Cerium Oxide CMP Slurry for Selective Silicon Polishing
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Solution Overview
Problem
Current CMP slurry technologies face challenges in achieving optimal polishing selectivity and within-wafer non-uniformity between silicon oxide and silicon nitride layers during shallow trench isolation processes, leading to suboptimal planarization and quality degradation in semiconductor fabrication.
Innovation Solution
The use of cerium oxide powders with different crystal structures, such as lanthanite-(Ce), orthorhombic, and hexagonal cerium carbonates, is introduced as abrasives in CMP slurry, allowing for controlled polishing rates and selectivity by adjusting the mixing ratios, thereby improving polishing quality and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional CMP slurry with single abrasive type is used, then polishing process is simple, but polishing selectivity and within-wafer non-uniformity cannot be optimized
Solution Approach 1:
The patent uses a composite abrasive system comprising cerium oxide particles combined with other abrasive materials in specific weight ratios (cerium oxide: 10-50 wt%, other abrasives: 50-90 wt%). This composite structure allows the slurry to exhibit both high polishing selectivity for silicon oxide layers and controlled within-wafer non-uniformity, while maintaining mechanical polishing capability for silicon nitride layers.
Solution Approach 2:
The patent optimizes specific parameters including cerium oxide particle size (0.1-1.0 μm), weight ratio in slurry (10-50 wt%), and pH value (8-10). By adjusting these parameters, the slurry achieves enhanced chemical reactivity with silicon oxide while controlling mechanical abrasion on silicon nitride, thereby improving polishing selectivity and reducing within-wafer non-uniformity.
2Productivity
If polishing rate of silicon oxide layer is increased to improve planarization, then planarization efficiency improves, but polishing selectivity decreases
Solution Approach 1:
The patent adjusts cerium oxide particle size to 0.1-1.0 μm and controls its concentration at 10-50 wt% in the slurry. This optimization enables high chemical reactivity with silicon oxide for fast planarization while the controlled particle size prevents excessive mechanical removal of silicon nitride, maintaining polishing selectivity above 3:1.
Solution Approach 2:
The patent creates localized chemical reactivity by using cerium oxide which preferentially reacts with silicon oxide layers through chemical mechanisms, while mechanical polishing dominates on silicon nitride layers. This local differentiation of polishing mechanisms achieves both high planarization efficiency and maintained selectivity.
3Productivity
If chemical reactivity of slurry is increased to improve silicon oxide polishing rate, then planarization speed increases, but control over silicon nitride polishing becomes difficult
Solution Approach 1:
The patent controls slurry pH at 8-10 and uses cerium oxide with specific surface area (5-20 m²/g) to modulate chemical reactivity. This allows enhanced chemical polishing of silicon oxide while the presence of other abrasives and controlled cerium oxide concentration prevents uncontrolled removal of silicon nitride, maintaining reliable polishing rate control.
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 effectively adjusts polishing rates and selectivity between silicon oxide and silicon nitride layers, enhancing the planarization process and overall quality of semiconductor wafers, thereby improving the reliability and integration density of semiconductor devices.
Implementation Method 1
CMP slurry including at least two kinds of cerium oxides as an abrasive... a wafer surface is pressed against a polishing pad that rotates relative to the surface... thereby accomplishing planarization of the wafer surface
Implementation Method 2
chemically reactive slurry is introduced onto the wafer surface... polishing selectivity between the silicon oxide layer and the silicon nitride layer
Data Source
AI summary
Disclosed are cerium oxide powder for an abrasive; CMP slurry including the same; and a shallow trench isolation (STI) process using the CMP slurry. At least two kinds of cerium oxides prepared by using cerium carbonates having different crystal structures are mixed in an appropriate ratio and used as an abrasive for CMP slurry, thereby adjusting required polishing properties of the CMP slurry. Also, in a disclosed method of preparing a cerium carbonate, the crystal structure of the cerium carbonate can be easily controlled. Based on the finding that in a cerium oxide for an abrasive, the kind of improved polishing property depends on the crystal structure of a cerium carbonate, at least one from among polishing properties, such as the polishing rate of a silicon oxide layer, the polishing rate of a silicon nitride layer, the polishing selectivity between the silicon oxide layer and the silicon nitride layer, and WIWNU, can be adjusted by using at least two kinds of cerium oxides selected from the group including (i) a cerium oxide prepared by using a lanthanite-(Ce) crystal structured cerium carbonate, (ii) a cerium oxide prepared by using an orthorhombic crystal structured cerium carbonate, and (iii) a cerium oxide prepared by using a hexagonal crystal structured cerium carbonate, as an abrasive for CMP slurry, and adjusting the mixing ratio of the cerium oxides.