SOI Substrate Surface Roughness and Particle Removal
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Solution Overview
Problem
The manufacturing of SOI substrates with transparent insulating substrates, such as silicon on quartz (SOQ) and silicon on glass (SOG), faces challenges including recognition issues by optical sensors due to smooth surfaces and significant particle accumulation post-sandblasting, which complicates cleaning and increases the risk of metal contamination.
Innovation Solution
A method involving the preparation of transparent insulating substrates with distinct surface roughnesses, where one surface is smoothed for silicon film formation and the other is roughened, combined with a cleaning process using HF followed by alkali cleaning to effectively remove particles and prevent re-adhesion, ensuring the substrate is recognizable and free of contaminants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the transparent insulating substrate surface is kept smooth, then the silicon film formation is facilitated, but the substrate cannot be recognized by optical sensors
Solution Approach 1:
The substrate has different surface qualities on different sides: the front surface (first main surface) is kept smooth with low roughness (RMS < 0.7 nm) to facilitate silicon film formation, while the back surface (second main surface) is roughened with higher roughness to enable optical sensor recognition. This local differentiation resolves the contradiction by applying different surface treatments to different regions of the same substrate.
2Difficulty of detecting and measuring
If sandblasting is applied to roughen the substrate surface for optical recognition, then the substrate becomes recognizable, but particles accumulate significantly on the surface
Solution Approach 1:
The harmful particles generated by sandblasting are removed through a two-step cleaning process: HF cleaning to dissolve sandblast residues and alkali cleaning to remove generated dust. This extraction of harmful elements resolves the contradiction by eliminating particles while preserving the roughened surface structure needed for optical recognition.
Solution Approach 2:
The surface is roughened by sandblasting before the cleaning process to create the recognition-friendly texture. By performing the roughening action in advance and then systematically removing particles through HF and alkali cleaning, the invention prepares the surface for both recognition and subsequent low-particle-state operation.
3Object-generated harmful factors
If HF cleaning is used to remove particles from the roughened surface, then particles are removed, but the surface becomes excessively smooth, decreasing the roughening effect
Solution Approach 1:
The surface is roughened by sandblasting before the cleaning process to create the recognition-friendly texture. By performing the roughening action in advance and then systematically removing particles through HF and alkali cleaning, the invention prepares the surface for both recognition and subsequent low-particle-state operation.
Solution Approach 2:
The cleaning process parameters (HF concentration, temperature, time) are optimized to remove particles while maintaining the roughness within the effective range for optical recognition. By controlling these parameters, the invention achieves particle removal without excessive smoothing that would eliminate the roughening effect.
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 approach allows for the easy manufacturing of SOI substrates with a roughened back surface that can be recognized by optical sensors, reducing particle contamination and preventing slippage during conveyance, while maintaining the effectiveness of the fogging treatment.
Implementation Method 1
The HF cleaning, however, has a problem of making the particle level rather worse. This is because the HF cleaning activates the surface of a glass or the like; moreover, fine pieces of the glass or the like released during the cleaning reattach to the surface
Implementation Method 2
A method involving the preparation of transparent insulating substrates with distinct surface roughnesses, where one surface is smoothed for silicon film formation and the other is roughened, combined with a cleaning process using HF followed by alkali cleaning to effectively remove particles and prevent re-adhesion
Data Source
Figure 1(a)~1(b)
Figure 2(a-1)~2(b-4)
Figure 3~4
AI summary
Provided is a method of easily producing a SOI substrate that is a transparent insulating substrate on one of the major surfaces of which a silicon thin film is formed while the major surface opposite to the surface on which the silicon thin film is formed is roughened. The method produces a SOI substrate that includes at least the transparent insulating substrate, and the silicon thin film formed on a first major surface which is one of the major surfaces of the transparent insulating substrate with a second major surface, the major surface opposite to the first major surface of the transparent insulating substrate, roughened. The method for producing the SOI substrate includes at least a process of preparing the transparent insulating substrate the surface roughness of the first major surface of which is less than 0.7 nm in RMS while the surface roughness of the second major surface is larger in RMS than the surface roughness of the first major surface, and a process of forming the silicon thin film on the first major surface of the transparent insulating substrate.