Multi-Zone CMP Profile Control for Inconsistent Underlayers
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Solution Overview
Problem
Existing chemical mechanical polishing (CMP) methods struggle to accurately determine the polishing endpoint due to variations in slurry composition, polishing pad condition, relative speed, initial thickness, and load, leading to non-uniformity within and between wafers, particularly when underlying doped semiconductor wafers contribute inconsistently to eddy current signals.
Innovation Solution
An in-situ monitoring system calculates an adjusted target thickness profile by fitting functions to sequences of effective thickness values, accounting for contributions from both the conductive layer and underlying layers, and uses this profile to modify polishing parameters and detect endpoints, compensating for inconsistent doping effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If eddy current monitoring is used to detect polishing endpoint, then real-time thickness monitoring is achieved, but measurement precision deteriorates due to inconsistent contributions from underlying doped semiconductor layers
Solution Approach 1:
The patent segments the eddy current signal into distinct contributions from the conductive outer layer and the underlying doped semiconductor layer. By analyzing the signal at different polishing stages and separating these overlapping contributions, the system can accurately attribute signal changes to the outer layer thickness rather than being confounded by variable underlayer responses.
Solution Approach 2:
The system performs preliminary characterization of the underlying layer's eddy current contribution before the outer layer is completely removed. By establishing a baseline signal profile from the doped substrate and underlying structures in advance, the system can subsequently subtract this known contribution from total measurements, isolating the outer layer thickness information.
2Manufacturing precision
If polishing time is used to determine endpoint, then process simplicity is maintained, but manufacturing precision deteriorates due to variations in material removal rate
Solution Approach 1:
The patent implements real-time feedback monitoring during the polishing process by continuously measuring eddy current signals and comparing them against target thickness values. The system provides feedback to the control mechanism, enabling dynamic adjustment of polishing parameters to maintain uniform material removal across the wafer surface despite variations in slurry composition, pad condition, or load.
Solution Approach 2:
The system transitions from static, time-based endpoint determination to dynamic, real-time thickness monitoring. By continuously adapting the monitoring and control parameters based on actual measured thickness values rather than relying on predetermined polishing times, the system achieves superior manufacturing precision while managing complexity through automated control algorithms.
3Measurement precision
If in-situ monitoring is implemented, then endpoint detection accuracy is improved, but device complexity increases due to additional sensors and signal processing
Solution Approach 1:
The eddy current monitoring system serves multiple functions simultaneously: it characterizes the underlying layer properties, tracks outer layer thickness in real-time, detects polishing endpoint, and provides feedback for process control. By making the monitoring system multi-functional rather than requiring separate systems for each purpose, the patent reduces overall device complexity while maintaining high measurement precision.
Solution Approach 2:
The monitoring system uses the polishing process itself to generate the measurement signal, rather than requiring separate measurement operations. The eddy current signal is naturally generated during polishing, and the system extracts thickness information from this self-generated signal, eliminating the need for additional measurement apparatus and reducing system complexity.
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 enhances the accuracy of thickness calculation and endpoint detection, reducing wafer-to-wafer and within-wafer non-uniformity by accounting for underlying layer contributions, thereby improving polishing control and uniformity.
Implementation Method 1
One monitoring technique is to induce an eddy current in the conductive layer and detect the change in the eddy current as the conductive layer is removed
Data Source
AI summary
A substrate is monitored during polishing with an in-situ monitoring system so as to generate a sequence of signal values. The sequence of signal values from the zone is converted into a sequence of effective thickness values for each of multiple zones. For each zone, a function is fit to the sequence of effective thickness values. An effective starting thickness profile for the layer at a start of polishing is determined using the fitted functions, and an adjusted target thickness profile is calculated based on an initial target profile, a starting thickness profile, and the effective starting thickness profile. A polishing parameter is modified based on the sequences of effective thickness values and the adjusted target thickness profile.