Adaptive CMP Polishing via Real-Time Optical Feedback
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Solution Overview
Problem
The CMP process often requires a second polishing cycle to achieve uniform film thickness due to differences in clearing times across annular regions, which increases process time and reduces product yield, as further polishing of thicker regions is hindered by thinner regions already at minimum thickness specifications.
Innovation Solution
A method that monitors film thickness in multiple annular regions during a single CMP cycle and adjusts retaining ring pressure and backside pressure in real-time using light interference signals to minimize pre-clearing time differences, allowing for uniform film thickness without extending the polishing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a second polishing cycle is performed to improve film thickness uniformity, then manufacturing precision is improved, but productivity deteriorates due to increased process time
Solution Approach 1:
The patent applies dynamic pressure adjustment during the polishing process by modifying retaining ring pressure and backside pressure based on real-time thickness measurements. This allows the polishing conditions to adapt mid-process, enabling single-cycle achievement of uniformity that previously required multiple cycles, thus resolving the contradiction between precision and productivity
Solution Approach 2:
The patent implements a feedback control system where thickness measurements are taken during polishing and used to adjust pressure parameters in real-time. This closed-loop control enables the system to self-correct thickness non-uniformity during a single polishing cycle, eliminating the need for a second cycle and thereby maintaining both high precision and productivity
2Manufacturing precision
If pressure adjustments are made during a single polish cycle to improve film uniformity, then manufacturing precision is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent changes physical parameters (pressure values) during the polishing process based on measured thickness data. By adjusting retaining ring pressure and backside pressure as controllable parameters, the system achieves better uniformity without requiring fundamentally new equipment, thus improving precision while limiting the increase in device complexity to parameter control rather than structural complexity
3Manufacturing precision
If real-time thickness monitoring is implemented to enable pressure adjustments, then manufacturing precision is improved, but device complexity increases due to additional measurement systems
Solution Approach 1:
The patent employs a measurement system that automatically provides thickness data during polishing, which then automatically triggers pressure adjustments. This self-service approach minimizes the need for complex external control systems and manual intervention, achieving improved precision while keeping the measurement and control integration relatively simple
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 ensures a single polish cycle achieves acceptable film thickness uniformity, reducing batch-to-batch non-uniformity and increasing yield by minimizing center-to-edge metal thickness variation and resistance differences across the substrate.
Implementation Method 1
monitoring film thickness in a plurality of annular regions on a substrate... incident light from an optical endpoint window moving underneath a wafer front side during a polish process passes through a dielectric layer and reflects off a metal etch stop layer... Reflected light from the etch stop layer and dielectric layer form a light interference signal that is collected by a detector
Data Source
AI summary
An adaptive feedback control method is provided for a chemical mechanical polish process to minimize a dielectric layer clearing time difference between two annular regions on a substrate. An optical system with an optical window passes below the polishing pad and detects reflected light interference signals from at least two annular regions. A pre-clearing time difference is determined and is used to calculate an adjustment to one or both of a CMP head membrane pressure and a retaining ring pressure. The pressure adjustment is applied before the end of the polish cycle to avoid the need for a second polish cycle and to reduce a dishing difference and a resistance difference in a metal layer in the at least two annular regions. In some embodiments, a second pressure adjustment is performed before the end of the cycle and different CMP head membrane pressure adjustments are made in different pressure zones.