CMP Platen Flexure Control for Thickness Uniformity
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges in achieving uniform material removal rates and thickness profiles due to variations in slurry distribution, polishing pad conditions, and inconsistent load on the substrate, leading to non-uniformities, particularly at the edges of the substrate.
Innovation Solution
A CMP apparatus with a platen featuring independently controllable annular flexures and a controller that adjusts the degree of deflection and dwell times to optimize the polishing process, using a Preston matrix to calculate control parameter values for targeted polishing and minimize differences between target and expected removal profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CMP processes are used with fixed platen shape, then the polishing process is simple to operate, but material removal rate varies and thickness profile is non-uniform, particularly at substrate edges
Solution Approach 1:
The platen is designed with flexible annular segments that can dynamically adjust their shape during polishing. The platen transitions from a fixed structure to a dynamic one where the annular segments can flex independently to apply different pressures to different radial zones of the substrate, enabling real-time compensation for thickness profile variations.
Solution Approach 2:
Different annular segments of the platen are made with different flexibilities or are independently controllable. This allows each segment to provide localized pressure control over specific radial zones of the substrate, enabling non-uniform pressure distribution that compensates for edge effects and achieves uniform thickness profile across the entire substrate.
2Manufacturing precision
If multiple control parameters including flexure deflection and dwell time are adjusted to correct thickness profile, then polishing uniformity improves, but control system complexity and computational requirements increase
Solution Approach 1:
The control system uses feedback from thickness measurements (either pre-measured substrate thickness profiles or real-time monitoring during polishing) to calculate optimal flexure deflection values and dwell time parameters. The controller adjusts these parameters iteratively to minimize differences between target and expected removal profiles, achieving uniform polishing through closed-loop control.
Solution Approach 2:
The system varies multiple control parameters including the degree of flexure deflection and carrier head dwell time at different radial positions. By changing these parameters dynamically during the polishing process, the system optimizes material removal rates across different zones and achieves the desired thickness profile uniformity.
3Productivity
If the carrier head is held stationary on the polishing pad, then the process is simple to control, but material removal rate is inconsistent and varies across the substrate surface
Solution Approach 1:
The carrier head is made to sweep periodically across the polishing pad in a controlled motion pattern. This periodic sweeping action ensures that different radial zones of the substrate receive consistent polishing treatment, improving material removal rate consistency while the motion control system manages the added complexity through programmed trajectories and timing.
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 enables radially-specific thickness profile correction, reduces within-wafer and wafer-to-wafer non-uniformity, and allows for more precise control of pressure on the substrate, improving polishing uniformity and throughput by compensating for edge region non-uniformities during polishing.
Implementation Method 1
an annular flexure surrounding or surrounded by the central section and having a top surface with a first edge adjacent to and coplanar with the upper surface and a second edge farther from the central section. An actuator is arranged to bend the annular flexure so as to modify a vertical position of the second edge of the annular flexure relative to the central section.
Implementation Method 2
chemical mechanical polishing, and more specifically to controlling platen shape in conjunction with carrier head sweep in chemical mechanical polishing
Implementation Method 3
A motor generates relative motion between the platen and the carrier head so as to polish an overlying layer on the substrate
Data Source
AI summary
A controller of a chemical mechanical polishing system is configured to cause a carrier head to sweep across a polishing pad in accord with a sweep profile. The controller is also configured to select values for a plurality of control parameters to minimize a difference between a target removal profile and an expected removal profile. The plurality of control parameters include a plurality of dwell time parameters. A relationship between the plurality of control parameters and a removal rate is stored in a data structure representing a first matrix which includes a plurality of columns including a column for each dwell time parameter and a row for each position on the substrate represented in the expected removal profile, and the controller is configured to, as part of selection of the values, calculate the expected removal profile by multiplying the first matrix by a second matrix representing control parameter values.