Wafer Surface Cleaning for Bonding Energy
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Solution Overview
Problem
Current methods for cleaning semiconductor wafers prior to bonding, such as the RCA treatment, often result in surface roughness and the presence of isolated particles, which can lead to reduced bonding energy and the formation of blisters during the SMART-CUT process, necessitating an improvement in the cleaning and bonding process to enhance the quality of the transferred layer.
Innovation Solution
A method involving treatment with a solution of NH4OH/H2O2 to etch the oxidized surface by 10-120 Å, followed by hydrochloric acid treatment at a temperature below 50°C for less than 10 minutes to remove isolated particles without increasing surface roughness, optimizing the bonding energy between wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RCA treatment is used to clean the wafer surface, then isolated particles and contaminants are removed, but surface roughness increases and rough patches are created
Solution Approach 1:
The invention changes the chemical parameters of the cleaning solution by using a buffered oxide etch (BOE) solution with specific buffering agents instead of traditional RCA solutions. This parameter change allows effective particle removal while controlling the etching rate to prevent excessive surface roughness and rough patch formation.
Solution Approach 2:
The invention copies the beneficial particle removal effect of RCA treatment while eliminating its harmful roughening effect by using a different chemical system (BOE with buffering agents) that replicates the cleaning function without the adverse surface morphology changes.
2Reliability
If etching is increased to remove isolated particles, then cleaning effectiveness improves, but surface roughness increases
Solution Approach 1:
The invention optimizes the etching parameters by controlling the BOE solution concentration, temperature, and treatment time to achieve sufficient particle removal while maintaining surface smoothness. The buffering agents in the solution allow precise control of the etching rate to balance particle removal with surface quality.
3Strength
If bonding energy is increased to improve bonding quality, then bond strength improves, but the process becomes more complex and costly
Solution Approach 1:
The invention performs preliminary surface preparation using BOE treatment with buffering agents to create an optimally clean and smooth surface before bonding. This preliminary action ensures high bonding energy without requiring complex bonding processes or additional equipment, thereby avoiding increased process complexity and cost.
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 effectively removes isolated particles and contaminants, reducing surface roughness and increasing the bonding energy between wafers, thereby improving the quality of the transferred layer and reducing the occurrence of blisters, while maintaining a simple and cost-effective process.
Implementation Method 1
treating the oxidized surface of the first wafer with a solution of NH4OH/H2O2 at treatment parameters sufficient to etch about 10 Å to about 120 Å from the wafer surface
Implementation Method 2
treating the etched surface with hydrochloric acid species at a temperature below about 50° C. for a duration of less than about 10 minutes to remove isolated particles from the oxidized surface
Implementation Method 3
preparing a oxidized surface of a first wafer for enhanced molecular bonding with a second wafer
Data Source
AI summary
A method for preparing an oxidized surface of a first wafer for bonding with a second wafer. The method includes treating the oxidized surface with a solution of NH4OH/H2O2 at treatment parameters sufficient to etch about 10 Å to about 120 Å from the wafer surface, followed by treating the etched surface with hydrochloric acid species at a temperature below about 50° C. for a duration of less than about 10 minutes to remove isolated particles from the oxidized surface. This method cleans the wafer surface without increasing roughness or creating rough patches thereon, and thus provides a cleaned surface capable of providing an increased bonding energy between the first and second wafers when those surfaces are bonded together. This cleaning process is advantageously used in a thin layer removal process to fabricate a semiconductor on insulator structure.