Single-Step CMP for Multi-Layer Film Stacks
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Solution Overview
Problem
Conventional chemical mechanical polishing (CMP) processes for semiconductor integrated circuits require multiple steps and separate chemistries to polish multi-layer stacks, increasing cycle time, cost, and defect density.
Innovation Solution
A single-step CMP process using a slurry with silica and/or ceria particles, under substantially the same polishing conditions, to polish a three-layer film stack, achieving planarization by controlling the removal rates of polysilicon, silicon oxide, and SiNx layers, with optical endpoint detection for precise thickness control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple CMP steps with different chemistries are used to polish multi-layer stacks, then manufacturing precision is improved, but productivity deteriorates
Solution Approach 1:
The patent combines multiple CMP steps with different chemistries into a single CMP step by using a slurry containing both silica particles (for polysilicon removal) and colloidal silica particles (for silicon oxide removal). This merging of functions allows simultaneous achievement of polysilicon layer removal and silicon oxide layer planarization, eliminating the need for separate CMP steps and chemical etch steps, thereby improving productivity while maintaining manufacturing precision
Solution Approach 2:
The slurry composition is designed to perform multiple functions: silica particles provide mechanical abrasion for polysilicon removal, while colloidal silica particles enable chemical-mechanical removal of silicon oxide. This multi-functional slurry system allows a single CMP process to handle what previously required multiple specialized steps, resolving the contradiction between precision and productivity
2Manufacturing precision
If multiple CMP steps with different chemistries are used to polish multi-layer stacks, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple process steps (polysilicon CMP, silicon oxide CMP, and chemical etch) into a single CMP step by combining the functional ingredients in one slurry formulation. This reduction from multiple separate processes to one integrated process directly reduces device complexity while maintaining the precision benefits through controlled removal rates of each layer
Solution Approach 2:
The single slurry composition is designed to universally handle multiple materials (polysilicon and silicon oxide) with different removal rate requirements. By making the slurry multi-functional, the patent eliminates the need for multiple specialized processes, thereby reducing device complexity without sacrificing manufacturing precision
3Manufacturing precision
If multiple CMP steps with different chemistries are used to polish multi-layer stacks, then manufacturing precision is improved, but loss of time increases
Solution Approach 1:
The patent merges sequential CMP and etch steps into a single concurrent CMP operation. The slurry contains silica particles for polysilicon mechanical removal and colloidal silica for silicon oxide chemical-mechanical removal, allowing both materials to be processed simultaneously in one step rather than sequentially, thereby eliminating time loss while maintaining precision
Solution Approach 2:
The single CMP process enables continuous removal of both polysilicon and silicon oxide layers without interruption or process changeover. The slurry composition maintains continuous useful action on both materials simultaneously, eliminating the idle time and transition time associated with multiple separate steps, thus reducing total processing time while preserving manufacturing precision
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 the number of CMP steps, achieves planarized surfaces, and ensures a uniformly clean semiconductor substrate, suitable for further processing, including deep trench isolation technology, by facilitating progressive removal and precise control of layer thicknesses.
Implementation Method 1
a slurry that includes chemicals and abrasive particles to remove a first layer
Implementation Method 2
a slurry that includes chemicals and abrasive particles
Implementation Method 3
Optical endpoint detection can be use to provide the controlled SiN thickness
Data Source
AI summary
A one-step CMP process for polishing three or more layer film stacks on a wafer having a multilayer film stack thereon including a silicon nitride (SiNx) layer on its semiconductor surface, and a silicon oxide layer on the SiNx layer, wherein trench access vias extend through the silicon oxide layer and SiNx layer to trenches formed into the semiconductor surface, and wherein a polysilicon layer fills the trench access vias, fills the trenches, and is on the silicon oxide layer. CMP polishes the multilayer film stack with a slurry including slurry particles including at least one of silica and ceria. The CMP provides a removal rate (RR) for the polysilicon layer > a RR for the silicon oxide layer > a RR for the SiNx layer. The CMP process is continued to remove the polysilicon layer, silicon oxide layer and a portion of the SiNx layer to stop on the SiNx layer. Optical endpointing during CMP can provide a predetermined remaining thickness range for the SiNx layer.