CMP Substrate Notch Detection Through a Liquid Column
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Solution Overview
Problem
Existing chemical mechanical polishing (CMP) systems face challenges in accurately detecting the angular position of a substrate notch in wet environments due to light scattering from liquid droplets with different refractive indices, leading to inaccurate readings and reduced measurement precision.
Innovation Solution
A liquid column is directed upward towards the substrate to ensure the light beam travels through a uniform medium, reducing scattering and enhancing measurement precision, while allowing notch detection without removing the substrate from the carrier head.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If light beam is used to detect substrate notch in wet environment, then detection capability is provided, but measurement precision deteriorates due to light scattering from liquid droplets
Solution Approach 1:
A liquid column is introduced as an intermediary medium between the light source and the substrate. This liquid column has a uniform refractive index that matches the polishing slurry environment, eliminating light scattering interfaces. The optical fiber transmits light through this intermediary liquid column to the substrate surface, enabling accurate notch detection without the scattering problems caused by air-liquid interfaces in conventional wet detection methods.
2Measurement precision
If substrate is removed from carrier head for detection, then measurement accuracy may improve, but manufacturing process complexity increases
Solution Approach 1:
The system enables self-service detection by allowing the substrate to remain on the carrier head during the measurement process. The optical detection system is designed to work directly with the substrate in its mounted state, using the carrier head structure itself as part of the detection environment. This eliminates the need for separate substrate removal operations and integrates detection into the normal manufacturing workflow.
3Measurement precision
If liquid flow rate is increased to ensure uniform medium, then light scattering is reduced, but liquid consumption increases
Solution Approach 1:
Instead of using continuous high-flow liquid, the system employs a controlled liquid column with optimized flow rate that maintains sufficient uniformity for accurate measurement. The liquid flow is applied partially - just enough to establish the uniform refractive index medium needed for optical detection, rather than excessive flow that would waste resources. The liquid column diameter and flow rate are optimized to achieve the minimum necessary uniformity.
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 improves notch detection accuracy by minimizing light scattering and environmental contamination, streamlining the manufacturing process and reducing costs by enabling in-situ detection.
Implementation Method 1
an optical fiber extending through a floor of the housing and positioned to direct a light beam through the liquid column onto the substrate when held by the carrier at the notch finding station and to receive reflections of the light beam from the substrate
Implementation Method 2
A liquid column is directed upward towards the substrate to ensure the light beam travels through a uniform medium, reducing scattering
Data Source
AI summary
A polishing apparatus has a polishing station, a notch finding station, and a substrate handling system to move a substrate therebetween. The substrate handling system includes a carrier to hold a substrate at the notch finding station. The notch finding station includes a housing including floor and sidewalls that form an open-topped reservoir, the sidewalls having a lower portion and an upper portion having an upper edge that is thinner than the lower portion, a passage to introduce a liquid into the open-topped reservoir to form a liquid column extending to the substrate, and an optical fiber extending through a floor of the housing and positioned to direct a light beam through the liquid column onto the substrate when held by the carrier at the notch finding station and to receive reflections of the light beam from the substrate.