Dual-Stage CMP Planarization Using Slurry Selection Ratios
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Solution Overview
Problem
The chemical mechanical polishing (CMP) process for planarizing semiconductor devices is challenging due to variations in material layer thickness, slurry composition, polishing pad conditions, and relative removal speeds, leading to incomplete planarization and performance issues in subsequent fabrication steps.
Innovation Solution
A method involving two polishing processes with different selection ratios and slurries, where the first process uses silicon dioxide and the second process uses cerium dioxide with a buffer reagent, both employing optical monitoring to determine endpoints and reduce step height, allowing for global planarization without the need for a polishing stop layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single CMP process is used for planarization, then the process is simple and fast, but the planarization is incomplete and step height remains between different areas
Solution Approach 1:
The polishing process is divided into two distinct stages: a first polishing process using a first slurry with specific composition (silicon dioxide ranging from 0.95% to 1.05% by weight) to perform initial material removal, and a second polishing process using a second slurry with different composition (cerium dioxide ranging from 1.45% to 1.85% by weight) to achieve final planarization. This segmentation allows each process to be optimized for its specific function, resolving the contradiction between planarization quality and process complexity.
2Productivity
If CMP process is used with variations in slurry composition and polishing conditions, then material removal occurs, but the material removal rate varies making endpoint determination difficult
Solution Approach 1:
The invention changes the chemical composition parameters of the slurry between the two polishing processes. The first slurry contains silicon dioxide at 0.95%-1.05% by weight, while the second slurry contains cerium dioxide at 1.45%-1.85% by weight. These parameter changes create distinct material removal characteristics for each process stage, enabling better control and detection of the polishing endpoint while maintaining high material removal efficiency.
3Measurement precision
If a polishing stop layer is added to determine endpoint, then endpoint detection is possible, but additional steps and materials are required increasing complexity and cost
Solution Approach 1:
The polishing process itself provides the endpoint detection mechanism through the distinct material removal characteristics of the two slurries. The second polishing process with cerium dioxide slurry naturally produces a detectable change when the underlying layer is exposed, eliminating the need for an additional polishing stop layer. This self-service approach achieves accurate endpoint determination without adding process complexity or material costs.
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 reduces processing time, simplifies endpoint determination, and improves the global planarization of semiconductor devices, enhancing the performance of subsequent fabrication processes while reducing costs by omitting the need for additional steps and materials.
Implementation Method 1
Chemical mechanical polishing (CMP) process is one accepted method of planarization. This planarization method typically requires polishing slurry, including at least one chemically reactive agent, and abrasive particles supplied to the exposed surface of the material layer against a rotating polishing pad.
Implementation Method 2
a second polishing process is performed on the material layer, wherein the second polishing process has a second selection ratio of relative speeds for removing the material layer at the first area to that at the second area, and the second selection ratio is greater than the first selection ratio
Data Source
AI summary
A method for planarizing semiconductor devices, wherein the method comprises steps as follows: At least one patterned metal layer is formed on a substrate. A material layer having a first area and a second area is provided on the patterned metal layer and the substrate, in which there is a step height existing between the first area and the second area. A first polishing process having a first selection ratio of relative speeds for removing the material layer at the first area to that at the second area is then performed on the material layer. Subsequently, a second polishing process having a second selection ratio of relative speeds for removing the material layer at the first area to that at the second area is performed on the material layer, and the second selection ratio is greater than the first selection ratio.