Borderless Contact Formation via Nitride Spacer Self-Alignment
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Solution Overview
Problem
Conventional methods for forming borderless contacts in semiconductor devices face challenges such as complex contact etches requiring in-situ cleans, issues with oxide fill due to high aspect ratios, and 'tooth' formation from nitride overetch, which slow down fabrication and reduce device performance.
Innovation Solution
The method involves depositing a nitride layer over conductive structures, forming spacers through blanket etching to expose top surfaces, followed by depositing an inter-metal dielectric layer and etching contact openings selectively to eliminate the need for in-situ cleans and reduce 'tooth' formation, allowing for uniform oxide deposition and improved fill characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional contact etch is performed to form borderless contacts, then contact openings are created to expose underlying LI lines, but polymer deposits form requiring in-situ cleans that impact chamber condition and slow fabrication
Solution Approach 1:
A spacer layer is deposited and patterned before the contact etch to define the contact opening locations. This preliminary patterning step allows the subsequent contact etch to proceed without forming polymer deposits that would require in-situ cleans, thereby maintaining chamber condition and preserving fabrication throughput while still achieving precise contact opening formation.
Solution Approach 2:
The spacer layer acts as an intermediary structure that mediates between the patterning step and the contact etch. By using the spacer as a self-aligned mask, the process eliminates the need for complex etch chemistries that generate polymer deposits, thus resolving the contradiction between manufacturing precision and productivity.
2Manufacturing precision
If nitride is etched during contact etch to expose metal lines, then borderless contacts are formed, but 'tooth' formation occurs on LI lines due to overetch
Solution Approach 1:
The nitride etch step is completely removed from the contact formation process. Instead of etching through nitride to expose metal lines, the process uses a spacer-based self-aligned approach where the contact etch stops at the metal-dielectric interface without requiring nitride removal. This extraction of the harmful nitride etch step eliminates tooth formation while maintaining contact opening precision.
Solution Approach 2:
The spacer layer is deposited and patterned in advance to define contact locations, eliminating the need for subsequent nitride etching. This preliminary action prevents overetching and tooth formation by providing a self-aligned mask that stops the etch precisely at the desired location without requiring overetch to reach the metal lines.
3Manufacturing precision
If high aspect ratio openings are created in nitride between LI lines, then contact openings are formed, but oxide fill problems occur
Solution Approach 1:
The spacer layer is deposited with controlled thickness and aspect ratio before the contact etch. By forming the spacer first, the process ensures that the subsequent contact openings have optimized dimensions that facilitate proper oxide fill, eliminating the high aspect ratio problems associated with direct nitride etching while maintaining precise contact opening formation.
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 simplifies the contact etch process, eliminates the need for in-situ cleans, reduces 'tooth' formation, and enhances oxide fill, leading to improved yield, reduced stack height, and lower reflectance, while maintaining contact quality.
Implementation Method 1
depositing a nitride layer over conductive structures
Implementation Method 2
depositing a nitride layer over conductive structures
Implementation Method 3
forming spacers through blanket etching
Implementation Method 4
forming spacers through blanket etching
Implementation Method 5
depositing an inter-metal dielectric layer
Implementation Method 6
depositing an inter-metal dielectric layer
Implementation Method 7
etching contact openings selectively to eliminate the need for in-situ cleans
Data Source
AI summary
A method is provided for forming a borderless contact to a local interconnect (LI) line on a substrate. Generally, the method includes steps of (i) depositing a nitride layer over a number of LI lines on the substrate, to substantially cover the LI lines; (ii) etching the nitride layer to form spacers adjacent to sidewalls of at least one of the number of LI lines and to expose at least a portion of a top surface of the LI line; (iii) depositing an inter-layer dielectric, such as an oxide, over the number of LI lines on the substrate and the spacers formed adjacent thereto; and (iv) performing a contact etch to etch contact openings through the inter-layer dielectric to expose the portion of the top surface of the underlying LI line. Other embodiments are also disclosed.