GaN Single Crystal Polishing via Oxidizing CMP
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Solution Overview
Problem
The existing polishing methods, such as CMP, face challenges in achieving high polishing efficiency and low surface roughness for gallium nitride (GaN) single crystal substrates, which are more difficult to process compared to silicon carbide (SiC) substrates, and often result in inefficient processing and surface scratches.
Innovation Solution
A polishing processing method using a CMP method with an oxidizing polishing liquid and specific ranges of oxidation-reduction potential (Eh) and pH, combined with either a loose or fixed polishing abrasive grain type pad, to enhance polishing efficiency and surface smoothness for GaN substrates. The oxidizing polishing liquid includes agents like potassium permanganate, and the pads are made of materials like polyurethane resin or epoxy resin with embedded abrasive grains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If diamond abrasive grains are used for polishing, then processing efficiency is improved, but surface roughness increases (Ra=10 nm)
Solution Approach 1:
The patent changes the chemical parameters of the polishing liquid by controlling oxidation-reduction potential (Eh) and pH to create an oxidizing environment. This chemical modification enables the use of diamond abrasive grains to achieve both high processing efficiency and low surface roughness by facilitating chemical reactions that reduce surface irregularities during mechanical polishing.
Solution Approach 2:
The patent employs a composite polishing system combining diamond abrasive grains (mechanical action) with an oxidizing polishing liquid containing specific chemicals like ammonium fluorosulfonate (chemical action). This composite approach creates a synergistic effect where chemical oxidation softens the GaN surface while diamond abrasives remove material, achieving both efficiency and precision.
2Manufacturing precision
If silica abrasive grains are used for polishing, then surface roughness decreases, but processing efficiency deteriorates and scratches occur
Solution Approach 1:
The patent modifies the polishing liquid parameters to be highly oxidizing with controlled pH (2.0-4.0) and Eh values. This creates a chemical environment that enhances the material removal rate, allowing less abrasive consumption and shorter polishing time while maintaining smooth surfaces, thus improving efficiency without sacrificing precision.
Solution Approach 2:
The patent introduces strong oxidizing agents (ammonium fluorosulfonate, ammonium persulfate, etc.) into the polishing liquid to accelerate chemical reactions at the polishing interface. This accelerated oxidation facilitates faster material removal and surface smoothing, resolving the contradiction between efficiency and surface quality.
3Reliability
If conventional CMP method is used for GaN substrates, then polishing can be performed, but processing time is excessive and surface quality is insufficient
Solution Approach 1:
The patent optimizes multiple parameters of the polishing liquid including oxidation-reduction potential (Eh: 200-400 mV), pH (2.0-4.0), and specific chemical concentrations (ammonium fluorosulfonate: 0.1-10 wt%). These parameter changes create ideal chemical conditions that dramatically accelerate the polishing rate while maintaining surface quality, reducing polishing time from conventional extended durations to efficient processing cycles.
Solution Approach 2:
The patent reduces reliance on purely mechanical polishing by introducing dominant chemical oxidation mechanisms. The oxidizing polishing liquid performs significant material removal and surface smoothing through chemical reactions, substituting for extended mechanical abrasion and thereby dramatically reducing processing time while improving surface quality.
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 achieves high polishing efficiency with low surface roughness and improved accuracy, reducing the consumption of expensive abrasive grains and minimizing scratches, while maintaining a favorable surface finish for GaN substrates.
Implementation Method 1
the polishing liquid is an oxidizing polishing liquid having an oxidation-reduction potential between Ehmin (determined by Eq. (1)) mV and Ehmax (determined by Eq. (2)) mV
Implementation Method 2
a plurality of polishing abrasive grains... loose polishing abrasive grain type polishing pad
Data Source
Figure 1~2
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AI summary
Provided is a method for polishing a single crystal substrate composed of gallium nitride GaN, which is a material that cannot be processed easily, by a CMP process with satisfactory polishing efficiency and satisfactory polishing performance. In the polishing by a CMP process, the surface of a single crystal substrate composed of gallium nitride GaN is polished using an abrasive-grain-containing polishing pad in the presence of an acidic polishing solution. In this manner, high polishing efficiency can be achieved properly while keeping the surface roughness at a low level. The polishing solution is an acidic polishing solution having an oxidation-reduction potential ranging from Ehmin mV (wherein Ehmin is a value determined in accordance with formula (1)) to Ehmax mV (wherein Ehmax is a value determined in accordance with formula (2)) and a pH value of 0.1 to 6.5. (1) Ehmin (mV) =-33.9pH + 750 (2) Ehmax (mV) = -82.1pH + 1491