Semiconductor Substrate Polishing With Staged pH Shift
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Solution Overview
Problem
Conventional flat-surface polishing methods for semiconductor substrates face challenges in achieving both high polishing efficiency and excellent surface smoothness in a single polishing process, as they struggle to balance the pH of the polishing fluid effectively.
Innovation Solution
A method and apparatus that control the pH of the polishing fluid by maintaining it in a strong acid range during a predetermined time using a pH adjuster, followed by stopping the pH adjuster to increase the pH, allowing for both rough and finish polishing in a single process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the polishing fluid includes weak acid and its soluble salt to suppress rapid pH increase, then polishing efficiency is improved, but surface quality (surface roughness) deteriorates
Solution Approach 1:
The polishing process is divided into two distinct stages: rough polishing with weak acid-containing fluid for high efficiency, and finish polishing with weak acid-free fluid for high surface quality. This segmentation allows each stage to optimize for its specific goal without compromise.
Solution Approach 2:
The polishing fluid composition is dynamically changed during the process. The fluid transitions from containing weak acid and soluble salt during rough polishing to being free of these components during finish polishing, allowing the system to adapt to different process requirements.
2Productivity
If the polishing operation maintains pH in strong acid range for extended time, then polishing efficiency is improved, but surface quality deteriorates
Solution Approach 1:
The polishing process uses periodic action by alternating between two fluid regimes: first using weak acid-containing fluid for rough polishing, then switching to weak acid-free fluid for finish polishing. This periodic change in fluid composition enables both high efficiency and high quality outcomes.
Solution Approach 2:
The rough polishing stage using weak acid-containing fluid is performed as a preliminary action to remove material efficiently before the finish polishing stage. This preliminary action prepares the surface for the subsequent high-quality finishing operation.
3Productivity
If the polishing operation uses weak acid and soluble salt to increase pH at constant rate, then polishing efficiency is improved, but it becomes difficult to obtain both high efficiency and low surface roughness in single process
Solution Approach 1:
The single polishing process is segmented into two sequential operations with different fluid compositions. The first operation uses weak acid-containing fluid for efficiency, while the second operation uses weak acid-free fluid for surface quality, allowing the system to achieve both goals that cannot be attained simultaneously in a single uniform process.
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 achieves high polishing efficiency and excellent surface smoothness by optimizing the pH transition during the polishing process, resulting in improved quality and reduced environmental impact.
Implementation Method 1
oxidation of a polished workpiece (i.e., material to be polished) by the permanganate ion in the polishing fluid
Implementation Method 2
the inclusion of the weak acid and its soluble salt in the polishing fluid serves to suppress a rapid reduction of a polishing rate, which could be caused by a rapid increase of the pH of the polishing fluid
Data Source
AI summary
A flat-surface polishing method of performing a polishing operation for polishing a flat surface of a semiconductor substrate by using a polishing pad with circulation and supply of a polishing fluid including permanganate and water. The flat-surface polishing method includes: (a) during a predetermined time from start of the polishing operation, performing the polishing operation, while maintaining pH of the polishing fluid in a strong acid range by dropping a pH adjuster into the polishing fluid; and (b) after the predetermined time has elapsed and until the polishing operation is completed, performing the polishing operation, while making the pH of the polishing fluid higher than the strong acid range by stopping dropping the pH adjuster into the polishing fluid. Also disclosed is a flat-surface polishing apparatus used for carrying out the flat-surface polishing method.