4
the etch-resistant layer is formed on the surface of the silicon substrate by chemical reaction between plasma generated from an oxygen gas and the silicon atoms
Implementation Method 5
an oxide film as an etch-resistant layer is formed on the silicon substrate by generating plasma from the oxygen gas
Implementation Method 6
the etch-resistant layer is formed on the surface of the silicon substrate by chemical reaction between plasma generated from an oxygen gas and the silicon atoms
Data Source
Figure 1
Figure 2
Figure 3(a)~4
AI summary
A plasma etching method capable of preventing a bowing shape and forming a tapering etching structure (hole or trench) having a smooth surface is provided. A first step in which a fluorine-containing gas and a nitrogen gas are used and plasma is generated from these gases simultaneously, and a silicon substrate K is etched by the plasma generated from the fluorine-containing gas while an etch-resistant layer is formed on the silicon substrate K by the plasma generated from the nitrogen gas is performed, and then a second step in which a fluorine-containing gas and an oxygen-containing gas are used and plasma is generated from these gases simultaneously, and the silicon substrate K is etched by the plasma generated from the fluorine-containing gas while an etch-resistant layer is formed on the silicon substrate K by the plasma generated from the oxygen-containing gas is performed, thereby forming a tapering etching structure H (hole or trench) having a wide top opening width and a narrow bottom width in the silicon substrate K.