CMP Pressure Control via Zone-Specific Optical Clearance Detection
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in determining the completion of planarization due to variations in slurry distribution, polishing pad condition, and load on the substrate, leading to inconsistent material removal rates and difficulties in detecting the thickness of certain materials, such as metals with high reflectivity, using existing optical monitoring techniques.
Innovation Solution
The method involves directing a light beam onto the substrate to generate measurements of reflected light intensity, sorting these measurements into zones, determining the time of layer clearance, and adjusting polishing pressures based on these measurements to ensure uniform clearance across the substrate, using a carrier head with independently adjustable pressure chambers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical monitoring is used to detect layer thickness during polishing, then real-time endpoint detection is improved, but measurement precision deteriorates for materials with high reflectivity
Solution Approach 1:
The patent introduces an intermediary layer or modifies the optical path to detect clearance events indirectly. Instead of directly measuring thickness of high-reflectivity materials, the system detects the moment when the overlying layer is cleared and the underlying layer is exposed, using this clearance event as a mediator to infer polishing endpoint without directly measuring the problematic high-reflectivity material thickness
Solution Approach 2:
The patent replaces direct thickness measurement mechanisms with a clearance detection mechanism. Instead of relying on continuous thickness measurement that fails for high-reflectivity materials, the system substitutes with a detection method that identifies the discrete event of layer clearance, thereby bypassing the measurement precision limitations for reflective materials
2Productivity
If polishing pressure is increased to improve material removal rate, then productivity is improved, but within-wafer non-uniformity worsens
Solution Approach 1:
The patent divides the polishing pressure control into multiple independent zones across the wafer surface. By segmenting the carrier head into zones with independently adjustable pressures, the system can apply different pressures to different regions, maintaining high overall material removal rate while compensating for local variations to achieve uniform clearance across the wafer
Solution Approach 2:
The patent implements local quality control by allowing different pressure levels in different zones of the carrier head. This enables the system to apply higher pressure where material removal is slow and lower pressure where material removal is fast, thereby maintaining high productivity overall while achieving uniform polishing results across the wafer surface
3Manufacturing precision
If polishing time is extended to ensure complete planarization, then manufacturing precision is improved, but loss of time worsens
Solution Approach 1:
The patent implements real-time feedback control during polishing by continuously monitoring for clearance events using optical detection. The system uses this feedback to dynamically adjust polishing parameters and determine the precise endpoint, allowing the process to stop as soon as planarization is complete rather than requiring extended fixed-time polishing, thereby achieving complete planarization with minimal time
Solution Approach 2:
The patent performs preliminary detection of clearance events during the polishing process to predict when planarization will be complete. By monitoring the polishing process in real-time and detecting clearance events, the system can anticipate the endpoint and adjust parameters accordingly, avoiding unnecessary extension of polishing time while ensuring complete planarization is achieved
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 reduces within-wafer non-uniformity, improves polishing throughput, and compensates for process drift, ensuring that the overlying layer is cleared simultaneously across the substrate, thereby enhancing the consistency and efficiency of the polishing process.
Implementation Method 1
directing a light beam onto the first substrate, the light beam reflecting from the first substrate to generate a reflected light beam
Data Source
AI summary
A method of controlling polishing includes polishing a first substrate having an overlying layer on an underlying layer or layer structure. During polishing, the substrate is monitored with an in-situ monitoring system to generate a sequence of measurements. The measurements are sorted into groups, each group associated with a different zone of a plurality of zones on the substrate. For each zone, a time at which the overlying layer is cleared is determined based on the measurements from the associated group. At least one second adjusted polishing pressure for at least zone is calculated based on a pressure applied in the at least one zone during polishing the substrate, the time for the at least one zone, and the time for another zone. A second substrate is polished using the at least one adjusted polishing pressure.