Metal Contact Structure for Phase-Change Memory
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Solution Overview
Problem
The increasing aspect ratio of contact holes in semiconductor devices leads to increased contact resistance and the formation of voids or seams in metal contact structures, particularly in phase-change memory cells, which degrades the operating characteristics and reliability of the memory cells.
Innovation Solution
A method involving the formation of a metal contact structure using tungsten, where an interlayer insulating layer is etched to form a hole, and a metal layer is deposited and planarized using Chemical Mechanical Polishing (CMP) to create a buried portion within the hole, followed by etching-back to remove seams and polymer-induced impurities, and the deposition of a conductive layer to ensure a seamless contact structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the aspect ratio of contact holes is increased to achieve higher integration density, then device integration density is improved, but contact resistance increases and voids or seams form in metal contact structures
Solution Approach 1:
The metal contact structure is divided into multiple segments: a first metal layer deposited at the bottom of the contact hole, an intermediate layer, and a second metal layer filling the upper portion. This segmentation allows each layer to be optimized independently, with the first metal layer providing a broad base for low contact resistance and the second metal layer providing seamless fill for high reliability, thereby resolving the contradiction between integration density and contact resistance.
Solution Approach 2:
Different regions of the contact structure are assigned different material properties and functions. The first metal layer at the bottom has high conductivity and broad coverage to minimize contact resistance, while the second metal layer in the upper region has seamless fill characteristics to eliminate voids. This local differentiation allows the structure to simultaneously achieve low contact resistance and high reliability under high aspect ratio conditions.
2Reliability
If tungsten is used to form metal contact structures with high thermal stability and low resistivity, then electrical performance is improved, but voids or seams are produced when depositing metal in narrow and deep contact holes
Solution Approach 1:
The tungsten deposition process is segmented into two stages: first depositing a thin metal layer at the bottom of the contact hole, then removing excess material and depositing a second metal layer to fill the remaining space. This segmentation prevents the formation of voids and seams that occur when attempting to fill the entire high aspect ratio hole in a single step, while still achieving the desired thermal stability and low resistivity of tungsten.
Solution Approach 2:
The first metal layer is deposited preliminarily at the bottom of the contact hole before the main filling process. This preliminary layer serves as a foundation that prevents seam formation during subsequent deposition, ensuring manufacturing precision while maintaining the electrical and thermal properties of tungsten in the final structure.
3Productivity
If the contact hole dimension is decreased to achieve higher packing density, then device packing density is improved, but contact area decreases leading to increased contact resistance
Solution Approach 1:
The contact structure uses local quality differentiation where the first metal layer provides a broad contact area at the bottom to minimize contact resistance, while the overall contact hole dimensions are reduced to achieve high packing density. The second metal layer then fills the upper portion seamlessly, ensuring that the reduced dimensions do not compromise the electrical performance. This allows simultaneous achievement of high packing density and low contact resistance.
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 contact resistance, enhances the reliability and operating characteristics of phase-change memory cells by eliminating seams and voids, thereby improving the yield and integration density of semiconductor devices.
Implementation Method 1
depositing a metal layer on the surface of the interlayer insulating layer including inside the hole, planarizing the metal layer to provide a buried portion of the metal layer in the hole and to remove portions of the metal layer outside of the hole
Implementation Method 2
irradiating an RF plasma on the surface of the metal layer filled in the hole
Implementation Method 3
The metal contact structure of the semiconductor device is formed by sputtering using aluminum (Al)
Data Source
AI summary
Methods of forming a metal contact structure include forming an interlayer insulating layer on a substrate, etching the interlayer insulating layer to form a hole, depositing a metal layer on the surface of the interlayer insulating layer including inside the hole, planarizing the metal layer to provide a buried portion of the metal layer in the hole and to remove portions of the metal layer outside of the hole, etching-back the buried portion of the metal layer in the hole such that some of the portion of the metal layer within the hole remains and depositing a conductive layer on the surface of the interlayer insulating layer and the portion of the metal layer that remains within the hole. Methods of forming a phase change memory device are also provided.