CMP Process Buffering Step for pH Shock and Scratch Prevention
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Solution Overview
Problem
The existing CMP processes face issues with pH shock and cross contamination due to the mixing of different slurries, leading to the formation of large particles that can scratch the wafer surface during polishing.
Innovation Solution
A CMP process that includes a buffering step using a soft polishing pad with a cleaning agent to adjust the pH value between two polishing processes, preventing residual slurry and particle contamination by removing at least a portion of the first slurry and cleaning agent, thereby avoiding pH shock and cross contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple polishing slurries with different pH values are used in sequence, then global planarization and pattern transfer accuracy are improved, but pH shock occurs causing slurry mixing and large particle formation that scratch the wafer surface
Solution Approach 1:
A buffering slurry with intermediate pH value is introduced between the first polishing slurry (pH 10-11) and the second polishing slurry (pH 5-6). This buffering slurry acts as a mediator that gradually transitions the pH environment, preventing direct mixing of incompatible slurries and avoiding the formation of large harmful particles that cause wafer surface scratching.
Solution Approach 2:
The buffering slurry is applied in advance before the second polishing slurry to pre-adjust the pH environment on the wafer surface. This preliminary action removes residual first polishing slurry and prepares the surface with an intermediate pH condition, preventing pH shock when the second slurry is subsequently applied.
2Productivity
If residue from the first slurry is not removed before applying the second slurry, then the polishing process is continuous and efficient, but cross contamination of materials occurs and large particles form
Solution Approach 1:
The buffering slurry serves as an intermediary cleaning and transition medium between the first and second polishing slurries. It chemically neutralizes and removes residual first slurry from the wafer surface through its intermediate pH properties, preventing cross contamination while maintaining process continuity.
Solution Approach 2:
The pH parameter of the slurry on the wafer surface is gradually changed from the high pH of the first slurry (10-11) to the intermediate pH of the buffering slurry, and then to the low pH of the second slurry (5-6). This gradual parameter transition prevents sudden pH shock that would cause slurry incompatibility and large particle formation.
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 minimizes residual particles and contaminants on the wafer surface, preventing damage and ensuring a smoother polishing process by maintaining a stable pH environment between the two polishing stages.
Implementation Method 1
a buffering process on the wafer is performed using a soft polishing pad with a cleaning agent to buffer the pH value in the first polishing process
Implementation Method 2
remove at least portion of the first slurry and the cleaning agent by the contact with the soft polishing pad simultaneously
Implementation Method 3
CMP is a process that utilizes the reagent within a slurry to react chemically with the front face of a wafer and produce an easily polished layer
Implementation Method 4
Together with the abrasive action provided by the abrasive particles in the slurry above a polishing pad, the protruding portion of the easily polished layer is gradually removed
Implementation Method 5
cerium oxide will carry a positive charge while the silicon oxide at a pH environment of about 5 will carry a negative charge. Thus, when the residue from the slurry SS25 contacts the slurry HSS (pH=5), they may clump together due to electrostatic attraction to form large particles
Data Source
AI summary
A CMP process is provided. A first polishing process on a wafer is performed using a first hard polishing pad with a first slurry. Then, a buffering process on the wafer is performed using a soft polishing pad with a cleaning agent to buffer the pH value in the first polishing process and to remove at least portion of the first slurry and the cleaning agent by the contact with the first soft polishing pad simultaneously. Thereafter, a second polishing process on the wafer is performed using a second hard polishing pad with a second slurry such that the pH value after the buffering process is between the pH value in the first polishing process and the pH value in the second polishing process. The method can avoid the scratch issue of wafer surface by particles resulting from pH shock and cross contamination.