CMP Pressure Control Using Cost Functions for Wafer Uniformity
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in achieving uniform material removal rates across substrates due to variations in initial thickness, slurry composition, polishing pad condition, relative speed, and load, leading to non-uniformity and potential underdamped or overdamped behavior.
Innovation Solution
A computer program product and method that utilizes an in-situ monitoring system to determine characterizing values for substrate regions, optimizing polishing parameters in real-time by minimizing a cost function subject to constraints, adjusting pressures in carrier head chambers to achieve uniformity and avoid oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CMP control methods are used, then the polishing process is simple to operate, but within-wafer non-uniformity (WIWNU) and edge exclusion occur due to variations in material removal rate
Solution Approach 1:
The carrier head is divided into multiple independently controllable pressure chambers that can apply different pressures to different regions of the substrate. This segmentation allows localized pressure adjustment to compensate for variations in material removal rate across the wafer surface, thereby reducing WIWNU and edge exclusion while maintaining overall process simplicity.
Solution Approach 2:
The control system dynamically adjusts pressure distribution across the carrier head chambers in real-time based on monitored polishing progress. This dynamic adaptation enables the system to respond to varying material removal rates during the polishing process, improving uniformity without requiring overly complex static control mechanisms.
2Manufacturing precision
If aggressive pressure adjustments are made to correct thickness variations, then polishing uniformity improves, but underdamped or overdamped oscillatory behavior occurs
Solution Approach 1:
The system continuously monitors polishing progress and thickness variations, then feeds this information back to adjust pressure distribution in real-time. This closed-loop feedback control prevents aggressive oscillatory adjustments by making incremental, data-driven pressure changes that maintain stability while achieving uniformity.
Solution Approach 2:
The control system modifies pressure parameters across different chambers in a coordinated manner, changing pressure magnitude and distribution to achieve target thickness uniformity. By carefully managing parameter transition rates and using predictive algorithms, the system avoids underdamped or overdamped oscillatory behavior while correcting thickness variations.
3Manufacturing precision
If real-time optimization of multiple objectives is performed, then polishing quality improves, but computational time and complexity increase
Solution Approach 1:
The control system pre-calculates pressure adjustment strategies and optimization parameters before and during the polishing process. By performing preliminary computations and using pre-established models, the system can execute real-time optimization of multiple objectives (thickness uniformity, pressure stability, endpoint achievement) without excessive computational delay during actual polishing operations.
Data Source
AI summary
Controlling a polishing system includes receiving from an in-situ monitoring system, for each region of a plurality of regions on a substrate being processed by the polishing system, a sequence of characterizing values for the region. For each region, a polishing rate is determined for the region, and an adjustment is calculated for at least one processing parameter. Calculation of the adjustment includes minimizing a cost function that includes, for each region, i) a difference between a current characterizing value or an expected characterizing value at an expected endpoint time and a target characterizing value for the region, and ii) a plurality of a projected future pressure changes over time for the region and/or a plurality of differences between projected future pressures over time and a baseline pressure for the region.