Individually Rotatable Platens for CMP Thickness Profile Control
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Solution Overview
Problem
Chemical mechanical polishing (CMP) processes face challenges with variations in material removal rates and subsequent thickness profiles due to factors like slurry distribution, polishing pad condition, and inconsistent load on the substrate.
Innovation Solution
A CMP apparatus with multiple concentric platens, where the inner and outer platens rotate at different speeds, and a controller that adjusts control parameters such as rotational speeds and dwell times to minimize the difference between a target and expected removal profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single polishing platen is used, then the device complexity is low, but the manufacturing precision of the substrate thickness profile deteriorates due to variations in material removal rate
Solution Approach 1:
The polishing apparatus is segmented into multiple independent platens (inner platen and outer platen) that can rotate at different speeds. Each platen acts as an independent polishing zone, allowing differential material removal rates across different radial positions of the substrate. This segmentation enables precise control of the thickness profile by adjusting the rotational speed of each platen independently.
Solution Approach 2:
Different regions of the substrate receive different polishing qualities through the multi-platen configuration. The inner platen provides one polishing condition while the outer platen provides another, allowing local optimization of material removal rates. The controller adjusts the rotational speeds of individual platens to achieve the desired thickness profile across different zones of the substrate.
2Manufacturing precision
If the carrier head is held stationary, then the device complexity is low, but the manufacturing precision deteriorates due to inconsistent load distribution on the substrate
Solution Approach 1:
The carrier head is transformed from a stationary component to a dynamic one with multiple degrees of freedom. It can rotate about a vertical axis and simultaneously translate radially, allowing the substrate to be positioned at different locations and orientations relative to the rotating platens. This dynamic positioning enables consistent load distribution and uniform material removal across the substrate surface.
Solution Approach 2:
The controller receives feedback about the substrate position and adjusts the carrier head's rotational and radial movements accordingly. By coordinating the carrier head's motion with the platen rotation speeds, the system maintains optimal contact pressure and material removal rates across different substrate regions, achieving uniform thickness profiling.
3Manufacturing precision
If multiple platens rotate at the same speed, then the control system is simple, but the manufacturing precision of the thickness profile deteriorates due to inability to control differential removal rates
Solution Approach 1:
The rotational speed parameter of the platens is changed from a uniform value to differential values. The controller independently adjusts the rotational speed of the inner platen and outer platen, creating different material removal rates in different radial zones. This parameter differentiation enables precise control of the thickness profile, particularly at the substrate edge where uniformity is most challenging to achieve.
Data Source
AI summary
A chemical mechanical polishing apparatus includes: an inner platen to support an inner polishing pad; an annular outer platen to support an outer polishing pad; a carrier head to hold a substrate; one or more motors to rotate the inner platen about a vertical axis at a first rotation rate and to rotate the outer platen about the vertical axis at a second rotation rate; and a controller configured to select values for multiple control parameters to minimize a difference between a target removal profile and an expected removal profile, the multiple control parameters including a first parameter representing a difference in rotational speeds between the inner and outer platens. The outer polishing pad can coaxially surround the inner platen, and an outer edge of the inner platen and an inner edge of the outer platen can be separated by a gap.