Polysilicon and STI CMP Slurry Guide
Shallow Trench Isolation and polysilicon steps require carefully balanced selectivity so the process self-terminates at the right depth. This guide explains how to select a polysilicon and STI CMP slurry and why precise control matters far more than raw speed.
The Role of STI and Polysilicon CMP
Shallow Trench Isolation (STI) electrically separates neighbouring devices and is one of the earliest CMP steps in the flow. After trenches are etched and filled with oxide, CMP removes the excess oxide and must stop precisely on a silicon-nitride layer so the active areas are protected and uniform. Polysilicon CMP, used for gates and certain structures, has its own balance of rate and control. For the selection method, see the selection framework; the pillar guide gives the wider context.
The STI Integration Flow
Understanding the slurry requires understanding the structure it polishes. In a typical STI flow, a pad oxide and nitride are deposited, trenches are etched through them into silicon, the trenches are filled with deposited oxide, and CMP then removes the oxide overburden down to the nitride. The nitride acts as both a polish stop and a protective cap over the active silicon. The slurry’s job is to clear the oxide and halt on the nitride with minimal dishing of the wide trenches in between.
Selectivity Is the Whole Game
The defining requirement for STI is oxide-to-nitride selectivity. The slurry must remove oxide quickly but slow dramatically when it reaches the nitride stop layer, so the step self-terminates at the correct depth across the whole wafer without over-polishing. This typically uses ceria-based high-selectivity chemistry tuned for a large selectivity ratio — see the oxide and dielectric ceria guide for the abrasive background and the composition guide for how additives set selectivity.
A high-selectivity STI slurry is designed to be partly self-limiting: as nitride is exposed, removal slows automatically, widening the process window and reducing sensitivity to small variations in polish time.
Fixed-Abrasive and Alternative Approaches
Beyond conventional high-selectivity slurries, some integrations have used fixed-abrasive pads (where the abrasive is embedded in the consumable rather than suspended in liquid) or reverse-tone and dummy-fill schemes to improve planarity on difficult layouts. These are integration choices that interact with slurry selection; the right combination depends on feature density and the planarity budget. For most flows, a tuned high-selectivity slurry remains the mainstream solution.
Control Over Speed
Unlike a bulk-removal step, STI rewards precise, uniform removal and a self-stopping characteristic far more than raw rate. Within-wafer uniformity and dishing of wide trenches are the key metrics. This is the opposite emphasis from a tungsten plug step, where high stable rate dominates — a good illustration of why slurry choice is always step-specific. Polysilicon steps similarly prize uniformity and stop control over speed.
Defect Modes
Trench dishing, nitride erosion, residual oxide and scratches are the principal defects. Wide trenches are prone to dishing because there is less surrounding nitride to support planarity, while dense active arrays can suffer nitride erosion that thins the protective cap. Both are managed through selectivity, abrasive and particle control, downforce and layout-aware integration, supported by a stable slurry and accurate endpoint.
Selecting Your STI or Polysilicon Slurry
Specify the oxide-to-nitride selectivity your integration requires, set dishing and erosion limits for your widest and densest features, and prioritise process-window robustness and uniformity over speed. Validate the self-stopping behaviour and dishing on your own structures rather than relying on a reference selectivity figure, and confirm the slurry is stable through your distribution and dilution scheme.
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Talk to the JEEZ slurry engineering team
From first slurry selection to defectivity optimisation and multi-source qualification, JEEZ — Jizhi Electronic Technology Co., Ltd. — helps you match the right polishing slurry to your material and process targets.
Contact JEEZ →Part of the JEEZ Polishing Slurry knowledge series. Reviewed and updated June 2026 by Jizhi Electronic Technology Co., Ltd.
