CMP Polishing Pad Window for In-Situ Endpoint Detection
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Solution Overview
Problem
Current chemical mechanical polishing (CMP) processes lack effective in-situ endpoint detection methods to determine when the desired surface planarity or layer thickness is reached, which can lead to over- or under-polishing of semiconductor substrates.
Innovation Solution
A polishing pad with a solid light-transmissive window, comprising a harder outer portion and a softer inner portion, both of which are co-planar with the polishing surface, allowing for improved optical monitoring and reduced risk of substrate scratching during CMP processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional single-layer polishing pad is used, then the polishing process is simple, but in-situ endpoint detection cannot be achieved and substrate scratching risk increases
Solution Approach 1:
The polishing pad is divided into multiple layers: a top polishing layer and a bottom window layer with different optical properties. The window layer contains a light-transmissive window that allows optical signals to pass through for in-situ endpoint detection, while the polishing layer provides the polishing function. This segmentation enables both polishing and optical detection functions to coexist without interfering with each other.
Solution Approach 2:
The light-transmissive window acts as an intermediary element that allows optical signals to penetrate through the polishing pad structure to reach the substrate and return reflected signals to detectors. This intermediary component enables optical monitoring without requiring direct optical access to the substrate, solving the detection problem while maintaining the integrity of the polishing pad structure.
2Strength
If a harder window material is used, then structural strength is improved, but substrate scratching risk increases
Solution Approach 1:
Different regions of the polishing pad are assigned different material properties: the polishing layer uses softer material (e.g., polyurethane with Shore A hardness 60-80) to minimize substrate scratching, while the window layer uses harder, light-transmissive material (e.g., quartz or glass) to provide structural strength and optical clarity. This local differentiation of material properties allows each region to optimize its specific function without compromising the other.
Solution Approach 2:
The polishing pad employs a composite structure combining dissimilar materials: a polymer-based polishing layer and a ceramic or glass window layer. This composite construction allows the harder window material to provide structural integrity and optical transmission while the softer polishing layer contacts the substrate to prevent scratching. The multi-material approach resolves the contradiction between strength and scratching prevention.
3Measurement precision
If the window surface is not co-planar with the polishing surface, then manufacturing is easier, but optical monitoring accuracy deteriorates
Solution Approach 1:
The window layer is pre-formed with a recessed region that is designed to accommodate the polishing layer and ensure that the top surface of the polishing layer is co-planar with the window surface. This preliminary structuring of the window layer facilitates subsequent assembly and ensures proper optical alignment without requiring complex post-processing or adjustment procedures.
Solution Approach 2:
The window layer incorporates a recessed region with specific depth parameters that compensate for the thickness of the polishing layer. By carefully controlling the recess depth parameter, the design ensures that the external surfaces of the window and polishing layer are co-planar, optimizing optical path alignment while maintaining manufacturability through standard fabrication tolerances.
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
Enables precise in-situ endpoint detection and reduces the likelihood of substrate scratching, enhancing the accuracy and yield of semiconductor substrate planarization by using a softer polishing pad that is compatible with existing CMP systems.
Implementation Method 1
a solid light-transmissive window in the aperture
Implementation Method 2
a detector that measures light reflected from the substrate
Data Source
AI summary
A polishing pad has an opaque polishing layer with an aperture therethrough and a polishing surface, and a solid light-transmissive window in the aperture. The solid light-transmissive window includes an outer portion secured to the polishing layer and an inner portion secured to the outer portion. The outer portion has a upper surface recessed relative to the polishing surface, whereas the inner portion has an upper surface that is substantially co-planar with the polishing surface.