Ultrasonic Needle Polishing for Wafer Flatness
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Solution Overview
Problem
Conventional CMP polishing methods using elastic polishing pads fail to achieve sufficient wafer surface flatness due to the pads following asperities, leading to issues like dishings and scratches, and are difficult to prevent scratches even when using harder pads.
Innovation Solution
A polishing device and method utilizing a polishing member with ultrasmall and ultrafine needle members that vibrate when in contact with the wafer surface, preventing the pads from following asperities and using a working fluid without abrasive grains to reduce scratch occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an elastic polishing pad is used to polish the wafer surface, then the polishing pad can conform to the wafer surface shape, but the polishing pad follows asperities causing steps to remain on the wafer surface after polishing
Solution Approach 1:
The invention changes the fundamental parameter of the polishing contact interface by replacing the elastic polishing pad with ultrasmall ultrafine needle members. These needles have a hardness of 700 HV or more (significantly harder than the wafer), preventing them from following asperities while still achieving effective polishing through vibration-induced material removal, thus resolving the contradiction between conformability and flatness achievement.
Solution Approach 2:
The invention substitutes the conventional mechanical rubbing action between elastic pad and wafer with a vibration-based mechanical removal process. The needle members vibrate at high frequency (100-10000 Hz) with small amplitude (0.1-10 μm), replacing the continuous pressure-based mechanical action with a dynamic vibration-based action that prevents asperity following while maintaining polishing effectiveness.
2Manufacturing precision
If a harder polishing pad is used to prevent following asperities, then wafer surface flatness improves, but scratches become more difficult to prevent
Solution Approach 1:
The invention applies mechanical vibration to the needle members at high frequency (100-10000 Hz) with small amplitude (0.1-10 μm). This vibration prevents the formation of large scratches by continuously breaking up material removal into tiny increments, while the hardness of the needle members (700 HV or more) prevents following of asperities, thus achieving both flatness improvement and scratch prevention simultaneously.
Solution Approach 2:
The invention introduces dynamic motion to the polishing process by vibrating the needle members during contact with the wafer surface. This dynamic action replaces the static pressure-based polishing with a time-varying vibration-based process, allowing the system to achieve both high flatness (by preventing asperity following) and low scratch formation (by distributing material removal over time through vibration cycles).
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 solution effectively achieves high wafer surface flatness, reduces dishing and scratch formation, and allows for more precise control over film thickness, enhancing the reliability of semiconductor devices.
Implementation Method 1
polishing of the workpiece surface is performed by bringing the needle member into contact with the workpiece surface and causing the needle member to vibrate
Data Source
AI summary
Disclosed are a polishing device and polishing method for forming a wafer with high flatness using a CMP process. For the polishing of the wafer, a polishing device including a chuck section and a polishing member having a needle member is used. In the polishing, the wafer is fixed on the chuck section and then, a working fluid containing no abrasive grains is supplied to a wafer surface as well as the needle member is pressed against the wafer surface and is caused to rapidly vibrate. By doing so, the needle member tip is caused to vibrate to rub the wafer surface, thereby performing the polishing. As a result, dishings due to asperities on the wafer surface or scratches extending over a wide range are prevented from occurring, so that the wafer with high flatness can be obtained.