Tungsten Plug Surface Planarity via Segmented Polishing
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Solution Overview
Problem
The formation of elemental tungsten metal plugs in resistance variable memory devices through chemical mechanical polishing often results in recessed, cracked, and roughened surfaces, leading to incomplete filling with chalcogenide glass and subsequent processing issues.
Innovation Solution
A method involving the formation of an electrically conductive plug by recessing the outermost surface of the conductive material within insulative material, followed by overfilling with a different conductive metal and polishing to achieve a smoother surface, thereby addressing the issues of surface roughness and incomplete filling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chemical mechanical polishing is used to form tungsten plugs, then the surface can be planarized, but the plug surface becomes recessed, cracked, and roughened
Solution Approach 1:
The patent divides the single polishing step into multiple sequential polishing steps with different polishing pads and conditions. The first polishing step uses a soft pad to planarize the surface, while subsequent steps use progressively harder pads to restore surface integrity and remove defects without excessive recess
Solution Approach 2:
The patent performs preliminary polishing actions with specific pad selections and pressures before final polishing. The intermediate polishing steps prepare the surface by removing cracks and roughness created in earlier steps, ensuring the final plug surface is both planar and intact
2Ease of manufacture
If silver is sputtered directly onto silver selenide, then the deposition process is simplified, but silver agglomeration occurs causing discontinuous covering
Solution Approach 1:
The patent introduces an intermediary chalcogenide glass layer between the silver selenide substrate and the silver deposit. This intermediary layer acts as a nucleation site that prevents silver agglomeration and ensures continuous, uniform silver coverage while maintaining process simplicity
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 method ensures a more complete and smooth filling of the conductive plug, enhancing the performance and reliability of resistance variable elements by reducing surface roughness and preventing agglomeration of subsequent deposited materials.
Implementation Method 1
The plug is typically formed by overfilling the opening with tungsten, followed by chemically mechanical polishing the tungsten back to at least the outermost surface of the insulative material
Implementation Method 2
The preferred manner of depositing silver in the fabrication of such devices is by sputtering, from a silver target
Data Source
AI summary
A method of forming an electrically conductive plug includes providing an opening within electrically insulative material over a node location on a substrate. An electrically conductive material is formed within the opening and elevationally over the insulative material. Some of the conductive material is removed effective to recess an outermost surface of the conductive material to from about 100 Angstroms to about 200 Angstroms from an outermost surface of the insulative material after said removing of some of the conductive material. After removing some of the conductive material, remaining volume of the opening over the conductive material is overfilled with an electrically conductive metal material different from that of the conductive material. The metal material is polished effective to form an electrically conductive plug within the opening comprising the conductive material and the metal material. Other aspects and implementations are contemplated.