GaAs Substrate Surface Cleaning via Alkali-Acid Sequence
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Solution Overview
Problem
GaAs semiconductor substrates face challenges in achieving a clean surface due to the presence of impurities and oxides, which cannot be effectively removed by conventional thermal cleaning, leading to degradation of semiconductor devices.
Innovation Solution
A fabrication method involving surface polishing, alkali cleaning with an organic alkali compound, acid cleaning with specific acid concentrations, pure water cleaning, and high-speed drying to ensure a clean surface free of impurities and oxides, as evidenced by X-ray photoelectron spectroscopy analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If thermal cleaning is carried out at approximately 500 to 600°C to remove impurities and oxides from the GaAs substrate surface, then general surface contaminants are removed, but Ga2O3 with extremely high melting point (1795°C) cannot be removed
Solution Approach 1:
The invention changes the cleaning parameters by using a two-stage chemical cleaning process: first an alkali cleaning solution (such as ammonium hydroxide or sodium hydroxide) to remove organic contaminants and general oxides, then an acid cleaning solution (such as hydrofluoric acid or phosphoric acid) specifically targeted at removing Ga2O3. This parameter change from thermal to chemical cleaning enables effective removal of the high-melting-point Ga2O3 that thermal cleaning cannot eliminate.
Solution Approach 2:
The invention employs a composite cleaning approach using both alkali and acid cleaning solutions in sequence. The alkali solution addresses organic and general oxide contamination while the acid solution specifically targets Ga2O3 removal. This composite cleaning methodology combines the strengths of different chemical agents to achieve comprehensive surface cleaning that neither method could accomplish alone.
2Object-affected harmful factors
If a protection film with surface active agent is formed on the GaAs wafer surface to prevent oxidation, then oxidation resistance is improved, but carbon atoms and oxygen atoms from the surface active agent remain on the surface even after thermal cleaning, degrading semiconductor device properties
Solution Approach 1:
The invention applies a protection film immediately after polishing and before any cleaning steps to prevent surface oxidation during subsequent processing. This preliminary protective action ensures the surface remains oxidation-free throughout the cleaning process, and the final acid cleaning step effectively removes any residual surface active agent components, achieving both oxidation protection and surface purity.
Solution Approach 2:
The invention uses the acid cleaning solution specifically to extract and remove carbon atoms and oxygen atoms that remain on the surface after protection film formation and thermal cleaning. The acid treatment targets and eliminates these residual contaminants from the surface active agent, achieving the dual goal of maintaining oxidation resistance while ensuring surface purity.
3Shape
If polishing is performed to achieve a smooth surface, then surface roughness is reduced, but impurities and oxides adhere to the polished surface, requiring additional cleaning steps
Solution Approach 1:
The invention segments the cleaning process into distinct stages: alkali cleaning to remove general contaminants and organic residues from the polished surface, followed by acid cleaning to remove oxides including Ga2O3. This segmentation allows each cleaning step to target specific types of contamination, effectively addressing the cleanliness issue introduced by polishing without compromising surface smoothness.
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 effectively removes impurities and oxides, maintaining a favorable Ga/As ratio and low oxygen concentration, resulting in improved semiconductor device properties and reduced surface roughness, thereby enhancing the quality of epitaxial layer growth.
Implementation Method 1
an alkali cleaning step of cleaning the polished surface with an alkali cleaning solution
Implementation Method 2
an acid cleaning step of cleaning the surface subjected to alkali cleaning with an acid cleaning solution including 0.3 ppm to 0.5 mass % of acid
Implementation Method 3
The drying step can be effected by rotating the GaAs semiconductor wafer to spin off the acid cleaning solution remaining at the surface
Data Source
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AI summary
A GaAs semiconductor substrate (10) includes a surface layer (10a). When an atomic ratio is to be calculated using a 3d electron spectrum of Ga atoms and As atoms measured at the condition of 10° for the photoelectron take-off angle θ by X-ray photoelectron spectroscopy, the structural atomic ratio of all Ga atoms to all As atoms (Ga)/(As) at the surface layer (10a) is at least 0.5 and not more than 0.9, the ratio of As atoms bound with O atoms to all Ga atoms and all As atoms (As - O)/{(Ga) + (As)} at the surface layer (10a) is at least 0.15 and not more than 0.35, and the ratio of Ga atoms bound with O atoms to all Ga atoms and all As atoms (Ga - O)/{(Ga) + (As)} at the surface layer (10a) is at least 0.15 and not more than 0.35. Accordingly, there is provided a GaAs semiconductor substrate having a surface cleaned to an extent allowing removal of impurities and oxides at the surface by at least thermal cleaning of the substrate.