Shallow Trench Isolation Planarization via Selective Etching
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Solution Overview
Problem
Conventional shallow trench isolation (STI) formation using chemical-mechanical planarization (CMP) processes leads to center-to-edge bias, non-uniformity, dishing of field oxide, oxide residue, and a large number of processing steps, resulting in yield loss and increased complexity.
Innovation Solution
A method for forming shallow trench isolation structures without using CMP, involving the deposition of a sacrificial planarizing layer, such as an organosilicate polymer, followed by a series of etch processes to planarize and remove the trench oxide layer, reducing surface variations and eliminating the need for CMP, thereby simplifying the process and reducing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If CMP process is used for STI formation, then planarization is achieved, but center-to-edge bias and non-uniformity occur
Solution Approach 1:
The patent removes the CMP process entirely from the STI formation sequence, extracting the problematic planarization step that causes center-to-edge bias. Instead, a purely etch-based approach is used where the trench oxide is selectively removed through etching processes, eliminating the source of non-uniformity and yield loss while achieving the necessary planarization effect without mechanical polishing
Solution Approach 2:
The patent replaces the mechanical CMP process with a chemical etching process. The mechanical polishing action is substituted by selective chemical etching that removes trench oxide material, achieving planarization through chemical means rather than mechanical abrasion, thereby eliminating the center-to-edge bias inherent in CMP
2Manufacturing precision
If CMP process is used for STI formation, then surface planarization is achieved, but dishing of field oxide occurs
Solution Approach 1:
The patent extracts the CMP step from the process flow, removing the mechanical action that causes dishing of the field oxide. The planarization function is achieved through selective etching that uniformly removes material without the compressive forces that cause dishing in CMP processes
Solution Approach 2:
The mechanical polishing action of CMP is replaced with chemical etching. The etching process selectively removes trench oxide through chemical reactions rather than mechanical abrasion, preserving the original shape and uniformity of the field oxide regions while achieving the desired surface planarization
3Ease of manufacture
If CMP process is used for STI formation, then excess dielectric is removed, but oxide residue remains on active areas
Solution Approach 1:
The patent replaces the mechanical CMP removal process with selective chemical etching. The etching process uses chemistry to selectively remove excess trench oxide based on material composition differences, achieving complete removal of excess dielectric without leaving carbon or oxide residues that are common problems with CMP
Solution Approach 2:
The patent changes the removal mechanism from mechanical to chemical, altering the fundamental parameter of how excess material is removed. The selective etching process exploits differences in chemical composition and reactivity between trench oxide and other materials, enabling precise removal without residue while maintaining cleanliness on active areas
4Manufacturing precision
If conventional STI formation with CMP is used, then trenches are filled and planarized, but a large number of processing steps are required
Solution Approach 1:
The patent merges multiple separate process steps into a more integrated sequence. The trench oxide removal and planarization functions, which are separate in conventional processes, are combined into a unified etching-based approach that achieves both objectives simultaneously, reducing the total number of discrete processing steps
Solution Approach 2:
The patent extracts and eliminates the CMP process step entirely from the STI formation sequence. By removing this intermediate planarization step and replacing it with selective etching, the overall process complexity is reduced while maintaining or improving the quality of the final STI structure
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 yield loss, minimizes center-to-edge bias, and decreases the complexity and cost of STI formation by eliminating CMP-related issues, resulting in more uniform and reliable trench isolation structures.
Implementation Method 1
a sacrificial planarizing layer is deposited over the trench oxide layer
Implementation Method 2
followed by a series of etch processes to planarize and remove the trench oxide layer
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A method of forming a trench isolation (e.g., an STI) for an integrated circuit includes forming a pad oxide layer and then a nitride layer over a semiconductor substrate, performing a trench etch through the structure to form a trench, depositing a trench oxide layer over the structure to form a filled trench, depositing a sacrificial planarizing layer, which is etch-selective to the trench oxide layer, over the deposited oxide, performing a planarizing etch process that removes the sacrificial planarizing layer and decreases surface variations in an upper surface of the trench oxide layer, performing an oxide etch process that is selective to the trench oxide layer to remove remaining portions of the trench oxide layer outside the filled trench, and removing the remaining nitride layer such that the remaining oxide-filled trench defines a trench isolation structure that projects above an exposed upper surface of the semiconductor substrate.